[ { "id": "thesis:4226", "collection": "thesis", "collection_id": "4226", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10232007-155443", "primary_object_url": { "basename": "Spotila_ja_1999.pdf", "content": "final", "filesize": 29963103, "license": "other", "mime_type": "application/pdf", "url": "/4226/1/Spotila_ja_1999.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The neotectonics of the San Bernardino Mountains and adjacent San Andreas Fault : a case study of uplift associated with strike-slip fault systems", "author": [ { "family_name": "Spotila", "given_name": "James Anthony", "clpid": "Spotila-James-Anthony" } ], "thesis_advisor": [ { "family_name": "Sieh", "given_name": "Kerry E.", "clpid": "Sieh-K-E" } ], "thesis_committee": [ { "family_name": "Sieh", "given_name": "Kerry E.", "clpid": "Sieh-K-E" }, { "family_name": "Wernicke", "given_name": "Brian P.", "clpid": "Wernicke-B-P" }, { "family_name": "Farley", "given_name": "Kenneth A.", "clpid": "Farley-K-A" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The San Bernardino Mountains have uplifted over the last few million years at the hub of structural systems along the southern San Andreas fault zone and represent an excellent opportunity to study the interplay between orogeny and transpressive strike-slip faulting. To attain a better understanding of the complex architecture of deformation in this range, I have constrained several basic kinematic aspects of its development. First, the timing and magnitude of rock uplift and exhumation of fault blocks have been constrained using the thermochronometry of radiogenic helium in apatite (Chapter 2). This has shown that small crustal slivers within the San Andreas fault zone were exhumed several kilometers over the last few million years, due to slip-partitioning along geometrically-complex, high-angle faults. Second, a detailed constraint on the vertical deformation field of the largest fault block in the range has been determined using a deeply weathered granite surface as a structural datum (Chapter 3). A structural analysis of this deformation pattern has provided the total displacements, slip rates, and subsurface geometries of the major thrust faults within the range (Chapter 4). As a whole, the San Bernardino Mountains appear to have uplifted within a complex system of both high and low-angle faults. The total horizontal plate motion accommodated by this uplift is on the order of 6 km and is focused tightly about a restraining bend in the San Andreas fault zone at San Gorgonio Pass. This suggests the entire range has been built due to convergence associated with a small geometric perturbation of a major strike-slip system.\r\n\r\nTo acquire a different perspective on the relationship of strike-slip faulting and uplift, I have also studied the deformation pattern around a restraining bend resulting from a single fault rupture. Structural analysis of surficial breaks at a slip gap during the 1992 Landers earthquake has revealed how complex, secondary thrust and normal faulting were induced to accommodate simple strike-slip motion where a through-going connection between two dextral fault segments has yet to develop (Chapter 5). This illustrates a single episode in the incremental evolution of a transpressive orogenic system.", "doi": "10.7907/z7g7-eb63", "publication_date": "1999", "thesis_type": "phd", "thesis_year": "1999" }, { "id": "thesis:4969", "collection": "thesis", "collection_id": "4969", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-12122006-135618", "primary_object_url": { "basename": "Wood_dj_1997.pdf", "content": "final", "filesize": 31660373, "license": "other", "mime_type": "application/pdf", "url": "/4969/1/Wood_dj_1997.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Geology of the Eastern Tehachapi Mountains and Late Cretaceous-Early Cenozoic tectonics of the southern Sierra Nevada Region, Kern County, California", "author": [ { "family_name": "Wood", "given_name": "David Judson", "clpid": "Wood-David-Judson" } ], "thesis_advisor": [ { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" } ], "thesis_committee": [ { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" }, { "family_name": "Wernicke", "given_name": "Brian P.", "clpid": "Wernicke-B-P" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Many geologic studies have inferred that the California continental margin in the vicinity of the western Mojave Desert was tectonically disrupted after emplacement of the Cretaceous Cordilleran batholith and prior to Neogene displacements on the San Andreas fault system. The causes of this regional deformation, however, are poorly understood. Located along the northern margin of this disrupted region at the southern end of the comparatively little deformed Sierra Nevada batholith, the eastern Tehachapi Mountains are ideally situated to study the possible mechanisms of this disruption. In view of this, the geology and structure of the eastern Tehachapi Mountains were investigated using geologic field mapping at scales of 1:6,000 through 1:24,000, detailed petrographic studies, and structural and kinematic analysis of deformation fabrics and structures in the field and in the lab. The study area is divided by a generally N trending shallowly SE dipping ductile-cataclastic fault zone called the Blackburn Canyon fault into the eastern Tehachapi gneiss complex in the footwall and the Oak Creek Pass complex in the hangingwall.\r\n\r\nThe eastern Tehachapi gneiss complex is composed of two different sequences of metasedimentary rocks that have been intruded by three generations of plutonic rocks. The Brite Valley group metasedimentary rocks consist largely of pelites and graphitic quartzite with subordinate marble. The Antelope Canyon group metasedimentary rocks consist of a lower section composed mostly of thinly laminated dirty quartzite overlain by an upper section of marble. The earliest intrusive rocks in the area (group I orthogneisses) are lithologically diverse and include granite augen gneiss, garnetiferous hornblende diorite gneiss, and hornblende biotite quartz diorite gneiss. Both groups of paragneiss and the group I orthogneisses are intruded by group II plutons of the Tehachapi Intrusive Complex. The Tehachapi Intrusive Complex is composed of comagmatic gabbro, quartz diorite, and tonalite and it is inferred to be continuous with the large ~100 Ma Bear Valley Springs tonalite pluton exposed to the west. The group III intrusives are small bodies and thin sheets of leucocratic biotite granite which intrude all of the other lithologies.\r\n\r\nThe rocks in the gneiss complex have had a complex deformational history. The metasedimentary rocks are folded into map-scale N to NW trending SW vergent isoclinal F1 folds. Later (?) intrusion of the group I orthogneisses was accompanied (?) and followed by amphibolite facies metamorphism and the localized formation of NE trending shallow plunging open to tight F2 folds. During (?) and after intrusion of the ~100 (?) Ma Tehachapi Intrusive Complex the gneiss complex was metamorphosed at amphibolite facies and deformed by map-scale open to tight NW trending SW vergent F3 folds. After much of the F3 folding the basement rocks in the Tehachapi Valley area appear to have been folded into a regional dextral-sense convex-west F4 oroclinal fold. In the later stages of F4 folding part of the southwest limb of the Tehachapi Valley orocline is inferred to have been transposed into a NW trending shallow NE dipping noncoaxial ductile shear zone called the eastern Tehachapi shear zone. The shear zone has a structural thickness of ~1 km, top to the S-SW shear sense, and most shearing appears to have occurred during greenschist facies retrograde metamorphism. The shear zone appears to continue to the north across Tehachapi Valley where it is inferred to merge with the steeply E dipping dextral-slip proto-Kern Canyon fault. Motion on the shear zone is inferred to have ended at about the time when the Late Cretaceous (?) group III leucogranites intruded. Following shear zone activity rocks in the gneiss complex locally were folded in gentle NE trending subhorizontal F5 folds. Late top to the NE shearing in the upper structural levels of the gneiss complex suggests that a normal fault may be concealed beneath the alluvium of Tehachapi Valley.\r\n\r\nThe lithologies and deformation history of the Oak Creek Pass complex are very different from the eastern Tehachapi gneiss complex. The Oak Creek Pass complex is composed mostly of granodioritic plutonic rocks (group IV intrusives) which commonly are cataclastically deformed and metamorphosed at greenschist and lower grade. Arkosic sandstones and conglomerates of the Late Cretaceous (?)-Eocene (?) Witnet Formation locally are unconformable above the granodiorite. Emplacement of the Oak Creek Pass complex above the eastern Tehachapi gneiss complex along the Blackburn Canyon fault took place after most of the activity along the eastern Tehachapi shear zone. Shear sense along the Blackburn Canyon fault is top to the S or SE. The Oak Creek Pass complex is divided into a number of structural plates by low-angle (?) ductile-cataclastic fault zones one of which is the NE trending Mendiburu Canyon fault. Synclinal F6 folding of the Witnet Formation and NW vergent overthrusting of the Witnet Formation by granitic rocks along the Mendiburu Canyon fault are interpreted to postdate motion along the Blackburn Canyon fault. Deformation of the Witnet Formation is inferred to be pre-Miocene in age based on correlation with a similar deformation across Tehachapi Valley.\r\n\r\nThe Brite Valley group metasedimentary rocks are suggested to correlate with the western facies of the Triassic-Jurassic age Kings sequence and the Antelope Canyon group rocks may correlate with the eastern facies of the Kings sequence or possibly with Late Proterozoic-Cambrian age rocks of the miogeocline. Juxtaposition of the two groups of metasedimentary rocks may have been along a cryptic structure that was active prior to intrusion of some of the group I plutons which are inferred to be mid-Cretaceous in age. Formation of the NE trending F2 folds between ~117 Ma and ~100 Ma is suggested to have resulted from the local reorientation of the regional stress field in the vicinity of a weak strike-slip (?) fault such that the direction of maximum compressive stress during the deformation was oriented subparralel to the trend of the Sierra Nevada batholith. The F3 folds, F4 folds, and the eastern Tehachapi shear zone are interpreted to have formed more or less sequentially during a protracted period of contractional deformation in the middle to lower crust of the southern Sierra Nevada batholith from ~100 Ma to ~80 Ma. Top to the S-SW motion along the shear zone may reflect the and underthrusting of Rand schist beneath the batholith at lower structural levels during low-angle Laramide subduction.\r\n\r\nThe Blackburn Canyon fault and a number of other previously identified low-angle faults in the southern Sierra Nevada region are suggested to be extensional faults along which part of the southern Sierra Nevada batholith was unroofed. The source region for the out of place Oak Creek Pass complex and other inferred allochthonous rocks is suggested to be the area in the Sierra Nevada east of the proto-Kern Canyon fault and south of South Fork Valley. Exposures of Witnet Formation may be the remnants of a synextensional sedimentary deposit that accumulated in a supradetachment basin. This inferred extensional exhumation of the southeastern Sierra Nevada may have begun as early as ~85-90 Ma and ended at ~80 Ma or later based on data from previous studies in the region. Thus, contractional deformation in the middle crust of the southern Sierra Nevada region may have been coeval with upper crustal extensional deformation in Late Cretaceous time.\r\n\r\nCorrelation of the Cretaceous structural histories of the eastern Tehachapi gneiss complex and the northern Salinian block in the Coast Ranges of central California supports previous suggestions that the two areas may have evolved in close proximity to one another. The relative westward offset of the Salinian block from the Sierra Nevada prior to the Neogene may in part be the result of Late Cretaceous-early Cenozoic (?) westward extrusion of wedges of middle to lower crust bounded by thrust faults below and E dipping extensional faults above in a manner analogous to recent models for deformation in the Himalayas. The upper plate rocks of the Blackburn Canyon fault appear to be rotated about 90\u00b0 clockwise relative to their inferred source region and the F4 folds in the Tehachapi area appear to have dextral vergence. The vergence of the folding and the sense of rotation both are consistent with Late Cretaceous dextral-oblique convergence indicated by plate motion models and with the presence of Late Cretaceous synbatholithic dextral transpressional and strike-slip shear zones in the Sierra Nevada to the north.", "doi": "10.7907/M8Z7-0W45", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:4033", "collection": "thesis", "collection_id": "4033", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10112005-111913", "primary_object_url": { "basename": "Wolf_ra_1997.pdf", "content": "final", "filesize": 8989655, "license": "other", "mime_type": "application/pdf", "url": "/4033/1/Wolf_ra_1997.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "The development of the (U-Th)/He thermochronometer", "author": [ { "family_name": "Wolf", "given_name": "Richmond Andrew", "clpid": "Wolf-Richmond-Andrew" } ], "thesis_advisor": [ { "family_name": "Farley", "given_name": "Kenneth A.", "clpid": "Farley-K-A" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "thesis_committee": [ { "family_name": "Farley", "given_name": "Kenneth A.", "clpid": "Farley-K-A" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Wernicke", "given_name": "Brian P.", "clpid": "Wernicke-B-P" }, { "family_name": "Burnett", "given_name": "Donald S.", "clpid": "Burnett-D-S" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

(U-Th)/He dating of apatite provides a tool for recording the low temperature (<100\u00b0C) history of the crust. A model based on stopping distances in apatite relates the fraction of alpha particles emitted from the crystal during U and Th decay to crystal size. Helium ages for different sized apatite aliquots are indistinguishable when corrected for the effects of alpha emission. Diffusion coefficients were measured by the incremental outgassing of helium from apatite. The measured range of diffusion parameters is nearly identical for apatites of different chemical composition, grain size, and grain morphology. Isothermal experiments are consistent with spherical diffusion domains which are smaller than the physical grain size.

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Helium ages may reflect complex thermal histories where samples spend considerable amounts of time in the region where helium is only partially retained. Therefore, the solution to the full radiogenic helium diffusion/production equation is used to interpret helium ages instead of Dodson's (1973) closure temperature formulation. The time required to achieve a steady state between helium production and diffusion at various temperatures can be determined, as well as the range of temperatures defining the helium partial retention zone (the region where helium retentivity is most sensitive to temperature). In general, this zone resides at ~40-80\u00b0C (~2±1 km depth for typical continental geothermal gradients). This is ~35\u00b0C cooler than the analogous apatite fission track partial annealing zone.

\r\n\r\n

Application of the (U-Th)/He method to natural systems has provided consistent results and useful geologic information. Helium ages from the Cajon Pass Drillhole decline from 41.1 to 0.3 Ma between 526 and 2018 m depth, and appear to be in equilibrium with the present thermal gradient. This is in contrast to the previous assertion that the region is in a thermal transient resulting from recent erosion. Helium ages from Mt. San Jacinto, California, decrease monotonically from 79 to 17 Ma with sample elevation, and suggest a modest (~7\u00b0) westward tilting of the block with no evidence of rapid exhumation during this period. Helium ages from Mt. San Jacinto and Cajon Pass are younger than other available thermochronometric techniques, consistent with predictions from laboratory diffusion data.

", "doi": "10.7907/kz3w-5t57", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:5516", "collection": "thesis", "collection_id": "5516", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:01132010-093747416", "primary_object_url": { "basename": "Nagy_ea_1997.pdf", "content": "final", "filesize": 17758433, "license": "other", "mime_type": "application/pdf", "url": "/5516/1/Nagy_ea_1997.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Extensional Deformation and Volcanism Within the Northern Puertecitos Volcanic Province, Sierra Santa Isabel, Baja California, Mexico", "author": [ { "family_name": "Nagy", "given_name": "Elizabeth Ann", "clpid": "Nagy-Elizabeth-Ann" } ], "thesis_advisor": [ { "family_name": "Stock", "given_name": "Joann M.", "orcid": "0000-0003-4816-7865", "clpid": "Stock-J-M" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" } ], "thesis_committee": [ { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Kirschvink", "given_name": "Joseph L.", "orcid": "0000-0001-9486-6689", "clpid": "Kirschvink-J-L" }, { "family_name": "Farley", "given_name": "Kenneth A.", "orcid": "0000-0002-7846-7546", "clpid": "Farley-K-A" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Stock", "given_name": "Joann M.", "orcid": "0000-0003-4816-7865", "clpid": "Stock-J-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

Geologic features at the western edge of the Gulf Extensional Province (GEP) in northeastern Baja California, Mexico, record details of Pacific-North American (PAC-NAM) plate boundary history prior to and during its establishment within the Gulf of California. Methods of study in Santa Isabel Wash (SIW) (informally named) in the northern Sierra Santa Isabel include geologic mapping of ~140 km^2 (1:20000 scale) along the northern margin of the Miocene-Pliocene Puertecitos Volcanic Province (PVP), ^(40)Ar/^(39)Ar geochronology, electron microprobe analysis, paleomagnetic study, and petrography. Local Neogene stratigraphy (spanning ~17-6 Ma) includes volcaniclastic breccias, basaltic to dacitic lava flows, and rhyolitic pyroclastic flow deposits. The completeness of the lithologic package improves stratigraphic correlations between the PVP and nearby regions.

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High-angle extension-related faults cut all rocks in SIW. The southeastward projection of the pre-6 Ma Matorni accommodation zone, which separates a northern region of greater and more prolonged extension from a less extended southern zone, may pass on the north side of SIW. Paleomagnetic analysis indicates no vertical axis rotations in SIW since 6 Ma. This contrasts with regions north of the Matomi accommodation zone where clockwise rotation has accompanied extensional deformation since 3-6 Ma. About 500 meters of post-6 Ma, E-side-down displacement occurs across two major, NNW-striking normal faults on the west side of SIW. These, and smaller synthetic and antithetic faults in the hanging walls, accommodate up to 4% E- to ENE-directed extension. Quaternary deformation is also documented.

\r\n\r\n

A new model developed to explain ENE-directed extension in northeastern Baja California partitions present-day PAC-NAM plate motion between NNW-striking, sinistral dip-slip faults and N- to NNW-striking, dextral (oblique?) strike-slip fault(s) in the northernmost Gulf of California. The model offers explanations for the geometry of plate motion accommodation between the latitudes of the Agua Blanca fault and the PVP, bathymetric features near Wagner and Consag basins, the position and jumps of nearby spreading centers since 6 Ma, the greater width and bend in coastline of the northernmost Gulf of California, the incorporation of the PVP into the GEP 2-3 Ma, and suggests a transitional tectonic scenario between oceanic spreading centers and continental transforms (\"Wagner Transition Zone\").

", "doi": "10.7907/znpy-3311", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:15047", "collection": "thesis", "collection_id": "15047", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10252022-202940570", "primary_object_url": { "basename": "Holk_GJ_1997.pdf", "content": "final", "filesize": 201279911, "license": "other", "mime_type": "application/pdf", "url": "/15047/1/Holk_GJ_1997.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "The Role of Water in the Magmatic and Tectonic Evolution of Metamorphic Core Complexes: A stable Isotope Study of the Southern Omineca Crystalline Belt, British Columbia, Canada", "author": [ { "family_name": "Holk", "given_name": "Gregory James", "clpid": "Holk-Gregory-James" } ], "thesis_advisor": [ { "family_name": "Taylor", "given_name": "Hugh P., Jr.", "clpid": "Taylor-H-P" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "thesis_committee": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Taylor", "given_name": "Hugh P., Jr.", "clpid": "Taylor-H-P" }, { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Wernicke", "given_name": "Brian P.", "orcid": "0000-0002-7659-8358", "clpid": "Wernicke-B-P" }, { "family_name": "Wyllie", "given_name": "Peter J.", "clpid": "Wyllie-P-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

The oxygen isotope data in this study delineate 2 major episodes of water-rock interaction related to the metamorphic, plutonic, and tectonic development of the metamorphic core complexes in the southern Omineca belt. Episode 1 is a Paleocene pre\u00ad-extensional metamorphic/magmatic-hydrothermal event. The occurrence of isotopically uniform quartz (\u03b4\u00b9\u2078O = 12.5 \u00b1 0.5\u2030) and feldspar (10.9 \u00b1 0.7\u2030) throughout different rock types indicates that much of a 6-km-thick section of the mid-crustal Selkirk allochthon underwent internally buffered \u00b9\u2078O/\u00b9\u2076O homogenization during Paleocene melting and decompression as it moved up the Monashee decollement thrust ramp. Areas of uniform \u03b4\u00b9\u2078O are those with the most leucogranite or those subjected to severe anatexis. Only locally, in the most impermeable (or refractory) zones did 180 exchange among the rocks, leucogranite melts, and aqueous fluids fail to go to completion (i.e., in the deepest parts of the section, in a marble-rich zone, around some thick amphibolites, and in most garnets). Evidence for \u00b9\u2078O/\u00b9\u2076O heterogeneity in the protoliths of these rocks is observed in stratigraphically correlative lower-grade units elsewhere in British Columbia, as well as in garnets that coexist with isotopically homogeneous quartz. A model is introduced utilizing water as a petrologic catalyst: fluids evolved during muscovite breakdown and partial melting of pelites produce \u00b9\u2078O/\u00b9\u2076O homogenization with only minor influx of external H\u2082O; this is followed by release of magmatic H\u2082O from these melts as they crystallize (triggering further melting of adjacent feldspathic assemblages) during and after the ~20 km uplift that occurred in the thrusting event that took place just prior to detachment faulting.

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Episode 2 is a series of Eocene synextensional meteoric-hydrothermal events affecting the shallow crust along all of the major detachment faults in the region, and along some parts of the Monashee decollement; these effects were locally enhanced by added heat from some synextensional alkaline intrusions (the Coryell plutons). Very large quartz-feldspar \u00b9\u2078O/\u00b9\u2076O disequilibrium effects were imprinted upon the rocks during exchange with hot meteoric waters (initial \u03b4\u00b9\u2078O ~ -15); the mineral most affected was feldspar (\u03b4\u00b9\u2078O down to -5.0). In the Valhalla core complex, the hanging wall rocks above the Slocan Lake fault are sufficiently uniform to allow us to apply open-system kinetic oxygen isotope exchange modeling, thereby placing constraints on the duration (1-3 Ma) and integrated fluid flux (\u2265 10\u2077 cm\u00b3H\u2082O/cm\u2082rock) for this hydrothermal metamorphism.

", "doi": "10.7907/pkn3-p364", "publication_date": "1997", "thesis_type": "phd", "thesis_year": "1997" }, { "id": "thesis:16183", "collection": "thesis", "collection_id": "16183", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09192023-212841699", "primary_object_url": { "basename": "Lee_W-J_1996.pdf", "content": "final", "filesize": 109440804, "license": "other", "mime_type": "application/pdf", "url": "/16183/1/Lee_W-J_1996.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Experimental Study on Liquid Immiscibility in Silicate-Carbonate Systems with Applications to Carbonatites", "author": [ { "family_name": "Lee", "given_name": "Woh-jer", "clpid": "Lee-Woh-jer" } ], "thesis_advisor": [ { "family_name": "Wyllie", "given_name": "Peter J.", "clpid": "Wyllie-P-J" } ], "thesis_committee": [ { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" }, { "family_name": "Wyllie", "given_name": "Peter J.", "clpid": "Wyllie-P-J" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Phase equilibrium experiments have been conducted in several silicate-carbonate systems to 2.5 GPa in order to understand the magmatic processes involved in the generation of carbonatite complexes. The studied phase fields were intersected by SiO\u2082-CaCO\u2083, NaAlSi\u2083O\u2088-CaCO\u2083, NaAlSiO\u2084-NaAlSi\u2083O\u2088-CaCO\u2083 and primitive nephelinite\u00ad (Na,Ca,Mg) carbonate, which along with the analyzed liquid and solid compositions were used to define the positions of the silicate-carbonate miscibility gap and liquidus field boundaries on various compositional projections. These boundaries exert controls on the evolution of silicate-CO\u2082 and carbonatitic magmas, and vary strongly with temperature, composition and pressure. The size of the miscibility gap decreases with increasing temperature and Mg/Ca of liquids. The extent of the Mg-free miscibility gap decreases with decreasing pressure, whereas the magnesian one shows an opposite trend. The immiscible carbonate-rich liquids could dissolve at most ~80 wt% CaCO\u2083 while still containing significant amounts of silicate and alkalis. The position of the silicate-calcite coprecipitation boundary becomes more carbonate-rich as pressure decreases, and as composition becomes more magnesian and aluminous. Calcite grew remarkably rounded in many experiments. A variety of liquid paths are compared with the field boundaries at different conditions. Partial melting of carbonated peridotite produces dolomitic carbonatites along the coprecipitation boundary, to CO\u2082-bearing, silica-undersaturated liquids in the primary silicate field. Both types of magmas could potentially ascend to the surface of the earth without much modification. None of them would reach the miscibility gap at mantle conditions. Within the crust, carbonated silicate liquids could either intersect the miscibility gap after substantial crystallization to exsolve alkali-bearing to alkalic carbonatitic liquids, or reach the coprecipitation boundary and evolve towards alkali-enrichment and silicate\u00ad depletion without immiscibility. Alkali-bearing, CaCO\u2083-rich immiscible liquids, when separating from their silicate parents, first precipitate silicate minerals during cooling until calcite is joined, and the residual liquids become more alkalic by further crystallization of calcite. It appears that most calciocarbonatites are cumulates from liquids along the coprecipitation boundary, whereas the natrocarbonatites at Oldoinyo Lengai are produced directly by immiscibility.", "doi": "10.7907/vpan-h802", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:16205", "collection": "thesis", "collection_id": "16205", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10102023-192037999", "primary_object_url": { "basename": "Thio_HK_1996.pdf", "content": "final", "filesize": 40616829, "license": "other", "mime_type": "application/pdf", "url": "/16205/1/Thio_HK_1996.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "1. Using Short-Period Surface Waves to Study Seismic Source and Structure. 2. Source Complexity of Large Strike-Slip Earthquakes", "author": [ { "family_name": "Thio", "given_name": "Hong Kie", "clpid": "Thio-Hong-Kie" } ], "thesis_advisor": [ { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" } ], "thesis_committee": [ { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" }, { "family_name": "Heaton", "given_name": "Thomas H.", "orcid": "0000-0003-3363-2197", "clpid": "Heaton-T-H" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

The availability of high dynamic range very broad band seismic data in recent years has greatly increased the level of detail and the speed with which we can study the seismic source. The work presented in this thesis draws heavily on the deployment of broad-band seismometers, both on a worldwide scale, with networks like IRIS, IRIS/IDA and GEOSCOPE, as well as on a local scale, using data from the TERRAscope network.\r\nThe routine study of seismicity in Southern California, like in other seismically active regions, has traditionally been carried out using dense arrays of high-gain short-period seismometers. With the addition of the very broad band instrumentation of TERRAscope we can improve this pursuit in several ways, one of which being the use of short period surface waves to study local earthquakes as described in chapter 1 of this thesis. Over the years, surface waves have proved to be very reliable and stable for moment tensor inversions. The method is very rapid, and because of the longer periods used they are more reliable for consistent estimation of earthquake moment. At short distances the surface waves arrive within a few minutes after an event has occurred at the stations, and with real-time telemetry we can obtain the size and mechanism for local earthquakes within minutes. The propagation corrections for surface waves are very straightforward so that this procedure can be made completely automatic. Armed with the results from above procedure, we can determine travel time residuals for a dense distribution of raypaths across Southern California. In chapter 2 we present tomographic inversions of these resid\u00aduals, for Love and Rayleigh waves at periods between 10 and 50 seconds. The results indicate that lateral variations of phase velocity of up to 10% exist in the area, and that these anomalies can have relatively short wavelengths.

\r\n\r\n

The 1994 Northridge earthquake provided a wealth of data to apply our moment tensor inversion to, and in chapter 3 we present a detailed analysis of the aftershock mechanisms in relation to the source complexity of the mainshock. We show that the orientation of the aftershock mechanisms changes away from the zone where rupture took place. We suggest that this change in mechanism reflects changes in fault geometry which have limited the extent of the Northridge rupture, leading to a high static stress drop.

\r\n\r\n

The issue of source complexity is discussed further in chapter 4, where we present a systematic study of the rupture of three large strike-slip earthquakes and compare these results with observation on the surface rupture. We find a very good correlation which suggests that the source complexity can be attributed to fault geometry, which tends to become simpler as slip accumulates along a fault. This provides an explanation for the high stress drops that are observed for earthquakes which occur along faults with low strain rates.

\r\n\r\n

Finally, in chapter 5 we compiled energy and moment estimates for earthquakes in Southern California, based on the results in the previous chapters. We find that the radiated seismic energy is not linearly related to the seismic moment, but that instead the\r\nenergy-moment ratio increases as a function of moment. We provide some suggestions as to the cause of this relationship, including a moment dependence of the specific fracture energy and a non-similarity of the frictional stress between different size earthquakes.

", "doi": "10.7907/s8s1-f531", "publication_date": "1996", "thesis_type": "phd", "thesis_year": "1996" }, { "id": "thesis:4375", "collection": "thesis", "collection_id": "4375", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11022007-110943", "primary_object_url": { "basename": "Gazis_ca_1995.pdf", "content": "final", "filesize": 57523337, "license": "other", "mime_type": "application/pdf", "url": "/4375/1/Gazis_ca_1995.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "An isotopic study of the fluid flow and thermal history of the 2.8 Ma Chegem ash-flow caldera and related intrusive rocks (Caucasus Mountains, Russia)", "author": [ { "family_name": "Gazis", "given_name": "Carey Alice", "clpid": "Gazis-C-A" } ], "thesis_advisor": [ { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" } ], "thesis_committee": [ { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Burnett", "given_name": "Donald S.", "clpid": "Burnett-D-S" }, { "family_name": "Stolper", "given_name": "Edward M.", "clpid": "Stolper-E-M" }, { "family_name": "Rossman", "given_name": "George Robert", "clpid": "Rossman-G-R" }, { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.\r\n\r\nThe 2.8 Ma Chegem caldera, an 11x15 km ash-flow caldera located in the Caucasus Mountains, presents a unique opportunity to study silicic magma systems because of its combination of youth, exposure and simplicity. Rapid uplift and erosion in the region has exposed over 2 km of flatlying caldera fill, consisting of densely welded tuff (rhyolitic to dacitic), overlain by glacial deposits and andesite flows and cut by a granodiorite porphyry intrusion. The Eldjurta Granite, whose age and composition are similar to the Chegem volcanics, is exposed in an adjacent river valley 10 km to the northeast. Major Mo-W deposits located in nearby skarns have prompted mineral-exploration drillholes (to 4 km depth) in the granite. An isotopic study of the rocks of the Chegem caldera and the Eldjurta Granite has been performed to examine their petrogenesis, fluid flow and thermal histories.\r\n\r\nBiotite and sanidine [...] ages for 8 Chegem Tuff samples and the granodiorite intrusion are analytically indistinguishable at 2.82 \u00b1 0.02 Ma. Thus, the Chegem Tuff was erupted, cooled and intruded by the granodiorite within < 50,000 yrs. In the nearby Eldjurta Granite, biotite and K-feldspar [...] ages for 11 samples, including 8 from the deep drillhole (to 3970m depth) yield ages between 0.83 \u00b1 0.29 Ma and 2.78 \u00b1 0.09 Ma. A decrease in biotite ages from 1.90 \u00b1 0.24 Ma near the roof of the granite to 0.83 \u00b1 0.29 Ma at 3970m depth, apparently records the uplift and cooling history of this pluton. The ages of the upper 10 samples imply an isotherm migration rate of 13 mm/yr, probably due to a combination of downward migration of isotherms and regional uplift.\r\n\r\nOxygen isotope studies of the intracaldera tuff, including 38 samples from a continuous 1405m-stratigraphic section, reveal a striking caldera-wide stratigraphic horizon of [...]-depleted rocks in which there is extreme disequilibrium between phenocrysts and groundmass (sometimes still glassy). All quartz and feldspar phenocrysts have \"normal\" igneous [...] values of [...]8.5 and [...]7.0, respectively. Whole-rock and groundmass [...] values are as low as -4.0 and -7.7, respectively. Infrared spectroscopic analyses of glassy pumices reveal that they contain 3.3 to 4.8 wt% water. The [...] and water speciation of these glasses reflects low-temperature hydration by meteoric water, whereas some of their [...] values require higher temperature water-glass interaction.\r\n\r\nPronounced disequilibrium between coexisting feldspar and groundmass or glass has never been observed before on this scale. It requires a hydrothermal event involving large amounts of low-[...] H2O at sufficiently high temperatures and short enough time that glass exchanges thoroughly but feldspar does not. The most likely process responsible for the [...] depletions at Chegem is a high-temperature (500-600\u00b0C), short-lived (10-25 years), vigorous meteoric-hydrothermal event similar to that which occurred at the Valley of Ten Thousand Smokes, Alaska. Mass balance calculations indicate fluid fluxes of [...] mol/[...]-sec over that time period. Sr isotopic studies reveal that this hydrothermal event caused increases in whole-rock [...], possibly because the hydrothermal waters attained radiogenic Sr from crystalline rocks which were incorporated in the caldera fill during caldera collapse.\r\n\r\n[...] ratios of unaltered Chegem volcanic and intrusive rocks range from 0.7044 to 0.7060, significantly lower than values for surrounding country rock (0.7070 to 0.7319). Thus, the Chegem magmas were probably derived from the mantle or lower crust. The [...] ratios correlate with major- and trace-element trends, indicating that the Chegem magma chamber was both isotopically and compositionally zoned. Compared to the Chegem rocks, the Eldjurta Granite has higher [...] (0.7069), [...] and [...], and so must have evolved separately at some time.\r\n", "doi": "10.7907/mjb1-6r66", "publication_date": "1995", "thesis_type": "phd", "thesis_year": "1995" }, { "id": "thesis:4372", "collection": "thesis", "collection_id": "4372", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-11022007-093001", "type": "thesis", "title": "Seismic Strain Rates and the State of Tectonic Stress in the Southern California Region", "author": [ { "family_name": "Huang", "given_name": "Weishi", "clpid": "Huang-Weishi" } ], "thesis_advisor": [ { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "thesis_committee": [ { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Stock", "given_name": "Joann M.", "orcid": "0000-0003-4816-7865", "clpid": "Stock-J-M" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

I determine 505 fault plane solutions from the first motions of P-waves for the\r\nbackground seismicity (3.0≤ M≤6.0, 1981-1991) and collect mechanisms of major\r\nearthquakes (M≥6.0, 1927-1994) from the literature in the southern California region.\r\nThen I study the seismic strain and tectonic stress fields in individual domains (ten in\r\ntotal) by analyzing these mechanism data. The seismic strain tensors are obtained by\r\ntensorial summation of individual seismic moment tensors. The tectonic stress tensors\r\nare determined by performing numerical inversions of the slip vector data, using\r\nAngelier's (1990) method. The findings are summarized as follows:

\r\n\r\n

(1) Of the 505 fault plane solutions for the 1981-1991 background seismicity, 54%\r\nare strike-slip (SF), 21 % reverse (RF), 17% normal (NF), and 8% oblique-slip\r\nfaulting (OS) events. The catalog of the major earthquakes for the period 1927-\r\n1994 also displays similar proportions of the faulting mechanisms;

\r\n\r\n

(2) The similarity of the focal mechanisms can be measured by a parameter, seismic\r\nconsistency (Sc) introduced by Apperson (1991). It is defined as the ratio of the\r\nscalar moment of the total moment tensor to the sum of the scalar moments of\r\nindividual moment tensors. In southern California, the Brawley fault (BYF)\r\ndomain shows the highest Sc (0.70), whereas the White Wolf fault (WWF)\r\ndomain displays the lowest Sc (0.44). Sc values in other domains vary between\r\nthe above two values;

\r\n\r\n

(3) The depths of possible low-angle faults inferred from the fault plane solutions\r\nvary from 20 km in the Transverse ranges where N-S convergence dominates, to\r\nonly 1 km in the southern Sierra Nevada fault (SSNF) domain where E-W divergence\r\ndominates. Our current data do not show the existence of a sigle unified\r\nseismically-active master detachment in the seismogenic zone;

\r\n\r\n

(4) The axes of the maximum principal stress, \u03b41. are oriented N6\u00b0E \u00b111\u00b0, whereas\r\nthose of the maximum principal strain, \u03b51 are oriented N5\u00b0E \u00b121\u00b0;

\r\n\r\n

(5) The strain and stress tensors are similar to each other in the Mojave (MVE), San\r\nJacinto (SJF), Elsinore (ESF), BYF, western and eastern Transverse Ranges\r\n(WTR, ETR) domains, but dissimilar in the central Transverse Ranges (CTR),\r\nNewport-Inglewood fault (NIF), WWF, and SSNF domains. Areas with small\r\nvalues of \u03a6 = (\u03b42 - \u03b43)/(\u03b41 - \u03b43) (<0.35) such as the WTR, CTR, and NIF domains are associated with more than 40% of RF events. Areas with \u03a6 values around 0.5\r\nsuch as the SJF, ETR, WWF, ESF, BYF, and MVE domains are associated with\r\nmore than 47% of SF events. The SSNF domain has a large \u03a6 (>0.65) and\r\nshows 49% of NF events, Variation of the state of stress appears to be in the\r\nTransverse Ranges where hypocenters are generally deep. Other areas show a\r\nrelatively stable state of stress throughout the seismogenic depth;

\r\n\r\n

(6) Seismic fraction of deformation, \u03b7, is a measure of the deformation mode. It is\r\ndefined as the ratio of seismic strain rate to the total deformation rate. Because of\r\nthe limited seismic data, we can usually estimate the apparent instead of the real\r\nseismic fraction of deformation. Therefore, caution must be exercised in applying\r\nthe values of \u03b7 to evaluations of seismic potential, In southern California, there\r\nare some indications that areas in which seismic deformation nearly accounts for\r\nthe total deformation are typically associated with cold and rigid batholithic rocks\r\nor high seismic velocity anomalies such as in the SJF, south central MVE, WWF,\r\nand possibly the ETR domains. However, areas with low seismic velocity\r\nanomalies are not free of earthquakes as seen, for example, in the BYF domain,\r\nwhich shows \u03b7 = 0.6-1.0. Other domains show \u03b7 < 0.4. The problem of whether the\r\nmissing deformation is being released aseismically or has accumulated elastically\r\nremains to be resolved.

", "doi": "10.7907/P2W6-3155", "publication_date": "1995", "thesis_type": "phd", "thesis_year": "1995" }, { "id": "thesis:6692", "collection": "thesis", "collection_id": "6692", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09282011-105846249", "primary_object_url": { "basename": "Donnellan_a_1992.pdf", "content": "final", "filesize": 42090513, "license": "other", "mime_type": "application/pdf", "url": "/6692/1/Donnellan_a_1992.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "A geodetic study of crustal deformation in the Ventura Basin region, Southern California", "author": [ { "family_name": "Donnellan", "given_name": "Andrea", "clpid": "Donnellan-Andrea" } ], "thesis_advisor": [ { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" } ], "thesis_committee": [ { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

The Ventura basin lies within the north-south compressive western Transverse Ranges in southern California. The basin is characterized by rapid north-south convergence on geologic time-scales, with Quaternary rates of convergence across the basin estimated to be approximately 20 mm/yr. Global Positioning System (GPS) observations carried out over a period of 2.7 years suggest rapid rates of convergence of 7 \u00b1 2 mm/yr on geodetic time scales. The deformation corresponds to a maximum shear strain rate of 0.6 \u00b1 0.1 \u03bcrad/yr with the azimuth of maximum\r\ncompression oriented 16\u00b0 \u00b1 8\u00b0 W. The dilatation rate of 0.3 \u00b1 .1 x 10^(-6)yr^(-1) indicates that a significant amount of compression is occurring. The strain rates of\r\n0.1 \u00b1 0.1 \u03bcrad/yr south of the basin are much lower. Strain rates calculated from the GPS measurements are consistent with those calculated from comparisons between GPS and historical triangulation data. The deformation in the basin region cannot be modeled as a megashear zone, which best describes much of California.

\r\n\r\n\r\n

The observed deformation can be modeled by creep on detachment faults both north and south of the basin. Faults near the surface are most likely locked. Rupture of the San Cayetano fault within the next 200 years is possible, resulting in an earthquake of moment magnitude 6.0-6.8. Based on the fault models, the south side of the basin is capable of producing a magnitude 5.5-6.0 earthquake. The models of the short-term deformation suggest that the observed rate is consistent with the geologic record, but that the observations have taken place over a small fraction of the earthquake cycle.

\r\n", "doi": "10.7907/ejva-6672", "publication_date": "1992", "thesis_type": "phd", "thesis_year": "1992" }, { "id": "thesis:6696", "collection": "thesis", "collection_id": "6696", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09302011-112951758", "primary_object_url": { "basename": "Worden_cb_1992.pdf", "content": "final", "filesize": 24311233, "license": "other", "mime_type": "application/pdf", "url": "/6696/1/Worden_cb_1992.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Interactive seismic imaging on a multicomputer and application to the Hosgri fault", "author": [ { "family_name": "Worden", "given_name": "Charles Bruce", "clpid": "Worden-C-B" } ], "thesis_advisor": [ { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" } ], "thesis_committee": [ { "family_name": "Harkrider", "given_name": "David G.", "clpid": "Harkrider-D-G" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Seitz", "given_name": "Charles L.", "clpid": "Seitz-C-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

We present a system designed to change the manner in which seismic reflection data is imaged, by enabling interactive response to user input. This approach greatly\r\neases the effort required to produce a seismic image and gives the analyst the flexibility to explore a wide range of models. We also argue that the ability to interact with the image can greatly aid in the interpretation process, and that the structural geologist charged with interpreting the image should be directly involved in the imaging\r\nprocess. Our approach differs from current seismic\r\nprocessing techniques that limit the ability of the seismic analyst to fully explore the imaging parameters. Current methods also provide the seismic interpreter with little information as to the robustness or reliability of the imaged structure.

\r\n\r\n

The interactive imaging system is implemented on a heterogeneous, medium-grained multicomputer. This machine is configured to provide the substantial performance required by the interactive imaging task. We discuss the\r\nimplementation of the system as four separate, but\r\ninterrelated tasks: data I/O, computation, image display, and user interface. Each of these functions is supported by hardware specifically suited to the task. The system software is designed to conceal as much of the parallel implementation as possible from a programmer wishing to add processing functions.

\r\n\r\n

The interactive system is applied to a portion of EDGE seismic refection profile RU-3 that crosses the Hosgri fault, offshore central California. From the imaged\r\nstructure we infer that the Hosgri is a near-vertical fault, with relatively recent strike-slip displacement. We see no evidence, however, of recent thrust faulting.

\r\n", "doi": "10.7907/arcb-zc42", "publication_date": "1992", "thesis_type": "phd", "thesis_year": "1992" }, { "id": "thesis:6289", "collection": "thesis", "collection_id": "6289", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04112011-111843025", "primary_object_url": { "basename": "Erel_y_1991.pdf", "content": "final", "filesize": 75012318, "license": "other", "mime_type": "application/pdf", "url": "/6289/1/Erel_y_1991.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Transport of Natural Lead and Cadmium in Rivers: Global Flux Implications", "author": [ { "family_name": "Erel", "given_name": "Yigal", "clpid": "Erel-Yigal" } ], "thesis_advisor": [ { "family_name": "Patterson", "given_name": "Clair C.", "clpid": "Patterson-C-C" }, { "family_name": "Morgan", "given_name": "James J.", "clpid": "Morgan-J-J" } ], "thesis_committee": [ { "family_name": "Stolper", "given_name": "Edward M.", "clpid": "Stolper-E-M" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Patterson", "given_name": "Clair C.", "clpid": "Patterson-C-C" }, { "family_name": "Morgan", "given_name": "James J.", "clpid": "Morgan-J-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

Lead and cadmium concentrations in marine and terrestrial ecosystems, in\r\nsurfaces of soils, and in the atmosphere have been highly elevated on a global scale due\r\nto industrial pollution. In order to ascertain the natural (rock-derived) levels of lead and\r\ncadmium in streams, pristine mountain watersheds in the Sierra Nevada, California were\r\nstudied for their lead and cadmium contents, and the transport of lead and cadmium was\r\nrelated to metal relatively uninfluenced by pollution that share similar transport patterns.\r\nIn addition, rock and unpolluted water samples from granodiorite, basalt and carbonate\r\nterrains were analyzed for the concentrations of lead, iron and other elements. Wholerock\r\nsamples as well as biotite and feldspar mineral separates were used for laboratory\r\nleaching and adsorption-desorption experiments to investigate the relationship between\r\nlead and iron chemistry under controlled conditions.

\r\n\r\n

The concentrations of lead and cadmium in the late-summer drainage are shown\r\nto be close to the natural levels that are controlled by the weathering of bedrock and soil.\r\nThis is demonstrated by measurements of 1) lead isotopic composition, and Fe/Pb ratios\r\nin stream water, ground water, soil and bedrock, and 2) the removal rate of excess\r\natmospheric lead and cadmium from the water as it flows downstream.

\r\n\r\n

After the spring snow-melt runoff, most of the lead in alpine streams originates\r\nfrom ground water, and has isotopic ratios that are consistent with values expected from\r\nbedrock and soil sources, indicating that this lead is not anthropogenic in origin. The\r\nlead found in unpolluted ground waters is more radiogenic than the lead in the bedrock\r\ndrained by these waters. A preferential release of radiogenic lead into waters and\r\nleached phases of rock and soil can be explained by the preferential weathering of\r\nradiogenic accessory minerals and to a lesser extent by a preferential release of U and Th\r\ndecay products due to the recoil effect.

\r\n\r\n

The lead uptake mechanism is proposed to be adsorption on oxy-hydroxide\r\nsurfaces. In contrast, the uptake of cadmium in the stream water is erratic and cannot\r\nbe explained by the same mechanism. Adsorption-desorption experiments suggest that\r\nlead coprecipitates and is adsorbed on particle surfaces, mainly ferric iron hydroxides.\r\nDue to a similar transport mechanism and comparable rate of release from common rock\r\nand soil minerals, the ratio between natural (rock-derived) lead and iron in rivers should\r\nbe similar to their average upper continental crustal molar ratio of 1:6,500.

\r\n\r\n

Experiments and speciation models indicate that complexation of lead by manmade\r\norganic compounds decreases the fraction of lead bound to surface sites. Such an\r\nindirect pollution effect mobilizes lead and decreases the Fe/Pb ratio in rivers regardless\r\nof any direct addition of anthropogenic lead.

\r\n\r\n

Many trace metals maintain their average upper continental crustal ratio with iron\r\nin unpolluted river water, river sediments and soils; However, large excesses of most\r\ntrace metals relative to iron are found in deep-ocean water. At the transition from fresh\r\nwater to saline ocean water, two processes take place: 1) rapid removal of iron (and\r\nother particle-forming elements) from the water column due to coagulation and settling;\r\nand 2) partial desorption of trace metals from particle surfaces. While more than 99% of\r\nthe riverborne iron settles to the sediment within the continental shelf, some of the trace\r\nmetals are released to solution as dissolved chloro-complexes and are further transported\r\nto the open sea. In addition, some of the trace metals attached to airborne and recycled\r\nsea-floor particles may desorb when these particles are in contact with sea water.

\r\n\r\n

The adsorption/desorption process in sea water account for the relative\r\nabundances of many trace metals in deep-sea water (not including REE). Furthermore,\r\nit is suggested that the observed concentrations of these trace metals in deep-ocean water\r\nare relatively unaffected by pollution and are largely determined by natural processes.

\r\n", "doi": "10.7907/1RX3-W586", "publication_date": "1991", "thesis_type": "phd", "thesis_year": "1991" }, { "id": "thesis:6323", "collection": "thesis", "collection_id": "6323", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:04132011-115331837", "primary_object_url": { "basename": "Rubin_cm_1991.pdf", "content": "final", "filesize": 329673042, "license": "other", "mime_type": "application/pdf", "url": "/6323/7/Rubin_cm_1991.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Structural, stratigraphic, and geochronologic analysis of the Alexander-Taku terrane boundary and the overlapping upper Jurassic to lower Cretaceous gravina sequence, southeast Alaska", "author": [ { "family_name": "Rubin", "given_name": "Charles Martin", "clpid": "Rubin-C-M" } ], "thesis_advisor": [ { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" } ], "thesis_committee": [ { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" }, { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

An imbricate thrust belt that extends along strike for over 2000 km overprints the tectonic boundary between two of the largest allochthonous crustal fragments (Intermontane and Insular superterranes) in the North American Cordillera and affects rocks west of the Coast Plutonic Complex in southeast Alaska, western British Columbia and northern Washington. Deformation was broadly coeval with mid-Cretaceous magmatism and involved the emplacement of west-directed thrust nappes over a structurally intact and relatively unmetamorphosed basement. The Paleozoic and lower Mesozoic Alexander terrane forms structural basement for much of the thrust belt, along a moderately northeast-dipping ramp.

\r\n\r\n

The western metamorphic belt of the Coast Plutonic Complex consists of the Alexander and Taku terranes, and the Upper Jurassic and Lower Cretaceous Gravina sequence. The Alexander terrane consists of lower Paleozoic metavolcanic and metasedimentary rocks (Descon Formation) and dioritic plutons that are unconformably overlain by Lower Devonian clastic strata (Karheen Formation). These rocks are overlain locally by Upper Triassic basalt rhyolite and marine clastic strata (Hyd Group). The Taku terrane consists of polydeformed and metamorphosed strata that are divided into anupper Paleozoic and lower Mesozoic assemblage (Alava sequence) and a lower Paleozoic assembtage (Kah Shakes sequence). The lower Paleozoic Kah Shakes sequence consists of Devonian orthogneiss, quartz-rich metasedimentary rocks, metabasalt, meta-silicic tuff, marble, cate-silicate, and quartzite. The quartz-rich metasedimentary rocks may be correlative with the lower Paleozoic and mid-Paleozoic Yukon-Tanana terrane, which represents an east-Pacific fringing arc complex built on continental slope and rise deposits. The upper Paleozoic and lower Mesozoic Alava sequence consists of crinoidal and argillaceous marble, carbonaceous phyllite, argillite, mafic flows, pillow breccia, pyroclastic tuff, and minor quartz-rich metasedimentary rocks. The upper Paleozoic part of the Alava sequence is probably correlative with the mid- to late Paleozoic portion of the Yukon-Tanana terrane. The Middle and Upper Triassic portion of the Alava sequence may represent a metamorphiC vestige of the Stuhini Group, now exposed on the western flank of the Coast Batholitic belt.

\r\n\r\n

Upper Jurassic and Lower Cretaceous metavolcanic and metasedimentary strata of the Gravina sequence unconformably overlie both the Alexander and Taku terranes. These rocks form two distinct lithotectonic units in southern southeast Alaska. The lower unit consists of coarse marine pyroclastic and volcaniclastic strata, mafic flows, breccia, and fine-grained tuff which are locally intruded by hypabyssal bodies of diorite and quartz diorite. Fine- to coarse-grained turbidites and related channel-fill deposits comprise the epiclastic part of the Gravina sequence. Conglomerate units contain mostly volcanic and plutonic lithic clasts that suggest they were derived from a composite igneous source. Clasts from the channel-fill deposits yield Pb-U zircon ages of 154 to 158 Ma. The pyroclastic and volcaniclastic rocks represent remnants of a Late Jurassic oceanic arc system that was constructed on a composite basement consisting of the Alexander and Taku terranes; the Taku terrane is inferred to represent the westernmost extent of the Stikine and Yukon-Tanana terranes. These data suggest that the Intermontane (Stikine and Yukon-Tanana terranes) and Insular (Alexander terrane) superterranes were juxtaposed prior deposition of the Upper Jurassic and Lower Cretaceous Gravina sequence.

\r\n\r\n

The lower Paleozoic to Early Cretaceous rocks were deformed in the mid-Cretaceous and tectonism was broadly coeval with arc magmatism. Deformation involved the emplacement of west-directed thrust nappes over a structurally intact and relatively unmetamorphosed basement. Mid-Cretaceous tonalite, granodiorite, and quartz diorite intrude rocks of the thrust belt and were locally affected by the deformation. Mid-Cretaceous deformation occurred during two episodes that were contemporaneous with the emplacement of sill-like plutonic bodies. Older structures record ductile southwest-vergent folding and faulting, regional metamorphism and contain a well developed axial-planar foliation. The second generation structures developed during the later stages of southwest-directed reverse faulting that juxtaposes rocks of contrasting metamorphic pressures and temperatures. The presence of syntectonic kyanite-staurolite-garnet-biotite assemblages in the more eastern high-strain zones indicates that at least some of the reverse faults were generated at depths in excess of 20 km during the later stages of thrust faulting and associated uplift.

\r\n\r\n

Paleocene and younger (?) deformation has also affected rocks on the western margin of the Coast Plutonic Complex. Younger fabrics are dominated by low to moderate west-dipping foliation surfaces that are axial planar to asymmetric east-vergent folds. The east-verging fabrics have transposed earlier mid-Cretaceous fabrics . Late Paleocene pegmatite dikes are highly deformed and are affected by the west-dipping structures. Exposure of mid-crustal level rocks might be related to a reversal in vergence during Paleocene time, in which deep levels of the mid-Cretaceous thrust system were transported upward along east-vergent structures. A swarm of hornblende-bearing diabase dikes cross-cut all structures and fabrics. These dikes trend northeast and mark a regional change in the overall regional strain patterns during Miocene time.

\r\n\r\n

Structural, stratigraphic and geochronologic data suggest that regional-scale deformation in southeast Alaska occurred between 113 Ma and 89 Ma. Rocks in the thrust belt were regionally uplifted by 70 Ma, at an average minimum rate of \u2248 0.9 mm/yr. Mid-Cretaceous deformation involved the collapse of marginal basin(s) and a magmatic arc, overprinting the older tectonic boundary between the Insular superterrane and the late Mesozoic western margin of North America (i.e., the Intermontane superterrane). Contractional deformation along the length of the thrust belt was broadly coeval with arc magmatism, and thus records intra-arc tectonism. Late Paleocene to Early Eocene deformation and uplift may mark the transition from contractional to extensional tectonism, and perhaps records the collapse of tectonically thickened crust.

", "doi": "10.7907/ZQ82-2077", "publication_date": "1991", "thesis_type": "phd", "thesis_year": "1991" }, { "id": "thesis:6029", "collection": "thesis", "collection_id": "6029", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09142010-081708512", "primary_object_url": { "basename": "Liu_w_1990.pdf", "content": "final", "filesize": 90332208, "license": "other", "mime_type": "application/pdf", "url": "/6029/1/Liu_w_1990.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Paleomagnetism of miocene sedimentary rocks in the Transverse ranges: the implications for tectonic history", "author": [ { "family_name": "Liu", "given_name": "Wei", "clpid": "Liu-Wei" } ], "thesis_advisor": [ { "family_name": "Sieh", "given_name": "Kerry E.", "clpid": "Sieh-K-E" } ], "thesis_committee": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Kanamori", "given_name": "Hiroo", "clpid": "Kanamori-H" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": " Reconstructions of the offset history of the San Andreas fault in southern California have relied mainly on the correlation of rocks and structures within the Central Transverse Ranges. Only a few Miocene basins exposed along the fault zone in this area are associated closely with the early activity of the San Andreas system. The age of these sedimentary rocks is therefore critical for constraining the early activity, and helping understand the history, of the San Andreas fault. This study refines the ages of three Miocene sedimentary rock units, the Cajon, Crowder, and type Punchbowl, and Mill Creek formations, along the San Andreas fault in the Central Transverse Ranges by paleomagnetic methods, in order to provide age constraints on structures and tectonic events in the area. In addition, these data can be used to determine the magnitude of net tectonic rotations that may have occurred in these rocks.\r\n\r\n Magnetic polarity stratigraphies have been developed for the top three units of the Cajon Formation and for the entire Crowder Formation in the Cajon Valley. By matching the magnetic polarity stratigraphies with the standard magnetic polarity time scale, the ages of the Cajon and the Crowder formations are constrained to range from at least 17 Ma to 12.7 Ma and from 17 Ma to 9 Ma, respectively. Although deposition of these two formations began at nearly the same time (about 17 Ma), the youngest rocks preserved in each unit differ in age by nearly 4 million years. In conjunction with their distinct sedimentary features, source areas, and geographic extent, this indicates that they were deposited in different basins. Hence, the offset along the Squaw Peak fault that now separates the units was probably on the order of at least several tens of kilometers.\r\n\r\n Because unit 6 of the Cajon Formation (ca. 13 Ma) and unit 5 of the Crowder Formation (9.0 Ma) are the youngest units obviously truncated by the Cajon Valley and Squaw Peak faults, respectively, and the 4.2 Ma Phelan Peak Formation is not offset by these faults, these two faults were active sometime between 13 and 9 Ma, respectively and 4.2 Ma. As the San Gabriel and Liebre Mountain faults were also active during these intervals of time, our results are compatible with the theory that the Cajon Valley and the Squaw Peak faults are the offset extensions of the San Gabriel and Liebre Mountain faults, respectively. This further supports the proposal that the total offset along the modern San Andreas fault during Pliocene and Pleistocene time has been 150 - 160 kilometers.\r\n\r\n A similar paleomagnetic stratigraphic study was conducted on the late Miocene Punchbowl Formation at the Devil's Punchbowl County Park of California. The magnetic polarity pattern obtained from the Punchbowl Formation can be matched unambiguously to the geomagnetic reversal time scale from chrons 5Ar to 4Br, which implies that the formation was deposited from about 12.5 to 8.5 Ma. Combined with our age constraints on the Cajon Formation, this demonstrates that the Cajon and Punchbowl formations were deposited during completely different periods of time. This confirms the interpretation of Woodburne and Golz (1972) that the two formations do not correlate. Hence, the distance between these two formations cannot be used to constrain the total offset along the San Andreas fault.\r\n\r\n The age of the Punchbowl Formation also constrains the activity of the Fenner fault, which may be an old strand of the early San Andreas system. The Punchbowl Formation is the oldest unit that is not offset by the Fenner fault. Although the Paleocene San Francisquito Formation is the youngest unit offset by the fault at Devil's Punchbowl, early Miocene rocks were offset by the San Francisquito and Clemens Well faults, which were suggested as offset portions of the Fenner fault (Powell, 1980). Hence, the Fenner fault was probably active between early Miocene time and 12.5 Ma. Timing of another strand of the early San Andreas system, the Punchbowl fault, is also constrained by our result. Based on the geologic data, the Punchbowl fault has had two episodes of activity, one immediately before the deposition of the Punchbowl Formation, another after its deposition. Therefore, our results constrain these two episodes to start at about 12.5 Ma and after 8.5 Ma, respectively.\r\n\r\n Tectonic rotations determined by anomalies in the paleomagnetic declination of these formations are quite different. In Cajon Valley, the Cajon Formation shows clockwise rotations of up to 26\u00b0, whereas rotation in the Crowder Formation is much less (at most 4\u00b0 clockwise). Rotations in the Cajon Formation were probably caused by differential thrusting along the Squaw Peak thrust system, complicated further by small contributions from drag on \"tear\" segment of the Squaw Peak and the San Andreas faults.\r\n\r\n Abnormal counterclockwise rotations (27.5\u00b0 \u00b1 4.3\u00b0) were found in the Punchbowl Formation, which are compatible with those interpreted in the Mint Canyon Formation (13\u00b0 \u00b1 30\u00b0) 40 to 50 km to the west. This suggests that the entire San Gabriel block between the San Andreas and San Gabriel faults may have been rotated counterclockwise. The rotation probably occurred as the San Gabriel block moved adjacent to the preexisting bent segment of the San Andreas fault, aided by the Mojave Desert block acting as a \"backstop.\" After correcting for this rotation, the Punchbowl and Fenner faults would be parallel to the San Andreas fault in this area. This supports the proposal that the Fenner and Punchbowl faults were strands of the early San Andreas system during Miocene time.\r\n\r\n There is little or no rotation in the Mill Creek Formation, which was exposed in an elongated block between two (or three) strands of the San Andreas fault. As the Mill Creek block is a long sliver in, and parallel to the strike of, the fault zone, it is thus difficult to rotate.\r\n\r\n Our results do not agree with the prediction that the entire Transverse Ranges have been rotated clockwise in Neogene time. They also suggest that the geometry of major faults along which rigid blocks move is critical for producing the rotation and for determining the sense of the rotation. If our interpretation is correct, it implies that the San Andreas fault has had its abnormal geometry since it formed, and that the fault itself and the San Bernardino Mountains have not been rotated since Miocene time. \r\n", "doi": "10.7907/W9W2-VR83", "publication_date": "1990", "thesis_type": "phd", "thesis_year": "1990" }, { "id": "thesis:1187", "collection": "thesis", "collection_id": "1187", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-03282006-103736", "primary_object_url": { "basename": "bursik-mi-1989.pdf", "content": "final", "filesize": 10369362, "license": "other", "mime_type": "application/pdf", "url": "/1187/5/bursik-mi-1989.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Late Quaternary Volcano-Tectonic Evolution of the Mono Basin, Eastern California", "author": [ { "family_name": "Bursik", "given_name": "Marcus Ivan", "clpid": "Bursik-Marcus-Ivan" } ], "thesis_advisor": [ { "family_name": "Sieh", "given_name": "Kerry E.", "clpid": "Sieh-K-E" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" } ], "thesis_committee": [ { "family_name": "Sieh", "given_name": "Kerry E.", "clpid": "Sieh-K-E" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Sturtevant", "given_name": "Bradford", "clpid": "Sturtevant-B" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

The Mono Basin of eastern California provides an ideal laboratory in which to study the interaction of volcanic and tectonic processes. The late Quaternary geological record of volcanic activity and range-front faulting is relatively complete in the basin. Range-front faults of the Sierra Nevada offset dateable late Pleistocene glacial moraines, thus affording the opportunity to estimate range-front slip rates. The first two chapters concern dating of moraines that are offset by range-front faults.

\r\n\r\n

In Chapter One, I discuss the ages of the glacial moraines of the Mono Basin and their correlation between canyons. I dated the moraines by studying their morphology and the relative weathering of granitic boulders atop their crests, and by use of the clast-sound velocity (CSV) dating technique. The CSV technique consists of measuring the p-wave speed (V\u209a) in morainal boulders. V\u209a decreases with age as boulders weather. Clast-sound velocities enabled statistical division of moraines in each canyon into differently weathered deposits. Relative weathering features of boulder surfaces further helped discern age differences between moraines in a single canyon. Finally, CSV, relative weathering and moraine morphology, considered together, allowed correlation of moraines to an established glacial sequence, and therefore, correlation between canyons. Regression of mean V\u209a against best estimates of glaciation ages within the glacial sequence provided a further check on the validity of the correlations.

\r\n\r\n

Moraines in all major canyons from Lee Vining south were correlative with the standard late Pleistocene sequence of Tioga, Tenaya, Tahoe and Mono Basin deposits. At Lundy Canyon, however, Tahoe and Tenaya moraines are poorly, if at all, preserved. The prominent moraines extending into the basin are probably of Tioga age. Poor preservation of Tenaya and Tahoe deposits may be due to the narrow, steep-sided morphology of Lundy Canyon, and rapid down-dropping on the range-front fault.

\r\n\r\n

In Chapter Two, I discuss the application of a new quantitative dating technique to the moraines of Lee Vining Canyon. At Lee Vining Canyon, I measured cross-sectional profiles of lateral moraines of different ages to determine whether the degree to which they have been degraded could be used as a relative-dating method. Correlation of the degree of moraine degradation against an independent measure of age suggested that relative ages of late Pleistocene lateral moraines can be inferred from moraine profiles.

\r\n\r\n

Analysis of the degradation of moraine profiles with a diffusion model resulted in equations that relate profile width and maximum slope angle to age. In accordance with the diffusion model, the functional relationship between profile width and estimated age was found to be nearly linear for the moraines of Lee Vining Canyon. Fits of model to data were good, despite evidence of transport of material by non-linear diffusive processes along some of the profiles.

\r\n\r\n

Maximum slope angle is inversely proportional to age according to the diffusion model. Regression of mean maximum slope angle against inverse age for the group of moraines from Lee Vining Canyon suggested that the relationship between the two variables is expressed by the diffusion model.

\r\n\r\n

Deviations of model profile shapes from true shapes suggested that in addition to moraine age, initial profile shape and non-diffusive degradation processes are important in controlling the relationship between slope parameters and age over spans of 10\u2074 years.

\r\n\r\n

In Chapter Three, I use moraine ages determined in Chapter One to estimate slip rates of range-front faults. For Chapter Three, I measured fault-scarp profiles on the dated lateral moraines of the Mono Basin to determine fault slip rates. I compared these data with what can be deduced about the extension rate due to dike intrusion underneath the Mono Craters. I then considered extension rates in the context of regional strain patterns to infer the mode of deformation and strain relief in the Mono Basin during late Quaternary time.

\r\n\r\n

The extension-rate data indicate that dikes are being intruded underneath the Mono Craters in response to crustal stretching, and because of this, are now accommodating elastic strain that was once accommodated by range-front normal faulting. The section of the range front near the craters accommodated as much as 1 mm/yr of extension until 40,000 to 70,000 years ago. For the past 40,000 to 70,000 years, this section of range front has become inactive, even though extension along the range front to north and south has continued at up to 0.9 mm/yr. Dikes have been intruding underneath the Mono Craters for the past 40,000 years. Depending upon the assumptions used to calculate dike intrusion rates, the dikes accommodate 1 mm/yr of tectonic extension that was previously accommodated by range-front faulting.

\r\n\r\n

Consideration of the extension rates in the context of regional tectonic strain patterns suggests that the Mono Craters are forming along one of the extensional boundary structures of a pull-apart basin, the other extensional boundary of which is the deactivated range-front segment.

\r\n\r\n

If the Mono Craters represent an early stage of caldera formation, then their formation within a pull-apart zone may indicate that this is an ideal tectonic environment in which to form certain types of calderas.

", "doi": "10.7907/mv55-ah24", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:238", "collection": "thesis", "collection_id": "238", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01192007-104328", "primary_object_url": { "basename": "Prentice_cs_1989.pdf", "content": "final", "filesize": 8049246, "license": "other", "mime_type": "application/pdf", "url": "/238/13/Prentice_cs_1989.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Earthquake Geology of the Northern San Andreas Fault Near Point Arena, California", "author": [ { "family_name": "Prentice", "given_name": "Carol Seabury", "clpid": "Prentice-Carol-Seabury" } ], "thesis_advisor": [ { "family_name": "Sieh", "given_name": "Kerry E.", "clpid": "Sieh-K-E" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" } ], "thesis_committee": [ { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Sieh", "given_name": "Kerry E.", "clpid": "Sieh-K-E" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

The northern segment of the San Andreas fault last ruptured in 1906, producing the great San Francisco earthquake. This study involves the collection and interpretation of geologic data from the segment of the northern San Andreas fault near Point Arena, California, to determine the recurrence interval and slip rate of this segment of the fault.

\r\n\r\n

Holocene sediments deposited on an alluvial fan preserve a record of prehistoric earthquakes near Point Arena, California. Excavations into the fan provided exposures of the sediments across the San Andreas fault zone. At least five earthquakes were recognized in the section. All of these occurred since the deposition of a unit that is approximately 2000 years old. Because deposition in this setting was intermittent and deposition of younger units involved the erosion of underlying units, it is likely that events occurred that were not recorded in the section. Radiocarbon dating of units in the section allows constraints to be placed on the dates of the earthquakes recognized. A buried Holocene (2356-2709 years old) channel has been offset a maximum of 64 \u00b1 2 meters. This implies a maximum slip rate of 25.5 \u00b1 2.5 mm/yr. These data suggest that the average recurrence interval for great earthquakes on this segment of the San Andreas fault is long - between about 200 and 400 years.

\r\n\r\n

Offset marine terrace risers near Point Arena and an offset landslide near Fort Ross provide estimates of the average slip rate across the San Andreas fault since Late Pleistocene time. Near Fort Ross, a landslide has been offset approximately 1.7 km across the San Andreas fault. Radiocarbon analysis of charcoal from this deposit indicates that the landslide is older than 43,700 years. This implies a slip rate of less than 39 mm/yr. Correlation of two marine terrace risers across the San Andreas fault near Point Arena suggests offsets of approximately 1.5 and 2.5 km. The U-series age of a solitary coral, altitudinal spacing and correlation with known global high sea-level stands suggest ages of 83,000 and 133,000 years for these surfaces, indicating slip rates of about 18-19 mm/yr since Late Pleistocene time.

\r\n\r\n

Tentative correlation of the Pliocene Ohlson Ranch Formation in northwestern Sonoma County with deposits 50 km to the northwest near Point Arena, provides piercing points to use in calculation of a Pliocene slip rate for the northern San Andreas fault. A fission-track age of 3.3 \u00b1 0.8 Ma was determined for zircons separated from a tuff collected from the Ohlson Ranch Formation. The geomorphology of the region, especially of the two major river drainages, supports the proposed 50 km Pliocene offset. This implies a Pliocene slip rate of at least 12-20 mm/yr.

\r\n\r\n

These rates for different time periods imply that the slip rate of the northern San Andreas fault has not changed by more than a factor of two since Pliocene time. The rates also imply that much of the Pacific-North American plate motion must be accommodated on other structures at this latitude.

", "doi": "10.7907/7Y6G-DE19", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:2759", "collection": "thesis", "collection_id": "2759", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06282007-082748", "primary_object_url": { "basename": "maher-ka_1989 .pdf", "content": "final", "filesize": 18356906, "license": "other", "mime_type": "application/pdf", "url": "/2759/43/maher-ka_1989 .pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Geology of the Jackson Mountains, Northwest Nevada", "author": [ { "family_name": "Maher", "given_name": "Kevin A.", "clpid": "Maher-Kevin-A" } ], "thesis_advisor": [ { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "thesis_committee": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Kirschvink", "given_name": "Joseph L.", "orcid": "0000-0001-9486-6689", "clpid": "Kirschvink-J-L" }, { "family_name": "Murray", "given_name": "Bruce C.", "clpid": "Murray-B-C" }, { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" }, { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

The Jackson Mountains are located in the western Great Basin in Humboldt County, northwest Nevada. The range contains a late Paleozoic to Mesozoic depositional sequence. This sequence records sedimentation, volcanism and deformation in a back-arc setting. The Mississippian to late Early Permian McGill Canyon Formation was deposited in basinal to slope to distal shelf environments, dominated by hemipelagic and turbiditic facies. In the Permian there was an volcanic arc andesite component, and a nearby contemporaneous carbonate platform shed olistostromes into the unit. The McGill Canyon was laid down in an area between the McCloud arc and the Havallah back-arc basin. The late Middle Triassic to middle Norian Bliss Canyon Formation was laid down in basinal to fore-reef to carbonate platform to lagoonal to terrigenous littoral environments. Both of these formations are of flap sequences deposited on an east-facing, back-arc margin. The Bliss Canyon represents the western margin of the Early Mesozoic marine basin of the western Great Basin. From the late Norian to the Bathonian, several stages of subearial volcanism and alluvial epiclastic sedimentation laid down the Happy Creek Formation, a thick arc andesite volcanic pile. The Happy Creek is part of the Early Mesozoic Cordilleran magmatic arc province. In the Bathonian, this volcanic pile was cut by a conjugate sinistral high-angle wrench fault system as volcanism waned. During the Callovian, sediments of the King Lear Formation filled in and then overlapped the wrench basins. These sediments were derived from the east, where a west-vergent thrust system was active. This phase of thrusting ceased by the Oxfordian. Arc-related silicic volcanism and alluvial to fluvial sedimentation within the King Tear continued into the Aptian, when the thrusts were reactivated during a second phase. Both phases of thrusting verged both east and west. Stocks, dikes and sills of the Early Mesozoic Intrusive suite are comagmatic with the volcanism in the Happy Creek and King Lear, and intrude the sedimentary units. This suite both plugs and is truncated by the wrench faults and the first phase of thrusting, but is cut by the second phase. The Jackson Mountains are part of the Black Rock terrane in northwest Nevada. Within this terrane, the rocks share a common tectonic history and stratigraphy distinct from the neighboring terranes, and are separated from them by Mesozoic thrust and strike-slip faults.

", "doi": "10.7907/DE6N-4051", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:237", "collection": "thesis", "collection_id": "237", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-01192007-082647", "type": "thesis", "title": "An \u00b9\u2078O/\u00b9\u2076O Study of Mesozoic and Early Tertiary Granitic Batholiths of the Southwestern North American Cordillera", "author": [ { "family_name": "Solomon", "given_name": "George Cleve", "clpid": "Solomon-George-Cleve" } ], "thesis_advisor": [ { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" } ], "thesis_committee": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" }, { "family_name": "Burnett", "given_name": "Donald S.", "clpid": "Burnett-D-S" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Wyllie", "given_name": "Peter J.", "clpid": "Wyllie-P-J" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

Abundant evidence from previous studies indicates that, as long as samples are collected well away from pluton margins, the whole-rock \u03b4\u00b9\u2078O value of an unaltered granitic pluton is not likely to vary by more than \u00b10.5 per mil from the original \u00b9\u2078O/\u00b9\u2076O composition of its source rocks. Therefore, granitic plutons may be viewed as \"remote-sensing probes\" which sample deep portions of the continental crust or upper mantle, and \u00b9\u2078O/\u00b9\u2076O studies of such plutons can provide detailed information on lithologic boundaries at depth. This thesis presents approximately 350 new \u00b9\u2078O/\u00b9\u2076O analyses of whole-rock and quartz powders from Mesozoic and Cenozoic granitic plutons in the Northern Great Basin (NGB) and Southern Basin and Range (SBR) provinces of the western United States. The samples were collected along two broad, regional traverses eastward from the Sierra Nevada Batholith (SNB) and the Peninsular Ranges Batholith (PRB) in California: (1) the NGB traverse from western Nevada, near Carson City, eastward to the area around Salt Lake City, Utah; (2) the SBR traverse in southeastern California (SECA), eastward from the Central and Eastern Transverse Ranges across the Mojave Desert to the Colorado River, and then southeastward into southern Arizona. Where available, wholerock major-element geochemistry, [\u03b5Nd, and (\u2078\u2077Sr/\u2078\u2076Sr)i analyses of the same samples by other workers are integrated with these \u00b9\u2078O/\u00b9\u2076O analyses. In addition, several hundred whole-rock \u00b9\u2078O/\u00b9\u2076O analyses and, where available, Nd and Sr isotopic data, have been taken from the literature and combined with the new results to compile a data base that provides virtually complete reconnaissance coverage of the batholithic terranes in the Cordillera of southwestern North America.

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Samples in the southern Arizona part of the SBR traverse were collected from Jurassic, late Cretaceous, and early Tertiary granitic plutons emplaced well within mapped boundaries of the > 1.5 Ga craton. The Jurassic plutons are metaluminous, alkali-calcic, epizonal syenites, monzodiorites and granodiorites (avg. whole-rock \u03b4\u00b9\u2078O: +6.7 to +7.4). The late Cretaceous plutons are metaluminous hornblende-bearing monzogranites and granodiorites (+7.4 < \u03b4\u00b9\u2078O < +9.9). The early Tertiary (Laramide) plutons are all peraluminous, leucocratic, two-mica granites (+8.2 < \u03b4\u00b9\u2078O < +9.0), which exhibit synkinematic and post-kinematic features. The Cretaceous suite is sliqhtly more \u00b9\u2078O-enriched and less oxidized than the Jurassic suite. The peraluminous two-mica granites, which are mineralogically closest to typical S-type plutons (as defined in SE Australia), have distinctly lower \u03b4\u00b9\u2078O values than most S-type granitic rocks throughout the world. We therefore classify all of these Arizona granites as basically I-type; there is no isotopic evidence for a major, pelitic, S-type source in southern Arizona. The two-mica granites probably represent highly fractionated \"first-melts\" of cratonal basement, while the epizonal Jurassic and Cretaceous plutons probably formed from \"drier\" melts that originated deeper in the crust.

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The samples in the Transverse Ranges and the SECA part of the SBR traverse were obtained from Triassic monzonites and syenogranites, Jurassic granodiorites and monzogranites, and late Cretaceous granodiorites, monzogranites, and two-mica granites. Most of these plutons are alkalicalcic to alkalis and were intruded upward through Precambrian basement rocks, with the exception of Cretaceous calc-alkaline monzogranites and rare two-mica granites emplaced west of cratonal basement rocks in the San Bernardino Mountains (SBM) and San Gabriel Mountains (SGM). The Triassic plutons (e.g. Mt. Lowe pluton) have uniformly low \u03b4\u00b9\u2078O values (+6.7 to +8.0). The Jurassic and Cretaceous magmas had \u03b4\u00b9\u2078O values between +6.7 and +9.3, including the two-mica granites of the Old Woman Mountains (+7.2 to +9.3), Cadiz Valley Batholith (+7.7 to +9), Chemehuevi Mountains (+7.8), and eastern SBM (+8.8 to +8.9). As in southern Arizona, these \"cratonal\" two-mica granites have lower \u03b4\u00b9\u2078O values than typical S-type plutons. In contrast, the Cretaceous plutons emplaced west of mapped cratonal basement in the SBM and SGM have high \u03b4\u00b9\u2078O values, between +8.5 and +10.8. This east-west change in primary whole-rock \u03b4\u00b9\u2078O marks a fundamental, regional \u00b9\u2078O/\u00b9\u2076O boundary, which we believe can be used to map the western edge of the craton in the Cordillera of the southwestern USA. The whole-rock \u03b4\u00b9\u2078O values of the plutons in the fault-reconstructed SGM terrane, the SBM terrane, and in the Little San Bernardino Mountains (LSB) can be contoured in a systematic fashion, and these contours are subparallel to the aforementioned regional \u00b9\u2078O/\u00b9\u2076O boundary.

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Nearly all of the Jurassic plutons in the SBR traverse were emplaced into shallow volcanic centers, and they show characteristics related to calderas, including hydrothermal alteration by heated low-\u00b9\u2078O meteoric waters. The altered plutons have \u03b4\u00b9\u2078O values ranging from -3.4 to +5.7, and where sampling density permits, contouring of \u03b4\u00b9\u2078O values reveals map patterns similar to those found at other meteoric-hydrothermal centers throughout the world. The best-studied of these Jurassic centers in this work is the Rodman-Ord Mountains (ROM) area, where the distinctive \u00b9\u2078O/\u00b9\u2076O map patterns produced by the Jurassic hydrothermal events have been used to estimate approximately 3 to 4 km of left-lateral strike-slip displacement along the late Cenozoic Camp Rock Fault. These SBR calderas are apparently part of a major Jurassic rift-system that extends from southeastern Arizona to the California-Nevada border. The low \u03b4\u00b9\u2078O values of the altered Jurassic plutons in SECA indicate that the paleoclimate in that portion of the rift was typical of mountainous regions today.

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The Oligocene to Jurassic plutons in the NGB traverse in Nevada and Utah are the same samples analyzed by Farmer and DePaolo (1983) in their Nd-Sr isotopic study of NGB plutonism: (1) calc-alkaline, metaluminous granodiorites and monzogranites intrude eugeoclinal Paleozoic allochthonous terranes between the SNB and the Roberts Mountain Thrust; (2) calc-alkaline, metaluminous to peraluminous granodiorites, monzogranites and two-mica granites intrude miogeoclinal terranes between the Roberts Mountain Thrust and the first outcrops of > 1.5 Ga cratonal basement going east; (3) alkali-calcic monzodiorites, granodiorites, and monzogranites intrude cratonal shelf sediments deposited on > 1.5 Ga craton in northeastern Nevada and western Utah. The primary, whole-rock \u03b4\u00b9\u2078O values in the first of the above groups exhibit the same geographic systematics discovered by Taylor and Silver (1978) for the PRB in southern and Baja California. There is a sharp, north-trending \u00b9\u2078O/\u00b9\u2076O boundary in western Nevada, analogous to the longitudinal \"\u00b9\u2078O-step\" down the center of the PRB. West of this boundary, the NGB plutons have \u03b4\u00b9\u2078O values that are uniformly lower than +8.5, and east of this boundary the plutons have \u03b4\u00b9\u2078O > +8.5, ranging up to +13.2. The highest \u00b9\u2078O/\u00b9\u2076O areas coincide with the second of the above groups, particularly where two-mica granite plutons occur. Just east of the Utah border, the third group of plutons exhibits \u03b4\u00b9\u2078O values < +9, and farther inland, \u03b4\u00b9\u2078O decreases to values as low as +6.7. This eastern boundary is inferred to be the same one we observe in the eastern Transverse Ranges in SECA.

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We use the \u00b9\u2078O/\u00b9\u2076O data from the NGB and SBR traverses, combined and augmented with literature-derived data on the PRB, SNB, and Idaho Batholith to provide a framework for viewing the subcrustal distribution of petrotectonic assemblages in much of the western United States. In conjunction with the Nd-, Pb- and Sr-isotopic signatures, the \u00b9\u2078O/\u00b9\u2076O data are used to map isotopic variations in the source regions of these plutons. This method yields a well-constrained model for the continental crust (especially when compared with earlier models that do not take into account the \u00b9\u2078O/\u00b9\u2076O values). Such studies are particularly helpful in constraining rock-types in these source regions, because \u00b9\u2078O/\u00b9\u2076O variations in rocks arise in a totally different manner than do the radiogenic isotope variations, which are mostly dependent upon age and upon various trace element concentrations.

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As discovered in the PRB by Taylor and Silver (1978), the \u03b4\u00b9\u2078O values of granitic rocks in the western United States define a series of sharp isotopic boundaries, independent of pluton lithologies, between different geographic groupings of granitic plutons. These are extremely well defined for the Cretaceous magmatic arc, for which three north-trending belts of plutons exist: (1) a Western Zone (WZ) of low-\u00b9\u2078O plutons with +5.5 < \u03b4\u00b9\u2078O < +8.5; (2) a Central Zone (CZ) of high-\u00b9\u2078O plutons with \u03b4\u00b9\u2078O between +8.5 and +13.2; and (3) an Eastern Zone (EZ) with variable \u03b4\u00b9\u2078O, typically lower than +9.0, but locally exhibiting plutonic centers with \u03b4\u00b9\u2078O > +9.0 (commonly associated with metamorphic core complexes). When (\u2078\u2077Sr/\u2078\u2076Sr)i values are taken into account, the Central Zone in the NGB must be divided into two geographic and geochemical entities; one lying west of a north-trending (\u2078\u2077Sr/\u2078\u2076Sr)i \"step\" (< 0.7080 to the west and > 0.7100 to the east), and one between this \u2078\u2077Sr/\u2078\u2076Sr \"step\" and the CZ-EZ boundary. The westernmost part is here termed the Central V-type subzone (CZ-V), and the eastern part is termed the Central S-type subzone (CZ-S). The CZ-S subzone is not present (except on a very small, local scale) south of approximately latitude 37\u00b0N, but it makes up approximately half of the Central Zone in the NGB, and dominates the CZ in the Idaho Batholith, north of the NGB. In contrast, the CZ-V subzone extends along the entire length of the Cordillera in the western USA, although it is very narrow north of 40\u00b0N latitude in the western portions of the Idaho Batholith.

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The three geographic \u00b9\u2078O/\u00b9\u2076O zones have boundaries coincident with several fundamental geologic features. The WZ occurs west of the quartz diorite line of Moore (1959) while the CZ is centered on the thickest portions of the late Precambrian-early Phanerozoic (0.3 to 1.5 Ga) Cordilleran geosyncline. The CZ in general lies east of the quartz diorite line, and west of the western limits of > 1.5 Ga Precambrian crystalline basement. The CZ-V subzone lies within the area of the geosyncline characterized by accreted terranes and dominated by eugeoclinal lithologies, whereas the CZ-S subzone appears to be associated with late Proterozoic miogeoclinal metasedimentary rocks. The EZ is located east of the western limit of older (> 1.5 Ga) crystalline basement and east of the thick geosynclinal sedimentary section. The EZ hosts most of the major porphyry copper deposits of the region, whereas the CZ hosts the known tungsten-skarn deposits.

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The isotopic data suggest that the Cordilleran granitic plutons are derived from varying proportions of the following major end-member components (largely by simple two-component mixing): (1) upper mantle and/or subducted oceanic crust, either an Oceanic Island Arc (OIA), or MORB-type source, with \u03b4\u00b9\u2078O = +6 to +7, (\u2078\u2077Sr/\u2078\u2076Sr)i ~ 0.702 to 0.704, and \u03b5Nd ~ +2 to +7; (2) \"eugeosynclinal\" sediments and altered volcanic rocks (SAV-type sources) with \u03b4\u00b9\u2078O = +10 to +13.5, (\u2078\u2077Sr/\u2078\u2076Sr)i ~ 0.705 to 0.710, and \u03b5Nd = -2 to -9; (3) \"miogeosynclinal\" continental margin sediments (MCM), with \u03b4\u00b9\u2078O > +10, (\u2078\u2077Sr/\u2078\u2076Sr)i > 0.715, and \u03b5Nd < -9; (4) some type of \"model lithospheric component\" in the lower continental crust (LCC, > 1.5 Ga) and/or upper mantle (SCL), having evolved, crustal characteristics and (\u2078\u2077Sr/\u2078\u2076Sr)i of about 0.705 to 0.710, with \u03b4\u00b9\u2078O values of +6.0 to +8.0 in the SBR and +7.5 to +9 in the NGB, and \u03b5Nd = -6 and -12 in the NGB and -4 and -10 in the SBR; and (5) mid-level continental crust of the craton (MCC) with \u03b4\u00b9\u2078O = +8 to +10, (\u2078\u2077Sr/\u2078\u2076Sr)i > 0.715, and \u03b5Nd < -12 to as low as -20. The latter values depend on the age of the crust.

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The simplest way to characterize each geographic \u00b9\u2078O/\u00b9\u2076O zone is by simple two-component melt-solid or solid-solid mixing of source-region materials, although the lack of specific isotopic data on the actual end-members precludes a rigorous evaluation of the relative importance of assimilation-fractional crystallization (AFC) processes. Western Zone: OIA-SAV with OIA dominant. Central V-type subzone: OIA-SAV with SAV dominant. Central S-type subzone: dominantly MCM with minor SAV, LCC, and OIA(?). Eastern Zone: dominantly LCC/SCL with widely varying proportions of some other end-members, such as MCC and/or a modified OIA mantle component (i.e., one that is older and more LIL-enriched than Cretaceous OIA or MORB, and thus one with a relatively high Sr content and high \u2078\u2077Sr/\u2078\u2076Sr ratio).

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Previous workers place the \"edge of the craton\" beneath the -0.706 (Kistler and Peterman, 1978) or -0.708 (Farmer and DePaolo, 1983) (\u2078\u2077Sr/\u2078\u2076Sr)i boundaries. However, we suggest that, in the NGB the (\u2078\u2077Sr/\u2078\u2076Sr)i \"step\" (0.708) is not the edge of the craton, but instead is probably a structural discontinuity that has juxtaposed an accreted terrane of eugeosynclinal volcanic and volcanogenic sedimentary rocks on the west against a late Precambrian sedimentary terrane on the east. The sharpness of this boundary implies that it is either the edge of an ancient rift-zone (Kistler and Peterman, 1978), a strike-slip fault, or a suture zone. The hypothetical late Precambrian metasedimentary basin that we infer east of the \u2078\u2077Sr/\u2078\u2076Sr \"step\" could represent an in-filled pull-apart basin, which opened during southward transport of the \"Mojavia\" terrane of Bennett and DePaolo (1987), thus explaining the east-trending boundary between the CZ and EZ that extends all the way across south-central Nevada.

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The isotopic differences inferred for the deep continental crustal sources (LCC/SCL) in the NGB (\u03b4\u00b9\u2078O = +7 to +9) and SBR (\u03b4\u00b9\u2078O = +6 to +8) bear on the structure of the craton. The \u03b4\u00b9\u2078O of the LCC/SCL component in SECA is similar to that in southern Arizona, implying that the \u00b9\u2078O/\u00b9\u2076O composition of LCC/SCL in the SBR was acquired after any of the hypothetical tectonic movements that shifted \"Mojavia\" from the NGB southward into southeastern California (Bennett and DePaolo, 1987). This means that: (1) a relatively low-\u00b9\u2078O source could have underplated the SBR (including Mojavia) after tectonic emplacement of \"Mojavia\" athwart the southern Arizona region; or (2) previous fusion events at 1.4 Ga and 1.1 Ga could have modified the SBR deep sources, such that the \u03b4\u00b9\u2078O of the LCC/SCL underneath the SBR was lowered relative to the equivalent zone in the NGB.

", "doi": "10.7907/T831-NP65", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:8067", "collection": "thesis", "collection_id": "8067", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02112014-112136459", "primary_object_url": { "basename": "Nourse_ja_1989.pdf", "content": "final", "filesize": 60754614, "license": "other", "mime_type": "application/pdf", "url": "/8067/2/Nourse_ja_1989.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Geological Evolution of Two Crustal Scale Shear Zones. Part I: The Rand Thrust Complex, Northwestern Mojave Desert, California. Part II: The Magdalena Metamorphic Core Complex, North Central Sonora, Mexico", "author": [ { "family_name": "Nourse", "given_name": "Jonathan Alan", "clpid": "Nourse-Jonathan-Alan" } ], "thesis_advisor": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "thesis_committee": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" }, { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Kirschvink", "given_name": "Joseph L.", "orcid": "0000-0001-9486-6689", "clpid": "Kirschvink-J-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

The geology and structure of two crustal scale shear zones were studied to understand the partitioning of strain within intracontinental orogenic belts. Movement histories and regional tectonic implications are deduced from observational data. The two widely separated study areas bear the imprint of intense Late Mesozoic through Middle Cenozoic tectonic activity. A regional transition from Late Cretaceous-Early Tertiary plutonism, metamorphism, and shortening strain to Middle Tertiary extension and magmatism is preserved in each area, with contrasting environments and mechanisms. Compressional phases of this tectonic history are better displayed in the Rand Mountains, whereas younger extensional structures dominate rock fabrics in the Magdalena area.

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In the northwestern Mojave desert, the Rand Thrust Complex reveals a stack of four distinctive tectonic plates offset along the Garlock Fault. The lowermost plate, Rand Schist, is composed of greenschist facies metagraywacke, metachert, and metabasalt. Rand Schist is structurally overlain by Johannesburg Gneiss (= garnet-amphibolite grade orthogneisses, marbles and quartzites), which in turn is overlain by a Late Cretaceous hornblende-biotite granodiorite. Biotite granite forms the fourth and highest plate. Initial assembly of the tectonic stack involved a Late Cretaceous? south or southwest vergent overthrusting event in which Johannesburg Gneiss was imbricated and attenuated between Rand Schist and hornblende-biotite granodiorite. Thrusting postdated metamorphism and deformation of the lower two plates in separate environments. A post-kinematic stock, the Late Cretaceous Randsburg Granodiorite, intrudes deep levels of the complex and contains xenoliths of both Rand Schist and mylonitized Johannesburg? gneiss. Minimum shortening implied by the map patterns is 20 kilometers.

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Some low angle faults of the Rand Thrust Complex formed or were reactivated between Late Cretaceous and Early Miocene time. South-southwest directed mylonites derived from Johannesburg Gneiss are commonly overprinted by less penetrative north-northeast vergent structures. Available kinematic information at shallower structural levels indicates that late disturbance(s) culminated in northward transport of the uppermost plate. Persistence of brittle fabrics along certain structural horizons suggests a possible association of late movement(s) with regionally known detachment faults. The four plates were juxtaposed and significant intraplate movements had ceased prior to Early Miocene emplacement of rhyolite porphyry dikes.

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In the Magdalena region of north central Sonora, components of a pre-Middle Cretaceous stratigraphy are used as strain markers in tracking the evolution of a long lived orogenic belt. Important elements of the tectonic history include: (1) Compression during the Late Cretaceous and Early Tertiary, accompanied by plutonism, metamorphism, and ductile strain at depth, and thrust driven? syntectonic sedimentation at the surface. (2) Middle Tertiary transition to crustal extension, initially recorded by intrusion of leucogranites, inflation of the previously shortened middle and upper crustal section, and surface volcanism. (3) Gravity induced development of a normal sense ductile shear zone at mid crustal levels, with eventual detachment and southwestward displacement of the upper crustal stratigraphy by Early Miocene time.

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Elucidation of the metamorphic core complex evolution just described was facilitated by fortuitous preservation of a unique assemblage of rocks and structures. The \"type\" stratigraphy utilized for regional correlation and strain analysis includes a Jurassic volcanic arc assemblage overlain by an Upper Jurassic-Lower Cretaceous quartz pebble conglomerate, in turn overlain by marine strata with fossiliferous Aptian-Albian limestones. The Jurassic strata, comprised of (a) rhyolite porphyries interstratified with quartz arenites, (b) rhyolite cobble conglomerate, and (c) intrusive granite porphyries, are known to rest on Precambrian basement north and east of the study area. The quartz pebble conglomerate is correlated with the Glance Conglomerate of southeastern Arizona and northeastern Sonora. The marine sequence represents part of an isolated arm? of the Bisbee Basin.

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Crosscutting structural relationships between the pre-Middle Cretaceous supracrustal section, younger plutons, and deformational fabrics allow the tectonic sequence to be determined. Earliest phases of a Late Cretaceous-Early Tertiary orogeny are marked by emplacement of the 78 \u00b1 3 Ma Guacomea Granodiorite (U/Pb zircon, Anderson et al., 1980) as a sill into deep levels of the layered Jurassic series. Subsequent regional metamorphism and ductile strain is recorded by a penetrative schistosity and lineation, and east-west trending folds. These fabrics are intruded by post-kinematic Early Tertiary? two mica granites. At shallower crustal levels, the orogeny is represented by north directed thrust faulting, formation of a large intermontane basin, and development of a pronounced unconformity. A second important phase of ductile strain followed Middle Tertiary? emplacement of leucogranites as sills and northwest trending dikes into intermediate levels of the deformed section (surficial volcanism was also active during this transitional period to regional extension). Gravitational instabilities resulting from crustal swelling via intrusion and thermal expansion led to development of a ductile shear zone within the stratigraphic horizon occupied by a laterally extensive leucogranite sill. With continued extension, upper crustal brittle normal faults (detachment faults) enhanced the uplift and tectonic denudation of this mylonite zone, ultimately resulting in southwestward displacement of the upper crustal stratigraphy.

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Strains associated with the two ductile deformation events have been successfully partitioned through a multifaceted analysis. Rf/\u00d8 measurements on various markers from the \"type\" stratigraphy allow a gradient representing cumulative strain since Middle Cretaceous time to be determined. From this gradient, noncoaxial strains accrued since emplacement of the leucogranites may be removed. Irrotational components of the postleucogranite strain are measured from quartz grain shapes in deformed granites; rotational components (shear strains) are determined from S-C fabrics and from restoration of rotated dike and vein networks. Structural observations and strain data are compatable with a deformation path of: (1) coaxial strain (pure shear?), followed by (2) injection of leucogranites as dikes (perpendicular to the minimum principle stress) and sills (parallel to the minimum principle stress), then (3) southwest directed simple shear. Modeling the late strain gradient as a simple shear zone permits a minimum displacement of 10 kilometers on the Magdalena mylonite zone/detachment fault system. Removal of the Middle Tertiary noncoaxial strains yields a residual (or pre-existing) strain gradient representative of the Late Cretaceous-Early Tertiary deformation. Several partially destrained cross sections, restored to the time of leucogranite emplacement, illustrate the idea that the upper plate of the core complex bas been detached from a region of significant topographic relief. 50% to 100% bulk extension across a 50 kilometer wide corridor is demonstrated.

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Late Cenozoic tectonics of the Magdalena region are dominated by Basin and Range style faulting. Northeast and north-northwest trending high angle normal faults have interacted to extend the crust in an east-west direction. Net extension for this period is minor (10% to 15%) in comparison to the Middle Tertiary detachment related extensional episode.

", "doi": "10.7907/S427-2704", "publication_date": "1989", "thesis_type": "phd", "thesis_year": "1989" }, { "id": "thesis:4031", "collection": "thesis", "collection_id": "4031", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10112005-103528", "type": "thesis", "title": "High Precision Thorium-230 Ages of Corals and the Timing of Sea Level Fluctuations in the Late Quaternary", "author": [ { "family_name": "Edwards", "given_name": "Richard Lawrence", "clpid": "Edwards-Richard-Lawrence" } ], "thesis_advisor": [ { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Stolper", "given_name": "Edward M.", "clpid": "Stolper-E-M" } ], "thesis_committee": [ { "family_name": "Stolper", "given_name": "Edward M.", "clpid": "Stolper-E-M" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "clpid": "Wasserburg-G-J" }, { "family_name": "Sieh", "given_name": "Kerry E.", "clpid": "Sieh-K-E" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Yung", "given_name": "Yuk L.", "clpid": "Yung-Y-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

Mass spectrometric techniques for the measurement of \u00b2\u00b3\u2070Th and \u00b2\u00b3\u2074U have been developed. These techniques have made it possible to reduce the analytical errors in \u00b2\u00b3\u2070Th dating of corals using very small samples. Samples of 8 x 10\u2077 atoms of \u00b2\u00b3\u2070Th can be measured to an accuracy of \u00b1130% (2 sigma), 6 x 10\u2078 atoms of \u00b2\u00b3\u2070Th can be measured to an accuracy of \u00b129%, and 3 x 10\u00b9\u2070 atoms of \u00b2\u00b3\u2070Th can be measured to an accuracy of \u00b12%. The time range over which useful data on corals can now be obtained ranges from 15 to 500,000 years. The error in age (based on analytical error) for a sample that is 18 years old \u00b13 years (2 sigma). The error is \u00b15 years at 180 years, \u00b144 years at 8294 years, and \u00b11 ky at 123.1 ky. For young corals, this approach may be preferable to \u00b9\u2074C dating.

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Fluctuations in climate result in changes in sea level because the ice stored in continental glaciers is ultimately derived from the ocean. Certain species of coral grow close to the sea surface. Fossils of these species therefore record the former height of the sea surface. The precision with which the age of a coral can now be determined makes it possible to determine, with some precision, the timing of sea level fluctuations in the late Quaternary. This record will allow a critical test of the Milankovitch hypothesis, which predicts the timing of Pleistocene climate fluctuations from changes in the distribution of solar insolation that result from changes in the earth's orbital geometry. Analyses of a number of corals that grew during the last interglacial period yield ages of 122 to 130 ky. The ages coincide with or slightly postdate the summer solar insolation high at 65\u00b0N latitude, which occurred 128 ky ago. This supports the idea that changes in Pleistocene climate can be the result of orbital forcing.

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Apparent fluctuations in sea level recorded on tectonically active shorelines are the result of both sea level change and vertical tectonic movement. If the record of sea level change is known (e.g., from the coral record in a stable area), this record can be subtracted from the record of apparent sea level change, in the tectonically active area, to yield a record of vertical tectonic movement. The precision with which coral ages can now be determined may allow us to resolve the ages of individual coseisimic uplift events and thereby date prehistoric earthquakes.

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This possibility has been examined at two localities, northwest Santo Island and north Malekula Island, Vanuatu. Previous work (Taylor et al., 1980, 1985a, 1987) showed (using the counting of annual growth bands to determine ages) that the tops of partially emerged coral heads at each locality died at the same time as the last major earthquake at each locality (MS = 7.5, 1973, on northwest Santo; and MS = 7.5, 1965, on north Malekula). It was concluded that the tops of these coral heads were killed by coseismic uplift. At each locality, there were also completely emerged coral heads, which were inferred to have been killed by earlier coseismic uplift events. These could not be dated by growth band counting because the coral heads were completely dead.

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The accuracy of \u00b2\u00b3\u2070Th ages of very young corals was tested by dating portions of three corals whose ages were known from the counting of growth bands. Within analytical error, the \u00b2\u00b3\u2070Th ages were the same as the growth band ages for all three samples (dates of growth by counting growth bands - A.D. 1971 to 1973, A.D. 1935 to 1939, and A.D. 1804 to 1810; dates of growth from \u00b2\u00b3\u2070Th measurements - A.D. 1969 \u00b1 3, A.D. 1932 \u00b1 5, and A.D. 1806 5 [2 sigma \u00b11) demonstrating that the \u00b2\u00b3\u2070Th ages were accurate.

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The \u00b2\u00b3\u2070Th growth dates of the surfaces of adjacent emerged coral heads, collected from the same elevation (1.2 m) on northwest Santo Island, were, within analytical error, identical (A.D. 1866 \u00b1 4 and A.D. 1864 \u00b1 4). This indicates that the corals died at the same time and is consistent with the idea that they were killed by coseismic uplift. Similar adjacent coral heads on north Malekula Island yielded \u00b2\u00b3\u2070Th growth dates of A.D. 1729 \u00b1 3 and A.D. 1718 \u00b1 5. The ages are similar but analytically distinguishable. The difference may be due to erosion of the outer, younger, portion of the latter coral head. Using the date of the large historical earthquake at each locality and the \u00b2\u00b3\u2070Th growth date of the emerged corals at each locality, recurrence intervals of 108 years for northwest Santo and 236 years for north Malekula are calculated.

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This experiment has shown that it is possible to date corals that grew in the past several centuries to accuracies of \u00b13 to \u00b15 years (2 sigma). The main problems with applying this approach to determine seismic histories will be associated with the preservation of fossil corals that have been killed by coseimic uplift and the ability to identify such features in the field.

", "doi": "10.7907/S2FW-0463", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:7536", "collection": "thesis", "collection_id": "7536", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03212013-080648923", "type": "thesis", "title": "Water in Silicate Glasses", "author": [ { "family_name": "Silver", "given_name": "Lynn Alison", "clpid": "Silver-Lynn-Alison" } ], "thesis_advisor": [ { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "thesis_committee": [ { "family_name": "Burnett", "given_name": "Donald S.", "clpid": "Burnett-D-S" }, { "family_name": "Eckert", "given_name": "Hellmut", "clpid": "Eckert-Hellmut" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

The speciation of water in a variety of hydrous silicate glasses, including simple and rhyolitic compositions, synthesized over a range of experimental conditions with up to 11 weight percent water has been determined using infrared spectroscopy. This technique has been calibrated with a series of standard glasses and provides a precise and accurate method for determining the concentrations of molecular water and hydroxyl groups in these glasses.

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For all the compositions studied, most of the water is dissolved as hydroxyl groups at total water contents less than 3-4 weight percent; at higher total water contents, molecular water becomes the dominant species. For total water contents above 3-4 weight percent, the amount of water dissolved as hydroxyl groups is approximately constant at about 2 weight percent and additional water is incorporated as molecular water. Although there are small but measurable differences in the ratio of molecular water to hydroxyl groups at a given total water content among these silicate glasses, the speciation of water is similar over this range of composition. The trends in the concentrations of the H-bearing species in the hydrous glasses included in this study are similar to those observed in other silicate glasses using either infrared or NMR spectroscopy.

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The effects of pressure and temperature on the speciation of water in albitic glasses have been investigated. The ratio of molecular water to hydroxyl groups at a given total water content is independent of the pressure and temperature of equilibration for albitic glasses synthesized in rapidly quenching piston cylinder apparatus at temperatures greater than 1000\u00b0C and pressures greater than 8 kbar. For hydrous glasses quenched from melts cooled at slower rates (i.e., in internally heated or in air-quench cold seal pressure vessels), there is an increase in the ratio of molecular water to hydroxyl group content that probably reflects reequilibration of the melt to lower temperatures during slow cooling.

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Molecular water and hydroxyl group concentrations in glasses provide information on the dissolution mechanisms of water in silicate liquids. Several mixing models involving homogeneous equilibria of the form H\u2082O + O = 2OH among melt species have been explored for albitic melts. These models can account for the measured species concentrations if the effects of non-ideal behavior or mixing of polymerized units are included, or by allowing for the presence of several different types of anhydrous species.

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A thermodynamic model for hydrous albitic melts has been developed based on the assumption that the activity of water in the melt is equal to the mole fraction of molecular water determined by infrared spectroscopy. This model can account for the position of the water-saturated solidus of crystalline albite, the pressure and temperature dependence of the solubility of water in albitic melt, and the volumes of hydrous albitic melts. To the extent that it is successful, this approach provides a direct link between measured species concentrations in hydrous albitic glasses and the macroscopic thermodynamic properties of the albite-water system.

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The approach taken in modelling the thermodynamics of hydrous albitic melts has been generalized to other silicate compositions. Spectroscopic measurements of species concentrations in rhyolitic and simple silicate glasses quenched from melts equilibrated with water vapor provide important constraints on the thermodynamic properties of these melt-water systems. In particular, the assumption that the activity of water is equal to the mole fraction of molecular water has been tested in detail and shown to be a valid approximation for a range of hydrous silicate melts and the partial molar volume of water in these systems has been constrained. Thus, the results of this study provide a useful thermodynamic description of hydrous melts that can be readily applied to other melt-water systems for which spectroscopic measurements of the H-bearing species are available.

", "doi": "10.7907/z336-zw46", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:490", "collection": "thesis", "collection_id": "490", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-02042005-111245", "primary_object_url": { "basename": "Manduca_cca_1988.pdf", "content": "final", "filesize": 22647149, "license": "other", "mime_type": "application/pdf", "url": "/490/21/Manduca_cca_1988.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Geology and Geochemistry of the Oceanic Arc-Continent Boundary in the Western Idaho Batholith near McCall", "author": [ { "family_name": "Manduca", "given_name": "Cathryn Clement Allen", "clpid": "Manduca-Cathryn-Clement-Allen" } ], "thesis_advisor": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" } ], "thesis_committee": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" }, { "family_name": "Stevenson", "given_name": "David John", "clpid": "Stevenson-D-J" }, { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

A major lithospheric boundary is preserved within the western Idaho Batholith. The juxtaposition of two suites of supracrustal rocks, exposed as sheets within intrusive rocks, is the expression of this boundary at the level of exposure. The western suite of mafic layered gneisses are inferred to be metamorphosed oceanic arc rocks; the eastern suite of biotite schist, quartzite and calc-silicate gneiss are inferred to be metamorphosed continental sedimentary rocks. Three broadly Cretaceous, plutonic and meta-plutonic complexes record the presence of the boundary at greater depth. The Hazard Creek complex, west of the supracrustal boundary, is comprised of epidote-bearing intrusives. The Little Goose Creek complex is comprised primarily of the porphyritic orthogneiss that intruded the supracrustal boundary. The Payette River complex, east of the supracrustal boundary, is comprised of large bodies of tonalite and granite.

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Each complex has a distinct geochemical character. The Hazard Creek complex is dominantly a tonalite-trondhjemite suite characterized by Ri less than .7045, \u03b4\u00b9\u2078O less than 8.4, high Sr, Na\u2082O and Al\u2082O\u2083 concentrations and low MgO, Rb and K\u2082O concentrations. Porphyritic orthogneiss in the Little Goose Creek complex has a remarkable range in Ri and \u03b4\u00b9\u2078O (.7042-.7097, 8.0-10.7). The porphyritic orthogneiss is interpreted as dominated by two components: one similar in composition to the Hazard Creek complex and a second, modeled as Precambrian sedimentary material, with high Ri, \u03b4\u00b9\u2078O and K\u2082O concentrations and lower Sr concentration. The Payette River complex has generally high Ri (.7076-.7100) and variable \u03b4\u00b9\u2078O (7.2-10.4). The geochemical changes indicate that the supracrustal boundary is the surface expression of a steeply-dipping structure which juxtaposes oceanic-arc lithosphere against continental lithosphere. An abrupt geochemical discontinuity preserved within the porphyritic orthogneiss, near the change in supracrustal rocks, may reflect an abrupt discontinuity at depth or may be due to the juxtapositon of portions of a stratified pluton. The juxtaposition of lithospheric blocks must have occured prior to intrusion of the porphyritic orthogneiss approximately 111 Ma, and most probably, occured before 118 Ma, prior to the beginning of plutonism. No structural evidence for the initial formation of the boundary is recognized; it is proposed to form by transform faulting or by rifting followed by convergence.

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Episodic or continuous deformation along the boundary began prior to 118 Ma and produced four sets of structures. The oldest structures are foliation and isoclinal folding of crystalloblastic gneisses which may have formed during rapid burial of oceanic-arc rocks west of the boundary. Compressive deformation, forming north-south striking steeply-dipping foliations and steeply-plunging lineations in the eastern portion of the Hazard Creek complex, was broadly coeval with its emplacement. Igneous foliation and lineation with similar orientation formed during emplacement of the Payette River complex around 90 Ma. The youngest penetrative deformation formed similarly oriented, mylonitic fabrics in a 10 km wide zone centered on the boundary. All but the oldest structures are inferred to have formed by flattening and vertical flow in response to east-west compression. Deformation is interpreted to represent the response of a preexisting lithospheric boundary to compressive stresses related to subduction of material to the west.

", "doi": "10.7907/JP15-KC07", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:7528", "collection": "thesis", "collection_id": "7528", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03192013-112511014", "primary_object_url": { "basename": "Ho-Liu 1988.pdf", "content": "final", "filesize": 29826328, "license": "other", "mime_type": "application/pdf", "url": "/7528/1/Ho-Liu 1988.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I. Attenuation Tomography. II. Modeling Regional Love Waves: Imperial Valley to Pasadena", "author": [ { "family_name": "Ho-Liu", "given_name": "Phyllis Hang-Yin", "clpid": "Ho-Liu-Phyllis-Hang-Yin" } ], "thesis_advisor": [ { "family_name": "Kanamori", "given_name": "Hiroo", "clpid": "Kanamori-H" }, { "family_name": "Harkrider", "given_name": "David G.", "clpid": "Harkrider-D-G" } ], "thesis_committee": [ { "family_name": "Harkrider", "given_name": "David G.", "clpid": "Harkrider-D-G" }, { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" }, { "family_name": "Kanamori", "given_name": "Hiroo", "clpid": "Kanamori-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

Abstract to Part I

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The inverse problem of seismic wave attenuation is solved by an iterative back-projection method. The seismic wave quality factor, Q, can be estimated approximately by inverting the S-to-P amplitude ratios. Effects of various uncertain ties in the method are tested and the attenuation tomography is shown to be useful in solving for the spatial variations in attenuation structure and in estimating the effective seismic quality factor of attenuating anomalies.

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Back-projection attenuation tomography is applied to two cases in southern California: Imperial Valley and the Coso-Indian Wells region. In the Coso-Indian Wells region, a highly attenuating body (S-wave quality factor (Q\u03b2 \u2248 30) coincides with a slow P-wave anomaly mapped by Walck and Clayton (1987). This coincidence suggests the presence of a magmatic or hydrothermal body 3 to 5 km deep in the Indian Wells region. In the Imperial Valley, slow P-wave travel-time anomalies and highly attenuating S-wave anomalies were found in the Brawley seismic zone at a depth of 8 to 12 km. The effective S-wave quality factor is very low (Q\u03b2 \u2248 20) and the P-wave velocity is 10% slower than the surrounding areas. These results suggest either magmatic or hydrothermal intrusions, or fractures at depth, possibly related to active shear in the Brawley seismic zone.

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No-block inversion is a generalized tomographic method utilizing the continuous form of an inverse problem. The inverse problem of attenuation can be posed in a continuous form , and the no-block inversion technique is applied to the same data set used in the back-projection tomography. A relatively small data set with little redundancy enables us to apply both techniques to a similar degree of resolution. The results obtained by the two methods are very similar. By applying the two methods to the same data set, formal errors and resolution can be directly computed for the final model, and the objectivity of the final result can be enhanced.

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Both methods of attenuation tomography are applied to a data set of local earthquakes in Kilauea, Hawaii, to solve for the attenuation structure under Kilauea and the East Rift Zone. The shallow Kilauea magma chamber, East Rift Zone and the Mauna Loa magma chamber are delineated as attenuating anomalies. Detailed inversion reveals shallow secondary magma reservoirs at Mauna Ulu and Puu Oo, the present sites of volcanic eruptions. The Hilina Fault zone is highly attenuating, dominating the attenuating anomalies at shallow depths. The magma conduit system along the summit and the East Rift Zone of Kilauea shows up as a continuous supply channel extending down to a depth of approximately 6 km. The Southwest Rift Zone, on the other hand, is not delineated by attenuating anomalies, except at a depth of 8-12 km, where an attenuating anomaly is imaged west of Puu Kou. The Ylauna Loa chamber is seated at a deeper level (about 6-10 km) than the Kilauea magma chamber. Resolution in the Mauna Loa area is not as good as in the Kilauea area, and there is a trade-off between the depth extent of the magma chamber imaged under Mauna Loa and the error that is due to poor ray coverage. Kilauea magma chamber, on the other hand, is well resolved, according to a resolution test done at the location of the magma chamber.

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Abstract to Part II

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Long period seismograms recorded at Pasadena of earthquakes occurring along a profile to Imperial Valley are studied in terms of source phenomena (e.g., source mechanisms and depths) versus path effects. Some of the events have known source parameters, determined by teleseismic or near-field studies, and are used as master events in a forward modeling exercise to derive the Green's functions (SH displacements at Pasadena that are due to a pure strike-slip or dip-slip mechanism) that describe the propagation effects along the profile. Both timing and waveforms of records are matched by synthetics calculated from 2-dimensional velocity models. The best 2-dimensional section begins at Imperial Valley with a thin crust containing the basin structure and thickens towards Pasadena. The detailed nature of the transition zone at the base of the crust controls the early arriving shorter periods (strong motions), while the edge of the basin controls the scattered longer period surface waves. From the waveform characteristics alone, shallow events in the basin are easily distinguished from deep events, and the amount of strike-slip versus dip-slip motion is also easily determined. Those events rupturing the sediments, such as the 1979 Imperial Valley earthquake, can be recognized easily by a late-arriving scattered Love wave that has been delayed by the very slow path across the shallow valley structure.

\r\n\r\n\r\n", "doi": "10.7907/fb8j-fs65", "publication_date": "1988", "thesis_type": "phd", "thesis_year": "1988" }, { "id": "thesis:7190", "collection": "thesis", "collection_id": "7190", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:08222012-144207263", "primary_object_url": { "basename": "Astiz_Delgado_lmdla_1987.pdf", "content": "final", "filesize": 39231778, "license": "other", "mime_type": "application/pdf", "url": "/7190/1/Astiz_Delgado_lmdla_1987.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "I. Source Analysis of Large Earthquakes in Mexico. II. Study of Intermediate-Depth Earthquakes and Interplate Seismic Coupling", "author": [ { "family_name": "Astiz Delgado", "given_name": "Luciana Maria de Los Angeles", "clpid": "Astiz-Delgado-Luciana-Maria-de-Los-Angeles" } ], "thesis_advisor": [ { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" } ], "thesis_committee": [ { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" }, { "family_name": "Kanamori", "given_name": "Hiroo", "clpid": "Kanamori-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

Along the coast of Mexico and Central America several seismic gaps were defined by the timing, location and extent of large earthquakes. Among these regions with high seismic potential, the Ometepec and Michoacan gaps have broken since 1980. The 1982 Ometepec doublet and the 1981-1986 Michoacan sequence are studied in detail in Part I.

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The seismic moment of each of the Ometepec doublet events is 2.8 x 1026 dyne cm. The first event involved a deeper asperity (at 20 km) that caused an incremental stress change large enough to trigger the second event at shallower depth. The second event is best modeled by two sources at 15 and 10 km depth. T he largest event of the Michoacan sequence occurred on September 19, 1985 (Mw = 8.0) and caused extensive structural damage and death to over ten thousand people in Mexico City. The first event of the sequence was the 1981 Playa Azul event, which broke the central part of the gap. It is 27 km deep and has a seismic moment of 7.2 x 1027 dyne cm. The seismic moment of the September 19, 1985 earthquake was released in two distinct events with the rupture starting in the northern portion of the seismic gap and propagating 95 km to the southeast with low moment release through the area already broken by the 1981 Playa Azul earthquake. The rupture propagated 125 km further southeast with an Mw = 7.5 event on September 21, 1985. Another aftershock occurred on April 30, 1986, 50 km to the northwest of the September 19 mainshock. The most recent Michoacan events are shallower, 17-22 km, than the Playa Azul earthquake, which has a higher stress drop suggesting a higher stress level at greater depths in the Michoacan gap. The slip vectors of these events are consistent with the convergence direction of the Cocos and North American plates.

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Part II investigates the relation of intermediate-depth earthquakes to the shallower seismicity, especially since these events may reflect the state of inter-plate coupling at subduction zones. A catalog of earthquake focal mechanisms was gathered, which includes all events listed by NOAA and ISC catalogs with M > 6 and depth between 40 to 200 km, that occurred between 1960 and 1984. The final catalog includes a total of 335 events; 47 were determined by this study. Focal mechanism solutions for intermediate-depth earthquakes with M > 6.8 can be grouped into four : 1) Normal-fault events (44%), and 2) reverse-fault events (33%), both with a strike nearly parallel to the trench axis. 3) Normal or reverse fault events with a strike significantly oblique to the trench axis (10%) and 4) tear faulting events (13%).

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Simple models of plate coupling and geometry suggest that Type 1 events occur at strongly coupled plate boundaries where a down-dip extensional stress prevails in a gently dipping plate. Continental loading may be another important factor. In contrast, large normal fault earthquakes occur at shallow depths in subduction zones that are decoupled. Type 2 events with strike subparallel to the subduction zone, most of them with near vertical tension axis, occur mainly in regions that have partially coupled or uncoupled subduction zones and the observed continuous seismicity\r\nis deeper than 300 km. In terms of our simple model, the increased dip of the downgoing slab associated with weakly coupled subduction zones and the weight of the slab may induce near vertical tensional stress at intermediate depth and, consequently, the change m focal mechanism from Type 1 to Type 2 events. Events of Type 3 occur where the trench axis bends sharply, causing horizontal extensional or compressional intraplate stress. Type 4 are hinge faulting events.

\r\n\r\n

We also investigate the temporal variation of the mechanism of large intraplate earthquakes at intermediate depths in relation to the occurrence of large underthrusting earthquakes in Chile. Focal mechanisms were determined for three large events (March 1, 1934: M = 7.1, d = 120 km, April 20, 1949: M = 7.3, d = 70 km and May 8, 1971: Mw = 7.2, d = 150 km), which occurred down-dip of the great 1960 Chilean earthquake (Mw = 9.5) rupture zone. The 1971 event is down-dip compressional, whereas the 1949 and the 1934 earthquake focal mechanisms are consistent with a down-dip te nsional mechanism. Published fault plane solutions of large intermediate-depth earthquakes (March 28, 1965 and November 7, 1981), which occurred down-dip of the Valparaiso earthquakes of 1971 (Mw = 7.8) and 1985 (Mw = 8.0) are also down-dip tensional. These results suggest that before a major thrust earthquake, the interplate boundary is strongly coupled and the subducted slab is under tension at intermediate depths; after the occurrence of an interplate thrust event, the displacement on the thrust boundary induces transient compressional stress at intermediate depth in the downgoing slab. This interpretation is consistent with the hypothesis that temporal variations of focal mechanisms of outer-rise events are due to changes of interplate coupling.

\r\n\r\n

The variation of intermediate-depth earthquake focal mechanisms with M \u2265 6 is examined region by region in relation to local variations of the strength of interplate coupling. In summary, regions that are mostly uncoupled present down-dip tensional stresses in a steeply-dipping slab probably induced by the negative buoyancy of the subducted lithosphere (e.g., North Scotia arc). Double seismic zones may be present in\r\npartially coupled regions in response to un bending of the downgoing slab (e.g., Northeast Japan). Lateral bending or tearing of the slab influences the stress distribution within the subducted plate (e.g., New Ireland). Subduction of topographic highs may also change the interplate coupling locally (e.g., Louiville ridge in T onga). Regions that are mostly coupled are generally shallow dipping and the observed continuous seismicity is at most 300 km deep. In these regions normal faulting events occur at the base of the coupled region (e. g. South America). In contrast, normal faulting events occur at the trench axis at uncoupled regions where the strains due to bending of the plate are largest. Temporal variations in the interplate coupling due to the occurrence of large thrust events at the plate boundary are suggested in several regions such as Middle America and Chile.

", "doi": "10.7907/278K-HZ75", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:7984", "collection": "thesis", "collection_id": "7984", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10092013-141757161", "type": "thesis", "title": "Seismic Reflection Experiments Imaging the Physical Nature of Crustal Structures in Southern California", "author": [ { "family_name": "Louie", "given_name": "John Nikolai", "clpid": "Louie-John-Nikolai" } ], "thesis_advisor": [ { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" } ], "thesis_committee": [ { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Clayton", "given_name": "Robert W.", "clpid": "Clayton-R-W" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" }, { "family_name": "Kanamori", "given_name": "Hiroo", "clpid": "Kanamori-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

Seismic reflection methods have been extensively used to probe the Earth's crust and suggest the nature of its formative processes. The analysis of multi-offset seismic reflection data extends the technique from a reconnaissance method to a powerful scientific tool that can be applied to test specific hypotheses. The treatment of reflections at multiple offsets becomes tractable if the assumptions of high-frequency rays are valid for the problem being considered. Their validity can be tested by applying the methods of analysis to full wave synthetics.

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Three studies illustrate the application of these principles to investigations of the nature of the crust in southern California. A survey shot by the COCORP consortium in 1977 across the San Andreas fault near Parkfield revealed events in the record sections whose arrival time decreased with offset. The reflectors generating these events are imaged using a multi-offset three-dimensional Kirchhoff migration. Migrations of full wave acoustic synthetics having the same limitations in geometric coverage as the field survey demonstrate the utility of this back projection process for imaging. The migrated depth sections show the locations of the major physical boundaries of the San Andreas fault zone. The zone is bounded on the southwest by a near-vertical fault juxtaposing a Tertiary sedimentary section against uplifted crystalline rocks of the fault zone block. On the northeast, the fault zone is bounded by a fault dipping into the San Andreas, which includes slices of serpentinized ultramafics, intersecting it at 3 km depth. These interpretations can be made despite complications introduced by lateral heterogeneities.

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In 1985 the Calcrust consortium designed a survey in the eastern Mojave desert to image structures in both the shallow and the deep crust. Preliminary field experiments showed that the major geophysical acquisition problem to be solved was the poor penetration of seismic energy through a low-velocity surface layer. Its effects could be mitigated through special acquisition and processing techniques. Data obtained from industry showed that quality data could be obtained from areas having a deeper, older sedimentary cover, causing a re-definition of the geologic objectives. Long offset stationary arrays were designed to provide reversed, wider angle coverage of the deep crust over parts of the survey. The preliminary field tests and constant monitoring of data quality and parameter adjustment allowed 108 km of excellent crustal data to be obtained.

\r\n\r\n

This dataset, along with two others from the central and western Mojave, was used to constrain rock properties and the physical condition of the crust. The multi-offset analysis proceeded in two steps. First, an increase in reflection peak frequency with offset is indicative of a thinly layered reflector. The thickness and velocity contrast of the layering can be calculated from the spectral dispersion, to discriminate between structures resulting from broad scale or local effects. Second, the amplitude effects at different offsets of P-P scattering from weak elastic heterogeneities indicate whether the signs of the changes in density, rigidity, and Lame's parameter at the reflector agree or are opposed. The effects of reflection generation and propagation in a heterogeneous, anisotropic crust were contained by the design of the experiment and the simplicity of the observed amplitude and frequency trends. Multi-offset spectra and amplitude trend stacks of the three Mojave Desert datasets suggest that the most reflective structures in the middle crust are strong Poisson's ratio (\u03c3) contrasts. Porous zones or the juxtaposition of units of mutually distant origin are indicated. Heterogeneities in \u03c3 increase towards the top of a basal crustal zone at ~22 km depth. The transition to the basal zone and to the mantle include increases in \u03c3. The Moho itself includes ~400 m layering having a velocity higher than that of the uppermost mantle. The Moho maintains the same configuration across the Mojave despite 5 km of crustal thinning near the Colorado River. This indicates that Miocene extension there either thinned just the basal zone, or that the basal zone developed regionally after the extensional event.

\r\n", "doi": "10.7907/e3d2-8b93", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:2928", "collection": "thesis", "collection_id": "2928", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-07192006-093757", "type": "thesis", "title": "Water Flow at the Base of a Surging Glacier", "author": [ { "family_name": "Brugman", "given_name": "Melinda Mary", "clpid": "Brugman-Melinda-Mary" } ], "thesis_advisor": [ { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" } ], "thesis_committee": [ { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" }, { "family_name": "Meier", "given_name": "Mark", "clpid": "Meier-M" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

Water tracing experiments were successfully conducted over a distance of ten kilometers along the base of Variegated Glacier for the purpose of characterizing the water drainage system of the glacier in the surging as compared to the non-surging state. Three tracing experiments were conducted, and fluorescent dyes, Rhodamine WT and Tinopal AMS, were injected into boreholes at separate locations. The two Rhodamine WT experiments were conducted over a 10 km distance, both during the most rapid surging motion of the glacier, and after its cessation.

\r\n\r\n

In each experiment, the terminus streams were monitored for stream discharge, sediment content and tracer concentration. Rhodamine WT tracer was significantly adsorbed on the suspended sediment, particularly during the surge. The adsorption behavior followed the Langmuir model, and calculated distribution coefficients of Kd = 100 to 1000 ml/g were measured for during the glacier surge. The Kd values measured after the surge were lower than during the surge by a factor of 10 to 1000. The much higher Kd values in the surging as compared to non-surging glacier states can be best explained by a factor of 10 to 1000 decrease in the modal and/or mean grain-size of the suspended sediment. The abundance of fine-grained sediment during the surge is probably due to increased grinding of rock material at the glacier bed.

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Theoretical models of tracer dispersion in a single tunnel, were compared to models of dispersion in linked-cavity systems to infer the details of water flow at the glacier bed. The broad, roughly symmetrical, dye-return curve measured during the glacier surge conforms to diffusive dispersion theory, and differs sharply from the highly asymmetrical dispersion curve measured after the surge. Results indicate the dispersion behavior, and calculated Manning roughness, of the post-surge Variegated Glacier is similar to those of glaciers that do not surge. The drainage system of the Variegated Glacier in the surging state is consistent with a model of tracer dispersion in an interconnecting network of conduits and cavities, and is strikingly different from the tunnel system indicated for the non-surging state.

\r\n", "doi": "10.7907/VSHG-G674", "publication_date": "1987", "thesis_type": "phd", "thesis_year": "1987" }, { "id": "thesis:2961", "collection": "thesis", "collection_id": "2961", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-07212008-101544", "primary_object_url": { "basename": "Sams_db_1986.pdf", "content": "final", "filesize": 27627137, "license": "other", "mime_type": "application/pdf", "url": "/2961/1/Sams_db_1986.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "U/Pb Zircon Geochronology, Petrology, and Structural Geology of the Crystalline Rocks of the Southernmost Sierra Nevada and Tehachapi Mountains, Kern County, California", "author": [ { "family_name": "Sams", "given_name": "David Bruce", "clpid": "Sams-David-Bruce" } ], "thesis_advisor": [ { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" } ], "thesis_committee": [ { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" }, { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

Field mapping, petrography, U/Pb zircon geochronology, and Rb/Sr geo-chemistry on the crystalline rocks of the southernmost Sierra Nevada and Tehachapi Mountains north of the Garlock fault have 1) generated a structural, geo-chemical, and geochronological framework; 2) demonstrated a continuation of Sierran plutonic and metasedimentary rocks into the Tehachapi Mountains; 3) indicated that the region, in particular the gneiss complex of the Tehachapi Mountains, represents the deepest exposed levels of the Sierra Nevada batholith; 4) placed constraints on possible mixing models between upper mantle and meta-sedimentary components to generate the observed geochemical signatures of the rocks; and 5) resolved a major mid-Cretaceous deformation event.

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The main crystalline rocks of the study area are the rocks of the Bear Valley Springs intrusive suite and the gneiss complex of the Tehachapi Mountains. The Bear Valley Springs suite is a mid-Cretaceous tonalite batholith complex with coeval gabbroic intrusives. The gneiss complex of the Tehachapi Mountains consists dominantly of early-Cretaceous orthogneiss, with subordinate paragneiss and local domains having granulite affinities. The orthogneisses are dominantly tonalitic in composition, with significant layers and domains of granodioritic to granitic and lesser dioritic to gabbroic gneiss. Quartz-rich metasedimentary rocks and marble constitute the main framework assemblage into which the plutonic rocks were emplaced. Field relations demonstrate assimilation of metasedimentary material into the orthogneisses and magma mixing between mafic, tonalitic, and anatectic granitic material derived from the metasediments.

\r\n\r\n

Crystalline rocks of the region, with the exception of metasedimentary framework rocks, fall into a narrow age range of 90-120 Ma, and exhibit three main age suites. Most samples have zircon populations with systematics indicative of igneous crystallization, with signs of zircon inheritance or entrainment in the vicinity of metamorphic septa. Strongly discordant samples are relatively rare, and include the granodiorite of Claraville (concordia intercepts of 90/1900 Ma), the paragneiss of Comanche Point (108/1450), and a quartzite in the Kings sequence metasedimentary framework rocks (1700 Ma upper intercept).

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The rocks in the first age suite (gneiss complex of the Tehachapi Mountains and augen gneiss of Tweedy Creek) exhibit a greater degree of deformation, especially under moderate to high grade conditions. Major deformational fabrics are expressed as gneissic banding, mylonitization, recrystallization, boudinaging, and transposition of internal contacts. Internally and externally concordant zircon systematics of the orthogneisses in this suite indicate igneous crystallization between 110-120 Ma. Discordant zircon systematics suggest entrainment of minor amounts of mid-Proterozoic zircon and/or open system lead loss in response to the 100 Ma magmatic culmination (Bear Valley Springs event).

\r\n\r\n

The second suite, 100\u00b12 Ma Bear Valley Springs intrusive suite (tonalite of Mount Adelaide, tonalite of Bear Valley Springs, hypersthene tonalite of Bison Peak, and metagabbro of Tunis Creek) contains igneous rocks which locally cross-cut the older suite. These rocks have a late-stage deformational fabric shown primarily in the tonalites as pervasive foliation and faint gneissic banding. The zircon systematics of this suite are internally and externally concordant, indicating igneous crystallization ages, with only local evidence of entrainment of mid-Proterozoic zircon. The deformation of the suite was synplutonic, with later phases within the suite lacking significant deformational fabrics. The major deformational fabrics exhibited in the Tehachapi and Bear Valley Springs suites may be the result of the intrusion of the tonalite batholith into the lower crust, and/or the result of intra-arc shearing that was preferentially concentrated in various intrusive bodies.

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The third suite, late deformational intrusive rocks, consists of units which cross-cut deformational features in both the older suites. These youngest rocks are themselves slightly to nondeformed. The members in the suite have ages of 90 Ma (granodiorite of Claraville), 93 Ma (tonalite stock at Tweedy Creek), and 94 Ma (pegmatite dike at Comanche Point).

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Field mapping and petrography have shown a southward continuation of Sierran plutonic and metasedimentary framework rocks to the region of Tejon Creek. The plutons show a constant age spread and overall composition throughout the region, with a greater degree of solidus to hot sub-solidus deformation exhibited southward. The metamorphic septa have a higher grade, and are more strongly deformed southwards, becoming migmatitic. The southern margin of the tonalite of Bear Valley Springs consists of a gradational contact with the hypersthene tonalite of Bison Peak, which is believed to represent the floor or conduit phase of the batholith. Along its southwestern margin, the tonalite of Bear Valley Springs grades into the gneiss complex of the Tehachapi Mountains through a region of tonalitic gneiss that appears to be derived through the mixing of tonalitic magmas and migmatitic melts produced from paragneiss components in the gneiss complex. Paleomagnetic and structural restoration of the southwestern margin of the tonalite indicates that it may represent the uptilted floor of the batholith that originally spread out over its gneissic substrate.

\r\n\r\n

The crystalline rocks of the southernmost Sierra Nevada represent the deepest exposed levels of the Sierra Nevada batholith. Saleeby and others (1986a) indicate a continual increase in depth of exposure from the central to southern part of the batholith. Elan (1985) shows metamorphic conditions of 3.0 kb and 700\u00b0C in the south-central Sierras, while Sharry (1981b) has suggested that parts of the gneiss complex have a deep-seated (8 kb) origin with rapid late-Cretaceous uplift. Granulitic nodules of similar character to parts of the gneiss complex have been described by Domenick and others (1983) as originating from a similar depth beneath the central Sierra. Gneissic granitoids have numerous lenses of mafic to ultramafic cumulates showing igneous crystallization under granulite facies conditions. The domains of \"granulite\" in the gneiss complex of the Tehachapi Mountains are believed to be hot, relatively dry zones in a crystallizing and deforming batholithic complex. Magmatic epidote-bearing tonalites and late stage sub-solidus autometamorphic garnet growth are further indicators of a deep (\u22656 kb) level of origin for the region.

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The \"granulites\" (metagabbro of Tunis Creek and hypersthene tonalite of Bison Peak) are interpreted to be of an igneous origin. Evidence for this interpretation consists of: relict olivine grains and cumulate textures; foliation believed to be the result of igneous flow; zoned plagioclase necessitating the presence of a magma; tonalites that contain epidote that is interpreted to be of magmatic origin; \u03b418O and Rb/Sr isotopic values in the igneous range; abundance of retro-grade but paucity of prograde mineral reactions; gradational contacts between plutonic units; and observed intrusive contacts. Pyroxene within the \"granulites\" is believed to be of a pyrogenic origin. The rocks typically have a retrograde assemblage that consists of olivine \u2192 orthopyroxene and pyroxene \u2192 amphibole. The mineral assemblages all point to a downward P-T path.

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Simple two-component mixing models have been constructed for samples from the southernmost Sierra Nevada, and involve incorporation of partial to complete melts of metasedimentary material into \"primitive\" upper mantle orogenic mafic magmas prior to crystallization. The two possible end-members are the quartzite-paragneiss of Comanche Point and the hypersthene tonalite of Bison Peak-metagabbro of Tunis Creek. Initial 87Sr/86Sr correlates directly with \u03b418O, and generally correlates inversely with Sr content for most of the samples. Simple isotopic mixing models indicate incorporation of up to 33% metasedimentary material in the granitic rocks, and up to 15% in the tonalites, with younger and more easterly samples requiring a larger metasedimentary component. The non-correlation of Sro with Sr content for some of the Pastoria Creek samples indicates an oceanic-affinity source with little interaction with continental crustal material. A number of samples appear to require a third, probable lower continental crustal and/or oceanic crustal-upper mantle component that may have a Paleozoic age.

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Based on Rb/Sr and K/Ar age systematics, the region was uplifted in a regional cooling event at ~85 Ma perhaps as part of regional thrusting event(s) in southern California. The crystalline rocks were subsequently exposed and unconformably overlapped by Eocene marine sediments. Paleomagnetic data suggest about 45-60\u00b0 of clockwise rotation between 80 and 16 Ma for the southern end of the Sierras, possibly as the result of the thrusting event responsible for the regional uplift.

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Saleeby and others (1986c) have suggested that the lower crust beneath the Sierra Nevada batholith is comprised in part by granulitic and mafic intrusive rocks. Experimental studies by Christensen and Fountain (1975) also suggest the presence of granulites in the lower continental crust. The interpretation that the study area represents the deepest exposed level of the southernmost Sierra Nevada batholith leads to the implication that granulitic-affinity rocks comprise the lower part of the continental crust. Therefore, this study provides some degree of confirmation to the aforementioned hypotheses.

\r\n", "doi": "10.7907/C883-H765", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:11427", "collection": "thesis", "collection_id": "11427", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03142019-142709345", "primary_object_url": { "basename": "Gehrels_ge_1986.pdf", "content": "final", "filesize": 112502537, "license": "other", "mime_type": "application/pdf", "url": "/11427/1/Gehrels_ge_1986.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Geologic and Tectonic Evolution of Annette, Gravina, Duke, and Southern Prince of Wales Islands, Southeastern Alaska", "author": [ { "family_name": "Gehrels", "given_name": "George Ellery", "orcid": "0000-0002-8564-8433", "clpid": "Gehrels-George-Ellery" } ], "thesis_advisor": [ { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" } ], "thesis_committee": [ { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" }, { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Stevenson", "given_name": "David J.", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Talyor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Berg", "given_name": "Henry C.", "clpid": "Berg-Henry-C" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

Annette, Gravina, Duke, and southern Prince of Wales Islands are underlain primarily by Cambrian (and perhaps Proterozoic) through Triassic volcanic, sedimentary, plutonic, and metamorphic rocks. These rocks belong to the Alexander terrane, which is a coherent tectonic fragment that underlies much of southeastern (SE) Alaska, the Saint Elias Mountains of British Columbia, Yukon, and eastern Alaska, and coastal regions of west-central British Columbia. Geologic mapping combined with U-Pb (zircon) geochronologic studies have delineated the major geologic units and features of these islands, and contribute to our understanding of the geologic and tectonic evolution of the Alexander terrane.

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The oldest rocks recognized on Annette, Gravina, Duke, and southern Prince of Wales Islands consist of greenschist- and amphibolite-facies metavolcanic and metasedimentary rocks of the Wales metamorphic suite. These rocks are locally intruded by dioritic and granodioritic metaplutonic rocks which yield U-Pb apparent ages of approximately 540-520 Ma (Middle and Late Cambrian). Rocks in the Wales suite were therefore deposited, at least in part, prior to Late Cambrian time, but their maximum depositional age is not known. The Wales suite and associated metaplutonic rocks are intruded by large dioritic to granitic plutons which yield U-Pb apparent ages in the 475-425 Ma (Middle Ordovician-Early Silurian) range and are probably overlain by Lower Ordovician-Lower Silurian volcanic and sedimentary rocks of the Descon Formation. However, depositional contacts between the Descon Formation and the older metamorphic rocks have not been demonstrated. Deformation, metamorphism, and uplift of rocks in the Wales metamorphic suite occurred during a Middle Cambrian-Early Ordovician tectonic event which I have referred to as the Wales \"orogeny.\" The term orogeny is used informally in this instance, as little is known about the regional and tectonic significance of this event.

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Ordovician-Early Silurian rocks on these islands are interpreted to have formed in an oceanic volcanic arc environment based on similarities with young or presently active volcanic arcs in the Circum-Pacific region. Characteristics of the volcanic-plutonic complex in the Alexander terrane which are similar to those in other magmatic belts include: 1) predominance of basaltic to andesitic volcanic rocks and dioritic to granodioritic and subordinate granitic plutonic rocks, 2) calc-alkaline affinity of the plutonic and volcanic rocks, as defined on AFM, FeO*/MgO versus SiO2, and La versus Nb diagrams and by an alkali-lime index of 56-62, 3) patterns of strong (50-100 times chondrites) light REE enrichments, moderate (5 to 20 times chondrites) heavy REE enrichments, and strong negative europium anomalies, 4) evolution of the magmatic system over a period of approximately 50 m.y., and 5) increasing potassium content with time in the plutonic rocks.

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Facies relations in Ordovician-Silurian strata in the southern part of the terrane generally record northwesterly paleogeographic trends, indicating that the interpreted arc trended oblique to the northnorth-westerly elongation of the terrane. Continuation of Ordovician-Silurian shallow-marine strata for over 600 km to the north-northwest indicates that the interpreted arc probably faced to the southwest and that the strata to the north accumulated in a back-arc environment. Protoliths of the Wales metamorphic suite may also have formed in a volcanic arc environment, but the penetrative deformation and regional metamorphism of these rocks precludes detailed analyses of protolith relations and composition.

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During middle Silurian-earliest Devonian time the Early Silurian and older rocks in the area were involved in a major tectonic event which I refer to as the Klakas orogeny. Manifestations of this orogeny on Annette, Gravina, Duke, and Prince of Wales Islands include: 1) cessation of the Ordovician-Early Silurian volcanism and plutonism, 2) deposition of middle and Upper Silurian polymictic conglomerate on northern Prince of Wales Island and regions to the north, 3) erosion or non-deposition of Silurian strata on Annette, Gravina, and Duke Islands and on central and southern Prince of Wales Island, 4) southwest-directed movement on thrust faults on southern Prince of Wales Island and perhaps on Annette Island, 5) deposition and deformation of a Lower Devonian talus breccia and penetrative brecciation of Ordovician rocks along thrust faults on southern Prince of Wales Island, 6) greenschist-and local amphibolite-facies regional metamorphism and penetrative deformation of Ordovician-Early Silurian rocks on Annette, Gravina, and Duke Islands, 7) emplacement, and perhaps generation by anatexis, of Late Silurian trondhjemite, sodic leucodiorite, and subordinate granite plutons, 8) several kilometers (perhaps as much as 10 km) of uplift of Late Silurian and older rocks prior to middle Early Devonian time, and 9) deposition of Lower Devonian conglomeratic red beds of the Karheen Formation in topographically rugged subaerial environments in some regions to the south, and in a northward tapering clastic wedge to the north. Previous workers recognized the stratigraphic manifestations of this orogenic event on central and northern Prince of Wales Island, but most relations to the south were recognized initially during this study.

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On southern Prince of Wales Island, Lower Devonian conglomeratic strata are overlain by shallow-marine limestone, mudstone, and siltstone of middle Early Devonian age, which are in turn overlain by deeper-water mudstone and graptolitic shale. Subsidence of the region below sea level following the Klakas orogeny therefore occurred during middle Early Devonian time and produced a marine transgression on a north-facing paleoslope. Lower Devonian strata on Annette, Gravina, and Duke Islands were deposited in shallow-marine environments, and only locally include polymictic conglomerate and coarser clastic strata. Andesitic volcanic rocks of probable Early Devonian age locally overlie the marine clastic strata and are the youngest Paleozoic rocks in the study area.

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Triassic strata herein referred to as the Hyd Group unconformably overlie the Devonian and older rocks on Annette and Gravina Islands. At the base of the section in most areas is a thick conglomerate or sedimentary breccia with meter-size clasts of Devonian and older rock in a poorly sorted matrix. These strata are overlain by a sequence, from bottom to top, of rhyolite and rhyolitic tuff, shallow-marine limestone, calcareous siltstone and limestone, and basalt flows and breccia. A UPb apparent age of 225 \u00b1 3 on the rhyolite combined with megafossil and conodont ages demonstrate that these strata were deposited during Late Carnian to Late Norian time, and place a minimum age constraint of 225 \u00b1 3 Ma on the Carnian-Norian boundary. A large body of pyroxene gabbro on Duke Island yields a U-Pb apparent age of 226 \u00b1 3 Ma, which demonstrates that this gabbro is not genetically related to the zoned (\"Alaskan-type\") ultramafic bodies on Duke Island (assuming that the ultramafic bodies are indeed Cretaceous in age!). Rather, the pyroxene gabbro is interpreted to be genetically related to the Triassic basaltic rocks. Intrusive relations indicate that hornblende gabbro on northeastern Duke Island is pre-Late Silurian in age, and is therefore not genetically related to the pyroxene gabbro or to the Cretaceous(?) ultramafic rocks.

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The unconformity at the base of the Triassic section records a major latest Paleozoic(?)-Triassic uplift and erosional event in the Alexander terrane, but this event was not associated with regional deformation or metamorphism. This lack of deformation combined with the occurrence of Triassic strata along the eastern margin of the terrane in SE Alaska and the bimodal (basalt-rhyolite) composition of the volcanic rocks suggest that the Triassic strata and their subjacent unconformity formed in an extensional environment. A major low-angle normal fault on southern Prince of Wales Island (the Keete Inlet fault) may also have moved during this interpreted extensional event.

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Jurassic and younger rocks intrude and overlie rocks in various terranes in western British Columbia and southern Alaska and demonstrate that the Alexander terrane has been adjacent to Wrangellia since Middle(?) Jurassic time, and to terranes to the east since Late Cretaceous-early Tertiary time. Regional sub-greenschist- to greenschist-facies metamorphism and moderate deformation of Cretaceous and older rocks along the eastern margin of the terrane are interpreted to have occurred during mid-Cretaceous-early Tertiary juxtaposition of the Alexander terrane against terranes to the east.

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North of Annette, Gravina, Duke, and southern Prince of Wales Islands the Alexander terrane is underlain primarily by Paleozoic marine clastic strata and limestone. Lower Paleozoic strata in some regions of the Saint Elias Mountains include Cambrian volcanic rocks which may be correlative with rocks in the Wales metamorphic suite, and a thick section of Ordovician-Devonian clastic strata and limestone. Upper Paleozoic clastic strata are widespread in the Saint Elias Mountains region but occur in only a few areas of southeastern Alaska, where they were generally deposited in tectonically stable, shallow-marine environments. Triassic strata to the north are generally similar to rocks on Annette and Gravina Islands, and are interpreted by other workers to have been deposited in a rift environment.

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A variety of geologic, paleomagnetic, and paleobiogeographic evidence suggests that the Alexander terrane occupied low paleolatitudes during much of Paleozoic and Mesozoic time, and did not reach its present latitude in the Cordillera until after Early Cretaceous time. Previous hypotheses were that the Alexander terrane was originally adjacent to rocks in the Sierra-Klamath region of California, and that both assemblages formed and evolved adjacent to the California continental margin. Comparison of the geologic and tectonic evolution of the Alexander terrane with that in the Sierra-Klamath region indicates, however, that the two assemblages have little in common and probably were not closely associated during Paleozoic time.

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Alternatively, I suggest that the early Paleozoic geologic and tectonic evolution of the Alexander terrane is remarkably similar to that in a dismembered orogenic belt which occurs in southeastern Australia (Lachlan Fold Belt), New Zealand, the Transantarctic Mountains and Byrd Land of Antarctica, and perhaps in tectonic fragments in Asia. Similarities between the Alexander terrane and the Lachlan Fold Belt include: 1) arc-type(?) volcanism and sedimentation during Cambrian time (and perhaps Proterozoic time in the Alexander terrane), 2) regional deformation and metamorphism of the Cambrian and older(?) rocks during Middle Cambrian-Early Ordovician time, 3) evolution of some regions in a volcanic arc environment during Ordovician time (into Early Silurian time in the Alexander terrane), 4) cessation of this volcanic arc activity during the onset of a Silurian-earliest Devonian orogenic event, which is manifest by regional uplift and erosion, deformation and regional metamorphism, anatectic(?) plutonism (and volcanism in the Lachlan Belt), 5) deposition of Lower Devonian and locally Silurian conglomeratic red beds, and 6) evolution in relatively stable marine environments from middle Early through Middle Devonian time.

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Comparison of paleolatitudes of the Alexander terrane (determined from paleomagnetic data) with paleolatitudes of eastern Australia (interpreted from continental reconstructions) indicates that the two regions occupied similar paleolatitudes from Ordovician to Late Devonian time. A similar comparison of declination data from the Alexander terrane indicates that both regions also rotated in a clockwise sense during this period. There are also similarities in lower Paleozoic fossils of the two regions, but some faunas from the Alexander terrane apparently bear stronger affinities with North American or Asian fossils.

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Based on the geologic, paleomagnetic, and, to some degree the paleobiogeographic similarities, I raise the possibility that the Alexander terrane formed and evolved along the paleo-Pacific margin of Gondwana, perhaps adjacent to rocks in eastern Australia, during early Paleozoic time. The data are not sufficient to draw correlations between the Alexander terrane and specific regions in this complex orogen, although I note that similarities are strongest with the Molong volcanic province in the Lachlan Belt of eastern Australia. The paleomagnetic data indicate that the terrane could have been associated with these rocks or with potential northern correlatives in tectonicfragments that now reside in Asia.

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The geologic, paleomagnetic, and paleobiogeographic(?) similarities between the Alexander terrane and the Lachlan Belt end in Middle Devonian-Early Carboniferous time. During this time the Lachlan Belt apparently underwent a major rifting episode, and the Alexander terrane began to evolve in tectonically stable marine environments. The paleolatitudes of the two regions also diverge at this time, with the Alexander terrane migrating northward toward the paleo-equator and eastern Australia continuing its southward movement. Carboniferous fauna from the Alexander terrane are reported by some workers to have \"Tethyan\" affinities, a fact that is consistent with the low paleolatitudes determined from the paleomagnetic data. Triassic faunas from the terrane are endemic to equatorial or perhaps more southerly regions in the eastern part of the paleo-Pacific basin, and paleomagnetic data from the terrane are most consistent with a paleolatitude of approximately 43\u00b0 South. In concert with the hypothesis that the terrane was adjacent to the paleo-Pacific margin of Gondwana during early Paleozoic time, I raise the possibility that the terrane was tectonically removed from the Gondwana margin, perhaps by rifting, during Middle Devonian-Early Carboniferous time, and migrated eastward across the paleo-Pacific basin during late Paleozoic time. Northward displacement apparently began after Late Triassic time, and ended during the mid-Cretaceous to early Tertiary juxtaposition of the terrane against fragments previously accreted to western North America.

", "doi": "10.7907/pavf-pm10", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:3283", "collection": "thesis", "collection_id": "3283", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-08302006-135307", "primary_object_url": { "basename": "Weldon_rj_1986.pdf", "content": "final", "filesize": 19393034, "license": "other", "mime_type": "application/pdf", "url": "/3283/1/Weldon_rj_1986.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "The Late Cenozoic Geology of Cajon Pass; Implications for Tectonics and Sedimentation along the San Andreas Fault", "author": [ { "family_name": "Weldon", "given_name": "Ray James, II", "clpid": "Weldon-Ray-James-II" } ], "thesis_advisor": [ { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" } ], "thesis_committee": [ { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Kirschvink", "given_name": "Joseph L.", "orcid": "0000-0001-9486-6689", "clpid": "Kirschvink-J-L" }, { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

The geology in Cajon Pass, southern California, provides a detailed record of strike slip activity on the San Andreas fault, compressional deformation associated with the uplift of the central Transverse Ranges and an excellent Cenozoic record of syntectonic sedimentation. Age control was established in all of the sediments deposited since the late Early Miocene, using biostratigraphy, magnetostratigraphy, fission-track dating of volcanic ashes, radiocarbon dating, soil development, and the relative stratigraphic and geomorphic position of the units. Tectonic deformation and sedimentation styles varied through time, reflecting the evolution of the San Andreas fault zone within the Pacific - North American plate boundary. Particular attention was paid to determining rates of tectonic deformation and establishing the timing of changes in deformational and depositional styles in the area.

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Progressive offset of radiocarbon-dated alluvial and paludal sediments have been used to determine the Holocene slip rate on the San Andreas fault in Cajon Pass. Four independent measurements of the slip rate yield an average of 24.5 \u00b1 3.5 mm/yr. The similarity of the four values, which span different intervals of time up to 14,400 years ago, suggest that the slip rate has been constant during this period.

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An excavation across the San Andreas fault provided some constraints on the timing of paleoearthquakes. Coupled with the historic record, this investigation indicates that the last earthquake associated with rupture on the fault in Cajon Pass occurred around 1700 AD. At least 2 earthquakes caused rupture on the San Andreas fault after 1290 AD and perhaps 6 earthquakes are recorded in the thousand year period before European settlement of southern California in the 1770s.

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Downcutting and erosion into the western San Bernardino Mountains, during the last 700,000 years, has created Cajon Pass as it exists today. The downcutting was punctuated by at least four pulses of channel aggradation that provide stratigraphic markers throughout the area. They are dated at 0.5 \u00b1 0.1 million, 55,000 \u00b1 10,000, 17,000 to 6,000, and 2000 to 300 years ago. These aggradational periods were caused by order of magnitude increases in sediment production associated with changes in the climate from relatively wet to dry conditions.

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The locus of the latest Pleistocene to early Holocene fill migrated upstream through time, with aggradation lasting only a few thousand years at any point in the drainage. Incision of the fill also migrated upstream, beginning long before the fill pulse reached the headwaters of the system. The fill terrace, or upper surface of the fill deposit, does not represent a time line or a surface down which water flowed everywhere at once. Thus, the use of a fill terrace as either a time or spacial reference line for tectonic studies, without accounting for the its transgressive character, can result in erroneous conclusions.

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During the early to middle Pleistocene, prior to the erosion of Cajon Pass, the southern part of the area was uplifted and coarse fan deposits were shed across the northern part of the area onto the Mojave Desert. Some of these sediments were derived from distinctive sources in the San Gabriel Mountains southwest of the San Andreas fault zone. Matching these distinctive facies in the deposits with their sources established offsets across the fault zone and made it possible to tie the uplift northeast of the fault to activity on the San Jacinto fault as it passed by across the San Andreas fault. The fan deposits are dated by a combination of bio-stratigraphy and magnetostratigraphy.

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The average slip rate across the combined San Andreas and San Jacinto faults is 37.5 \u00b1 2 mm/yr during the Quaternary Period. The six determinations of the slip rate show no evidence for rate changes during the Quaternary Period. The slip rate on the San Andreas fault alone was determined by one offset of be 21 \u00b1 7 mm/yr. The record of contemporaneous activity on the San Jacinto fault to the southeast requires that the San Andreas fault's rate be close to the upper limit of this range.

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Contemporaneous activity on the San Andreas and San Jacinto faults is uplifting the high, eastern San Gabriel Mountains and deforming the San Andreas fault plane. The geometry of this deformation is such that uplift of the country on the northeast side of the San Andreas fault occurs. This hypothesis is supported by the northwest migration of the uplift at the slip rate on the San Andreas fault, and the style of surface deformation that is characteristic of folding over a steeply dipping lateral ramp at depth.

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A kinematic model was constructed to determine the role of the San Andreas fault in the Pacific - North American plate boundary. The Quaternary slip rates determined for the San Andreas fault in Cajon Pass and the slip vectors associated with the geometry of the fault zone were combined with an assumption of rigid block motion away from the faults and published slip rates for the other major faults in southern California. The model produces internally consistent motions for all of the blocks. Vector sums of the slip rate across the Pacific - North American boundary yield only the relative plate motion if the path includes the western Transverse Ranges. The model solution indicates that the western Transverse Ranges are not part of the San Andreas system but are a left-step in a separate coastal system that currently accommodates about 1/3 of the Pacific - North American plate motion.

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The southeastern San Bernardino Mountains are being uplifted because of a left step in the arcuate trace of the San Andreas fault. The western San Bernardino Mountains and the eastern San Gabriel Mountains are being uplifted by the deformation associated with the junction of the San Andreas and San Jacinto faults. Because the convergence in this area can be explained by local geometry, it is clear that southern California cannot be part of the Pacific plate, colliding at the plate rate into North America across the Transverse Ranges. Instead, southern California appears to be a sliver between the San Andreas system and the coastal system, and is rotating counterclockwise as it translates northwest, transferring the convergence to the coastal system.

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The middle to late Quaternary uplift of the Cajon Pass area was the culmination of the uplift of the San Bernardino Mountains that began in the Miocene. Three distinct phases of uplift have been recognized, suggesting a long-term interaction between the strike-slip activity on the San Andreas system and the compressional tectonics of the Transverse Ranges. The San Bernardino Mountains began to take shape following a pervasive earliest Miocene unconformity. Broad, homogeneous basins, separated by mature uplands of moderate to low relief developed across the southwest-draining regional paleoslope. The earliest activity on the San Andreas fault is believed to be associated with this early extensional phase.

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Late Miocene to early Pliocene, south-directed thrusting uplifted the \"proto\" San Bernardino Mountains, creating steep, south-facing relief along the San Andreas. During this time the San Gabriel fault was the most (and perhaps only) active trace of the San Andreas system. Thrusting stopped as the San Andreas fault became active again, probably coincident with the beginning of the opening of the Gulf of California, 5 million years ago. Pliocene and earliest Pleistocene sedimentation took place in narrow east-west trending, structurally controlled basins created by the Mio-Pliocene thrusting.

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Early to middle Pleistocene, north-directed thrusting across a shallow, south-dipping ramp uplifted the broad central plateau of the San Bernardino Mountains, and created the North Frontal fault system. During the middle and late Quaternary, this activity was largely replaced by south-directed thrusting and lateral ramping on steep, north-dipping planes along the San Andreas fault. This activity produced the tremendous relief and regionally-extensive north-dipping structural blocks in the San Gorgonio and Cajon Pass areas, and continues today. The structures and geomorphology of the range reflects its varied history; different parts of the range are as old as late Early Miocene and as young as the Holocene.

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All three phases of uplift appear to be related to the southern Big Bend in the San Andreas fault system, which has existed since the Miocene. Contemporaneous and alternating periods of thrusting and strike-slip activity has created bedrock \"flaps\", displaced fault slivers and strand switching that are responsible for the complex geology associated with San Andreas fault through the Transverse Ranges. Recognition of these features with detailed field work will greatly expand our knowledge of the tectonics and seismic hazards associated with the San Andreas system in southern California.

", "doi": "10.7907/9WJY-2A97", "publication_date": "1986", "thesis_type": "phd", "thesis_year": "1986" }, { "id": "thesis:7477", "collection": "thesis", "collection_id": "7477", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02142013-085850235", "type": "thesis", "title": "Studies of the Crust-Mantle System Beneath Southern California", "author": [ { "family_name": "Humphreys", "given_name": "Eugene Drake", "orcid": "0000-0002-1916-8378", "clpid": "Humphreys-Eugene-Drake" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

A back-projection method of tomographic reconstruction is adapted to inverted seismic travel-time data. The problems encountered in inverting these data include ray set inhomogeneity and anisotropy and the three-dimensionality of the space interrogated. Jacobi iteration, deconvolution and variable ray weighting are shown to work well in augmenting the basic back-projection method to produce a well-focused image. Applications of the various focusing algorithms are shown to have a degree of success that depends on the ray geometry used. Also, the ability to reconstruct an accurate image when the data include moderate amounts of noise is shown to be good.

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P-wave teleseismic travel time delays recorded by the southern California array are inverted with the tomographic method to obtain variations in the P-wave velocity structure to a depth of 750 km. Two major anomalies are imaged. A curtain-like E-W trending high velocity feature is found directly beneath the Transverse Ranges. This feature is about 50 km in thickness, extends in depth to a maximum of about 250 km on its eastern end, and attains a maximum velocity that is about 3% greater than average mantle at the same depth beneath southern California. A zone of low-velocity material is found in the uppermost 100 km beneath the region of the Salton Trough. The seismic velocities here are depressed by about 4%.

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These anomalous regions are interpreted to be related to the geologic processes that have been active recently in southern California. Scaling relations are used to estimate that the Transverse Range anomaly is about 500\u00b0C colder and 1% more dense than average southern California mantle of the same depth, while the Salton Trough anomaly is about 1/2% less dense and contains about 3% melt. The density distribution drives a flow of upper mantle material from the Salton Trough region towards the Transverse Ranges, where it sinks into the mantle to form the feature seen beneath these ranges. Mantle flow results in tractions that act on the base of the lithosphere to produce stresses within the lithosphere that are tensile in the Salton Trough and compressive in the Transverse Ranges. These stresses are thought to account for the physiography seen in these provences.

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The southern California crust is modeled using late Quaternary slip rates on major faults, and a kinematic description is determined that has: 1) only local sites of convergence in the Transverse Ranges, and 2) the occurrance of significant strain rates near to the southern California coast, including the western Transverse Ranges.

", "doi": "10.7907/j2xf-gq29", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:7983", "collection": "thesis", "collection_id": "7983", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10092013-140441093", "primary_object_url": { "basename": "Le Bras_r_1985.pdf", "content": "final", "filesize": 26322234, "license": "other", "mime_type": "application/pdf", "url": "/7983/1/Le Bras_r_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Methods of Multiparameter Inversion of Seismic Data Using the Acoustic and Elastic Born Approximations", "author": [ { "family_name": "Le Bras", "given_name": "Ronan", "orcid": "0000-0003-2439-6938", "clpid": "Le-Bras-Ronan" } ], "thesis_advisor": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

This thesis presents two different forms of the Born approximations for acoustic and elastic wavefields and discusses their application to the inversion of seismic data. The Born approximation is valid for small amplitude heterogeneities superimposed over a slowly varying background. The first method is related to frequency-wavenumber migration methods. It is shown to properly recover two independent acoustic parameters within the bandpass of the source time function of the experiment for contrasts of about 5 percent from data generated using an exact theory for flat interfaces. The independent determination of two parameters is shown to depend on the angle coverage of the medium. For surface data, the impedance profile is well recovered.

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The second method explored is mathematically similar to iterative tomographic methods recently introduced in the geophysical literature. Its basis is an integral relation between the scattered wavefield and the medium parameters obtained after applying a far-field approximation to the first-order Born approximation. The Davidon-Fletcher-Powell algorithm is used since it converges faster than the steepest descent method. It consists essentially of successive backprojections of the recorded wavefield, with angular and propagation weighing coefficients for density and bulk modulus. After each backprojection, the forward problem is computed and the residual evaluated. Each backprojection is similar to a before-stack Kirchhoff migration and is therefore readily applicable to seismic data. Several examples of reconstruction for simple point scatterer models are performed. Recovery of the amplitudes of the anomalies are improved with successive iterations. Iterations also improve the sharpness of the images.

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The elastic Born approximation, with the addition of a far-field approximation is shown to correspond physically to a sum of WKBJ-asymptotic scattered rays. Four types of scattered rays enter in the sum, corresponding to P-P, P-S, S-P and S-S pairs of incident-scattered rays. Incident rays propagate in the background medium, interacting only once with the scatterers. Scattered rays propagate as if in the background medium, with no interaction with the scatterers. An example of P-wave impedance inversion is performed on a VSP data set consisting of three offsets recorded in two wells.

\r\n", "doi": "10.7907/14q2-fa62", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:7982", "collection": "thesis", "collection_id": "7982", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10092013-134453343", "type": "thesis", "title": "Crustal Structure in Southern California from Array Data", "author": [ { "family_name": "Hearn", "given_name": "Thomas Martin", "orcid": "0000-0003-3926-4815", "clpid": "Hearn-Thomas-Martin" } ], "thesis_advisor": [ { "family_name": "Harkrider", "given_name": "David G.", "clpid": "Harkrider-D-G" } ], "thesis_committee": [ { "family_name": "Harkrider", "given_name": "David G.", "clpid": "Harkrider-D-G" }, { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

Crustal structure in Southern California is investigated using travel times from over 200 stations and thousands of local earthquakes. The data are divided into two sets of first arrivals representing a two-layer crust. The Pg arrivals have paths that refract at depths near 10 km and the Pn arrivals refract along the Moho discontinuity. These data are used to find lateral and azimuthal refractor velocity variations and to determine refractor topography.

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In Chapter 2 the Pn raypaths are modeled using linear inverse theory. This enables statistical verification that static delays, lateral slowness variations and anisotropy are all significant parameters. However, because of the inherent size limitations of inverse theory, the full array data set could not be processed and the possible resolution was limited. The tomographic backprojection algorithm developed for Chapters 3 and 4 avoids these size problems. This algorithm allows us to process the data sequentially and to iteratively refine the solution. The variance and resolution for tomography are determined empirically using synthetic structures.

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The Pg results spectacularly image the San Andreas Fault, the Garlock Fault and the San Jacinto Fault. The Mojave has slower velocities near 6.0 km/s while the Peninsular Ranges have higher velocities of over 6.5 km/s. The San Jacinto block has velocities only slightly above the Mojave velocities. It may have overthrust Mojave rocks. Surprisingly, the Transverse Ranges are not apparent at Pg depths. The batholiths in these mountains are possibly only surficial.

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Pn velocities are fast in the Mojave, slow in Southern California Peninsular Ranges and slow north of the Garlock Fault. Pn anisotropy of 2% with a NWW fast direction exists in Southern California. A region of thin crust (22 km) centers around the Colorado River where the crust bas undergone basin and range type extension. Station delays see the Ventura and Los Angeles Basins but not the Salton Trough, where high velocity rocks underlie the sediments. The Transverse Ranges have a root in their eastern half but not in their western half. The Southern Coast Ranges also have a thickened crust but the Peninsular Ranges have no major root.

\r\n", "doi": "10.7907/B6HA-4P68", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:2474", "collection": "thesis", "collection_id": "2474", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06062005-132701", "primary_object_url": { "basename": "Scott_pf_1985.pdf", "content": "final", "filesize": 7436790, "license": "other", "mime_type": "application/pdf", "url": "/2474/1/Scott_pf_1985.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Applications of the Kirchhoff-Helmholtz Integral to Problems in Body Wave Seismology", "author": [ { "family_name": "Scott", "given_name": "Patricia Frances", "clpid": "Scott-Patricia-Frances" } ], "thesis_advisor": [ { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" } ], "thesis_committee": [ { "family_name": "Clayton", "given_name": "Robert W.", "orcid": "0000-0003-3323-3508", "clpid": "Clayton-R-W" }, { "family_name": "Harkrider", "given_name": "David G.", "clpid": "Harkrider-D-G" }, { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

This thesis describes a procedure for evaluating the Kirchhoff-Helmholtz integral and presents applications of it which involve the interpretation of amplitude and travel time anomalies of body waves. The method of integration is a summation of single point evaluations of the integrand and requires that spacing of these evaluations on the surface be small compared to the wavelength of the incident disturbance. The technique predicts amplitudes, travel times and waveforms of acoustic potentials that propagate through a homogeneous medium and interact with three-dimensional curved boundaries. Results from test models compare well with optical solutions for reflections off planar interfaces and rigid spheres and transmissions through planar interfaces.

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The reflected integral solution is used to simulate the effect of an idealized mountain on the amplitude and waveforms on pP. This structure causes multiple arrivals, phase shifts, and amplitude anomalies in the synthetic reflection profile. Also the effects of spall on pP waves generated by explosions are simulated by specifying position dependent reflection coefficient on the surface of integration. These experiments predict frequency dependent amplitude anomalies and travel time delays of the reflections.

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The transmitted solution is used to model the effect of several idealized crust-mantle boundary structures on teleseismic P waves generated by explosions. The structures are upwarps and product travel time residuals as a function of delta and azimuth which have the same magnitude as residuals observed for NTS tests within Pahute Mesa. The structure causes early complicated low amplitude waveforms and late simple high amplitude waveforms. Thus they cause systematic amplitude variations with azimuth, delta, and source location. The magnitude of predicted variation is less than the observed ab amplitude variation with azimuth of Pahute Mesa tests; however, it is approximately the same as the observed ab variation at a given station as a function of test location within the mesa.

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The integral method is extended to include a symmetric velocity function in the medium and is used to model ScS waves which propagate through a JB Earth and reflect off a bumpy core-mantle boundary. Solutions with this extension establish that isovelocity Kirchhoff solutions are sufficient to predict the relative amplitude and travel time anomalies of ScS arising from core-mantle boundary relief. Isovelocity modeling shows that upwarps 300 to 600 kilometers wide and at least 10 kilometers high cause precursors to ScS and amplitude reductions of the same magnitude as the observations. However, the height is not mechanically feasible; therefore, the anomalous observations must originate elsewhere.

", "doi": "10.7907/tckd-xm91", "publication_date": "1985", "thesis_type": "phd", "thesis_year": "1985" }, { "id": "thesis:9925", "collection": "thesis", "collection_id": "9925", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09132016-161520143", "primary_object_url": { "basename": "Hill_ri_1984.pdf", "content": "final", "filesize": 201454228, "license": "other", "mime_type": "application/pdf", "url": "/9925/1/Hill_ri_1984.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Petrology and Petrogenesis of Batholithic Rocks, San Jacinto Mountains, Southern California", "author": [ { "family_name": "Hill", "given_name": "Robert Ian", "clpid": "Hill-Robert-Ian" } ], "thesis_advisor": [ { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" } ], "thesis_committee": [ { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Wyllie", "given_name": "Peter J.", "clpid": "Wyllie-P-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

A combined field and laboratory study of plutonic rocks from the San Jacinto Mountains of southern California was conducted in order to investigate the nature and origins of strontium and oxygen isotope heterogeneities within batholithic rocks.

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Geological mapping has allowed differentiation of three major and many minor masses of plutonic rock. Contacts between units are offset up to 6 km by faults of the Neogene San Jacinto fault system, which has a total right-lateral displacement of 29\u00b11 km. The early small intrusives range from olivine gabbro through granite. They were intruded by three larger plutons of relatively homogeneous biotite-hornblende-titanite tonalite. The oldest major intrusive unit, Unit I, is an elongate body of dimensions 40x8 km. Before complete solidification it was intruded by Unit II, an irregular tabular mass 25 km long and a few kilometers wide. Unit III, in turn, intruded Unit II before it was completely solidified, producing a roughly rectangular mass 20x12 km that appears to funnel in downwards.

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Mineral foliations and banding, schlieren, and xenolith orientations within each unit usually parallel the nearest contact. Alignment of foliations and apparent flow-sorting and scour features seem to reflect flow patterns within each chamber. Mlfic synplutonic dikes (quartz diorite to tonalite) intruded into the tonalites, and were commonly broken up and redistributed as linearly extensive xenolith trains. From these relationships it is interpreted that: 1) magma adjacent to pluton walls had considerable yield strength, as it could fracture to allow dike emplacement; 2) magmatic flow adjacent to pluton walls was capable of moving material some distances (up to km) to create the xenolith trains; and 3), that the dikes are potentially the feeders through which material was added to the inflating magma chambers. Each major tonalite unit spans a limited compositional range of from mafic tonalite (Colour Index > 15) to low-K granodiorite (Colour Index < 10). Volumetrically minor felsic differentiates extend the compositional range through to granodiorite. Units I and II average slightly more mafic overall compositions than does Unit III. All units are comprised of plagioclase (An30-40) [50-55%], quartz[20-30%], K-feldspar[1-8%], biotite (10-15%], hornblende[0-5%], titanite[0-2%] and accessory zircon, apatite, allanite and ilmenite. Variations in mineral abundances are geographically systematic only within Unit III, which grades from marginal mafic tonalite to central low-K granodiorite.

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Mineral compositions throughout the major tonalites are remarkably uniform. The An content of the bulk plagioclase falls from An40 \u00b1 1 in the most mafic tonalites to An30 in low-K granodiorites; Mg/(Mg + Fe) of biotite and hornblende drop similarly from 0.44 to 0.36. The entire observed range of plagioclase compositions within the major tonalites is An44 to An25 (and to An47 in mafic xenoliths). The sole opaque mineral is almost pure ilmenite. This homogeneity of mineral compositions implies remarkable stability of physico-chemical conditions throughout crystallization of each unit.

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Major and trace element abundances reflect the general homogeneity of these rocks. Most have SiO2 in the range 63-68 wt.%; minor felsic differentiates extend to 71 wt.%. 60% of analyzed samples from Unit III fall in the restricted compositional range 66-68 wt.% SiO2; the majority of samples from Units I and II are more mafic than this. Major elements (excepting K2O) define excellent linear arrays on Harker diagrams. K2O shows a diffuse curvilinear pattern. Trace elements generally considered \"compatible\" (including the transition metals), and Sr also define linear arrays on Harker diagrams. Other trace elements, especially Ba, Rb, Pb, Th, U and REE show more complex behaviour. \"Mafic\" tonalites, (<65.5 wt.% SiO2) have simply covarying trace element endowments. Minor felsic differentiates, collected on the basis of field evidence for in situ fractionation, have higher Si, K, Rb, Ba, U and Th. \"Normal\" tonalites (66.5 < SiO2 < 70.0) have trace element and K endowments intermediate between the mafic tonalites and the felsic differentiates.

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Mafic tonalites, comprising about half the exposed rocks, crystallized from liquids which derived their geochemical characteristics before injection into the high-level magma chambers. The minor felsic differentiates are considered end-products of fractional crystallization within the magma chamber; the \"normal\" tonalites are interpreted as crystallizing from liquids of intermediate character, i.e., mixtures of \"primitive\" and fractionated liquids.

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Measured primary \u03b418O values vary from +9.0 to +10.6. Metasedimentary country rocks have \u03b418O values of +11.5 to +13.5. Exchange of oxygen between plutons and country rock is minor and limited to narrow border zones. Within Unit III primary \u03b418O correlates with position. A marginal zone of variable values (+9.0-+10.0) gives way to regularly increasing values (+10.0-+10.5) inwards. Primary \u03b418O correlates with Colour Index. Within the central part of Unit III the observed range in \u03b418O values can be explained by crystallization of modally variable rocks from a liquid of constant 18O/16O (to\u00b10.2 per mil). The \u03b418O values of the more mafic marginal rocks (and of mafic rocks from Units I and II) also correlate with Colour Index; lower SiO2 rocks have lower \u03b4180. This correlation cannot simply result from varying mineral abundances, but must reflect variations in \u03b4180 values of the liquids from which these rocks crystallized.

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Calculated initial 87Sr/86Sr (Sri) varies substantially among rocks from each major tonalite unit (Unit I: 0.7060-0.7076; Unit II: 0.7060-0.7074; Unit III: 0.7058-0.7073). These variations appear geographically regular at the kilometer scale within each pluton. The complex patterns, however, differ fundamentally from the general regular west-to-east increase in Sri reported for the batholith (Early and Silver, 1973), and observed in the small early intrusives from the San Jacinto Mountains (0.7057-0.7077). Sri within these rocks shows no identified correlation with other geochemical and petrological parameters.

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The Sr isotope data indicate that melt production, transport, and crystallization processes combined were not capable of completely homogenizing initial variations in Sri within the liquids from which these rocks crystallized. This further implies that either the time scale for convection was large compared to that for crystallization, or that the length scale for convection was small compared to the size of the plutons. Field evidence suggests considerable flow within the magma chamber; estimation of rheological parameters suggest that flow was within a laminar flow convective regime.

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The combined observations are compatible with crystallization from an intermittently recharged, continuously fractionating system. Recharge tended to buffer both the thermal and chemical properties of liquids within the magma chamber; it gave a mechanism for introducing isotopic variations that are incorporated into this continuously crystallizing system. The mafic dikes are suggested to be conduits through which some of these liquids were injected into the various magma chambers. Chemical buffering by continued recharge is also compatible with the observation that the majority of these rocks have geochemical features interpreted as resulting from the action of processes prior to injection of liquids into the high-level magma chambers.

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Rocks with low Sri (0.7058-0.7068) generally have intermediate \u03b418O values (+9.7-+10.3), and fall near the low-\u03b418O side of the batholithic trend defined by Taylor and Silver (1978). Rocks with high Sri (>0.7072) cover the entire observed range in \u03b418O values (+9.0-+10.6), and overlap the field defined for the San Jacinto - Santa Rosa Mountains block by Taylor and Silver. These data require involvement of material from three isotopically distinct source materials in the generation of these rocks. Two of these components (one with low Sri, low \u03b418O; one with high Sri, high \u03b418O) are common to the bulk of the batholith to the south and west. The third (high Sri, low \u03b418O) seems unique to the San Jacinto - Santa Rosa Mountains block; its relative importance within the San Jacinto rocks appears to correlate negatively with SiO2, suggesting that it was associated with relatively mafic liquids. The oxygen isotopic data imply that as much as 35% of this component may be present in some rocks. This component has isotopic and inferred geochemical characteristics compatible with old, slightly enriched (in Rb relative to Sr) subcontinental lithosphere. The low-Sri, low-\u03b418O component appears to be either (or both) normal depleted mantle or (subducted) oceanic crust. Tile oxygen data imply that the third (high-Sri, high-\u03b418O) component has had a prior history at the Earth's surface; it could be either sediment, or igneous material altered at low temperatures such as hydrothermally altered oceanic crust. Geochemical features (K, Rb, LREE abundances) appear more compatible with sedimentary material.

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These data are compatible with, but do not prove, a model for this source region as being a mixture of normal depleted mantle, oceanic crust, old slightly enriched \"subcontinental lithosphere\", and subducted sediment. This model source contains variously 0-35% (oxygen atom basis) subcontinental lithosphere, up to 25% sedimentary component, and apparently requires material of both basaltic (oceanic crust) and depleted mantle composition to balance isotope systematic systematics.

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Tile combined data show 1) that the source volumes for the batholithic rocks were heterogeneous at the scale of hundreds of meters or greater, 2) that the effects of these source heterogeneities were at least partially preserved throughout melt production, transport, and crystallization, and 3) that the net effect of a persistent recharge-fractional crystallization process within the magma chambers was to buffer the composition of the bulk of the rock near that of the early-crystallizing solids.

", "doi": "10.7907/9x01-1n85", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:11236", "collection": "thesis", "collection_id": "11236", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:10172018-114703911", "primary_object_url": { "basename": "Hofmeister_AM_1984.pdf", "content": "final", "filesize": 138472836, "license": "other", "mime_type": "application/pdf", "url": "/11236/1/Hofmeister_AM_1984.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "A Spectroscopic and Chemical Study of the Coloration of Feldspars by Irradiation and Impurities, Including Water", "author": [ { "family_name": "Hofmeister", "given_name": "Anne Marie", "clpid": "Hofmeister-Anne-Marie" } ], "thesis_advisor": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "thesis_committee": [ { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

Natural smoky color or smoky color induced by ionizing radiation develops only in potassium feldspars (KAlSi3O8) free of water bound in the feldspar structure. Neither fluid inclusion water nor \u2261SiOH have an effect. The optical absorption spectra of the smoky color consist of polarized bands at 11600, 16200, 19100, and 27200 cm-1, whose integrated intensities are linearly correlated with the integrated intensity of a broad, asymmetric first derivative at geff = 2.027 in electron paramagnetic resonance (EPR) spectra. This hole center forms only in KAlSi3O8 without structurally bound H2O, and in microcline is resolved into an asymmetric six-line pattern at geff = 2.024 and a single derivative at geff = 2.009 which are Si-O- -K and a hole shared between two nonbonding oxygens (NBO) on Si. In analogy to coloring in quartz and glass, the 11600 cm-1 band is caused by a hole trapped between two NBO's on silicon, the 16200 and 27200 cm-1 bands are due to the Si-O- -K center, and the 19100 cm-1 band results from a hole trapped on an oxygen attached to two aluminums. Smoky centers do not develop in feldspars with structural water because irradiation mobilizes protons which, while diffusing, destroy centers in their path, and finally then settle in sites similar to their original site. Smoky color also develops in sodic plagioclases, but high Al content inhibits its formation in labradorite.

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Amazonite color is intrinsic and controlled by an absorption minimum between three overlapping bands in the ultraviolet and a broad band in \u03b2 at 630, or one UV band and a broad band in \u03b2 at 720 nm, or both superimposed. Comparison of EPR to optical integrated intensities shows that all three colors are connected with a first derivative at geff = 1.56 and two satellites of about 1/7 intensity at geff of 1.83 and 1.39. Analysis of the EPR pattern shows that this center is Pb3+ 31% of the time, with the hole located on coordinating oxygens for the remaining 69%. This center is only produced in samples which have in addition to Pb, H2O structurally bound in the lattice. The dependence of color intensity on the smaller molar concentration of structural water or lead implies that lead and structural water in a 1:1 ratio produce color centers in amazonite. The first order reaction kinetics of amazonite color formation by irradiation and the observation that water is not consumed in the process suggests that Pb2+ is oxidized to Pb3+ by the product OH of the irradiation-induced dissociation of water while H concurrently destroys a hole center on an oxygen, and is followed by the regeneration of the water molecule. The kinetics also show that the radiation necessary for the coloration is provided by internal decay of 40K. The two end-member color types (630 or 720 nm) occur for microcline or orthoclase local structure, respectively. Al/Si disorder increases first locally, and then overall as larger amounts Pb or H2O are incorporated, so that crystals with intermediate Pb contents have both color types. A spectrally similar blue radiation color also occurs for Pb-bearing sodic plagioclases.

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Gemmy labradorite phenocrysts from one Steens Mountain basalt flow in Rabbit Basin, Oregon, sometimes possess a pink schiller, or more rarely a transparent red or green coloration. Direct microprobe analysis of the schiller flakes show that these are metallic copper. XRF analysis of the different colored zones revealed that only the copper content varies with color: colorless samples, or sections of crystals, have 0-35 ppm Cu; greens average 80 ppm Cu; reds average 135 ppm Cu; while schiller bearing labradorites have 50 to 240 ppm Cu. Spectral similarity of the red color to copper-ruby color of glass shows that the red arises from the intrinsic absorption of colloidal Cuo particles that are too small to scatter light (ca. 4 to 22 nm). Spectra from the green regions strongly resemble that of amazonite. Because the temperature of exsolution is subsolidus and proportional to Cu content, diffusion proceeds more rapidly for crystals with higher Cu content and results in formation of larger particles. The Cuo reduction at low temperature (800\u00b0C) involves formation of hole center (O-) that is captured by Pb2+ to form the green amazonite color (Pb3+). At high temperatures (~ 900 to 1100\u00b0C) the reduction of Cu is controlled by whatever reactions occur in the basalt to keep fO2 along the QFM buffer. Migration of Cuo may cause the variation of Cu concentrations in a single sample; but the variation of Cu content among different crystals suggests that the composition of the megacrysts was not constant and changed in response to an increasing copper content in the melt as crystallization of the labradorite proceeded.

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The coloration process in feldspar strongly resembles that in glasses for both radiation colors (smoky) and exsolution phenomena (Cuo colloids, Cuo schiller) and also that of radiation colors in other crystalline solids (smoky quartz, Pb3+ or Tl2+ in KCl). Although quartz and glass are structurally and chemically similar to feldspar, KCl is not, suggesting that for the most part it is the behavior of the chemical impurity on an atomic level which controls the coloring mechanism.

\r\n", "doi": "10.7907/bj75-5674", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:11316", "collection": "thesis", "collection_id": "11316", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:12142018-091056975", "primary_object_url": { "basename": "Shaw_HF_III_1984.pdf", "content": "final", "filesize": 99999823, "license": "other", "mime_type": "application/pdf", "url": "/11316/1/Shaw_HF_III_1984.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Sm-Nd and Rb-Sr Isotopic Systematics of Tektites and Other Impactites, Appalachian Mafic Rocks, and Marine Carbonates and Phosphates", "author": [ { "family_name": "Shaw", "given_name": "Henry Francis, III", "orcid": "0000-0003-0681-5430", "clpid": "Shaw-Henry-Francis-III" } ], "thesis_advisor": [ { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" } ], "thesis_committee": [ { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" }, { "family_name": "Bercaw", "given_name": "John E.", "clpid": "Bercaw-J-E" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Wasserburg", "given_name": "Gerald J.", "orcid": "0000-0002-7957-8029", "clpid": "Wasserburg-G-J" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

This thesis is made up of three separate studies, each using the Sm-Nd and Rb-Sr isotopic systems to solve a problem of geologic interest.

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In the first study it is shown that Sm-Nd and Rb-Sr analyses of tektites and other impactites can be used to place constraints on the age and provenance of the target materials which were impact melted to form these objects. Tektites have large negative values of \u03b5Nd(0) which are uniform within each tektite group, while the \u03b5Sr(0) values are large positive and show considerable variation within each group. The chemical, trace element, and isotopic compositions of tektites are consistent with their production by melting of sediments derived from old continental crust. Each tektite group is characterized by a uniform Nd model age, TNdCHUR, interpreted as the time of formation of the crustal segment which weathered to form the parent sediment for the tektites: (1) ~1.15AE for Australasian tektites; (2) ~1.9AE for Ivory Coast tektites; (3) ~0.9AE for moldavites; (4) ~0.65AE for North American tektites; and (5) ~0.9AE for high-Si irghizites. Sr model ages, TSrUR, are variable within each group, reflecting Rb-Sr fractionation during weathering and sedimentation. In the favorable limit of very high Rb/Sr ratios TSrUR approaches the time of sedimentation of the parent material which melted to form the tektites. Australasian tektites are derived from ~0.25AE sediments, moldavites from ~0.0AE sediments, and Ivory Coast tektites from ~0.95AE sediments. The parent sediments of the other tektite groups have poorly constrained ages. The isotopic data on the moldavites and Ivory Coast tektites are consistent with their derivation from the Ries and Bosumtwi Craters, respectively. Irghizites are isotopically distinct from the Australasian tektites and are probably not related. Sanidine spherules from an iridium-rich Cretaceous-Tertiary boundary clay were heavily overprinted with seawater-derived Sr and Nd during diagenesis. The inferred initial isotopic composition of the sanidine itself is \u03b5Nd(T) = +2 and \u03b5Sr(T) = +5. These results show that the spherules were not derived from old continental crust or meteoritic potassium feldspar. These objects may represent an impact melt of a mixture of basaltic oceanic crust and overlying sediments and are consistent with an oceanic impact at the Cretaceous-Tertiary boundary. The isotopic data are also consistent with an origin by authigenic growth of the spherules from young detrital material.

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The second study in this thesis uses the Sm-Nd and Rb-Sr isotopic systematics of mafic rocks from the Appalachians to place constraints on their origin. Isotopic analyses of modern oceanic basalts and ophiolites have shown that both modern and ancient oceanic crust have a characteristic Nd and Sr isotopic signature indicative of derivation from a depleted mantle reservoir. It also appears that the Nd isotopic system is not appreciably disturbed by metamorphism. These isotopic characteristics have been extended to the Pt. Sal, Kings-Kaweah, and Josephine Ophiolites of California. These characteristics are used in an attempt to identify pieces of proto-Atlantic oceanic crust among the mafic and ultramafic rocks of the Appalachians. Sm-Nd mineral isochrons for the Baltimore Mafic Complex, Md (BMC) yield an age of 490\u00b120 My which is interpreted as the igneous crystallization age. BMC whole rock samples do not define isochrones and have initial isotopic compositions of -6.4 < \u03b5Nd(T) < -2.2, +51 < \u03b5Sr(T) < +115. \u03b5Nd(T) and \u03b5Sr(T) are anti-correlated. This is not the signature of depleted mantle and oceanic crust, but is similar to old continental crust. It is proposed that the BMC is a mafic continental intrusion, possibly subduction related, which was contaminated with old continental crust during emplacement. Whole rock samples from the Thetford Mines Complex, Qe (TMC) do not define isochrons and have -1.5 < \u03b5Nd(T) < +4.2, +2.6 < \u03b5Sr(T) < +114. These data do not in any way reflect the signature of normal oceanic crust. These results are in contrast with geologic relationships which show the TMC to have the characteristics of an ophiolite complex. The TMC is chemically and isotopically similar to a class of other ophiolites which have affinities to modern boninites. The TMC may therefore represent an ophiolite formed under an arc complex. The Chunky Gal Amphibolite, N.C., Lake Chatuge complex, N.C., and Hazen's Notch Amphibolite, Vt., were found to have a depleted mantle signature with +5 < \u03b5Nd(T) < +8 and may be fragments of oceanic crust. The Webster-Addie body, N.C., has \u03b5Nd(T) ~-1, \u03b5Sr(T) ~+30 and is not isotopically similar to oceanic crust or the other North Carolina mafic bodies analyzed. From these isotopic results it is clear that Appalachian mafic rocks have diverse origins, some are continental intrusives (BMC), others are probably fragments of oceanic crust (Vermont and N. Carolina amphibolites). Future models for the development of the Appalachians must allow for these various origins. The possibility that some ophiolites are not normal oceanic crust but have an origin in a partially continental setting or as anomalous oceanic crust will require further attention.

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The final study is an exploration of the possibility of establishing the Nd isotopic variations in seawater over geologic time by analysing a marine sedimentary phase which records and preserves the \u03b5Nd(T) value of the seawater in which it formed. Apatite and CaCO3 (calcite and aragonite) are examined as possible such phases. Modern biogenic and inorganic calcite and aragonite were found to have low REE concentrations: Nd = 0.2 to 65 ppb. The \u03b5Nd(0) values of Atlantic (-8.3 to -9.6) and Pacific (-0.1 to -1.3) carbonates are distinctly different and reflect the isotopic composition of Nd in the seawater in which they formed. The high concentrations of REE measured in limestones and carbonate fossils cannot be primary but must be due to the presence of other phases in the carbonate of the introduction of REE during diagenesis. Modern biogenic apatite also has a low REE content (<150 ppb Nd), but appears to quickly scavenge REE from seawater. Levels up to 1000 ppm Nd can be reached by this process. Inorganically precipitated apatite from phosphorites also has high concentrations of seawater-derived REE. A seawater-like REE pattern with a characteristic negative Ce-anomaly is often preserved by sedimentary apatite and apatite samples of the same age from different localities bordering a common sea record a common value of \u03b5Nd(T). These characteristics suggest that apatite can be used to trace the evolution of \u03b5Nd(T) in ancient seawater. The values of \u03b5Nd(T) in seawater as inferred from analyses of conodonts and phosphorite apatite range between -1.7 and -8.9 over the last 700My. These values lie in the range of modern seawater values and show no evidence for drastic changes in the sources for Nd in seawater during this time. High values of seawater \u03b5Nd(T) in the Triassic and latest Precambrian may correlate with the breakup of large continental landmasses. The initial \u03b5Nd(T) = -15.0 of the 2AE old Rum Jungle phosphorite requires the presence of -1.5AE old continental crust at 2AE ago. This demonstrates how the \u03b5Nd value of ancient seawater can be used to constrain the age of the exposed crust as a function of time.

", "doi": "10.7907/x0zc-7w22", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:11183", "collection": "thesis", "collection_id": "11183", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:09142018-134243270", "primary_object_url": { "basename": "Larson_PB_1983.pdf", "content": "final", "filesize": 119780322, "license": "other", "mime_type": "application/pdf", "url": "/11183/1/Larson_PB_1983.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "I. An \u00b9\u2078O/\u00b9\u2076O Investigation of the Lake City Caldera, San Juan Mountains, Colorado. II. \u00b9\u2078O/\u00b9\u2076O Relationships in Tertiary Ash-Flow Tuffs from Complex Caldera Structures in Central Nevada and the San Juan Mountains, Colorado", "author": [ { "family_name": "Larson", "given_name": "Peter Brennan", "clpid": "Larson-Peter-Brennan" } ], "thesis_advisor": [ { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" } ], "thesis_committee": [ { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" }, { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

Part I. 18O/16O analyses were made on 355 samples in and around the 11 by 14 km Lake City caldera, which formed 23 m.y. ago in response to the eruption of the rhyolitic Sunshine Peak Tuff. All of the major lithologies and hydrothermal alteration facies were analyzed, and a detailed \u03b418O map was made of the caldera and its surroundings. Intracaldera facies Sunshine Peak Tuff consists of three members interbedded with landslide debris and megabreccias shed into the caldera during eruption and collapse. Asymmetric resurgence within the Lake City caldera followed collapse and was accompanied by intrusion of a flat-topped, granitic magma centered in the resurgent dome. Ring magmatism produced dike-like intrusions along the northern ring fault and the Red Mountain-Grassy Mountain quartz latite ring dome on the eastern caldera margin. The caldera was emplaced into older Tertiary volcanic rocks and Precambrian granitic rocks.

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Based on analyses of outflow-facies samples and of the least altered intracaldera facies, we can demonstrate that the caldera-fill Sunshine Peak Tuff originally was isotopically very homogeneous, with an initial igneous \u03b418O value of +7.2 to +7.3. Thus, 18O depletions in the hydrothermally altered tuff could be compared without worrying about the complicating factor of different initial \u03b418O values. Nearly all the rocks within the caldera and outside the caldera within at least 3 km of the ring fault were altered by meteoric-hydrothermal fluids, and depleted in 18O down to values as low as \u03b418O = -3.1. Erosion has exposed the hydrothermally altered caldera-fill rocks and the upper contact of the altered resurgent intrusion in the western and central part of the caldera, providing about 2 km of vertical exposure. Because of post-alteration regional eastward tilting, the eastern part of the caldera has not been extensively eroded, and the original topography of the ring dome and the top of the caldera-fill rocks are locally preserved. This differential erosion from west to east furnishes a unique opportunity to study water-rock interactions in a caldera-type hydrothermal system from near-surface environments down through 3 km into the sub-volcanic intrusion that drove the hydrothermal convection.

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Elevation and proximity to fractures exerted the strongest control on 18O-depletions in the Precambrian granite and the older volcanic rocks. The lowest alSo values are found in rocks from the Eureka graben, a highly-fractured and extensively altered zone that extends SW from the caldera. Low \u03b418O values also occur adjacent to the caldera ring fault. Those samples of the Precambrian granite and of the older volcanic rocks that are located at the greatest depths below the mid-Tertiary erosion surface have the lowest \u03b418O values. At present-day, constant elevations, \u03b418O values are lowest in the western part of the study area than in the eastern part; this is a result of the regional eastward tilting. The above effects are best interpreted as indicating higher water/rock ratios near the permeable fractures and higher temperatures at greater depth.

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The \u03b418O values within the Lake City caldera are controlled by elevation, proximity to permeable zones, and proximity to the resurgent intrusive rocks. \u03b418O values decrease systematically with stratigraphic depth within the caldera. The lowest \u03b418O values are found along the western ring fault, along resurgence-related fractures, in the permeable megabreccia units, and along the contact of the resurgent intrusion. Mineralogic alteration facies within the caldera show complementary patterns. Intense argillization is found along fractures near the resurgent intrusion. Rocks adjacent to the resurgent intrusion have been hornfelsed but not intensely mineralogically altered. Weak argillization in stratigraphically shallow Sunshine Peak Tuff grades into both of these alteration regimes and also grades downward into chlorite-calcite alteration. These data show that the resurgent intrusion was the \"heat engine\" that drove the Lake City hydrothermal system. Alteration in and near the intrusion occurred at high temperatures (\u2248 400\u00b0C) and intermediate water/rock ratios. Away from the resurgent intrusion, water-rock interaction in the permeable zones (megabreccia units and fractures) occurred at lower temperatures (200\u00b0C to 300\u00b0C) and high water/rock ratios. The regional eastward tilting has raised low-18O rocks in the western part of the caldera to higher elevations than stratigraphically equivalent rocks in the eastern part of the caldera. Mineralogical alteration patterns are also similarly displaced.

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Near-surface solfataric alteration is centered on a brecciated zone in the Red Mountain-Grassy Mountain quartz-latite dome on the eastern caldera margin. \u03b418O values of hydrothermal quartz from this alteration zone are high (> +11) and decrease gradationally with depth. Vein quartz \u03b418O values from deeper levels within the caldera lie on the deeper projection of the solfataric quartz \u03b418O trend. These data can be successfully modelled using an upward-flowing, boiling, 18O-shifted meteoric water as a hydrothermal fluid. This model shows that the same fluids responsible for vein quartz precipitation also produced the shallow solfataric alteration. High \u03b418O values were also measured from a number of other solfatarically altered areas in the San Juan Mountains (Red Mountain district near Silverton, Calico Peak near Rico, Engineer Pass, Carson Camp, and the Summitville district). These alteration zones, some of which are economically mineralized, were also apparently produced by boiling meteoric-hydrothermal fluids.

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Deeply-circulated, 18O-shifted, meteoric waters were the primary source of hydrothermal fluids in the Lake City hydrothermal system. By analogy with other deeply eroded caldera hydrothermal systems studied by other workers, such fluids probably rose along deep extensions of the fractured, permeable Lake City ring fault zone. At the present level of exposure, fluids in the Lake City hydrothermal system were apparently drawn into the central part of the resurgent dome along the permeable, outward-dipping, megabreccia units. Flow was directed upward along permeable fractures where these fractures intersected the megabreccia units. A strong thermal gradient existed around and over the resurgent intrusion. Recharge into this hydrothermal system was basically radially inward toward the caldera, but flow was greatly enhanced through the permeable, highly fractured, Eureka graben.

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Part II. Oxygen isotope studies were made on 60 samples from the central Nevada caldera complex, which consists of three nested calderas that erupted from 32 to 25 m.y. ago. 18O/16O analyses were also made on 96 samples from the central San Juan caldera complex, Colorado, which contains 7 ash-flow tuffs, each erupted from separate, nested collapse structures between 28 and 26 m.y. ago. The sequence of ash-flow tuffs erupted from the earliest of the three central Nevada calderas began with the giant Tuff of Williams Ridge and Morey Peak (+ 2500 km3), followed by the Mbnotony Tuff (3000 km3), and finally by various ash flow tuffs erupted from the youngest caldera (400 km3). In the San Juan complex, the earliest ash-flow was the Fish Canyon Tuff, which is also the largest of these ash-flows (> 3000 km3). Of the six other major ash-flow tuffs erupted from the central San Juan complex, none exceeds 1000 km3 in volume.

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Previous studies of other complex calderas at Yellowstone National Park and in southwest Nevada indicated that the later eruptions have \u03b418O values 3 per mil lower than rocks erupted early in the cycles. However, in the present study, no large negative shifts in \u03b418O were found. The various eruptions in both central Nevada and the central San Juans were remarkably uniform in 18O/16O, although small shifts of about -0.2 to -0.3 per mil were found in both suites of rocks in going from the early ash-flows to a later set. The indicated range of \u03b418O values of these quartz-latite and rhyolite magmas was 9.1 to 9.8 in the central Nevada complex and 6.6 to 7.5 in the central San Juan complex. The higher \u03b418O values in central Nevada probably indicate melting of sedimentary or metasedimentary country rocks at depth, whereas in Colorado, the low-18O, lower part of the craton was very likely involved in the melting process.

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\u03b418O fractionations between coexisting phenocryst minerals in all of the ash-flow tuffs and lava flows from these two complexes are larger at the bases of the units (tops of the magma chambers) and smaller at the tops of the units (deeper levels of the magma chambers). These relationships show that temperature gradients existed in virtually all these magmas prior to eruption (cooler at the top and hotter at deeper levels).

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It is not clear why some complex caldera magmas become depleted in 18O with time, and others do not. No relationship exists between the duration of caldera magmatism and low-18O rocks, nor between the size of the eruptions and these 18O depletions. However, the large 18O depletions found to date occur only in caldera complexes younger than about 15 to 20 m.y., corresponding to the initiation of Basin-Range extension in the western United States. Perhaps Basin-Range faults allow meteoric fluids to penetrate deeply into fairly high-temperature regions of the crust. These younger magmas might then be able to melt or assimilate larger amounts of altered, 18O depleted rocks during their ascent. A correlation also appears to exist between the 18O depletions and the major-element chemistry of the rocks. All of the low-18O ash-flow tuffs contain abundant high-silica rhyolites (consistently ranging up to or above 77 percent SiO2). The large silica contents of these magmas indicate very strong differentiation, suggesting prolonged assimilation-fractional crystallization in a stable magma chamber without the renewed addition much primitive, unfractionated magma having a \"normal\" \u03b418O value. It is tentatively concluded that ash-flow magmas strongly depleted in o1eo will be produced only if: (1) there is a pre-history of intense fracturing, caldera collapse, and extensive meteoric-hydrothermal activity, followed by (2) the development of a stable, strongly differentiated, zoned magma chamber, whose roofward portion is in close proximity to low-18O, hydrothermally altered roof rocks for an extended interval of time (> 100,000 years ?).

", "doi": "10.7907/aeb1-ct78", "publication_date": "1984", "thesis_type": "phd", "thesis_year": "1984" }, { "id": "thesis:3919", "collection": "thesis", "collection_id": "3919", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-10042006-112842", "type": "thesis", "title": "Analysis of Upper and Lower Mantle Structure Using Shear Waves", "author": [ { "family_name": "Lay", "given_name": "Thorne", "orcid": "0000-0003-2360-4213", "clpid": "Lay-Thorne" } ], "thesis_advisor": [ { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" } ], "thesis_committee": [ { "family_name": "Helmberger", "given_name": "Donald V.", "clpid": "Helmberger-D-V" }, { "family_name": "Kanamori", "given_name": "Hiroo", "orcid": "0000-0001-8219-9428", "clpid": "Kanamori-H" }, { "family_name": "Anderson", "given_name": "Donald L.", "clpid": "Anderson-D-L" }, { "family_name": "Stevenson", "given_name": "David John", "orcid": "0000-0001-9432-7159", "clpid": "Stevenson-D-J" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Hager", "given_name": "Bradford H.", "clpid": "Hager-B-H" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

This thesis addresses the fundamental problem of determining the radial and lateral structure of the earth's interior using body wave observations. My approach is a cautious one, involving detailed analysis of a substantial data set in which I attempt to isolate the contributions from radial and lateral structure in both the upper and lower mantles. This is an elusive task, as I am concerned with the 2 or 3% fluctuations about standard earth models, which produce rather subtle effects on teleseismic signals. However, this is the level of precision to which the three dimensional structure of the earth must be determined if we are to map the dynamical and compositional configuration of the earth. Studies similar to those described here cannot be conducted on a detailed global basis, given the intrinsic limitations due to station and earthquake distribution, so I have repeatedly emphasized the qualitative implications of my results, as they probably provide a representative sampling of the subtle, but significant heterogeneity of the earth.

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The topics addressed in the following work appear unrelated at first glance, ranging from determination of the detailed shear velocity structure at the base the mantle to variations in attenuation and velocity structure of the upper mantle. However, the data set used throughout is largely the same, and this in itself indicates the need to consider all of the complexity discussed herein for future progress to be made in mapping the three dimensional structure of the earth with a high level of confidence.

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The first chapter of the thesis presents results of a waveform analysis of transversely polarized SH signals that propagate through the lowermost mantle. The waveforms of these phases show clear interference patterns due to interaction with a discontinuous shear velocity increase about 280 km above the core-mantle boundary. This discontinuity, which has not been detected previously, is manifested in signals sampling three widely separated portions of the lower mantle, and hence is a good candidate for a global radial earth structure. Very detailed inspection of the signals reveals evidence for lateral variations in the depth of the discontinuity, which provides a procedure by which to map the structure of the D\" region in detail. Analysis of the relative amplitudes of SH and ScSH signals reveals that the velocity gradient above the core boundary is consistent with the smoothly varying gradients in most gross earth models, but evidence for local high velocity gradients at the base of the mantle is detected in ScSV signals.

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Chapter II presents a travel time analysis of the same data set used in Chapter I, which was motivated by the observation of large amplitude and travel time anomalies in the S and ScS data. An emphasis is placed on isolating the portions of the S and ScS paths which are anomalous. A strong empirical case is made for the existance of localized regions with scale lengths of 1000 to 2000 km and 2% velocity anomalies within the lower mantle at depths from 1000 to 2700 km. The long period signals traversing these regions show as much as a factor of 2 amplitude enhancement or diminution. This result demonstrates that both amplitude and travel time anomalies are induced by lateral structure in the portion of the mantle assumed to be homogeneous in most seismological studies.

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The third chapter is an analysis of the influence of upper mantle variations in attenuation, velocity structure and receiver structure on the S and ScS signals analyzed in the lower mantle studies. These variations contaminate and complicate the interpretation of any data set used to study deeper earth structure. Along with evidence for very strong and abrupt variations in upper mantle properties, results are presented which indicate the inadequacy of assumptions that are frequently made about the nature of long period body-wave receiver functions.

", "doi": "10.7907/65TN-KN39", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:5590", "collection": "thesis", "collection_id": "5590", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:03112010-141459869", "primary_object_url": { "basename": "Lewis_re_1983.pdf", "content": "final", "filesize": 17296708, "license": "other", "mime_type": "application/pdf", "url": "/5590/1/Lewis_re_1983.pdf", "version": "v7.0.0" }, "type": "thesis", "title": "Geology of the Hackberry Mountain Volcanic Center, Yavapai County, Arizona", "author": [ { "family_name": "Lewis", "given_name": "Richard Edwin", "clpid": "Lewis-Richard-Edwin" } ], "thesis_advisor": [ { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" } ], "thesis_committee": [ { "family_name": "Shoemaker", "given_name": "Eugene Merle", "clpid": "Shoemaker-E-M" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" }, { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

The Hackberry volcano in central Arizona, is a large dacitic volcano of late Miocene age. Most of the Hackberry Mountain area is underlain by Miocene volcanic rocks, primarily basalt and dacite. The oldest are a heterogeneous group of basalt flows, the Hickey Formation, erupted from local cinder cones. They were superseded by a homogeneous group of basalt flows, the Thirteenmile Rock Basalt, erupted from vents east of the area. Pyroclastics from the Hackberry volcano intertongue with the upper part of the Hickey Formation and all of the Thirteenmile Rock Basalt. There were seven episodes of these pyroclastics, collectively termed the Towel Creek Tuff, that were formed early in the history of the Hackberry volcano. This unit contains numerous dacitic ignimbrites and air-fall tuffs. Coarse, interstratified breccias occur in the upper parts of these deposits; they are capped by reworked tuffs. The sequence of air-fall tuff, ignimbrite, and breccia suggests a Pelean style of eruption.

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After cessation of the pyroclastic activity, the volcano was intruded by a dacite stock, the Sally May Dacite. The stock probably extruded above the ground surface; because of its location, size (diameter of 8 km), petrography, and chemistry, the stock is believed to be the material of the magma chamber for the Towel Creek Tuff. The stock reached the surface without producing an attendant pyroclastic deposit. The fact that the stock rose to the surface without an accompanying paroxysmal eruption indicates that it was volatile-poor though still hot. Application of Stokes Law shows that it was unable to rise by buoyant forces alone; its upward migration apparently was facilitated by regional extension. The stock was hydrothermally altered at low temperature after its emplacement.

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Two rhyolite plugs intruded the stock. One was apparently the conduit for a rhyolite flow nearly eight kilometers in length. This plug was later disrupted, possibly by an eruption driven by fluids in the altered stock. The volcanic activity culminated with the extrusion of a thick dacite flow, the Hackberry Mountain Dacite.

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The Hackberry volcano was active for 2.2 to 3.9 m.y. The presence of basic xenoliths in the dacitic rocks suggests that its long life was the consequence of the injection of basaltic magma into the dacitic magma chamber. The dacite in all deposits of this volcano are petrographically similar.

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The Hackberry Mountain area forms the southeastern margin of the Verde Valley, a sedimentary basin in which the Verde Formation accumulated. Fluviatile sandstones of the Verde Formation intertongue with the upper Hickey and lower Thirteenmile Rock Basalt in the northwestern part of this area, and the Verde grades upward into lacustrine sediments younger than all the volcanic rocks, but still of Miocene age. The Verde Valley formed primarily by subsidence along northwest-trending normal faults, many of which occur in the area studied. The faults in the Hackberry area are commonly interconnected and have a net offset of 400 meters, downdropped southwest. The margin of the basin occurs here because the amount of subsidence decreases, and, more importantly, the Hackberry volcano formed a topographic boundary.

", "doi": "10.7907/6sbf-7765", "publication_date": "1983", "thesis_type": "phd", "thesis_year": "1983" }, { "id": "thesis:2981", "collection": "thesis", "collection_id": "2981", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-07252007-135803", "primary_object_url": { "basename": "Powell_re_1981.pdf", "content": "final", "filesize": 18615907, "license": "other", "mime_type": "application/pdf", "url": "/2981/16/Powell_re_1981.pdf", "version": "v3.0.0" }, "type": "thesis", "title": "Geology of the Crystalline Basement Complex, Eastern Transverse Ranges, Southern California: Constraints on Regional Tectonic Interpretation", "author": [ { "family_name": "Powell", "given_name": "Robert Edward", "clpid": "Powell-Robert-Edward" } ], "thesis_advisor": [ { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" } ], "thesis_committee": [ { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" }, { "family_name": "Saleeby", "given_name": "Jason B.", "clpid": "Saleeby-J-B" }, { "family_name": "Sieh", "given_name": "Kerry E.", "orcid": "0000-0002-7311-2447", "clpid": "Sieh-K-E" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Allen", "given_name": "Clarence R.", "clpid": "Allen-C-R" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

About 3000 km2 within the crystalline basement complex of the Eastern Transverse Ranges in the Chuckwalla, Orocopia, Eagle, Cottonwood, Hexie, Little San Bernardino, and Pinto Mountains of Riverside County, California were mapped at scales of 1:36,000 and 1:62,500 and compiled at 1:125,000 (Plate I). Pre-Jurassic(?) (i.e., older than the Mesozoic batholiths) rocks of the crystalline complex comprise two lithologically distinct terranes. These terranes are called the Joshua Tree and San Gabriel terranes for regions of southern California in which their lithologies were initially characterized. The two terranes are superposed along a previously unrecognized low-angle fault system of regional extent, the Red Cloud thrust.

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During the course of this study, the structurally lower Joshua Tree terrane has been defined as a stratigraphically coherent group of crystalline rocks that consists of Precambrian granite capped by a paleo-weathered zone and overlain nonconformably by orthoquartzite that interfingers westward with pelitic and feldspathic granofelses. The quartzite contains near-basal quartz/quartzite clast conglomerates, and has well-preserved cross-bedding that appears upright wherever it has been observed. Pelitic and feldspathic granofelses crop out to the west of the quartzite exposures in four lithologically different belts that trend northnorthwest throughout the area mapped. These lithologic belts are interpreted to have been derived from stratigraphically interfingering sedimentary protoliths deposited in a basin offshore from a quartzose beach-sand protolith. In proximity to the early Red Cloud thrust, this whole stratigraphic package was pervasively deformed to granite gneiss, stretched pebble conglomerate, lineated quartzite, and schist.

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A northeast-trending pattern of metamorphic isograds was orthogonally superimposed on the northnorthwest-trending protoliths of the Pinto gneiss. A central andalusite zone, located in the southern Little San Bernardino and Hexie, and northern Eagle Mountains, is flanked to the northwest and southeast by sillimanite zones. Coincident with this symmetrical distribution of aluminosilicates is an asymmetrical distribution of other pelitic mineral zones, with prograde cordierite-aluminosilicate-biotite- and K-feldspar-aluminosilicate-bearing assemblages to the northwest in the northern Little San Bernardino and Pinto Mountains, staurolite-bearing assemblages in a narrow zone in the southern Little San Bernardino-Hexie and northern Eagle Mountains, and retrograde chlorite-muscovite-bearing assemblages in the southernmost Little San Bernardino, Cottonwood, southern Eagle, Orocopia, and Chuckwalla Mountains. One occurrence of chloritoid-sillimanite in the central Eagle Mountains is apparently also retrograde. The crossing isograds are interpreted to result from a temporal increase in PH2O relative to PT from south to north through the field area. Comparison of the pelitic assemblages with experimental studies suggests peak conditions of PT \u2248 3.5 to 4 kb, T \u2248 525 to 625\u00b0C. The early prograde metamorphism pre-dated the thrusting event; the retrograde stage may have overlapped in time with the emplacement of the San Gabriel terrane allochthon. Cordierite-orthoamphibole-bearing assemblages are present in one stratigraphic zone of the Pinto gneiss.

\r\n\r\n

In this study, the Precambrian lithologies of the San Gabriel terrane are viewed as a three-part deep crustal section, with uppermost amphibolite grade pelitic (Hexie) gneiss intruded by granodioritic (Soledad) augen gneiss at the highest level, retrograded granulite (Augustine) gneiss at an intermediate level, and syenite-mangerite-jotunite at the lowest level exposed in the Eastern Transverse Ranges. The Hexie gneiss, characterized by sillimanite-garnet-biotite-bearing assemblages, is thrust over andalusite-bearing granofels of the Pinto gneiss.

\r\n\r\n

The Red Cloud thrust system is inferred to have developed in three or four sequential structural events: 1) early thrusting that probably moved parallel to the ENE mineral lineations recorded in both plates; 2) regional folding of the initial thrust surface around NNE-trending axes; 3) later thrusting that broke with some component of westward movement across a fold in the older thrust surface to produce a stacking of crystalline thrust plates of the two terranes; 4) continued or renewed folding of both thrust faults with eventual overturning toward the SW. It is consistent with all observations to date to link these structural events into a single regional tectonic episode that resulted in westward-vergent allochthonous emplacement of the San Gabriel terrane over Joshua Tree terrane. The thrust timing can only be loosely bracketed in time between 1195 m.y. and 165 m.y. ago.

\r\n\r\n

The pre-batholithic terranes and the westward-vergent Red Cloud thrust are considered to be exotic with respect to the pre-batholithic rocks and structures exposed to the north and east of the field area. The bounding discontinuity has been obliterated by intrusion of both suites of Mesozoic batholithic rocks.

\r\n\r\n

The Mesozoic plutonic rocks comprise two batholithic suites, both of which intrude the Joshua Tree and San Gabriel terranes and the Red Cloud thrust system. NW-SE trending belts of plutonic lithologies have been mapped within each suite: the oldest lithology of the younger suite intrudes the youngest lithology of the older suite. The older suite, Jurassic(?), lying to the NE, appears to have an alkalic character; the younger suite, Cretaceous(?), appears calc-alkaline. The older suite consists of biotite- and K-feldspar-bearing gabbro-diorites intruded by low-quartz monzogranites. The younger suite includes hornblende-biotite-sphene granodiorite intruded by porphyritic monzogranites, intruded in turn by nonporphyritic monzogranite.

\r\n\r\n

The Eastern Transverse Ranges south of the Pinto Mountain fault are defined by several Cenozoic E-W left-lateral strike-slip faults that have a cumulative westward displacement from S to N of about 50 km. The left-lateral faults are interpreted to form part of a conjugate fault set with complementary right-lateral faults in the Mojave and Colorado Deserts. Along the western boundary of the Eastern Transverse Ranges in the Little San Bernardino Mountains, the crystalline rocks have been pervasively cataclasized by an event that post-dates intrusion of the Cretaceous(?) plutonic rocks. The cataclasis is attributed to the Vincent-Orocopia-Chocolate Mountain thrust that is thought to superpose the diverse pre-batholithic and batholithic rocks of the Eastern Transverse Ranges above Pelona-type schist. The cataclastic foliation is folded along the length of the Little San Bernardino Mountains in an antiform that is inferred to be cored with Pelona-type schist. This fold may have formed a single antiformal feature comprising all the crystalline-rock antiforms now recognized along the San Andreas fault that are cored by Pelona-type schist. Displacements of the piercing points formed by the antiformal axis apparently indicate 220 km of right-lateral offset on the present San Andreas strand and about 80 km of right-lateral offset along a fragmented older San Andreas strand that consisted of the San Francisquito, Fenner, and Clemens Well faults and a buried extension of this fault beneath the alluvial fill of the valley between the Chocolate and Chuckwalla Mountains.

\r\n", "doi": "10.7907/F22F-YX04", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:15234", "collection": "thesis", "collection_id": "15234", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05302023-213210418", "primary_object_url": { "basename": "Criss_RE_1981.pdf", "content": "final", "filesize": 109196813, "license": "other", "mime_type": "application/pdf", "url": "/15234/1/Criss_RE_1981.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "An \u00b9\u2078O/\u00b9\u2076O, D/H and K-Ar Study of the Southern Half of the Idaho Batholith", "author": [ { "family_name": "Criss", "given_name": "Robert Everett", "orcid": "0000-0002-6484-1875", "clpid": "Criss-Robert-Everett" } ], "thesis_advisor": [ { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" } ], "thesis_committee": [ { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Lowenstam", "given_name": "Heinz A.", "clpid": "Lowenstam-H-A" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

\u03b4\u00b9\u2078O and \u03b4D measurements provide powerful tools for the study of igneous rock petrogenesis. Among the noteworthy contributions of such studies have been the demonstration that massive quantities of hydrothermal fluids have interacted with considerable portions of the earth's upper crust, that the majority of such fluids are derived from ordinary meteoric surface waters, and that similar fluids appear to be involved in the formation of many ore deposits. This thesis presents the results of a combined \u03b4\u00b9\u2078O, \u03b4D, K-Ar and petrographic study, whose principal goal was to elucidate the characteristics and thermal history of a series of hydrothermal systems developed within the Idaho batholith during the Eocene, about 40-45 m.y. ago.

\r\n\r\n

The hydrothermal activity of concern is related to a period of intense magmatism and tectonism in Idaho termed the Eocene event. This period was characterized by intrusion of epizonal granite batholiths, formation of the cogenetic Challis volcanic field, block faulting, ring faulting, and ore deposition. The effects are very widespread but are most conspicuous in the east-central portion of the southern half (Atlanta lobe) of the Idaho batholith, the region which was studied in most detail.

\r\n\r\n

The effects of the widespread hydrothermal activity are easily monitored against the relatively uniform primary character of the Mesozoic granitoids, which originally had whole-rock \u03b4\u00b9\u2078O values of 9.5\u00b11.5 and biotite \u03b4D values of -70\u00b15 permil. The Eocene meteoric waters in this region had \u03b4\u00b9\u2078O and \u03b4D values of about -16 and -120 permil respect\u00adively, and interaction and exchange of the rocks with deep circulating fluids derived from these waters produced major heavy isotope depletions in the rocks, such that the whole-rock \u03b4\u00b9\u2078O and biotite \u03b4D values became as low as -4.5 and -176 permil. However, the rates of isotopic exchange of various minerals with the fluid are not identical, and the new results prove that feldspar exchanged \u00b9\u2078O with the fluid at least four times as fast as did coexisting quartz, and that biotite exchanged D with the fluid at a much faster rate than did coexisting muscovite. These differential effects are important because they allow the primary isotopic compositions to be deduced from altered rocks, and have the still unproven potential of indicating something of the temperature-time history of the hydrothermal interactions.

\r\n\r\n

Widespread propylitization of the rocks occurred concurrently with the \u03b4\u00b9\u2078O and \u03b4D exchange effects. The most commonly observed petro\u00ad graphic changes are the development of chlorite and sericite, whose quantities generally increase in crude proportion to the amount of \u00b9\u2078O exchange. Such hydration effects are generally not conspicuous in previously studied hydrothermal areas associated with gabbroic plutons, which indicates that the hydrothermal interactions in Idaho occurred at relatively low temperatures (generally <350\u00b0C, see below).

\r\n\r\n

Systematic mapping of the \u03b4\u00b9\u2078O and \u03b4D depletions of the rocks has provided some startling new insight on the ancient hydrothermal systems in Idaho. The largest well-studied low-\u00b9\u2078O anomaly, termed the Sawtooth Ring Zone (SRZ), is a 5 to 15 km wide annulus of low \u00b9\u2078O rock (average ~2 permil) which has an outer diameter of 40 X 60 km. D/H effects in the rocks are often discernible more than 25 km outside of the periphery of this feature, the larger size being attributable to the extreme sensitivity of the \u03b4D value to alteration under conditions of low water/rock ratios. The low-\u00b9\u2078O ring is centered on the Eocene Sawtooth batholith and its outlying plutons, and a large aeromagnetic anomaly suggests that Eocene rocks in fact underlie the entire SRZ region. These data provide good evidence that the SRZ is coincident with a high-permeability ring fracture zone associated with a giant Eocene caldera.

\r\n\r\n

Several smaller low-\u00b9\u2078O zones have also been mapped in the Atlanta lobe, and their clearcut spatial association with the Eocene intrusives provides an important mapping and interpretative tool in the region. Furthermore, most of the productive mines in the Atlanta lobe are located near the periphery of these low-\u00b9\u2078O zones (along the \"outer\" +8 permil \u03b4\u00b9\u2078O contour); this association links these deposits with the Tertiary hydrothermal activity and has great potential as an exploration tool.

\r\n\r\n

K-Ar age data provide important complementary information about the geology of the region and on the thermal characteristics of the ancient geothermal systems. The apparent ages of Mesozoic biotites systematically decrease from about 95 m.y. along the east and west margins of the Atlanta lobe to <45 m.y. near the Eocene plutons, the latter ages being approximately concordant with those of the Eocene plutons themselves. However, there is a significant \"age gap\" between 45 and 53 m.y. No strong correlations of the apparent ages with the \u03b4\u00b9\u2078O, \u03b4D or K\u2082O contents of the \"biotite\" separates were noted, and the majority of the apparent ages in any given locality are in fact correlated simply with the elevation. These observations suggest that most of the ages were produced by uniform, constant uplift (~0.15 mm/yr) of the batholithic terrane through the Ar \"blocking temperature\" (~300\u00b0C) during the early Tertiary. This uplift continued through the Eocene but was modified by the formation of a regional dome probably related to the intrusion of a gigantic volume (~25,000 km\u00b3) of Eocene magma. However, rocks collected near the contacts with the Eocene plutons, or at the lowest elevations in the overall region, definitely suffered catastrophic Ar loss during the Eocene; the apparent ages of these rocks do not correlate with the elevation and indicate that temperatures were high (>300\u00b0C). A model of the ancient temperature distribution is derived from these data and indicates that 1) most of the hydrothermal activity occurred at temperatures of 150-350\u00b0 C and persisted to depths of at least 7 km below the earth's surface, 2) many of the outcropping Eocene intrusives were intruded at depths of 5 to 7 km, and 3) a significant proportion (>1/3) of the heat provided to the circulating fluids was provided by the ordinary geothermal gradient in the older rocks, although the driving force for the circulation was clearly provided by the thermal energy of the Eocene plutons.

\r\n\r\n

All of the above properties bear on the nature of modern geothermal systems at deep levels which are presently inaccessible to view, and a close analogy of the SRZ may be made with the region at Yellowstone, Wyoming. The evidence presented for the extensive lateral migration of fluids, the depth of circulation and the thermal properties of these fluids are of particular importance, and helps explain the incredibly high fluid and thermal discharge rates currently observed within the Yellowstone caldera. The lack of definite evidence for low-\u00b9\u2078O magmas in Idaho contrasts with the recent discovery of voluminous extrusions of such magmas at Yellowstone, and suggests that such magmas are produced at the top of silicic magma chambers and are inevitably erupted, commonly as H\u2082O-rich ash flow sheets. last, the intense deep-level circulation patterns of the annular SRZ zone contrast with the surface intercaldera discharge systems currently observed at Yellowstone, and may indicate that significant geothermal reserves may be tapped at deep levels by drilling into the ring fracture zones of modern caldera-related systems.

", "doi": "10.7907/dc2n-5n03", "publication_date": "1981", "thesis_type": "phd", "thesis_year": "1981" }, { "id": "thesis:8100", "collection": "thesis", "collection_id": "8100", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02272014-085454874", "primary_object_url": { "basename": "Joesten-rl-1974.pdf", "content": "final", "filesize": 76432892, "license": "other", "mime_type": "application/pdf", "url": "/8100/1/Joesten-rl-1974.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Metasomatism and Magmatic Assimilation at a Gabbro-Limestone Contact, Christmas Mountains, Big Bend Region, Texas", "author": [ { "family_name": "Joesten", "given_name": "Raymond Leonard", "clpid": "Joesten-Raymond-Leonard" } ], "thesis_advisor": [ { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" } ], "thesis_committee": [ { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Ahrens", "given_name": "Thomas J.", "clpid": "Ahrens-T-J" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

A composite stock of alkaline gabbro and syenite is intrusive into limestone of the Del Carmen, Sue Peake and Santa Elena Formations at the northwest end of the Christmas Mountains. There is abundant evidence of solution of wallrock by magma but nowhere are gabbro and limestone in direct contact. The sequence of lithologies developed across the intrusive contact and across xenoliths is gabbro, pyroxenite, calc-silicate skarn, marble. Pyroxenite is made up of euhedral crystals of titanaugite and sphene in a leucocratic matrix of nepheline, Wollastonite and alkali feldspar. The uneven modal distribution of phases in pyroxenite and the occurrence' of nepheline syenite dikes, intrusive into pyroxenite and skarn, suggest that pyroxenite represents an accumulation of clinopyroxene \"cemented\" together by late-solidifying residual magma of nepheline syenite composition. Assimilation of limestone by gabbroic magma involves reactions between calcite and magma and/or crystals in equilibrium with magma and crystallization of phases in which the magma is saturated, to supply energy for the solution reaction. Gabbroic magma was saturated with plagioclase and clinopyroxene at the time of emplacement. The textural and mineralogic features of pyroxenite can be produced by the reaction 2( 1-X) CALCITE + ANXABl-X = (1-X) NEPHELINE+ 2(1-X) WOLLASTONITE+ X ANORTHITE+ 2(1-X) CO2. Plagioclase in pyroxenite has corroded margins and is rimmed by nepheline, suggestive of resorption by magma. Anorthite and wollastonite enter solid solution in titanaugite. For each mole of calcite dissolved, approximately one mole of clinopyroxene was crystallized. Thus the amount of limestone that may be assimilated is limited by the concentration of potential clinopyroxene in the magma. Wollastonite appears as a phase when magma has been depleted in iron and magnesium by crystallization of titanaugite. The predominance of mafic and ultramafic compositions among contaminated rocks and their restriction to a narrow zone along the intrusive contact provides little evidence for the generation of a significant volume of desilicated magma as a result of limestone assimilation.

\r\n\r\n

Within 60 m of the intrusive contact with the gabbro, nodular chert in the Santa Elena Limestone reacted with the enveloping marble to form spherical nodules of high-temperature calc-silicate minerals. The phases wollastonite, rankinite, spurrite, tilleyite and calcite, form a series of sharply-bounded, concentric monomineralic and two-phase shells which record a step-wise decrease in silica content from the core of a nodule to its rim. Mineral zones in the nodules vary 'with distance from the gabbro as follows:

\r\n0-5 m CALCITE + SPURRITE + RANKINITE + WOLLASTONITE
\r\n5-16 m CALCITE + TILLEYITE \u00b1 SPURRITE + RANKINITE + WOLLASTONITE
\r\n16-31 m CALCITE + TILLEYITE + WOLLASTONITE
\r\n31-60 m CALCITE + WOLLASTONITE
\r\n60-plus CALCITE + QUARTZ

\r\n\r\nThe mineral of a one-phase zone is compatible with the phases bounding it on either side but these phases are incompatible in the same volume of P-T-XCO2.

\r\n\r\n

Growth of a monomineralio zone is initiated by reaction between minerals of adjacent one-phase zones which become unstable with rising temperature to form a thin layer of a new single phase that separates the reactants and is compatible with both of them. Because the mineral of the new zone is in equilibrium with the phases at both of its contacts, gradients in the chemical potentials of the exchangeable components are established across it. Although zone boundaries mark discontinuities in the gradients of bulk composition, two-phase equilibria at the contacts demonstrate that the chemical potentials are continuous. Hence, Ca, Si and CO2 were redistributed in the growing nodule by diffusion. A monomineralic zone grows at the expense of an adjacent zone by reaction between diffusing components and the mineral of the adjacent zone. Equilibria between two phases at zone boundaries buffers the chemical potentials of the diffusing species. Thus, within a monomineralic zone, the chemical potentials of the diffusing components are controlled external to the local assemblage by the two-phase equilibria at the zone boundaries.

\r\n\r\n

Mineralogically zoned calc-silicate skarn occurs as a narrow band that separates pyroxenite and marble along the intrusive contact and forms a rim on marble xenoliths in gabbro. Skarn consists of melilite or idocrase pseudomorphs of melili te, one or two . stoichiometric calcsilicate phases and accessory Ti-Zr garnet, perovskite and magnetite. The sequence of mineral zones from pyroxenite to marble, defined by a characteristic calc-silicate, is wollastonite, rankinite, spurrite, calcite. Mineral assemblages of adjacent skarn zones are compatible and the set of zones in a skarn band defines a facies type, indicating that the different mineral assemblages represent different bulk compositions recrystallized under identical conditions. The number of phases in each zone is less than the number that might be expected to result from metamorphism of a general bulk composition under conditions of equilibrium, trivariant in P, T and uCO2. The \"special\" bulk composition of each zone is controlled by reaction between phases of the zones bounding it on either side. The continuity of the gradients of composition of melilite and garnet solid solutions across the skarn is consistent with the local equilibrium hypothesis and verifies that diffusion was the mechanism of mass transport. The formula proportions of Ti and Zr in garnet from skarn vary antithetically with that of Si Which systematically decreases from pyroxenite to marble. The chemical potential of Si in each skarn zone was controlled by the coexisting stoichiometric calc-silicate phases in the assemblage. Thus the formula proportion of Si in garnet is a direct measure of the chemical potential of Si from point to point in skarn. Reaction between gabbroic magma saturated with plagioclase and clinopyroxene produced nepheline pyroxenite and melilite-wollastonite skarn. The calcsilicate zones result from reaction between calcite and wollastonite to form spurrite and rankinite.

\r\n\r\n", "publication_date": "1974", "thesis_type": "phd", "thesis_year": "1974" }, { "id": "thesis:8092", "collection": "thesis", "collection_id": "8092", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:02202014-142721576", "type": "thesis", "title": "Oxygen, Carbon, and Hydrogen Isotope Studies of Contact Metamorphism", "author": [ { "family_name": "Shieh", "given_name": "Yuch-Ning", "clpid": "Shieh-Yuch-Ning" } ], "thesis_advisor": [ { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" } ], "thesis_committee": [ { "family_name": "Taylor", "given_name": "Hugh P.", "clpid": "Taylor-H-P" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Albee", "given_name": "Arden Leroy", "clpid": "Albee-A-L" }, { "family_name": "Burnett", "given_name": "Donald S.", "orcid": "0000-0001-9521-8675", "clpid": "Burnett-D-S" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "

The O18/O16, C13/C12, and D/H ratios have been determined for\r\nrocks and coexisting minerals from several granitic plutons and their contact\r\nmetamorphic aureoles in northern Nevada, eastern California, central Colorado,\r\nand Texas, with emphasis on oxygen isotopes. A consistent order of O18/O16, C13/C12, and D/H enrichment in coexisting minerals, and a correlation between isotopic fractionations among coexisting mineral pairs are in general\r\nobserved, suggesting that mineral assemblages tend to approach isotopic\r\nequilibrium during contact metamorphism. In certain cases, a correlation is\r\nobserved between oxygen isotopic fractionations of a mineral pair and sample\r\ndistance from intrusive contacts. Isotopic temperatures generally show good\r\nagreement with heat flow considerations. Based on the experimentally\r\ndetermined quartz-muscovite O18/O16 fractionation calibration curve, temperatures are\r\nestimated to be 525 to 625\u00b0C at the contacts of the granitic stocks\r\nstudied.

\r\n\r\n

Small-scale oxygen isotope exchange effects between intrusive and\r\ncountry rock are observed over distances of 0.5 to 3 feet on both sides of the\r\ncontacts; the isotopic gradients are typically 2 to 3 per mil per foot. The\r\ndegree of oxygen isotopic exchange is essentially identical for different\r\ncoexisting minerals. This presumably occurred through a diffusion-controlled\r\nrecrystallization process. The size of the oxygen isotope equilibrium systems\r\nin the small-scale exchanged zones vary from about 1.5 cm to 30 cm. A\r\nxenolith and a re-entrant of country rock projecting into on intrusive hove\r\nboth undergone much more extensive isotopic exchange (to hundreds of feet);\r\nthey also show abnormally high isotopic temperatures. The marginal portions\r\nof most plutons have unusually high O18/O16 ratios compared to \"normal\"\r\nigneous rocks, presumably due to large-scale isotopic exchange with meta-sedimentary\r\ncountry rocks when the igneous rocks were essentially in a molten\r\nstate. The isotopic data suggest that outward horizontal movement of H2O\r\ninto the contact metamorphic aureoles is almost negligible, but upward movement\r\nof H2O may be important. Also, direct influx and absorption of water from the\r\ncountry rock may be significant in certain intrusive stocks.

\r\n\r\n

Except in the exchanged zones, the O18/O16 ratios of pelitic rocks\r\ndo not change appreciably during contact metamorphism, even in the cordierite\r\nand sillimanite grades; this is in contrast to regional metamorphic rocks which\r\ncommonly decrease in O18 with increasing grade. Low O18/O16 and C13/C12\r\nratios of the contact metamorphic marbles generally correlate well with the\r\npresence of calc-silicate minerals, indicating that the CO2 liberated during\r\nmetamorphic decarbonation reactions is enriched in both O18 and C13 relative to the carbonates.

\r\n\r\n

The D/H ratios of biotites in the contact metamorphic rocks and their\r\nassociated intrusions show a geographic correlation that is similar to that shown\r\nby the D/H ratios of meteoric surface waters, perhaps indicating that meteoric\r\nwaters were present in the rocks during crystallization of the biotites.

\r\n\r\n", "doi": "10.7907/JJY7-J871", "publication_date": "1969", "thesis_type": "phd", "thesis_year": "1969" }, { "id": "thesis:2788", "collection": "thesis", "collection_id": "2788", "cite_using_url": "https://resolver.caltech.edu/CaltechETD:etd-06302006-083245", "primary_object_url": { "basename": "Raychaudhuri_b_1960.pdf", "content": "final", "filesize": 11453881, "license": "other", "mime_type": "application/pdf", "url": "/2788/1/Raychaudhuri_b_1960.pdf", "version": "v2.0.0" }, "type": "thesis", "title": "Studies of Amphibolites and Constituent Hornblendes From an Area of Progressive Metamorphism Near Lead, South Dakota", "author": [ { "family_name": "Raychaudhuri", "given_name": "Bimalendu", "clpid": "Raychaudhuri-Bimalendu" } ], "thesis_advisor": [ { "family_name": "Engel", "given_name": "Albert Edward John", "clpid": "Engel-A-E-J" } ], "thesis_committee": [ { "family_name": "Engel", "given_name": "Albert Edward John", "clpid": "Engel-A-E-J" }, { "family_name": "Kamb", "given_name": "W. Barclay", "clpid": "Kamb-W-B" }, { "family_name": "Silver", "given_name": "Leon T.", "clpid": "Silver-L-T" }, { "family_name": "Epstein", "given_name": "Samuel", "clpid": "Epstein-S" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The progressive metamorphism and origin of the amphibolites of the Lead-Deadwood area, S. Dakota, are considered in detail. Eighty specimens of amphibolite were collected along a belt 3 miles long extending across the entire garnet zone and part of the staurolite zone of the enclosing meta-sediments. These amphibolites were studied petrographically and from them thirty-four were used for modal analysis and chemical analyses for total iron (as Fe2O3), CaO, TiO2, K2O, MnO and trace elements. Twelve of the constituent hornblendes were analysed for all major and minor elements and trace elements. The other 22 constituent hornblendes were analysed for total iron (as Fe2O3), CaO, TiO2, K2O, MnO and trace elements. Seven of the constituent horn-blendes and six constituent plagioclases were used for optical determinations and x-ray diffractometric studies.\r\n\r\nOn the basis of relict texture some of the amphibolites are concluded to be definitely ortho-amphibolites. Field relations of a few hornblende-bearing rocks suggest that they have meta-sedimentary origin. The origin of the remaining majority of the amphibolites is inconclusive.\r\n\r\nThe metamorphism of the amphibolites is essentially iso-chemical throughout the range of conditions represented by the appearance of successively the garnet and the staurolite isophases in the enclosing meta-sediments. What fluctuations in composition are observed appear to be random in character, attributable to minor variations in original composition or to retrograde alteration.\r\n\r\nThe compositions of the constituent hornblendes do not show any significant correlation with intensity of metamorphism and the average composition remains roughly constant throughout the sequence.\r\n\r\nThe concentrations of the various components in the horn-blendes seem to be closely related to the concentrations of the same components in the corresponding amphibolites. The ratios of the concentrations of the various components between horn-blende and amphibolite do not show any significant trend with metamorphic rank and are reasonably constant over the range of metamorphic conditions represented here.\r\n\r\nThe composition of the hornblendes is closely related to specific gravity and broadly related to dimensions of unit cells but there is no close correlation between composition and optics. Size of unit cells in hornblendes appear to be unrelated to metamorphic rank.", "doi": "10.7907/V56J-JE76", "publication_date": "1960", "thesis_type": "phd", "thesis_year": "1960" } ]