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.
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 ± 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.
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.
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 ± 0.1 million, 55,000 ± 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.
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.
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.
The average slip rate across the combined San Andreas and San Jacinto faults is 37.5 ± 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 ± 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.
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.
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.
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.
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.
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.
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.
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.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Albee, Arden Leroy}, } @phdthesis{10.7907/cw33-9d88, author = {Quick, James Edward}, title = {Part I: Petrology and Petrogenesis of the Trinity Peridotite, Northern California. Part II: Petrogenesis of Lunar Breccia 12013}, school = {California Institute of Technology}, year = {1981}, doi = {10.7907/cw33-9d88}, url = {https://resolver.caltech.edu/CaltechTHESIS:08102018-101338734}, abstract = {Part I presents the results of a petrologic investigation of the Trinity peridotite, an enormous ultramafic massif in northern California. The Trinity is an easterly dipping sheet several km thick and composed of a diverse assemblage of ultramafic rocks including dunite, harzburgite, lherzolite, plagioclase lherzolite and clinopyroxene-rich dikes. Because of this diversity and the limited serpentinization, it is an excellent natural laboratory for studying the petrogenesis of ultramafic rocks. The structural history of the peridotite was outlined by detailed field mapping at scales of 1:31,250 and 1:240 at the northeast margin of the massif in the vicinity of Mount Eddy and China Mountain during the summers of 1977-1978. A combined petrographic and electron microprobe investigation was made on selected samples to determine their petrology, mineral chemistry and major element whole rock compositions.
The Trinity peridotite is inferred to have originated in the upper mantle at a depth of not less than ~30 km and perhaps as deep as 100 km based on textural evidence for a transition from the spinel lherzolite (>10 kb) stability field to the plagioclase lherzolite (<10 kb) stability field, and on high equilibration temperatures (>1150° C.) preserved in cores of large pyroxene grains. During ascent through the mantle, the rocks deformed plastically, partially melted and reacted with transient melts derived from greater depth. Plastic deformation produced two generations of folds and a penetrative foliation. Pervasive partial melting of the plagioclase lherzolite produced feldspathic segregations, plagioclase-rich veins and resorption textures in pyroxenes and spinel; the composition of the veins suggests that this melt was essentially basaltic. Another melt, not in equilibrium with the peridotite, but also of basaltic affinity, passed through the peridotite, reacted with the ultramafic wall rocks to produce large tabular dunite bodies surrounded by zones of harzburgite and lherzolite, and crystallized clinopyroxene-rich dikes. The end of the ascent of the Trinity through the mantle is marked by intrusion of gabbro, hornblende diorite, diabase and albite granite, and the onset of brittle deformation circa 450-480 m.y. based on zircon ages of the granites (Mattinson and Hopson, 1972). The Trinity was subsequently thrust into the crust at about 380 m.y. based on Rb-Sr dates on rocks of the underlying Central Metamorphic Belt. It is suggested that the passage of the Trinity through the mantle may have occurred beneath an actively spreading back-arc basin.
Part II of this thesis is a petrologic investigation of Lunar Rock 12013, one of the most significant lunar samples because of its extreme enrichments in incompatible elements (K, REE, U, etc.) and abundant “granitic” material.
Rock 12013 is best interpreted as a complex mixture of two polymict, impact generated breccias–one black, the other gray. The black breccia is a fragment-laden melt-rock formed by mixing cold, impact-derived mineral and lithic clasts with superheated impact melt of basalted composition. The melt is now crystallized to an aphanite of minute grain size. The gray breccia was also formed as a mixture of melt and impact-derived clasts, but the melt was granitic and crystallized to a fine grained felsite. The clasts in the breccias were derived from lithologies common in Highlands breccias, with the gray breccia dominated by feldspathic gabbro and basalt clasts and the black breccia dominated by quartzofeldspathic and norite clasts. A combined neutron activation, petrographie and electron microprobe analysis demonstrates that the incompatible elements in 12013 are concentrated in the melt-derived lithologies. The origin and relationships of the melts is problematic. Textural relations suggest that the two melts coexisted but did not mix, and some aspects of their major element abundances are compatible with a genetic relationship involving silicate liquid immiscibility (SLI). However, details of their trace element abundances are incompatible with SLI.
It is suggested that 12013 is exotic to the Apollo 12 site and was formed by an impact(s) into a terrane of norite and quartofeldspathie plutonic rocks, gabbro and basalt hypabyssal or extrusive rocks, and a thin regolith cover. The two breccia were derived from different parts of this terrane and mixed violently in the ejecta cloud. Most of the radiometric clocks were reset by this event, and Rb-Sr, U-Th-Pb and 40Ar-39Ar yield ages of ~4.0 AE. Rb-Sr data, however, may be interpreted to suggest an age for the felsite protolith of ~4.5 AE. An alternative explanation, consistent with the petrography of the rock, is that the Rb-Sr data reflect mixing and partial equilibration at 4.0 AE of materials no older than 4.2 AE.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Albee, Arden Leroy}, } @phdthesis{10.7907/EEHY-DG27, author = {Beaty, David W.}, title = {Part I. Comparative petrology of the Apollo 11 mare basalts. Part II. The oxygen isotope geochemistry of the Abitibi greenstone belt}, school = {California Institute of Technology}, year = {1980}, doi = {10.7907/EEHY-DG27}, url = {https://resolver.caltech.edu/CaltechETD:etd-02232006-092342}, abstract = {NOTE: Text or symbols not renderable in plain ASCII are indicated by […]. Abstract is included in .pdf document.
PART I. Over the past decade a wealth of geochemical and petrological information has been accumulated on the Apollo ll basalts. These data indicate that the 73 thus far identified basalts can be divided into five petrologic groups which must represent at least five separate igneous cooling units. These five igneous bodies range in age from 3.90 b.y. to 3.60 b.y. Photogeologic studies of the landing site indicate that three mare units are present, and that the lunar module set down on the oldest of the three. The exposure age data suggest that the high-K flow(s) is the surficial rock type at the landing area, and is therefore probably the oldest of the three mare units. The three low-K groups of samples are older than (and underlie) the high-K basalts, and were apparently excavated by West Crater. By studying the size frequency distribution and the inferred cooling rates of the individual samples, it is possible to calculate the formation thicknesses within the 30 m-deep West Crater. This suggests that A=9 m, B1=2 m (and may be an ejecta blanket), B2=>8 m and B3=6 m. Because the Group D samples have not been dated, it is not known whether they lie above or below the high-K unit. They may, however, represent one of the two younger mare units present near the landing site.
PART II. A variety of petrologic, geochemical and geophysical evidence indicates that the modern oceanic crust interacts on a massive scale with seawater. To evaluate whether or not similar processes were taking place in the Archean, the well preserved Abitibi greenstone belt was studied using oxygen isotopes and the petrographic microscope. In thin section, all of the volcanic rocks in the Abitibi area are found to have been subjected to a hydrothermal process of some sort. The original igneous minerals have been largely replaced by secondary hydrous minerals such as chlorite, epidote and actinolite. The metamorphic assemblages range from the prehnite-pumpellyite facies in the core of the Blake River syncline to greenschist facies adjacent to the large Kenoran granitic batholiths. The structural relations are such that the metamorphic grade decreases in a general way with structural height; the lowest temperature rocks are those which are highest in the volcanic pile.
[…] is also correlated with structural height. In each of five widely separated traverses (Benoit, Ben Nevis, Noranda, Skead, Timmins), […] increases upwards through the stratigraphic section (typically +6 to +10 from base to top). In the Benoit area […] and structural height also correlate with the silica content of the volcanic rocks. Silica content and the degree of petrographic recrystallization are not correlated, however, whereas […] and the degree of recrystallization are. This indicates that the gradient in […] is a relic igneous feature and that the gradient in […] is a hydrothermal alteration feature. Additional evidence that these rocks have undergone isotopic exchange comes from the mineral separate data. Relic clinopyroxene in the basalts has […] +5.5, and quartz phenocrysts in the rhyolites are +7.6, indicating that these lavas were not erupted as high-[…] magmas; they have undergone subsolidus enrichments in […] of 0-4 per mil. Using temperatures inferred from the metamorphic assemblages, […] of the fluid responsible for producing these […] shifts can be calculated. Assuming an open system, water flux within 100°C of the final metamorphic temperature, and using the feldspar geothermometer, the hydrothermal fluid has […] = 0 ± 2 and alteration took place under conditions of high water/rock ratio. The oxygen isotopic effects are associated with the prehnite-pumpellyite facies burial metamorphism, which is thought to have taken place during the formation of the volcanic pile. Since the pile formed in a marine environment the only logical source for such large amounts of fluid is seawater itself.
Oxygen isotopic study of the Amulet “A” massive sulfide deposit indicates that it was formed by a fluid with, a similar […] (0.5 ± 1.0). Similar deposits in the Phanerozoic (Cyprus, Kuroko, Gulf of California) are thought to have originated from heated seawater circulating through the oceanic crust. The fact that the Amulet ore fluid is indistinguishable from the inferred Archean seawater indicates that analagous hydrothermal processes were taking place in the Archean. At the Kidd Creek mine, however, the ore-forming solution is thought to have had […] between +6 and +9. This fluid could either have been derived from normal-[…] seawater through evaporation or exchange with high-[…] country rocks, or it could have been some sort of metamorphic fluid. This indicates that massive sulfide ore deposits have formed by more than one mechanism, and that the simple seawater-hydrothermal model may not be generally applicable.
Less extensive data from other greenstone belts throughout the world indicate that like Abitibi, all have undergone […]-enrichments relative to primary igneous values. By mass balance, these […]-enrichments must have caused a complementary […]-depletion in some other oxygen reservoir. That reservoir was apparently not seawater, nor has it been discovered in the geologic record. Because the oxygen isotopic exchange process is self-buffering, the consistent […]-enrichments in greenstone belts throughout history suggests that they were not the dominant form of submarine volcanism in the Archean. This, combined with the apparent destruction of the low-[…] reservoir, suggests that seafloor spreading volcanism was also taking place in the early Precambrian. This is consistent with a variety of geological, geophysical, geochemical, isotopic and petrologic data which indicate that greenstone belts resemble modern island arcs in a number of important respects.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Albee, Arden Leroy and Taylor, Hugh P.}, } @phdthesis{CaltechTHESIS_https://thesis.library.caltech.edu/id/eprint/11139, author = {Labotka, Theodore Charles}, title = {Geology of the Telescope Peak Quadrangle, California and Late Mesozoic Regional Metamorphism, Death Valley Area, California}, school = {California Institute of Technology}, year = {1978}, url = {https://resolver.caltech.edu/CaltechTHESIS:08012018-084644606}, abstract = {The Telescope Peak Quadrangle lies in the central Panamint Mountains which form the western boundary of Death Valley, California. The oldest rocks in the quadrangle consist of an 1800 m.y. complex of augen gneiss, quartzofeldspathic gneiss, and muscovite-biotite schist. These rocks were intruded approximately 1400 m.y. ago by porphyritic quartz monzonite in the World Beater Dome area. The earlier Precambrian rocks are unconformably overlain by the later Precambrian Pahrump Group. The Pahrump Group is comprised of the Crystal Spring Formation, Beck Spring Dolomite, and Kingston Peak Formation. These formations show variations in thicknesses and lithologies within the quadrangle which indicate that the Pahrump Group was deposited in a dynamic environment. The lithologies and thicknesses of the Crystal Spring Formation and Beck Spring Dolomite indicate that most of the quadrangle was underlain by a platform of earlier Precambrian basement which stood above sea level in the World Beater Dome area (World Beater Island) and which dropped off into deeper water near Tuber Canyon. The distribution of locally derived conglomerates in the lower Kingston Peak Formation and the presence of a local unconformity at the base indicate that at the end of Beck Spring Dolomite deposition, World Beater Island and adjacent areas to the north were uplifted, and the lower Kingston Peak Formation was deposited in eastern and western basins separated by the uplift. Continued deposition buried the uplift, and upper units in the Kingston Peak Formation include diamictite which grades northward into fine-grained greywacke, pillow basalt inter bedded in the diamictite, micaceous limestone, conglomerate, and argillite. The Pahrump Group is unconformably overlain by later Precambrian Noonday Dolomite, Johnnie Formation, Stirling Quartzite and Cambrian and Precambrian Wood Canyon Formation. The rocks were regionally metamorphosed at low pressure and intruded by leucocratic, muscovite-bearing granite about 80 m.y. ago. Folding occurred after this metamorphism and a north-northwest-trending anticline and World Beater Dome were formed. Retrograde metamorphism accompanied the folding event. Subsequently, low-angle normal faults developed, the Miocene Little Chief stock was intruded, large masses of monolithologic breccia formed, and the Panamint Mountains were uplifted along the Panamint Valley fault zone.
Regional metamorphic terrains in the Panamint Mountains and in the Funeral Mountains show marked differences in the physical conditions attained during metamorphism. The Panamint Mountains exhibit low pressure regional metamorphism, and the characteristic assemblages developed in pelitic schists are andalusite + staurolite + biotite and andalusite + cordierite + biotite. Isograds based on the appearance of sillimanite in pelitic rocks and tremolite and diopside in calcareous rocks indicate a westward increase in metamorphic grade toward an 80 m.y. muscovite granite pluton. A higher pressure metamorphic terrain was developed in the Funeral Mountains, and mineral assemblages in pelitic rocks are characterized.by the presence of kyanite. Garnet, staurolite, and kyanite isograds have been delineated and show that the grade increases toward the structual culmination of the Funeral Mountains, Migmatites occur in the highest grade area (sillimanite + garnet + biotite +muscovite + quartz), and the metasedimentary sequence was intruded by muscovite granite. The reaction chloritoid -> staurolite + garnet + chlorite is recorded in the Funeral Mountains, but in the Panamint Mountains the coexistence of chloritoid + biotite indicates that the garnet + chlorite join became unstable prior to the breakdown of chloritoid. Microprobe data on coexisting mineral assemblages, chemographic analysis of mineral facies in pelitic schists, and available experimental data indicate that the extremes in physical conditions attained during metamorphism were ~3 kb, ~600°C in the Panamint Mountains and ~8.5 kb, ~700°C in the Funeral Mountains. The sequence of tectonic and metamorphic events in the two areas is similar, but the facies series represent greatly different P/T gradients.
Assemblages in calciferous schist from the low pressure environment in the Panamint Mountains are characterized by quartz + epidote + calcic amphibole + chlorite + biotite in the trernolite zone and by quartz + epidote + calcic amphibole + garnet + biotite, quartz + epidote + diopside + calcic amphibole, and quartz + epidote + diopside + grossular in the diopside zone. Muscovite or microcline are common additional phases. Assemblages which occur in quartz + epidote + muscovite or quartz + epidote + microcline rocks are potentially useful for delineation of metamorphic grade and distinction between lower and higher pressure facies series. The compositions of calcic amphiboles formed in a low pressure environment generally fall in the series tremolite-pargasite and are related to the continuous break down of epidote and chlorite.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Albee, Arden Leroy}, } @phdthesis{10.7907/ha25-qf72, author = {Goldman, Don Steven}, title = {Crystal-Field and Mössbauer Applications to the Study of Site Distribution and Electronic Properties of Ferrous Iron in Minerals with Emphasis on Calcic Amphiboles, Orthopyoxene and Cordierite}, school = {California Institute of Technology}, year = {1977}, doi = {10.7907/ha25-qf72}, url = {https://resolver.caltech.edu/CaltechTHESIS:12072020-163044493}, abstract = {The electronic absorption spectroscopy of ferrous iron is sensitive to the geometry of the coordination site in which it resides. This sensitivity enables ferrous iron in multiple sites in a mineral to be distinguished. The spectra of ferrous iron in the M(2) site in orthopyroxene, (Mg,Fe)SiO₃, are used as a model for the spectroscopic properties of iron in a distorted site. The splitting of the ⁵T_(2G) ground state is observed to be 2350 cm⁻¹ enabling a theoretical point-charge model to be developed using C_(2V) symmetry. The intensity of the near infrared bands due to the splitting of the ⁵E_G state are found to linearly correlate with the concentration of ferrous iron in the M(2) site. From this correlation, calibrations are established for the intensities of the near infrared bands so that quantitative site distributions can be determined for single orthopyroxene crystals from optical spectra. Thermally induced cation disorder allows assignments to be made for spin-allowed and spin-forbidden ferrous iron bands originating from both the M(1) and M(2) sites.
The electronic absorption and Mössbauer spectra of calcic amphiboles, Ca₂(Mg,Fe)₅Si₈O₂₂(OH)₂, are reinterpreted to include previously neglected contributions from ferrous iron in the calcium-rich M(4) site. Bands due to ferrous iron in M(l), M(2) and M(3) sites are examined in the electronic spectra and the intensity of the Fe²⁺/Fe³⁺ intervalence charge-transfer band is found to linearly correlate with the ferric iron content. Next nearest neighbor variations of ferric iron and aluminum are found to affect the ferrous iron peak parameters in the Mössbauer spectra of calcic amphiboles which impairs the capability of determining accurate site distributions.
Ferrous iron is found to be present in the channel cavities and the octahedral site in cordierite, (Mg,Fe)₂Al₄Si₅O₁₈, osumilite, K(Mg,Fe)₂Al₃(Si₁₀Al₂)O₃₀, and beryl, Be₃Al₂Si₆O₁₈. In cordierite, two types of water are suggested to be present in the channel cavities that differ in crystallographic orientation and relationship to other channel constituents, whereas osumilite is found to be virtually anhydrous. In cordierite, cation migration within the channels is suggested to occur after dehydration which could explain the observed change in the lattice geometry. The blue color in these minerals is suggested to be due to intervalence charge transfer between ferrous iron and channel ferric iron. Electronic spectra suggest that structural state variations occur in osumilite, whereas significant variations in cordierite are not apparent. Ferric iron in tetrahedral coordination in osumilite is indicated from Mössbauer spectra.
The effect of site size and distortion on the spectroscopic properties of ferrous iron in terms of band position, intensity and polarization anisotropy is examined. As a non-centrosymmetric site becomes larger, absorption bands migrate to longer wavelengths (lower energy), become more intense, and exhibit greater polarization anisotropy among each other. For these sites, intensification is correlated with a decrease in the quadrupole splitting determined from Mössbauer spectra. The spectroscopy of ferrous iron in large sites is distinctly different from that observed from ferrous iron in smaller sites.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Albee, Arden Leroy}, } @phdthesis{10.7907/wht4-n543, author = {Dymek, Robert F.}, title = {Mineralogic and Petrologic Studies of Archaean Metamorphic Rocks from West Greenland, Lunar Samples, and the Meteorite Kapoeta}, school = {California Institute of Technology}, year = {1977}, doi = {10.7907/wht4-n543}, url = {https://resolver.caltech.edu/CaltechTHESIS:12042020-191103512}, abstract = {In Part I of this thesis, petrographic and electron microprobe data are reported for samples from a series of high-grade Archaean gneisses, collected on Langø, an island in the northwest corner of the Godthåb District of West Greenland. Rocks with a wide variety of bulk compositions occur that all preserve evidence for two distinct episodes of metamorphic mineral growth. Syn- to post-tectonic hornblende granulite grade metamorphism (MI) was followed by post-tectonic amphibolite grade metamorphism (MII) at a later time. In potassium feldspar bearing gneisses, MI assemblages, in addition to quartz and plagioclase are: garnet + biotite (brown) ± sillimanite; cordierite + biotite (brown) ± sillimanite; and biotite (brown). In potassium feldspar- free gneisses, MI assemblages, in addition to quartz and plagioclase are: cordierite + garnet + biotite (brown); and orthopyroxene + biotite (brown) ± cordierite. As a result of MII, cordierite and garnet have been replaced by kyanite + biotite (green). Brown biotite is Ti-rich (>1.0 wt% TiO₂), whereas green biotite is Ti-poor (≾1.0 wt% TiO₂), and an examination of biotite analyses suggests that Ti is incorporated in that mineral via a vacancy-forming substitution. In mafic rocks, MI assemblages include various combinations of hornblende (green-brown) + clinopyroxene ± orthopyroxene ± garnet ± biotite, with plagioclase and rarely quartz. However, garnet and clinopyroxene do not occur together. As a result of MII, pyroxene has been replaced by calcic amphibole that differs in color (pale green to blue green) and composition (Na, K, Al, Ti are lower; Si, Mg, Fe³⁺ are higher) from the MI varieties. MI hornblende and plagioclase have an extremely large, compositional range, which correlate with one another in terms of Al/(Al+Si) and Na/(Na+Ca), and suggest that their compositions are controlled by rock composition, and not by metamorphic grade at these conditions.
The composition of coexisting pyroxenes, the position of the kyanite-sillimanite boundary, and the composition of garnet (cores) and cordierite constrain the pressure and temperature for MI to lie between ~7-8 kb and ~700-800°C. Temperatures calculated from Fe-Mg partitioning between garnet (rims) and MII biotite suggest ~450°C for MII, and the occurrence of kyanite would indicate a pressure of 3-4 kb for this temperature. The MI event can be ascribed with certainty to regional metamorphic-magmatic activity at ca. 2.8 AE (Black et al., 1973), whereas MII may correspond to regional heating during the emplacement of the Qôrqut Granite at ca. 2.5 AE (Baadsgaard and Collerson, 1976), or to a regional thermal event at ca. 1.6 AE identified in isotopic studies (Pankhurst et al., 1973).
The pressure and temperature estimated for MI imply a thermal gradient of ca. 30°C/km, and a minimum crustal thickness of 20 km at the time of metamorphism. The petrologic characteristics of MI are similar to medium-P facies series metamorphism found in younger orogenic belts, and nothing “unique” can be ascribed to this Archaean metamorphic event, based on the presently-available data and observations. Parts II and III of this thesis are a series of published papers that involve mineralogic and petrologic studies of Apollo 15, 16, and 17 lunar samples and the meteorite Kapoeta.
Parts II and III of this thesis are a series of published papers that involve mineralogic and petrologic studies of Apollo 15, 16, and 17 lunar samples and the meteorite Kapoeta.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Albee, Arden Leroy}, } @phdthesis{CaltechTHESIS_https://thesis.library.caltech.edu/id/eprint/4361, author = {Anderson, James Rodney}, title = {The polymetamorphic sequence in the Paleozoic rocks of northern Vermont : a new approach using metamorphic veins as petrologic and structural markers}, school = {California Institute of Technology}, year = {1977}, url = {https://resolver.caltech.edu/CaltechETD:etd-11012006-140440}, abstract = {The sequence of metamorphic events that have affected the lower and middle Paleozoic rocks of northern Vermont has been defined in this study. The use of metamorphic veins as structural and petrologic markers has helped to establish the correspondence between deformational and mineral growth features. The effects of the major metamorphic events have been followed through the area along several traverses, the longest of which is 50 miles in length. The study combines detailed analysis of the sequence of structural elements with electron microprobe and petrographic analysis of the mineral growth in the metamorphic veins and host rock.
Much of the history of the chemical path of the vein and host rock systems is preserved in zoned grains and grains included in other minerals. The zoning trends in certain key minerals such as plagioclase, amphibole, muscovite, and coexisting calcite and ankerite indicate that the grade of each rock system was changing with time. The path of the systems can be followed in considerable detail. Not only are the effects of changing grade during a single event typically preserved, but also the effects of several superimposed mineral growth events can be preserved in a sample.
Five major metamorphic events and several minor events have occurred in northern Vermont. The two oldest events affected only the Cambrian and Ordovician rocks; these events are designated Oa and Ob. Event Oa involved widspread biotite grade mineral growth and the formation of a secondary bedding schistosity. Ob is the most prominent of the pre-Silurian events and is Late Ordovician in age. It produced high grade mineral growth in the Green Mountains and in the Worcester Mountains; in the latter area staurolite-kyanite grade assemblages occur. There was also widespread formation of small scale isoclinal folds with east-west axial trends during Ob. Major east-west trending folds of the same generation occur locally.
Three events affected both the pre-Silurian rocks and the Silurian and Devonian rocks. These events are Middle to Late Devonian in age. Da is the oldest of the three and produced biotite to garnet grade or higher mineral growth over the entire study area. Da was also a significant deformational event, responsible for the formation of major and minor north-south trending folds. Event Db mainly involved deformation, but biotite grade mineral growth occurred in rocks where the axial plane foliation associated with Db was developed. Folds formed during Db have north-south trends and are most prominent in the eastern part of the area. The last major event, Dc, was a period of mineral growth without associated deformation and was widespread in extent. The highest grade mineral growth of Dc, up to staurolite-andalusite and sillimanite grades, has a close spatial relationship to the intrusive bodies of the New Hampshire plutonic series. In areas far from such plutons, this mineral growth is biotite grade or absent.
Metamorphic veins are associated with each of the major events except Db. The veins are discontinuous and have a general chemical correspondence to mineral growth of the same generation in the adjacent host rock. Differences in the relative timing of growth in the veins and host rocks occur in some instances, so that the correspondence is fairly complicated. The veins appear to have formed during the metamorphic events from material derived locally in the host rocks.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Albee, Arden Leroy}, } @phdthesis{10.7907/V1ZV-F079, author = {McDowell, Stewart Douglas}, title = {The intrusive history of the Little Chief granite porphyry stock, central Panamint Range, California : I. Structural relationships. II. Petrogenesis, based on electron microprobe analyses of the feldspars}, school = {California Institute of Technology}, year = {1967}, doi = {10.7907/V1ZV-F079}, url = {https://resolver.caltech.edu/CaltechETD:etd-09252007-084230}, abstract = {NOTE: Text or symbols not renderable in plain ASCII are indicated by […]. Abstract is included in .pdf document.
The Little Chief stock of Upper Miocene (?) age, located in the central Panamint Range near Death Valley, California, crops out over an area of 2.5 by 4.5 miles and through an elevation range of 6300 feet. It is a crosscutting diapir-like body with contact attitudes ranging from vertical to 80° outward except along the eastern margin, where the contact attitudes range from 45° outward to 35° inward. The stock appears to neck downward into a thin, east-west, dike-like body at a depth of less than 6000 feet below the present surface.
The stock has lifted a nearly rectangular “trapdoor” of later Precambrian and Precambrian (?) rocks bounded by vertical faults on the north, west, and south. The trapdoor opens to the west with a vertical throw of 3000 feet on the western margin and with a roughly north-south hinge line located just east of the stock. East of the hinge line, the trapdoor has been slightly depressed. The trapdoor offsets an earlier set of westward-dipping normal faults along which a porphyry dike swarm has been intruded.
The stock consists of two intrusive phases, a south and a slightly later north phase. The stock magma moved to a position roughly 6000 feet below the present surface and formed the westward-dipping normal faults by stretching the sedimentary rocks over the magma chamber roof, which were immediately injected by the porphyry dikes. The magma moved to the present level, truncating the normal faults and associated dikes, forming the trap door, and doming the sediments of the roof. The interior of the north phase then moved slightly upward to the present level, disrupting the eastern part of the trapdoor and renewing movement on some of the trapdoor faults.
The stock is a hornblende-biotite granite porphyry with 2-10mm normally-zoned sanidine and plagioclase in a quartz-alkali feldspar-plagioclase groundmass. Detailed electron microprobe analyses yield the following feldspar compositions. The plagioclases have distinct normally-zoned layers separated by abrupt compositional gaps. The gaps formed by sporadic, abrupt water pressure decreases as the magma moved upward. Assimilation of water-rich calcic material caused large calcic oscillations on the plagioclase zones. Zonation in the outermost edges of the plagioclase phenocrysts to very low-Or plagioclase could be due to […] increase and/or the effect of the peristerite solvus on the ternary feldspar solvus.
Sanidine coexisted with […] plagioclase in a magma chamber 12,000 feet below the present level, which had an undifferentiated, unsaturated […] core surrounded by a differentiated, saturated […] exterior. This […] variation was equalized as the magma moved up to its present position, where the groundmass crystallized at […] some 7000 feet below the contemperaneous ground surface.
Sanidine was removed from equilibrium, due to its rapid crystallization and shift of the feldspar boundary on […] increase, at different times. It was rimmed by […] plagioclase in the water-poor core of the magma chamber before the magma started to move upward. Toward the exterior sanidine began to be replaced by sodic oligoclase as the magma moved upward, and in the water-rich exterior parts sanidine exsolved to a patch perthite while the system was 50 percent melt, and the K-phase was then replaced by sodic oligoclase. In the very water-rich parts, sanidine crystallized in equilibrium until the groundmass was formed.
During upward movement assimilation of dolomitic rock formed a contaminated marginal phase which was then intruded by uncontaminated magma and carried upward as inclusions.
Fracturing of the roof of the present stock led to volatile concentration in certain restricted portions of the stock, and formation of quartz macrocyrsts, graphic textures, pegmatitic pods, coarse lamellar perthite in the sanidine, and numerous vugs.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Albee, Arden Leroy}, } @phdthesis{10.7907/0ZA2-QX80, author = {Hollister, Lincoln Steffens}, title = {Electron microprobe investigations of metamorphic reactions and mineral growth histories, Kwoiek area, British Columbia}, school = {California Institute of Technology}, year = {1966}, doi = {10.7907/0ZA2-QX80}, url = {https://resolver.caltech.edu/CaltechTHESIS:03282016-092324853}, abstract = {The Kwoiek Area of British Columbia contains a pendant or screen of metamorphosed sedimentary and volcanic rocks almost entirely surrounded by a portion of the Coast Range Batholith, and intruded by several dozen stocks. The major metamorphic effects were produced by the quartz diorite batholithic rocks, with minor and later effects by the quartz diorite stocks. The sequence of important metamorphic reactions in the metasedimentary and metavolcanic rocks, ranging in grade from chlorite to sillimanite, is:
Continuous reactions, occurring between reactions 5 and 7, are:
A. chlorite + (high Ti) biotite + Al2O3 (from plagioclase?)→ garnet + staurolite + (low Ti) biotite + O2
B. muscovite (phengitic) → garnet + staurolite +muscovite (less phengitic) + O2 (?)
Detailed electron microprobe work on garnet, staurolite, biotite, and chlorite shows that:
An important implication of zoned minerals is that the effective composition of a system in a phase lies on the join between the homogeneous minerals (if there are two) and not within three-or- four-phase fields when a zoned mineral, such as garnet or staurolite, is present in the assemblage.
Study of the three aluminum silicates found in the Kwoiek Area showed that a constant pressure change in polymorphs from andalusite to kyanite to sillimanite took place with increasing temperature. This transition series is best explained by the metastable formation of andalusite.
Photographic materials on pages 15, 121, 160, 162, and 164 are essential and will not reproduce clearly on Xerox copies. Photographic copies should be ordered.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Albee, Arden Leroy}, }