The first chapter of this thesis documents a provenance study, in which orthoquartzite clasts deposited in the Miocene Sespe Formation are linked to the Mesoproterozoic Shinumo Quartzite. The Sespe Formation outcrops in the Santa Monica Mountains and the Santa Ana Mountains, both in California. The Shinumo Quartzite outcrops only in Grand Canyon. We determine that the Shinumo Quartzite can be distinguished from other sources that may feed the Sespe Formation through its unique combination of a moderate paleomagnetic inclination and 1.2, 1.4, and 1.7 Ga detrital zircon spectrum peaks. This provenance link places an important constraint on the drainage of a paleo-Colorado River from Grand Canyon during Miocene time.
The second and third chapters of this thesis are hinged upon a geologic mapping project on Isla Ángel de la Guarda, a microcontinental block, in Baja California, Mexico. A plate reorganization at the end of the late Miocene andesitic arc marks the transfer of Baja California and the not-yet-rifted Isla Ángel de la Guarda to the Pacific plate from the North American plate. Between 3 and 2 Ma, the plate boundary jumped again, northward along the Ballenas Transform fault. In this Pliocene time, units mapped in this study were deposited.
The oldest units mapped are Miocene-Pliocene volcanic flows, for which we have no lower age constraint. The oldest volcanic flow dated is a Pliocene andesite lava (3.916 ± 0.088 Ma from 40Ar/39Ar). We map Miocene to Pliocene volcanic flows and Pliocene to Quaternary sedimentary units in two field areas. The sedimentary units are probably results of Pliocene rifting-related basin subsidence. Geochemical data from X-ray fluorescence indicate that lavas are compositionally similar to ~12 Ma arc-related rocks mapped in the Puertecitos Volcanic Province. In the southern field area, the sedimentary units are overlain by a Pliocene basaltic andesite with an 40Ar/39Ar age of 2.754 ± 0.021 Ma. We map several NNE-striking faults throughout both field areas, which cut NNW-striking bedding in Pliocene units. The Pliocene volcanic flows and sedimentary units were probably tilted before faulting, and the faults are likely linked to the Northern Salsipuedes Basin, offshore of the island in the Ballenas Channel. Both of these events may be results of 3-2 Ma rifting.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Stock, Joann M.}, } @phdthesis{10.7907/XTZX-X107, author = {Witkosky, Rebecca Amber}, title = {Tectonics in Nevada and Southern California: Subsidence of the Ediacaran Johnnie Formation, Cumulative Offset Along the Lavic Lake Fault, and Geomorphic Surface Development Along the Southern San Andreas Fault}, school = {California Institute of Technology}, year = {2019}, doi = {10.7907/XTZX-X107}, url = {https://resolver.caltech.edu/CaltechTHESIS:01172019-113222535}, abstract = {While we know the ages and tectonic histories of many critical geologic events in the history of the Earth, there are still questions regarding the timing of key events and structures that have and continue to influence life on this planet. This thesis includes three separate studies in Nevada and southern California: two potential new methods for measuring/organizing geologic time, and also an analysis of the long-term displacement along an active fault in the eastern California shear zone. In Chapter II, we used tectonic subsidence modeling to find that the Shuram carbon isotopic excursion in the Ediacaran Johnnie Formation likely occurred from 585-579 Ma, and that incision of the Rainstorm Member shelf occurred during the 579 Ma Gaskiers glaciation. The pre-Shuram-excursion chemostratigraphic carbon isotope profiles from the Khufai Formation in Oman and the type locality of the Johnnie Formation in Nevada are both generally positive and therefore possibly correlative. In Chapter III, we determined the cumulative tectonic offset along the Lavic Lake fault, an active structure that ruptured with >5 m of coseismic slip in the 1999 Mw 7.1 Hector Mine earthquake. We calculated a net slip of 960 +70/-40 m, based on the slip vector formed by a vertically separated lithologic contact and a horizontally separated older cross fault. The net slip we calculated is significantly less than a previous estimate that was based on an offset magnetic gradient, a disparity that may be explained by considering off-fault deformation, as well as the unknown depth and nature of the source of the magnetic contrast. In Chapter IV, we explored using a new method for the relative dating of Quaternary geomorphic surfaces, which is based on the positive correlation between increased spectral contrast in thermal hyperspectral airborne imagery and surface age. With field data, we found that desert varnish scores, desert pavement scores, and vegetation spacing estimates also correlate positively with surface age, implying that these factors could contribute to the increased spectral contrast in airborne remote sensing spectra. Additionally, the general increase in the band depth of airborne spectra at 9.16 μm could be due to increasing clay mineral abundance in progressively heavier desert varnish coatings on older surfaces. The positive correlation observed in this study between surface age and spectral contrast in airborne spectra can perhaps be used to develop a method for relative dating of varnished geomorphic surfaces elsewhere. All of the chapters in this thesis are broadly related by the concepts of geologic time and tectonic activity, which are two aspects of modern geology that are intrinsic to the science as a whole.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Stock, Joann M. and Wernicke, Brian P.}, } @phdthesis{10.7907/Z9JM27NJ, author = {Price, Jason Brian}, title = {I: Normal Faulting on the Austroalpine ‘Overthrust’ Constrained by Thermochronometry and Kinematic Analysis, Central Alps, Graubünden Region, Switzerland. II: Clumped Isotope Thermometry of Carbonate Phases Associated with the Copper Deposits of Kennecott, Alaska}, school = {California Institute of Technology}, year = {2017}, doi = {10.7907/Z9JM27NJ}, url = {https://resolver.caltech.edu/CaltechTHESIS:05142017-011958758}, abstract = {I. A compilation of 362 cooling ages, including 52 newly reported in this study, from nine thermochronometric systems, 40K/39Ar amphibole, 40K/39Ar white mica, 87Rb/86Sr white mica, 40K/39Ar biotite, 87Rb/86Sr biotite, zircon and apatite fission track, zircon and apatite (U-Th)/He, indicate that the base of the Austroalpine allochthonous ‘orogenic lid’ was not in full thermal equilibrium with its Penninic substrate until at least the middle Oligocene, approximately 29-28 Ma, to allowably as late as the early Miocene, ca. 18 Ma. There is about a factor-of-five difference in cooling rates between the hanging wall (ca. 4°C/m.y.) and footwall (ca. 20°C/m.y.) during this period. In addition, there are demonstrably higher metamorphic grades, including blueschist- and eclogite-facies, in the Pennine footwall compared to lower greenschist-facies in the Austroalpine hanging wall. Together these two facts demonstrate that hot, high-pressure Penninic nappes were forced upward against the cold, low-pressure overriding Austroalpine plate in a very short time window of approximately 7-10 m.y. between the time of peak metamorphism during the Eocene and the time of thermal equilibration with the overriding plate during the Oligo-Miocene. The most likely mechanism to produce such a cold-on-hot juxtaposition is a normal fault, and therefore, we conclude that an important period of nappe emplacement in the Central Swiss Alps occurred concurrently with orogen-perpendicular normal fault motion at the base of the Austroalpine allochthon persisting well into the Oligocene and possibly into the early Miocene, post-dating the 32-30 Ma age of the Bergell intrusion.
Mesoscopic structural measurements made at the top and bottom of the Pennine zone in eastern Switzerland indicate multiple, spatially heterogeneous directions of movement. At the top, in the Oberhalbstein Valley, movement directions vary from dominantly top-east to top-south-southeast a very minor top-north component within Pennine rocks of the Martegnas shear zone and no preferred movement direction within the Austroalpine hanging wall. Near Piz Toissa, a minimum of two kilometers of nearby structural section in the Err and Platta nappes have been faulted out. At the bottom of the Pennine zone in Val Lumnezia and the Chur Rhein Valley at Trimmis, we observe top-northwest, top-north, and top-northeast movements. In Val Lumnezia, the Sub-Penninic Scopi zone (Gotthard cover rocks) shows movement in a top-northwest direction; the superjacent Peidener imbricate fault zone, a relatively thin (ca. 50 to 100 m thick) structural zone consisting of Scopi zone lithologies, shows movement in a northeasterly direction; above that, the basal Penninic Bündnerschiefer shows no dominant movement direction. To the east, in the Chur Rhine Valley, movement is well defined as exclusively top-north. Therefore, movement directions in the lower Bündnerschiefer are broadly top-north but heterogeneous in direction along strike between Val Lumnezia and Chur Rhein Valley, and, as first suggested by Weh and Frotizheim (2001), it may be erroneous to regard the basal Pennine thrust as a simple through-going structure. In Val Lumnezia, the Scopi-Peidener-Pennine nappes resemble a “jelly sandwich” in which the thick Pennine mass utilized the Peidener zone to move in an oblique sinistral-normal slip sense past the southeast-dipping allochthonous Scopi zone and its east-dipping Gotthard “massif” substrate. If the Peidener zone continues northeastward beneath alluvial cover of the Chur Rhein Valley, it may serve as a late, NE-directed shear zone that separates the Pennine nappes from European units. If so, it would explain the apparent truncation and progressive omission of allochthonous elements of European affinity along the zone from southwest to northeast beneath alluvium of the Chur Rhein Valley. We therefore infer that the direct juxtaposition of Penninic units to the east with the Helvetic autochthon to the west at the latitude of Trimmis records an episode of top-northeast, orogen-parallel strike-slip and extensional movement.
Zircon (U-Th)/He (ZHe) cooling ages from the Oberhalbstein Valley indicate that the Austroalpine-Pennine contact was still active at ca. 27 Ma, and that the Martegnas shear zone was active, in part, between ca. 27 and 24 Ma. It is likely that the Piz Toissa klippe formed around this time during the late Oligocene. The pattern of much younger ZHe ages at the bottom of the Pennine zone is independent of any nappe boundaries, including the Peidener imbricate fault zone, but is consistent with the rise of the Aar massif during the Miocene. Tectonic movements, as recorded by the mesostructure in the Austroalpine, Penninic, and Sub-Penninic domains, and local ZHe cooling ages generally support the conclusion drawn strictly from cooling ages that the Pennine zone was emplaced en masse as a coherent ‘piston’ or ‘mega-pip’ during Oligocene to early Miocene time (approximately 29 to 18 Ma), well after juxtaposition of Apulia with cratonic Europe (continent-continent collision) and during the development of Alpine topography and the peripheral basins (viz. Molasse and Lombardi). Additional top-north movement and late uplift and flexure of the nappe stack, along with the Aar massif, occurred primarily in middle to upper Miocene time, following the post-collisional structural interposition of the Pennine zone between Europe and Apulia.
Calculated compositions for δ18Owater vary from -4.2 to +11.0‰. The most depleted water precipitated hydrothermal baroque dolomite, whereas the most enriched water was associated with recrystallized limestone wallrock on the periphery of the orebody. Waters that precipitated calcite+copper vary from -1.1 to +9.3‰.
Intriguingly, rhythmic layering in zebra dolomite can be resolved in ∆47 space, and preliminary data indicate that the coarser-grained baroque dolomite bands precipitated at temperatures 5-10°C cooler than the surrounding, finer-grained dolomite wall rock bands.
The calculated values of δ18Owater support a genetic model that invokes redox changes associated with fluid mixing as the likely mechanism responsible for copper deposition. In this model a sulfidic, basinal fluid having δ18O similar to seawater mixes with a cuprous fluid having heavier δ18O (5 to 8‰) which was derived from the Nikolai Greenstone during prehnite-pumpellyite-facies metamorphism.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Wernicke, Brian P.}, } @phdthesis{10.7907/Z92F7KDC, author = {Swanson, Erika McGoldrick}, title = {Structural and Clumped-Isotope Constraints on the Mechanisms of Displacement Along Low-Angle Detachments}, school = {California Institute of Technology}, year = {2015}, doi = {10.7907/Z92F7KDC}, url = {https://resolver.caltech.edu/CaltechTHESIS:10242014-133410215}, abstract = {Despite years of research on low-angle detachments, much about them remains enigmatic. This thesis addresses some of the uncertainty regarding two particular detachments, the Mormon Peak detachment in Nevada and the Heart Mountain detachment in Wyoming and Montana.
Constraints on the geometry and kinematics of emplacement of the Mormon Peak detachment are provided by detailed geologic mapping of the Meadow Valley Mountains, along with an analysis of structural data within the allochthon in the Mormon Mountains. Identifiable structures well suited to constrain the kinematics of the detachment include a newly mapped, Sevier-age monoclinal flexure in the hanging wall of the detachment. This flexure, including the syncline at its base and the anticline at its top, can be readily matched to the base and top of the frontal Sevier thrust ramp, which is exposed in the footwall of the detachment to the east in the Mormon Mountains and Tule Springs Hills. The ~12 km of offset of these structural markers precludes the radial sliding hypothesis for emplacement of the allochthon.
The role of fluids in the slip along faults is a widely investigated topic, but the use of carbonate clumped-isotope thermometry to investigate these fluids is new. Faults rocks from within ~1 m of the Mormon Peak detachment, including veins, breccias, gouges, and host rocks, were analyzed for carbon, oxygen, and clumped-isotope measurements. The data indicate that much of the carbonate breccia and gouge material along the detachment is comminuted host rock, as expected. Measurements in vein material indicate that the fluid system is dominated by meteoric water, whose temperature indicates circulation to substantial depths (c. 4 km) in the upper crust near the fault zone.
Slip along the subhorizontal Heart Mountain detachment is particularly enigmatic, and many different mechanisms for failure have been proposed, predominantly involving catastrophic failure. Textural evidence of multiple slip events is abundant, and include multiple brecciation events and cross-cutting clastic dikes. Footwall deformation is observed in numerous exposures of the detachment. Stylolitic surfaces and alteration textures within and around “banded grains” previously interpreted to be an indicator of high-temperature fluidization along the fault suggest their formation instead via low-temperature dissolution and alteration processes. There is abundant textural evidence of the significant role of fluids along the detachment via pressure solution. The process of pressure solution creep may be responsible for enabling multiple slip events on the low-angle detachment, via a local rotation of the stress field.
Clumped-isotope thermometry of fault rocks associated with the Heart Mountain detachment indicates that despite its location on the flanks of a volcano that was active during slip, the majority of carbonate along the Heart Mountain detachment does not record significant heating above ambient temperatures (c. 40-70°C). Instead, cold meteoric fluids infiltrated the detachment breccia, and carbonate precipitated under ambient temperatures controlled by structural depth. Locally, fault gouge does preserve hot temperatures (>200°C), as is observed in both the Mormon Peak detachment and Heart Mountain detachment areas. Samples with very hot temperatures attributable to frictional shear heating are present but rare. They appear to be best preserved in hanging wall structures related to the detachment, rather than along the main detachment.
Evidence is presented for the prevalence of relatively cold, meteoric fluids along both shallow crustal detachments studied, and for protracted histories of slip along both detachments. Frictional heating is evident from both areas, but is a minor component of the preserved fault rock record. Pressure solution is evident, and might play a role in initiating slip on the Heart Mountain fault, and possibly other low-angle detachments.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Wernicke, Brian P.}, } @phdthesis{10.7907/CN29-YV40, author = {Williams, Nneka Njeri Akosua}, title = {Defining the Relationship between Seismicity and Deformation at Regional and Local Scales}, school = {California Institute of Technology}, year = {2013}, doi = {10.7907/CN29-YV40}, url = {https://resolver.caltech.edu/CaltechTHESIS:09052012-110119932}, abstract = {In this thesis, I use source inversion methods to improve understanding of crustal deformation along the Nyainquentanglha (NQTL) Detachment in Southern Tibet and the Piceance Basin in northwestern Colorado. Broadband station coverage in both regions is sparse, necessitating the development of innovative approaches to source inversion for the purpose of studying local earthquakes.
In an effort to study the 2002-2003 earthquake swarm and the 2008 Mw 6.3 Damxung earthquake and aftershocks that occurred in the NQTL region, we developed a single station earthquake location inversion method called the SP Envelope method, to be used with data from LHSA at Lhasa, a broadband seismometer located 75 km away. A location is calculated by first rotating the seismogram until the azimuth at which the envelope of the P-wave arrival on the T-component is smallest (its great circle path) is found. The distance at which to place the location along this azimuth is measured by calculating the S-P distance from arrivals on the seismogram. When used in conjunction with an existing waveform modeling based source inversion method called Cut and Paste (CAP), a catalog of 40 regional earthquakes was generated.
From these 40 earthquakes, a catalog of 30 earthquakes with the most certain locations was generated to study the relationship of seismicity and NQTL region faults mapped in Google Earth and in Armijo et al., 1986 and Kapp et al., 2005. Using these faults and focal mechanisms, a fault model of the NQTL Region was generated using GOCAD, a 3D modeling suite. By studying the relationship of modeled faults to mapped fault traces at the surface, the most likely fault slip plane was chosen. These fault planes were then used to calculate slip vectors and a regional bulk stress tensor, with respect to which the low-angle NQTL Detachment was found to be badly misoriented. The formation of low-angle normal faults is inconsistent with the Anderson Theory of faulting, and the presence of the NQTL Detachment in a region with such an incongruous stress field supports the notion that such faults are real.
The timing and locations of the earthquakes in this catalog with respect to an anomalous increase in the eastward component of velocity readings at the single cGPS station in Lhasa (LHAS) were analyzed to determine the relationship between plastic and brittle deformation in the region. The fact that cGPS velocities slow significantly after the 2002-2003 earthquake swarm suggests that this motion is tectonic in nature, and it has been interpreted as only the second continental slow slip event (SSE) ever to be observed. The observation of slow slip followed by an earthquake swarm within a Tibetan rift suggests that other swarms observed within similar rifts in the region are related to SSEs.
In the Piceance Basin, CAP was used to determine source mechanisms of microearthquakes triggered as a result of fracture stimulation within a tight gas reservoir. The expense of drilling monitor wells and installing borehole geophones reduces the azimuthal station coverage, thus making it difficult to determine source mechanisms of microearthquakes using more traditional methods. For high signal to noise ratio records, CAP produced results on par with those obtained in studies of regional earthquakes. This finding suggests that CAP could successfully be applied in studies of microseismicity when data quality is high.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Wernicke, Brian P.}, } @phdthesis{10.7907/4KPY-X114, author = {Verdel, Charles Steven}, title = {I. Cenozoic Geology of Iran: An Integrated Study of Extensional Tectonics and Related Vulcanism. II. Ediacaran Stratigraphy of the North American Cordillera: New Observations from Eastern California and Northern Utah}, school = {California Institute of Technology}, year = {2009}, doi = {10.7907/4KPY-X114}, url = {https://resolver.caltech.edu/CaltechETD:etd-09182008-092505}, abstract = {
I. Glacigenic deposits in the Death Valley region occur within the Neoproterozoic Kingston Peak Formation. In the Panamint Range, immediately west of Death Valley, these strata are ≥1000 m thick and are continuously exposed for nearly 100 km along the strike of the range. Although these strata are variably metamorphosed and locally exhibit pronounced ductile strain, original sedimentary textures are well preserved throughout the range. Diamictic strata occur in two distinct intervals, a lower one comprising the Limekiln Spring and Surprise Members, and an upper one known as the Wildrose Sub-member of the South Park Member. Each of these intervals are succeeded by well defined cap carbonates, which, from oldest to youngest, are the Sourdough Member of the Kingston Peak and the Sentinel Peak Member of the overlying Noonday Formation. Between the two glacial successions, the Sourdough and sub-Wildrose South Park units comprise a ~300 m thick interglacial succession that includes platform carbonate deposition. Sparse lonestones and striated clasts, along with the impressive lateral continuity of diamictic units, support a glacial origin. Chemostratigraphic profiles of δ13C through the Sourdough (-3‰ to +2‰, increasing upward) and Sentinel Peak (-3‰ +/- 1‰) suggest correlation with the Sturtian and Marinoan caps, respectively. Potentially economic U deposits (secondary brannerite) occur in graphitic schists of the Limekiln Spring Member and sub-economic U and Th (hosted by detrital monazite) occur within quartz-pebble conglomerates in the South Park Member. The strata contain no fossils, radiometric age control, or primary magnetizations.
The combined lithostratigraphic and chemostratigraphic data form the basis for a revised, more complete stratigraphic framework for the Noonday Formation. A composite section shows that, where most complete, the Noonday consists of three members, from the base upward, the Sentinel Peak, Radcliff, and Mahogany Flats members. New mapping and chemostratigraphic data permit robust regional correlation of a thin dolostone marker horizon at the base of the Noonday in the Panamint Range as little as 2 m thick (Sentinel Peak Member) with a tube-bearing microbial dolostone in the eastern Death Valley region more than 200 m thick. The data also reveal that the Radcliff Member is bounded by disconformable surfaces and their correlative conformities. These surfaces are recognizable throughout the region and are used to construct a regionally unified stratigraphic nomenclature.
A key finding of this study is the construction of a chemostratigraphic profile spanning most of Noonday time. This was greatly aided by the discovery of carbonatebearing strata in the lower part of the Radcliff Member in the Tucki Mountain area of the Panamints, and relating their stratigraphic position to upper Radcliff and younger Noonday strata in the Wildrose Canyon area. The chemostratigraphic profile is a remarkable match for the Maiberg cap carbonate sequence in Namibia, including the decline to a minimum at -5‰, a recovery to near 0‰, and then subsequent decline to -2‰. Globally, profiles through many post-Marinoan sequences are either too condensed or lack sufficient carbonate to record these features, including the sections in the eastern Death Valley region. (Halverson et al. 2005). As such, the Panamint profiles represent the first relatively complete record of the post-Marinoan C-isotopic recovery outside of southern Africa. Correlation of these curves (1) firmly places the Noonday at the base of the Ediacaran Period, (2) indicates deposition of ~200 m of Sentinel Peak and Radcliff strata occurred between 635 and 632 Ma, (3) supports the hypothesis that the Wildrose Diamictite of the Kingston Peak Formation, which lies in sharp contact below the Sentinel Peak Member, represents at least part of the Marinoan glacial interval; (4) helps identify correlative cap carbonate sequences in key Laurentian sections, which include the Ravensthroat Formation in the MacKenzie Mountains, dolostones capping the upper diamictite of the Pocatello Formation in eastern Idaho, and the middle part of the Mina el Mezquite Formation in Sonora. The Noonday C-isotopic profile confirms that the details of relatively rapid, complex variations in ocean chemistry observed in basal Ediacaran strata in Namibia are globally reproducible.
Within the inter-glacial succession, new mapping in the northern Panamints has documented the presence of a previously unrecognised suite of coarse sedimentary rocks herein defined as the Argenta Member of the Kingston Peak Formation. The Argenta consists largely of poorly-sorted breccias and conglomerates containing an assemblage of gravel-sized clasts dominated by granitic gneiss, schist, feldspar augens, vein quartz and quartzite fragments, and locally carbonate rocks. These compositions indicate derivation from a basement provenance and record deposition in alluvial-fan to coarse-braided fluvial settings; their textural and compositional immaturity implies relatively short distances of transport. Mapping shows that the Argenta defines wedge-shaped packages as much as 200 m thick and that the base of the Argenta is a significant angular unconformity. Combined, these features are evidence that deposition occurred during a phase of extensional tectonism interpreted as recording the initial dismemberment of the Rodinia supercontinent. Best estimates place the timing of this tectonism at ca. 650 – 700 Ma.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Wernicke, Brian P.}, } @phdthesis{10.7907/SZ62-KD58, author = {Abolins, Mark Joseph}, title = {I. Stratigraphic constraints on the number of discrete neoproterozoic glaciations and the relationship between glaciation and ediacaran evolution. II. The Kwichup Spring thrust in the northwestern Spring Mountains, Nevada : implications for large-magnitude extension and the structure of the Cordilleran thrust belt}, school = {California Institute of Technology}, year = {1999}, doi = {10.7907/SZ62-KD58}, url = {https://resolver.caltech.edu/CaltechETD:etd-04202006-152208}, abstract = {Part I: Stratigraphic constraints on the number of discrete neoproterozoic glaciations and the relationship between glaciation and ediacaran evolution.
Stratigraphic and structural observations in the Death Valley region provide new insights into two topical problems. First, stratigraphic observations provide a better understanding of the number of discrete Neoproterozoic glaciations and the relationship between glaciation and the diversification of the first animals. Detailed stratigraphic investigations reveal incised valleys within the Neoproterozoic Johnnie Formation. The size (>150 m) and regional extent of the valleys, and the carbon isotope signature of underlying carbonates show that the valleys are probably glacioeustatic in origin. The incised valleys help to complete the Neoproterozoic glacial record in the western United States. The incised valleys and a pair of glacial diamictites in the underlying Kingston Peak Formation represent two to three discrete Neoproterozoic glaciations. This record of two to three glaciations matches the global Neoproterozoic glacial record. The incised valleys provide the youngest evidence for large-scale Neoproterozoic glaciation in the western United States. Correlation of the Johnnie valleys with incised valleys in the uppermost Caddy Canyon Formation of Idaho and Utah shows that this glaciation occurred before 580 Ma. These findings suggest that diverse Ediacaran faunas post-date the youngest major Neoproterozoic glaciation by tens of millions of years.
Second, structural and stratigraphic observations provide new constraints on the magnitude of extension in the Death Valley extended domain. These observations reveal a thrust fault in the northwestern Spring Mountains, NV. Correlation of this thrust fault with thrusts in other ranges constrains the translation of those ranges relative to the Spring Mountains. While these correlations are not unique, the most plausible correlations require large-magnitude extension in the Death Valley area and north of Las Vegas Valley.
Correlation of contractile structures in the northwestern Spring Mountains and Specter Range with Permo-Triassic structures in the Cottonwood Mountains may provide a link between the Permo-Triassic thrust belt in the Cottonwood Mountains and the Central Nevada thrust belt. The Central Nevada thrust belt may be at least in part Permo-Triassic in age, and may represent a foreland fold and thrust belt which developed inboard of the Golconda allochthon during its emplacement.
Part II: The Kwichup Spring thrust in the northwestern Spring Mountains, Nevada : implications for large-magitude extension and the structure of the Cordilleran thrust belt.
Approximately 170 km(2) of new mapping in the northwestern Spring Mountains reveals contractile structures related to a regional thrust fault called the Kwichup Spring thrust. The Kwichup Spring thrust involves at least 1.4 km of stragraphic throw. Along much of its length, the Kwichup Spring thrust has been reactivated or excised by a normal fault.
Stratigraphic and structural evidence suggest that the Kwichup Spring thrust correlates with the Montgomery thrust in the Montgomery Mountains. Correlation of these two thrusts requres a reappraisal of the geometry of the Cordilleran thrust belt in Nevada and southeastern California. The Kwichup Spring - Montgomery thrust probably correlates with either the Clery thrust in the Funeral Mountains or the Panamint thrust in the Panamint Mountains. Both possible correlations require large (>115 km) west-northwest translation of the Panamint and Cottonwood Mountains with respect to the Spring Mountains during Neogene extension.
Before this large-scale translation, the Panamint and Cottonwood Mountains were positioned along the southern projection of the Central Nevada thrust belt of Taylor and others (1993). Since contractile structures in the Cottonwood Mountains are Permo-Triassic, the Central Nevada thrust belt may be at least in part Permo-Triassic.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Wernicke, Brian P.}, } @phdthesis{10.22002/D1.1718, author = {Brady, Robert John}, title = {The Geology of the Gold Butte Breakaway Zone and the Mechanical Evolution of Normal Fault Systems}, school = {California Institute of Technology}, year = {1998}, doi = {10.22002/D1.1718}, url = {https://resolver.caltech.edu/CaltechTHESIS:02012019-101059213}, abstract = {The Gold Butte breakaway zone is the easternmost and oldest of the major Tertiary normal fault systems in the central Basin and Range province of the southwestern U.S. The normal faults of the breakaway zone crop out across the South Virgin Mountains (SVM), and define a narrow boundary zone between the Colorado Plateau and the highly extended central Basin and Range Province. Geochronologic data, including 40Ar/39Ar muscovite ages, (U-Th)/He apatite ages, and (U-Th)/Pb monazite ages, suggest that extension within the breakaway zone occurred rapidly at ~15 Ma, consistent with earlier work (Fitzgerald, 1991). Approximately 400 km2 of the SVM was mapped at a scale of 1:12 000. This mapping shows that extension initiated on a set of steeply west dipping normal faults. Later faults soled into the earlier faults rather than cutting them, requiring motion to continue on both fault sets, with the earlier faults remaining active to dips of less than 30°. Total extension across the SVM is at least ~21 km. The latest deformation to affect the region was isostatic uplift of the footwall to the Lakeside Mine Fault Zone, with resultant formation of a basement dome and associated folding and late stage faulting adjacent to the dome. Seismic reflection data suggest that the crustal thickness of the region is 30 to 35 kilometers. When combined with the high average elevation of the denuded basement block, this suggests that extension of the upper crust has been compensated by emplacement of fluid mid to lower crust. The lower crust and Moho are seismically transparent, so the lower crust is probably not made up of basaltic intrusions; rather, it has probably flowed in from surrounding areas. A mechanical model has been developed which considers the behavior of an elastic upper crust isostatically compensated by flow in the lower crust. This model shows that gradual isostatic upwarping of the thinning region should generate compressional flexural stresses near the base of the elastic upper crust. These stresses may shut down the active faults and force new normal faults to root outside of the extended region.
}, address = {1200 East California Boulevard, Pasadena, California 91125}, advisor = {Wernicke, Brian P.}, }