<p> Reduced intrusion-related gold (RIRG) deposits have been documented around the globe, and have been best studied in Alaska and Yukon, but few examples have been documented in Nevada. One occurrence in Nevada is the Jurassic Bald Mountain deposit in eastern Nevada; however, for most Nevada occurrences there has been insufficient work that establishes a genetic connection to intrusions or determines their age. </p><p> Buffalo Canyon is a gold prospect located near the historic Berlin mining area in northern Nye County, Nevada, where gold, silver, copper, lead and zinc were mined in the past from mesothermal quartz veins. Buffalo Canyon contains the more recently discovered Everson prospect, a poorly defined gold deposit, which has characteristics of RIRG deposits. The district includes a series of intrusions emplaced into Triassic metasedimentary and metavolcanic rocks. These previously undated intrusions vary in composition from diorite to granodiorite and granite. U-Pb dating of zircons by LA-ICPMS has revealed distinct intrusive events in the Jurassic, Cretaceous, and Oligocene. Metaluminous, biotite-pyroxene diorite stocks to porphyritic granodiorite dikes have been dated at 162.03 + 0.91 Ma and 158.72 + 0.94 Ma, respectively. Peraluminous, ilmenite-bearing leucogranite plugs and dikes have been dated at 81.96 + 0.43 Ma and 82.9 + 0.30 Ma, respectively. A variety of Oligocene dikes and small plugs that include quartz-monzodiorite, quartz monzonite, dacite and granite are metaluminous to peraluminous and locally ilmenite-bearing. Four dates of Oligocene intrusions fall within error of each other. They yielded dates of 25.13 + 0.29, 24.9 + 0.30, 24.8 + 0.40 Ma and 24.6 + 0.30 Ma. </p><p> Country rocks at Buffalo Canyon, particularly those near Jurassic intrusions, are metamorphosed to biotite hornfels. Biotite hornfels is overprinted by sodic-calcic alteration that is likely related to Jurassic intrusive activity, and consists primarily of actinolite + albite in veins and disseminated patchworks. Mesothermal quartz veins have a Au-Ag-(Sb-Pb-As-Cu) geochemical signature, are composed predominantly of moderately deformed, recrystallized quartz and contain liquid CO₂-bearing fluid inclusions. Mesothermal quartz veins are hosted within Jurassic intrusions and are post-Luning-Fencemaker thrust (mid-Jurassic) deformation. Small volumes of Oligocene intrusive rocks are variably altered to muscovite-tourmaline or propylitic assemblages. Base-metal sulfide mineralization occurs as veins and replacements, both of which are associated with tourmaline as a dominant gangue mineral. Base-metal sulfide mineralization has a Ag-Pb-Zn-Sb-As-(Au-Bi-Cu-Mo) signature. </p><p> Free gold within low sulfide, 1-10cm thick, sheeted, crack-seal quartz veins with locally developed sericite-tourmaline envelopes define the bulk of the Everson gold mineralization. Other gangue minerals in these veins include muscovite, tourmaline and fluorite. The veins have a Au-Te-(Mo-Bi-Sn) signature and high Au:Ag ratios (>1:1). The quartz in these gold-bearing veins contain common hypersaline brine and coexisting vapor-rich fluid inclusions, indicative of trapping within the two-phase brine + vapor field. Combined with estimated thicknesses of older and coeval Oligocene volcanic rocks, the fluid inclusions suggest the deposit formed at &lt;~3 km paleodepth. The Everson-related quartz veins also cross-cut mapped Jurassic intrusive rocks, sodic-calcic veins, base-metal sulfide mineralization, and Oligocene granitic intrusions. Muscovite and tourmaline + fluorite associated with alteration and mineralization suggest a greisen-like style of alteration and mineralization. The preponderance of evidence suggests that most gold mineralization at Buffalo Canyon is Oligocene in age, related to a felsic intrusion that only crops outs locally, but is likely extensive in the subsurface. Buffalo Canyon bears strong similarities to typical RIRG systems, and there are likely additional unknown examples within Nevada. A significant outcome of this study is that Buffalo Canyon formed in the Oligocene, related to volcanism during slab rollback that led to the ignimbrite flare-up in the central Nevada. Though most RIRG systems in Nevada could indeed be Mesozoic, the research on Buffalo Canyon opens the possibility that similar deposits may also be related to much younger intrusions that may be largely covered by coeval Tertiary volcanic rocks.</p><p>

<p> Voluminous Eocene dikes in the North Cascades are thought to provide insights into the regional strain field during postulated ridge&ndash;trench interaction in the Pacific Northwest. One understudied area with a large number of dikes is spatially associated with the elongate (NW-SE), ~46 Ma granodioritic Duncan Hill pluton. The ~80 km2 study area contains the shallow part of this pluton and the host schist of the Twentyfive Mile Creek unit and tonalite and migmatite of the Cretaceous Chelan Complex. Field observations and petrographic analyses indicate that the dikes in the study area can be sub-divided compositionally and texturally into three types: intermediate-mafic, granite porphyry, and rhyolite. Extension magnitudes from the dikes (n=438) are ~4% to 7%. The dikes have predominantly steep dips, but vary widely in strike and define a broadly bimodal pattern of NW (301&deg;) and NE (026&deg;) strikes. Orientations indicate that the Duncan Hill pluton did not modify the strain field, whereas the strong foliation and anisotropy in the Twentyfive Mile Creek unit may be responsible for some of the NW strikes. The NE-striking dikes likely record the regional NW-SE extension that was active when they intruded. From the data collected in this study, it cannot be ruled out that the NW-striking dikes intruded at different times and under a different regional strain field. This work has shown that dike orientations in the study area are much more complex than those documented elsewhere in the North Cascades.</p><p>

Neoproterozoic and early Paleozoic sedimentary deposits of the North American Cordillera record large fluctuations in global biogeochemical cycles, the establishment and diversification of multiple eukaryotic clades, the fragmentation of the supercontinent Rodinia, and the protracted development and subsequent demise of the western and northern Laurentian passive margins. Here, I put forth new tectono-, bio-, and chemo-stratigraphic models for the ~780-540 Ma Windermere Supergroup of western North America and “pre-Mississippian” stratigraphy of northern Alaska that refine previous models for the Neoproterozoic and early Paleozoic tectonic and environmental evolution of Alaska and northwest Canada. First, I present an updated model for early Windermere (780–720 Ma) sedimentation in NW Canada through a detailed study of the Callison Lake Formation of the Mount Harper Group, spectacularly exposed in the Coal Creek and Hart River inliers of the Ogilvie Mountains of Yukon, Canada. Twenty-one detailed measured stratigraphic sections are integrated with geological mapping, facies analysis, and new Rhenium-Osmium (Re-Os) geochronology to provide a depositional model for the Callison Lake Formation. Mixed siliciclastic, carbonate, and evaporite sediments record a complex subsidence history in which episodic basinal restriction and abrupt facies change can be tied accumulation in marginal marine embayments formed in discrete hangingwall depocenters of a major Windermere extensional fault zone. New organic-rich rock Re-Os ages of 752.7 ± 5.5 and 739.9 ± 6.1 Ma bracket Callison Lake sedimentation and constrain early Windermere sedimentation in NW Canada to post-date the eruption of the Gunbarrel Large Igneous Province by ~30 million years and predate the successful rift-drift transition by ~200 million years. In order to accommodate coeval extensional and compressional tectonism, abrupt facies change, and Neoproterozoic fault geometries, I propose that NW Canada experienced strike-slip deformation during the ~740–660 Ma early fragmentation of Rodinia. Second, I integrate carbon and oxygen isotope chemostratigraphy, sequence stratigraphy, geochronological data, and microfossil biostratigraphy from the Callison Lake Formation to highlight the potential for margin-wide correlation of Neoproterozoic successions in North America. Here, I also report the discovery of abundant and well-preserved vase-shaped microfossils in the Callison Lake Formation, dated with Re-Os geochronology at 739.9 ± 6.1 Ma, that share multiple species-level taxa with a well-characterized and coeval assemblage from the Chuar Group, Grand Canyon, Arizona dated with U-Pb on zircon from an interbedded tuff at 742 ± 6 Ma. The overlapping age and species assemblages from these two deposits suggests biostratigraphic utility, at least within Neoproterozoic basins of Laurentia, and perhaps globally. Sequence stratigraphic data from the Callison Lake Formation and other basal Windermere successions in northwest Canada delineate four major depositional sequences that are broadly coeval with similar stratigraphic packages in the ~780–720 Ma Chuar-Uinta Mountain-Pahrump basins of the western United States. The new Re-Os age also confirms the timing of the Islay carbon isotope excursion (ICIE) in northwest Canada, which predates the onset of the Sturtian glaciation by >15 million years. Here, I hypothesize that this carbon isotope excursion represents a primary perturbation to the global carbon cycle and explore a number of models for its origin related to the duration of the excursion. Together, these data provide global calibration of sedimentary, paleontological, and geochemical records on the eve of profound environmental and evolutionary change. Finally, I present an updated model for the origin of the Arctic Alaska–Chukotka microplate, a composite Cordilleran “suspect” terrane that comprises the greater portion of the modern continental margin of the Amerasian Basin of the Arctic Ocean, through a detailed study of pre-Mississippian stratigraphy in the Shublik, Sadlerochit, and British Mountains of the northeastern Brooks Range, Alaska. An exotic, non-Laurentian origin of Arctic Alaska–Chukotka has been proposed based on paleobiogeographic faunal affinities and various geochronological constraints from the southwestern portions of the microplate. Here, I report new early Paleozoic trilobite and conodont taxa that support a Laurentian origin for the North Slope of Arctic Alaska, as well as new Neoproterozoic–Cambrian stratigraphic correlations and igneous and detrital zircon geochronological data, that are both consistent with a Laurentian origin and profoundly different from those derived from similar-aged strata in the southwestern portions of Arctic Alask¬a–Chukotka. The North Slope terrane is accordingly interpreted as allochthonous with respect to its current position in northwestern Laurentia, but most likely originated further east along the Canadian Arctic or North Atlantic margins. These data demonstrate that Paleozoic construction of the composite Arctic Alaska¬–Chukotka microplate resulted from juxtaposition of the exotic southwestern parts of the microplate against the northern margin of Laurentia during protracted Ordovician(?)–Carboniferous Caledonian and Ellesmerian tectonism. / Earth and Planetary Sciences

Within this dissertation, I document different time intervals during the Neoproterozoic through the early Cambrian (1000 – 525 Ma), one of the most dynamic and non-uniformitarian intervals in the history of the Earth. This thesis focuses on two time periods of change within this time interval: 1) The pre-Cryogenian-Cryogenian transition (~800-635 Ma) and 2) the Ediacaran-Cambrian Transition (~551-525 Ma). To begin, I use a combination of detailed mapping, regional stratigraphy, and geochronology to reinterpret the depositional and tectonic setting of the ~750-730 Ma Beck Spring Dolomite and its bounding units in Death Valley, California. Instead of being deposited in an interior seaway in a long-lived aulacogen as Rodinia rifted apart, I suggest that this unit was accommodated by strike-slip motion that could have represented a margin-wide event along the west coast of Laurentia. The true rift to drift did not occur until the latest Ediacaran to earliest Cambrian. Late Ediacaran to early Cambrian datasets from the Great Basin in the western USA are integrated to refine the biological and environmental changes that occur across the Ediacaran-Cambrian Boundary. In my third chapter, two new horizons of exceptionally preserved Ediacaran fauna that include Conotubus and Gaojiashania are documented. These fossils were previously only known from South China. The Conotubus horizon occurs just below the most negative δ13C values in the basal Cambrian δ13C excursion, establishing it as the youngest Ediacaran fossil to date. These fossils are placed into a high-resolution δ13C chemostratigraphic framework, allowing for regional and global correlation. Three δ13C chemostratigraphic curves from the Great Basin combined with five sections from Western Mongolia show that instead of a single, rapid δ13C excursion at the Ediacaran-Cambrian Boundary, there is one broad excursion with more secondary structure than has been previously documented. Together, these data suggest the nadir of the δ13C excursion is younger than 541 Ma and provide a new framework to interpret Ediacaran-Cambrian biostratigraphy, chemostratigraphy, and U/Pb ash ages globally. The final chapter focuses on the earliest Cambrian in Southwest Mongolia. By using extensive field data, I construct a basin-wide facies model and age model for the Zavkhan Basin. I place the early Cambrian fossil horizons into this new framework and correlate the composite dataset from Mongolia with others globally. In doing so, I reinterpret the tempo and patterns of evolution during this critical interval in Earth history. The following chapters cover diverse events in Earth history that better constrain topics ranging from the breakup of the supercontinent Rodinia to environmental change across the Ediacaran-Cambrian Boundary to rates of evolutionary change during the early Cambrian. All of these topics, however, are united by a multidisciplinary approach that combines original field observations with geochemical, geochronological, stratigraphic, and paleontological datasets to constrain the origin and timing of the coevolution of life and the environment in the deep past. / Earth and Planetary Sciences

This dissertation investigates natural deformation processes over multiple earthquake cycles in the seismically active, southern Junggar basin, NW China and additionally explores the capabilities of 3D geomechanical restoration as an effective tool for fractured reservoir characterization. Chapter 1 presents a detailed 3D fault model of the active Southern Junggar Thrust (SJT) – constrained by seismic reflection data – in the southern Junggar basin. This work demonstrates the significance of mid-crustal detachments as a physical mechanism to accommodate destructive, multi-segment earthquakes in active thrust sheets. Moreover, it highlights the efficacy of surface folds to delineate fault geometries at depth in the absence of subsurface data constraints. Chapter 2 describes active thrust sheet deformation across the Tugulu anticline, which sits in the hanging wall of the SJT, from Late Quaternary to present. Holocene terrace deformation records of surface faulting and folding yield consistent fault slip rates. We develop a quantitative method for extracting fault slip rates from terrace fold geometries using a mechanical modeling approach, yielding a 250 kyr history of SJT slip. This study provides new insights into natural fold growth associated with fault slip. Moreover, it addresses several shortcomings of traditional seismic hazards assessment methodologies. Chapter 3 characterizes the styles, timing, and sequence of deformation across southern Junggar. Southern Junggar underwent extension followed by tectonic inversion and shortening, forming a series of imbricate structural wedges. A kinematic model for the evolution of shear fault-bend fold wedges is presented. We discuss the implications of structural style, fold growth and thrusting sequence on the ~175 Myr evolution of this fold-and-thrust belt and its petroleum system. Chapter 4 investigates the impact of natural fold strains on fractured reservoir properties in the Permian Basin, West Texas. This study details the ability of 3D geomechanical restorations to accurately model natural strain distributions associated with fold growth. Modeled strains from geomechanical restorations are integrated with proxies for natural deformation and production data to describe how tectonic strain impacted observed gas production, water cuts and reservoir temperatures. When used in conjunction with additional datasets, geomechanical restoration shows promise for predictive abilities in characterizing conventional and unconventional fractured reservoir properties. / Earth and Planetary Sciences

The Neoproterozoic and Paleozoic evolution of global climate, tectonics, ocean geochemistry, and biological diversification are recorded in stratigraphic successions globally. The rock record of southwestern Mongolia has potential to reveal additional constraints as it is in the early stages of exploration. It has been known for several years that Cryogenian passive margin sedimentation on the Zavkhan Terrane hosts evidence for Neoproterozoic glaciation, and that overlying early Cambrian strata host rich records of small shelly fossils; however, the geological context for these critical records has been previously lacking. Although these unknowns can be regarded as local geologic uncertainties, together they hold implications to test existing tectonic and crustal growth models of the Central Asian Orogenic Belt (CAOB), preservation potential of geochemical proxies within carbonate dominated strata, and biologic milestones as recorded in Paleozoic sediments. To understand and interpret the above implications, methods of field geology, litho- and chemo-stratigraphy, geochemistry, petrography, fluid inclusion and clumped isotope thermometries, and U-Pb zircon geochronology were used. As a result, the tectonic origin and travels of the Zavkhan Terrane during the Neoproterozoic to early Paleozoic is refined and models of apparent crustal growth in the CAOB are re-assessed. Global Cryogenian and Ediacaran carbon and strontium isotope curves are constructed from limestonedominated successions of the Tsagaan-Olom Group of the Zavkhan Terrane and are integrated with available geochronologic and geochemical data from around the globe. Finally, dolomitization is shown to greatly alter primary geochemical signatures, including carbon isotope values of carbonate rocks. / Earth and Planetary Sciences

<p> Large-volume silicic ignimbrites erupt from reservoirs that vary in composition, temperature, volatile content and crystallinity. The 9.7 Ma Devine Canyon Tuff (DCT) of eastern Oregon is a large-volume (>250 km³), compositionally zoned and variably welded ignimbrite. The ignimbrite exhibits heterogeneous trace element compositions, variable volatile content and crystallinity. These observations were utilized in the investigation into the generation, accumulation and evolution of the magmas composing the DCT. Building off previous research, pumices were selected from the range of trace element compositions and analyzed with respect to crystallinity, mineral abundances and assemblages. The DCT displays a gradational trace element enrichment and decrease in crystallinity from least evolved, dacite, at &sim;22% crystals to most evolved high-silica rhyolite at 3% crystals. Two distinct mineral populations of feldspar and clinopyroxene were identified in previous work, one belonging to the rhyolitic magma and the other to the dacitic magma. Volatile content derived from melt inclusion Fourier Transform Infrared (FTIR) spectrometer analysis revealed an increase in water content from 1.2 to 3.7 wt.% in the most evolved rhyolite. The DCT exhibits low and variable &delta;¹⁸O signatures, 4.52&permil; to 5.76&permil;, based on &delta;¹⁸O values measured on quartz and sanidine. Low &delta;¹⁸O signatures of all DCT rhyolites suggest the incorporation of hydrothermally altered crust into the melt. Furthermore, quartz phenocrysts from all high-silica rhyolite groups display dark oscillatory zoned cores and Ti-rich bright rims. </p><p> These data provide insight into how these magmas were generated and subsequently stored in the crust. Commonalities of petrographic and compositional features among rhyolites, especially the zoning characteristics of quartz phenocrysts, exclude the possibility of storage and evolution in multiple reservoirs. Envisioning a scenario where all magmas are stored within a single reservoir prior to eruption and assuming rhyolites A and D are the product of partial melting. The mixing of A and D rhyolites produced rhyolite B, and subsequent mixing of intermediate rhyolite B and end-member rhyolite D generated rhyolite C. However, some trace element inconsistencies, between mixing model and observed intermediate rhyolites suggest a secondary process. Post mixing, rhyolites B and C require some modification by fractional crystallization to account for LREE and other inconsistencies between mixed models and observed rhyolites. Finally, the origin of the dacite is likely through mixing of group D rhyolite and an intrusive fractionated basalt, which could have led to the eruption of the Devine Canyon Tuff.</p><p>

<p> The stratigraphy and sedimentology of carbonate shelf deposits of the Ordovician Trenton Group exposed in the Mohawk Valley of Central New York are well documented. A similar level of detail for the laterally equivalent and overlying Utica Shale in the region is lacking. This is due to the more enigmatic nature of mudstones, and difficulties of observing fine sedimentary structures and layering in weathered outcrop exposures. The recent availability of numerous slabbed drill cores through these strata presents an unparalleled opportunity to study the Utica Shale in a high level of detail for the first time. Fine-scale observations, in addition to XRF spectroscopy and rock hardness analysis, for the Utica Shale and Dolgeville Formation have revealed new sedimentary features, depositional sequences, and geochemical variability. </p><p> Five unique lithofacies have been defined based on lithology and sedimentary and biogenic structures. They reflect a variety of transport and depositional processes, including turbidity currents, debris flows, contour currents, and wave reworking; in addition to low energy suspension settling of mud. Far from a monotonous interval of mudstones, the Utica Shale in Central New York reflects deposition in a dynamic marine environment that was shallow enough to allow for wave and current reworking of sediment, as well as mixing of oxygenated surface waters with more anoxic bottom waters. Subtle changes in bulk rock elemental concentrations through the Utica Shale and Dolgeville Formation are the result of changing source terrains, sedimentation rate, benthic redox conditions, and tephra deposition.</p><p>

Joints as opening-mode fractures play important roles as indicators of tectonic stress fields and as pathways for underground fluid flow. This thesis analytically investigates the relationships among cross joint geometry, orientations and ratios of remote principal stresses, and fluid pressure. Results show that main trends of cross joints are perpendicular to the least far field stresses during cross joint formation, and cross joint paths can be used to determine relative magnitudes of remote principal stresses. Based on the theoretical derivation, cross joint geometries are grouped into five main categories: curving-parallel, curving-perpendicular, quasi-curving-parallel, quasi-curving-perpendicular and non-curving geometries. By introducing the concepts of effective stress and effective remote principal stress ratio, it is demonstrated that connectivity between cross joints and the pre-existing joint is improved for joints that form under relatively high pore pressures.

A hemipelagic/pelagic sequence from Conset Bay, Barbados, West Indies, was prepared and reviewed to establish the radiolarian biostratigraphy and zonation of the area. This study shows that the sequence extends from the Middle Eocene, Dictyoprora mongolfieri zone, to the Late Eocene, Thyrsocyrtis bromia zone. Two zones, the Podocyrtis ampla zone and the Podocyrtis mitra zone have not been identified although the sequence appears to be stratigraphically continuous. Their absence is related to a sampling gap where an interval of the outcrop is covered with slope wash. The Conset Bay sediments are characterized by extensive reworking of older taxa from several stratigraphic level throughout the time span covered in the present study.