Geology Commons^™

Integrated Studies Of Intracontinental Deformation In The Interior Western Usa, Cretaceous To Recent, Jacob Oliver Thacker

Earth and Planetary Sciences ETDs

The advent of plate tectonic theory satisfactorily explained a number of deformation belts around the world. However intracontinental deformation (deformation inboard of a plate margin) remains poorly understood in plate tectonic models. In order to further our understanding of intracontinental tectonics and its effects, this dissertation examines paleotectonic and neotectonic settings within the interior western USA.

Chapter 1 focuses on late Miocene–Recent deformation inboard of the San Andreas plate margin fault and its role on the integration history of the lower Colorado River. The neotectonic analysis included geometric and kinematic fault data collected in key geologic units to characterize the …

Structural And Geochronologic Constraints On The Duration Of The Picuris Orogeny And Demise Of An Orogenic Plateau, Northern Nm, Daniel J. Young

Earth and Planetary Sciences ETDs

Metasedimentary and igneous basement rocks in northern New Mexico record episodic pulses of tectonism during cratonic growth from 1.8 to 1.38 Ga. Continued challenges involve parsing the deformational features attributable to the Yavapai Orogeny (1.71-1.68 Ga), Mazatzal orogeny (1.66-1.60 Ga), and Picuris orogeny (1.5-1.38 Ga) in this region and understanding how older structures may have been overprinted and reactivated to explain the observed strain. This paper presents regional cross-sections of the 1.7 Ga Vadito, 1.68 to 1.50 Ga Hondo, and 1.5-1.45 Ga Trampas groups of the Picuris Mountains and Rio Mora areas of northern New Mexico combined with new geochronologic …

Landscape Evolution Of The Southern Colorado Plateau Using Low-Temperature Apatite Thermochronology And Detrital Zircon And Sanidine Provenance Studies, Carmen L. Winn

Earth and Planetary Sciences ETDs

Chapter 1: Westernmost Grand Canyon

Conflicting hypotheses about the timing of carving of the Grand Canyon involve either a 70 Ma (“old”) or < 6 Ma (“young”) Grand Canyon. This paper evaluates the controversial westernmost segment of the Grand Canyon where the following lines of published evidence firmly favor a “young” Canyon. 1) North-derived Paleocene Hindu Fanglomerate was deposited across the present track of the westernmost Grand Canyon, which therefore was not present at ~55 Ma. 2) The 19 Ma Separation Point basalt is stranded between high relief side canyons feeding the main stem of the Colorado River and was emplaced before these tributaries and the main canyon were incised. 3) Geomorphic constraints indicate that relief generation in tributaries and on plateaus adjacent to the westernmost Grand Canyon took place after 17 Ma. 4) The late Miocene-Pliocene Muddy Creek Formation constraint shows that no river carrying far-traveled materials exited at the mouth of the Grand Canyon until after 6 Ma.

Interpretations of previously-published low-temperature thermochronologic data conflict with these lines of evidence, but are reconciled in this paper via the integration of three methods of analyses on the same sample: apatite (U-Th)/He ages (AHe), ⁴He/³He thermochronometry (⁴He/³He), and apatite fission-track ages and lengths (AFT). “HeFTy” software was used to generate time-temperature (t-T) paths that predict all new and published ⁴He/³He, AH, and AFT data to within assumed …

Basal Travertine Of The Bouse Formation: Geochemistry, Diagenesis And Implications For The Integration Of The Colorado River, Christina Ferguson

Earth and Planetary Sciences ETDs

The Pliocene Bouse Formation is discontinuously exposed in the lower Colorado River region and is a record of the first arrival of the Colorado River to the Gulf of California 5 million years ago. It consists broadly of a lower carbonate member (travertine, marl, and bioclastic units) and an upper siliciclastic member (claystone, mudstone, and Colorado River sands). This paper focuses on the basal travertine (synonymous with “tufa”) unit of the lower carbonate member. Because of its basal position and its chemical encrustation of pre-Bouse topography, the travertine can offer insight into the earliest depositional settings and may be a …

Interpreting Amalgamation Processes Of A Fluvial Sandstone Of The Nacimiento Formation In The San Juan Basin, New Mexico, Keely Elizabeth Miltenberger

Earth and Planetary Sciences ETDs

Outcrop studies of fluvial sand bodies are important for the study of fluid transport and storage capabilities because the deposits are heterogeneous. 3-D photogrammetry was used to evaluate the amalgamation processes of a multi-storey sheet sandstone in the San Juan Basin, NM. The Angel Peak member was deposited in the proximal-medial transition of a distributive fluvial system by a meandering river during the Paleocene. Within the study area, amalgamation occurred by avulsion and reoccupation of channel-belts to produce five storeys of the multi-storey sheet sandstone. Within each storey is evidence of processes that are internal to a channel-belt, such as …

Crustal Structure Beneath The East Coast Magnetic Anomaly From Seismic Refraction Tomography, Collin C. Brandl

Earth and Planetary Sciences ETDs

Syn-rift igneous addition is necessary for successful continental breakup. Past investigations of passive margins have focused on strike perpendicular structure, but potential field anomalies indicate that significant crustal variations may be present. Data from 21 ocean bottom seismometers was acquired as part of the Eastern North American Margin Community Seismic Experiment and was used for tomographic inversion to create 2D velocity models of the margin that are representative of crustal structure. Crustal thickness varies along-strike from ~20 km to ~24 km and a high velocity (Vp > 7 km/s) layer is present at the base of the crust above the Moho. …

Eutherian Biogeography During The Puercan North American Land Mammal Age (Paleocene, Earliest Danian): Problems And Potential Solutions, Jason Sterling Silviria

Earth and Planetary Sciences ETDs

The Puercan North American Land Mammal Age (NALMA) is the earliest major North American terrestrial biochron of the Cenozoic era, spanning roughly the first one million years of the Paleogene period (Paleocene epoch, Danian stage; ~66.04-65.12 Ma). It is typified by the explosive ecomorphological diversification of the mammalian clade Eutheria (particularly our subclade, Placentalia), following the annihilation of non-avian dinosaurs and “archaic” mammal groups during the Cretaceous/Paleogene (K-Pg) mass extinction event. The spatiotemporal mode and tempo of Puercan eutherian diversification has long been the subject of debate, with disagreements over biogeographic zonation. The traditional model – based largely on well-sampled, …

Single Crystal Elasticity Of Hydrous Fe-Bearing Wadsleyite At High-Pressure Condition, Zhiyuan Ren

Earth and Planetary Sciences ETDs

The 410-discontinuity separating the uppermost mantle from the transition zone is commonly believed to be caused by the olivine-wadsleyite transformation. However, the velocity change at the 410-discontinuity predicted by the standard pyrolitic model is not completely consistent with the seismic observations, leading to questions about the accuracy of the seismic models, or uncertainties of the mineral physics predictions. More regional seismic observations suggest that the depth, sharpness, and velocity jumps at the 410-discontinuity are different at different places, caused by thermal and/or compositional heterogeneities in the upper mantle. To explain the inconsistencies between the mineral physics and seismic models and …

Evaluating Sources Of Hydrochemical Variability And Mixing In The Upper Gila River, New Mexico, Pavel Vakhlamov

Earth and Planetary Sciences ETDs

This study of the upper reaches of the Gila River basin in southwestern New Mexico reveals both spatial and seasonal patterns in physical and hydrochemical parameters. Monsoonal precipitation, temporal variability in water chemistry of streams in the upper Gila watershed is significantly impacted by surface runoff due to variability in landscape cover features, as well as surface area of the catchment. However, during base flow regimes spring inputs are the dominant drivers of solute concentrations and chemical variability.

Geothermal sources play a major role in salinization of the southwestern stream systems. Prolonged water/rock interaction combined with high temperature, pressure result …

Architecture And Evolution Of The Peace Vallis Distributive Fluvial System, Gale Crater, Mars, Zachary E. Gallegos

Earth and Planetary Sciences ETDs

The Peace Vallis alluvial fan, located within Gale crater on the planet Mars, is a distributive fluvial system indicating a wet climate in Mars’ past. The Mars Science Laboratory rover instrument ChemCam, with the high-resolution Remote Micro-imager, was utilized to remotely explore the Peace Vallis alluvial fan and surrounding areas area. The Peace Vallis imaging campaigns 1 and 2, led by Dr. Horton Newsom and Zachary Gallegos respectively, acquired 20 distinct rover observations with a total of 243 individual images to investigate the fan. Using visual interpretation of the images and GIS techniques, this study interprets the processes and products …

Constraining The Oxygen Values Of The Late Cretaceous Western Interior Seaway Using Marine Bivalves, Camille H. Dwyer

Earth and Planetary Sciences ETDs

The Western Interior Seaway (WIS) remains an oceanographic enigma, including its circulation, similarity to the open ocean, and the fidelity of geochemical proxies to reconstruct paleoenvironments. Across the late Campanian and early Maastrichtian I test whether: 1) the WIS had unique δ¹⁸O_VPDB compared to other marine settings, 2) increasing oceanographic restriction changed the stable isotope composition, and 3) biases, e.g., taxonomy or diagenesis, influenced stable isotope compositions. Results indicate distinct δ¹⁸O_VPDB in the WIS compared to other marine settings. δ¹⁸O_VPDB values were stable through time, suggesting insignificant oceanographic restriction and a …

Natural Salinization Of The Jemez River, New Mexico: An Insight From Trace Element Geochemistry, Jon K. Golla

Earth and Planetary Sciences ETDs

The Jemez River, a tributary of the Rio Grande in north-central New Mexico, receives thermal water input from the geofluids of the Valles Caldera, an active, high-temperature, liquid-dominated geothermal system. We focus on a ∼50-km portion of the northern Jemez River. This research extends previous decadal work (Crossey et al., in prep., 2013) on major chemistry in the river by characterizing the response of 16 trace elements to geochemical contributions from geothermal waters (McCauley, Spence, Soda Dam, and Jemez Springs springs and San Ysidro mineral waters), an area with copious hydrothermal degassing (Hummingbird), and two major tributaries (Rio San Antonio …

Early Mississippian Ocean Anoxia Triggering Organic Carbon Burial And Enhancing Late Paleozoic Ice Age Onset: Evidence From Uranium Isotopes Of Marine Limestones, Keyi Cheng

Earth and Planetary Sciences ETDs

The Early Mississippian (Tournaisian) positive δ¹³C excursion (or TICE) is one of the largest recorded in the Phanerozoic and the organic carbon (OC) burial associated with its development is hypothesized to have driven global cooling and increased glaciation. We are testing the hypothesis that expanded ocean euxinia/anoxia drove widespread OC burial and the TICE and we are testing this hypothesis using uranium isotopes (δ²³⁸U) of Lower Mississippian marine limestones from southern Nevada as a global seawater redox proxy.

δ²³⁸U trends record a prominent mid-Tournaisian negative excursion (~0.30‰ magnitude) lasting ~1 My. The lack of …

Melt Inclusions And Their Application - New Perspective On The Subsurface Architecture Of Cerro Negro Volcano, Nicaragua, John M. Hamilton

Earth and Planetary Sciences ETDs

Volatiles are the drivers of volcanic eruptions and monitoring and measurement in quiescent times are the key in determining when unrest within a volcanic system is beginning leading to possible cataclysms. Previous studies have focused on direct measurements from volcanic plumes or fumaroles, however, this study proposes the use of melt inclusions from tephra to determine volatile contents from the 1992 eruption of Cerro Negro Volcano, Nicaragua. The analysis of melt inclusions adds a new technique to the volatile analytical toolbox and can help to determine volatile contents from past eruptions and their subsequent evolution within a volcanic system.

Though …

Northeastern China 4.2ka Database, Louis A. Scuderi, Xiaoping Yamg, Samantha Ascoli, Hongwei Li

Paleoclimate Datasets

The Hunshandake Sandy Lands of northeastern China, currently a semiarid lightly vegetated region, were characterized by perennial lakes and forest stands in the early and middle Holocene. Well-developed dark grassland-type paleosols (mollisols) at the southern edge of the Hunshandake OSL-dated to between 6.93 +0.61 and 4.27 +0.38 ka along with lacustrine sands at higher elevations that date to between 5.7 +0.3 and 5.2 +0.2 ka and thick gray lacustrine sediments suggest a wetter climate. Between 4.2 and 3.8 ka, the region experienced extreme drying that was exacerbated by lake overflow drainage and sapping that depleted the groundwater table. The region …

Mineralogy, Petrology, And Geochemistry Of The Unique Silica-Rich Ungrouped Achondrite Northwest Africa 11575, Mya Ann Habermann

Earth and Planetary Sciences ETDs

We report here on a unique, newly discovered, silica-rich ungrouped achondrite Northwest Africa 11575 (NWA 11575). NWA 11575 is one of four known silica-rich ungrouped achondrites, presenting evidence for igneous processes resulting in evolved compositions early in the history of the solar system. It is unique from the other silica-rich ungrouped achondrites in that it has pyroxene compositional trends matching those of lunar samples and martian meteorites; contains quartz and potassium feldspar; and contains oxygen, hydrogen, and chromium isotopes that are similar to those of LL chondrites. Together, these four silica-rich ungrouped achondrites provide evidence for evolved compositions resulting from …

Insights Into Fluid-Rock Interactions On The Cv3 Carbonaceous Chondrite Asteroid: The Complex Record In The Allende-Like Cv3 Chondrite, Nwa 2364., Jessica Marie Johnson

Earth and Planetary Sciences ETDs

The two subgroups of the CV3 chondrites, oxidized and reduced, contain primitive solar system materials that provide many insights into early solar system processes. Both subgroups record significant evidence of secondary alteration that has modified their primary characteristics. In this work, we have studied the petrography, mineralogy, and oxygen isotopic composition of the NWA 2364 CV3_OxA chondrite and a large lithic inclusion using SEM, electron microprobe, FIB/TEM, and laser fluorination oxygen isotope analyses in order to characterize their alteration histories in detail. The NWA 2364 host and lithic inclusion consist of chondrules, Calcium-Aluminum-rich Inclusions (CAIs), and fine-grained matrix. In …

Widespread, Prolonged Microbial Limestone Deposition And Large, Rapid Sulfur Isotope Excursions: A New Perspective On The Early Triassic From The Western U.S., Brad M. Jeffrey

Earth and Planetary Sciences ETDs

The Early Triassic records a ~5 My period of marine biological recovery following the end-Permian mass extinction (EPME, ~252 My). Global oceans were characterized by warm sea-surface temperatures (SSTs), widespread anoxia, and major perturbations to the carbon cycle, the collective result of repeated massive Siberian Traps eruptions and associated global climate feedbacks. Globally widespread microbial deposits (stromatolites, thrombolites) developed in shallow marine environments. Several marine isotope records (C, O, S, U) indicate repeated, large-magnitude shifts related to paleoceanographic events during the recovery of marine ecosystems following the EPME.

Chapter 1 describes and interprets a widespread (~400 km along strike) Smithian …

Mantle-To-Surface Neotectonic Connections In The San Juan Mountains Documented By 3he/4he, Co2 Flux Meaurements, And Hydrochemical Analysis Of The Geothermal System Near Rico, Colorado, Benjamin D. Holt

Earth and Planetary Sciences ETDs

This project investigates the controls on geothermal fluids and their conduit systems which may account for high mantle helium components of geothermal fluids in intracratonic continental regions. The field laboratory is the western San Juan Mountains of southwestern Colorado where the structural setting and hydrochemistry of carbonic springs suggest potential connections among surface hot springs, fault networks, CO2 degassing, significant geothermal potential, young volcanic and plutonic rocks (< 7 Ma), and low-velocity upper mantle. The Rico Hot Springs have the highest mantle volatile component of any spring in Colorado with air-corrected values of 3He/4He = 5.88 RA indicating 73% mantle helium component. This near-MORB mantle helium value at Rico indicates that volatiles degassing from the mantle must be rapidly transmitted into the groundwater system along deep-seated faults such that accumulation of 4He from radiogenic crust has not swamped mantle-derived primordial 3He. Geologic features that are important for volatile transport and spring chemistry controls include a complex conduit system and fault network involving the Precambrian-cored Rico Dome, ~4 Ma intrusive rocks at Calico Peak and Priest Gulch, and a low-velocity upper mantle. Therefore, Rico and the surrounding region is a natural laboratory for studying geothermal fluid and mantle volatile pathways. Additional noble gas analyses and hydrochemistry data were gathered from regional springs and modeled via chemical geothermometers. New noble gas measurements from this study, paired with literature values, reveal highest air corrected 3He/4He at Rico (4.09-5.88 RA), Dunton (3.11-4.54 RA), Geyser Warm Spring (3.39 RA), and Paradise Warm Spring (2.72 RA). Water volume is dominated by meteoric fluids as shown by stable isotope data but hydrochemistry indicates high TDS, high CO2, and high He come from a geothermal fluid endmember. Variable mixing and water-rock interactions are processes that can explain chemistry variations between spatially proximal springs. CO2 flux measurements (up to 36.2 g/m2/hr) vary across structural features and demonstrate that the faults act as pathways for CO2 flux suggesting ongoing degassing. Overall, we find that local high mantle helium signature is localized directly above regions of lowest upper mantle velocity in the San Juan mantle anomaly and is derived from neotectonic mantle melts in those regions.

Post-Impact Light Vapor Incorporation During Lunar Formation Based On Triple Oxygen Isotopes, Erick J. Cano

Earth and Planetary Sciences ETDs

Initial triple oxygen isotope analyses of lunar samples showed them to be indistinguishable from Earth, which led to numerous papers aimed at explaining the similarities. Recent high-precision analyses suggested either a subtle enrichment in Δ'¹⁷O or virtually no difference between the Earth and Moon. Herein we expand on previous studies by correlating the triple oxygen isotope measurements with different lunar lithologies. We show that these data can be explained by mixing between a light vapor phase, generated during the Giant Impact, and the residual material from the proto-lunar impactor ‘Theia’. There is a general decrease in Δ'^{17 …}

Sedimentology And Stratigraphy Of Core Stl14: An Early Pleistocene-To-Present Paleoclimate Archive From Stoneman Lake, Arizona, Spencer Staley

Earth and Planetary Sciences ETDs

An 80 m lacustrine sediment core (STL14) from Stoneman Lake, Coconino County, Arizona, contains a sedimentary sequence of at least 1.5 million years, chronicling the complete history of basin infill and recording an extensive and high-resolution archive of climatic and hydrologic fluctuations. Lake levels in this small, internally-drained catchment are sensitive to changes in regional hydrologic balance. Consistent groundwater inflow, even during regionally dry episodes in the lake’s history, has prevented complete desiccation of the lake and sustained continuous lacustrine deposition except for one soil horizon. Multiproxy analysis of sedimentological indicators including lithofacies, color, wet bulk density, magnetic susceptibility, preliminary …

Radionuclides In Rainwater And Their Impact On Background Radiation, Damien M. Milazzo

Earth and Planetary Sciences ETDs

Radioactive waste has accrued throughout the continental United States and in the Oceans surrounding the country. Significant quantities of the waste are poorly documented regarding their location and the radioisotopes contained in the waste. Locating the waste is not an easy matter, as its locations are not well documented, and its method of disposal may be covered with plants, soils, and sediments. A common tool used to locate the waste is a gamma spectrometer, which measure the gamma emissions spectrum of radionuclides. The effectiveness of this tool when utilized to locate gamma emitting waste may be reduced due to the …

Natural Trace Element Salinization Of The Jemez River, New Mexico By Geothermal Springs And Major Tributaries, Jon K. Golla, Laura J. Crossey, Abdul-Mehdi S. Ali, Karl E. Karlstrom

Shared Knowledge Conference

The Jemez River (JR), a tributary of the Rio Grande, is in north-central New Mexico within the Jemez Mountains, which houses the active, high-temperature (≤ 300 oC), liquid-dominated Valles Caldera geothermal system (VC). This work focuses on the northern portion of the JR, spanning a reach from the East Fork JR to the town of San Ysidro. Previous decadal work during low-flow or baseflow conditions (~10-20 cfs) has identified and characterized significant major-solute contributions from two outflow expressions of the VC, Soda Dam Springs and Jemez Hot Springs, and two major tributaries, Rio San Antonio and Rio Guadalupe. There is …

Crustal Seismic Anisotropy Of The Ruby Mountains Core Complex And Surrounding Northern Basin And Range, Justin T. Wilgus

Earth and Planetary Sciences ETDs

Metamorphic core complexes (MCC) are distinctive uplifts that expose deeply exhumed and deformed crustal rocks due to localized extensional deformation. Consequently, their detailed structure provide a window into deep crustal mechanics. The North American Cordillera contains numerous MCC, one of which is the Ruby Mountains core complex (RMCC) located in the highly extended northern Basin and Range. To constrain the extent to which anisotropy below the RMCC deviates from the regional Basin and Range average and test the depth dependence of crustal anisotropy we conduct a radial anisotropy investigation below the RMCC and surrounding northern Basin and Range. Data from …

Dense-Array Teleseismic Imaging Of The Southern Albuquerque Basin, Tori S. Finlay

Earth and Planetary Sciences ETDs

The southern Albuquerque basin is a complex area of high extension, multiple orogenies, and ongoing uplift from a midcrustal magma body in which geophysical coverage is sparse. In this thesis, I capitalize on recent innovations in dense-array processing techniques to create virtual source reflection profiles from five teleseismic events during the deployment of the Sevilleta array. The Sevilleta array consisted of ~800 vertical component nodes with ~300 m spacing deployed for 10 days in February of 2015. Virtual source reflection profiles are created by using the free surface of the earth as a virtual seismic source, yielding profiles that mimic …

Magma Mixing At Oldoinyo Lengai: A Mineralogical And Trace Element Analysis Of The 2007-8 Eruption., Nicole Thomas, Tobias P. Fischer Dr., Adrian J. Brearley Dr.

Earth and Planetary Sciences ETDs

Chapter I:

The 2007-8 eruption at Lengai was highly explosive, reaching plinian proportions, and the anhydrous nature of the nephelinite magma at Lengai, does not explain this highly volatile behavior. The increase in volatiles in a low H2O nephelinite magma could occur from decompression melting of magma injection from a deeper source. Two distinct nephelinite compositions were identified in a mineralogical analyses of the ash erupta: a highly evolved nephelinite (OL2), with less than 3% glass from the magma chamber, as indicated by the highly peralkalinic feldspathoid: combeite (Na2Ca2Si3O9), commonly found in Lengai eruptive products (Dawson 1966, 1998), and a …

Investigation Of Molluscan Survivorship Across The Cenomanian-Turonian Boundary Event Using Ecological Niche Modeling, Agathe E. Carrier

Earth and Planetary Sciences ETDs

In the beginning of the Late Cretaceous, the Western Interior Seaway experienced the effects of a global ocean anoxic event (OAE2, or the Bonarelli Event) across the Cenomanian-Turonian (C/T) boundary (~94 Ma). This event resulted in major environmental and biological disturbances creating significant biotic turnover, with recent research suggesting near mass extinction levels in some clades. In this study we utilize a paleobiological application of a modern ecological modeling technique (PaleoENM), to test whether changes in species’ survivorship and distribution patterns across this event relate to changes in their predicted suitable habitat area and abiotic niche dimensions.

Results suggest that …

Birth And Evolution Of The Virgin River: ~1 Km Of Post-5 Ma Uplift Of The Western Colorado Plateau, Cory J. Walk

Earth and Planetary Sciences ETDs

The uplift history of the Colorado Plateau has been debated for over a century with still no unified hypotheses for the cause, timing, and rate of uplift. 40Ar/39Ar dating of semi-continuous basaltic volcanism over the past ~6 Ma within the Virgin River drainage system, southwest Utah and southern Nevada, provides a way to calibrate differential river incision and compare patterns of basaltic migration, mantle velocity structure, channel steepness, lithology, incision history and the birth and evolution of the Virgin River. New detrital sanidine ages constrain the arrival of the Virgin River across the Virgin Mountains to a maximum depositional age …

A Speleothem Record Of Climate Variability In Southwestern North America During Marine Isotope Stage 3, Justin G. Peinado

Earth and Planetary Sciences ETDs

During Marine Isotope Stage 3 (MIS-3) of the last glacial period, there were rapid transitions between warm and cold climates referred to as Dansgaard-Oeschgerr (DO) events. In Southwestern North America (SWNA), two speleothem paleoclimate records document changes in moisture source delivery in response to DO-events during MIS-3, but do not address potential changes in effective moisture for the region. In this study, we introduce a new high-resolution speleothem paleoclimate record from Carlsbad Cavern in the Guadalupe Mountains. The speleothem, sample BC-5, grew continuously from 46-31 kya during the latter half of MIS-3, based on U-Th dating. We also tied stable …

New Geochemical And Isotopic Approaches To Shallow Crust Landform Evolution, David Decker

Earth and Planetary Sciences ETDs

Many researchers have studied the Guadalupe Mountains in detail and starting with King (1948), many of them have speculated about the timing of the uplift of the Guadalupe block. There are several competing hypotheses including Laramide, Basin and Range, and Rio Grande Rifting uplift scenarios. Using uranium-lead dating of scalenohedral spar found in small vug caves throughout the study area, I have dated the episodes of spar formation to two major phases, 36 to 33 Ma and 30 to 27 Ma. These two episodes of spar formation are in good agreement with the time frame of the ignimbrite flare up …