Physical Sciences and Mathematics Commons^™

Cambrian Trilobites From The Nounan Dolomite And Lower St. Charles Formation (Upper Marjuman To Lower Sunwaptan; Miaolingian To Furongian Series), Smithfield Canyon, Northern Utah, Frederick A. Sundberg, Hannah R. Cothren, Carol M. Dehler

Geosciences Faculty Publications

The trilobite faunas that occur with the Steptoean Positive Isotope Carbon Excursion (SPICE) at Smithfield Canyon, Utah, have been reported, but not illustrated. Given the importance of the SPICE at this section for international correlations, the trilobites from new collections from the upper Nounan Dolomite to lower St. Charles Formation at Smithfield Canyon are reported herein and integrated with the previously reported taxa. Trilobite assemblages indicate that the upper Cedaria to the Ellipsocephaloides biozones (Miaolingian Series, Guzhangian Stage to Furongian Series, Jiangshanian Stage) are present stratigraphically below or above the SPICE.

Some of the taxa reported herein may represent new …

An Actionable Anti-Racism Plan For Geoscience Organizations, Hendratta N. Ali Ph.D., Sarah L. Sheffield, Jennifer E. Bauer, Rocío P. Caballero-Gill, Nicole M. Gasparini, Julie Libarkin, Kalynda K. Gonzales, Jane Willenbring, Erika Amir-Lin, Julia Cisneros, Dipa Desai, Maitri Erwin, Elisabeth Gallant, Kiara Jeannelle Gomez, Benjamin A. Keisling, Robert Mahon, Erika Marín-Spiotta, Leiaka Welcome, Blair Schneider

Geosciences Faculty Publications

Geoscience organizations shape the discipline. They influence attitudes and expectations, set standards, and provide benefits to their members. Today, racism and discrimination limit the participation of, and promote hostility towards, members of minoritized groups within these critical geoscience spaces. This is particularly harmful for Black, Indigenous, and other people of color in geoscience and is further exacerbated along other axes of marginalization, including disability status and gender identity. Here we present a twenty-point anti-racism plan that organizations can implement to build an inclusive, equitable and accessible geoscience community. Enacting it will combat racism, discrimination, and the harassment of all members.

Fire Suppression Impacts On Fuels And Fire Intensity In The Western U.S.: Insights From Archaeological Luminescence Dating In Northern New Mexico, Christopher I. Roos, Tammy M. Rittenour, Thomas W. Swetnam, Rachel A. Loehman, Kacy L. Hollenback, Matthew J. Liebmann, Dana Drake Rosenstein

Geosciences Faculty Publications

Here, we show that the last century of fire suppression in the western U.S. has resulted in fire intensities that are unique over more than 900 years of record in ponderosa pine forests (Pinus ponderosa). Specifically, we use the heat-sensitive luminescence signal of archaeological ceramics and tree-ring fire histories to show that a recent fire during mild weather conditions was more intense than anything experienced in centuries of frequent wildfires. We support this with a particularly robust set of optically stimulated luminescence measurements on pottery from an archaeological site in northern New Mexico. The heating effects of an October 2012 …

Structural Controls On Crustal Fluid Circulation And Hot Spring Geochemistry Above A Flat‐Slab Subduction Zone, Peru, Brandt E. Scott, Dennis L. Newell, M. J. Jessup, T. A. Grambling, C. A. Shaw

Geosciences Faculty Publications

Hot spring geochemistry from the Cordillera Blanca and Cordillera Huayhuash, Peru, reveal the influence of crustal‐scale structures on geothermal fluid circulation in an amagmatic region located above a flat‐slab subduction zone. To test the influence of contrasting modes of faulting in these regions, springs were targeted along the Cordillera Blanca detachment fault, within its hanging wall, in the footwall of the detachment, and in the Cordillera Huayhuash. Hot springs along the Cordillera Blanca detachment fault zone are associated with recent extension and normal faulting, and those in its footwall and the Cordillera Huayhuash are located in the Marañon fold and …

Hematite (U-Th)/He Thermochronometry Detects Asperity Flash Heating During Laboratory Earthquakes, Melissa S. Chapot, Alexis K. Ault, Greg Hirth, Robert G. Mcdermott

Geosciences Faculty Publications

Evidence for coseismic temperature rise that induces dynamic weakening is challenging to directly observe and quantify in natural and experimental fault rocks. Hematite (U-Th)/He (hematite He) thermochronometry may serve as a fault-slip thermometer, sensitive to transient high temperatures associated with earthquakes. We test this hypothesis with hematite deformation experiments at seismic slip rates, using a rotary-shear geometry with an annular ring of silicon carbide (SiC) sliding against a specular hematite slab. Hematite is characterized before and after sliding via textural and hematite He analyses to quantify He loss over variable experimental conditions. Experiments yield slip surfaces localized in an ∼5–30-µm-thick …

Crustal Composition And Moho Variations Of The Central And Eastern United States: Improving Resolutionand Geologic Interpretation Of Earthscope Usarray Seismic Images Using Gravity, H. L. Zhang, D. Ravat, Anthony R. Lowry

Geosciences Faculty Publications

EarthScope's USArray Transportable Array has shortcomings for the purpose of interpreting geologic features of wavelengths less than the Transportable Array station spacing, but these can be overcome by using higher spatial resolution gravity data. In this study, we exploit USArray receiver functions to reduce nonuniqueness in the interpretation of gravity anomalies. We model gravity anomalies from previously derived density variations of sedimentary basins, crustal V_p/V_s variation, Moho variation, and upper mantle density variation derived from body wave imaging informed by surface wave tomography to estimate V_p/V_s. Although average densities and density contrasts for …

What Can We Learn From X‐Ray Fluorescence Core Scanning Data? A Paleomonsoon Case Study, Daniel Gebregiorgis, Liviu Giosan, Edmund Hathorne, Pallavi Anand, Katrina Nilsson-Kerr, Anna Plaß, Andreas Lückge, Steven Clemens, Martin Frank

Geosciences Faculty Publications

X‐ray fluorescence (XRF) core scanning of marine and lake sediments has been extensively used to study changes in past environmental and climatic processes over a range of timescales. The interpretation of XRF‐derived element ratios in paleoclimatic and paleoceanographic studies primarily considers differences in the relative abundances of particular elements. Here we present new XRF core scanning data from two long sediment cores in the Andaman Sea in the northern Indian Ocean and show that sea level related processes influence terrigenous inputs based proxies such as Ti/Ca, Fe/Ca, and elemental concentrations of the transition metals (e.g., Mn). Zr/Rb ratios are mainly …

Mariana Serpentinite Mud Volcanism Exhumes Subducted Seamount Materials: Implications For The Origin Of Life., Patricia Fryer, C. Geoffrey Wheat, Trevor Williams, Christopher Kelley, Kevin Johnson, Jeffrey Ryan, Walter Kurz, John W. Shervais, Elmar Albers, Barbara Bekins, Baptiste Debret, Jianghong Deng, Yanhui Dong, Philip Eickenbusch, Emanuelle Frery, Yuji Ichiyama, Richard Kevorkian, Et Al.

Geosciences Faculty Publications

The subduction of seamounts and ridge features at convergent plate boundaries plays an important role in the deformation of the overriding plate and influences geochemical cycling and associated biological processes. Active serpentinization of forearc mantle and serpentinite mud volcanism on the Mariana forearc (between the trench and active volcanic arc) provides windows on subduction processes.  Here, we present (1) the first observation of an extensive exposure of an undeformed Cretaceous seamount currently being subducted at the Mariana Trench inner slope; (2) vertical deformation of the forearc region related to subduction of Pacific Plate seamounts and thickened crust; (3) recovered Ocean …

Oxygen Isotopes In Authigenic Clay Minerals: Toward Building A Reliable Salinity Proxy, Daniel Gebregiorgis, Daniel M. Deocampo, Fred Longstaffe, A. Simpson, Gail M. Ashley, Emily Beverly, Jeremy Delaney, Javier Cuadros

Geosciences Faculty Publications

Most clay minerals in sedimentary environments have traditionally been considered to be of detrital origin, but under certain conditions, authigenic clay minerals can form at low temperature through the transformation of precursor clays or as direct precipitates from lake water. Such clay minerals can hold important information about the prevailing climatic conditions during the time of deposition. We present the first quantitative reconstruction of salinity in paleolake Olduvai based on the oxygen‐isotope composition of authigenic clay minerals. We provide a framework illustrating that the isotopic signature of authigenic lacustrine clay minerals is related to the isotopic composition of paleo‐waters, and …

Sampling Methods For Luminescence Dating Of Subsurface Deposits From Cores, Michelle Nelson, Tammy M. Rittenour, Harriet Cornachione

Geosciences Faculty Publications

Study of subsurface deposits often requires coring or drilling to obtain samples for sedimentologic and geochemical analysis. Geochronology is a critical piece of information for stratigraphic correlation and rate calculations. Increasingly, luminescence dating is applied to sediment cores to obtain depositional ages. This paper provides examples and discussion of guidelines for sampling sediment core for luminescence dating. Preferred protocols are dependent on the extraction method, sedimentology, core integrity, and storage conditions. The methods discussed include subsampling of sediment in opaque core-liners, cores without liners, previously open (split) cores, bucket auger samples, and cuttings, under red lighting conditions. Two important factors …

Postmagmatic Tectonic Evolution Of The Outer Izu‐Bonin Forearc Revealed By Sediment Basin Structure And Vein Microstructure Analysis: Implications For A 15 Ma Hiatus Between Pacific Plate Subduction Initiation And Forearc Extension, Walter Kurz, Peter Micheuz, Gail L. Christeson, M. Reagan, John W. Shervais, Steffen Kutterolf, A. Robertson, Kurt Krenn, K. Michibayashi, D. Quandt

Geosciences Faculty Publications

International Ocean Discovery Program Expedition 352 recovered sedimentary‐volcaniclastic successions and extensional structures (faults and extensional veins) that allow the reconstruction of the Izu‐Bonin forearc tectonic evolution using a combination of shipboard core data, seismic reflection images, and calcite vein microstructure analysis. The oldest recorded biostratigraphic ages within fault‐bounded sedimentary basins (Late Eocene to Early Oligocene) imply a ~15 Ma hiatus between the formation of the igneous basement (52 to 50 Ma) and the onset of sedimentation. At the upslope sites (U1439 and U1442) extension led to the formation of asymmetric basins reflecting regional stretch of ~16–19% at strain rates of …

Nanoscale Evidence For Temperature-Induced Transient Rheology And Postseismic Fault Healing, Alexis K. Ault, Jordan L. Jensen, Robert G. Mcdermott, F.-A. Shen, B. R. Van Devener

Geosciences Faculty Publications

Friction-generated heat and the subsequent thermal evolution control fault material properties and thus strength during the earthquake cycle. We document evidence for transient, nanoscale fault rheology on a high-gloss, light-reflective hematite fault mirror (FM). The FM cuts specularite with minor quartz from the Pleistocene El Laco Fe-ore deposit, northern Chile. Scanning and transmission electron microscopy data reveal that the FM volume comprises a2+ suboxides. Sub–5-nm-thick silica films encase hematite grains and connect to amorphous interstitial silica. Observations imply that coseismic shear heating (temperature >1000 °C) generated transiently amorphous, intermixed but immiscible, and rheologically weak Fe-oxide and silica. Hematite regrowth in …

Evaluation Of The Geothermal Potential Of The Western Snake River Plain Based On A Deep Corehole On The Mountain Home Afb Near Mountain Home, Idaho, Thomas E. Lachmar, Thomas G. Freeman, James Andrew Kessler, Joseph F. Batir, James P. Evans, Dennis L. Nielson, John W. Shervais, Xiwei Chen, Douglas R. Schmitt, David D. Blackwell

Geosciences Faculty Publications

A geothermal exploration corehole was drilled to a total depth of 1821.5 m on the Mountain Home Air Force Base near Mountain Home, Idaho. The corehole was used to collect an unusually large amount of data, including uniaxial compressive stress (UCS) experiments on core samples, to evaluate the geothermal potential of the western Snake River Plain. In addition, unlike many exploration holes in this region, a fluid entry was encountered at 1745.3 m and flowed artesian to the surface. A maximum temperature of 149.4 °C was calculated for the entry. A temperature log run on the corehole from 3 to …

Innovations In (U–Th)/He, Fission Track, And Trapped Charge Thermochronometry With Applications To Earthquakes, Weathering, Surface‐Mantle Connections, And The Growth And Decay Of Mountains, Alexis K. Ault, Cécile Gautheron, Georgina E. King

Geosciences Faculty Publications

A transformative advance in Earth science is the development of low‐temperature thermochronometry to date Earth surface processes or quantify the thermal evolution of rocks through time. Grand challenges and new directions in low‐temperature thermochronometry involve pushing the boundaries of these techniques to decipher thermal histories operative over seconds to hundreds of millions of years, in recent or deep geologic time and from the perspective of atoms to mountain belts. Here we highlight innovation in bedrock and detrital fission track, (U–Th)/He, and trapped charge thermochronometry, as well as thermal history modeling that enable fresh perspectives on Earth science problems. These developments …

Thermotectonic History Of The Kluane Ranges And Evolution Of The Eastern Denali Fault Zone In Southwestern Yukon, Canada, Robert G. Mcdermott, Alexis K. Ault, Jonathan Saul Caine, Stuart N. Thomson

Geosciences Faculty Publications

Exhumation and landscape evolution along strike‐slip fault systems reflect tectonic processes that accommodate and partition deformation in orogenic settings. We present 17 new apatite (U‐Th)/He (He), zircon He, apatite fission‐track (FT), and zircon FT dates from the eastern Denali fault zone (EDFZ) that bounds the Kluane Ranges in Yukon, Canada. The dates elucidate patterns of deformation along the EDFZ. Mean apatite He, apatite FT, zircon He, and zircon FT sample dates range within ~26–4, ~110–12, ~94–28, and ~137–83 Ma, respectively. A new zircon U‐Pb date of 113.9 ± 1.7 Ma (2σ) complements existing geochronology and aids in interpretation …

Deformation Conditions During Syn-Convergent Extension Along The Cordillera Blanca Shear Zone, Peru, Cameron A. Hughes, Micah J. Jessup, Colin A. Shaw, Dennis L. Newell

Geosciences Faculty Publications

Strain localization across the brittle-ductile transition is a fundamental process in accommodating tectonic movement in the mid-crust. The tectonically active Cordillera Blanca shear zone (CBSZ), a ∼200-km-long normal-sense shear zone situated within the footwall of a discrete syn-convergent extensional fault in the Peruvian Andes, is an excellent field laboratory to explore this transition. Field and microscopic observations indicate consistent top-down-to-the-southwest sense of shear and a sequence of tectonites ranging from undeformed granodiorite through mylonite and ultimately fault breccia along the detachment.

Using microstructural analysis, two-feldspar and Ti-in-quartz (TitaniQ) thermometry, recrystallized quartz paleopiezometry, and analysis of quartz crystallographic preferred orientations, we …

Volcanic Stratigraphy And Age Model Of The Kimama Deep Borehole (Project Hotspot): Evidence For 5.8 Million Years Of Continuous Basalt Volcanism, Central Snake River Plain, Idaho, Katherine E. Potter, Duane E. Champion, Robert A. Duncan, John W. Shervais

Geosciences Faculty Publications

The Snake River Plain of central Idaho represents the world’s best example of a mantle hotspot track impinging upon continental crust and provides a record of bimodal volcanism extending over 12 Ma to the present. Project Hotspot recovered almost 2 km of continuous drill core from the Kimama borehole, located in central Idaho on the axial volcanic zone. The Kimama drill core represents the most complete record of mafic volcanism along the Yellowstone–Snake River Plain hotspot track.

A total of 432 basalt flow units, representing 183 basalt flows, 78 basalt flow groups, and 34 super groups, along with 42 sediment …

Pace And Process Of Active Folding And Fluvial Incision Across The Kantishna Hills Anticline, Central Alaska, A. M. Bender, R. O. Lease, P. J. Haeussler, Tammy M. Rittenour, L. B. Corbett, P. R. Bierman, M. W. Caffee

Geosciences Faculty Publications

Rates of northern Alaska Range thrust system deformation are poorly constrained. Shortening at the system's west end is focused on the Kantishna Hills anticline. Where the McKinley River cuts across the anticline, the landscape records both Late Pleistocene deformation and climatic change. New optically stimulated luminescence and cosmogenic 10Be depth profile dates of three McKinley River terrace levels (~22, ~18, and ~14–9 ka) match independently determined ages of local glacial maxima, consistent with climate‐driven terrace formation. Terrace ages quantify rates of differential bedrock incision, uplift, and shortening based on fault depth inferred from microseismicity. Differential rock uplift and incision (≤1.4 …

Magmatic Response To Subduction Initiation: Part 1. Fore-Arc Basalts Of The Izu-Bonin Arc From Iodp Expedition 352, John W. Shervais, Mark Reagan, Emily A. Haugen, Renat R. Almeev, Julian A. Pearce, Julie Prytulak, Jeffrey G. Ryan, Scott A. Whattam, Marguerite Godard, Timothy Chapman, Hongyan Li, Walter Kurz, Wendy R. Nelson, Daniel Heaton, Maria Kirchenbaur, Kenji Shimizu, Tetsuya Sakuyama, Yibing Li, Scott K. Vetter

Geosciences Faculty Publications

The Izu-Bonin-Mariana (IBM) fore arc preserves igneous rock assemblages that formed during subduction initiation circa 52 Ma. International Ocean Discovery Program (IODP) Expedition 352 cored four sites in the fore arc near the Ogasawara Plateau in order to document the magmatic response to subduction initiation and the physical, petrologic, and chemical stratigraphy of a nascent subduction zone. Two of these sites (U1440 and U1441) are underlain by fore-arc basalt (FAB). FABs have mid-ocean ridge basalt (MORB)-like compositions, however, FAB are consistently lower in the high-field strength elements (TiO2, P2O5, Zr) and Ni compared to MORB, with Na2O at the low …

The Ages2 (Awards For Geochronology Student Research 2) Program: Supporting Community Geochronology Needs And Interdisciplinary Science, Rebecca M. Flowers, J. Ramón Arrowsmith, Vicki Mcconnell, James R. Metcalf, Tammy M. Rittenour, Blair Schoene

Geosciences Faculty Publications

Geochronology is essential in the geosciences. It is used to resolve the durations and rates of earth processes, as well as test causative relationships among events. Such data are increasingly required to conduct cutting-edge, transformative, earth-science research. The growing need for geochronology is accompanied by strong demand to enhance the ability of labs to meet this pressure and to increase community awareness of how these data are produced and interpreted. For example, a 2015 National Science Foundation (NSF) report on opportunities and challenges for U.S. geochronology research noted: "While there has never been a time when users have had greater …

The Role Of Fault-Zone Architectural Elements On Pore Pressure Propagation And Induced Seismicity, John P. Ortiz, Mark A. Person, Peter S. Mozley, James P. Evans, Susan L. Bilek

Geosciences Faculty Publications

We used hydrogeologic models to assess how fault‐zone properties promote or inhibit the downward propagation of fluid overpressures from a basal reservoir injection well (150 m from fault zone, Q = 5000 m3/day) into the underlying crystalline basement rocks. We varied the permeability of the fault‐zone architectural components and a crystalline basement weathered layer as part of a numerical sensitivity study. Realistic conduit‐barrier style fault zones effectively transmit elevated pore pressures associated with 4 years of continuous injection to depths of approximately 2.5 km within the crystalline basement while compartmentalizing fluid flow within the injection reservoir. The presence of a …

Alaskan Marine Transgressions Record Out-Of-Phase Arctic Ocean Glaciation During The Last Interglacial, Louise Farquharson, Daniel Mann, Tammy M. Rittenour, Pamela Groves, Guido Grosse, Benjamin Jones

Geosciences Faculty Publications

Ongoing climate change focuses attention on the Arctic cryosphere’s responses to past and future climate states. Although it is now recognized the Arctic Ocean Basin was covered by ice sheets and their associated floating ice shelves several times during the Late Pleistocene, the timing and extent of these polar ice sheets remain uncertain. Here we relate a relict barrier-island system on the Beaufort Sea coast of northern Alaska to the isostatic effects of a previously unrecognized ice shelf grounded on the adjacent continental shelf. A new suite of optically stimulated luminescence dates show that this barrier system formed during one …

Durmid Ladder Structure And Its Implications For The Nucleation Sites Of The Next M >7.5 Earthquake On The San Andreas Fault Or Brawley Seismic Zone In Southern California, Susanne U. Jänecke, Daniel K. Markowski, James P. Evans, Patricia Persaud, Miles Kenney

Geosciences Faculty Publications

We integrated new geologic data with published geophysical data to document that the southernmost San Andreas fault zone, onshore of the Salton Sea, southern California, is a transpressional, 1–4-km-wide ladder-like structure. This newly identified Durmid ladder structure is a voluminous right-reverse fault zone that broadens across Durmid Hill around rotating domains of regularly spaced, left- and right- lateral cross faults. The active East Shoreline fault zone of the San Andreas fault forms the southwest margin of this fault zone, and it is generally parallel to the main strand of the San Andreas fault zone for >30 km, deforms Pliocene to …

Heat/Mortality Sensitivities In Los Angeles During Winter: A Unique Phenomenon In The United States, Adam J. Kalkstein, Laurence S. Kalkstein, Jennifer K. Vanos, David P. Eisenman, Paul Grady Dixon Ph.D.

Geosciences Faculty Publications

Background: Extreme heat is often associated with elevated levels of human mortality, particularly across the mid-latitudes. Los Angeles, CA exhibits a unique, highly variable winter climate, with brief periods of intense heat caused by downsloping winds commonly known as Santa Ana winds. The goal is to determine if Los Angeles County is susceptible to heat-related mortality during the winter season. This is the first study to specifically evaluate heat-related mortality during the winter for a U.S. city. Methods: Utilizing the Spatial Synoptic Classification system in Los Angeles County from 1979 through 2010, we first relate daily human mortality to synoptic …

Experimental Study Of Gravitational Mixing Of Supercritical Co2, Dennis L. Newell, J. William Carey, Scott N. Backhaus, Peter Lichtner

Geosciences Faculty Publications

CO₂ injection into saline aquifers for sequestration will initially result in buoyant supercritical (sc)CO₂ trapped beneath the caprock seal. During this period, there is risk of CO₂ migration out of the reservoir along wellbore defects or fracture zones. Dissolution of the scCO₂ plume into brine results in solubility trapping and reduces this risk, but based on diffusion alone, this mechanism could take thousands of years. Gravitational (density-induced) mixing of CO₂-saturated brine is shown to significantly accelerate this process in computational studies, but few experimental efforts have confirmed the phenomenon. Here, constant-pressure, 3-dimensional bench-scale experiments …

Evidence For Cyclical Fractional Crystallization, Recharge, And Assimilation In Basalts Of The Kimama Drill Core, Central Snake River Plain, Idaho: 5.5-Million-Years Of Petrogenesis In A Mid-Crustal Sill Complex, Katherine E. Potter, John W. Shervais, Eric H. Christiansen, Scott K. Vetter

Geosciences Faculty Publications

Basalts erupted in the Snake River Plain of central Idaho and sampled in the Kimama drill core link eruptive processes to the construction of mafic intrusions over 5.5 Ma. Cyclic variations in basalt composition reveal temporal chemical heterogeneity related to fractional crystallization and the assimilation of previously-intruded mafic sills. A range of compositional types are identified within 1,912 m of continuous drill core: Snake River olivine tholeiite (SROT), low K SROT, high Fe-Ti, and evolved and high K-Fe lavas similar to those erupted at Craters of the Moon National Monument. Detailed lithologic and geophysical logs document 432 flow units comprising …

Effects Of Carbon Dioxide And Clouds On Temperature, Hyunsoo Lee, Hee Woon Cheong

Geosciences Faculty Publications

With the observed rise in temperature, many researchers have tried to identify the causes of such climate change to help mitigate its effects. The objective of this study is to determine whether, under the same carbon dioxide (CO 2 ) concentrations, CO 2 with lower cloud coverage would raise the temperature at a greater rate than CO 2 with higher cloud coverage. The hypothesis was tested through big data analysis and modeling. The relationships between the temperature and the CO 2 emissions, the temperature and the cloud coverage, and the CO 2 emissions and the cloud coverage were identified using …

Effect Of An 860-M Thick, Cold, Freshwater Aquifer On Geothermal Potential Along The Axis Of The Eastern Snake River Plain, Idaho, Thomas E. Lachmar, Thomas G. Freeman, Christopher J. Sant, Jeffrey R. Walker, Joseph F. Batir, John W. Shervais, James P. Evans, Dennis L. Nielson, David D. Blackwell

Geosciences Faculty Publications

A 1912-m exploration corehole was drilled along the axis of the eastern Snake River Plain, Idaho. Two temperature logs run on the corehole display an obvious inflection point at about 960 m. Such behavior is indicative of downward fluid flow in the wellbore. The geothermal gradient above 935 m is 4.5 °C/km, while the gradient is 72–75 °C/km from 980 to 1440 m. Projecting the higher gradients upward to where they intersect the lower gradient on the temperature logs places the bottom of the cold, freshwater Snake River Plain aquifer, which suppresses the geothermal gradient at this location, at least …

Usarray Imaging Of Continental Crust In The Conterminous United States, Xiaofei Ma, Anthony R. Lowry

Geosciences Faculty Publications

The thickness and bulk composition of continental crust provide important constraints on the evolution and dynamics of continents. Crustal mineralogy and thickness both may influence gravity anomalies, topographic elevation, and lithospheric strength, but prior to the inception of EarthScope’s USArray, seismic measurements of crustal thickness and properties useful for inferring lithology are sparse. Here we improve upon a previously published methodology for joint inversion of Bouguer gravity anomalies and seismic receiver functions by using parameter space stacking of cross correlations of modeled synthetic and observed receiver functions instead of standard H-κ amplitude stacking. The new method is applied to estimation …

High-Pressure Granulite Facies Overprinting During The Exhumation Of Eclogites In The Bangong-Nujiang Suture Zone, Central Tibet: Link To Flat-Slab Subduction, Xiu Zheng Zhang, Qiang Wang, Yong Sheng Dong, Chunfu Zhang, Qing Yun Li, Xiao Ping Xia, Wang Xu

Geosciences Faculty Publications

The geometric transformation of a descending plate, such as from steep to flat subduction in response to a change from normal to overthickened oceanic crust during subduction, is a common and important geological process at modern or fossil convergent margins. However, the links between this process and the metamorphic evolution of the exhumation of oceanic (ultra)high-pressure eclogites are poorly understood. Here we report detailed petrological, mineralogical, phase equilibria, and secondary ion mass spectrometry zircon and rutile U-Pb age data for the Dong Co eclogites at the western segment of the Bangong-Nujiang suture zone, central Tibet. Our data reveal that the …