Geology Commons^™

Fault Structure, Deformation Mechanisms, And Why Fault Zones Matter To Society, Elizabeth S. Petrie, David A. Ferrill, Kelly K. Bradbury, James P. Evans

Geosciences Faculty Publications

Faults are widespread geologic structures that form in sediment and all rock types, occur in all tectonic regimes, and can be a blessing or a curse to society. Faults and fault zones act as conduits for underground movement of water and as plumbing systems for aquifers and springs essential for human habitation in many semi-arid and arid regions worldwide. Faults also provide pathways for natural oil and gas migration and high-permeability zones in hydrocarbon reservoirs, as well as barriers contributing to trapping and reservoir compartmentalization. By enhancing permeability in many geothermal energy systems, faults can be essential for fluid circulation …

Earth Orbital Rhythms Links Timing Of Deccan Trap Volcanism Phases And Global Climate Change, Thomas Westerhold, Edoardo Dallanave, Donald Penman, Blair Schoene, Ursula Röhl, Nikolaus Gussone, Junichiro Kuroda

Geosciences Faculty Publications

At the end of the Cretaceous, the massive Deccan trap (DT) volcanic eruptions are regarded as the primary driver of global climate deterioration. Accurate age models are key to unravel the sequence of events related to DT volcanism onset and effects on the global climate system. We establish a direct geochemical link between DT volcanism as recorded in marine osmium isotopic data and global climate change documented in benthic foraminifera carbon and oxygen isotope records. Based on our state-of-the-art astronomically calibrated age model, two major shifts in marine ¹⁸⁷Os/¹⁸⁸Os at 66.49 and 66.28 million years ago are …

Karst Hydrologic Memory Supplements Streamflow During Dry Periods In Snow-Dominated, Mountainous Watersheds, Hyrum Tennant, Bethany T. Neilson, Devon Hill, Dennis L. Newell, James P. Evans, Seohye Choi, James P. Mcnamara, Nathaniel Ashmead, Tianfang Xu

Geosciences Faculty Publications

Analysis of PRISM and SNOTEL station data paired with USGS streamflow gage data in the western United States shows that, in snow-dominated mountainous watersheds, streamflow regimes differ between watersheds with karst geology and their non-karst neighbours. These carbonate aquifers exhibit a spectrum of flow paths encompassing karst conduits, including large fractures or voids that transmit water readily to springs and other surface waters, and matrix flow paths through soils, highly fractured bedrock, or porous media bedrock grains. A well-connected karst aquifer will discharge a large portion of its accumulated precipitation to surface water via springs and other groundwater flow paths …

Signatures Of Fluid-Rock Interactions In Shallow Parts Of The San Andreas And San Gabriel Faults, Southern California, James P. Evans, Kaitlyn Crouch, Caroline Studnicky, Sharon Bone, Nicholas Edwards, Samuel M. Webb

Geosciences Faculty Publications

We examine deformed crystalline bedrock in the upper parts of the active San Andreas and ancient San Gabriel Faults, southern California, to 1) determine the nature and origin of micro-scale composition and geochemistry of fault-related rocks, 2) constrain the extent of fluid-rock interactions, and 3) determine the interactions between alteration, mineralization, and deformation. We used drill cores from a 470 m long inclined borehole through the steep-dipping San Gabriel Fault and from seven inclined northeast-plunging boreholes across the San Andreas Fault zone to 150 m deep to show that narrow fault cores 10 cm to 5 m wide lie within …

Sensitivity Of Ocean Circulation To Warming During The Early Eocene Greenhouse, Sandra Kirtland Turner, Andy Ridgwell, Allison L. Keller, Maximilian Vahlenkamp, Adam K. Aleksinski, Philip F. Sexton, Donald E. Penman, Pincelli M. Hull, Richard D. Norris

Geosciences Faculty Publications

Multiple abrupt warming events ("hyperthermals") punctuated the Early Eocene and were associated with deep-sea temperature increases of 2 to 4 °C, seafloor carbonate dissolution, and negative carbon isotope (δ¹³C) excursions. Whether hyperthermals were associated with changes in the global ocean overturning circulation is important for understanding their driving mechanisms and feedbacks and for gaining insight into the circulation's sensitivity to climatic warming. Here, we present high-resolution benthic foraminiferal stable isotope records (δ¹³C and δ¹⁸O) throughout the Early Eocene Climate Optimum (~53.26 to 49.14 Ma) from the deep equatorial and North Atlantic. Combined with existing …

Magmatic Conditions Aiding Synconvergent Extension Above The Peruvian Flat Slab, Tyler A. Grambling, Micah J. Jessup, Dennis L. Newell, Nadine L. Grambling, Coleman D. Hiett

Geosciences Faculty Publications

The Cordillera Blanca and Cordillera Huayhuash contain some of the highest topography in the Andes and provide insight into tectonomagmatic processes associated with the onset of flat-slab subduction. These adjacent ranges shared a similar history of deformation and exhumation prior to the late Miocene, when synconvergent extension began in the Cordillera Blanca. Magmatism in the Cordillera Huayhuash has been inferred as coeval with magmatism in the Cordillera Blanca. Yet, extension, which has been correlated with magmatic heat flow, is limited to the Cordillera Blanca. New zircon U-Pb dates and trace and rare earth element concentrations from the Cordillera Blanca batholith …

Implications And Hydrographs For Two Pre-Bonneville Pluvial Lakes And Double Geosols From 14 Osl-Irsl Ages In Cache Valley, Ne Bonneville Basin, Robert Q. Oaks Jr., Susanne Jänecke, Tammy Rittenour, Thad Erickson, Michelle Nelson

Geosciences Faculty Publications

In the northeastern Great Basin, USA, thirteen new optically stimulated luminescence (OSL) ages and one infrared stimulated luminescence (IRSL) age show that two deep pluvial lakes preceded the Bonneville lake cycle in Cache Valley during marine oxygen-isotope stages (MIS) 6 (213-191 ka) and 4 (56-71 ka), respectively. Our new data define quantitative hydrographs of the Little Valley and Cutler Dam lake cycles in both Cache Valley and the main Bonneville basin. In western Cache Valley, excavation of a faulted, east-plunging spit has sequentially exposed these deposits and overlying MIS 3 Fielding humid-over-arid double geosols that end westward at a strand …

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 …

Geothermal Play Fairway Analysis, Part 1: Example From The Snake River Plain, Idaho, John W. Shervais, Jacob Deangelo, Jonathan M. Glen, Dennis L. Nielson, Sabodh Garg, Patrick Dobson, Erika Gasperikova, Eric Sonnenthal, Lee M. Liberty, Dennis L. Newell, Drew Siler, James P. Evans

Geosciences Faculty Publications

The Snake River Plain (SRP) volcanic province overlies the track of the Yellowstone hotspot, a thermal anomaly that extends deep into the mantle. Most of the area is underlain by a basaltic volcanic province that overlies a mid-crustal intrusive complex, which in turn provides the long-term heat flux needed to sustain geothermal systems. Previous studies have identified several known geothermal resource areas within the SRP. For the geothermal study presented herein, our goals were to: (1) adapt the methodology of Play Fairway Analysis (PFA) for geothermal exploration to create a formal basis for its application to geothermal systems, (2) assemble …

Shallow Composition And Structure Of The Upper Part Of The Exhumed San Gabriel Fault, California: Implications For Fault Processes, Kaitlyn Crouch, James P. Evans

Geosciences Faculty Publications

Quantifying shallow fault zone structure and characteristics is critical for accurately modeling the complex mechanical behavior of earthquakes as energy moves within faults from depth. We examine macro- to microstructures, mineralogy, and properties from drill core analyses of fault-related rocks in the steeply plunging ALT-B2 geotechnical borehole (total depth of 493 m) across the San Gabriel Fault zone, California. We use macroscopic drill core and outcrop-sample analyses, core-based damage estimates, optical microscopy, and X-ray diffraction mineralogic analyses to determine the fault zone structure, deformation mechanisms, and alteration patterns of exhumed deformed rocks formed in a section of the fault that …

Regolith And Host Rock Influences On Co2 Leakage: Active Source Seismic Profiling Across The Little Grand Wash Fault, Utah, Lee M. Liberty, Jonathan Yelton, Elin Skurtveit, Alvar Braathen, Ivar Midtkandal, James P. Evans

Geosciences Faculty Publications

Understanding carbon dioxide (CO₂) reservoir to surface migration is crucial to successful carbon capture and sequestration approaches; especially fault/reservoir interactions under injection pressure. Through seismic imaging, we explore regolith and shallow stratigraphy across the Little Grand Wash fault. The presence of natural CO₂ seeps, travertine and tufa deposits confirm modern and ancient fault-controlled CO₂ leakage. We consider this an analogue for a long-failed sequestration site. We estimate bulk porosity and fracture density for host rock, regolith, and fault zone from petrophysical relationships. When combined with existing geochemical and geological data, we characterize a 60 m wide …

The Mechanics Of Initiation And Development Of Thrust Faults And Thrust Ramps, Sarah S. Wigginton, Elizabeth S. Petrie, James P. Evans

Geosciences Faculty Publications

This study integrates the results of numerical modeling analyses based on outcrop studies and structural kinematic restorations to evaluate the mechanics of thrust fault initiation and development in mechanically layered sedimentary rocks. A field-based reconstruction of a mesoscopic thrust fault at Ketobe Knob in central Utah provides evidence of thrust ramp nucleation in competent units, and fault propagation upward and downward into weaker units at both fault tips. We investigate the effects of mechanical stratigraphy on stress heterogeneity, rupture direction, fold formation, and fault geometry motivated by the geometry of the Ketobe Knob thrust fault in central Utah; the finite …

The Economic Contribution Of Utah's Energy And Mining Industries, Tanner J. Mccarty, Zuyi Wang, Man-Keun Kim, James Evans

Geosciences Faculty Publications

Utah’s abundant energy and mineral resources are used to heat homes, drive industry, and keep the lights on. Effectively managing these energy and mineral resources and their associated supply chains requires knowledge of their economic value and how they currently contribute to Utah’s economy. This report calculates the total economic contribution of Utah’s energy and mining industries for 2019 and 2020. Each industry makes substantial contributions to Utah’s gross domestic product, employment, and tax base. Table 1 displays each industry’s economic contribution to Utah’s economy.

Collectively, these industries contributed over 10% to Utah's total Gross Domestic Product (GDP), supported over …

Redefining The Age Of The Lower Colorado River, Southwestern United States: Forum Reply, R. S. Crow, J. Schwing, K. E. Karlstrom, M. Heizler, P. A. Pearthree, P. K. House, S. Dulin, Susanne U. Jänecke, M. Stelten, L. J. Crossey

Geosciences Faculty Publications

No abstract provided.

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.

Redefining The Age Of The Lower Colorado River, Southwestern United States, R. S. Crow, J. Schwing, K. E. Karlstrom, M. Heizler, P. A. Pearthree, P. K. House, S. Dulin, Susanne U. Jänecke, M. Stelten, L. J. Crossey

Geosciences Faculty Publications

Sanidine dating and magnetostratigraphy constrain the timing of integration of the lower Colorado River (southwestern United States and northern Mexico) with the evolving Gulf of California. The Colorado River arrived at Cottonwood valley (Nevada and Arizona) after 5.24 Ma (during or after the Thvera subchron). The river reached the proto–Gulf of California once between 4.80 and 4.63 Ma (during the C3n.2r subchron), not at 5.3 Ma and 5.0 Ma as previously proposed. Duplication of section across newly identified strands of the Earthquake Valley fault zone (California) probably explains the discrepancy. The data also imply the start of focused plate motion …

Lidar Reveals >150 Km Of New Holocene Ruptures And Faults In Northeast Basin-And-Range Province, N Utah And Se Idaho, Susanne U. Jänecke, Nathaniel R. Ellis, Robert Q. Oaks Jr., Carly M. Lee, James P. Evans

Geosciences Faculty Publications

Cache Valley is a N-trending graben in N-central Utah and SE Idaho. The East Cache fault zone (ECFZ) appears to be the master fault due to the high mountain in its footwall, its inversion of the Providence thrust fault, and the deep sedimentary basin in its hanging wall. However, trenching in 1990s showed more Holocene ruptures within the West Cache fault zone (WCFZ, 4) than ECFZ (1). We use LIDAR data to document post-Bonneville paleo-earthquakes along known and newly documented normal faults of the WCFZ. New faults with scarps occur throughout the ~105 km long and 5-10 km wide WCFZ. …

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 …

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 …

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 …