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Articles 1 - 11 of 11
Full-Text Articles in Physical Sciences and Mathematics
Record Of Paleofluid Circulation In Faults Revealed By Hematite (U-Th)/He And Apatite Fission-Track Dating: An Example From Gower Peninsula Fault Fissures, Wales, Alexis K. Ault, Max Frenzel, Peter W. Reiners, Nigel H. Woodcock, Stuart N. Thomson
Record Of Paleofluid Circulation In Faults Revealed By Hematite (U-Th)/He And Apatite Fission-Track Dating: An Example From Gower Peninsula Fault Fissures, Wales, Alexis K. Ault, Max Frenzel, Peter W. Reiners, Nigel H. Woodcock, Stuart N. Thomson
Geosciences Faculty Publications
Fault rock low-temperature thermochronometry can inform the timing, temperature, and significance of hydrothermal fluid circulation in fault systems. We demonstrate this with combined hematite (U-Th)/He (He) dating, and sandstone apatite fission-track (AFT) and apatite and zircon (U-Th)/He (He) thermochronometry from fault-related fissures on the Gower Peninsula, Wales. Hematite He dates from 141 ± 5.1 Ma to 120 ± 5.0 Ma overlap with a 131 ± 20 Ma sandstone infill AFT date. Individual zircon He dates are 402–260 Ma, reflecting source material erosion, and imply a maximum Late Permian infill depositional age. Burial history reconstruction reveals modern exposures were not buried …
Foreland-Directedpropagation Of High-Grade Tectonism In The Deep Roots Of A Paleoproterozoic Collisionalorogen, Sw Montana, Usa, Cailey B. Condit, Kevin H. Mahan, Alexis K. Ault, Rebecca M. Flowers
Foreland-Directedpropagation Of High-Grade Tectonism In The Deep Roots Of A Paleoproterozoic Collisionalorogen, Sw Montana, Usa, Cailey B. Condit, Kevin H. Mahan, Alexis K. Ault, Rebecca M. Flowers
Geosciences Faculty Publications
The study of deeply exhumed ancient collisional belts offers important constraints on geologic processes and properties complementary to inaccessible portions of the crustal column in active orogens. The ca. 1.8−1.7 Ga Big Sky orogeny in southwest Montana is a major convergent belt associated with the Proterozoic amalgamation of Laurentia. New structural, petrologic, and geochronologic data from the Northern Madison Range, crossing the NE-SW trend of the belt, record key information about the internal dynamics of the orogen. At least two phases of Big Sky−related deformation are preserved, both nearly coeval with peak metamorphic conditions of ∼0.9−0.8 GPa and >700 °C. …
Linking Hematite (Uth)/He Dating With The Microtextural Record Of Seismicity In The Wasatch Fault Damagezone, Utah, Usa, Alexis K. Ault, Peter W. Reiners, James P. Evans, Stuart N. Thomson
Linking Hematite (Uth)/He Dating With The Microtextural Record Of Seismicity In The Wasatch Fault Damagezone, Utah, Usa, Alexis K. Ault, Peter W. Reiners, James P. Evans, Stuart N. Thomson
Geosciences Faculty Publications
Techniques directly dating fault slip are few, limiting the ability to interpret the rock record of seismicity. Hematite is commonly found in fault zones, amenable to (U-Th)/He dating, and slip surface hematite may be reset by shear heating events and/or recrystallization. Glossy hematite-coated fault surfaces in the Wasatch fault footwall damage zone, Utah (USA), exhibit evidence of hematite cataclasis and preserve Pliocene hematite (U-Th)/He dates. Apatite (U-Th)/He and fission track data from the host gneiss indicate footwall unroofing through ∼2 km by ca. 4.5 Ma. Internally reproducible but disparate hematite (U-Th)/He dates 4.5 Ma and younger from isolated locations on …
Hot Faults:Iridescent Slip Surfaces With Metallic Luster Document High-Temperature Ancientseismicity In The Wasatch Fault Zone, Ut, Usa, James P. Evans, Mitchell R. Prante, Susanne U. Janecke, Alexis K. Ault, Dennis L. Newell
Hot Faults:Iridescent Slip Surfaces With Metallic Luster Document High-Temperature Ancientseismicity In The Wasatch Fault Zone, Ut, Usa, James P. Evans, Mitchell R. Prante, Susanne U. Janecke, Alexis K. Ault, Dennis L. Newell
Geosciences Faculty Publications
We document new geological indicators of ancient seismicity in the form of highly reflective, iridescent, hematite-coated fault surfaces. Small faults that cut the Paleoproterozoic Farmington Canyon Complex in the footwall damage zone of the Brigham City segment of the Wasatch fault (Utah, USA) are smooth to striated surfaces, tens of square centimeters to 30 m2 in area. The dull-rusty to high-metallic luster and moderate- to high-gloss surfaces exhibit multicolored elliptical iridescent patches ∼0.5–3 cm across. Preexisting hematite crystals were deformed during slip on 1–200-mm-thick slip surfaces. Textural observations, X-ray diffraction, X-ray photoelectron spectroscopy, electron backscattered diffraction analysis, surface metrology, and …
Phanerozoic Surface History Of The Slavecraton, Alexis K. Ault, Rebecca M. Flowers, Samuel A. Bowring
Phanerozoic Surface History Of The Slavecraton, Alexis K. Ault, Rebecca M. Flowers, Samuel A. Bowring
Geosciences Faculty Publications
New apatite (U-Th)/He (AHe) thermochronometry data and key geologic constraints from Slave craton kimberlites are used to develop a model for the Phanerozoic burial, unroofing, and hypsometric history of the northwestern Canadian shield. AHe dates range from 210 ± 13 to 382 ± 79 Ma, are older in the eastern Slave craton and decrease westward, and resolve the spatial extent, thickness, and history of now-denuded sedimentary units. Results indicate Paleozoic heating to temperatures ≥85–90°C, suggesting regional burial beneath ≥2.8 km of strata while the region was at sea level, followed by the westward migration of unroofing across the craton. This …
Microtextural Constraints On The Interplay Between Fluidrockreactions And Deformation, Alexis K. Ault, Jane Selverstone
Microtextural Constraints On The Interplay Between Fluidrockreactions And Deformation, Alexis K. Ault, Jane Selverstone
Geosciences Faculty Publications
Schists from two mylonitic localities in the footwall of a low-angle normal fault in the eastern Alps record different degrees of embrittlement during exhumation, depending on the extent to which fluid–rock reactions proceeded. At one site, graphitic schists preserve textural evidence for two metamorphic reactions that modified XCO2XCO2 and/or fluid volume: (1) reaction between graphite and aqueous fluid that increased XCO2XCO2 without changing the molar amount of fluid, and (2) replacement of titanite by rutile, calcite, and quartz. The latter reaction involved net consumption of increasingly CO2-rich fluid. Areas where the first reaction proceeded are associated with abundant Mode I …
A Faculty Workshop On Student Assessment, Iris M. Totten, Kirsten Nicolaysen, Sheryl Hodge, Mary S. Hubbard
A Faculty Workshop On Student Assessment, Iris M. Totten, Kirsten Nicolaysen, Sheryl Hodge, Mary S. Hubbard
Geosciences Faculty Publications
A faculty workshop was conducted that showcased assessment activities that could be incorporated into undergraduate and graduate geology courses. Fourteen different types of student assessment were presented. Workshop participants were asked to respond to questions about their familiarity and use of each type before and immediately following the workshop. In addition, they were asked to indicate how likely they would be to incorporate each type of assessment in their student grading practices in the future. Results suggest relatively high familiarity and use of the more traditional types of assessments (e.g., instructor- and commercially-produced pencil and paper exams, group projects, and …
Paleomagnetic Dating Of Fault Slip In The Southern Rocky Mountains, Usa, And Itsimportance To An Integrated Laramide Foreland Strain Field, T. F. Wawrzyniec, Alexis K. Ault, J. W. Geissman, E. A. Erslev, S. D. Fankhauser
Paleomagnetic Dating Of Fault Slip In The Southern Rocky Mountains, Usa, And Itsimportance To An Integrated Laramide Foreland Strain Field, T. F. Wawrzyniec, Alexis K. Ault, J. W. Geissman, E. A. Erslev, S. D. Fankhauser
Geosciences Faculty Publications
The Laramide orogen of the U.S. Cordillera formed in the latest Cretaceous, and deformation lasted into the earliest Oligocene. Along and proximal to the eastern and northern margins of the Colorado Plateau, deformation associated with this event mainly took place along reactivated structures. Related tectonic models invoke some role for the plateau either as a stress guide transmitting compression to the foreland or as a freely rotating microplate. Models dominated by northward displacements of the Colorado Plateau also require covariance between timing and magnitude of dextral strike-slip deformation in the eastern domain and thrust deformation in the northern domain. Here …
Structural Evolution And Vorticity Of Flow During Extrusion And Exhumation Of The Greater Himalayan Slab, Mount Everest Massif, Tibet/Nepal: Implications For Orogen-Scale Flow Partitioning, M. J. Jessup, R. D. Law, M. P. Searle, Mary S. Hubbard
Structural Evolution And Vorticity Of Flow During Extrusion And Exhumation Of The Greater Himalayan Slab, Mount Everest Massif, Tibet/Nepal: Implications For Orogen-Scale Flow Partitioning, M. J. Jessup, R. D. Law, M. P. Searle, Mary S. Hubbard
Geosciences Faculty Publications
The Greater Himalayan Slab (GHS) is composed of a north-dipping anatectic core, bounded above by the South Tibetan detachment system (STDS_ and below by the Main Central thrust zone (MCTZ). Assuming simultaneous movement on the MCTZ and STDS, the GHS can be modelled as a southward-extruding wedge or channel. New insights into extrusion-related flow with the GHS emerge from detailed kinematic and vorticity analyses in the Everest region. At the highest structural levels, mean kinematic vorticity number (Wm) estimates of 0.74-0.91 (c. 45-28% pure shear) were obtained from sheared Tethyan limestone and marble from the Yellow Band on Mount Everest. …
Great Plains Workshop Held To Prepare For Usarray Deployment, Mary S. Hubbard, S. S. Gao, K. H. Liu, K. E. Nicolaysen, C. G. Oviatt
Great Plains Workshop Held To Prepare For Usarray Deployment, Mary S. Hubbard, S. S. Gao, K. H. Liu, K. E. Nicolaysen, C. G. Oviatt
Geosciences Faculty Publications
Relative to most parts of North America, the Great Plains region, which is bordered by the Rocky Mountain Front on the west and the Mississippi River on the east, has been understudied in terms of the structure, formation, and evolution of the underlying crust, mantle, and core. The anticipated arrival of the USArray portable seismic stations, which will cover the entire United States regardless of surface geology and tectonic activities, and the deployment of the accompanying flexible array stations and the permanent seismic stations in this area, will fill this gap and address numerous problems related to the structure and …
High Plains To Rio Grand Rift: Late Cenozoic Evolution Of Central Colorado, E. M. Leonard, Mary S. Hubbard, S. A. Kelley, E. Evanoff, C. S. Siddoway, C. G. Oviatt, M. Heizler, M. Timmons
High Plains To Rio Grand Rift: Late Cenozoic Evolution Of Central Colorado, E. M. Leonard, Mary S. Hubbard, S. A. Kelley, E. Evanoff, C. S. Siddoway, C. G. Oviatt, M. Heizler, M. Timmons
Geosciences Faculty Publications
No abstract provided.