Implications of Thrust and Detachment Faulting for the Structural Geology of the Thermo Hot Springs KGRA, Utah

Implications of Thrust and Detachment Faulting for the Structural Geology of the Thermo Hot Springs KGRA, Utah PDF

Author: Ronald L. Bruhn

Publisher: Utah Geological Survey

Published: 2012

Total Pages: 27

ISBN-13:

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This 23 page report is an initial investigation into the role that low-angle faulting may play in the formation of the Thermo Hot Springs Known Geothermal Area (KGRA), within the Sevier geothermal anomaly of southwestern Utah. The stratigraphy and structures exposed in the southern mineral mountains are used as an analog for studying the subsurface stratigraphy and the detachment fault within the Thermo Hot Springs KGRA.

Geothermochronometric and Stratigraphic Constraints on the Structural and Thermal Evolution of Low-angle Normal Fault Systems

Geothermochronometric and Stratigraphic Constraints on the Structural and Thermal Evolution of Low-angle Normal Fault Systems PDF

Author: Michael Gordon Prior

Publisher:

Published: 2016

Total Pages: 352

ISBN-13:

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The structural evolution of low-angle normal faults (detachment faults) has been an extensively debated topic since the initial recognition of these structures throughout the western U.S. Cordillera and their subsequent identification within extensional provinces across the globe. An improved understanding of how detachment faulting occurred at a variety of scales within continental extensional provinces can help refine structural models of how complex detachment fault systems evolved during progressive extensional deformation. This dissertation addresses the evolution of detachment fault systems using a thermochronometric approach that is coupled to hanging wall stratigraphic data in order to evaluate how the thermal history along detachment faults can evolution inform our understanding of the spatial, geometric, and temporal evolution of these fundamental extensional structures. Evaluating the accuracy of thermochronometrically-derived fault slip rates within large magnitude extensional systems has important implications for slip rate interpretations that can be significantly affected by various structural complexities within the footwall and hanging wall. Three new and distinct case studies are presented in order to understand the temporal and spatial development of low-angle normal fault systems and the resulting metamorphic core complexes that have developed within varied extensional settings. Chapter 1 utilizes (U-Th)/He thermochronometry to understand the significance of small-scale (100's to 1000 m scale) fault blocks within the Bullfrog Hills-Bare Mountain detachment fault system that accommodated transtensional deformation within the southern Walker Lane in southwestern Nevada. The timing of Miocene extensional exhumation was determined in the Bullfrog Hills and Bare Mountain Nevada as well as the effects of several main detachment faults, faults with multiple segments, small scale incisement and excisement detachment faults, and preexisting contractional structures on detachment fault evolution and the interpretation of thermochronometric data from within detachment fault domains. Chapter 2 focused on evaluating the larger scale (km to 10's of km) structural evolution of progressive detachment fault breakaways that developed along the Buckskin-Rawhide detachment fault system during large-magnitude (~40-50 km) Miocene displacement in the lower Colorado River extensional corridor of west-central Arizona. By coupling geothermochronometry data from within the pre-and synextensional sedimentary record preserved within the Lincoln Ranch hanging-wall basin, this study constrains the timing of a tertiary detachment fault breakaway and provides new insights on the timing of subaerial footwall exposure. Chapter 3 applies a high-density sampling strategy along an ~55 km long, slip-parallel transect within the Harquahala Mountains of west-central Arizona, one of the lesser studied examples of a classic Cordilleran metamorphic core complex in the lower Colorado River extensional corridor. Apatite and zircon (U-Th)/He ages throughout the Eagle Eye detachment fault footwall are combined with geothermochronometry data from sedimentary and basaltic hanging-wall rocks in order to determine the inception and duration of extension, fault displacement magnitude, fault slip rates, fault geometry, and timing of subaerial footwall exposure along the Eagle Eye detachment fault. New results are used to evaluate the structural evolution of the regionally correlative lower Colorado River extensional corridor detachment fault system at the southern extent of the Whipple tilt domain, which has important implications for the coherent behavior of regionally extensive continental detachment fault systems.

Thermal and Structural Constraints on the Tectonic Evolution of the Idaho-Wyoming-Utah Thrust Belt

Thermal and Structural Constraints on the Tectonic Evolution of the Idaho-Wyoming-Utah Thrust Belt PDF

Author: Shay M. Chapman

Publisher:

Published: 2013

Total Pages:

ISBN-13:

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The timing of motion on thrust faults in the Idaho-Wyoming-Utah (IWU) thrust belt comes from synorogenic sediments, apatite thermochronology and direct dating of fault rocks coupled with good geometrical constraints of the subsurface structure. The thermal history comes from the analyses of apatite thermochronology, thermal maturation of hydrocarbon source rocks and isotope analysis of fluid inclusions from syntectonic veins. New information from zircon fission track and zircon (U-Th)/He analysis provide constraints on the thermal evolution of the IWU thrust belt over geological time. These analyses demonstrate that the time-temperature pathway of the rocks sampled never reached the required conditions to reset the thermochronometers necessary to provide new timing constraints. Previous thermal constraints for maximum temperatures of IWU thrust belt rocks, place the lower limit at ~110°C and the upper limit at ~328°C. New zircon fission track results suggest an upper limit at ~180°C for million year time scales. ID-TIMS and LA-ICPMS of syntectonic calcite veins suggest that new techniques for dating times of active deformation are viable given that radiogenic isotope concentrations occur at sufficient levels within the vein material. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/151236

Deformation Processes at the Leading Edge of the Sevier Fold and Thrust Belt, Southwest Utah

Deformation Processes at the Leading Edge of the Sevier Fold and Thrust Belt, Southwest Utah PDF

Author: William Joseph Michael Chandonia

Publisher:

Published: 2017

Total Pages: 105

ISBN-13:

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"Deformation processes leading to formation and abandonment of 'triangle zones' along the leading edge of the Sevier fold and thrust belt are investigated near Kanarraville, Utah through construction of a detailed geologic map and cross-section along Spring Creek. Here the eastern limb of the Kanarra fold, a Sevier structure, is well exposed along the Hurricane Cliffs due to uplift and erosion of the footwall of the Hurricane Fault. The east-verging Kanarra fold changes from upright to overturned within Spring Creek. Within the fold limb, parasitic folds, minor thrust faults, and duplex structures result in local tectonic overthickening of units and demonstrate overall east-directed tectonic transport. Results from construction of the geologic cross-section indicate the Kanarra fold is a fault propagation fold forming above a blind thrust ramp - the 'Kanarra thrust'. In addition, the Taylor Creek thrust system, a system of west-directed thrust faults (backthrusts) as previously mapped along strike to the south, is inferred to be folded and overturned within the line of section. A combination of east-directed fault-related folding, the presence of a west-directed major backthrust, and the beginnings of tectonic overthickening, represent basic structural elements of a nascent 'triangle zone'. This triangle zone appears to have been abandoned prior to becoming fully developed. Merging of the Kanarra thrust and the folded Taylor Creek backthrust creates an effective west-dipping ramp that circumvented development of the triangle zone by enabling the Kanarra thrust to continue to cut up section through the Navajo Sandstone (Jn). These results suggest triangle zones may be less likely to fully develop in association with fault-propagation folds in comparison to fault bend folds"--Abstract, page iii.

Styles of Continental Contraction

Styles of Continental Contraction PDF

Author: Stefano Mazzoli

Publisher:

Published: 2006

Total Pages: 188

ISBN-13: 9780813724140

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"This Special Paper includes a selection of material on the various contractional styles and modes of deformation in internal and external zones, and in deep and shallow parts of orogens. The collection of case studies discusses a broad range of processes and phenomena, including thrust tectonic styles (detachment-dominated vs. thick-skinned, or crustal ramp-dominated) in different subduction and collision orogens; modes and timing of thrust-fold and fabric development; the role of tectonic inversion processes and of strain localization vs. distributed deformation; and syn-convergence extensional deformation (and related tectonic exhumation) in orogens. Case studies are from the Zagros, the Apennines, the Appalachians, the Tasmanides of Eastern Australia, and the Moine Thrust Belt. A review of the main subduction- and collision-related orogens of the world is also provided, including the Alps, the Himalayas, the North American Cordillera, the Andes, the Caledonides of Scotland, the Appalachians, the Alice Springs orogeny in Australia, and the Aleutian and Makran accretionary wedges."--Publisher's website.

Along Strike Variability of Thrust-fault Vergence

Along Strike Variability of Thrust-fault Vergence PDF

Author: Scott R. Greenhalgh

Publisher:

Published: 2014

Total Pages: 31

ISBN-13:

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The kinematic evolution and along-strike variation in contractional deformation in overthrust belts are poorly understood, especially in three dimensions. The Sevier-age Cordilleran overthrust belt of southwestern Wyoming, with its abundance of subsurface data, provides an ideal laboratory to study how this deformation varies along the strike of the belt. We have performed a detailed structural interpretation of dual vergent thrusts based on a 3D seismic survey along the Wyoming salient of the Cordilleran overthrust belt (Big Piney-LaBarge field). The complex evolution of the thrust faults that parallel the overthrust belt is demonstrated by the switching of the direction of thrust fault vergence nearly 180° from east to west. The variation in thrust-fault geometry suggests additional complexities in bulk translation, internal strains, and rotations. The thrust zone is composed of two sub-zones, each with an opposing direction of fault vergence, located on the eastern toe of the Hogsback thrust in southwestern Wyoming. The northern west-vergent thrust is a wedge thrust and forms a triangle zone between its upper thrust plane and the lower detachment that has formed in a weak shale layer (the Cretaceous K-Marker bed). Thrusts to the south have a frontal ramp geometry and are consistent with the overall thrust orientation of the Cordilleran overthrust belt located immediately to the west. The two thrust sub-zones are small, relative to the main Hogsback thrust to the west, and adjacent to each other, being separated by a transfer zone measuring in the hundreds of meters along strike. The transfer zone is relatively undisturbed by the faults (at the scale of seismic resolution), but reflections are less coherent with some very small offsets. The thrusts are thin-skinned and located above a shallow-dipping single detachment (or décollement) that is shared by faults in both sub-zones. Lateral growth of the thrust faults link along strike to form an antithetic fault linkage. Structural restoration of thrust faults shows varied amounts of shortening along strike as well as greater shortening in stratigraphic layers of the west-vergent fault to the north. Results from a waveform classification and spectral decomposition attribute analysis support our interpretations of how the variations in the detachment may govern the structural development above it. The kinematic evolution of the dual-verging thrust faults is likely controlled by local pinning within the transfer zone between the thrust-fault sub-zones as well as by changes in the competence of the strata hosting the detachment and in the thickness of the thrust sheet. The analysis and interpretation of dual-vergent thrust structures in the Cordilleran overthrust belt serve as an analog to better understand complex fold, fault, and detachment relations in other thrust belts.

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