Browsing by Subject "Thermochronometry"
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Item Geothermochronometric and stratigraphic constraints on the structural and thermal evolution of low-angle normal fault systems : case studies from southwestern Nevada and west-central Arizona(2016-12) Prior, Michael Gordon; Stockli, Daniel F.; Behr, Whitney M; Ketcham, Richard A; Spencer, Jon E; Wells, Michael LThe 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.Item Investigating the effect of high-angle normal faulting on unroofing histories of the Santa Catalina-Rincon and Harcuvar metamorphic core complexes, using apatite fission-track and apatite and zircon (U-Th)/He thermochronometry(2013-12) Sanguinito, Sean Michael; Ketcham, Richard Alan, 1965-The formation and evolution of metamorphic core complexes has been widely studied using low temperature thermochronometry methods. Interpretation of these data has historically occurred through the lens of the traditional slip rate method which provides a singular rate that unroofing occurs at temporally as well as spatially, and assumes unroofing is dominated by motion on a single master detachment fault. Recently, several new studies have utilized (U-Th)/He ages with a higher spatial density and greater nominal precision to suggest a late-stage rapid increase in the rate of unroofing. This analysis is based on the traditional slip rate method interpretation of broad regions of core complexes that display little to no change in age along the slip direction. An alternative interpretation is presented that instead of a change in slip rate, there may have been a change in the style of unroofing, specifically caused by the transfer of displacement from low-angle detachment faulting to high-angle normal faults. Apatite fission-track (AFT), and apatite and zircon (U-Th)/He (AHe and ZHe) analyses were applied to samples from the Santa Catalina-Rincon (n=8 AHe, and n=9 ZHe) and Harcuvar (n=12 AFT, n=16 AHe, and n=17 ZHe) metamorphic core complexes in an attempt to resolve the possible thermal effects of high-angle normal faulting on core complex formation. Samples from the Harcuvars were taken along a transect parallel to slip direction with some samples specifically targeting high-angle normal fault locations. The AFT data collected here has the advantage of improved analysis and modeling techniques. Also, more than an order of magnitude more data were collected and analyzed than any previous studies within the Harcuvars. The AFT ages include a trend from ~22 Ma in the southwest to ~14 Ma in the northeast and provide a traditional slip rate of 7.1 mm/yr, similar to previous work. However, two major high-angle, detachment-parallel normal faults were identified, and hanging-wall samples are ~3 m.y. older than the footwalls, indicating high-angle normal faults rearranged the surface expression of the distribution of thermochronometer ages to some extent. AHe ages range from 8.1 Ma to 18.4 Ma but in general decrease with increasing distance in the slip direction. ZHe ages generally range between 13.6 Ma and 17.4 Ma. A series of unexpectedly young AFT ages (10-11 Ma), given by three complete samples and distinct population modes in others, suggest that some parts of the range underwent a later-stage unroofing event possibly caused by high-angle faulting. Confined fission-track length distributions were measured for Harcuvar samples and modeled using the modeling software HeFTy to infer thermal histories and calculate local cooling rates. These imply a component of steady cooling in some parts of the range, evidence of a different departure from a single-detachment dominated model.Item Thermo-tectonic record of hyperextension, structural inversion, and foreland basin evolution of the eastern and central Pyrenees(2019-09-17) Odlum, Margaret Larkin; Stockli, Daniel F.; Fildani, Andrea; Horton, Brian K.; Ketcham , Richard; van der Beek, PeterDirect constraints on processes associated with rifting and mantle exhumation are necessary to understand the thermal and structural evolution of continental rift systems, and the role of pre-existing crustal architecture on orogenesis and foreland basin development. This work constrains the Early Cretaceous hyperextension history along the Iberia-European margin and how rift inheritance affected the structural and foreland basin evolution of the Late Cretaceous-Oligocene Pyrenean orogeny. Chapters 1 and 2 aim to understand the thermal and structural evolution of the North Pyrenean basement massifs during Early Cretaceous rifting and hyperextension using multi-mineral thermochronometry. These chapters integrate zircon, apatite, and rutile U‐Pb ages from the Agly and Saint Barthélémy massifs that provide new constraints to understand the decoupled versus coupled extensional evolution, exhumation timing of the middle‐lower crust, and the age of juxtaposition of the upper crust granitic pluton with middle crustal gneisses, and fluid-rock interactions along a detachment fault. Novel method integration and approaches using apatite were developed and implemented in these chapters to best interpret the apatite U-Pb ages to gain the most insight into thermal, structural, and fault zone processes in the Early Cretaceous rift system’s distal margin. Chapters 3 and 4 use the sedimentary record in the pro-wedge foreland basins of inversion and orogenesis to understand the provenance, hinterland evolution, and the role of extensional inheritance on the orogenic phase of the margin. This work shows that the eastern Pyrenean foreland basin deposits were sourced from Corsica-Sardinia and the Catalan Coastal Ranges during the Late Cretaceous-Paleocene, and the Pyrenees beginning in the Eocene. Detrital mineral trends across the basins suggest that the pro-wedge foreland basin developed and remained segmented throughout the Late Cretaceous-Oligocene. The results from these chapters highlight the dominant control of inherited structures and rift basins on controlling the sediment provenance and foreland basin architecture in inverted rift systems. The dissertation aims to show the structural evolution of the Early Cretaceous rifting and thermal and structural processes that were operating within the continental crust at the rift margin, and how this inherited rift architecture affected the orogenic evolution and foreland basin development during the Pyrenean orogeny. These results add to our overall understanding of the structural and thermal evolution during rifting and continental break-up and role of rift inheritance in the evolution of superimposed orogenic systems and their associated foreland basins