Uplift of the Teton Range is primarily controlled by displacement across the range-front Teton normal fault. The Tetons comprise the footwall block while the hanging wall encompasses Jackson Hole valley and a portion of the Snake River. Relative to the rest of the Rocky Mountains, the Tetons experienced the majority of uplift very recently, substantiating the need for a detailed investigation integrating structural analysis and bedrock thermochronometry. New low-temperature cooling ages are documented in three vertical transects across the Teton Range and at low elevations parallel to the Teton fault. Samples adjacent to the Teton fault are consistently young (~9 Ma) and represent a minimum estimate for the onset of Teton fault-related uplift. Modeling of time-temperature histories supports a ~9-11 Ma onset of rapid uplift, indicating that the Teton fault likely originated as a Basin and Range-type structure. A maximum throw of ~8 km occurs proximal to the Grand Teton, while the average throw for the entire ~100 km along-strike fault length is ~3.3 km. Thus, the geometry of the Teton fault is comparable to traditional scaling relationships dictating a correlation between fault length and displacement. Inversion of the typical (U-Th)/He (AHe) and fission track (AFT) relationship in a few of the Teton Range samples is a result of intense zoning, primarily in apatite from Precambrian layered gneisses. Nonetheless, both the AHe and AFT ages consistently indicate slight differential uplift of the Tetons between the Late Oligocene and Middle Miocene. HeFTy models indicate that doming of the Precambrian-Paleozoic unconformity occurred prior to ~50 Ma. However, by ~15 Ma, rapid cooling of the Mount Moran section essentially "flattened" the unconformity. Thus, the modern domed shape is a result of displacement across the Teton fault, allowing the unconformity to be used as a proxy for fault deformation. Moreover, reconstruction of the unconformity and volume calculations produced an average depth to incision of ~0.3 km and a long-term erosion rate of 0.18 mm/yr. Compared to the long-term uplift rate of 0.22 mm/yr, this provides a quantitative explanation for the modern Teton topography. / Master of Science

The Pacific-North America plate boundary in central and southern California has a complex tectonic history, and constraints are poor for inception of an extensional fault system linked to the southern San Andreas fault, a major tectonic element of this plate boundary. Furthermore, decades of research has shown relationships between climate, tectonics, and surface processes in most orogens across the globe (e.g. Alps, Himalaya, Andes, Alaska Ranges), however the role climate plays in modulating erosion and mass fluxes from extensional mountains blocks to sedimentary basins over 104-5 yr timescales is debated. In the eastern California-Walker Lane shear zone, exposures of sedimentary basin fill allow inversion of erosion- and sediment-flux rates from a linked catchment-fan system within an extensional block. In this dissertation, I present two field and geo-thermochronology based studies that explore research topics related by common tectonic setting and geography within the Pacific-North America plate boundary. First I present new low-temperature thermochronology (apatite U-Th-Sm/He) and thermal history modeling to document the kinematic evolution of the Santa Rosa mountains, where the cooling history constrains initiation timing of the west Salton Detachment fault, and the southern San Andreas fault system. I document an age of ca. 8 Ma for exhumation initiation of the Santa Rosa block, from paleodepths of ~4.5–3 km, at vertical rates of ~0.15–0.36 mm/yr, accelerating to ~1.3 km/Ma since ca. 1.2 Ma during initiation of the San Jacinto fault zone. Second, I present a new data set of cosmogenic radionuclide-derived burial ages and paleodenudation rates (26Al/10Be) from the Pleasant Canyon complex in the Panamint Range, and show that denudation rate and sediment flux have varied by a factor of ~2x since the middle Pleistocene. I conclude high frequency variability is driven by climate change, and not tectonic perturbations, as supported by published constraints for exhumation timing. The middle Pleistocene transition from 40–100 ka periodicity may drive the observed changes, a tentative conclusion that makes testable predictions for stratigraphic records of past climate in other locations. Empirical evidence for climate-modulated erosion and sediment flux provides valuable constraints for numerical models of landscape evolution and sedimentary basin architecture. / Ph. D.

Exhumed faults record the temperatures produced by earthquakes. We show that transient elevated fault surface temperatures preserved in the rock record are quantifiable through microtextural analysis, fault-rock thermochronometry, and thermomechanical modeling. We apply this approach to a network of mirrored, minor, hematite-coated fault surfaces in the exhumed, seismogenic Wasatch fault zone, UT, USA. Polygonal and lobate hematite crystal morphologies, coupled with hematite (U-Th)/He data patterns from these surfaces and host rock apatite (U-Th)The data, are best explained by friction-generated heat at slip interface geometric asperities. These observations inform thermomechanical simulations of flash heating at frictional contacts and resulting fractional He loss over generated fault surface time temperature histories. Temperatures of >similar to 700-1200 degrees C, depending on asperity size, are sufficient to induce 85-100% He loss from hematite within 200 pm of the fault surface. Spatially-isolated, high temperature microtextures imply spatially -variable heat generation and decay. Our results reveal that flash heating of asperities and associated frictional weakening likely promote small earthquakes (M-w approximate to -3 to 3) on Wasatch hematite fault mirrors. We suggest that similar thermal processes and resultant dynamic weakening may facilitate larger earthquakes. (C) 2017 Elsevier B.V. All rights reserved.

No description available.

No description available.

Long, linear, high-relief escarpments mark many of the world's passive margins. These Great Escarpments have been interpreted to be the result of isostatic flexure, parallel slope retreat, and divide migration which accompanies rifting. It is unclear whether all these escarpments share this origin. Also uncertain is whether these features are formed via stable, steady-state processes or by climatic shifts or tectonic rejuvenation. The Blue Ridge Escarpment, eastern North America's great escarpment, is no different. A number of hypotheses attempt to explain the Blue Ridge Escarpment. These include lithologic variation between Blue Ridge and Piedmont rocks, the distance to ultimate base level, as well as, escarpment retreat resulting from post/syn-rift warping or faulting. We approach this problem from two directions. The first involves topographic comparisons and geologic observations to recognize and track divide migration. The second approach uses U-Th/He thermochronometry along two scarp-normal transects. Topographic analysis used data extracted from DEMs to compare three zones - the Upland, the Piedmont and the scarp zone itself. Parameters such as relief, drainage density, hypsometry, and slope are often used as proxies for relative erosion rates and the degree of maturity of a landscape. Results from these analyses indicate that the Upland and Piedmont zones are distinct landscapes, sharing very few topographic similarities, yet neither appears significantly more erodible than the other. Examination of parameters in the proximity of the escarpment point toward more rapid erosion here. Field evidence of this rapid scarp erosion (and thus divide migration) lies in the presence of beheaded stream channels, cobble roundness, and clast provenance. U-Th/He thermochronometry is a low temperature technique that allows us to calculate when rock cooled below 60-70C. Temperature is used as a proxy for depth, from which we can extract an exhumation rate. This method allows us to further test scarp genesis hypotheses. Preliminary results show older ages (~160) from the Upland surface than on the Piedmont lowland (~100 Ma). This confirms that the Piedmont surface is distinct from the Upland and demonstrates that it has experienced greater erosion. There is also some indication that ages "jump" across the Bowens Creek/Brevard fault system. Lastly, the ages appear to become younger approaching the escarpment which is indicative of scarp migration. As these results are preliminary, more data is required to prove or disprove these conclusions. / Master of Science

Globally, deformation along obliquely converging plate margins produce a wide variety of complex fault patterns, including crustal pop-ups, fault duplex structures, restraining bends, and flower structures. Depending on the plate velocity, plate obliquity, crustal rheology, length-scale, and climate, the evolution of faulting into translational and vertical strain can range in complexity and fault slip partitioning (i.e. vertical vs. horizontal strain). In this dissertation I studied two restraining bends to understand how these factors influence patterns of deformation along two major plate boundaries: The North American-Caribbean and the North AmericanPacific plate boundaries. First, I estimate the exhumation and cooling history along the Blue Mountains restraining bend in Jamaica using multiple thermochronometers. Three phases of cooling have occurred within Jamaica: 1) initial rock crystallization and rapid emplacement of plutons from 75-68 Ma, 2) slow cooling from 68-20 Ma, and 3) two-stage exhumation from 20 Ma – Present. During the most recent phase of Jamaica’s cooling history, two stages of exhumation have been identified at 0.2 mm/yr (20 – 5 Ma) and ~1 mm/yr (5 Ma – Present). Given the plate velocity to exhumation rate ratio during the most recent phase, we suggest that the climate of Jamaica increases the erosivity of the Blue Mountain suite, whereby the Blue Mountains may be in an erosional stead-state. Second, I studied the long-term evolution of a restraining bend at San Gorgonio Pass in southern California by relating fault kinematics within the uplifted San Bernardino Mountains to the nearby Eastern California shear zone. Using highresolution topography (i.e. UAV and lidar surveys), I studied the plausibility of faulting along two potentially nascent faults within the San Bernardino Mountains, namely the Lone Valley and Lake Peak faults. We found that while both faults display evidence for Quaternary faulting, deciphering true fault slip rates was challenging due to the erosive nature of the mountainous landscape. Coupled with evidence of Quaternary faulting along other faults within the San Bernardino Mountains, we suggest a western migration of the Eastern California shear zone. / PHD

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. / text

The kinematics and architecture of orogenic systems may be heavily influenced by climate, but little research has focused on the long-term effects of glacial erosion on orogenesis. Low-temperature thermochronometry and subsidiary structural, earthquake relocation, and offshore seismic reflection data from the St. Elias orogen are the basis for a new architectural model and demonstrate an association between glacial denudation and orogenic evolution. These data show that exhumation and deformation within the St. Elias orogen are focused across a thin-skinned fold and thrust belt on the windward flank, whereas the leeward flank functions as a deformational backstop. A previously unrecognized structure beneath the Bagley ice field separates these domains with south-side-up motion. This structure is interpreted to be a backthrust, making the orogen doubly-vergent. Suggestive of accelerated fault motion in response to climate change, bedrock cooling rates within the hanging wall of the backthrust and across the entire subaerial wedge accelerated ~ten-fold coeval with the onset of intense glacial conditions. Within the orogenic wedge, the zone of highest Quaternary exhumation (5 km/myr (±25%)) is focused around a narrow zone where the glacial equilibrium line altitude (ELA) intersects mean topography. This zone of rapid exhumation, not present prior to the onset of intense glacial conditions, cuts across the structural trend of the orogen and is more narrowly focused than the zone of orographic precipitation. Augmented glacial erosion around glacial ELA also coincided with a regional shift in deformation away from prominent forethrusts including the North American-Yakutat terrane suture (Chugach St. Elias fault) and the seaward deformation front (Pamplona zone). Accelerated denudation across the subaerial wedge thus appears to have forced the redistribution of strain along the backthrust and a series of forethrusts that lie beneath the zone of highest glacial flux, which in turn are systematically truncated by the backthrust. In a cause and effect response, the expansion of glaciers therefore appears to have resulted in an orogen scale structural reorganization and a narrowing of the orogenic wedge to preserve topographic slope. The focusing of long-term erosion around glacial ELA and the structural response of the orogenic wedge to Cenozoic climate change have not previously been observed in a real-world orogenic system and imply a high degree of coupling between climate and tectonics in this glacially-dominated orogen. / Ph. D.

Le Tibet est le plateau le plus élevé et le plus étendu au monde. La formation de ce plateau, en arrière de l’Himalaya, résulte d’interactions complexes entre facteurs tectoniques et climatiques, ainsi que de la morphologie antérieure au soulèvement. Afin d’évaluer l’influence relative de ces différents facteurs, cette thèse s’appuie sur l’étude de l’évolution du relief des bordures du plateau en couplant analyse géomorphologique, étude de la sédimentation syn-formation du plateau et reconstitution de l’exhumation à partir de la thermochronologie de basse température.Cette approche a permis de mettre en évidence que le plateau du Tibet était déjà haut, aussi bien sur ses bordures est que ouest dès 35 Ma, soit seulement 20 Ma après la collision Inde-Asie. Il apparait donc que le plateau se serait soulevé soit en un bloc, soit de façon précoce par ses marges Ouest et Est, plutôt qu’en se propageant du sud vers le nord et vers l’est comme proposé par de nombreux modèles.Dans l’Ouest Tibet, l’existence d’un réseau de drainage anciennement connecté avec celui de l’Indus, a permis le développement précoce d’un relief significatif (supérieur à 1000 m) avant 35 Ma lors de la surrection du plateau. Ce relief est ensuite préservé dans un contexte d’érosion très faible (quelques dizaine de mètres par million d’années) associé à une évacuation des produits d’érosion vers le bassin de l’Indus. Cette connexion avec l’Indus est ensuite coupée probablement suite aux mouvements de la faille du Karakorum.A l’Est, la formation du relief est probablement plus ancienne que dans l’Ouest Tibet, car vers 35 Ma cette région, bien que déjà surélevée, est caractérisée par l’existence d’un vaste réseau fluviatile en tresse, impliquant une faible pente, ainsi qu’un relief local soumis à des précipitations plus au nord. La création du relief actuel, marqué par des rivières fortement encaissées, est probablement liée à l’évolution de la mousson sud-est asiatique ainsi qu’au fonctionnement de la faille du Fleuve rouge. / Tibet is the widest and highest plateau on Earth. Tectonics, climate evolution and ante-surrection geomorphology are the main factors controlling the plateau formation. In order to assess the relative influence of these factors, we study the relief evolution on the plateau edges using geomorphic analysis, sedimentology and exhumation rates based on low-temperature thermochronometry.The results show that the western and eastern plateau edges were already at high elevation at ca 35 Ma, only 20 Ma after the India-Asia collision. This favors an “en bloc” uplift model for the plateau.In western Tibet, the hydrographic network was connected to the Indus river, allowing the early development of a >1000 m amplitude relief, probably before 35 Ma. The relief was preserved due to low erosion conditions. Western Tibet was then isolated from the Indus drainage network due to the Karakorum fault slip.The relief formation in Eastern Tibet is older than in western Tibet: at ca 35 Ma, in the Jianchuan area (northern Yunnan), which was already at high elevation, was a large braided river system. This implies a moderate regional slope. It also implies a local relief further north and significant precipitations.