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. / Vertical motions along faults produce uplift of mountain blocks, often with steep high topography, which is accompanied by subsidence of adjacent sedimentary basins. Understanding cycles of fault initiation, uplift, and eventual degradation of mountainous fault blocks through erosion is a fundamental goal of the geoscience community, as is inversion of records of past environmental conditions preserved in sedimentary basins. The Pacific-North America plate boundary in California, USA, is composed of several major fault systems that provide an opportunity to study vertical uplift and erosion of mountains, and the sedimentary basins that preserve records of changes in erosion rates through time. In this context, I present a dissertation composed of two original research articles. In Chapter Two, I use thermochronometry in the Santa Rosa Mountains, Coachella Valley, to constrain initiation timing and vertical uplift rates for an extensional fault system called the west Salton detachment fault (WSDF). Localization of the plate boundary in Coachella Valley led to initiation of the WSDF and the southern San Andreas fault system at ca. 8 Myr ago, timing which may reflect a global plate-tectonic driver. Vertical uplift of the Santa Rosa Mountains via the WSDF was moderate during the time between ca. 8–1.2 Myr, then vertical uplift increased four-fold during the initiation of a new strike-slip fault within the southern San Andreas system. In Chapter Two, I use rare isotopes called cosmogenic radionuclides in sediment from basin stratigraphy to constrain the magnitude and variability of erosion in the Pleasant Canyon catchment of the Panamint Mountains since ca. 1.5 Myr ago. The mean erosion rate for Pleasant Canyon is 36 ± 8 mm/kyr, and individual samples vary by up to 2x, indicating erosion rates were not constant through time. The timescales of variability, and evidence from basin stratigraphy suggest that glacial-interglacial climate change produced the observed changes in erosion in this mountain block. This conclusion makes testable predictions for other unglaciated catchments in extensional fault blocks, while evidence of climate-induced changes in sediment fluxes from mountains to basins has potential implications to recovering information about past climate change from stratigraphy.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/77695 |
| Date | 19 May 2017 |
| Creators | Mason, Cody Curtis |
| Contributors | Geosciences, Spotila, James A., Romans, Brian W., Gill, Benjamin C., Law, Richard D. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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