Tectonics as recorded by thermochronometry, deformed datums, and submarine landscapes in western North America

Abstract

Since the Mesozoic, the west coast of North America has experienced near continuous right-lateral shear. Over this time, a series of exotic crustal terranes accreted to and translated along the expanding westward edge of the continent. In this dissertation, I use low-temperature thermochronomtery, geologic map interpretation, geophysics, and geomorphic analysis, to explore the effects of this tectonic regime on deformation and landscape development. First, I determine the geologic history of the Wallowa and Bald Mountain Batholiths of Northeast Oregon to better understand whether the mountains they underlie formed in response to Miocene lithospheric delamination. I find that both batholiths were exhumed to the near surface during early to mid-Cretaceous terrane amalgamation and accretion. Multiple subsequent phases of localized uplift in the Cenozoic led to the mountainous landscape seen today. Building on this research, I use the distribution of the Miocene Columbia River Flood Basalt, in conjunction with crustal thickness estimates, to investigate the crustal structure responsible for Miocene to present strain partitioning in the Pacific Northwest, USA. From this analysis, I find that CRB deformation is correlated with crustal thickness, with less deformed regions having thinner crust. Turning to the north, I use low-temperature thermochronometry to estimate the timing of exhumation of the island archipelago Haida Gwaii. I determine that exhumation began with the passage of the Yakutat terrane, not as a result of transpression-induced subduction initiation as hypothesized in previous studies. Finally, I analyze the morphology of the seafloor along the Queen Charlotte Fault for the impact of tectonics. I find that transpression between the Pacific and North American plates determine the morphology of continental slope channel networks and whether the continental shelf is actively accumulating sediment. Across each of these studies, there is a common conclusion that the landscapes we observe today record multistage geologic histories.