The Dynamic Interplay between Miocene to post-Miocene Magmatism, Tectonism, and Geomorphology in NE Oregon
Datum
2020-12-08
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University of Oregon
Zusammenfassung
The Miocene to post-Miocene geologic history of Northeastern Oregon and West-Central Idaho is difficult to parse because this area has experienced several dramatic events. Within 35 km of each other, there are exposures of the Chief Joseph Dike Swarm (CJDS) the fed the youngest large igneous province (LIP) on Earth: the Columbia River Basalt Group (CRBG), and Hells Canyon --- the deepest canyon in North America. Our understanding of these dikes and how they relate to the impingement of the Yellowstome plume and the movement of magma vertically in the crust during the eruption of this LIP are limited as most studies in the region have focused on the surface flows. Similarly, the age and origin story for Hells Canyon remain unknowns. This is despite a long history of research into the age and origin of the less deep Grand Canyon.
In the first chapter , I leverage a dataset of never before digitized maps of 4279 dikes within the CJDS to make key observations of the structure and mechanics of this swarm. I combine these data with field observations of cross-cutting relationships to constrain changes in the upper crustal stress field during the eruption of the CRBG and measure the amount of dilation accommodated by the upper crust due to diking.
The second and third chapters are focused on investigating Hells Canyon, namely I seek to answer the questions of "When did Hells Canyon Form?" and "Why is it there?" The second chapter makes use of an elevation transect of low-temperature thermochronometers collected from the highest peaks above the canyon to the deepest points in the Canyon. These data reveal a long-lived story of cooling related to exotic terrane accretion and translation on the margin of North America. Forward modeling of our data reveals a potential cooling signature favoring canyon incision at $\sim$ 4 Ma.
The third and final chapter discusses the landscape response to canyon incision. Close examination of tributaries streams reveals a pattern of knickpoints emblematic of a drainage divide which was incised through. The reaches above the knickpoints on these tributaries are an anachronism from the pre-capture time.
Beschreibung
Schlagwörter
Hells Canyon, Stream Power, Tectonic Geomorphology, Thermochronology