Tectonic-Climate Interactions And Glacial History Within The Chugach And Kenai Mountains, Alaska
Valentino, Joshua D
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The architecture and morphology of a mountain range is fundamentally controlled by the combination of rock uplift and distribution of precipitation. This relationship attributes fluctuations in climate to the erosion of orogens, sedimentation rates, and geodynamics of the crust. Glaciers are the most effective climate driven erosive processes, where the frequency of glacial periods has a direct impact on the structure of mountain ranges through time. The late Cenozoic global cooling period was the beginning of a series of many glaciations which increased erosion in orogens experiencing fast rock uplift. We characterize the threshold for the onset of effective glacial erosion and record the increase in erosion rate during the late Cenozoic in the Chugach and Kenai Mountains of Alaska. We utilized low temperature thermochronometry and cosmogenic dating to constrain the spatial and temporal distribution of exhumation and glacial history in order to characterize the net effect of glaciers on an orogen that experiences slow rock uplift. We constrain the spatial distribution of exhumation and characterize the landscape along the Kenai Peninsula, underlain by the transition from flat slab to normal subduction. The region is characterized by old AHe ages which mimic the subduction angle of the down going plate and decrease away from an exhumational hotspot at a syntax in the Chugach Mountains. We attribute the long term exhumational characteristic of the Kenai Peninsula to subduction and underplating of sediment shed from the accreting Yakutat microplate to the east. A delineation of the glacial history using 10Be cosmogenic dating depict a series of glacial advances which date to the early and late Wisconsin. We find that the asynchronuity of glaciation across maritime and continental Alaska is controlled by steep orographic precipitation gradients which result from upper plate deformation. Finally, we observe an increase in erosion since the late Cenozoic using both AHe and cosmogenic dating and conclude that it is possible for the onset of effective glacial erosion in regions that experience slow to moderate rock uplift and that climate drives erosion rates in these regions.
- Doctoral Dissertations