DOES CLIMATE CHANGE AFFECT EXHUMATION? IDENTIFYING THE LINK BETWEEN TECTONICS, CLIMATE AND OFFSHORE SEDIMENT DEPOSITION IN SOUTHEASTERN ALASKA

The St. Elias Mountains in Southeastern Alaska are the tallest coastal mountain range on Earth and are a result of the subduction and subsequent collision of the Yakutat microplate with the North American plate. The St. Elias orogen developed over a period of substantial global climate change including the intensification of glaciation in the Northern Hemisphere during the Plio-Pliestocene transition at around 2.5 Ma and the shift to ~100 kyr glacial cycles during the mid-Pleistocene transition from 1.2-0.7 Ma. This study investigates whether these global climate shifts enhanced glacial erosion and promoted changes in the rates and spatial patterns of rock exhumation in the St. Elias orogen. The Gulf of Alaska archives sediment deposits eroded from the St. Elias orogen and provides a record of erosional fluxes onshore. We examine the offshore sedimentary deposits from five boreholes drilled by IODP Expedition 341 along a transect from offshore of the Bering glacier, through the continental shelf, and down into the deep-sea Surveyor fan. Biostratigraphic and magnetostratigraphic data from the cores establish the timing of sediment deposition and provide an up to 10 myr record of deposition. We date sediments from various depths in each borehole using detrital zircon fission-track thermochronology to quantify rock exhumation in the St. Elias orogen. By comparing the zircon cooling ages with the stratigraphic ages we are able to calculate the lag time and identify temporal variations as an indicator for changes in the source rock exhumation rates. Future work includes identifying sediment provenance using U/Pb dating of single zircon grains in an attempt to identify changes in spatial exhumation patterns, which may correlate with major climatic shifts.