Single grain heavy mineral provenance of garnet and amphibole in the Surveyor fan and precursor sediments on the Gulf of Alaska abyssal plain — Implications for climate-tectonic interactions in the St. Elias orogen

Abstract

The St. Elias orogen formed as a result of the northwestward drift of the Yakutat terrane along and final collision with the Alaska margin in the Miocene. Its exhumation coincided with changing glacial conditions that are considered to have strongly interacted with mountain building processes. A significant part of the record of these tectonic-climatic interactions is stored in sediments on the Gulf of Alaska abyssal plain including the Surveyor fan. Our study examines temporal provenance changes of Miocene through Pleistocene sediments of the Surveyor fan, Gulf of Alaska, to constrain the dynamics of exhumation and mass transfer from the evolving St. Elias orogen to the adjacent Surveyor deep sea fan. We present single grain geochemical data of amphibole and garnet and 40Ar/39Ar cooling ages of biotite and amphibole together with point counting data of heavy minerals from sands and silts from two sites in the distal and proximal fan, drilled by IODP expedition 341 in 2013 (sites U1417 and U1418, respectively).A shift in heavy mineral composition during the Miocene, predating the onset of glaciation, points to a tectonically-induced change in erosion centers and sediment transport, probably caused by the rise of the St. Elias Mountains. Garnet and amphibole data suggest the Chugach metamorphic complex is the main sediment source, implying input to the Surveyor fan from sources relatively far in the north during the Miocene. Changing provenance signals from the Miocene to Pliocene suggest rising input from the lower grade metamorphic areas at the southern flanks of the orogen, indicating the advance of glaciers to the tidewater line, providing material from this flanking region. Higher input from the Chugach metamorphic complex in all Pleistocene sediments suggests the Northern Hemisphere glaciation at the Plio-Pleistocene boundary caused erosion and sediment yield from the interior of the orogen. Climatic changes at the mid-Pleistocene transition did not cause significant changes in the provenance signal.