Provenance of the Surveyor Fan and Precursor Sediments in the Gulf of Alaska—Implications of a Combined U-Pb, (U-Th)/He, Hf, and Rare Earth Element Study of Detrital Zircons

Abstract

The history of exhumation and denudation of the Cenozoic St. Elias orogen is stored in the sediments of the Miocene to Holocene Surveyor Fan, Gulf of Alaska. The orogeny of the mountain belt coincides with major climatic events leading to varying degrees of glaciation that are considered to have strongly interacted with mountain-building processes. In order to assess the relative influence of climate and tectonics on erosion patterns and to reconstruct sediment routing to the ocean, we combine zircon U-Pb dating and (U-Th)/He thermochronology with analysis of rare earth elements and Hf isotopes of zircons of sands and silts from Integrated Ocean Drilling Program expedition 341 sites U1417 and U1418 in the Surveyor Fan. All Miocene to Pleistocene sediments show similar U-Pb age spectra, indicating that the main source areas remained the same during different stages of glaciation. A prominent age component at 50–60 Ma can be linked to the Chugach Metamorphic Complex and the Sanak-Baranof plutonic belt in the mountain range. Older grains can be referred to low-grade metamorphic sources within the Chugach, Prince William, and Yakutat terranes. A decrease in 50–60 Ma igneous and metamorphic zircons implies a reduction of input from the Chugach Metamorphic Complex and the Sanak-Baranof plutonic belt. This indicates that the southward advance of glaciers toward the ocean, together with tectonic changes from the Miocene to the Pliocene, triggered a higher contribution from the newly glaciated areas. During times of increased glaciation in the Pleistocene, glaciers appear to have been nested in the same area as before. Our data do not give evidence of a general change in the drainage systems or the tectonic setting during the Pleistocene but also do not prove the absence of such.