Erosional history of the Prydz Bay sector of East Antarctica from detrital apatite and zircon geo‐ and thermochronology multidating

Abstract

Approximately 98% of East Antarctica is covered by the East Antarctic Ice Sheet (EAIS), which has covered parts of the continent since the early Oligocene (34 Ma) and obscures evidence about the region's tectonic and erosional history. To better constrain the subglacial record, we analyzed geo‐ and thermochronologic dates of Oligocene‐Quaternary sediments from Prydz Bay, which drains ∼16% of the EAIS. We used multidating techniques, measuring U‐Pb, fission track, and (U‐Th)/He dates on apatite and zircon grains and40Ar/39Ar dates on hornblende grains to determine crystallization and cooling ages. Apatite and zircon U‐Pb dates and hornblende40Ar/39Ar dates are dominantly ∼500 Ma, recording Pan‐African metamorphism and magmatism. Zircon fission track dates record cooling at ∼250–300 Ma and ∼120 Ma from Permian‐Triassic (300‐201 Ma) rifting and Cretaceous (120 Ma) magmatic resetting. Mean apatite fission track dates decrease from ∼280‐210 Ma in early Oligocene samples, with lag times decreasing from ∼250‐180 My, indicating increasing erosion rates. Miocene‐Quaternary (10.7‐0 Ma) samples show a smaller range from ∼180 to ∼150 Ma. Youngest measured apatite He ages also decrease from ∼100 Ma to ∼25 Ma in Oligocene‐Miocene samples. These results indicate increasing erosion rates (<0.02 km/My to >0.2 km/My) in catchments draining to Prydz Bay in the early Oligocene, with slower erosion since the late Miocene. This erosion was likely achieved by glacial incision into pre‐existing valleys, reaching depths of ∼2.8–3.0 km by the late Miocene. This is consistent with EAIS models showing a transition to less erosive, cold‐based conditions following the mid‐Miocene climatic optimum.