Episodic erosion in West Antarctica inferred from cosmogenic ~3He and ~(10)Be in olivine from Mount Hampton

摘要

The polar climate of Antarctica results in the lowest erosion rates on Earth. The low long-term erosion history of high elevation mountain tops that are exposed above the ice preserve a record of climate change that can be accessed using cosmogenic nuclides. However, unravelling the complexity of the long-term denudation histories of Antarctic summits is frequently hampered by intermittent ice cover. The aim of this work is to identify denudation rate changes in a surface that has been continuously exposed since the middle Miocene. We have measured stable ( He-3) and radioactive (Be-10) cosmogenic nuclides in olivine from Iherzolite xenoliths from the summit of the Mount Hampton shield volcano within the West Antarctic Ice Sheet. The peak (3200 m) has never been covered by the current ice sheet and local ice caps, consequently the data record the subaerial erosion history of a mountain top within the Antarctic interior. The Be-10 concentrations in the olivines yield minimum exposure ages (33 to 501 ka) that are significantly younger than those derived from the cosmogenic He-3 (90 to 1101 ka). The data reveal a complex exposure history that provide an integrated long-term erosion rate of between 0.2 and 0.7 m/My that is most likely caused by mechanical weathering. Inverse modelling shows that the data are readily explained by episodic erosion, consisting of one to five erosion pulses that may record major regional climatic changes. (C) 2018 Elsevier B.V. All rights reserved.