Timing and patterns of glacial incision along the eastern Antarctic Peninsula: Insights from low-temperature thermochronometry

Abstract:

Glaciers played an important role in shaping the topography of the Antarctic Peninsula (AP), but the timing and patterns of valley incision, and the extent to which the modern topography was controlled by glaciers, remain largely unconstrained. In this work, we use apatite (U-Th)/He thermochronometry to test hypotheses on the timing and patterns of km-scale topographic changes along the AP, because its low closure temperature makes it sensitive to km-scale changes in topography. We present twelve new bedrock apatite (U-Th)/He thermochronometric ages from Drygalski Glacier, Hektoria Glacier and Green Glacier which drain on the eastern side of the northern AP. The samples span elevations of 300 to 1200m, which allows us to constrain how much valley incision occurred since the onset of glaciation. We use the 3D thermo-kinematic model Pecube to calculate (U-Th)/He ages at the bedrock sample locations and investigate three plausible and simplified patterns of topographic change. Specifically, we constructed models where the modern topography (a glacially-dissected plateau) evolved from a flat plateau (no initial relief), a fluvial network (~1 km of initial relief) or underwent no topographic change (steady-state) and the onset of topographic change occurred at either 30 Ma, 14.5 Ma or 6 Ma. These times were selected to test whether onset of topographic change was concurrent with or followed the onset of glaciation along the Antarctic Peninsula, the end of the mid-Miocene climatic optimum and enhanced erosion in Patagonia, respectively. We compare the calculated thermal ages with the measured (U-Th)/He ages for the study area to determine which of our hypothetical scenarios from the model best describe the data.