Abstract

Valley networks in mountain ranges record the interactions between climate, tectonics, and geology. While drainage network analysis has transformed our understanding of these interactions in subaerial settings, the landscape evolution of ice-covered orogens is poorly known. The Gamburtsev Subglacial Mountains are a _{600 km-long mountain range situated beneath the East Antarctic Ice Sheet, the largest ice sheet on Earth. These mountains are thought to have been an important nucleation site for the ice sheet approximately 34 million years ago and are now buried beneath} 2 km of ice. Airborne geophysical surveying has revealed that the Gamburtsevs are characterised by a rugged, incised landscape, but their geological structure and uplift history remain enigmatic.

This talk will explore how radio-echo sounding (radar) data can be used to extract valley networks and longitudinal profiles from the Gamburtsevs. We combine analysis of these valley profiles with gravity and magnetic anomalies to infer details of the tectonic and geomorphic development of the mountains. For example, channel steepness indices and their relationship with magnetic anomalies allow us to confirm the positions of major geological boundaries that may date back to Gondwana assembly. Drainage basin analysis and stream power incision modelling are used to show that the morphology of the valley networks is largely consistent with fluvial incision that occurred prior to Eocene/Oligocene glaciation. This relic landscape is now preserved beneath the non-erosive centre of the East Antarctic Ice Sheet. Tectonic geomorphic analysis suggests that the routing of Gamburtsev fluvial systems was likely influenced by extensional faulting within East Antarctica, which may have controlled pre-glacial base level and the locations of interior sediment depocentres. We use these findings, together with independent estimates of denudation rates, to evaluate competing scenarios for the mechanism(s) and timing of Gamburtsev mountain uplift and valley incision. Finally, through numerical ice-sheet modelling, we examine how the uplift of these mountains may have played a crucial role in governing the nature and timing of the initial growth of the East Antarctic Ice Sheet.