Quantifying Tectonic and Erosion-Driven Uplift in the Gamburtsev Subglacial Mountains of East Antarctica

Abstract:

The Gamburtsev Subglacial Mountains (GSM) are a paradoxical tectonic feature as, despite their heavily dissected Alpine-type topography, they are located on Precambrian cratonic lithosphere. The GSM is significant because it is a key nucleation site for the development of the East Antarctic Ice Sheet (EAIS), ~34 Ma.

Permian rifting and Cretaceous strike-slip faulting have been advanced as possible tectonic triggers for GSM uplift. However, more recent interpretations of detrital thermochronology data argue against major Cretaceous exhumation. This raises the question of whether Cenozoic erosion and the associated isostatic response were sufficient to drive a substantial part of the uplift of the GSM. To address this question, we have used new compilations of gravity and bedrock topography, together with spectral (free-air admittance and Bouguer coherence) models to estimate the effective elastic thickness of the lithosphere (T_e) and landscape evolution models to evaluate the effects of erosional unloading and flexural rebound. We find that, unusually for continents, the coherence between free-air gravity anomalies and bedrock topography in the GSM is high (>0.5) and that T_e is anomalously low (15 - 25 km), in contrast to previously reported values of up to ~70 km. We also find that by calculating a peak accordance surface and then differencing it with the observed bedrock topography two fundamentally different styles of erosion: Alpine-style dendritic fluvial and glacial incision in the GSM and major EAIS outlet glacier-type erosion in the Lambert Rift (LR).

Using a variety of continuous elastic plate models for different T_e scenarios, we have quantified the spatial distribution and magnitude of flexural uplift in both the GSM and LR. Although the pattern of peak uplift is affected by T_e, the total amount of flexural uplift is not as sensitive. We estimate 500 m of uplift in the GSM and up to 1.2 km in the LR. The age of the uplift is not clear, but landscape evolution modeling based on low T_e and long-term erosion rates suggest an age for the incision in the range 80-300 Ma.