Accretionary orogen unveiled beneath the Gamburtsev Sublglacial Mountains in East Antarctica

Abstract

The Gamburtsev Subglacial Mountains (GSM) in central East Antarctica are  completely buried beneath the East Antarctic Ice Sheet. The GSM are known to be underlain by anomalously thick crust (~50–60 km) and ~200 km thick Precambrian lithosphere, but their crustal-scale geology remains less well- studied. Little is known about the 3D heterogeneity in crustal architecture beneath the GSM, and how this may relate to larger-scale tectonic processes responsible for Gondwana amalgamation.Here, we use airborne gravity and aeromagnetic anomalies to explore the crustal architecture of the GSM in unprecedented detail. The gravity and magnetic images show three distinct geophysical domains, and a dense lower crustal root is modelled beneath the northern and central domains. We propose that the root may reflect magmatic underplating, associated with Pan-African age back-arc basin formation and inversion, followed by the collision of Australo-Antarctica and Indo-Antarctica. The high frequency linear magnetic patterns parallel to the Gamburtsev Suture zone, suggest that the upper crustal architecture is dominated by thrust and strike-slip faults, formed within a large-scale transpressional fault system.We calculated a 2D gravity and magnetic model along a passive seismic profile to investigate the crustal architecture of the GSM, with the aid of depth to magnetic source estimates.   By combining the crustal model with  geological constraints, we propose a new evolutionary model suggesting that the crust of the northern and central GSM domains formed part of a cryptic accretionary orogen, of proposed Pan-African (~650-550 Ma?) age. The inferred accretionary stage was followed by continental collision (~540-520 Ma?) along the Gamburtsev suture, which is linked here to Gondwana amalgamation.