Permian-Triassic rifting shaped subglacial landscape of western Wilkes Land, East Antarctica

Sedimentary basins under the East Antarctic Ice Sheet preserve the record of poorly-understood plate tectonics and geodynamic processes that have shaped the East Antarctic landscape. These basins host some of the largest glacial catchments in East Antarctica and are key to understand how tectonic forcing and Cenozoic glacial activity have combined to drive topographic change through time.

In this study, we investigate the tectonic origin and erosional history of one such subglacial basin in western Wilkes Land, the Knox Rift, to improve our knowledge of tectonic and topographic evolution in the region. Previously, modelling of airborne gravity and magnetic data suggested that the Knox Rift may constitute a Mesozoic rift basin. Its flanks exhibit elevated and rugged topography (~1200 m), while its central depression hosts the Denman and Scott Glaciers, two of the largest ice streams in the region.

We quantify the timing of rifting and the magnitude of regional uplift and erosion using a combination of low temperature thermochronology from outcropping basement rocks and detrital zircon U-Pb analysis of glacial moraines sourced from the Knox Rift. Time-temperature modelling of zircon and apatite (U-Th)/He basement ages is consistent with exhumation and erosion during rifting in the Permian-Triassic (280-220 Ma), with 3 younger (200-170 Ma) apatite (U-Th)/He ages indicating rift reactivation during the Early Jurassic. U-Pb detrital zircon geochronology and Pb-loss modelling also confirms the presence of a sedimentary infill in the Knox Rift that is Permian in age.

Our new data suggest that the main rifting phase in the Knox Rift is consistent with continental extension in East Gondwana during the Permian-Triassic, which we interpret may have largely affected this sector of East Antarctica. We propose that the present-day topography of this region is – at least at longer wavelengths – tectonically-driven by Permian-Triassic rifting. Average slow erosion rates (~2.6 km since 250 Ma) support the preservation of topographic features since the cessation of Permian-Triassic rifting. The spatial correlation of younger Jurassic apatite (U-Th)/He ages with the Scott and Denman ice streams also suggest that Cenozoic glacial erosion may have exploited pre-existing tectonic/topographic features, thus supporting a tectonic control on the location of these ice streams.