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-understoodplate tectonics and geodynamic processes that have shaped the East Antarctic landscape. Thesebasins host some of the largest glacial catchments in East Antarctica and are key to understand howtectonic forci...
| Main Authors: | , , , , |
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| Format: | Conference Object |
| Language: | English |
| Published: |
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2019
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| Subjects: | |
| Online Access: | https://www.isaes2019.org:12090/home/ http://ecite.utas.edu.au/136133 |
| Summary: | Sedimentary basins under the East Antarctic Ice Sheet preserve the record of poorly-understoodplate tectonics and geodynamic processes that have shaped the East Antarctic landscape. Thesebasins host some of the largest glacial catchments in East Antarctica and are key to understand howtectonic forcing and Cenozoic glacial activity have combined to drive topographic change throughtime. In this study, we investigate the tectonic origin and erosional history of one such subglacial basin inwestern Wilkes Land, the Knox Rift, to improve our knowledge of tectonic and topographic evolutionin the region. Previously, modelling of airborne gravity and magnetic data suggested that the KnoxRift may constitute a Mesozoic rift basin. Its flanks exhibit elevated and rugged topography (~1200m), while its central depression hosts the Denman and Scott Glaciers, two of the largest ice streamsin the region. We quantify the timing of rifting and the magnitude of regional uplift and erosion using acombination of low temperature thermochronology from outcropping basement rocks and detritalzircon U-Pb analysis of glacial moraines sourced from the Knox Rift. Time-temperature modelling ofzircon and apatite (U-Th)/He basement ages is consistent with exhumation and erosion during riftingin the Permian-Triassic (280-220 Ma), with 3 younger (200-170 Ma) apatite (U-Th)/He agesindicating rift reactivation during the Early Jurassic. U-Pb detrital zircon geochronology and Pb-lossmodelling 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 continentalextension in East Gondwana during the Permian-Triassic, which we interpret may have largelyaffected 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 slowerosion rates (~2.6 km since 250 Ma) support the preservation of topographic features since thecessation of Permian-Triassic rifting. The spatial correlation of younger Jurassic apatite (U-Th)/Heages with the Scott and Denman ice streams also suggest that Cenozoic glacial erosion may haveexploited pre-existing tectonic/topographic features, thus supporting a tectonic control on thelocation of these ice streams. |
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