New airborne radar, magnetic and gravity data reveal the subglacial boundary between the Weddell Sea Rift, a major extensional structure underlying the Weddell Sea Embayment, and West Antarctica. The >500 km wide Weddell Sea Rift separates East Antarctica from the Ellsworth Whitmore Mountains and other crustal blocks of West Antarctica, and was a major focus for Jurassic extension during the early stages of Gondwana break-up. The new subglacial topography shows the inland extent of the Weddell Sea Rift in a broad Coastal Basin which connects to a newly-identified Ellsworth Trough to the west and two groups of en-echelon basins to the south. These Transitional Basins and Marginal Basins resulted from dominantly sinistral movement along the newly identified, ~75 km wide, strike-slip Pagano Fault Zone that forms the regional tectonic boundary between East and West Antarctica. Digitally enhanced aeromagnetic data, combined with the gravity data indicates the extent of Proterozoic granitic basement, volcanic rocks of a Middle Cambrian rift, Jurassic granites, and post Jurassic rifting sedimentary infill. To estimate depth to magnetic sources we applied a combination Euler deconvolution (in 2D and 3D), Werner, and analytical signal methods, which helped constrain two new joint magnetic and gravity models for the region. The models suggest that granitic Proteozoic crust similar to that exposed at Haag Nunataks extends southeast of the Ellsworth Mountains as far as the flanks of the Coastal Basin. The Jurassic granites are modelled as 5.6 to 8 km thick and are not underlain by significant upper crustal mafic intrusions, contrary to previous interpretations based on reconnaissance aeromagnetic data. The new data demonstrate that the granites were emplaced at the transition between the thicker crust of the Ellsworth-Whitmore Mountains block and the inland termination of the Weddell Sea Rift and within the Pagano Fault Zone. Bouguer anomaly models, coupled with independent geochemical constraints and seismic evidence from the adjacent Ronne Ice Shelf, lend support to the hypothesis that the Middle Jurassic granites are related to a process of widespread magmatic underplating beneath the broad Weddell Sea rifted margin.
- continental rifting
- strike-slip faulting