The spatial and temporal evolution of strain during the separation of Australia and Antarctica

• Published in: Geochemistry, Geophysics, Geosystems
• Main Authors: Ball, Philip, Eagles, Graeme, Ebinger, Cynthia, McClay, Ken, Totterdell, Jennifer
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2013
• Subjects: Antarctic; Antarc*; Antarctica
• Online Access: https://epic.awi.de/id/eprint/33230/; https://epic.awi.de/id/eprint/33230/1/ggge20160.pdf; https://doi.org/10.1002/ggge.20160; https://hdl.handle.net/10013/epic.41811; https://hdl.handle.net/10013/epic.41811.d001

A re-evaluation of existing onshore and offshore gravity, magnetic, seismic reflection, and well data from the Australo-Antarctic margins suggests that magmatism and along-strike lithospheric heterogeneities have influenced the localization of initial rifting. The 3D crustal architecture of the Australian and Antarctic margins, which formed during multiple rifting episodes spanning ~80 My, reveal local asymmetries along strike. Rift structures from the broad, late Jurassic (165-145 Ma) rift zone are partially overprinted by a narrower, mid-to-late Cretaceous rift zone ~100 Ma, which evolved in highly extended crust. This late-stage rift zone is located within a region of heterogeneous crust with faults that cut late syn-rift strata, interpreted as a continent ocean transition zone. This late stage transitional rift is populated by seismically identified rift-parallel basement highs and intra-crustal bodies with corresponding positive Bouguer gravity and magnetic anomalies. These undrilled features can be interpreted as exposures of exhumed mantle rocks, lower crustal rocks and/or as discrete magmatic bodies. Our results suggest that strain across an initially broad Australo-Antarctic rift system (165-145 Ma) migrated to a narrow rift zone with some magmatism at 100-83 Ma. Breakup did not occur until ~53 Ma within the eastern Bight-Wilkes and Otway-Adélie margin sectors, suggesting a west to east propagation of seafloor spreading. The prolonged eastwards propagation of seafloor spreading processes and the increased asymmetry of the Australian-Antarctic margins coincides with a change from rift-perpendicular to oblique rifting processes, which in turn coincide with along- strike variations in cratonic to Palaeozoic lithosphere.