Cenozoic deformation in the George V Land continental margin (East Antarctica)

This investigation is based on the analysis of multichannel seismic data collected in the continental shelf of the George V Land, between 140°E and 155°E on the East Antarctic margin. Most of the East Antarctic continental shelf is covered by permanent, thick sea and terrestrial ice and it is therefore still unexplored. This is the reason why the tectonic deformation affecting the Antarctic margin during the Mesozoic rift from the Australian plate and the Cenozoic post-rift phase is poorly known. The few coastal polynyas (such as the Mertz polynya, in the George V Land continental shelf) are the only places where the oldest sedimentary section can be studied with the existing technology. The data presented were not collected to address tectonic questions, however the relevance of this study is to document for the first time the occurrence of rift and post-rift tectonic structures in the sedimentary section near the coast, where the oldest sediment section is shallowest. These considerations are particularly relevant as Mertz-Ninnis trough, also known as George V Basin is located near the area of transition (around the Spencer Fracture Zone) between the extensionally-dominated Wilkes Land-Great Australian Bight Basin conjugate segment of the Australian-Antarctic Rift and the transtensional, strike-slip kinematics of the Otway Basin-South Tasman Rise-Oates Land segment. The tectonic structure in the George V Land sector presented in this study is two-fold with two rift phases: one being connected to the breakup process and the later one associated to a change in plate rotation. A former extensional phase opened structural grabens, with axis oriented WNW-ESE and possibly NE-SW. A latter transpressional phase reactivated previous structures and tilted, faulted and folded sedimentary strata, located in the inner continental shelf. The first tectonic phase is likely related with the Cretaceous rifting between the Antarctic and Australian plates. The second tectonic phase might be related to the onset of the fast spreading phase of Pacific-Indian Ocean, that caused uplift, inversion and folding of post-rift strata in a narrow east-west oriented region, near coastal basement outcrop, in Paleocene-Eocene times.