The Bruce Rise Area, East Antarctica: Formation of a Continental Margin near the Greater India - Australia - Antarctica Triple Junction
H.M.J. Stagg1*, J.B. Colwell1, I. Borissova1, T. Ishihara2 & G. Bernardel1
1Petroleum & Marine Division, Geoscience Australia, Canberra ACT - Australia
2Geological Survey of Japan, Tsukuba - Japan
Received 22 May 2005; accepted in revised form 23 February 2006
Abstract - Geophysical data acquired by Australia and Japan from 1994–2002 on the deep-water continental margin offshore from Queen Mary Land, East Antarctica, allow a regional interpretation of the geology and tectonic history of this sector of the Antarctic margin. The margin formed mainly in the Cretaceous, adjacent to the pre-breakup triple junction that developed between Greater India, Australia and Antarctica in the Jurassic and Cretaceous.
The continental slope is dominated by the Bruce Rise, a mid-slope marginal plateau which is conjugate to the Naturaliste Plateau on the southwest Australian margin. Seismic data show that the margins of the Bruce Rise are underlain by shallow acoustic basement. This basement has been faulted which has led to the deposition of probable Cretaceous rocks in small half-graben. Basement deepens further inboard and the total sediment thickness in this area is at least 3.5 km. The post-rift sedimentary cover is probably rarely more than 1 km thick and often contains a prominent bottom-simulating reflector of unknown origin. The eastern and northern margins of the Bruce Rise are sharply defined by faulting: the extremely steep (up to 20° gradient), northwest-trending eastern margin is controlled by the Vincennes Fracture Zone, while the E–W trending northern margin is down-faulted by about 6–7 km across several major, high-angle faults. The western flank is poorly defined, with no seismic lines extending landward of the lower slope.
Oceanward of the Bruce Rise, the deep-water Shackleton Basin is highly variable in structure and seismic character and its origins are uncertain. West of the Bruce Rise, the crust appears to be oceanic. Potential field modelling, the identification of Early Cretaceous seafloor spreading magnetic anomalies and similarities of seismic character with oceanic crust in the Enderby Basin to the west of the Kerguelen Plateau, suggest that this crust was generated during the separation of Greater India from Australia–Antarctica. This crust also contains several prominent seaward-dipping reflector sequences (SDRS). The basement between the northern flank of the Bruce Rise and the fast-spreading crust of the Australian–Antarctic Basin to the north has seismic characteristics suggesting that, despite the presence of interpreted seafloor spreading magnetic anomalies, fragments of continental crust may also be present. Alternatively, these fragments may comprise oceanic crust that has subsequently been faulted during the period of very slow spreading between Australia and Antarctica in the Late Cretaceous.
*Corresponding author (howard.stagg@ga.gov.au)