HR: 0800h
AN: T11A-1249    [Abstracts]
TI: A Marine Geophysical Study of the Wilkes Land Margin, Antarctica
AU: * Close, D I
EM: david.close@worc.ox.ac.uk
AF: Dept. of Earth Science, University of Oxford, Parks Road, Oxford, OX13PR United Kingdom
AU: Watts, T B
EM: tony@earth.ox.ac.uk
AF: Dept. of Earth Science, University of Oxford, Parks Road, Oxford, OX13PR United Kingdom
AU: Stagg, H M
EM: howard.stagg@ga.gov.au
AF: Geoscience Australia, GPO Box 378, Canberra, ACT 2601 Australia
AB: During the Austral summers of 2000-01 and 2001-02, Geoscience Australia (GA) acquired $\sim$10,000 line km of seismic reflection, magnetic and gravity data across the Wilkes Land margin (WLM), East Antarctica, from 100-150E. Previous studies indicate that the WLM formed during the Late Cretaceous rifting of Australia and Antarctica. Deep-penetrating, 36-fold, seismic reflection data provide constraints on sediment and crustal structure as deep as the lower crust. The seaward extent of stretched continental crust and extetnded pre- and syn-rift sediments can be mapped off the central and east WLM. A region of massively stretched continental crust, subsided to abyssal plain depths, is imaged off Terre Ad\`{e}lie (137-140E). This block is interpreted to represent a sunken marginal plateau that was once conjugate to the Otway basin and the South Tasman Rise (STR). Identification of isochrons older than anomaly 21n over oceanic crust on the WLM is equivocal. Slow seafloor spreading at the Southeast Indian Ridge following rifting (Cande & Mutter, 1982) and widely-spaced data contribute to the difficulties in identifying the earliest isochrons. Anomaly 34y has previously been interpreted as the oldest isochron on the WLM; however, these seismic reflection data indicate the presence of stretched continental crust beneath this magnetic anomaly. Process-oriented gravity modelling has been completed for 12 transects across the Wilkes Land margin. A zone of weakened (as evidenced by low effective elastic thickness, Te) crust occurs at the continent-ocean transition (COT). The margin as a whole (including stretched continental crust), however, exhibits high strength (Te $\sim$30 km) relative to other passive rift margins. Loading of the Wilkes Land margin occurred almost entirely in the Tertiary, and specifically during an interval of polythermal glaciation between 34-9 Ma. High, modelled Te values demonstrate that the Wilkes Land margin flexurally supports the massive sediment load and that the lithosphere has remained strong despite rifting, or has regained strength since rifting. Evidence from seismic, magnetic and gravity data indicates massive crustal thinning and a wide, extended rift-zone, characterised by interpreted exhumed mantle peridotites. In-situ, fertile mantle peridotites recovered over 400 km from the shelf-break off east Wilkes Land support this interpretation of the geophysical data.
DE: 4207 Arctic and Antarctic oceanography
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting