No abstract available

The continental margin of East Antarctica between Dronning Maud and George V Lands shows no evidence of widespread breakup-related volcanism, other than adjacent to the southern Kerguelen Plateau, and it therefore constitutes one of the largest tracts of non-volcanic rifted margin on the planet. The integrated interpretation of deep-seismic, velocity and potential field data acquired in 2001/02 shows that there are first-order structural variations between the two main sectors of this margin. In the west, the Enderby Land margin formed by the separation of Greater India from Antarctica, commencing in the Valanginian (ca. 131 Ma). Seawards of a major basement fault zone underlying the continental slope, deep-seated continental crust is characterised by high-angle brittle faulting; seismic data provide little information on the style of the deeper crustal deformation. The other prominent structural features of this margin are a sharp continent-ocean boundary (COB), characterised by an oceanwards step-up in the basement level of up to 1 km, and an earliest phase of ocean crust that is distinctive for its rich internal reflection fabric and strong Moho reflection. Potential field modelling indicates that the gross margin structure is relatively simple, and that both the continental and oceanic crusts have behaved as a semi-rigid plate that has been depressed landwards by the thick (4-9 km) post-rift sediment loading. In the east, the Wilkes Land margin formed during the separation of Australia and Antarctica, commencing with very slow seafloor spreading in the early Campanian (ca. 83 Ma). This margin is dominated by the broad and highly structured transition from the attenuated continental crust inboard on the margin, to the mechanically extended and largely amagmatic oceanic crust that formed during the initial seafloor spreading. From inboard to outboard across this zone, the structuring is characterised by: ? plastic and brittle deformation of the lower continental crust and upper mantle; ? a ridge of interpreted serpentinised peridotite that can be traced along strike on the margin for a distance of at least 800 km; ? a sedimentary basin outboard of the ridge that appears to be underlain by fragments of crystalline continental crust; and ? a COB between mechanically extended continental and oceanic crust that is complex and not readily delineated. The structures of the Wilkes Land margin are very similar to those on the conjugate southern Australian margin, indicating that at least the final stage of rifting between Antarctica and Australia was inherently symmetrical. The wide differences between the structural styles documented on the Enderby and Wilkes Land margins indicate that tectonic processes forming non-volcanic rifted margins may differ significantly depending on a range of factors that may include pre-existing heterogeneities in the continental crust, the thermal regime and the pre-breakup intra-plate stress regime.

Geoscience Australia is custodian of ship-track magnetic and gravity data from close to 700 marine surveys conducted between 1960 and 2009. These data were last combined and levelled in the late 1990s. New levelling has been motivated by specific requirements within projects being conducted as part of the Australian Government's Energy Security Program (2006-2011). These projects rely on marine potential-field datasets to help constrain sediment thickness and basement architecture in remote offshore basins. Recently-levelled datasets cover: 1) the Capel and Faust basins, deepwater basins about 800 km off the east coast, and 2) the southwest margin of the Australian continent. The levelling involved the following steps: consistent computation of gravity anomalies; splitting lines into straight-line segments to facilitate cross-over computations; low-pass line filtering where necessary; editing to remove problematic ship-tracks; and levelling to minimise cross-over misties. Using methods developed by Intrepid Geophysics for the late-1990s Australia-wide work, magnetic data were levelled by minimising misclosures around loops and then gridded and merged with aeromagnetic data in onshore and near-shore areas. Gravity data were levelled using a polynomial technique and satellite-altimeter-derived gravity data as a reference surface. The resulting levelled datasets provide information at a higher-resolution than is available from satellite-derived gravity measurements or from global compilations of magnetic data. Despite this, the levelled datasets are limited to areas of specific scientific or exploration interest, which highlights the need for levelled datasets that cover the whole of Australia's marine jurisdiction.

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In January 2000, the Australian Geological Survey Organisation (AGSO) completed a major, 25-day seabed swath-mapping and geophysical survey off southeast Australia for the National Oceans Office (NOO) and Environment Australia (EA). The survey, named AUSTREA-l and designated as AGSO Cruise 222, used the 85-m French oceanographic and geoscience research vessel L 'Ata/ante, departing Noumea on 18 December 1999 and ending in Hobart on 11 January 2000. The survey covered 11,000 km and mapped about 120,000 km2 of seabed - an area about 1.5 times the size of Tasmania. The work was done for marine zone planning and management, for assessment of seabed living and non-living (petroleum and mineral) resources, and geological and biological research, as a major step towards implementation of Australia's Oceans Policy and Australia's Marine Science and Technology Plan, and in particular, the development of the Southeast Regional Marine Plan by the National Oceans Office. Data collected included Simrad EM 12D swath-bathymetry and backscatter imagery, 6- channel GI-gun seismic, digital 3.5 kHz sub-bottom profiles, gravity and total field magnetics. Also collected was oceanographic information - XBTs to 1800 m depth and underway ADCP (current), sea surface temperature and salinity measurements. Weather and sea conditions were generally favourable, though stormy conditions with 30-35 knot winds and associated rough seas were encountered at times. Data quality was mostly excellent. The survey mapped the volcanic slopes of Lord Howe Island and Ball's Pyramid to the 12 nautical mile outer limits of a proposed Marine Protected Area, revealing a rugged terrain of volcanic cones, flows and canyons likely to harbour diverse benthic communities. The steep and narrow rifted continental margin off the NSW South Coast was shown to be deeply dissected by canyons and to contain gigantic continental fauit blocks fuld ?syw-ift volcanic seamounts and ridges. The survey completed mapping of the huge Bass Canyon complex off southeast Victoria, revealing detailed morphology of tributary canyons up to 1000 m deep adjacent to the Gippsland oil fields. Important fishing grounds of the Southeast Trawl Fishery were mapped off Tasmania, including volcanic and carbonate pinnacle terrain off St Helens, volcanic seamounts of the Southern Hills, and the heads of canyon systems incised into the sedimented upper slope off west Tasmania. Mapping of the Tasmanian Seamounts Marine Protected Area, south of Hobart, was completed, with thirty additional volcanic seamounts found just east and north of the MP A. The seismic profiles confirmed the existence of potential frontier petroleum basins off the east, southern and west coasts of Tasmania. Parts of the deeply-canyoned upper and mid slope of the Otway Basin were mapped off northwest Tasmania, Victoria and South Australia. The Great Australian Bight Benthic Protected Area of the GAB Marine Park was fully surveyed below the 500 m isobath and was shown to be generally a uniform slope, with the gigantic Nullarbor Canyon crossing its southeastern comer, gouged into deformed Late Cretaceous sediments. A full set of shipboard maps was provided to the National Oceans Office; copies of the digital swath-data are held for NOO at AGSO. All data from the cruise will be jointly managed by AGSO, NOO and EA.

Legacy product - no abstract available

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Legacy product - no abstract available

Legacy product - no abstract available

This paper develops a crustal model of the conjugate, oblique-slip continental margins of George V Land, east Antarctica, and the Otway Basin, southeast Australia, based on the interpretation of seismic and sample data.