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In 2001 and 2002, Australia acquired an integrated geophysical data set over the deep-water continental margin of East Antarctica from west of Enderby Land to offshore from Prydz Bay. The data include approximately 7700 km of high-quality, deep-seismic data with coincident gravity, magnetic and bathymetry data, and 37 non-reversed refraction stations using expendable sonobuoys. Integration of these data with similar quality data recorded by Japan in 1999 allows a new regional interpretation of this sector of the Antarctic margin. This part of the Antarctic continental margin formed during the breakup of the eastern margin of India and East Antarctica, which culminated with the onset of seafloor spreading in the Valanginian. The geology of the Antarctic margin and the adjacent oceanic crust can be divided into distinct east and west sectors by an interpreted crustal boundary at approximately 58°E. Across this boundary, the continent-ocean boundary (COB), defined as the inboard edge of unequivocal oceanic crust, steps outboard from west to east by about 100 km. Structure in the sector west of 58°E is largely controlled by the mixed rift-transform setting. The edge of the onshore ArchaeanProterozoic Napier Complex is downfaulted oceanwards near the shelf edge by at least 6 km and these rocks are interpreted to underlie a rift basin beneath the continental slope. The thickness of rift and pre-rift rocks cannot be accurately determined with the available data, but they appear to be relatively thin. The margin is overlain by a blanket of post-rift sedimentary rocks that are up to 6 km thick beneath the lower continental slope. The COB in this sector is interpreted from the seismic reflection data and potential field modelling to coincide with the base of a basement depression at 8.0-8.5 s two-way time, approximately 170 km oceanwards of the shelf-edge bounding fault system. Oceanic crust in this sector is highly variable in character, from rugged with a relief of more than 1 km over distances of 10-20 km, to rugose with low-amplitude relief set on a long-wavelength undulating basement. The crustal velocity profile appears unusual, with velocities of 7.6-7.95 km s )1 being recorded at several stations at a depth that gives a thickness of crust of only 4 km. If these velocities are from mantle, then the thin crust may be due to the presence of fracture zones. Alternatively, the velocities may be coming from a lower crust that has been heavily altered by the intrusion of mantle rocks. The sector east of 58°E has formed in a normal rifted margin setting, with complexities in the east from the underlying structure of the N-S trending Palaeozoic Lambert Graben. The Napier Complex is downfaulted to depths of 8-10 km beneath the upper continental slope, and the margin rift basin is more than 300 km wide. As in the western sector, the riftstage rocks are probably relatively thin. This part of the margin is blanketed by post-rift sediments that are up to about 8 km thick. The interpreted COB in the eastern sector is the...

We document the interpretation of three crustal sections from coincident deep seismic reflection, gravity and magnetic data acquired on Australia's southern margin: one section from the Naturaliste Plateau and the Diamantina Zone; and two in the Great Australian Bight (GAB). Interpretations are based on an integrated study of deep multichannel seismic, gravity and magnetic data, together with sparse sonobuoy and dredging information.All interpreted sections of the margin show a transition from thinned continental crust, through a wide continent ocean transition zone (COTZ). In the GAB the transition is to slow sea-floor spreading oceanic crust that dates from breakup in the Campanian (c. 83 Ma); in the Naturaliste-Diamantina margin the earliest oceanic crust is undated. The COTZ on these margins is geologically and geophysically complex, but interpretation of all data, including dredge hauls, is consistent with the presence of a mixture of modified continental lower crust, breakup related volcanics and exhumed continental mantle. Serpentinized detachment faults are not well imaged, but have been inferred from high-amplitude magnetic signatures interpreted to arise from magnetite associated with the hydration of peridotites. Alternative models for the structure of the COTZ, involving either mafic underplating or aborted sea-floor spreading, have been explored, but are considered unlikely on this margin.Similarity in the final architecture of these margins has major implications for the nature of rifting in the Southern Rift System, and may point to the entire 4000 km-long system being non-volcanic in character.Second-order differences in geometry and morphology of the two areas studied are unlikely to be a function of strain rate. Instead, they probably reflect complexities owing to the multiple tectonic events that occurred during final Gondwanide fragmentation. The most dramatic of these is the impact of hotspot activity in the Kerguelen Plateau, which commenced some 50 Ma prior to final breakup in that sector.

Geochemistry, Geophysics, Geosystems, v. 4, n. 9, p. 1071, 2003. http://dx.doi.org/10.1029/2003GC000535International audienceMicrocontinents appear to commonly form on young continental margins close to hot spots, butdifficulties in understanding their geology and evolution have inhibited assessment of their globaldistribution and significance. Thick volcanic accumulations in areas affected by hot spot magmatismonly complicate the issue. Elan Bank, a large western salient of the Kerguelen Plateau, is amicrocontinent that originally lay between India and Antarctica in Gondwana. Recent regional platetectonic reconstructions suggest that during Gondwana breakup, Elan Bank and India initially separatedfrom Antarctica, and Elan Bank became isolated in the Southern Ocean via a ridge jump to the northbetween Elan Bank and India. In Albian time (108 Ma), voluminous magmatism attributed to theKerguelen hot spot overprinted and radically altered the original microcontinent and its surroundings.Recent ODP investigations, deep seismic reflection data, and a wide-angle seismic line on Elan Bankallow us to gain the first insight into the feature’s integrated crustal structure and geological evolutionand the adjacent continent-ocean transition zone. Our analysis shows that Elan Bank’s crust is at least16 km thick. The upper igneous crust consists of a 2–3 km thick layer with seismic velocities rangingfrom 4.4 to 5.9 km/s that can be interpreted as the result of accumulation of lava flows originating fromthe Kerguelen hot spot. Seismic velocities at the base of the crust are as low as 6.6 km/s, which isconsistent with a fragment of thinned continental crust 14 km thick. A high velocity body, located atdepths of 5 to 10 km, could be interpreted as plutonic rocks emplaced during the major regionalmagmatic episode. On the basis of deep seismic reflection data, we interpret extensional structuresbeneath the volcanic flows. In Albian time, when the area was affected by the Kerguelen hot spot,volcaniclastic material and lava flows accumulated in faulted grabens and basins both on the bank andwithin the continent-ocean transition zone to the south, creating the appearance of flat, unstructuredbasement. The seismic structure and inferred composition of Elan Bank revealed by this study contributeto our understanding of microcontinent formation as well as provide a template for identifyingmicrocontinents in accreted terranes and mountain belts

Acreage release by the Australian Government in 2010 offers exploration opportunities in the frontier Mentelle Basin for the first time. The Mentelle Basin is a large deep-water basin on the southwest Australian margin. It consists of a large, very deep water (2,000—4,000 m) depocentre in the west and several depocentres in the east, in water depths of 500–2,000 m. The major depocentres are estimated to contain 7–11 km of sediments. Initial rifting in the Mentelle Basin occurred in the Early Permian, followed by thermal subsidence during the Triassic to Early Jurassic. In the Middle Jurassic renewed extension led to the accumulation of very thick sedimentary successions in half-graben depocentres. Early Cretaceous continental breakup was accompanied by extensive volcanism resulting in a thick syn-breakup volcanic succession in the western Mentelle Basin. Assessment of the petroleum prospectivity of the Mentelle Basin is based on correlations with the adjacent Vlaming Sub-basin. These correlations suggest that the Mentelle Basin depocentres are likely to contain multiple source rock intervals associated with coals and carbonaceous shales, as well as regionally extensive reservoirs and seals within fluvial, lacustrine and marine strata. Petroleum systems modelling suggests that potential source rocks are thermally mature and commenced generation in the Early Cretaceous. The Mentelle Basin offers a wide range of play types, including faulted anticlines and fault blocks, sub-basalt anticlines and fault blocks, drape and forced fold plays, and a large range of stratigraphic and unconformity plays.