seismics
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Seismic reflection, seismic refraction and portable broadband data collected within Western Australia's Yilgarn Craton, in particular the Eastern Goldfields Province, are providing detailed images of several of its highly mineralized terranes as well as new insights into the crustal architecture of the region. When the results from these seismic techniques are integrated, the results are providing a better understanding of the structure of the crust and lithosphere beneath the Yilgarn Carton, from the surface to depths in excess of 300 km.
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Pending
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Integration of conventional interpretation of deep-seismic data with potential field modelling is a powerful tool for elucidating the geology of continental margins and particularly the continent-ocean transition zone (COT). Recent work carried out on the Wilkes Land margin of East Antarctica using new seismic and potential field data shows the power of combining these techniques. In this study, the initial deep-seismic interpretation was combined with sonobuoy- and stacking-derived velocity information to provide a starting model for the potential field modelling; the potential field model and aspects of the seismic interpretation were iterated until a consistent interpretation was reached. The most important observations from the COT zone on the Wilkes Land margin include: ? The outer edge of the COT, that is the point at which the crustal type becomes 100% oceanic, is much further offshore than previously interpreted from seismic data and seafloor spreading anomalies, and lies beneath the deep ocean basin. ? The COT is dominated by a basement ridge complex which may represent serpentinised, unroofed mantle peridotites and associated intrusions and extrusions related to decompression melting, similar to features inferred on the conjugate southern Australian margin. ? The lower crust is inhomogeneous, probably due to massive localised intrusion landward of the COT; however, pre-existing inhomogeneities cannot be ruled out. ? The base of the crust has considerable relief landward of the COT, increasing from ~10 km to 16 km depth over a distance of about 40 km.
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New deep-seismic data acquired from offshore East Antarctica by Australia provide more than 40 crossings of the continent-ocean transition (COT) along the 5500 km length of the continental margin that was formerly adjacent to the east coast of India and the southern margin of Australia prior to East Gondwana breakup. As volcanic activity is relatively subdued on this margin, except in the vicinity of the southern Kerguelen Plateau, the data provide a window into the late-rift and post-rift stages of formation of a non-volcanic rifted margin. Three characteristic margin segments are interpreted in the data. From west to east, these are: Offshore Enderby Land to Prydz Bay (38-80oE): The COT is not clearly defined in this zone, probably due in part to the effect of the Kerguelen hot spot in the Late Cretaceous. Delineation of the COT here will rely heavily on potential field modelling. Queen Mary Land 90-105oE): southeast of the Kerguelen Plateau, the margin is dominated by Bruce Rise, a continental marginal plateau that was formerly conjugate to the Naturaliste Plateau off southwest Australia. The transition from continental to oceanic crust is sharp, in apparent contrast to the conjugate margin off southwest Australia. Wilkes Land (105-140oE): in the area formerly conjugate to southern Australia, the margin is characterised by a broad zone of deeply-subsided continental and transitional crust beneath the inner edge of the deep ocean basin in an area previously considered to have been oceanic crust formed by seafloor spreading.
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Legacy product - no abstract available
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Legacy product - no abstract available
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In a unique study, 44 land-based recorders distributed throughout Tasmania, SE Australia, were deployed to record seismic energy from an encircling array of marine normal-incidence reflection shot lines. We invert refraction and wide-angle reflection traveltimes for crustal structure, with the principal outcome being a map of the Tasmanian Moho. Key tectonic inferences from this map include: (1) the Arthur Lineament metamorphic belt in NW Tasmania overlies a major change in crustal thickness (over 5 km) and probably represents the NW limit of deformation in Tasmania during the Mid-Late Cambrian Tyennan Orogeny, (2) thickening of the crust beneath central northern Tasmania may be associated with the juxtaposition of the Eastern and Western Terranes during the Mid-Devonian Tabberabberan Orogeny, and (3) the difference in crustal thickness between the east and west coasts reflects the presence of differing strain regimes during the Cretaceous break-up of Gondwana. No evidence is found for thin-skinned deformation.
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Crustal reflectivity and bulk seismic velocity variation in the crust do not always closely correlate. Even the most prominent reflection horizons do not always follow iso-velocity contours. These are the major conclusions of co-interpretation of refraction/wide-angle reflection data and conventional reflection profiles on the North West Australian Margin (NWAM).
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Contained in: Proceedings of papers presented at an industry workshop held in Perth, 20 June 2002. Edited by K.F. Cassidy (See link)
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Data from 50 sonobuoys were recorded over the Capel and Faust Basins, 800 km to the east of Australia in water depths 1500-2000 m, during a 2006 seismic survey (GA302) for Geoscience Australia's Big New Oil programme. These data were interpreted and forward modelled by ray-tracing to provide an estimate of P-wave velocities in the upper sedimentary section, and hence constrain estimates of sediment thickness. Also recorded were gravity and magnetic anomaly data which, in conjunction with the very high quality seismic reflection data, provided additional constraints upon the velocity models. Typical ranges in four model layers below water were: 1.9, 2.3-3.0, 3.6-4.7, 5-5.3 km/s. Gravity models based on these results were compared to features identified on depth converted seismic reflection lines and indicate that sediment thickness at densities approximating 2.3 t/m3 may reach 5 km in several localities.