Structure of the southeast Australian lithosphere from a transportable seismic array experiment
Abstract
In contrast to the ancient Proterozoic and Archean terranes of central and western Australia, eastern Australia consists of an outward stepping series of fold belts that largely formed between the Middle Cambrian and Triassic as a result of convergence along the proto-Pacific margin of east Gondwana. In southeast Australia, the Delamerian Orogen abuts the Precambrian cratons to the west and incorporates the Adelaide Fold Belt in South Australia. The younger Lachlan Orogen is located to the east of the Delamerian Orogen, and underlies much of Victoria and New South Wales. Tasmania, an island state to the south of Victoria, contains elements of both older Precambrian cratonic lithosphere and younger accretionary orogenic terrane. The tectonic evolution of the Lachlan orogen may have involved multiple coeval subduction zones or orogen-parallel strike-slip tectonics, but a consensus on this issue remains elusive, with competing tectonic models ranging between accretionary oceanic systems to largely intra-cratonic settings. Large new geophysical datasets capable of probing beneath the extensive Mesozoic-Cainozoic volcanic and sedimentary cover sequences that obscure large tracts of the underlying Palaeozoic basement are crucial to achieving a better understanding of this region. In 1998, a 40 element seismic array was deployed in western Victoria with the aim of studying the lithospheric transition zone between the Delamerian and Lachlan orogens by exploiting relative arrival times from distant earthquakes. This deployment began what is now known as the WOMBAT project, an ambitious transportable array experiment that aims to cover eastern Australia with seismometers at 50 km intervals. To date, over 550 sites have been occupied in Tasmania, Victoria, South Australia and New South Wales. The vast amount of passive data that has been recorded provides unprecedented insight into the deep structure beneath southeast Australia. This presentation will focus on recent imaging results obtained from the WOMBAT experiment. These include: (1) 3-D P-wave teleseismic tomography obtained by combining residuals from adjacent arrays; (2) ambient noise tomography for both group and phase velocity maps; (3) joint inversion of passive and active source data in Tasmania; (4) receiver function inversion using data from three-component stations. The teleseismic tomography results clearly reveal the lithospheric transition between the Delamerian and Lachlan orogens as a marked W-E high-low velocity contrast that extends from southern Victoria to northern NSW. Ambient noise tomography from the mainland arrays reveals sedimentary basins as marked velocity lows, and clearly elucidates the presence of pre-Tertiary infrabasins beneath the Murray Basin. In Tasmania, the ambient noise tomography and joint passive and active source tomography elucidate a major lithospheric boundary and associated crustal deformation. Current efforts are focused on attenuation tomography which has started to show promising results in Tasmania, with coherent patterns of differential t* residuals obtained from the spectral ratios of teleseismic P-waves.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.S51C..01R
- Keywords:
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- 7205 SEISMOLOGY / Continental crust;
- 7218 SEISMOLOGY / Lithosphere;
- 7270 SEISMOLOGY / Tomography;
- 8110 TECTONOPHYSICS / Continental tectonics: general