Continental Growth Along the Proto-Pacific Margin of East Gondwana in Australia: Insights from Seismic Tomography
Abstract
The Tasmanides of eastern Australia is a complex series of Palaeozoic to early Mesozoic orogens that is juxtaposed against the eastern margin of the Precambrian shield region of central and western Australia. The subduction-accretion process responsible for its emplacement was accommodated by retreat of the proto-Pacific plate along the eastern margin of Gondwana, which incorporated both Australia and Antarctica. Despite a protracted period of plate convergence, the orogenic process in the Pacific has not been terminated through continent-continent collision, as would be the case if it conformed with the classic Wilson Cycle of continent break-up and reassembly. In this study, passive seismic data from the WOMBAT array - the largest transportable seismic array in the southern hemisphere - is used to image the crust and upper mantle beneath eastern Australia, and provide unique insight into a region of complex continental growth that spans terrrane of Archean, Proterozoic, Palaeozoic and Mesozoic origin. The two primary datasets that are exploited are teleseismic body waves and surface waves extracted from ambient noise. A modified form of teleseismic tomography, adapted to explicitly include the crust and Moho in the 3-D P-wave model and account for sequential deployment of arrays, is used to invert the body wave arrival time data. Transdimensional tomography is used to invert the ambient noise surface wave data for 3-D shear wave structure. Insights and observations from the new imaging results include (1) the location of the eastern boundary of Precambrian Australia at depth, which is further east than previously thought; (2) the clear separation of the Curnamona Province and Archean Gawler Craton by a low velocity zone in the upper mantle beneath the Adelaide Fold Belt; (3) the presence of a large scale orocline embedded within the Lachlan Orogen, as delineated by the fast axis of azimuthal anisotropy in the crust; (4) evidence for an embedded continental fragment, possibly sourced from the break-up of Rodinia, within the accretionary terrane; and (5) widespread Cenozoic volcanism along the eastern seaboard of Australia only occurring beneath regions of thinner lithosphere (< 110 km thick).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2016
- Bibcode:
- 2016AGUFM.T21F..04R
- Keywords:
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- 7218 Lithosphere;
- SEISMOLOGYDE: 8103 Continental cratons;
- TECTONOPHYSICSDE: 8110 Continental tectonics: general;
- TECTONOPHYSICSDE: 8120 Dynamics of lithosphere and mantle: general;
- TECTONOPHYSICS