HR: 0800h
AN: T51A-0294    [Abstracts]
TI: Proto-orogeny: stratigraphy, tectonics and neotectonics at the northern Australia collisional margin
AU: * Keep, M
EM: myra.keep@uwa.edu.au
AF: School of Earth and Geographical Sciences, M004, The University of Western Australia, 35 Stirling Hwy, Nedlands, Perth, 6009, Australia
AU: Haig, D W
EM: dwhaig@cyllene.uwa.edu.au
AF: School of Earth and Geographical Sciences, M004, The University of Western Australia, 35 Stirling Hwy, Nedlands, Perth, 6009, Australia
AB: The ongoing arc-continent collision at the northern Australian margin causes a variety of crustal responses, both at the collisional front and in the hinterland. From fieldwork in East Timor (collisional front) and extensive seismic structural interpretation across the North West Shelf (hinterland) we propose that continental collision initiated with the arrival of an offshore plateau of the Australian margin at the subduction zone at 10.8 Ma, and that remnants of this collided plateau occur throughout Timor. Detailed stratigraphic analyses and biostratigraphic age determinations have been crucial to re-evaluating the stratigraphy of East Timor, and thus re-defining kinematic and geodynamic models for deformation in this very young orogenic belt. Using these tools in addition to structural mapping and geochemical analyses, we have significantly altered age determinations and tectono-stratigraphic affinities for key units (e,g the type section of the Miocene is a thrust stack of Triassic-Cretaceous material), recognised new stratigraphic associations (e.g. thick Australian-derived pelagites in association with thrust slices of exotic material), identified a previously unrecognised slices of ocean floor material, and documented new structural relationships between Australian and exotic units (shear zones, identification of a crush breccia terrane boundary along late, high-angle faults). In addition we have recognised various basaltic compositions indicating both mid-ocean ridge and ocean-island basalts within thrust sequences, at unique structural levels, and proposed new, well-constrained models, for tectonic events. Significant shortening at the collisional front protected much of the hinterland from collisional strain, to the extent that shortening behind the collision is limited to approximately 1per cent. We attribute hinterland deformation to elastic flexure and structural re-amplification of pre-existing topography. Further west, the collisional segment of the margin transitions into a passive margin, where deformation is dominated by far-field stresses generated elsewhere along the Australian plate margin, generating anomalous intraplate seismicity.
DE: 8000 STRUCTURAL GEOLOGY
DE: 8004 Dynamics and mechanics of faulting (8118)
DE: 8011 Kinematics of crustal and mantle deformation
DE: 8038 Regional crustal structure
DE: 8104 Continental margins: convergent
SC: Tectonophysics [T]
MN: 2007 Fall Meeting