Mapping Tertiary mid-ocean ridge subduction and slab window formation beneath Sundaland using seismic tomography

Abstract

Based on tectonic reconstructions, Whittaker et al. (2007) proposed that a slab window formed beneath Sundaland between 70 and 43 Ma, due to subduction of the Wharton Basin spreading ridge between India and Australia. They suggest that extension in the Java Sea region at this time was exacerbated as a result of upwelling asthenosphere associated with the slab window. Active ridge subduction and subsequent slab window formation can severely affect basin formation, heatflow and petroleum systems development on the overriding margin. A slab window forms between diverging plates when a mid-ocean ridge is subducted, leading to anomalous thermal effects like increased mantle wedge temperatures and thermal gradients in the overlying crust. Whittaker et al.?s (2007) kinematic reconstructions rely on restoring now-subducted lithosphere based on preserved ocean crust, but the inherent uncertainties in this process call for an independent evaluation of this model. Mantle seismic tomography models provide qualitative boundary conditions for modelled tectonic histories. We compare seismic tomography models with the model of Whittaker et al. (2007) at a range of mantle depths to confirm the existence of a slab window, and obtain bounds for its maximum regional extent. We identify a break in the high-velocity, down-going Indian-Australian slab at depths between 950-1350 km and longitudes between 85° and 110°, supporting the presence of a slab window. However, we find that the window is located approximately 5° further north and 10°-15° further west than previously proposed, implying that the Wharton Ridge was subducted farther west than previously suggested.