HR: 0800h
AN: T51A-0322    [Abstracts]
TI: Buoyancy control on continent subduction and implications for the dynamics of India-Asia convergence
AU: Goes, S
EM: s.goes@imperial.ac.uk
AF: Imperial College London, Dept. Earth Sci. and Eng., London, SW7 2AZ, United Kingdom
AU: * Capitanio, F A
EM: fabio.capitanio@sci.monash.edu.au
AF: Monash University, School of Mathematical Sciences, Clayton Victoria, 3800, Australia
AU: Morra, G
EM: morra@tomo.ig.erdw.ethz.ch
AF: ETH Zurich, Institute of Geophysics, Zurich, CH-8093, Switzerland
AB: At some point during their evolution, most trenches encounter continental lithosphere. Because average continental lithosphere is positively buoyant, collision is often the result. However, there is evidence that some continental crust and lithosphere does get subducted. For example, Indian plate kinematic reconstructions show that Meso-Cenozoic subduction consumed a highly heterogeneous lithosphere including small oceanic basins and substantial portions of the flanking continental lithosphere, which had undergone various degrees of extension. Here we study how continental lithosphere can affect the subduction process in general, and to what extent it can be responsible for the variations in plate motions during Greater Indian continent subduction and subsequent collision onto Asian plate. We model a visco-elastic slab, which subducts without external forcing, i.e. driven by slab pull and ridge push only, into a passive viscous mantle. We find that lithospheric buoyancy is the primary control on continental subductability. Only if a significant amount of upper crust is stripped off, and the mantle lithosphere is not strongly melt depleted, does continental lithosphere become negatively buoyant. If in addition, the lower crust is eclogitized, continental lithosphere can even be as negatively buoyant as old oceanic lithosphere. Oceanic slab pull and ridge push modulate to which depth continental material is subducted (usually between 100 and 400 km) before subduction stalls, but can not change whether sustained continental subduction occurs or not. However, the combination of continental buoyancy, slab pull and ridge push strongly affects the partitioning of subduction velocities, i.e. plate advance, subduction velocity and trench motions. We find that the combination of a decreased slab pull, due to continent subduction, and continued strong ridge push is required to explain the peculiar overturned morphology of the Indian upper mantle slab, and match the variations in relative trench advance and subduction rates, including the strong trench advance which resulted in indentation.
DE: 8104 Continental margins: convergent
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8157 Plate motions: past (3040)
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting