HR: 1330h
AN: T32B-0929    [PDF]
TI: Thermal Signatures and Deformation of Detached Slabs in the India-Asia Collision
AU: * Jarvis, G T
EM: jarvis@yorku.ca
AF: York University, Department of Earth and Atmospheric Science 4700 Keele St., Toronto, ON M3J 1P3 Canada
AU: Shahnas, H
EM: shahnas@yorku.ca
AF: York University, Department of Earth and Atmospheric Science 4700 Keele St., Toronto, ON M3J 1P3 Canada
AB: Seismic tomographic studies have revealed the existence of cold patches at depths of one to two thousand km below the Indian sub-continent. These are believed to be the residuals of former subducting slabs detached from India when it collided with Eurasia at about 45 Ma. If this interpretation is correct, something must have slowed their natural rate of descent; otherwise the remnants of the sinking slab would have sunk to the base of the mantle during this period of time. In the present study we investigate the effects of a depth-dependent viscosity as a potential explanation for the retarded sinking process. We have employed finite differences in a full cylindrical shell model in order to eliminate side-boundary effects. The material properties are set on a Lagrangian grid which initially comprises a series of regular four-node elements in polar coordinates. This information is then mapped to an Eulerian mesh on which the momentum and energy equations are solved. The Lagrangian grid deforms on the basis of the updated velocity field obtained at each time step. The information exchange between the Eulerian frame and its Lagrangian counterpart is repeated at each time step and provides a new material configuration on the Eulerian mesh for the subsequent step of time evolution. The path of the slab remnants is precisely tracked by the Lagrangian grid. The deformation style of the tracker grid demonstrates how and where the resistance occurs which holds the slab in mid-mantle depths for a geological time of 50 to 100 My. Our numerical results suggest that a step-like viscosity change at depth of 700 km could account for the observed slow rate of descent of the slab remnants.
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8121 Dynamics, convection currents and mantle plumes
SC: Tectonophysics [T]
MN: 2003 Fall Meeting