HR: 0830h
AN: T21D-0486    [PDF]
TI: Localization of Shear Along a Strong Inclusion in a Continuous Deformation Model: An Application to the Altyn Tagh Fault
AU: * Dayem, K E
EM: dayem@colorado.edu
AF: University of Colorado, Department of Geological Sciences, Campus Box 399, Boulder, CO 80309 United States
AU: Houseman, G A
EM: greg@earth.leeds.ac.uk
AF: University of Leeds, School of Earth Sciences, Leeds, LS2 9JT United Kingdom
AU: Molnar, P
EM: molnar@cires.colorado.edu
AF: University of Colorado, Department of Geological Sciences, Campus Box 399, Boulder, CO 80309 United States
AB: Two end-member descriptions are commonly used to describe deformation of the lithosphere in continental collision zones. One assumes that deformation occurs on discrete faults that extend through the crust and into the upper mantle. The second treats the continental lithosphere as a viscous fluid that deforms continuously, with faults occurring only in the brittle upper crust. The first description uses the existence of strike-slip faults with large offsets and rapid slip as an argument that deformation is not continuous on a lithospheric scale. Here we apply the second view to examine the effects of a marked contrast in strength (or viscosity) on the localization of shear strain along the discontinuity using thin viscous sheet calculations with continuous displacement fields. Two parameters are varied to examine a range of lithospheric properties: the stress-strain exponent n, which relates strain rate to a power of stress, and the Argand number Ar, a measure of buoyancy force relative to viscous stress. We find that a shear zone develops in the weaker material just outside the rigid inclusion when the discontinuity is oblique to the principal convergence direction. The width of this zone narrows along the rigid inclusion with increasing strain, increasing n, and increasing Ar. When applied to the scale of the Tarim Basin, the results indicate the development of a shear zone approximately 100 km wide, comparable to the width of the Altyn Tagh fault zone. The formation of this shear zone does not require strain-weakening of the material or fault zones that extend through the lithosphere.
DE: 8110 Continental tectonics--general (0905)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting