HR: 09:30h
AN: T31D-07    [Abstracts]
TI: How Slab Geometry,Trench Velocity and Viscous Stress Vary in Subduction Systems
AU: * Royden, L H
EM: lhroyden@mit.edu
AF: M.I.T., MIT 54-1026, Cambridge, MA 01890 United States
AB: We have developed semi-analytic, quasi-3D model that provides a dynamically consistent means of computing trench motion, slab geometry and viscous stresses during subduction. In steady-state, trench migration rates vary almost linearly with slab buoyancy and the velocity of the lower mantle and are similar to the range of observed rates for mantle viscosities of ~2.10²⁰ Pa s. Slab dip is not greatly affected by slab buoyancy but denser slabs subduct at slightly shallower angles than more buoyant slabs. Surprisingly, prominent effects on trench migration rates and slab geometry are exerted by the structure and density of the frontal prism and over-riding lithosphere, indicating that near-surface geology plays an important role in regulating subduction. In particular, flat slab subduction seems to be related to the development of high topography near the trench. In general, slabs extending from the surface to the base of the upper mantle are over-supported by viscous stresses in the shallow (<100 km) mantle and under-supported by viscous stresses at greater depth. Thus deeper parts of the subduction system act as an 'engine' for subduction while shallower parts act as a 'brake' on trench motion. Our results show that rates of trench migration respond rapidly as variably buoyant slab material passes into the subduction zone. Trench migration rates can change by a factor of two or more in as little as 2 m.y. after anomalously dense or shallow lithosphere enters the system; during subduction of alternating tracts of dense and buoyant lithosphere, oscillations in subduction rate (i.e. between ~40 and 80 mm/yr) occur with periods as short as 5 Ma.
DE: 1207 Transient deformation (6924, 7230, 7240)
DE: 1219 Gravity anomalies and Earth structure (0920, 7205, 7240)
DE: 1240 Satellite geodesy: results (6929, 7215, 7230, 7240)
SC: Tectonophysics [T]
MN: Fall Meeting 2005