HR: 0830h
AN: T41C-0243    [PDF]
TI: The Dynamics of Slab detachment: Process Initiated by Melting of Subducted Crust
AU: * Gerya, T
EM: taras.gerya@ruhr-uni-bochum.de
AF: Institut of Geology, Mineralogy and Geophysics, SFB 526, Ruhr-Universiy Bochum, Universitaetstrasse 150, Bochum, D-44780 Germany
AU: * Gerya, T
EM: taras.gerya@ruhr-uni-bochum.de
AF: Institute of Experimental Mineralogy Russian Academy of Sciences (at present Alexander von Humboldt Foundation Fellow), Chernogolovka, Moscow, 142432 Russian Federation
AU: Yuen, D
EM: davey@krissy.geo.umn.edu
AF: University of Minnesota Supercomputing Institute and Department of Geology and Geophysics Institute of Experimental Mineralogy Russian Academy of Sciences, University of Minnesota, Minneapolis, MN 55455-0219 United States
AB: It is well recognized that slab detachment or breakoff is a realistic geological process, as shown by recent tomographic imaging [1]. Using 2-D upper-mantle model with an area of 660 km deep and 2000 km wide we have investigated with a finite-difference and marker numerical technique the multi-resolutional character of thermomechanical phenomena related to this complex geological process. We have used up to 50 million markers on a shared-memory computer for delineating the complex multiscale structures in the composition, viscosity, accumulated strain, shear heating, and other field variables. Our experiments show that this process can be initiated by slab weakening due to the thermal relaxation of the slab and related melting of the subducted oceanic crust. The melting propagates within the subducted oceanic crust at the top of the slab occurring at the restricted depth interval of 100 to 200 km defined by the non-linear dependence of wet solidus temperature of the oceanic crust with pressure. The detachment process is self-accelerating due to the strain and thermal erosion focussing and strong thermal feedback from the shear heating. Slab detachment develops around 10% faster with viscous dissipation included, thus showing the importance of shear heating in this process. Detached slab rapidly fall down having a tendency of coherent rotation. This may produce near horizontal relatively cold slab fragments laying on denser mantle at 660 km discontinuity. Influence of a temperature- and pressure-dependent thermal conductivity for the process of thermal relaxation of the slab is significant. Overall 20% increase in thermal conductivity of mantle produce 20% decrease in timescale of detachment. This support the idea that breakoff process is mainly driven by focussed thermal erosion with timescale linearly dependent on heat conductivity. Rapid changes in topography and significant volcanic activity due to the massive melting of subducted oceanic crust during the slab detachment process are plausible consequences of this vigorous geodynamic scenario. [1] Levin, V., Shapiro, N., Park, J. and M. Ritzwoller, Seismic evidence for catastrophic slab loss beneath Kamchatka, Nature, 418, 763-767, 2002.
DE: 3210 Modeling
DE: 3230 Numerical solutions
DE: 3640 Igneous petrology
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8150 Plate boundary--general (3040)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting