HR: 14:10h
AN: V33D-03 INVITED    [Abstracts]
TI: Multi-scale dynamics near the Moho: The role of mass and energy exchange between the crust, sub-continental lithosphere and asthenosphere in crustal development
AU: * Dufek, J
EM: dufek@berkeley.edu
AF: University of California, Berkeley, 307 McCone Hall, Berkeley, CA 94720, United States
AU: Huber, C
EM: chuber@seismo.berkeley.edu
AF: University of California, Berkeley, 307 McCone Hall, Berkeley, CA 94720, United States
AB: Although there are a wide range of models for the genesis and evolution of continental crust, a nearly universal feature of these models, either overt or implicit, is a statement of the mass balance problem: the mean continental crust is significantly more silicic relative to what is thought to be the mean influx of mantle melts. Revised estimates for mantle melt flux into the crust are even greater than previously posited, further exacerbating the mass balance problem (Dimalanta, et al, 2002; Jicha, et al., 2006). Geophysical observations, xenolith suites, and improved understanding of lower crustal phase assemblages and rheologies have all contributed to the view that crustal level material can potentially be involved in a delamination event and return to mantle depths, providing one process that may alleviate the mass balance problem and preferentially removes mafic components. This two-way coupling of material between the mantle and crust has specific implications for the thermal and chemical evolution of the underlying mantle. Here we assess melting processes occurring at multiple scales at or below the Moho discontinuity, along with equivalent processes occurring in the lower crust. We combine three types of physical modeling, finite volume, finite element, and lattice boltzmann techniques to understand the bulk dynamics, stress evolution and fine-scale segregation and reaction of melts with the surrounding residuum. We use fine scale models to develop "sub-grid" models to understand better how large-scale motions translate into melting and segregation at the fine-scale. We find that a thermally mature crust, due to a combination of increased thickness and elevated melt flux, promotes homogeneity of intermediate composition melts in the lower crust. Stochastic numerical simulation of melt intrusion in the lower crust indicates that provided that pressure is greater than ~9 kbar, and melting and extraction has proceeded to ~0.2 volume fraction or greater, the phase assemblage and rheology will favor density instabilities. The downwelling garnet pyroxenites generate return flow in the mantle that can produce excess melt and brings deeper reservoir material into the sub- continental lithosphere, providing a source for episodic production of mantle heterogeneity.
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8121 Dynamics: convection currents, and mantle plumes
DE: 8137 Hotspots, large igneous provinces, and flood basalt volcanism
DE: 8412 Reactions and phase equilibria (1012, 3612)
DE: 8439 Physics and chemistry of magma bodies
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting