HR: 09:00h
AN: DI41B-05    [Abstracts]
TI: Stability of a Compressible Hydrous Melt Layer Above the Transition Zone
AU: * Youngs, B A
EM: bryony.youngs@yale.edu
AF: Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, CT 06520-8109, United States
AU: Bercovici, D
EM: david.bercovici@yale.edu
AF: Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, CT 06520-8109, United States
AB: The transition zone water-filter model (Bercovici and Karato, Nature, 2003) provides a possible explanation for the conflicting geochemical and geophysical evidence about layering and chemical heterogeneity in the mantle. The model proposes that ambient upwelling mantle undergoes dehydration melting upon leaving the highly water- soluble transition zone, and the resulting melt filters out incompatible elements leaving a relatively dry and depleted source region for MORBs It is crucial to the model that the melt phase be denser than the solid phase such that it becomes trapped above the 410-km boundary where it can be entrained by slabs and recirculated into the deeper mantle. Because the melt phase is significantly more compressible than the solid phase it is expected that a density crossover occurs with increasing pressure. There is evidence to suggest this density crossover exists above the transition zone and as such the melt phase will be more dense than the solid. However, the depth of the density crossover is not well constrained. Thus, we investigate the stability of a compressible melt layer which intersects the density crossover. Analytic models of Rayleigh-Taylor type instabilities are used to determine the effects of compressibility and crossover location on the instability growth rates. Subsequently, more realistic models incorporating continual injection of new melt from below and entrainment of melt by slabs are employed to determine the overall effect on layer stability and evolution that results from an intrinsically unstable segment at the melt layer's top.
DE: 3215 Instability analysis
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting