1995 Fall AGU Abstract

My abstract was temporarily mislaid by AGU during their e-mail submission process. Hence, it does not appear in the Abstract Volume for the Fall 1995 AGU Meeting. However, it appears in the Additional Abstracts section of the At-Meeting Program. The abstract is reproduced here in its entirety.

Bina, C. R.
Synthetic Mantle Images by Free Energy Minimization

Free energy minimization methods, applied to sets of mineral thermodynamic properties, permit calculation of stable phase assemblages as functions of pressure, temperature, and composition. Incorporation of thermoelastic properties permits calculation of aggregate elastic properties for the resulting stable phase assemblages, thus allowing geophysical forward modeling of (for example) relative buoyancies and seismic wave velocities.

A stochastic optimization method is particularly well-suited to studies which encompass both sharp and gradual phase transitions as well as to analyses which incorporate metastability. Such a method is also well-suited to use of parallel processing.

Application to forsterite-fayalite phase diagrams illustrates the dependence of the sharpness and slope of phase boundaries upon pressure, temperature, and composition.

Application to subduction zone thermal structures illustrates broadening and uplift of alpha -> beta and beta -> gamma transitions and depression of the gamma -> pv + mw transition. It also reveals regions of Fe-rich gamma stability in the cold core of the slab and highlights the buoyancy contributions of the phase transitions. Velocity and buoyancy contributions arising from metastable persistence of lower pressure phases can also be imaged.

Application to mantle plume thermal structures illustrates depression of the alpha -> beta -> gamma transition series and uplift of the gamma -> pv + mw transition. It also reveals how the stability of (Mg,Fe)SiO3 perovskite (relative to mixed oxides) in the mantle is highly sensitive to the thermodynamic properties of silica polymorphs (e.g., stishovite).

Extension to more complex systems (e.g., containing (Mg,Fe)SiO3 ilmenite, Al2O3, CaO, and 2-D compositional variations) is straightforward.

Copyright © 1995 American Geophysical Union
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