Kinetics of High Pressure Phase Transformations of (Mg,Fe)SiO3 Pyroxene and Implications for Metastability in Subducting Lithosphere
Abstract
Olivine and (Mg,Fe)SiO3 pyroxene are the most abundant minerals in subducting oceanic lithosphere. The cool interior of the slab is thought to kinetically inhibit the transformation of anhydrous olivine and enstatite to their high-pressure polymorphs, allowing metastable olivine and enstatite to persist into the mantle transition zone (MTZ). The metastable persistence of olivine into the MTZ is an essential part of the transformational faulting model of deep focus earthquakes. Previous studies have explored the kinetics and mechanisms of polymorphic phase transitions in olivine using analogs, the end Mg2SiO4 member and natural (Mg1.8,Fe0.2)SiO4. These studies are generally consistent with metastable persistence of anhydrous olivine into the MTZ. However, the addition of relatively small amounts of H2O greatly increase olivine-transformation rates and make metastable persistence hydrous olivine into the MTZ unlikely (Diedrich et al. 2009). Experimental studies of MgSiO3 enstatite transformation kinetics have shown that enstatite is much slower to transform than olivine (Hogrefe et al. 1994). We have performed a series of high-pressure experiments in which we transform spheres of San Carlos enstatite (Mg0.9,Fe0.1)SiO3 and measure reaction-rim thicknesses to determine transformation rates. By comparing our results with those from Hogrefe et al. (1994) we will examine the effect of Fe on the transformation kinetics of the enstatite to stishovite + wadsleyite and enstatite to akimotoite reactions. An improved understanding of enstatite reactions is needed to determine if it is likely to persist metastably into the MTZ and affect slab buoyancy or cause deep-focus earthquakes.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMDI23A2369L
- Keywords:
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- 1042 GEOCHEMISTRY / Mineral and crystal chemistry;
- 3611 MINERALOGY AND PETROLOGY / Thermodynamics;
- 3613 MINERALOGY AND PETROLOGY / Subduction zone processes;
- 3924 MINERAL PHYSICS / High-pressure behavior