Catalysis of the Olivine to Spinel Transformation by High Clinoenstatite

Science  25 Aug 1995:
Vol. 269, Issue 5227, pp. 1095-1098
DOI: 10.1126/science.269.5227.1095


Although enstatite is a major constituent of the Earth's upper mantle and subducting lithosphere, most kinetic studies of olivine phase transformations have typically involved single-phase polycrystalline aggregates. Transmission electron microscopy investigations of olivine to spinel and modified spinel (β phase) reactions in the (Mg, Fe)2SiO4-(Mg,Fe)SiO3 system show that transformation of olivine in the stability field of spinel plus phase begins with coherent nucleation of spinel on high-clinoenstatite grains. These observations demonstrate that high clinoenstatite can catalyze the transformation by enhancing nucleation kinetics and therefore imply that secondary phases can influence reaction kinetics during high-pressure mineral transformations.