Experimental Petrology of Garnet Lherzolite Melting

University Of California-Davis, Davis CA

Investigators

Abstract

Lesher EAR-0001245 This program investigates melting of nominally anhydrous garnet peridotite between 3 and 5.5 GPa using the octahedral multianvil apparatus. The goals of the experiments are determination of 1) high pressure solidii in P-T space, 2) the compositions of near-solidus melts and crystals, 3) the specifics of the melting reaction, and 4) the functional relationships between temperature and melt fraction required to determine melt productivity. We are performing experiments on a range of garnet lherzolite compositions that differ in the proportion of clinopyroxene. These compositions extend the observational basis for peridotite melting of typical MORB mantle to possible analogs for plume mantle. The experiemts employ micro-exchange techniques to characterize the compositions of melt fractions below 0.1, and more classical approaches at higher melt fractions. Exhaustive P-T calibration work in our laboratory above 3 GPa ensures a level of reproducibility and control of sample environment in the multianvil apparatus similar to that routinely achieved in the piston-cylinder apparatus at lower pressures. The fundamental phase equilibrium data at high pressures obtained in this study will contribution to the very limited experimental database for garnet peridotite melting. Such data are essential for quantitative modeling of melting of peridotite by mantle upwelling beneath ocean spreading ridges, oceanic lithosphere, and continents.