MATERIAL TRANSPORT IN LASER-HEATED DIAMOND ANVIL CELL MELTING EXPERIMENTS

Olivine from San Carlos, Arizona, Fa0.093 was compressed in a diamond anvil cell and melted under the action of a Nd:YAG laser. Stripes of melted material wert formed by scanning the sample under the laser. Scanning electron microscopy and x-ray microanalysis of the recovered samples reveal large-scale (approximately 100-mu-m) transport of material through the sample, caused by the laser-induced melting. Early-crystallizing phases form at the beginning of the laser-melted stripe; incompatible elements and late-crystallizing phases am concentrated at the end of the stripe. This behavior is exploited to determine melting behavior of high-pressure silicate assemblages of olivine composition. At pressures where beta-spinel is the phase melted, relative strengths of partitioning can be estimated for the incompatible elements studied. Iron was found to partition into the melt from beta-spinel less strongly than calcium, and slightly more strongly than manganese. At higher pressures, where a silicate perovskite/magnesiowustite assemblage is melted, it is determined that silicate perovskite is the liquidus phase, with iron-rich magnesiowustite accumulating at the end of the laser-melted stripe.