This proposal describes a 2-year program to experimentally investigate the petrology of the lower mantle, the single largest region of the earth. Using the laser-heated diamond cell, a natural garnet peridotite composition will be taken to P-T conditions existing throughout the lower mantle . A combination of in situ X-ray diffraction and quenched-product analysis will be used to determine: (1) the identity and quantity of major phases present; (2) the major-element partitioning between these phases as a function of pressure; (3) the equations of state of the phases, and hence of the assemblage for direct comparison with the seismological profiles of the lower mantle; and (4) the solidus temperature of the assemblage from which tight constraints on the deep-mantle geotherm could be obtained. Year 1 will concentrate on sub-solidus equilibria, and Year 2 will concentrate on solidus/liquidus equilibria of the natural peridotite composition as well as reconnaissance (solid-state and liquid) equilibria of an iron-enriched composition. These experiments are a direct extension of techniques used in prior work that successfully determined the ultrahigh P/T equilibria of individual natural minerals, and they would represent the first time that an actual rock assemblage had been studied at the conditions existing throughout the bulk of the mantle.
