Experimental Studies on Melting (Mg, Fe)O Ferropericlase

Yale University, New Haven CT

Investigators

Abstract

The origin and subsequent evolution of the Earth and other planets in our own and other solar systems is dictated by several factors including original composition and the melt behavior of the constituent phases. However, estimates of the melting temperature of Earth's mantle, which comprises more than three-quarters of the Earth's volume and nearly two-thirds of its mass, remain controversial and elusive. The conditions at which the mantle melts and solidifies is especially important for understanding compositional heterogeneity, which constrains deep structure and mixing and is crucial for inferring the thermo-chemical evolution of the Earth, from planetary accretion and the magma ocean, to continental growth, the formation of the oceans and atmosphere, and the current state of the core-mantle boundary. Currently the mantle is nearly entirely solid, but it has not always been this way. During the formation of the Earth, the mantle was likely completely molten - a magma ocean - before it began to solidify as it cooled. How the mantle crystallized, i.e., from the top, the bottom, or somewhere in between, is unknown. Evidence for melt at the core-mantle boundary, at least in pockets, is strong, as it is near the surface. Investigating the melt behavior of one of the most abundant minerals in the mantle, ferropericlase (Mg, Fe)O, at high pressures will test hypotheses on Earth's formation and elucidate the geochemistry of the deep mantle. Additionally, this experimental investigation will help constrain current temperatures of the Earth by estimating the temperatures at the core-mantle boundary. The experiments will be studied by 2-dimensional mapping of temperature, composition and texture of sample materials placed under the extreme high-pressure, high-temperature conditions of the Earth's early mantle as produced by a laser-heated diamond-anvil cell, in order to identify the conditions at which melting occurs and its subsequent influence on the composition and morphology of the molten and surrounding regions.