This proposal aims to develop new isotopic tools designed to constrain the core formation process in the Earth. We will use isotopic fractionations imparted by metal-silicate equilibration during core formation to obtain new and firm constraints on (i) the physical and chemical processes during formation of the Earth's core; and (ii) on the origin of volatile elements and the volatile accretion history of the Earth. The underlying concept of our approach is to compare observed mantle-core isotopic fractionations (determined on natural samples) to the experimentally-determined isotope fractionation between liquid metal (core analogue) and liquid silicate (mantle analogue). Since the magnitude of isotope fractionation is strongly temperature-dependent, this comparison will enable us to evaluate core formation temperatures. I propose to use the stable isotope systematics of W, Mo and Cr to assess as to whether core formation temperatures for the Earth, Moon, Mars and asteroids are different, as would be expected if metal segregation in the Earth involved metal-silicate equilibration in a deep magma ocean. If instead all bodies have similar core formation temperatures, then formation of the Earth's core most probably involved some disequilibrium induced by direct core mergers during accretion from differentiated bodies. The second major theme of the proposed research uses Ge and Sb stable isotopes to trace the origins of Earth's volatiles. The combined investigation of Ge and Sb isotope fractionations in natural samples and metal-silicate equilibration experiments will enable us to determine as to whether Ge and Sb, and with them other volatile elements, show an isotope signature resulting from core formation. Identifying such a signature would provide the unequivocal evidence that volatile elements were delivered to the Earth during core formation and not subsequently, after the core had formed.
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