A NEW LOOK AT DIFFERENTIATION OF THE EARTH FROM MELTING EXPERIMENTS ON THE ALLENDE METEORITE

CARBONACEOUS chondrites contain approximately solar abundances of the non-volatile elements1, but are much more FeO-rich2 than upper mantle peridotites3 or hypothetical 'chondritic' mantle compositions4,5. If the Earth accreted from unfractionated, primitive meteoritic debris similar to the carbonaceous chondrites, how then did it become a fractionated, layered body with a crust, mantle and core? Here I report the results of high-pressure melting experiments on the Allende CV3 carbonaceous chondrite, which address this question and provide a new look at the Earth's earliest stage of differentiation. Multi-anvil experiments at 24, 26 and 26.5 GPa show that FeO-rich magnesiowüstite is an abundant crystallizing phase at temperatures near the Allende silicate liquidus. If a chondritic Earth experienced a high-temperature molten stage, then during cooling and crystallization, FeO-rich magnesiowüstite could be segregated to the deepest levels of the Earth's interior. Magnesiowüstite fractionation may thus have depleted the initial FeO content of the primitive chondritic mantle and contributed to the formation and growth of the Earth's core. © 1990 Nature Publishing Group.