Phase relations of a carbonaceous chondrite at lower mantle conditions

The phase relations of Allende meteorite, which belongs to the CV carbonaceous chondrites, were investigated at 22-25 GPa and 1600-2300 degreesC. With increasing pressure, the liquidus phase changes from garnet to Mg-perovskite at about 24.5 GPa. Magnesiowustite crystallizes as the second phase throughout the investigated pressure range, and the solidus curve coincides with the appearance of ringwoodite below 23 GPa, Mg-perovskite at 23-24 GPa and Ca-perovskite above 24 GPa. Immiscible silicate and metallic liquid phases are present in the entire melting range, and a single metallic liquid persists below the solidus down to at least 1600 degreesC. The Kd(Fe/Mg)(crystal/silicateliq.) is well below unity for magnesiowustite (0.7-0.8), garnet (0.35-0.39) and Mg-perovskite (0.34). Ni and S are strongly partitioned into the metallic liquid, and the Ni and Fe partition coefficients between metallic liquid and coexisting minerals are relatively constant with variations in pressure or temperature. An important factor controlling D-metalliq./crystal of Fe and Ni is the oxygen fugacity. Our results provide further constraints on models for early Earth differentiation and core formation. (C) 2004 Elsevier B.V. All rights reserved.