超高圧下での元素分配からみた初期地球の分化

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We measured the partition coefficients for lithophile elements between mantle minerals, such as Mg-perovskite and magnesiowustite, and magma at high pressure. The partition coefficients at temperatures around 4000K at high pressures estimated by extrapolating the observed partition coefficients are in the range from 0.5 to 2 for the most lithophile elements. Thus, the abundance of lithophile elements in the mantle does not deviate significantly from the chondritic value even after fractionation of the high pressure minerals at temperatures around 4000K. Thus the chondritic relative abundance of refractory lithophile elements in the primitive upper mantle is consistent with the frractionation of the high pressure phases in the deep magma ocean extending to the lower mantle depth. We also measured the partition coefficients for some siderophile elements such as Co and Ni between metallic melt and silicate melt at high pressure and temperature. The results suggest that the core-mantle separation occurred after the metal-silicate equilibrium in the deep magma ocean at the lower mantle depth. The partition coefficients for Re and Pd between metallic melt and silicate melt indicate that the partition coefficient for Pd is one order of magnitude greater than that for Re, which can not produce the chondritic relative abundance of Re and Pd in the mantle by metal-silicate equilibrium. Thus, the highly siderophile elements in the mantle such as Re and Pd which have about 0.003 times of the chondritic abundance can be accounted for by the late veneer, i.e., accretion of a small amount of C1 chondritic material after core formation of the Earth.
特定非営利活動法人日本火山学会の論文
1997-04-25

超高圧下での元素分配からみた初期地球の分化

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