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GEOCHEMISTRY OF MANTLE-CORE DIFFERENTIATION AT HIGH PRESSURE

机译：高压下地幔微分的地球化学

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THE apparent excess of siderophile (iron-loving) elements in the Earth's mantle has been a long-standing enigma in the geochemistry of mantle-core differentiation(1,2). Although current models have proved successful in explaining some aspects of this problem(3-7), important questions remain. In particular, the mantle's near-chondritic ratio of nickel to cobalt (close to that expected for the material from which the Earth formed) is hard to explain, given the markedly different ambient-pressure partitioning behaviour of these elements between iron-alloy and silicate melts(3-8). Here we report experimental results which show that both elements become less siderophile with pressure, but the effect is much more pronounced for Ni, so that the partition coefficients of the two elements become essentially equivalent at an extrapolated pressure of similar to 28 GPa. The absolute and relative abundances of Ni and Co in the mantle are therefore consistent with alloy-silicate chemical equilibrium at high pressure, indicating that core formation may have taken place in a magma ocean with a depth of 750-1,100 km. We also find that, unlike Ni and Co, sulphur becomes more siderophile with pressure, Sulphur's increased affinity for iron with depth could make it the dominant light element in the Earth's core. [References: 30]
机译：地球地幔中明显存在嗜铁（铁元素）元素一直是地幔核分化地球化学的一个长期谜团（1,2）。尽管目前的模型已被证明可以成功解释该问题的某些方面（3-7），但仍然存在重要的问题。特别是，由于铁和硅酸盐之间这些元素在环境压力下的分配行为明显不同，因此很难解释地幔中镍与钴的近软骨比（接近于地球形成材料所预期的比率）。融化（3-8）。在这里，我们报告的实验结果表明，两种元素在压力下的亲铁性均降低，但对于Ni的影响更为明显，因此，在类似于28 GPa的外推压力下，两种元素的分配系数基本相等。因此，地幔中Ni和Co的绝对和相对丰度与高压下的合金-硅酸盐化学平衡相一致，这表明岩心形成可能发生在岩浆海洋中，深度为750-1,100 km。我们还发现，与Ni和Co不同，硫在压力下变得更加亲铁，而Sulphur对铁的亲和力随着深度的增加而增加，这可能使其成为地球核心中占主导地位的轻元素。 [参考：30]

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