Evidence for a late chondritic veneer in the Earth's mantle from high-pressure partitioning of palladium and platinum
Evidence for a late chondritic veneer in the Earth's mantle from high-pressure partitioning of palladium and platinum
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DOI：
10.1038/35019050
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发表时间：
2000-07
期刊：
影响因子：
64.8
通讯作者：
A. Holzheid;P. Sylvester;H. O’Neill;D. Rubie;H. Palme
中科院分区：
文献类型：
--
作者：
A. Holzheid;P. Sylvester;H. O’Neill;D. Rubie;H. Palme
适度亲铁的“亲铁”元素（如镍和钴）在硅酸盐液体中的高压溶解度已经被用来表明，在早期地球上，形成核的金属和硅酸盐地幔之间的平衡建立在岩浆海洋的底部。但是，只有在高压下的金属-硅酸盐分配系数比在一个大气压下实验测定的分配系数低几个数量级时，才能用这样的模型解释地球上地幔中高度亲铁元素（如铂族元素铂、钯、铱、钌和锇）的观测浓度（参考文献，）。在这里，我们提出了一个实验测定的钯和铂在硅酸盐熔体中的溶解度作为压力的函数到16 GPa（对应于约500公里的深度在地球上）。我们发现，钯和铂的金属硅酸盐分配系数，来自溶解度，不随压力而降低，也就是说，钯和铂保留了强烈的偏好，即使在高压下的金属相。因此，在上地幔中观察到的钯和铂的丰度似乎是最好的解释，“晚单板”除了南极物质的上地幔停止核心形成。
The high-pressure solubility in silicate liquids of moderately siderophile ‘iron-loving’ elements (such as nickel and cobalt) has been used to suggest that, in the early Earth, an equilibrium between core-forming metals and the silicate mantle was established at the bottom of a magma ocean,. But observed concentrations of the highly siderophile elements—such as the platinum-group elements platinum, palladium, rhenium, iridium, ruthenium and osmium—in the Earth's upper mantle can be explained by such a model only if their metal–silicate partition coefficients at high pressure are orders of magnitude lower than those determined experimentally at one atmosphere (refs ,,,,,). Here we present an experimental determination of the solubility of palladium and platinum in silicate melts as a function of pressure to 16 GPa (corresponding to about 500 km depth in the Earth). We find that both the palladium and platinum metal–silicate partition coefficients, derived from solubility, do not decrease with pressure—that is, palladium and platinum retain a strong preference for the metal phase even at high pressures. Consequently the observed abundances of palladium and platinum in the upper mantle seem to be best explained by a ‘late veneer’ addition of chondritic material to the upper mantle following the cessation of core formation.