Core Formation and Mantle Differentiation on Mars
Core Formation and Mantle Differentiation on Mars
复制标题
火星上的地核形成和地幔分异
DOI：
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发表时间：
2013
期刊：
影响因子：
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通讯作者：
T. Kleine
中科院分区：
文献类型：
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作者：
K. Mezger;V. Debaille;T. Kleine
火星陨石（SNC 陨石）的地球化学研究对火星的化学和地球动力学演化产生了重要的约束。这些样本可能不能代表整个火星；然而，它们对火星上的早期分化过程提供了限制。火星样本的大部分成分意味着存在与行星吸积同时形成的金属核心。只有当火星在其历史早期拥有大规模的岩浆海洋，允许金属熔体与熔融硅酸盐有效分离时，火星地幔中高亲铁元素的强烈消耗才有可能。岩浆海洋的凝固产生了化学异质性，其古老的起源体现在在来自火星的不同陨石群中观察到的异质 142Nd 和 182W 丰度。 SNC 陨石中测量到的同位素异常表明，在短命同位素 146Sm 和 182Hf 的生命周期内，火星地幔内发生了主要的化学分馏。 Hf-W数据与火星在几百万年内的快速吸积一致，或者与火星在核心形成过程中的几次大的撞击和不完全金属硅酸盐平衡的更长时间的吸积历史一致。与地球相比，早期形成的化学异质性仍然保留在火星上，尽管通过混合过程略有改变。只有当火星在其历史的最初几千万年之后没有经历有效的全地幔对流或剧烈的板块构造式过程时，才有可能保存这种古老的化学差异。
Geochemical investigation of Martian meteorites (SNC meteorites) yields important constraints on the chemical and geodynamical evolution of Mars. These samples may not be representative of the whole of Mars; however, they provide constraints on the early differentiation processes on Mars. The bulk composition of Martian samples implies the presence of a metallic core that formed concurrently as the planet accreted. The strong depletion of highly siderophile elements in the Martian mantle is only possible if Mars had a large scale magma ocean early in its history allowing efficient separation of a metallic melt from molten silicate. The solidification of the magma ocean created chemical heterogeneities whose ancient origin is manifested in the heterogeneous 142Nd and 182W abundances observed in different meteorite groups derived from Mars. The isotope anomalies measured in SNC meteorites imply major chemical fractionation within the Martian mantle during the life time of the short-lived isotopes 146Sm and 182Hf. The Hf-W data are consistent with very rapid accretion of Mars within a few million years or, alternatively, a more protracted accretion history involving several large impacts and incomplete metal-silicate equilibration during core formation. In contrast to Earth early-formed chemical heterogeneities are still preserved on Mars, albeit slightly modified by mixing processes. The preservation of such ancient chemical differences is only possible if Mars did not undergo efficient whole mantle convection or vigorous plate tectonic style processes after the first few tens of millions of years of its history.