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首页> 外文期刊>Contributions to Mineralogy and Petrology >Melting of clinopyroxene + magnesite in iron-bearing planetary mantles and implications for the Earth and Mars
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Melting of clinopyroxene + magnesite in iron-bearing planetary mantles and implications for the Earth and Mars

机译：含铁行星地幔中亚铁斜辉石+菱镁矿的熔化及其对地球和火星的影响

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The assemblage clinopyroxene + magnesite was observed in Earth’s high-pressure metamorphic samples, and its stability in subducting slabs was confirmed by experiments. Recent studies also suggested that the fO2 variations observed in SNC meteorites can be explained by polybaric graphite-CO-CO2 equilibria in the Martian mantle. Although there is no direct evidence for the stability of the cpx + mc assemblage in Mars mantle, its high-pressure–high-temperature decomposition to cpx + fo + CO2 makes it a good analogue for the source of carbon metasomatism, in particular, to study nakhlites formation. Iron, which is present in the Earth’s and Martian mantles, may, however, influence the speciation of carbon. We performed experiments on a clinopyroxene + magnesite assemblage at 1.8 and 3.0 GPa and temperatures corresponding to the Earth’s and Martian mantles. The role of iron and of fO2 was investigated by (1) replacing all or part of the magnesite by siderite FeCO3, (2) adding Fe0 and (3) using graphite C capsules. A carbonate-silicate melt forms at both Earth and Mars conditions. Clinopyroxene and olivine are the main solid phases in the iron-free experiments. Fe2+ and Fe0 decrease their melting temperatures and increase the silicate fraction in the melt. The produced carbonate-silicate melts may be involved in the formation of some carbon-rich lavas on Earth (e.g., carbonatites, ultramafic lamprophyres, or kamafugites). Our results may also be used to interpret ophiolite samples or inclusions. In particular, we show that wüstite may form in equilibrium with carbonate-silicate melt in opx-(and silica-) poor regions of the mantle below 3 GPa. Our results also confirm the hypothesis of carbon metasomatism in the Martian nakhlites source. Immiscibility or reduction could explain the absence or rarity of C in Martian lavas.
机译：在地球的高压变质样品中观察到了组合的斜辉石+菱镁矿，并通过实验证实了其在俯冲平板中的稳定性。最近的研究还表明，在SNC陨石中观察到的fO2变化可以用火星地幔中的多气压石墨-CO-CO2平衡来解释。尽管没有直接证据表明cpx + mc组合在火星地幔中具有稳定性，但是其高压-高温分解为cpx + fo + CO2使其成为碳交代作用的良好模拟来源，特别是研究nakhlites的形成。然而，存在于地球和火星地幔中的铁可能会影响碳的形态。我们在1.8 GPa和3.0 GPa以及温度对应于地球和火星地幔的斜辉石+菱镁矿组合上进行了实验。通过（1）用菱铁矿FeCO3代替全部或部分菱镁矿，（2）添加Fe0和（3）使用石墨C胶囊来研究铁和fO2的作用。在地球和火星条件下都会形成碳酸盐-硅酸盐熔体。 Clinopyroxene和橄榄石是无铁实验中的主要固相。 Fe2 +和Fe0降低了它们的熔融温度并增加了熔体中的硅酸盐含量。产生的碳酸盐-硅酸盐熔体可能参与了地球上一些富碳熔岩的形成（例如，碳酸盐岩，超镁铁质的煌斑岩或kafufugites）。我们的结果也可用于解释蛇绿岩样品或包裹体。特别是，我们表明，在低于3 GPa的地幔中opx-（和二氧化硅）贫乏地区，辉石可能与碳酸盐-硅酸盐熔体平衡形成。我们的研究结果也证实了火星纳克力人碳源交代作用的假说。不溶性或还原性可以解释火星熔岩中C的缺乏或稀有性。

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