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arXiv 1012.5325astro-ph.EP
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地球硅酸盐蒸气大气中的化学分馏

Chemical Fractionation in the Silicate Vapor Atmosphere of the Earth

Kaveh Pahlevan, David Stevenson, John Eiler

摘要:

尽管月球起源问题的重要性,月球的化学成分并不确切。然而,近年来,月球样品的同位素组成已被确定为高精度,并发现与地球地幔无法区分,尽管在太阳系广泛的同位素异质性。在巨型撞击假说的背景下,如果原月球盘和撞击后的地球经历湍流混合成为一个单一的均匀的水库,而系统是广泛熔化和部分蒸发,这种同位素均匀性的水平可以演变。在不存在液-气分离的情况下,这样的模型导致月球继承了陆地岩浆海洋的化学成分。因此,湍流混合模型提出了硅酸盐地球和月球之间化学差异的问题。在这里,我们将探讨与月球成分相关的一种环境中液体-蒸汽分离的后果:大撞击后地球的硅酸盐蒸汽大气。我们使用模型大气来量化降雨通过富集蒸气中的高层大气而产生化学差异的程度,并表明合理的参数可以产生硅酸盐月球相对于地球的FeO/MgO比的假设增强地幔。此外,我们表明,液-气分离也产生可测量的质量依赖的同位素偏移之间的硅酸盐地球和月球和精确的硅同位素测量可以用来限制在月球历史的最早时期的化学分馏的程度。这种方法有可能解决关于月球化学成分的长期问题。

英文摘要:

Despite its importance to questions of lunar origin, the chemical composition of the Moon is not precisely known. In recent years, however, the isotopic composition of lunar samples has been determined to high precision and found to be indistinguishable from the terrestrial mantle despite widespread isotopic heterogeneity in the Solar System. In the context of the giant-impact hypothesis, this level of isotopic homogeneity can evolve if the proto-lunar disk and post-impact Earth undergo turbulent mixing into a single uniform reservoir while the system is extensively molten and partially vaporized. In the absence of liquid-vapor separation, such a model leads to the lunar inheritance of the chemical composition of the terrestrial magma ocean. Hence, the turbulent mixing model raises the question of how chemical differences arose between the silicate Earth and Moon. Here we explore the consequences of liquid-vapor separation in one of the settings relevant to the lunar composition: the silicate vapor atmosphere of the post-giant-impact Earth. We use a model atmosphere to quantify the extent to which rainout can generate chemical differences by enriching the upper atmosphere in the vapor, and show that plausible parameters can generate the postulated enhancement in the FeO/MgO ratio of the silicate Moon relative to the Earth's mantle. Moreover, we show that liquid-vapor separation also generates measurable mass-dependent isotopic offsets between the silicate Earth and Moon and that precise silicon isotope measurements can be used to constrain the degree of chemical fractionation during this earliest period of lunar history. An approach of this kind has the potential to resolve long-standing questions on the lunar chemical composition.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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