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arXiv 1708.04767physics.geo-ph
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超地幔中MgSiO3后钙钛矿结构的相变

Phase transitions in MgSiO3 post-perovskite in super-Earth mantles

Koichiro Umemoto, Renata M. Wentzcovitch, Shunqing Wu, Min Ji, Cai-Zhuang Wang, Kai-Ming Ho

摘要:

形成地球的主要地幔硅酸盐的最高压力形式是MgSiO 3后钙钛矿(PPv)。了解PPv在TPa压力下的命运是了解超级地球型系外行星矿物学的第一步,可以说它们与地球的相似性是最有趣的。模拟其内部结构需要了解稳定的矿物相,其在压缩下的特性和主要元素丰度。极压下的PPv的几项研究支持的概念,一系列的压力诱导的解离转变产生的元素氧化物SiO2和MgO的最终聚集形式在~3 TPa。然而,这些研究都没有解决地幔成分的问题,特别是主要元素丰度通常表示为三个主要变量,Mg/Si和Fe/Si比和Mg#,在地球上。在这里,我们表明,关键的组成参数,镁/硅比,其值在地球的地幔仍然是有争议的,是一个重要的成分建模相变和内部结构的超地球地幔。具体来说,我们已经确定了新的相变序列,包括新的重组反应,决定性地依赖于这个比例。这是一个新的复杂程度,以前没有解决,但证明是必不可少的建模的性质和数量的内部层在这些岩石地幔。

英文摘要:

The highest pressure form of the major Earth-forming mantle silicate is MgSiO3 post-perovskite (PPv). Understanding the fate of PPv at TPa pressures is the first step for understanding the mineralogy of super-Earths-type exoplanets, arguably the most interesting for their similarities with Earth. Modeling their internal structure requires knowledge of stable mineral phases, their properties under compression, and major element abundances. Several studies of PPv under extreme pressures support the notion that a sequence of pressure induced dissociation transitions produce the elementary oxides SiO2 and MgO as the ultimate aggregation form at ~3 TPa. However, none of these studies have addressed the problem of mantle composition, particularly major element abundances usually expressed in terms of three main variables, the Mg/Si and Fe/Si ratios and the Mg#, as in the Earth. Here we show that the critical compositional parameter, the Mg/Si ratio, whose value in the Earth's mantle is still debated, is a vital ingredient for modeling phase transitions and internal structure of super-Earth mantles. Specifically, we have identified new sequences of phase transformations, including new recombination reactions that depend decisively on this ratio. This is a new level of complexity that has not been previously addressed, but proves essential for modeling the nature and number of internal layers in these rocky mantles.

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