Solubility of molecular hydrogen in silicate melts and consequences for volatile evolution of terrestrial planets
Solubility of molecular hydrogen in silicate melts and consequences for volatile evolution of terrestrial planets
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DOI：
10.1016/j.epsl.2012.06.031
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发表时间：
2012-09-01
影响因子：
5.3
通讯作者：
Foley, N. T.
中科院分区：
文献类型：
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作者：
Hirschmann, M. M.;Withers, A. C.;Foley, N. T.
我们目前的实验从0.7至3 GPa，量化的H-2在硅酸盐熔体中的溶解度下控制的氢逸度（F（H2））。两个实验系列，一个在合成玄武岩+COH和其他与合成安山岩+OH，进行了使用双胶囊技术施加的f（H2）的范围内，对样品。通过FTIR和西姆斯分析了淬火玻璃。这两个系列都遵循简单的溶解度定律，其中分子H-2浓度与f（H2）成正比，分子H-2的偏摩尔体积为11 cm（3）/mol。安山质熔体中的溶解度系统大于玄武岩液体中的熔体的离子孔隙度（IP）控制的关系一致。外推的基础上IP允许估计的溶解度H-2的橄榄岩熔体适用于岩浆海洋。硅酸盐熔体（其中H2O包括分子H2O和OH-）中的H-2/（H-2+H2O）比随着条件变得更还原、随着压力增加和随着总H增加而增加。在早期地球和类地行星以及今天地球深部的某些条件下，H-2可能是溶解的H的重要部分，并且在高压下它可能超过“水”（H2O和OH-）。因此，岩浆H-2可能会影响挥发分的初始分布和类地行星的氧化还原演化，以及当今地球深部含水熔体的形成和命运。在高压下与富铁合金平衡的熔体中的含水物质，例如在岩浆海洋的核心形成过程中，可能主要是H-2，而不是H2O。因此，通过去除Fe氢化物将H-2传递到地核不需要与残余地幔的氧化相耦合。虽然月球玄武岩大大减少，溶解的H-2分子的分数是小，由于低总H浓度。外推到地球深部潜在含水部分熔融的条件表明，主要的岩浆挥发物可能是H-2，而不是H2O。岩浆H-2很小的部分比重（低压时为0.18 g/cm（3））可能为深部部分熔体提供显著的正浮力。(C)2012爱思唯尔有限公司版权所有。
We present experiments from 0.7 to 3 GPa that quantify solubility of H-2 in silicate melts under controlled hydrogen fugacities (f(H2)). Two experimental series, one on synthetic basalt+COH and other with a synthetic andesite+OH, were conducted using a double capsule technique to impose a range of f(H2), on the samples. Quenched glasses were analyzed by FTIR and SIMS. Both series follow simple solubility laws in which molecular H-2 concentrations are proportional to f(H2) and with a partial molar volume of molecular H-2 of 11 cm(3)/mole. Solubilities in andesitic melt are systematically greater than in basaltic liquid in a relationship consistent with control by the ionic porosity (IP) of the melts. Extrapolation based on IP allows estimation of the solubility of H-2 in peridotitic melts applicable to magma oceans. The H-2/(H-2+H2O) ratio in silicate melts (where H2O includes molecular H2O and OH-) increases as conditions become more reduced, with increasing pressure, and with increasing total H. Under some conditions prevailing in the early Earth and terrestrial planets as well as in the deep Earth today, H-2 can be a significant fraction of the dissolved H and at high pressure it may exceed "water" (H2O and OH-). Therefore, magmatic H-2 may influence the initial distribution of volatiles and the redox evolution of terrestrial planets, as well as the ongoing formation and fate of hydrous melts in the deep Earth today. Hydrous species in melts in equilibrium with Fe-rich alloy at high pressure, for example during core formation from a magma ocean, could be chiefly H-2, rather than H2O. Hence, delivery of H-2 to the core by removal of Fe hydride need not be coupled to oxidation of the residual mantle. Although lunar basalts are much reduced, the fraction of H dissolved as molecular H-2 is small owing to low total H concentrations. Extrapolation to conditions of potential hydrous partial melting in the deep Earth suggests that the chief magmatic volatile may be H-2 rather than H2O. The very small partial specific density of magmatic H-2 (0.18 g/cm(3) at low pressure) may provide significant positive buoyancy to deep partial melts. (C) 2012 Elsevier B.V. All rights reserved.