Effect of structural water on the elasticity of orthopyroxene
Effect of structural water on the elasticity of orthopyroxene
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DOI：
10.2138/am-2021-7843
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发表时间：
2022-03
影响因子：
3.1
通讯作者：
M. Hou;Wencai Zhou;M. Hao;Florian Tian-Siang Hua;J. Kung;Dongzhou Zhang;P. Dera;Jin S. Zhang
中科院分区：
文献类型：
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作者：
M. Hou;Wencai Zhou;M. Hao;Florian Tian-Siang Hua;J. Kung;Dongzhou Zhang;P. Dera;Jin S. Zhang
摘要斜方辉石是地球上地幔中一种主要的无水矿物，其晶体结构中含有高达百万分之几百的水，并将水输送到地球深部。为了研究结构水对斜方辉石弹性的影响，我们用布里渊散射光谱测量了Mg_（1.991）Al_（0.065）Si_（1.951）O_6在842-900 ppm水和1.64 ± 0.20 wt% Al_2 O_3条件下的单晶弹性。含水含Al斜方辉石的最佳拟合单晶弹性模量（Cis）、体积模量（KS 0）和剪切模量（G 0）确定为：C11 = 235（2）GPa、C22 = 173（2）GPa、C33 = 222（2）GPa、C44 = 86（1）GPa、C55 = 82（1）GPa、C66 = 82（1）GPa、C12 = 75（3）GPa、C13 = 67（2）GPa和C23 = 49（2）GPa，KS0 = 111（2）GPa，G0 = 78（1）GPa。基于本研究和先前研究结果的系统分析表明，掺入842-900 ppm H2O将使C13增加12.0（7）%，使C23减少8.6（8）%。在考虑不确定性时，对C11、C22、C33、C44、C66、KS 0和VP的影响即使不可忽略，也是微小的。C55、C12、G 0和VS不受结构H2O存在的影响。虽然实验室实验表明，铁，铝轴承斜方辉石可以主机高达0.8重量%的H2O在其结构中，未来的高压-温度弹性测量的斜方辉石与更高的H2O含量需要帮助更好地量化这种效果。
Abstract As a major nominally anhydrous mineral (NAM) in the Earth’s upper mantle, orthopyroxene could host up to several hundred parts per million H2O in its crystal structure and transport the H2O to the deep Earth. To study the effect of structural H2O on the elasticity of orthopyroxene, we have measured the single-crystal elasticity of Mg1.991Al0.065Si1.951O6 with 842–900 ppm H2O and 1.64 ± 0.20 wt% Al2O3 at ambient conditions using Brillouin spectroscopy. The best-fit single-crystal elastic moduli (Cijs), bulk (KS0), and shear (G0) modulus of the hydrous Al-bearing orthopyroxene were determined as: C11 = 235(2) GPa, C22 = 173(2) GPa, C33 = 222(2) GPa, C44 = 86(1) GPa, C55 = 82(1) GPa, C66 = 82(1) GPa, C12 = 75(3) GPa, C13 = 67(2) GPa, and C23 = 49(2) GPa, KS0 = 111(2) GPa, and G0 = 78(1) GPa. Systematic analysis based on the results presented in this and previous studies suggests that the incorporation of 842–900 ppm H2O would increase C13 by 12.0(7)% and decrease C23 by 8.6(8)%. The effects on C11, C22, C33, C44, C66, KS0, and VP are subtle if not negligible when considering the uncertainties. The C55, C12, G0, and VS are not affected by the presence of structural H2O. Although laboratory experiments show that Fe,Al-bearing orthopyroxenes can host up to 0.8 wt% H2O in its structure, future high-pressure-temperature elasticity measurements on orthopyroxene with higher H2O content are needed to help better quantify this effect.