An Experimental Investigation of the Relative Strength of the Silica Polymorphs Quartz, Coesite, and Stishovite
An Experimental Investigation of the Relative Strength of the Silica Polymorphs Quartz, Coesite, and Stishovite
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DOI：
10.1029/2018gc007842
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发表时间：
2019-04
期刊：
影响因子：
3.7
通讯作者：
S. Hunt;M. Whitaker;E. Bailey;E. Mariani;C. Stan;D. Dobson
中科院分区：
文献类型：
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作者：
S. Hunt;M. Whitaker;E. Bailey;E. Mariani;C. Stan;D. Dobson
在这项研究中，石英、硅辉石和硅辉石与橄榄石参考样品在850±50℃的高压下同时变形。橄榄石变形的有效应力指数(n)为6.9−2.2+3.1，表明橄榄石中存在peerls蠕变机制。石英和钴矿具有非常相似的强度和变形机制，分别为n = 2.8−0.9+1.2和2.9−0.9+1.3，这与之前的幂律蠕变测量结果一致。硅辉石的变形值为n = 8.1−2.7+3.7，强度大于橄榄石和其他硅晶。针长石的高应力指数大于幂律蠕变的高应力指数，表明它可能（但不确定）是由佩尔斯蠕变变形的。因此，SiO2矿物的流变学受到硅配位和密度变化的强烈影响，硅配位和密度从石英和硅长辉石的4倍变化到硅长辉石的6倍。如果Si配位效应可以推广，那么与桥辉石形成相关的Si配位（和密度）的增加可以解释地球660公里深度附近粘度增加10倍到100倍的现象。
In this study, quartz, coesite, and stishovite were deformed concurrently with an olivine reference sample at high pressure and 850 ± 50 °C. Olivine deformed with an effective stress exponent (n) of 6.9−2.2+3.1 , which we interpret to indicate that the Peierls creep deformation mechanism was active in the olivine. Quartz and coesite had very similar strengths and deformed by a mechanism with n = 2.8−0.9+1.2 and 2.9−0.9+1.3 , respectively, which are consistent with previous measurements of power law creep in these phases. Stishovite deformed with n = 8.1−2.7+3.7 and was stronger than both olivine and the other silica polymorphs. The high stress exponent of stishovite is greater than that typically observed for power law creep, indicating it is probably (but not certainly) deforming by Peierls creep. The rheology of SiO2 minerals appears therefore to be strongly affected by the change in silicon coordination and density from fourfold in quartz and coesite to sixfold in stishovite. If the effect of Si coordination can be generalized, the increase in Si coordination (and density) associated with bridgmanite formation may explain the tenfold to 100‐fold viscosity increase around 660 km depth in the Earth.