Hydrolytic weakening in olivine single crystals
Hydrolytic weakening in olivine single crystals
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DOI：
10.1002/2017jb014004
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发表时间：
2017-05
期刊：
影响因子：
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通讯作者：
J. Tielke;M. Zimmerman;D. Kohlstedt
中科院分区：
文献类型：
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作者：
J. Tielke;M. Zimmerman;D. Kohlstedt
通过对San卡洛斯橄榄石单晶在含水条件下的变形实验，研究了位错蠕变过程中水解弱化的微观物理过程。使用与晶体一起密封在镍胶囊中的滑石或水镁石向晶体供应氢气。使用气体介质装置在温度1050°至1250°C、围压300 MPa、差应力45至294 MPa、合成应变率1.5 × 10 - 6至4.4 × 10 - 4 s-1下进行变形实验。对于滑石缓冲（即，水和斜方辉石缓冲）样品在高温下，应变速率对应力的依赖性遵循幂律关系，应力指数（n）为1.22.5，激活能为1.490 kJ/mol。水镁石缓冲样品比滑石缓冲样品变形更快，但含有相似的氢浓度，表明应变速率受含水条件下斜方辉石活性的影响。n值和应变速率对斜方辉石活性的依赖性与发生在爬升控制的位错蠕变机制中的水解弱化一致，该机制与含水条件下晶格扩散和无水条件下管道扩散控制的变形相关。变形后电子背散射衍射数据的分析表明，具有[100] Burgers矢量的位错在爬升控制区占主导地位，而具有[001]的位错在滑移控制区占主导地位。实验确定的本构方程的比较表明，在含水条件下的晶体变形1至2个数量级的速度比在无水条件下。
Deformation experiments on single crystals of San Carlos olivine under hydrous conditions were performed to investigate the microphysical processes responsible for hydrolytic weakening during dislocation creep. Hydrogen was supplied to the crystals using either talc or brucite sealed in nickel capsules with the crystal. Deformation experiments were carried out using a gas medium apparatus at temperatures of 1050° to 1250°C, a confining pressure of 300 MPa, differential stresses of 45 to 294 MPa, and resultant strain rates of 1.5 × 10−6 to 4.4 × 10−4 s−1. For talc‐buffered (i.e., water and orthopyroxene‐buffered) samples at high temperatures, the dependence of strain rate on stress follows a power law relationship with a stress exponent (n) of ∼2.5 and an activation energy of ∼490 kJ/mol. Brucite‐buffered samples deformed faster than talc‐buffered samples but contained similar hydrogen concentrations, demonstrating that strain rate is influenced by orthopyroxene activity under hydrous conditions. The values of n and dependence of strain rate on orthopyroxene activity are consistent with hydrolytic weakening occurring in the climb‐controlled dislocation creep regime that is associated with deformation controlled by lattice diffusion under hydrous conditions and by pipe diffusion under anhydrous conditions. Analyses of postdeformation electron‐backscatter diffraction data demonstrate that dislocations with [100] Burgers vectors are dominant in the climb‐controlled regime and dislocations with [001] are dominant in the glide‐controlled regime. Comparison of the experimentally determined constitutive equations demonstrates that under hydrous conditions crystals deform 1 to 2 orders of magnitude faster than under anhydrous conditions.