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Dislocation Creep of Diopside Aggregates Under Unsaturated Hydrous Conditions at a Confining Pressure of 300 MPa
Journal of Geophysical Research: Solid Earth ( IF 3.9 ) Pub Date : 2024-12-22 , DOI: 10.1029/2024jb029472
Jianfeng Li, Maoshuang Song, Hao Wang, Guinan Zhang, Shenghua Mei, Xiaodong Zheng, Xiaoning Wang, Zhexuan Jiang

To understand the dislocation creep behavior of clinopyroxene in the upper mantle, hot-pressed diopside aggregates without predrying treatment were triaxially deformed under water-unsaturated conditions at a confining pressure of 300 MPa, temperatures of 1323–1523 K, and strain rates of 10−6–10−4 s−1, using a Paterson gas-medium apparatus. Fourier transform infrared measurements of the water contents of the samples before and after deformation revealed that water diffusion loss occurred during the deformation process. A simple diffusion model based on Fick's law was established to predict the variation in the water content with respect to time during deformation. Fitting the mechanical data with a power flow law yielded a stress exponent n of 4.3 ± 0.3, an activation energy Q of 427 ± 31 kJ/mol and a water content exponent r of 1.2 ± 0.2 for the dislocation creep of the diopside aggregates under water-unsaturated conditions. When the flow law was extrapolated to anhydrous and water-saturated conditions, the calculated flow strengths of the diopside aggregates were generally in agreement with the strengths determined directly by deformation experiments, but there also existed contribution from grain boundary water under water-saturated conditions. The results of our study indicate that the strength of diopside or upper mantle clinopyroxene is comparable to the strength of olivine under anhydrous conditions but weaker than that of olivine under water-saturated conditions in the dislocation creep regime. Therefore, diopside might dominate the rheological behavior in some clinopyroxene-enriched and hydrous regions of the upper mantle.

中文翻译:


透辉石聚集体在300 MPa围压下不饱和含水条件下的位错蠕变



为了了解斜辉石在上地幔中的位错蠕变行为,在水非饱和条件下,在 300 MPa、1323–1523 K 的温度和 10 −6 –10 −4 s −1 的应变速率下,使用 Paterson 气体介质装置对未经预干燥处理的热榨透辉石聚集体进行三轴变形。对变形前后样品含水量的傅里叶变换红外测量表明,水在变形过程中发生了扩散损失。建立了基于 Fick 定律的简单扩散模型,用于预测变形过程中含水量随时间的变化。用功率流定律拟合力学数据,在水非饱和条件下透辉石聚集体的位错蠕变±应力指数 n 为 4.3 0.3,活化能 Q 为 427 ± 31 kJ/mol,含水指数 r 为 1.2 ± 0.2。当流律外推到无水和水饱和条件下时,计算出的透辉石聚集体的流动强度与变形实验直接确定的强度基本一致,但在水饱和条件下,晶界水也存在贡献。我们的研究结果表明,透辉石或上地幔斜辉石的强度与无水条件下的橄榄石强度相当,但在位错蠕变状态下,透辉石或上地幔斜辉石的强度弱于水饱和条件下的橄榄石。因此,透辉石可能在上地幔中一些富含斜辉石和含水区域的流变行为中占主导地位。
更新日期:2024-12-23
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