Low Friction Coefficient of Phyllosilicate Fault Gouges and the Effect of Humidity: Insights From a New Microphysical Model
Low Friction Coefficient of Phyllosilicate Fault Gouges and the Effect of Humidity: Insights From a New Microphysical Model
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DOI：
10.1029/2019jb018683
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发表时间：
2020-06
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影响因子：
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通讯作者：
S. D. Hartog;D. Faulkner;C. Spiers
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文献类型：
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作者：
S. D. Hartog;D. Faulkner;C. Spiers
断层滑动通常局限于富含层状硅酸盐的断层沟槽中，这与实验室实验中测量的干层状硅酸盐（尤其是湿层状硅酸盐）相对较低的摩擦系数相一致。然而，控制这些低摩擦系数的微物理仍然不清楚。本文在微观结构观测的启发下，提出了一种微物理模型，用于预测纯干层状硅酸盐和湿层状硅酸盐的摩擦系数绝对值。实验产生的层状硅酸盐沟槽表明，剪切是由沿着（001）晶粒/血小板界面的滑动控制的，这些界面通过基底解理来消除重叠的晶粒边缘障碍。在白云母亚临界裂纹扩展数据的约束下，我们推导了一个包含后者亚临界裂纹扩展方程的模型。在湿度和滑移速度对摩擦系数的影响方面，对白云母的模型预测显示出与室温下的实验相似的趋势。预测的摩擦系数绝对值很难与实验值进行比较，因为它主要取决于原子尺度（001）滑动阻力，而现有实验数据对其约束很差。与实验数据的进一步差异可以通过晶粒尺寸、晶粒长径比和孔隙率对摩擦系数的影响来解释。虽然之前已经提出了许多定性解释，以解释层状硅酸盐表现出的低摩擦系数，特别是在有水存在的情况下，但我们的研究为定量的、基于物理的模型提供了新的一步。
Fault slip is often localized in phyllosilicate‐rich fault gouges in a manner consistent with the relatively low friction coefficients measured for dry and especially wet phyllosilicates in laboratory experiments. However, the microphysics controlling these low friction coefficients remains unclear. Here, we propose a microphysical model, inspired by microstructural observations, for the prediction of the absolute value of the friction coefficient of pure dry and wet phyllosilicates. Experimentally produced phyllosilicate gouges suggest that shearing is controlled by sliding along (001) grain/platelet interfaces operating in series with removal of overlapping grain edge barriers by basal cleavage. We derive a model incorporating a subcritical crack propagation equation for the latter, constrained by subcritical crack growth data for muscovite. Model predictions for muscovite show similar trends regarding the effects of humidity and slip velocity on friction coefficient as do experiments at room temperature. The absolute value predicted for the friction coefficient is difficult to compare with experimental values, as it critically depends on atomic scale (001) sliding resistance, which is poorly constrained by available experimental data. Further discrepancies with experimental data can be explained by effects of varying grain size, grain aspect ratio, and porosity on the friction coefficient. While numerous qualitative explanations have been proposed previously for the low friction coefficient exhibited by phyllosilicates, especially in the presence of water, our study provides a new step toward a quantitative, physically based model.