Frictional properties of phyllosilicate‐rich mylonite and conditions for the brittle‐ductile transition
Frictional properties of phyllosilicate‐rich mylonite and conditions for the brittle‐ductile transition
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DOI：
10.1002/2015jb012489
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发表时间：
2015-12
期刊：
影响因子：
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通讯作者：
Lei Zhang;Changrong He
中科院分区：
文献类型：
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作者：
Lei Zhang;Changrong He
为了解天然富页硅酸盐糜棱岩沿着断层深度的摩擦特性，在温度100-600°C、有效正应力100-300 MPa、加载速率0.04-1.0 µm/s条件下，对模拟糜棱岩断层泥进行了摩擦实验。实验结果表明，在200°C以上的温度下，糜棱岩泥的摩擦强度随温度呈系统性增加，范围为0.52-0.73。在200-300 MPa的正应力条件下，糜棱岩泥的速度依赖性显示出在200 - 300°C之间的温度下从初始速度强化（区域1）到速度弱化行为（区域2）的转变，并随着温度的升高转变回速度强化行为（区域3）。后者的过渡也被发现是促进较慢的加载速率。糜棱岩断层泥的摩擦稳定性也表现出很强的压力敏感性。虽然在100 MPa法向应力条件下不存在区域3中的速度强化行为，但在更高的有效法向应力下，稳定摩擦行为显著增强，其中向速度强化的转变温度随着有效法向应力而降低。微观结构分析表明，速度依赖性从速度弱化到速度强化的转变对应于碎裂流到以糜棱岩结构（S-C组构）为特征的半脆性过程的转变。糜棱岩组构的形成是由于层状硅酸盐的塑性变形与硬碎屑（石英和斜长石）的热活化粒度减小相结合。我们的研究结果可能有助于限制富层状硅酸盐断裂带内地震发生的深度范围，并暗示有效正应力的变化可能影响断裂行为。
To understand frictional properties of natural phyllosilicate‐rich mylonite along fault depth, friction experiments on simulated mylonite gouge were conducted at temperatures of 100–600°C, effective normal stresses of 100–300 MPa, and loading rates of 0.04–1.0 µm/s. Experimental results show that at temperatures above 200°C, frictional strength of the mylonite gouge exhibits systematic increase with temperature, in the range of 0.52–0.73. Under 200–300 MPa normal stress conditions, velocity dependence of mylonite gouge shows a transition from initial velocity‐strengthening (Regime 1) to velocity‐weakening behavior (Regime 2) at a temperature between 200 and 300°C and transitions back to velocity‐strengthening behavior (Regime 3) as temperature increases. The latter transition is also found to be promoted by slower loading rates. Friction stability of the mylonite gouge also exhibits a strong pressure sensitivity. While velocity‐strengthening behavior in Regime 3 is absent under 100 MPa normal stress condition, stable frictional behavior is significantly enhanced at higher effective normal stresses, with the transition temperature to velocity strengthening decreasing with effective normal stress. Microstructural analysis shows that the transition of velocity dependence from velocity weakening to velocity strengthening corresponds to transition from cataclastic flow to semibrittle process featured by mylonitic structures (S‐C fabrics). The formation of mylonitic fabrics is due to plastic deformation of phyllosilicates combined with thermally activated grain size reduction of hard clasts (quartz and plagioclase). Our results may help constrain depth range of seismogenesis within phyllosilicate‐rich fault zone and imply that variation of effective normal stress may affect faulting behavior.