QUANTITIVE INFLUENCE OF WEAK PHASE LAYER ON STRENGTH OF FAULT GOUGE

doi:10.3969/j.issn.0253-4967.2015.06

Abstract

Abstract:

We investigated frictional sliding behavior of mixture gouges of quartz with various weight proportions of biotite and their structured equivalents with same weight proportions of biotite as layers embedded in quartz gouge. Our experiments were performed under effective confining pressure of 200MPa, pore pressure of 30MPa, temperature of 100℃ and the shear displacement rate of 1.22μm/s. The results show that for structured gouges with biotite layers embedded in quartz gouge as a weak structure, the strength has a power law decreasing trend with increasing weight proportions of biotite. The fault gouges can be weakened significantly by as little as 5wt% biotite, and 30wt% biotite corresponds to a beginning point of less sensitive strength change in response to increasing biotite proportion. On the other hand, the strength of mixed gouges shows a linear decreasing trend with increasing biotite proportion. Microstructures of deformed samples show that in mixed gouges, biotite and quartz are both sheared and grain size extremely reduced, and their contributions to overall strength have a close relation with their respective contents. However, in structured gouges, the shear deformation mainly occurred in the weak biotite layers with no shears crossing the quartz gouge. These results confirm the importance of the weak fabric in its effect on frictional strength. If the weak minerals form foliations and interconnected arrangements, it will lead to weakness of fault zones.

Key words: biotite, quartz, weak structure, coefficient of friction

摘要：

分别对不同含量的黑云母、石英均匀混合和黑云母以软弱层形式夹于石英中的2种断层泥在温度为100℃, 有效围压为200MPa, 水压为30MPa, 剪切滑动速率为1.22μm/s的条件下进行摩擦实验。实验发现, 当黑云母以软弱层存在时, 强度随含量的增加呈负幂次衰减关系, 5%的含量就会对强度产生很大的降低作用, 当含量达到30%后, 强度受含量的影响便不再显著, 逐渐趋于稳定。而对于均匀混合样品, 强度随黑云母含量的增加呈单调线性递减关系, 即云母含量越高对应强度越低。显微结构显示, 在混合样品中, 黑云母和石英共同承担了变形的作用, 分配关系与各自所占含量保持一致。而在含软弱层的样品中, 变形与矿物含量间的关系不大, 主要集中在黑云母软弱层中发生, 而石英的变形程度不大。文中研究的结果定量地描述了软弱层对断层强度的显著影响, 表明一旦岩石中的弱矿物富集并且连通, 则会大大降低断层的强度, 对弱断层或高角度逆断层的形成具有一定的启示意义。

关键词: 黑云母, 石英, 软弱层, 摩擦强度

CLC Number:

P313

LU Zhen, HE Chang-rong. QUANTITIVE INFLUENCE OF WEAK PHASE LAYER ON STRENGTH OF FAULT GOUGE[J]. SEISMOLOGY AND GEOLOGY, 2015, 37(1): 68-80.

路珍, 何昌荣. 软弱成分层对断层泥强度的影响[J]. 地震地质, 2015, 37(1): 68-80.

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