The origin of S-C mylonites and a new fault-zone model
The origin of S-C mylonites and a new fault-zone model
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DOI：
10.1016/0191-8141(89)90035-7
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发表时间：
1989
影响因子：
3.1
通讯作者：
T. Shimamoto
中科院分区：
文献类型：
--
作者：
T. Shimamoto
本文综合了模拟岩盐剪切带的力学行为和变形结构的实验数据，特别是S-糜棱岩的内部结构及其力学意义。岩盐是唯一的矿物，迄今为止，脆性剪切变形之间的完全过渡到完全韧性剪切流动的位错滑移制度已被实验研究下，可能会遇到沿着断层或板块边界的大剪切应变。剪切带的变形结构与糜棱岩和碎裂岩相似。实验结果为进一步研究断层岩，特别是糜棱岩的成因提供了理论依据，也为建立一个符合实际的断层模型提供了理论依据。（即压力不敏感的非弹性区域），存在一种称为“半延性”的广泛而独特的区域，其中变形织构与延性区域中形成的织构几乎相同，然而，剪切阻力与压力有关，在低压部分可能发生潜在的不稳定断层运动。在煮盐剪切带实验中，在半韧性和韧性制度的特征纹理是类似糜棱岩面理，它形成在最大伸长的方向。在半韧性体制，近均匀的剪切变形，形成均匀和普遍的叶理的特点，转变为非均匀变形后的临界剪切应变和应变局部化诱导潜在的不稳定断层运动。应变局部化后的内部滑移主要是沿Y型Riedel剪切线滑移，该剪切线平行于剪切区边界，与R1和一些P型Riedel剪切线相互连接。这些集中变形的剪切面与所谓的“S-糜棱岩”的内部结构非常相似。因此，半韧性体系是S-糜棱岩形成的主要候选者，并且至少有一些S-糜棱岩必须在孕震深度形成。这种解释与最近报道的交织的假玄武玻璃和糜棱岩是一致的。它还表明，重结晶的岩盐颗粒（大概主要是变形后）的大小随剪切应变的增加而减小，但不与剪切应力，这是一致的，与应变集中，已被证实在世界上许多糜棱岩的粒度减小。因此，从再结晶晶粒的流动应力的估计需要非常小心，可能经常是mistaken.Existing故障模型进行了严格审查的角度来看的岩盐实验，并提出了一个新的故障模型，断裂带分为脆性，半脆性，半韧性和韧性制度的深度增加。断层的抗剪强度在半韧性区最高，孕震深度可能向下延伸到半韧性区的上部。因此，半韧性制度出现作为一个主要的利益方面的manyS-Cmylonites的岩石成因，模拟大型和大型浅层地震沿着预先存在的故障和板块边界，并定量评估其边界的板块的力学相互作用的区域。
This paper presents a synthesis of experimental data on mechanical behaviour and deformation textures of simulated halite shear zones with special regard to the internal structures ofS-Cmylonites and their mechanical implications. Halite is the only mineral so far for which a complete transition between brittle shearing deformation to fully ductile shearing flow in the dislocation glide regime has been studied experimentally under large shear strains that may be encountered along faults or plate boundaries. Moreover, deformation textures in the shear zones are similar to those of mylonites and cataclasites. Thus the experimental results provide an insight into the petrogenesis of fault rocks, mylonites in particular, and the establishment of a realistic fault model.Between the brittle regime and the fully ductile regime (i.e. pressure-insensitive inelastic regime), there exists a wide and distinct regime called ‘semiductile’ in which deformation textures are nearly identical to those developed in the ductile regime, yet the shear resistance is pressure-dependent, and potentially unstable fault motion can occur in the low pressure part. In cooking salt shear-zone experiments, the characteristic texture in the semiductile and ductile regimes is foliation resembling mylonitic foliation, which formed in the direction of maximum elongation. In the semiductile regime, nearly homogeneous shearing deformation, characterized by the formation of uniform and pervasive foliation, changes into heterogeneous deformation after a critical shear strain and this strain localization induces potentially unstable fault motion. The primary mode of internal slip after the strain localization is slip alongYRiedel shears, parallel to the shear-zone boundary, interconnected withR1and somePRiedel shears. These shear surfaces of concentrated deformation are very similar to the internal structures of so-called ‘S-Cmylonites”. Hence, the semiductile regime is the primary candidate for the formation ofS-Cmylonites, and at least someS-Cmylonites must have formed at seismogenic depths. This interpretation is consistent with recently reported interlaced pseudotachylytes and mylonites. It is also shown that the size of recrystallized halite grains (presumably mostly postdeformational) decreases with increasing shear strains, but not with the shear stress, and this is consistent with the grain-size reduction with strain concentration which has been confirmed for many mylonites in the world. Thus, estimation of flow stress from recrystallized grains needs to be done with great care and might often be erroneous.Existing fault models are critically examined from the viewpoint of the halite experiments, and a new fault model is proposed whereby fault zones are divided into brittle, semibrittle, semiductile and ductile regimes with increasing depth. The shear resistance of faults is highest in the semiductile regime, and the seismogenic depth is likely to extend down to the upper part of this regime. The semiductile regime thus emerges as an area of primary interest with regard to the petrogenesis of manyS-Cmylonites, modelling of large and great shallow earthquakes along pre-existing faults and plate boundaries, and quantitative evaluation of the mechanical interactions of plates across their boundaries.