Fault zone architecture and lithology-dependent deformation mechanisms of the Himalayan frontal fold-thrust belt: Insights from the Nahan Thrust, India
Fault zone architecture and lithology-dependent deformation mechanisms of the Himalayan frontal fold-thrust belt: Insights from the Nahan Thrust, India
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喜马拉雅额叶褶皱逆冲带的断层带结构和岩性相关变形机制：印度纳汉逆冲断层的见解
DOI：
10.1130/b36246.1
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Tomioka Naotaka
中科院分区：
文献类型：
--
作者：
Sarkar Dyuti Prakash;Ando Jun-ichi;Ghosh Gautam;Das Kaushik;Dasgupta Prabir;Tomioka Naotaka
脆性浅地壳断层通常形成复杂的断裂带结构，具有不同的结构域，显示出不同的显微结构、矿物学和变形机制。这些域的发展通常受原岩的强度和成分、变形的物理条件、流体进入和响应于应力积累和同震滑动的穿时断层生长的控制。在这里，我们研究了断层岩的显微结构，矿物学，运动学的那汉逆冲断层，在主前锋逆冲断层附近，代表在喜马拉雅造山带的构造活动带。那汉逆冲断层的特征是红色和灰色断层泥层交替，以及单一的黑色断层泥层。电镜和X射线衍射分析结果表明，红色断层泥层的原岩为泥质砂岩，而灰色和黑色断层泥层的原岩为砂岩。显微结构表明，最初的分布变形（无应力蠕变），随后是一个长期的脆性变形事件，和后来的无应力蠕变阶段。脆性阶段以应力逐步局部化、裂缝发育、碎裂、摩擦滑动和地震滑动为标志。黑色断层泥层是主要的滑动带，具有微细的微米级滑动带，带内有蒸汽逸出构造和粘土碎屑聚集体，表明地震滑动过程中存在地震断层和摩擦加热。地震破裂在黑色断层泥层中的优先成核表明，在那汉逆冲断层中，地震滑动具有强烈的岩性依赖性。我们还得出结论，在那汉逆冲断层的原始岩性的变化造成的不均匀性。
Brittle shallow crustal faults typically develop a complex fault zone architecture with distinct structural domains that display diverse microstructures, mineralogy, and deformation mechanisms. The development of such domains is typically controlled by the strength and composition of the protoliths, physical conditions of deformation, fluid ingress, and diachronous fault growth in response to stress accumulation and co-seismic slip. Herein, we studied the microstructure-mineralogy-kinematics of fault rocks in the Nahan Thrust, in the vicinity of the Main Frontal Thrust that represents a tectonically active zone in the Himalayan orogen. The Nahan Thrust is characterized by alternating red and gray gouge layers, and a single black gouge layer. Our results from electron microscopy and X-ray diffractometry indicate that the protolith of the red gouge layers is argillaceous sandstone, whereas that of the gray and black gouge layers is sandstone. Microstructures suggest an initially distributed deformation (aseismic creep), followed by a protracted brittle deformation event, and a later aseismic creep stage. The brittle stage is marked by progressive localization of stress, fracture development, cataclasis, frictional sliding, and seismic slips. The black gouge layer acted as the principal slip zone and exhibited ultrafine bands of micrometerscale slip zones with vapor escape structures and clay clast aggregates, indicating seismic faulting and frictional heating during seismic slips. The preferential seismic rupture nucleation in the black gouge layer indicates a strong lithological dependence on seismic slip in the Nahan Thrust. We also conclude that heterogeneity within the Nahan Thrust resulted from primary lithological variations of the protoliths.