Fluid environment controls along-strike variation in slip style: Midcrustal geological signatures from the Red River fault, China

Geology Pub Date : 2024-02-28 DOI:10.1130/g51865.1
Qingbao Duan, Å. Fagereng, Jianye Chen, Thomas Blenkinsop
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Abstract

The slip style of continental midcrustal shear zones plays a crucial role in determining the seismogenic potential of faults, but it remains poorly understood because geological observations that can be directly tied to seismic behavior are scarce. We describe frictional-viscous shear zones in the Red River fault, China, which consists of two segments with distinct seismic behaviors and fluid availabilities. The northern segment hosts moderate to large earthquakes, and midcrustal fault slip is localized into mylonitized pseudotachylyte-bearing layers where dynamically recrystallized quartz records flow stresses exceeding 100 MPa and accelerated viscous creep. The southern segment is dominantly aseismic but active microseimically. Fault slip is accommodated in several mylonitized cataclasite layers, comprising interconnected biotite and intervening fractured clasts, with evidence for pervasive dissolution-precipitation creep. Microstructures, paleopiezometry, and microphysical modeling suggest transient aseismic slip in response to increased strain rates during viscous creep at <50 MPa. We interpret that along-strike variations in fluid environment control fault slip styles and seismic behaviors. The dry and strong northern segment is capable of nucleating large earthquakes, while greater fluid availability in the southern segment activates dissolution-precipitation creep at low driving stresses, which limits interseismic elastic strain accumulation at frictional-viscous transition depths. In this model, compaction-driven fluid pressurization and dilatant hardening are invoked to explain the aseismic slip transients in the southern segment.
流体环境控制着沿走向的滑动方式变化:中国红河断层的地壳中层地质特征
大陆地壳中层剪切带的滑动方式在决定断层的致震潜力方面起着至关重要的作用,但由于可直接与地震行为联系起来的地质观测资料很少,因此人们对这种滑动方式的了解仍然很少。我们描述了中国红河断层的摩擦粘性剪切带,该断层由两段组成,具有不同的地震行为和流体利用率。北段发生中到大地震,地壳中段断层滑动局部进入岩浆岩化假水帘洞含水层,动态再结晶的石英记录了超过 100 兆帕的流动应力和加速粘性蠕变。南段主要处于无地震状态,但微震活跃。断层滑动被容纳在几个麦饭石化的白云母岩层中,这些岩层由相互连接的黑云母和中间断裂的碎屑岩组成,有证据表明存在普遍的溶解-沉淀蠕变。微观结构、古地层测量和微物理模型表明,在小于50兆帕的粘性蠕变过程中,应变速率的增加导致了瞬态地震滑动。我们解释说,流体环境的沿脉变化控制着断层的滑动方式和地震行为。干燥而坚固的北段能够引发大地震,而南段较多的流体可在低驱动应力下激活溶解-沉淀蠕变,从而限制了摩擦-粘性转换深度的震间弹性应变累积。在这一模型中,压实驱动的流体增压和扩张硬化被用来解释南段的地震滑移瞬变。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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