Strain Localization and Weakening Processes in Viscously Deforming Rocks: Numerical Modeling Based on Laboratory Torsion Experiments
Strain Localization and Weakening Processes in Viscously Deforming Rocks: Numerical Modeling Based on Laboratory Torsion Experiments
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粘性变形岩石中的应变局部化和弱化过程：基于实验室扭转实验的数值模拟
DOI：
10.1029/2018jb016917
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Dresen
中科院分区：
文献类型：
--
作者：
Döhmann;M.J.E.A;Nardini;Rybacki;Dresen
粘性下地壳中的局部化过程在很大范围内产生韧性剪切带，影响长期岩石圈变形和地震周期中断层的力学响应。在这里，我们使用厘米尺度的数值模型，以获得详细的洞察应变局部化和流变弱化的粘性变形岩石中所涉及的过程。我们的二维笛卡尔模型以含有单一弱Solnhofen石灰岩包裹体的卡拉拉大理石样品的高温和高压扭转实验为基准。该模型成功地再现了体应力应变瞬态和最终应变分布在实验中观察到的应用一个简单的，一阶软化定律，模仿流变弱化。我们发现，局部应力集中形成的夹杂物尖端启动主机矩阵内的应变局部化。在传播的剪切区的尖端处，弱化发生在过程区内，该过程区随着时间从夹杂物尖端向基体扩展。流变弱化是剪切区局部化的前提条件，剪切区的宽度受软化程度的控制。在高应变下引入第二软化步骤，在局部剪切带内形成高应变层，类似于糜棱岩中超糜棱岩带的形成。这些结果阐明了韧性剪切带形成和成熟过程中应力和应变速率的瞬态演化。
Localization processes in the viscous lower crust generate ductile shear zones over a broad range of scales affecting long‐term lithosphere deformation and the mechanical response of faults during the seismic cycle. Here we use centimeter‐scale numerical models in order to gain detailed insight into the processes involved in strain localization and rheological weakening in viscously deforming rocks. Our 2‐D Cartesian models are benchmarked to high‐temperature and high‐pressure torsion experiments on Carrara marble samples containing a single weak Solnhofen limestone inclusion. The models successfully reproduce bulk stress‐strain transients and final strain distributions observed in the experiments by applying a simple, first‐order softening law that mimics rheological weakening. We find that local stress concentrations forming at the inclusion tips initiate strain localization inside the host matrix. At the tip of the propagating shear zone, weakening occurs within a process zone, which expands with time from the inclusion tips toward the matrix. Rheological weakening is a precondition for shear zone localization, and the width of this shear zone is found to be controlled by the degree of softening. Introducing a second softening step at elevated strain, a high strain layer develops inside the localized shear zone, analogous to the formation of ultramylonite bands in mylonites. These results elucidate the transient evolution of stress and strain rate during inception and maturation of ductile shear zones.
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