Intermediate-depth earthquake generation and shear zone formation caused by grain size reduction and shear heating
Intermediate-depth earthquake generation and shear zone formation caused by grain size reduction and shear heating
复制标题
粒度减小和剪切加热引起的中深度地震发生和剪切带形成
作者：
M. Thielmann;A. Rozel;B. Kaus;Y. Ricard
中深地震的物理基础一直是一个谜;一些研究支持热失控或脱水反应作为其产生的可行机制。在这里，我们提出了完全耦合的热力学模型，研究粒度演化和能量反馈对剪切带和假玄武玻璃形成的影响。我们的研究结果表明，粒度减小削弱了热失控之前的岩石，并显着降低了热失控所需的临界应力，使其更有可能导致在较浅的深度中深地震。此外，粒度减小的剪切带，这与现场和实验室的观察，假玄武玻璃岩嵌入在同时形成的糜棱岩基质。初始化局部化的临界应力的降低对大尺度地球动力学具有重要意义，因为这种机制可能诱发岩石圈尺度的剪切带和俯冲起始。我们认为，粒度减小和剪切加热的组合解释了中深地震的发生和大规模剪切带的形成。
The underlying physics of intermediate-depth earthquakes have been an enigmatic topic; several studies support either thermal runaway or dehydration reactions as viable mechanisms for their generation. Here we present fully coupled thermomechanical models that investigate the impact of grain size evolution and energy feedbacks on shear zone and pseudotachylite formation. Our results indicate that grain size reduction weakens the rock prior to thermal runaway and significantly decreases the critical stress needed for thermal runaway, making it more likely to result in intermediate-depth earthquakes at shallower depths. Furthermore, grain size is reduced in and around the shear zone, which agrees with field and laboratory observations where pseudotachylites are embedded in a simultaneously formed mylonite matrix. The decrease in critical stress to initialize localization has important implications for large-scale geodynamics, as this mechanism might induce lithosphere-scale shear zones and subduction initiation. We suggest that the combination of grain size reduction and shear heating explains both the occurrence of intermediate-depth earthquakes and the formation of large-scale shear zones.