Abstract Deep ocean drilling revealed that shallow seismic slip in subduction zones is localized along weak pelagic clay, resulting in devastating tsunamis. However, the actual conditions of earthquake faulting in the deeper portions of subduction zones are largely unknown. The Jurassic chert–clastic complex in central Japan was formed under a cold subduction zone, within which the termination stage of superanoxia in the Middle Triassic was recorded in the pelagic sedimentary rocks. We conducted structural and Raman spectroscopic analyses of the fault rocks distributed along the thrust fault branched from the plate-boundary decollement. The results show that preferential melting of illite, thermal erosion, wall-rock fracturing, and increased carbonization are recorded along a few millimeter-thick pseudotachylyte derived from the black carbonaceous mudstone. A comparison of the clast volume fraction between the pseudotachylyte and black carbonaceous mudstone indicates that half amount of the clasts in the pseudotachylyte originate from the incorporation of fractured wall rocks composed of pelagic chert. Thermal modeling using the thermal diffusivities of wall rocks and the measurement of wall-rock fracture density suggest that fractured wall rocks represent thermal fracturing associated with the alpha–beta transition of quartz in the chert. Our pseudotachylyte study suggests that seismic slip at the deeper portions of the subduction zones is localized along the black carbonaceous mudstone flanked with chert. The intensely fractured wall rocks may be characteristic of pseudotachylyte, which accompanies quartz-rich wall rocks with high thermal diffusivities. The coseismic thermal fracturing of wall rocks potentially affects the dilatancy-induced fluid pressure drop in the slip zone and the reduction of wall-rock stiffness, resulting in the generation of frictional melt and acceleration of seismic slip.

中文翻译：

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日本中部侏罗纪增生杂岩的远洋沉积岩中记录的摩擦熔融和热压裂

摘要 深海钻探表明，俯冲带的浅层地震滑动沿弱的远洋粘土定位，导致毁灭性的海啸。然而，俯冲带较深部分地震断层的实际情况在很大程度上是未知的。日本中部侏罗系燧石-碎屑杂岩形成于冷俯冲带下，其中远洋沉积岩记录了中三叠世超缺氧的终止阶段。我们对沿从板块边界滑脱分支的逆冲断层分布的断层岩进行了结构和拉曼光谱分析。结果表明，伊利石优先熔融、热侵蚀、围岩压裂、并且沿着源自黑色碳质泥岩的几毫米厚的拟速凝液记录到碳化增加。拟速凝岩与黑色碳质泥岩碎屑体积分数的比较表明，拟速凝岩中一半的碎屑来源于由远洋燧石组成的裂隙围岩的掺入。使用围岩的热扩散系数和围岩裂缝密度测量的热模拟表明，破裂的围岩代表了与燧石中石英的 α-β 转变相关的热破裂。我们的pseudotachylyte 研究表明，俯冲带较深部分的地震滑动位于黑色碳质泥岩，两侧是燧石。强烈破碎的围岩可能是伪速凝岩的特征，它伴随着具有高热扩散率的富含石英的围岩。围岩的同震热压裂潜在地影响滑移区剪胀引起的流体压降和围岩刚度的降低，导致摩擦熔体的产生和地震滑移的加速。