Drilling during IODP NanTroSEIZE Expedition 316 led to the recovery of cores from the basal décollement in the frontal part of the Nankai accretionary prism and from a splay fault branching from the décollement at 25‐km landward of the prism toe. The core from the splay fault shows a main shear zone and two secondary shear zones. The main shear zone can be divided into two subzones. The upper subzone consists of a 1.2‐mm thick foliated gouge zone truncated downward by a through‐going fault encompassing a 0.4‐mm thick weakly foliated gouge interval. A nearby 200‐μm thick granular injection vein is interpreted as derived from the fault. The lower subzone consists of a foliated clayey gouge. A 70‐μm thick granular injection vein is also observed along this subzone. In the basal décollement core, microstructures consist of foliated gouge along a flat‐lying shear zone and seven flat‐lying or gently dipping secondary or incipient shear zones above. A redox front lies beneath the main shear zone. The shear zone and the redox front are truncated by a fault surface outlined by microbreccia developed at the expense of the overlying foliated gouge. Foliated gouge from the shear zones is tentatively interpreted as resulting from slow slip or aseismic creep. The weakly foliated gouge, the microbreccia, and the granular injection veins are interpreted as resulting from coseismic slip. The presence of the redox front beneath the main shear zone of the décollement fault core is interpreted as a consequence of oxidizing fluid flow along the microbreccia‐bearing fault.

中文翻译：

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日本西南部南海增生棱镜上张裂和褶皱断层的变形结构（IODP NanTroSEIZE远征316）：断层岩石缓慢和快速滑动的证据

在IODP NanTroSEIZE远征316期间进行的钻探导致从南开增生棱镜前部的基底d陷岩层中恢复了岩心，并从棱镜脚趾向后25公里处的裂岩体分支出了一个八角形断层。八字错的核心显示了一个主剪切区和两个辅助剪切区。主剪切区可分为两个子区。上部分区由一个1.2毫米厚的叶状凿孔区域组成，该区域被贯穿的断层向下截断，该贯穿断层包括一个0.4毫米厚的弱叶状凿孔间隔。附近的200μm厚的颗粒状注入静脉被解释为是由断层引起的。下部分区由叶状黏土凿组成。沿该分区还观察到一条70μm厚的颗粒状注入静脉。在基础装饰岩心的微结构由沿着平坦的剪切带的叶状凿子和上面的七个平坦或缓和的次级或初剪带组成。氧化还原前沿位于主剪切区下方。剪切带和氧化还原前沿被微角砾岩勾勒出的断层表面截断，该断层表面以上覆的叶状凿孔为代价。剪切带上的叶状凿子被初步解释为缓慢的滑动或地震蠕变。弱叶状凿，微角砾岩和粒状注入静脉被解释为同震滑动造成的。纵断层断层岩心的主剪切带下方存在氧化还原锋，这是由于沿微角砾岩断层的氧化流体流动的结果。