Lithification processes in subduction zones and their influence on the structural style of accretionary prisms

矩级为Mw bbbb9的大型逆冲地震主要发生在增生边缘，例如2004年12月（印度尼西亚）发生的苏门答腊地震，造成了毁灭性的后果。地震期间沿板块界面的灾难性滑动始于所谓的发震带。俯冲逆冲构造上不稳定滑动发生的原因仍然存在争议，因为到目前为止还没有对活动的大逆冲构造的发震带进行采样。对于地震核作用的开始，最被接受的假设之一是深度的吸积棱镜的岩化作用。岩化作用还影响了棱柱的结构样式，导致锥度角减小，这被认为与发震带的出现有关。一系列成岩-低温变质反应被认为是导致岩化的原因，但这些过程在活动增生棱镜中的身份和时空分布在很大程度上是未知的。本研究旨在确定南开活动增生三棱镜中关键的成岩-低t变质作用。在这项研究中，一组独特的样本包括：1)综合海洋钻探计划（IODP）海底2公里深处的样本；2)2012年夏天由R/V Sonne回收的源自内楔内部的泥火山碎屑喷出物；3)来自Shimanto带（日本）的陆上样本，这是一个位于吸积棱镜腹地的化石吸积棱镜。样品温度达到孕震带的下倾极限，覆盖了前俯冲、外楔和内楔的不同构造段。提出了一套全面的岩石学分析，以识别和表征导致岩化的成岩到低t变质过程。该研究与实验室物理性质测量相辅相成，以评估岩化对深度机械和水文地质性质的影响。随钻测井数据的利用将限制楔形岩化过程的时空发生。库仑楔分析将用于评估这些过程对俯冲带弧前构造样式和造震产状的影响。

Megathrust earthquakes with moment magnitudes Mw>9 occur mainly on accretionary margins such as the Sumatra event in Dec. 2004 (Indonesia) which had devastating consequences. The catastrophic slip along the plate interface during earthquakes initiates in the so-called seismogenic zone. The cause for the onset of unstable slip on the subduction thrust is still subject to debate, because the seismogenic zone of an active megathrust zone has not been sampled so far. One of the most accepted hypotheses for the onset of earthquake nucleaction is the lithification of the accretionary prism at depth. Lithification also affects the structural style of the prism and causes a decrease in taper angle, which is supposed to be linked to the occurrence of the seismogenic zone. A suite of diagenetic to low-temperature (T) metamorphic reactions is believed to cause the lithification but the identity and spatio-termporal distribution of these processes in active accretionary prisms is largely unknown. The proposed study aims to identify key diagenetic to low-T metamorphic processes in the active Nankai accretionary prism. For the research a unique sample set exits that comprise 1) samples from the Integrated Ocean Drilling Program (IODP) up to 2 km depth below the seafloor, 2) clastic ejecta from mud volcanoes that originate from the interior of the inner wedge recovered in summer 2012 with R/V Sonne and 3) onshore samples from the Shimanto Belt (Japan), a fossil accretionary prism in the hinterland of the accretionary prism. The samples experienced temperatures up to the downdip limit of the seismogenic zone and cover the different tectonic segments of pre-subduction, outer and inner wedge. A comprehensive suite of petrograhic analysis is proposed to identify and characterize the diagenetic to low-T metamorphic processes that cause lithifiation. The research is complemented with laboratory physical property measurements to assess the impact of lithification on mechanical and hydrogeological properties at depth. Utilization of logging-while-drillling data will constrain the spatio-temporal occurrence of the lithification processes in the wedge. Coulomb wedge analysis will be employed to assess the implications of the processes on the structural style of the subduction zone forearc and the occurrence of seismogenesis.