苏门答腊汇聚板块边缘沉积输入和演化与地震活动关系：IODP 362航次岩芯中的磁学记录

The input and evolution of the incoming sediments at the convergent plate-boundary play an important role in the nature of seismogenesis. Composition, texture properties and their formation mechanisms of the magnetic minerals in input sediments are important window to decipher their initial and evolving properties, and understand such processes on related convergent margins. In the present proposal, magnetic fabric and mineral magnetic studies will be conducted on deep-sea sediments from the International Ocean Discovery Program (IODP) Expedition 362, Sumatra Seismogenic Zone at the forearc of the north Sumatran subduction zone, where the Mw ~9.2 earthquake and devastating tsunami occurred in 2004. The relationship between magnetic properties, mineralogical, geochemical and isotope compositions, and textural features will be fully explored. The goals of these works are: (i) To assess compaction and induration state of the input sediments that eventually form the interior and base of the accretionary prism and develop into the décollement. (ii) To address characteristics and mechanisms of structural deformation, as well as history and evolution of tectonic stress field at plate convergent boundary since the late Miocene. (iii) To explore magnetic responses of the diagenetic alterations of the input sediments and magnetic records of the previous earthquakes at convergent boundary, including the 2004 event. All these results are expected to contribute important magnetic evidences for evaluation of the role of thick sedimentary subduction zone input sections in driving shallow slip and amplifying earthquake at the Sumatra subduction zone where submarine fan-influenced sections are being subducted.

汇聚板块边缘沉积输入和演化对汇聚边缘地震的孕育发生具有深刻影响，汇聚边缘沉积物中磁性矿物的组成与结构是追踪和解译沉积输入和沉积演化的重要切入点。本项目选择国际大洋发现计划(IODP) 362航次在2004年印度尼西亚苏门答腊Mw 9.2级地震发生海域—苏门答腊俯冲前缘钻取的深海沉积物为研究对象，以系统的磁组构和岩石磁学测量与分析为基础，以配套样品的矿物组成、化学成分、显微结构和同位素特征之间的相互关系为桥梁，揭示汇聚边缘输入沉积物的压实与固结状态；结合区域构造背景，重塑晚中新世以来，苏门答腊汇聚边缘构造应力场及其演化历史；探讨汇聚边缘沉积输入、成岩演化与地震活动的磁学响应特性及其机制。为认识和理解汇聚边缘沉积输入和沉积演化与地震孕育发生之间的内在联系提供重要磁学依据。

汇聚板块边缘沉积输入和演化对汇聚边缘地震的孕育发生具有深刻影响，汇聚边缘沉积物中磁性矿物的组成与结构是追踪和解译沉积输入和沉积演化的重要切入点。本项目选择国际大洋发现计划(IODP) 362航次在2004年印度尼西亚苏门答腊Mw 9.2级地震发生海域—苏门答腊俯冲前缘钻取的深海沉积物为研究对象，通过系统的磁组构、岩石磁学和古地磁学测量与分析，配套样品的矿物组成、化学成分和显微结构分析，探讨了汇聚边缘沉积输入、成岩演化与地震活动的磁学响应特性及其机制。目前取得了以下主要成果：（1）厘清了钻井与取心诱发沉积物变形的磁组构特征及其对古地磁记录可靠性的影响，建立了钻井和取心诱发沉积物变形的磁组构识别方法；（2）基于部分岩石物性数据开展了旋回地层学分析，建立了U1480站位7 Ma以来、分辨率为20 ka的地质年代格架；（3）揭示了浊流与生物扰动对胶黄铁矿形成与保存的调控作用，发现了一种新的胶黄铁矿形成机制；（4）揭示了俯冲前缘沉积物脱水硬化的岩石磁学与古地磁学记录；（5）全面系统地梳理了断层岩磁学研究所取得的进展，并对未来发展进行了展望。