苏拉威西海与古南海对向俯冲系统的三维地震观测及板块活动机制

North Borneo and the adjacent sea areas record the process from the beginning of the subduction to the stop of the proto-South China Sea and the Sulawesi Sea, and is a natural laboratory for studying the mechanism of the double subduction system and collisional orogeny. This application aims to reveal the plate activity mechanism of the double subduction system in the area, and utilizes 30 broadband ocean bottom seismometers (OBS) deploy in the surrounding sea areas and 45 land seismic observation stations deployed onshore to carry out 3D onshore-offshore seismic observation. Using air-gun array and high-frequency OBS to carry out active source deep seismic sounding, and using the active/passive source combined imaging technology to obtain the three-dimensional structural information of the crust and upper mantle in the study area. Then, the simulation analysis of the evolution process of the North Borneo and the adjacent sea under the action of the subduction system will be carried out, and the relationship among the extent of the subduction plate, the thickening of overlying crust and the continuous process of the double subduction system will be discussed. Based on the international cooperative observations of this application, conducting cooperative research can not only enhance the scientific and technological exchanges between China and ASEAN countries, but also serve the “Belt and Road Initiative”, and help to obtain valuable seismic observation data in the region. Deep seismological evidence will be provided for scientific problems such as the geological tectonic causes of the rapid uplift of the basement, the deep structure of the lithosphere at different subduction stages, and the mechanism of the plate movement.

北婆罗洲及邻海记录了古南海和苏拉威西海从俯冲开始到停止的过程，是研究对向俯冲系统、碰撞造山机制的天然实验室。本申请以揭示该区对向俯冲系统的板块活动机制为研究目标，利用在该区布设的45台地震观测台和周边海域布设的30台海底宽频带地震仪，开展海陆联合三维地震观测；同时利用海上气枪阵列与高频OBS开展深地震人工探测，并采用主/被动源联合成像技术，获得研究区地壳上地幔的三维结构信息；随后开展对向俯冲系统作用下北婆罗洲及邻海的演化过程进行模拟分析，讨论俯冲下插板片与上覆地壳增厚的程度及其双俯冲系统持续过程之间的关系。以本申请的国际合作观测为基础，开展合作研究不仅能够增进我国与东盟国家的科技交流，服务于“一带一路”倡议，而且有助于获得该区域宝贵的地震观测资料，为探索俯冲起始至消亡过程转变导致基底迅速隆起的地质构造成因、比较处于不同俯冲阶段的岩石圈深部结构、揭示板块活动机制等科学问题提供深部地震学证据。

本项目以揭示北婆罗洲和苏拉威西俯冲带演变过程为目标，组织实施了苏拉威西海三维海底地震观测实验(2019投放27台OBS，2020回收12台)，参加了基金委2021-8南沙海域开放航次；项目采集、收集了南海南部至北苏拉威西俯冲带区一批原始地球物理数据。为揭示被动向主动陆缘转换的关键廊带的深部结构特征提供了新的地球物理依据。通过多种建模成像及联合反演，获得了北婆罗洲及苏拉威西海俯冲带地区的深部结构。通过动力学数值模拟研究，还原了研究区俯冲过程，获得两点主要认识。1：北苏拉威西俯冲带为“诱发”的俯冲起始和“自发”的海沟后撤。在俯冲起始阶段，年轻的苏拉威西海板片必须借助水平方向的外力作用才能完成下插，当洋壳到达60km深度后会逐渐榴辉岩化，控制俯冲的主应力逐渐向俯冲板片的负浮力转变，随后板片自我持续俯冲、海沟的后撤和大陆地壳的伸展则主要受控于俯冲板片自身的负浮力。2：苏拉威西俯冲带没有足够的水能进入热地幔楔角以产生足够的熔融岩浆是导致其火山岛弧缺失的主要原因。只有与苏拉威西类似的、初始俯冲角度小的年轻海盆在俯冲起始后会存在“岛弧缺失”的历史，推测上覆板块“热”且“轻”是造成初始俯冲角度小的原因。正在实施的2023印尼龙目岛海陆联合地震观测剖面将为深入认识以上科学问题提供更多的地球物理观测依据。