南海西南次海盆深部结构及洋壳增生模式

南海是我国走向深海大洋战略的突破口，作为其重要组成部分的西南次海盆，具有渐进式海底扩张特征，从东北段岩浆作用主导向中段构造拉伸主导转变，可能存在超薄型地壳，是研究南海构造演化及动力学机制的关键区，也是未来我国实施大洋莫霍面钻探计划的重要目标之一。本项目拟在西南次海盆开展高密度、跨洋盆的主动源OBS探测，结合团队已有的数据基础（多波束水深、深反射地震剖面、OBS折射数据、重磁热数据），采用纵/横波速度联合反演、重磁震相互约束和三维张裂的热力学-动力学耦合数值模拟方法，获得高精度的岩石圈尺度速度结构、密度结构和热结构，重点解决：1）研究区中段精细的地壳和上地幔结构及分界面特征；2）探明埋深最浅的莫霍面潜在位置；3）揭示洋壳增生方式及机制。研究成果将为构建南海的动力学演化模式提供重要的科学证据，为我国钻穿莫霍面计划提供备选钻址，推进人类对地幔的直接观测。

The South China Sea (SCS) is a breakthrough of China's deep ocean strategy. As an important component of SCS, the Southwest Sub-basin shows propagating extension and seafloor spreading, with magma-dominant in the northeast segment and tectonic-dominant in the middle segment. The Southwest Sub-basin, where there may be existing ultrathin crust, is a key area to understand the tectonic process and dynamic mechanism of SCS, and is also one of the important goals for China to implement the Moho-drilling program in the future. An active-source OBS profile with dense station interval is proposed to carry out in the eastern part of the middle segment of the Southwest Sub-basin. Combined with the data from study team (multi-beam bathymetry, MCS, OBS, gravity, magnetic and heat flow), the methods of joint P and S wave velocity inversion, gravity-magnetic-seismic mutual constraint and thermodynamic-dynamic coupling numerical simulation of three-dimensional tensile crack will be taken into obtaining high-precision lithosphere-scale velocity, density and thermal structure. We will focus on solving the scientific questions as following: 1) the fine crustal and mantle structure at the middle segment of our study area; 2) the potential location of the shallowest Moho; 3) pattern and mechanism of oceanic crust formation. Our research results will provide important scientific evidence for the construction of the dynamic evolution model of the SCS, and the alternative drilling sites for China's Moho-drilling project which will promote direct observation of the mantle.