南海深海记录与周边的地质对比研究

Recent advances in the South China Sea (SCS) Deep program and ocean drilling program have lead to important progresses in deep sea basin’s development and infill, as well as in the evolution history of the geological environment, mostly in the northern part of the SCS. However, geologic records from the southern part of the SCS may have closer responses to the opening and closure of the SCS. According to existing tectonic hypotheses, the opening of the SCS may be closely associated with the subduction of the “Proto-South China Sea” located just north of Borneo; the collision between Australia and proto-Asia may have resulted in the termination of the SCS spreading. With the rapid development of offshore gas and petroleum exploration in the southern part of the SCS, major advances of geologic investigations from the ocean floor to earth surface have been achieved in the region, indicating that wealth information about the past and present existence of the SCS exists in the geologic records of islands that surround the SCS. For this reason and to complement the lack of research coverage of deep sea basins under the SCS Deep program, there is an urgent need to initialize a synthesis program that will coordinate international collaborations on the geologic correlation between land and sea, especially focusing on the southern part of the SCS. This project will use the approach of comparison of structural and depositional unconformities, and conduct geologic investigations and ocean-land correlation in the geologic windows of Taiwan, Luzon, Mindoro, Palawan, and the Sabah area of Borneo, which have been directly affected by the subduction of both Proto-SCS and today’s SCS. Results from this research will add new scientific evidence bearing on the key questions of the South China Sea Deep Project, such as ‘The Timing and Process of Seafloor Spreading’.

近年来随着南海深部计划和大洋钻探的进展，在深海盆的发育与充填和地质环境的演变等方面取得重要成果，研究工作基本上集中在南海北部。然而南海深海盆扩张的始、终都可能与南部有密切关系：根据假说，婆罗洲北“古南海”的俯冲消亡，可能曾引起南海的扩张；澳大利亚板块与古亚洲的碰撞，可能导致南海扩张的终止。随着南海南部油气勘探的迅速发展，南海南部从海底到地面的地质研究已有重大进展，表明南海周边的岛屿地质，蕴含着南海前世今生的丰富信息。为此，在大计划的集成阶段，迫切需要组织以南海南部为重点、以海陆对比为切入点、以国际合作为途径的集成项目，以补充大计划海底研究的不足。本项目拟从对比构造和沉积不整合面入手，在直接受到‘古南海’和‘现代南海’俯冲影响的南海地质窗口(台湾、吕宋、民都洛、巴拉望及婆罗洲沙巴地区)进行野外地质工作及海陆地质记录对比，为“重大计划”中的“海底扩张的年代与过程”等科学问题补充新的科学依据。

南海周边的陆块和岛屿地质记录蕴含着南海构造演化历史的丰富信息。在南海深海盆发现的诸多科学问题和假设迫切需要在南海海盆和周边陆地的地质记录中进一步寻求答案和补充。为此我们以南海成因模式、扩张与演化历史、和俯冲消亡过程为科学目标，利用古地磁学对已有南海深海盆样品开展详细的退磁实验恢复南海运动学特征，开展南海深海盆与周边陆上地质记录对比的综合研究。在直接受到‘古南海’和‘现代南海’俯冲影响的南海地质窗口(台湾、菲律宾巴拉望、马来西亚婆罗洲、印度尼西亚纳土纳群岛和越南等地)取得的沉积地层学、生物地层学、构造地质学、同位素年代学和古地磁学等学科研究成果。这些成果包括：（1）婆罗洲沙巴地区观察到了“古南海”的地质证据。古南海玄武岩之上有深海相燧石含早白垩纪放射虫化石，指示古南海于白垩纪早期至侏罗纪中晚期形成；（2）印度尼西亚纳土纳岛的古地磁结果和锆石SHRIMP U-Pb同位素年龄揭示该岛东北端出露的花岗岩形成时代为77-79 Ma；（3）南海样品（IODP 349航次U1431、U1433站位）的古地磁学研究工作进一步细化这两个站位地层的年代标尺，补充和验证磁性地层的完整性和准确性。U1431站位和南海东部次海盆自停止扩张之后可能发生了数百公里的向北移动；4）南海地质窗口的古地磁构造旋转研究表明菲律宾巴拉望在渐新世发生了~19°顺时针旋转，中新世时发生了~23°逆时针旋转；台湾兰屿岛和绿岛在上新世以来由于菲律宾海板块和弧陆向东斜向碰撞发生了~30°顺时针垂向旋转；越南东南部地区新第三纪以来发生了~40°顺时针旋转。以上成果表明通过海陆结合和地质记录对比和学科交叉研究，可以帮助反演南海的扩张历史，推动西太平洋地区新生代构造演化的研究。