长江第一弯虎跳峡的贯通——来自于地表地貌和弹性挠曲的数值模拟分析

2022,96(8):2942-2954
郑勇1,2, 李海兵1,2, 潘家伟1,2, 杨少华1,2, 龚正3
1) 南方海洋科学与工程广东省实验室（广州），广东广州，511458;2. 2)自然资源部深地动力学重点实验室，中国地质科学院地质研究所，北京，100037;3) 中国地震局地球物理研究所，北京，100081
摘要：以往注入南海的古金沙江的袭夺及其相关的长江第一弯的形成不仅造成了南海一系列盆地内部充填物质的急剧变化，同时还记录了与南海北部边缘海扩张相关的构造活动机制的重大变革。尽管如此，由于缺乏直接证据，对于金沙江东流和长江第一弯形成的时间和机制还存在较大分歧。鉴于此，本研究通过TTLEM和LIFFE模型直接对虎跳峡的贯通和下切过程开展数值模拟分析。结果显示虎跳峡现今深切峡谷的形成是两阶段地表快速侵蚀的产物。而其初始的贯通应形成于中新世中期(~15 Ma)前后，和虎跳峡背斜的形成同期，与大理断裂系大规模走滑兼具逆冲运动直接相关。随后，进入第四纪(~2 Ma)以来，大理断裂系的构造活动由压扭转变为张扭性。虎跳峡由于地壳的弹性挠曲变形再次快速下切，剥蚀厚度达到~3 km，最终形成了现今的地貌样式。结合区域的其他研究结果，我们认为伴随着印度板块向欧亚板块之下持续的俯冲，青藏高原东南缘南东向的物质运移曾发生过一系列构造活动机制的重大转变，不仅引起了区域内断裂系统活动性质的转换，造成了大型水系的袭夺和重组，同时还与南海海盆的扩张和最终形成紧密关联。
关键词：南海；金沙江；长江第一弯；数值模拟；弹性挠曲；物质运移

Connection of the Tiger Leaping Gorge near the First Bend of the Yangtze River: new insights from numerical modelling of geomorphology and elastic flexure deformation

Zheng Yong1,2, Li Haibing1,2, Pan Jiawei1,2, Yang Shaohua1,2, Gong Zheng3
1) Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou, Guangdong 511458, China;2) Key Laboratory of Deep- Earth Dynamics of Ministry of Natural Resources, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China;3) Institute of Geophysics, China Earthquake Administration, Beijing 100081, China
Abstract：The capture of the Paleo- Jinsha River which once flowed into the South China Sea as well as the formation of the First Bend of the Yangtze River not only resulted in a sharp change of the filled materials in basins, but also recorded the tectonic movement mechanisms of the northern margin of the South China Sea. However, owing to shortage of direct evidences, the timing and origin of the east- flow river and the Great Bend formation is still debated. Thus, this study performed numerical modelling based on both TTLEM and LIFEE models to simulate the connection and incision processes of the Tiger Leaping Gorge. The results show that the present- day deep- cutting Tiger Leaping Gorge resulted from two phases of rapid exhumations. Its initial connection formed at ~15 Ma during the Mid- Miocene contemporaneous with the folding of the anticline along the Tiger Leaping Gorge, corresponding to the widespread large- scale strike- slip faulting with thrust component of the Dali fault system. Since Quaternary, deformation pattern shifted from transpression into transtension. The Tiger Leaping Gorge started a new rapid incision owing to the crustal elastic flexure with an exhumation amount of ~3 km, resulting in the sent landscape. Combining other results, we suggest that with the continuous underthrusting of the India Block to the Eurasia Block, several major changes in tectonic movement mechanisms have been triggered by the eastward material migration along the southeastern margin of the Tibetan Plateau. These major changes not only caused the shifts of faulting characteristics, resulting in the capture and reorganization of regional large- scale river systems, but also were related to the expansion and formation of the South China Sea.
Key words：South China Sea; Jinsha River; First Bend of the Yangtze River; numerical simulation; Dali fault system; elastic flexure
收稿日期：2022-05-28
基金项目：本文为南方海洋科学与工程广东省实验室（广州）人才团队引进重大专项（编号GML2019ZD0201）、国家自然科学基金项目（编号4941016，42072240，41830217）、科技部项目(编号2021FY100101，2019QZKK0901)，地质调查项目(编号DD20221630)和中国地震局地球物理研究所基本科研业务费项目（编号DQJB20B21）联合资助的成果。
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