中印度洋海盆板内构造及其对印度-欧亚板块碰撞作用的响应

One of the most intensively studied and strongly debated issues in plate tectonics is the timing and models of the India-Eurasia collision, and most studies of the India-Eurasia collision are based on continental works. The Central Indian Ocean Basin (CIOB) is currently located in the center of the Northeast Indian Ocean and in north of the Indo-Australian Plate. The CIOB opened at Early Cretaceous due to India separating from Antarctica, and experienced the India-Eurasia collision event. Intraplate tectonics in the CIOB, including aseismic ridges, oceanic microplates and oceanic thrust faults, are ambiguously postulated to be responses of the India-Eurasia collision event. Whereas, which types of intraplate tectonics are records of the India-Eurasia collision event and by what methods of analyzing these intraplate tectonics to resolve the controversial issues of the India-Eurasia collision need to be further studied. In our study, we attempt to resolve these problems by submarine intraplate tectonic evidences: we firstly plan to calculate the magma production rates along the aseismic ridges, build magnetic anomaly inversion models, and calculate the stratum shortening of the oceanic thrust faults; and then attempt to confirm the timing of the India-Eurasia initial collision by occurrences of abrupt decreases of magma production rates, to divide phases of the India-Eurasia collision by formation time of various oceanic microplates, and to analyze the waning effects of the India-Eurasia collision by changes of the shortening rates of the oceanic thrust faults.

印度-欧亚板块碰撞一直是板块构造的热点问题之一，目前就其初始碰撞时间和碰撞模式等问题主要基于陆地研究并存在众多争议。位于东北印度洋中部、印度-澳大利亚板块内部的中印度洋海盆，其海底扩张起始于早白垩世印度与南极洲的分离、经历了印度-欧亚板块碰撞过程。海盆内无震海岭、洋内微板块和洋内逆冲断层等板内构造的形成，被笼统地推测为是对印度-欧亚板块碰撞作用的响应。但哪些板内构造是印度-欧亚碰撞事件在海盆扩张过程中的记录、如何利用这些板内构造来解决印度-欧亚碰撞时间和碰撞模式等问题尚不明确。本项目拟以以上三种板内构造为研究对象，通过岩浆通量计算、海底磁异常反演和逆冲断层地层缩短量计算等方法，建立无震海岭与印度-欧亚碰撞启动、微板块形成与碰撞阶段划分、洋内逆冲断层启动与碰撞作用衰亡的关联，为解决陆地研究中有争议的印度-欧亚初始碰撞时间、碰撞模式和碰撞阶段划分等问题提供海底构造的依据。

印度-欧亚板块的初始碰撞时间和碰撞模式一直是板块构造的热点问题，但多基于陆地研究且存在多种争议，未能从洋底证据来提供制约。为此，本项目以东北印度洋板内构造为切入点，解析并发现洋内洋中脊的突然死亡或跃迁、微板块的形成、岩浆通量的持续稳定突增是对印度-欧亚板块碰撞作用的响应，具体表现为：①查格斯-拉克代夫海岭和东经九十度海岭分别为延伸至印度西、东边缘的地幔柱成因的无震海岭，其岩浆通量分别自52-50 Ma和49-47 Ma持续稳定突增，分别揭示了印度西缘、东缘与欧亚板块的“软碰撞”启动时间；②分割印度西南和非洲板块的中印度洋洋中脊于~41 Ma突然向南远距离（>200 km）跳跃，分割印度东南和南极洲板块的沃顿洋中脊于~38 Ma突然死亡并向南迁移至现今东南印度洋洋中脊位置、其残留的死亡洋中脊围限了Mammerickx微板块的形成，分别揭示了印度西缘、东缘与欧亚板块的“硬碰撞”启动时间。结果表明，印度西缘-欧亚板块和印度东缘-欧亚板块的软碰撞时间分别为52-50 Ma和49-47 Ma、硬碰撞时间分别为~41 Ma和~38 Ma，从而建立了印度-欧亚两阶段、向东穿时性的碰撞模式，为解决陆地研究中有争议的印度-欧亚初始碰撞时间和碰撞模式问题提供洋底新依据。