尼泊尔及南侧邻区元古宙以来的构造-沉积演化

The Tectonosedimentary Evolution since Proterozoic in Nepal and Its Southern Adjacent Areas

迄今,尼泊尔及其南侧邻区元古宙以来的构造-沉积演化尚缺乏系统性研究.为了促进区域地质认识,结合前人研究成果及新的研究发现,对尼泊尔低喜马拉雅带及以南的构造-沉积演化首次进行系统性总结与讨论.结果表明:尼泊尔低喜马拉雅带及以南与印度地盾北缘在地质历史中的构造-沉积演化息息相关,且自元古宙以来,发育了被动大陆边缘→陆内裂谷→被动大陆边缘→前陆盆地等不同构造演化阶段的沉积响应;尼泊尔西部的Dailekh群属于~1.8 Ga以前或前哥伦比亚超大陆之前的被动大陆边缘沉积;Vindhyan超群为下断上坳的陆内裂谷沉积,尼泊尔境内的Lakharpata群相当于下Vindhyan群;Gondwana超大陆裂解导致由北往南形成一系列初始发育时间越来越晚的裂谷盆地;Surkhet群至Siwalik群为被动大陆边缘至前陆盆地沉积,其中,Surkhet群Swat/Subathu组是喜马拉雅南侧地质历史上最后一套海相沉积地层,也是被动大陆边缘向前陆盆地转换期的沉积响应;Siwalik群大规模的磨拉石建造标志着喜马拉雅快速和大幅度隆升,该群沉积成岩后,印度-欧亚板块进一步的挤压作用导致了地质历史上迄今为止最后一次强烈的构造运动,形成MFT与Siwalik褶皱带,并奠定了喜马拉雅带现今构造格局.

At present,the tectonosedimentary evolution since Proterozoic in Nepal and its southern adjacent area is still lacking of systematic research.In order to promote divisional geological understanding of the area,the author intends to combine the previous and the new research results to systematically summarize and discuss the tectonosedimentary evolution of the Lesser Himalaya of Nepal and its southern areas.The results show that,the tectonosedimentary evolution in the less Himalaya of Nepal and its southern areas are closely related to the northern part of the Indian shield in the geological history;since Proterozoic,it has experienced the following different stages of tectonic evolution in turn,that is from passive continental margin to intracontinental rift to passive continental margin to foreland basin;the Dailekh Group in western Nepal deposited in the passive continental margin before~1.8 Ga or before the pre-Columbia supercontinent;the Vindhyan supergroup deposited in an intracontinental rift(its lower part deposited in graben and its upper part deposited in depression),and the Lakharpata group in Nepal is equivalent to the lower Vindhyan group;the break-up of Gondwana supercontinent resulted in the formation of a series of rift basins with gradually late initial development time from north to south;the Surkhet Group and the Siwalik Group are deposited in passive continental margin to foreland basin,and the Swat/Subathu Formation of Surkhet Group is the last set of marine sedimentary strata in the geological history of the southern Himalayas,and it is also the key sedimentary response during the passive continental margin changing to the foreland basin;the large-scale molasse formation of the Siwalik Group marked the rapid and substantial uplift of the Himalayas,and after the group’s sedimentation and diagenesis,the further compression of the Indo-Eurasian plate led to the last strong tectonic movement in geological history so far,forming the MFT and Siwalik fold belts,and forming the present tectonic framework of the Himalaya.