【作者】 宋春彦；

【导师】 王剑；

【作者基本信息】 中国地质科学院 ， 古生物学与地层学， 2012， 博士

【摘要】 羌塘盆地位于特提斯构造域东段,青藏高原中北部；其北侧边界为金沙江缝合带,南侧边界为班公-怒江缝合带。羌塘盆地是在特提斯地质背景下经历了晚古生代至新生代多期旋回演化历史的复合沉积盆地。羌塘中生代盆地发育于古特提斯洋关闭的关键时期,并伴随着中特提斯洋的演化而演化。因此,羌塘中生代盆地对于认识古特提斯洋向中特提斯洋的演化过程具有重要的指示意义。同时,羌塘中生代盆地也是我国最大的海相中生代盆地,其油气资源前景非常巨大,是我国油气勘探的重点区域。基于其重要的地质意义和应用价值,本文选择羌塘中生代沉积盆地的演化作为研究对象。以沉积学方法为主,岩石学和同位素科学等多学科方法相结合进行系统研究和综合分析,具体应用沉积体系、沉积相等研究手段对羌塘发育的中生代地层进行系统对比和研究,在此基础上划分了盆地的沉积充填序列,并恢复中生代八个主要地质时期的岩相古地理面貌,最后在古地磁研究基础上结合前人成果讨论了盆地的演化过程。结果显示,羌塘中生代沉积盆地的演化可划分为两个时间段,羌塘晚三叠世古风化壳作为盆地转换的标志。古风化壳之下藏夏河组的地球化学特征表明,晚三叠世卡尼期,羌塘北部为发育于可可西里碰撞造山带前缘的前陆盆地,同碰撞花岗岩可能为其主要物源。古风化壳之上那底岗日组火山岩地球化学结果表明,盆地性质已经转为被动大陆边缘裂陷盆地,火山岩的SHRIMP锆石U-Pb年龄显示羌塘中北部裂陷活动开始于-220Ma(即诺利晚期),主裂陷期为220-205Ma；南羌塘坳陷的裂陷活动可能开始于诺利早期,结束于早侏罗世。早-中侏罗世期间,羌塘盆地由裂陷盆地逐渐过渡为坳陷盆地。锆石裂变径迹测年结果表明,羌塘中生代盆地萎缩时限为-147-128Ma,盆地的关闭可能发生于86-87Ma。羌塘中生代盆地的演化可归纳为2大的演化个阶段,即早三叠世-晚三叠世卡尼期前陆盆地阶段和晚三叠世诺利期-早白垩世裂陷-坳陷阶段,后者又可细分为羌南裂陷阶段、羌北裂陷阶段、整体坳陷阶段、萎缩与关闭阶段。沉积学研究表明,羌塘中生代盆地主要发育六个沉积充填系列,分别为裂陷前时期为前陆盆地沉积充填；同裂陷期主体表现为冲洪积相沉积充填；坳陷早期以大面积发育滨岸相沉积为特征；主坳陷期盆地经历了两次大规模海侵和一次海退沉积,并分别以台地相碳酸盐岩沉积和滨岸-潮坪相沉积为主；盆地萎缩期盆地内主要发育以粗碎屑岩、蒸发岩为主的三角洲相-泻湖相沉积。盆地早期粗碎屑岩为油气提供了很好的储集空间,中期碳酸盐岩、泥岩为良好的烃源岩,晚期膏盐岩、油页岩又是良好的区域盖层,因此,整个羌塘中生代盆地的沉积充填构成了一良好的油气生储盖组合。更多还原

【Abstract】 The Qiangtang basin is located in the east part of the Tethys realm and the central-northern Tibetan Plateau, and bounded by Jinshajiang suture zone to the north and Bangong-Nujiang suture zone to the south, respectively. The Qiangtang basin is a large composite basin which experienced Paleozoic-Cenozoic multi-cycle evolution. The Mesozoic Qiangtang basin bagan to form in the closure of the Paleo-Tethyan ocean, and existed with the Mid-Tethyan ocean. So the Mesozoic Qiangtang basin has great implications for the Mid-Tethyan ocean. The Mesozoic Qiangtang basin is the largest Mesozoic marine basin which has bright oil and gas prospect, and is a key exploration area. Allow for the geological significance and the application value, we selected the Mesozoic Qiangtang basin as the research object.The sedimentology, the petrology and the isotopic geochemistry are the main research methods. Based on the correlation and analysis of the Mesozoic strata in the Qiangtang, divided the filling sequences, reconstructed the lithofacies paleogeography. At the end, based on the paleomagnetic results and the achievements of the predecessors, the basin evolution was discussed.It is suggested that, the evolution of the Mesozoic Qiangtang basin can be divided into two periods, and the paleowethering crust marked the basin changing. The geochemistry data of the Zangxiahe Formation indicates that the Carnian basin of the Qiangtang is a foreland basin, and the main provenance is the syncollision granites.The geochemistry results of the Nadigangri Formation in Qiangtang basin show that the basin is a rift basin after the paleowethering crust. The rifting started at about220Ma, and persisted at205Ma in the central-nothern Qiangtang. The rifting of the southern Qiangtang may start in the early Norian and ended in the early Jurassic.The Qiangtang basin gradually changed into depressive basin from the early Jurassic to the late Jurassic. The zircon fission track data indicated the basin shrinkage occurred in between147and128Ma and the basin closure maybe started in87-86Ma.The research results of sedimentology show that the Mesozoic Qiangtang basin experienced six filling sequences:the foreland filling before the rifting, the synrifting alluvial-deluvial filling, the littoral facies filling in the early depression, two transgressive and one regressive and the mesa-tidal flat carboniferous sediment in the main depression stage, coarse clastic rocks and evaporation filling in the shrinkage and closure stage.The early coarse clastic rocks are the reservoir, the carbonate rocks and the mudstones in the middle stage are the main hydrocarbon source rocks, the evaporation rocks and the oil shale in the late stage are good seal rocks, so the Mesozoic filling rocks in the Qiangtang basin formed a super source-reservoir-seal combination.更多还原