青藏高原腹地二叠纪火山岩连续剖面的精细古地磁学研究

The Qinghai-Tibet Plateau is considered to be ideal natural laboratory for building a new theory of continental dynamics. The plate boundary between the Gondwanaland and Eurasia plates, which play an important role in understanding plateau internal structure and evolutionary history of the Tethys, remain hotly debated. Lhasa, south / north Qiangtang region in the Qinghai-Tibet Plateau may be a key place to study these problems. In order to obtain a high quality paleomagnetic data with accurate age control in northern Qiangtang block, this project intends to carry out a refined paleomagnetic studies on the permian volcanic rocks in Zhouqiongmalu areas of Tanggula township, east China. This studies based on the accumulation of the Qinghai-Tibet plateau paleomagnetic research we has completed, and associates research techniques of paleomagnetism, magnetostratigraphy, volcanic chronology, rock magnetism and magnetic fabric analysis. Combined with the early reported paleomagnetic data from the permian sedimentary strata from the western part of the northern Qiangtang Range, which primary origin of the magnetization is confirmed by positive fold-, reversal-, and baked contact tests, this project aim to reconstruct paleogeographic location and kinematic characteristics of the northern Qiangtang block in late Paleozoic, ascertain the collision process between Lhasa and south / north Qiangtang blocks, determine the plate boundary of Gondwana and Eurasia plates.

青藏高原是建立新的大陆动力学理论的最佳天然实验室。冈瓦纳与欧亚大陆界线研究是地学界持续的研究热点，界线位置、性质的确定在特提斯洋演化过程研究中占据最为重要的位置。拉萨、南/北羌塘地块被认为是解决这一科学问题的关键地区。本项目在本人已参与完成的青藏高原古地磁研究项目的基础上，拟将标准古地磁学研究手段与火山岩同位素年代学、磁性地层学及岩石磁学、岩石磁组构分析等方法有机结合，以青海省格尔木市唐古拉山乡周琼玛鲁二叠纪那益雄组火山岩连续剖面为具体研究对象，开展精细古地磁学研究，以期获得羌北地块东段具有精确年龄控制的高质量古地磁数据。并结合前期在羌北地块西段二叠纪沉积地层中获得的可通过褶皱、倒转和烘烤检验的古地磁数据，确定羌北块体晚古生代的古地理位置及其运动学特征，研究其与拉萨、南羌塘地块之间的碰撞拼合过程，为恢复青藏高原古特提斯演化历史，厘定冈瓦纳与欧亚大陆的界线、碰撞时限及古地理位置提供定量约束。

青藏高原是环球巨型特提斯域东部的主体，是被周边四大古老稳定地块（华北、塔里木、扬子、印度）围限的超级造山系统。青藏高原是古生代以来欧亚大陆不断向南增生，冈瓦纳古陆北缘微陆块不断解体、北移、拼贴到欧亚大陆南缘而产生的。冈瓦纳大陆和欧亚大陆的界线研究是地学界几十年持续的研究热点，界线位置、性质的确定在特提斯洋演化过程研究中占据最为重要的位置。羌塘地块位于青藏高原腹地，夹持于班公湖-怒江缝合带和西金乌兰—金沙江缝合带之间。被认为是研究青藏高原特提斯演化和两大陆界线位置的关键地区。本项目以羌塘地块东段那益雄火山岩剖面作为重点研究对象，结合古地磁学、火山岩年代学、岩石磁学和岩石磁组构等研究，获得了一个有精确年龄控制古地磁数据，并获得了该套火山岩的年代学和地球化学数据。获得了一批相关时代的古地磁数据，初步建立了羌北地块晚古生代的视极移曲线。结合前期在羌塘地块西段沉积地层中获得的古地磁结果，描绘出羌北地块晚古生代的古地理位置及其运动学特征。研究结果可为恢复青藏高原羌塘块体古特提斯演化阶段的古地理位置及碰撞拼合过程，厘定冈瓦纳与欧亚大陆界线、封闭的时限等提供可靠的定量约束。本研究的成果对于研究青藏高原古特提斯演化，厘定冈瓦纳和欧亚大陆的界限等具有重要的意义。