青藏高原拉萨块体中-晚侏罗世沉积岩与火山岩的古地磁对比研究

The tectonic properties, oceanic basin size, closing time and intracontinental deformation of the Tethyan represent by Bangong-Nujiang suture (BNS) zone are one of the key points in the study of the Tethys problem. However, the closure time of this oceanic basin is still controversial. The kinematic characteristics of the Terranes (Lhasa and Qiangtang terrane) on the sides of BNS, especially the change of their position which include the change of absolute position and relative position of adjacent block are the key to solve this problem. In this project, we will combine the method of paleomagnetism with isotopic chronology, rock magnetism and simulated magnetic inclination shallow to obtain the reliable paleomagnetic data from the Middle-Late Jurassic sedimentary and volcanic rocks (Tukari formation, Renduo formation and Jienu group). Comparing the magnetic inclination differentia between sedimentary and volcanic rocks, the paleomagnetic results could be revised. Our data combine with previous results from Lhasa and Qiangtang terranes, the paleogeographic and kinematic characteristics of this two terrane will be restoration during the Mesozoic. Our results also provide the quantitative constraints on the the closing time of Bangong-nujiang Tethyan, and the tectonic evolution of Lhasa and Qiangtang terranes after the Indian plate collision.

班公湖-怒江缝合带所代表特提斯洋（班怒洋）的构造属性、洋盆规模、关闭时间及闭合后陆内变形量是研究特提斯问题的关键点之一，然而班怒洋的闭合时间至今仍存争议。闭合前后其两侧块体（拉萨和羌塘块体）的运动学特征，尤其是它们的位置变化（绝对位置及相邻块体相对位置的变化），是厘清这一问题的关键。本项目拟将构造古地磁学研究手段与火山岩同位素年代学、岩石磁学及磁倾角浅化机理模拟等方法有机结合，以拉萨块体新识别出的中-晚侏罗世吐卡日组、仁多组沉积岩和接奴群火山岩-沉积岩为具体研究对象，开展精细的古地磁学研究，并比对不同岩性之间由压实作用引起的磁倾角浅化差异，以期获得拉萨块体中-晚侏罗世可靠的古地磁数据。结合前人的研究结果，确定拉萨与羌塘块体中生代的古地理位置和运动学特征，为恢复班怒洋闭合过程、闭合时间以及印度板块碰撞前后该区大地构造演化过程提供定量约束。

班公湖—怒江缝合带所代表特提斯洋的关闭时间及闭合后陆内变形量是研究特提斯问题的关键点之一，然而，由于班公-怒江特提斯洋复杂的演化过程使其闭合时间至今仍存争议。闭合前后其两侧块体（拉萨和羌塘块体）的古位置，是厘清这一问题的关键。本项目以古地磁为主要研究手段，针对拉萨地块晚侏罗世和早白垩世地层开展了详细的磁学及碎屑锆石年代学测试分析工作，获得了两个有野外检验的古地磁极位置，在此基础之上，对拉萨块体和羌塘块体古地磁数据进行了系统的总结和分析，并利用G-plates重建了班公湖-怒江特提斯洋收缩过程。本项目结果显示：晚侏罗世时期，拉萨块体已移动至北半球低纬度地区，此时并未完成与羌塘块体的碰撞拼合，夹于两块体间的班公湖怒江特提斯洋仍有一定的规模。结合前人成果推测：约在105-95Ma期间，拉萨地块和羌塘地块发生碰撞，从而导致班公湖-怒江特提斯洋的消亡。目前，部分研究成果已经公开发表或是正在发表过程中。