昌都地区侏罗纪古地磁研究及其古地理意义

The evolution and closure of the Bangong-Nujiang Tethys Ocean (BNTO) accompanied by the convergence and collision of the Qiangtang and Lhasa blocks. The processes involved in the evolution of the BNTO and the Qiangtang-Lhasa collision are key factors to understand the early evolution history and geodynamics of the central Tibetan Plateau. However, the evolution and closure process of the BNTO have remained controversial, and there is lack of paleogeographic evidence for the diachronous closure model for the BNTO. Knowledge of the paleogeographic reconstruction for the eastern portion of the BNTO is significant to resolve these questions. In this study, we are planning to carry out a comprehensive paleomagnetic study on the Jurassic rocks in the Changdu area. Based on these new Jurassic paleomagnetic results from the studied areas and compared with paleomagnetic results from the Lhasa block, we will reconstruct the paleogeography and drift history of the eastern portion of the Qiangtang block and the relationship between the Qiangtang and Lhasa blocks during the Jurassic. Moreover, we will reconstruct the tectonic evolution of the eastern portion of the BNTO during the Jurassic. This study will provide reliably paleomagnetic constraint on the evolution and closure of the BNTO.

班公湖-怒江特提斯洋演化及闭合伴随着羌塘地块与拉萨地块的汇聚-碰撞，并对青藏高原中部早期形成与演化产生了重要的影响。但是目前对这一古大洋演化及闭合过程的研究还存在巨大争议，且自东向西呈剪刀状逐渐闭合模式也缺少大洋东部直接的古地理证据。研究班公湖-怒江特提斯洋东部古地理对重建其演化及闭合模式具有重要意义。本申请项目拟选择青藏高原羌塘地块东部昌都地区侏罗系地层开展详细的古地磁研究，重建羌塘地块东部侏罗纪时期的古地理位置及其运动学过程。综合对比现有拉萨地块侏罗纪古地磁数据，研究羌塘地块和拉萨地块东部侏罗纪时期的相对运动关系，并综合地质资料探讨班公湖-怒江特提斯洋东部侏罗纪古地理演化历史，从而为探讨班公湖-怒江特提斯洋演化及闭合过程提供重要的科学依据。

本项目主要对羌塘地块和拉萨地块侏罗-白垩纪地层开展了古地磁研究，获得羌塘地块和拉萨地块早白垩世可靠的原生古地磁数据，并从羌塘地块昌都地区侏罗系红层中获得了重磁化分量。基于以上古地磁结果，探讨了班公湖-怒江洋演化与闭合过程。在GSA Bulletin、Tectonophysics、Earth-Science Review和岩石学报等期刊发表SCI论文4篇。主要成果简要介绍如下：（1）自羌塘地块东部昌都地区中-晚侏罗世红层中获得了白垩纪重磁化分量，根据重磁化的时代及机制约束了羌塘地块和拉萨地块东部碰撞时限；（2）获得了羌塘地块早白垩世可靠古地磁数据，为班公湖-怒江特提斯洋西部演化及闭合和拉萨地块与羌塘地块西部汇聚-碰撞过程提供了古地磁定量约束；（3）获得了拉萨地块东部早白垩世可靠古地磁数据，限定了拉萨地块早白垩世古地理位置及展布形态，定量约束了羌塘地块和拉萨地块碰撞以来亚洲大陆内部构造缩短量；（4）综合现有的数据，从古地磁角度对拉萨地块与羌塘地块聚合过程进行了限定。以上成果限定了班公湖-怒江特提斯洋中生代的演化历史和拉萨地块与羌塘地块的聚合过程，为重建青藏高原古地理格局和探讨青藏高原形成与演化提供了新的依据。