青藏高原古-新特提斯洋转换阶段关键块体裂解-汇聚过程的古地磁约束

Largely due to the lack of high-quality paleomagnetic data, the transition phase about the gradually Paleo-Tethys extinction and the Neo-Tethys expansion as well as the details of kinematic process accompanied the open and close of Paleo-Neo Tethys has remained unclear till now. The Qiangtang block and the Lhasa block are considered to be one of the key areas to explore these issues. This project, with the overall scientific goal of “Tethys Earth Dynamic System”, intends to subtly reconstruct the process of rifting-aggregating of main blocks in the Tibtan Plateau (e.g., the Qiangtang and Lhasa blocks) during the late Paleozoic and Mesozoic period. Based on years of tectonic magnetism work we’ve conducted on the major blocks in the Tibet, we will continue to focus on the key points and weakness of the existing paleomagnetic data, complement and improve the critical pole positions of key areas in key time windows. By graphing the Apparent Polar Wander Path (APWP) and modelling, we can not only quantatively describe the process of rifting-drifting-aggregating of these blocks, but also explain the expansion, subduction and extinction of the Paleo-Neo Tethys from the perspective of kinematics. Further, based on geological and geophysical data, we are going to analyze the evolution history of the areas, study their kinship with the ancient continent and discuss the time-space conversion of the Neo-Tethys in the Tibetan Plateau. This work can provide foundational scientific materials for achieving the overall goal of the Tethys Earth Power System Major Research Project and solving the core scientific problem about “universal dynamics of unidirectional aggregation of the Earth's multiple lands”.

目前对古特提斯消亡与新特提斯扩张的时空转换过程及新特提斯洋扩张的细节尚不清楚，青藏高原腹地的羌塘和拉萨等块体被认为是研究该问题的关键地区之一。本申请围绕“特提斯地球动力系统”总体科学目标，拟对羌塘和拉萨等关键块体在晚古生代-中生代的裂解-汇聚过程精细重建。在多年青藏块体构造磁学研究积累的基础上，重点针对现有古地磁数据薄弱点和关键点继续展开工作，补充和完善关键地区、关键时代的关键极位置。通过绘制块体的古地磁视极移曲线和构建数据模型，定量描绘块体裂解-旋转-漂移-聚合的运动轨迹，从运动学角度回答古、新特提斯洋的扩张、俯冲和消亡过程。结合地质和地球物理资料，分析块体的位置变化和演化历史，研究它们与古大陆的亲缘关系，探讨青藏高原古-新特提斯洋时空转换和新特提斯洋扩张历史与过程。该项工作可为实现特提斯地球动力系统重大研究计划总体目标和解决“地球多陆块单向聚合动力学”这一核心科学问题提供定量基础材料。

青藏高原的形成涉及多个特提斯地块的裂解、漂移和碰撞，以及多个大洋(特提斯大洋)的开合。然而，在古特提斯和新特提斯大洋转换过程中，主要地块的裂解和汇聚过程仍然需要澄清。本项目以“特提斯构造域多陆块单向聚合动力学”这一核心科学问题为导向，针对青藏高原主要地块的运动学开展构造磁学研究。我们根据专家组的建议制定了课题研究计划并组织实施。尽管该项目在四年的实施期间遭遇了三年疫情，但我们仍然在北羌塘地块(NQB)、南羌塘地块(SQB)和拉萨地块获得了一批可靠的古地磁资料，为重建这些地块的古地理位置提供了可靠的依据。根据获得的古地磁资料，建立了地块的视极移曲线，模拟了地块在特提斯的运动学轨迹，总结了地块在东特提斯域向北聚集的运动学模式。结合地质证据，进一步讨论了特提斯域演化过程中多个特提斯大洋的开合过程和古-新特提斯洋转换过程。主要认识如下：(1)NQB古生代位于南半球中低纬，可能与印支地块相连，中晚二叠世开始快速北移，晚三叠世与欧亚大陆合并；(2)SQB起源于冈瓦纳-印度的北缘，早二叠世与“Cimmerian”大陆一起从冈瓦那大陆分裂出来，中二叠世向北迁移至南半球22°，然后迅速向北漂移，并于晚三叠世拼贴至欧亚大陆南缘。(3)拉萨地块可能起源于冈瓦纳-澳大利亚大陆北缘，中二叠世之前从冈瓦纳大陆分离出来，中二叠世-晚三叠世位于南半球中低纬地区。结合地质和地球物理证据，我们认为SQB的分裂-漂移-拼合是特提斯域演化的重要事件，导致了古特提斯洋的消亡和新特提斯洋的打开；中晚二叠世NQB的快速北移是“Cimmerian”地块向北运动的结果，NQB于晚三叠世与欧亚大陆汇聚，在青藏高原形成多条古特提斯缝合带。拉萨地块在侏罗纪快速北移，在晚侏罗世-早白垩世拼贴到欧亚大陆，拉萨地块的裂解和拼合形成了青藏高原两条新特提斯缝合带。本项研究为“特提斯构造域多陆块单向聚合动力学”提供了关键约束。