青藏高原东南缘地块新生代侧向逃逸运动及其对地壳构造变形的控制作用

In the southeast edge of Tibetan Plateau, crustal blocks experienced intense lateral extrusion movement because of continuous northward extruding of Indian Plate in to the Eurasia in the Cenozoic. The discrepant lateral extrusion movement and different extrusion rate of adjacent blocks would induce intense crustal tectonic deformation in the southeast edge of Tibetan Plateau. However, because of lacking sufficient understanding about the Cenozoic motion feature of crustal material and the evolution of boundary strike-slip faults in the southeast edge of Tibetan Plateau, it is impossible to reasonably discuss the Cenozoic lateral extrusion process of crustal blocks which constitute the southeast edge of Tibetan Plateau. In this item, paleomagnetism, rock magnetic fabric and isotope chronology studies will be applied in the Cretaceous, Paleogene and Pliocene sedimentary rock and volcanic rock in the Chuandian Block and Baoshan Block, combining with previously published paleomagnetic data of the Simao Terrane and Tengchong Block, we try to comprehensively discuss the process of Cenozoic lateral extrusion movement of blocks and difference between extrusion rate of adjacent blocks in the southeast edge of Tibetan Plateau, and reveal the evolution of Cenozoic crustal boundary strike-slip faults and the dynamic mechanics of international curstal tectonic deformation in the southeast edge of Tibetan Plateau. Furthermore, the results will provide better constraints on quantitatively evaluating the function of crustal block lateral extrusion movement in the huge latitudinal crustal shortening in the south edge of Eurasia in the Cenozoic.

青藏高原东南缘地块新生代受印亚板块间近南北向挤压作用发生了强烈的东南侧向挤出逃逸运动。不同地块间侧向挤出方式和速率的差异造成了青藏高原东南缘强烈的新生代地壳构造变形。但是目前对于青藏高原东南缘新生代地块运动特征及主要边界走滑断裂带构造演化的研究程度还较低，极大限制了对地块侧向逃逸方式、逃逸距离以及其在青藏高原东南缘地壳构造变形中所起重要作用的认识。本项目拟对川滇地块和保山地块白垩纪、古近纪和上新世地层开展古地磁和岩石磁组构研究，结合主要地块边界断裂活动演化的同位素年代研究，综合分析青藏高原东南缘地块新生代东南侧向挤出逃逸过程及相邻地块侧向逃逸速率的差异，揭示新生代不同地质时期相邻地块间的相互作用方式，探讨青藏高原东南缘边界走滑断裂带新生代活动演化历史，以及地块内部地壳构造变形的动力背景，并定量评价地块侧向挤出逃逸在新生代欧亚大陆南缘巨大南北向地壳缩短中起到的作用和贡献。

通过对青藏高原东部及东南缘晚白垩世和新生代沉积地层的构造磁学研究，定量恢复了晚白垩世时期拉萨地块的古形态，约束了青藏高原东南缘各地块体侧向挤出逃逸的差异性，并深入探讨了青藏高原东南缘新生代地壳构造变形对地块边界走滑断裂系构造演化的控制作用。主要取得了以下4项研究成果：（1）提出同构造沉积现象是导致拉萨地块白垩纪古地磁数据存在显著差异的主要因素之一，并建立了沉积地层古地磁数据的同构造沉积矫正法。通过对印度-欧亚大陆初始碰撞之前拉萨地块的古形态的恢复，提出印度板块与欧亚大陆发生了斜向平行碰撞，碰撞过程和新特提斯洋的闭合过程不存在穿时性；（2）青藏高原东南缘地壳顺时针旋转变形启动时间为~25.7 ± 2.5 Ma，标志着印度板块和西缅甸地块北向揳入欧亚大陆，形成东喜马拉雅构造节的初始时间。这一时间显著滞后于崇山及高黎贡韧性剪切带等地体边界构造带的初始活动年代(~33–32 Ma)，表明了二者动力机制的差异；（3）腾冲地体、保山地体、兰坪-思茅地体新生代侧向旋转挤出逃逸运动学特征存在显著的差异性，表明青藏高原东南缘新生代地壳运动及其动力机制并不能简单的通过“刚性块体沿走滑断裂带的侧向挤出逃逸模型”及“下地壳粘性通道流模型”来描述；（4）青藏高原东南缘多个镶嵌地块间的差异性南向挤出逃逸控制了地块边界构造带活动和构造演化。