川东——武陵山地区的深部结构与陆内变形机制初探

Preliminary study on the deep structure and intra-continental deformation in the eastern Sichuan and Wuling mountains region

川东—武陵山地区位于华南大陆西部,远离板块边缘,区内发育有典型的侏罗山式褶皱系,且变形后未经历强烈的岩石圈伸展和岩浆作用改造,是研究陆内挤压变形过程与机制的理想场所.本文总结了针对川东—武陵山地区的构造地质和地球物理探测研究进展,梳理了该区褶皱-断裂系统的形成时间、演化过程、可能的壳内变形机制与深-浅构造耦合关系,指出了目前存在的问题并展望了下一步研究的方向.在形成和演化史方面,川东—武陵山地区的褶皱-逆冲作用主要发生于晚侏罗-早白垩世,并在新生代晚期发生了断裂系走滑方向的反转,对前期构造起到强烈改造作用,形成了现今逆冲兼走滑的断裂系统.在深部结构与控制要素方面,该区壳内变形主要受控于扬子块体和江南造山带之间的陆内汇聚作用,这种陆内汇聚作用不仅导致中上地壳朝北西的逆冲推覆作用,也促使扬子块体的Moho界面发生错断并向南东方向下插.然而,由于对该区中、北部和面积性的地球物理探测目前尚缺乏,难以从区域性视角研究该区的深部结构与构造过程,对壳内滑脱层是否普遍存在、研究区的差异化构造变形和演化机制等难以提供直接约束,深部结构研究尚有待进一步加强.

The eastern Sichuan-Wuling Mountains area is located in the western part of the South China continent,far away from the plate boundary,and a typical Jurassic mountain fold system developed in this area.This region is an ideal place for studying the intra-continental deformation process and mechanism,because it has not undergone strong lithospheric extension and magmatic transformation after the intra-continental compression deformation.In this study,we summarize the recent research progress of structural geology and geophysical exploration in this area,propose the possible intra-crustal deformation mechanism and the deep-shallow structure coupling relationship,and further point out the deficiencies existed at present and prospects for the future research direction.The fold-thrust in the eastern Sichuan-Wuling Mountains area mainly formed in the Late Jurassic-Early Cretaceous.In the late Cenozoic,the strike-slip direction of the fault system was reversed and changed the early structure,resulting in the current thrust and strike-slip fault system.We preliminarily propose that the intra-crustal deformation in this area is mainly controlled by the intra-continental convergence between the Yangtze block and the Jiangnan orogen.This intra-continental convergence leads not only to the northwest thrusting of the middle and upper crust,but also to the breakoff of the Moho discontinuity of the Yangtze block and its southeast underthrusting.However,due to the lack of geophysical exploration in the central,northern part and regional areas of this region,it is difficult to study the deep structure and tectonic process of it from a regional perspective.Further research on deep structures of this region needs to be strengthened,so as to solve the remained scientific questions,including the spread of the detachment zone,the differential structure,deformation style and evolution process,and so on.