大巴山前陆带东段神农架地区构造变形研究

TECTONIC DEFORMATION FEATURES OF SHENNONGJIA REGION IN EASTERN DABASHAN FORELAND STRUCTURAL BELT

神农架地区位于大巴山前陆弧形构造带东段,以阳日断裂为界,可分为北带基底拆离带和南带神农架隆起,北带以E-W走向的基底拆离和盖层滑脱为特征,古生界盖层褶皱紧闭;南带神农架隆起周缘的盖层变形特征各异,北缘变形较弱,东缘变形很强,其西、南周缘发育特征的裙边状褶皱构造,南缘裙边褶皱以枢纽大角度倾伏为典型特征。古构造应力场反演结果显示,该区主要受控于近S-N向主压应力作用;受到神农架、黄陵两个隆起相向对挤作用,神农架隆起东缘主压应力方向为NW-SE向,两个不同方向的应力场可能均与早燕山期大巴山强烈的陆内造山作用有关。综合分析和对比结果显示,大巴山前陆构造带东段的构造演化历史经历了印支雏形期和早燕山定型期两个构造演化阶段,神农架基底隆起对大巴山前陆弧型构造带的形成起到了限制作用,神农架地区的构造变形研究对于探讨大巴山前陆弧形带的形成和演化具有重要的指导意义。

Shennongjia is located in the eastern part of Dabashan foreland are-shaped structural belt. With the Yangri fault as a boundary, this region can be divided into the northern and southern parts. The northern part is characterized by W - E trending basement-involved detachment and cover folding, with the Palaeozoic cover closely folded. The southern part, named Shennongjia basement uplift, has different deformation features in the periphery, with deformation weak in northern margin but strong in the eastern one. As to this uplift, there are skirt-like fold structures in its western and southern margins, and the southem ones were characterized by fold hinge with large plunge angle. From the field analysis of fault kinematics and paleo-tectonic stress inversion from slip vectors, we can see that the region was mainly controlled by S - N compression stress field, but the stress field of the eastern margin was changed into NW - SE because of the compression from Shennongjia and Huangling uplift. Regional structural analysis and comparison showed that the eastern part of Dabashan foreland structural belt experienced Indosian primary formation stage and Yanshan final formation stage, and the Shennongjia basement uplift played a role of restriction in the formation of Dabashan foreland are-shaped structural belt. The research on the deformation of Shennongjia has great significance to understanding the formation and evolution of the Dabashan foreland arc-shaped structural belt.