Abstract: Under continuous N-S convergence between the Indian and Eurasian continents, the Sichuan-Yunnan block on the southeastern margin of the Tibetan Plateau has undergone southeastward extrusion and clockwise rotation since late Cenozoic along the right-lateral Red River to the southwest and left-lateral Xianshuihe-Xiaojiang Fault systems to the northeast. However, the surface deformation along the front part of the block in central Yunnan, where the Red River and Xianshuihe-Xiaojiang Fault systems join each other, is characterized by transtension instead of transpression, as indicated by the presence of a series of grabens and horsts along the Xiaojiang Fault system, penetrating the central Yunnan antiform in N-S direction. To explain such contradiction between the field data and theoretical modeling, a mechanic model is constructed in this study, based on the geologic and geomorphic features of the central Yunnan antiform, and the results illustrate that the generation of the E-W extension occurring along the Xiaojiang Fault strands is predominated by stress and strain patterns across the antiform.

Key words: Xiaojiang Fault system, Chuandian block, central Yunnan Plateau, Chuxiong Basin, antiform, synform

摘要： 在印度和欧亚大陆晚新生代SN向陆内汇聚作用下,川滇地块沿鲜水河-小江左行走滑断裂和红河-哀牢山右行走滑断裂发生SE向逃逸和顺时针旋转,这必然造成其南缘的滇中、楚雄等地区地壳发生挤压缩短和隆升。然而,在滇中高原,SN向的小江断裂系发生张扭性运动,沿断裂出现众多的第四纪伸展和拉分盆地,这反映出滇中高原在晚新生代处于近EW向的伸展环境。力学分析与地质现象之间的矛盾暗示有一种尚未被揭示的伸展变形机制。文中根据该地区的地质和地貌特征论证了晚新生代滇中背形构造的存在,揭示出是背形构造的应力分布状态导致了滇中高原上部地壳EW向伸展的发生,从而使得小江断裂发生分裂并伴随伸展构造的发育。

关键词: 小江断裂系, 川滇地块, 滇中高原, 楚雄盆地, 背形构造, 向形构造