哀牢山中段地质构造特征

TECTONIC CHARACTERISTICS OF THE MIDDLE SECTION OF THE AILAO MOUNTAINS

通过１：５万区调工作发现，在哀牢山存在一个规模巨大的“顺层”构造滑脱带，并以该滑脱带为界将哀牢山群变质岩系分割为上、下二部分，两者在变质作用、构造变形、原岩建造及岩浆活动等方面，均具有明显的不同特点。本区曾经受过复杂的伸、缩、旋、剪和升降等构造作用的叠加与改造，按其构造变形序次和复合关系大体有三期：早期（三叠纪之前）为大陆伸展作用条件下的“变质核杂岩”形成阶段；中期（与三叠纪时期古特提斯的关闭有关）又经历了大陆碰撞作用下的逆冲推覆构造阶段；后期（燕山末─喜马拉雅期）又发生平移剪切和山脉强烈隆升，并在红河断裂带东侧伴生有正断层的下降作用。

Through 1: 50000-scale regional surveys,a gigantic tectonic detachment zone has been found in the Ailaoshan Group,and with the detachment zone as the boundary the metamorphic series of the Ailaoshan Group may be divided into the upper and lower parts. Both parts show notably different features in respect to metamorphism,tectonic deformation,protolith formationand magmatism. This area has undergone superimposition and reworking of different complextectonic processes such as extension,compression,torsion,shear and uplift and subsidence.According to the tectonic deformation stages and compounding relationships,three phases of tectonism may be distinguished:(1)the early phase (prior to the Triassic)was a stage of formationof the 'metamorphic core complex'under the conditions of continental extension;(2)the middlephase(related to the Triassic Paleo-Tethys closure)witnessed overthrusting under the conditions of continental collision;(3)the late phase(terminal Yanshanian-Himalayan)again sawstrike-slip shear and strong uplift,accompanied by subsidence due to mormal-faulting on theeastern side of the Honghe River fault zone.