昌宁-孟连地区火山岩系基本特征及构造环境的认识

BASIC FEATURES OF VOLCANIC ROCK SERIES IN CHANGNING MENGLIAN REGION AND THEIR STRUCTURAL ENVIRONMENT

昌宁-孟连地区是我国研究古特提斯演化的重点地区之一，该区不同时代火山岩的性质为大地构造演化提供了重要依据。（1）变质火山岩，由玄武岩-玄武安山岩及偏碱性玄武岩所组成，时代可能为晚一中元古代，具有大洋中脊型玄武岩特征；（2）下石炭统火山岩，由橄榄玄武岩-碱性橄榄玄武岩组成，具裂谷洋盆玄武岩特征；．（3）上二叠统火山岩，为一套高镁质偏碱性的基性一超基性火山岩，具快速张裂之裂谷洋盆玄武岩特征；（4）上二叠统-三叠系火山岩，为一套碱性中基性火山岩，以爆发相为主，其喷发环境显示由浅水相向陆相的转化，具弧后裂谷火山岩特征。上列各期火山岩展示，昌宁-孟连地区大地构造发展是从残留洋盆经历过两度“打开-闭合”的过程。晚古生代（石炭纪-二叠纪）该区从被动大陆边缘裂陷逐渐发展为局部具有新生洋壳性质之裂谷系环境。

1. The metamorphic volcanic rocks consist of basalt-basaltic andesite and meta alkalic basalt with the feature of mid-ocean ridge basalt, whose age probably is Late-Middle Proterozoic;2. The Lower Carboniferous volcanic rocks are formed by olivine baalt-alkalic olivine basalt characterized by those of rift ocean basin;3. The Upper Permian volcanic rocks are a series of high Mg meta-alkalic basic-ultrabasic ones with the features of basalt in the rift ocean basin of rapid opening;4.The Upper Fermian-Triassic volcanic rocksare a suite of alkalic interme-diate basic ones, mainly in explosive facies, in the transional environment from shallow water to land. And they are characterized by the volcanic rock of badkarc rift. The volcanic rocks mentioned above show the geotectonic development of ChangningMenglian region experienced 2 'opening-closing' processes of the relict ocean basin. In late Palaezoic (Carboniferous-Permian), this region gradually became a rift system l0cally with the nature of newly emerging ocean crust from a fault depression of passive continental margin.