西藏东部早-中三叠世火山-沉积盆地地质特征

Geological Characteristics of the Early-Middle Triassic Volcano-Sedimentary Basin in the Eastern Tibet

西藏东部存在四条NW-SE向大致平行分布的早-中三叠世地层条带,自东向西分别为普水桥组、瓦拉寺组条带,马拉松多组-加指拉组条带,夏牙村组条带和竹卡群条带。我们通过地层岩性及其自WN向ES均有火山岩减少和沉积岩增多趋势、区域构造特征、盆地延入云南西部中三叠世地层沉积具趋同性等特征,认为藏东四个条带的早-中三叠世地层,在沉积时为统一火山-沉积盆地。早-中三叠世期间,该火山-沉积盆地沉积作用自东向西不断推进,中三叠世盆地范围最大、海水最深,在江达-芒康-线出现半深水-深水复理石沉积。火山活动贯穿盆地发展全过程,其中WN部和WS部火山活动最强烈,火山活动主要为中酸性火山岩及火山碎屑岩,随着中三叠世强烈地火山喷发,于中三叠世拉丁中期结束盆地发展历史。盆地形成和演化过程中,海水从东部侵入。

There are four northwest-southeast extending Early-Middle Triassic strata belts in eastern Tibet, the Pushuiqiao-Walasi Formations belt, Malasongduo-Jiazhila Formations belt, Xiayacun Formation belt and Zhuka Group belt, which are exposed westwards roughly in parallel. Based on the analysis of the lithologic-sedimentary characters and their spatial variation, the similar tendency of sedimentary strata-increasing and volcanic beds-decreasing from northwest to southeast, and of the regional tectonic features, we extract a conclusion that these four isolated Early-Middle Triassic strata belts formed in a uniform volcano-sedimentary basin, whose transgression and related sedimentation advanced from east to west. The basin reached its largest size with deepest water in Middle Triassic time, when there occurred bathyal flysch along Jiangda-Mangkang line. The volcanism accompanied the whole evolution process of the basin with the intensivest volcanic activity in the northwest and southwest areas.