藏北那曲地区中三叠世地层的新发现及其地质意义

Discovery of Middle Triassic strata in the Nagqu area, northern Tibet, China, and its geological implications

在1∶25万那曲县幅区域地质调查过程中,根据岩石组合、化石鉴定结果及其中火山岩的特征,从中晚侏罗世拉贡塘组中分离出一套新地层,命名为嘎加组。嘎加组是由硅质岩、砂屑灰岩、砾屑灰岩、碳酸盐岩和火山岩组成的一套浅水相沉积物。从硅质岩中采获的放射虫有拉丁期的Tritorissp.,Triassocampesp.,Pseudostylosphaerasp.,Muelleritortissp.,Annulotriassocampesp.等。岩石组合、沉积序列和火山岩形成环境判别指示该套地层为岛弧型建造,初步判断该套地质体的形成与特提斯洋早期消减、消亡过程有关。

During the 1：250000 regional geological survey of the Nagqu Sheet, a new sequence of strata is separated from the Mid-Late Jurassic Lagongtang Formation according to the rock association, fossil identification and characteristics of volcanic rocks. This new sequence of strata is named the Gajia Formation. This formation is a sequence of neritic deposits composed of siliceous rocks, calcarenite, calcirudite, carbonate rocks and volcanic rocks. The radiolarians collected from the siliceous rocks are Ladinian Tritoris sp., Triassocampe sp., Pseudostylo sphaera sp., Muelleritortis sp. and Annulotriassocampe sp. The rock association, sedimentary sequences and volcanic rocks indicate that this sequence of strata formed in an island-arc environment and it is preliminarily judged that formation of this sequence is related to the process of early-stage consumpuon and extinction of the Tethys Ocean.