西藏南部拉孜-江孜一带的白垩系

白垩纪,在西藏南部地质历史上,是一个重要的阶段,发生了剧烈的火山喷发、岩浆侵入以及褶皱运动。沿雅鲁藏布江一线,以大规模的超基性岩带为标志,又是一条重要的地质界线,被称为“断块缝合线”或“板块缝合线”,近年来受到广泛的重视。在超基性岩带两侧,拉孜-江孜一带,最广泛发育的是白垩纪地层,厚度巨大,岩相极其复杂,而且含有可采煤层。因此,对这一带白垩系的研究,具有重要的经济价值和理论意义。

THE CRETACEOUS OF LAZE-JIANGZE DISTRICT, SOUTHERN XIZANG

The Cretaceous being widely spread in Laze-Jiangze district, southern Xizang, may be subdivided into three sedimentary zones:1. North of the ultrabasic belt occurs the well-known Rikaze Group of Late Cretaceous, which is composed of conglomerate and coal-bearing detrital deposits in the basal part, red sandstone and conglomerate in the lower part, limestone in the middle and flysch in the upper, respectively named the Qiuwu Formation, Qiabulin Formation, Sangzugang Formation and Angren Formation.2. To the south of this belt the Qiabulin Formation is overlain, by volcanic and siliceous deposits called Laze Group.3. East of Jiangze the Cretaceous overlying conformably the Jurassic is mainly composed of siliceous and calcareous shale in the lower part (Jiabula Formation), and siliceous flysh-like deposits with exotic blocks in the upper (Zongzhuo Formation). They are roughly assigned respectively to the early and late Cretaceous in age.These three zones may be correlated with those in the northern part of the western Himalaya.Finally, this paper discusses the pre-Cenomanian folding phase and the paleogeogra-phical outline.