用现代地层学方法判别冈瓦纳大陆的北界

Recognition of the northern boundary of Gondwanaland using modern stratigraphic techniques

在深入研究 1∶10 0万“改则幅”和“日土幅”区调中大量原始资料和青藏高原生物地理区系与地壳演化的基础上 ,用现代地层学方法 ,重点研究羌塘地块和唐古拉地块的属性及冈瓦纳大陆的北界。笔者首先排除了推覆构造对建立古大陆边缘造山带原地岩系地层层序的严重干扰 ,对羌塘地块和唐古拉地块的地层层序进行了重建 ,提出了羌塘地块古大陆边缘现代地层学格架的演化模式。羌塘地块古大陆边缘有两个不同属性而又相互关联的地层体 ,现今呈一西一东的分布格局 ,向洋 (古特提斯洋 )一侧为以深水砂泥复理石和放射虫硅质岩为主的沉积组合类型 ,向陆一侧为以浅水碎屑、碳酸盐为主的沉积组合类型。从而证实了古特提斯洋存在一个向羌塘地块古大陆边缘倾斜的俯冲消减带。它导致羌塘地块古大陆边缘活化造山运动 ,并于中二叠世末期与唐古拉地块碰撞 ,形成晚海西褶皱带。探讨了不同时期不同地块骨骼同位素的演变特征及其成因解释。论述了羌塘地块生物地理区系的发生、发展、消亡与羌塘地块同冈瓦纳大陆分裂、向北漂移 (导致新特提斯洋形成 )及同唐古拉地块碰撞 (导致古特提斯洋消亡 )的板块活动关系。

The present paper addresses the research on the attributes of the Qiangtang and Tanggula blocks and on the recognition of the northern boundary of Gondwanaland which focuses on the reestablishment of the stratigraphic framework along the margins of the Qiangtang block, referenced to the data from the 1∶1000000 Gerze and Rutog Sheets and biogeographic provinces and crustal evolution of the Qinghai Xizang Plateau. There are two stratigraphic bodies which are different in character but correlated in origin, and aligned in the eastern and western margins of the Qiangtang block: deep water dominated sandy and muddy flysch and radiolarian silicalite dominated sedimentary associations on the oceanward side, and shallow water siliclastic and carbonate dominated sedimentary associations on the landward side, implying that a northward dipping subduction zone once occurred in the Palaeo Tethys and once collided with the Tanggula block during the latest Permian, resulting in the formation of the late Hercynian fold belt. In addition, this paper also deals, in detail, with isotopic evolution and genesis of the skeletal fragments from various blocks of different ages, and the relationship between the initiation, development and termination of the biogeographic provinces in the Qiangtang block and rifting apart from Gondwanaland and northward drift (which led to the formation of the Neo Tethys) and the collision of this block with the Tanggula block (which led to the termination of the Palaeo Tethys).