中生代之前柴达木的演化研究

摘要

现今柴达木盆地的形成,中生代以来的构造运动起到了关键性作用,但是柴达木地块在中生代以前的演化也具有重要的意义.基于前人的研究,系统论述了柴达木在中生代以前的发展演化.柴达木盆地存在一个统一的前震旦系克拉通基底,基底存在双重结构,包括元古宙结晶基底和古生代褶皱基底.柴盆周边古老山体出露有下元古界区域热变质作用形成的达肯大坂群和金水口群,以及中上元古界的小庙群、冰沟群和丘吉东沟群.柴盆基底多登—小柴旦一线可能存在一个东西向的"中央断裂带",断裂带西北部的基底塑型强、埋深大,新生界地层发育;而东南部基底具刚性,埋深较浅,第三系不发育,地表主要为第四系盖层.自显生宙以来柴达木的演化,是与新元古代联合古陆的裂解,再到二叠纪中期北半球劳亚古陆形成的大地构造演化背景一致的;寒武纪时,柴达木地块还处于南半球低纬度,后逐渐向北漂移,至二叠纪时已位于北纬12.7°.关于柴达木盆地的形成,特别是中生代后逐渐演化为现今盆—山模式,主要是受到周边断裂带的控制,即柴北缘断裂带、东昆仑断裂带和阿尔金断裂带.因此,柴达木地块的演化,是在与周边地块不断适应、调整过程中实现的.%Qaidam Basin is an intramontane basin.Tectonic movement since the Mesozoic has been critical for the formation of the Qaidam Basin.However, evolution of the Qaidam Basin landmass before the Mesozoic is also very important.Based on preceding research by other scholars, this paper systematically discusses the evolution of the Qaidam landmass before the Mesozoic.Qaidam Basin has a unitized pre-Sinian craton basement with a dual structure which includes Protozoic eon crystalline substrate and Paleozoic folding substrate.In the old mountain arounding the Qaidam Basin, it disclosed the Dakendaban Rock Group and the Jinshuikou Rock Group of the lower Protozoic, which were formed by thermal metamorphism, and Xiaomiao, Binggou and Qiujigou Rock Groups of the middle and upper Protozoic.In the basement of the Qaidam Basin, there possibly existed a west-east oriented "Central Fault System" along the Duodeng-Xiaochaidan line.The substrate of the northwestern part overlay by the Cenozoic strata is plastic, well-developed and deep, while the substrate of the southeastern part is rigid, shallow and formed mostly Quaternary strata at the surface.During the Cambrian, the Qaidam landmass was still located in the lower latitude of the southern hemisphere, then gradually moved northward, and reached 12.7°N in Permian.The formation and evolution of the Qaidam Basin since the Mesozoic, especially the current Basin-and-Range pattern, is mainly controlled by the fault systems around the Qaidam Basin.These consist of the northern Qaidam fault system, the eastern Kunlun fault system and the Altyn Tagh fault system.The evolution of the Qaidam landmass is accompanied by molding, and adjusting to other landmass around it.