被肢解的“西域克拉通”

Broken “Western China Craton”.

塔里木、柴达木、阿拉善地块古生代期间并非被多岛 -小洋盆分隔的微陆块 ,而是具有统一发展共性的克拉通——西域板块 ,它具有新元古代早期克拉通化形成的基底和震旦系冰碛岩以及亲扬子型下古生界的盖层 ,震旦纪 -早古生代期间它和扬子 -华南、澳大利亚板块同属于东冈瓦纳超级大陆的一部分。它和扬子 -华南板块类似 ,具有非稳定克拉通的多裂解特征 ,北祁连 -满加尔坳陷就是它寒武纪 -中奥陶世最大的坳拉槽 ,此后晚奥陶世、晚泥盆世和早二叠世末又在多处出现裂陷槽 ,而其他部位在整个古生代期间则为稳定的克拉通 ,程度不同地发育了克拉通盆地沉积 ,这对该区古生界的含油气评价极为重要。古特提斯洋的封闭完成了西域板块的构造就位 ,使它成为古亚洲大陆的西南隅 ,羌塘、拉萨板块的拼贴引起它印支、燕山期的板内变形 ,而对西域板块最大的肢解作用发生在喜马拉雅期 ,印度与亚洲大陆板块的碰撞所引起的走滑、推覆构造使它发生了大位移的错位 。

Similarities are shown to exist among the Tarim, Qaidam and Alashan blocks including their cratonized Neoproterozoic basement, the Sinian drift sheet and Yangtze type lower Paleozoic cover. It is therefore proposed that they are derived from a unique Craton — the “Western China Craton” of identical evolution, but not micro continental blocks of Mesozoic age separated by oceans with small islands. The Craton is, during Sinian through early Paleozoic and together with the south China sub plate and Australian sub plate, part of the eastern Gondwana supercontinent, and has, similar to the Yangtze South China Craton, characteristics of complicatedly broken unstable Craton. The North Qilian Manji'er depression is the largest Aulacogen formed during Cambrian through mid Ordovician. Aulacogens were also formed along different zones during late Ordovician, late Devonian and early Permian, respectively, while the main part remained stable craton with different degrees of sedimentation in cratonic basins during Paleozoic, providing important clues to the oil gas exploration in the Paleozoic in the area. The Western China Craton is tectonically localized at the southwest of the Paleao Asian continent due to the closing of the Tethys. The juxtaposition of the Qiangtang and Lahsa plates onto the Asian plate resulted in Indosinian Yanshanian intraplate deformation. The most important broken event in the Western China Craton occurred during the Himalayan stage with large scale displacements by strike slip and thrusting owing to the collision between the Indian plate and the Asian plate. Then the present tectonic framework was formed.