天山山脉地貌特征、地壳组成与地质演化

Geomorphological features, crustal composition and geological evolution of the Tianshan Mountains

天山位于亚洲中部,东西向延伸,由中亚诸国向南西凸出的弧形山系与其间的大型盆地,中国境内北西、北东走向的山系与其间长轴近东西走向的盆地和蒙古西南部的低山戈壁等组成,东西延长近4000km,南北宽逾150km。天山山脉与两侧的盆地多以逆冲断层为界,盆地的基底下插于天山山脉之下。天山山脉及毗邻地区的地壳主要由前震旦纪古陆碎块、古生代陆缘岩系和洋岩石圈残片等组成。从构造方面看,该山脉及毗邻地区的地壳可以划分为15个单元。大致以东经90°线为界,以西地区南侧的南天山碰撞带为向南凸出的弧形构造带,北侧的古陆碎块和其间的碰撞带呈北西走向斜列展布,构成巨型帚状构造;以东地区为相间排列的近东西走向的古活动陆缘或岛弧及其间的碰撞带。天山山脉形成于古生代晚期古洋盆关闭以后,现今山脉的地貌特征则是新生代晚期地壳变动的产物。天山山脉形成以后的地质演化可以划分为石炭纪末至二叠纪初同碰撞—后碰撞构造岩浆活动阶段、二叠纪早—中期幔源岩浆活动与壳幔相互作用阶段和二叠纪晚期以来的陆内演化阶段。

Located in Central Asia and extending in an E-W direction, the Tianshan Mountains are composed of arcuate mountain systems convex southwestward and large basins between them in Central Asian countries, NW- and NE-trending mountain systems and basins with nearly E-W-strike long axes between them in China and low mountains and gobies in southwestern Mongolia. The mountains are nearly 4000 km long from east to west and 〉150 km wide from north to south. They are mostly separated from the basins on either side by thrusts and the basement of the basins is underthrust beneath the Tianshan Mountains. The crust consists predominantly of fragments of pre-Sinian continents, Paleozoic continental-margin rock series and oceanic lithospheric slices. The crust of the mountains and adjacent areas may be divided into 15 tectonic units. Roughly with the longitude 90° E as the boundary, in the region west of the boundary the South Tianshan collision zone in the south is an arcuate tectonic zone convex southward and the cratonic fragments and the collision zone between them in the north are an echelon in a NW direction, forming a huge brush structure; in the region east of the boundary there occur the nearly E-W-trending active paleo-continental margins or island arcs and collision zones between them which are arranged alternately. The Tianshan Mountains formed after the closing of the Late Paleozoic oceanic basin and the geomorphological features of the present mountains are the production of Late Cenozoic crustal movement. The geological evolution after the formarion of the Tianshan Mountains may fall into the stage of terminal Carboniferous-initial Permian syncollisional-postcollisional tectonomagmatism, stage of Early-Mid Permian mantle-derived magmatism and crust-mantle interaction and stage of intracontinental since the Late Permian.