柴达木路乐河地区新生代碎屑组分变化及其对构造隆升的指示

Compositional variation of Cenozoic detritus in the Lulehe area, Qaidam Basin, and its implications for Tibetan Plateau tectonic uplift

碎屑组分变化是反映盆地物源演化历程的重要物质表现。路乐河地区作为柴达木盆地的重要组成部分,沉积地层记载着印度-欧亚板块碰撞以来青藏高原北缘造山带的构造隆升过程。高长石组分含量、物源方向及毗邻山脉岩性对比揭示,路乐河物源主要受南祁连和赛什腾山控制,其碎屑组分变化对毗邻造山带构造活动具有很好的耦合性。新生代53.5~2.9Ma期间,路乐河地区存在3次物源转换事件,发生时间依次同印度-欧亚板块碰撞及高原内部构造隆升事件相吻合。其中早期50.1~46.6Ma,南祁连山的快速抬升是对大陆初始碰撞的远程响应;44.5Ma,高原以垂向增生和推覆构造发育为特点,赛北断裂高速剥露,致使路乐河地区物源发生转变;渐新世末期(22.6Ma),青藏高原准同时整体隆升,赛什腾山和南祁连山协同为路乐河地区供给沉积物。所获认识为深入了解高原隆升演化和板块碰撞远程效应提供新的沉积依据。

The change of detrital composition is a typical manifestation of the evolutionary process of sedimentary sources. As an important part of the Qaidam Basin, the sedimentary strata in Lulehe have recorded tectonic uplift evolution of northern Tibetan since the Indo-Asian collision. All signatures, along with high feldspar content, provenance and contrast with adjacent mountain rocks, reveal that the source region for Lulehe mainly came from Qilian and Saibei thrust. And there existed a coupling relationship between the change of clastic composition content and surrounding orogen. Three significant depositing transformation events occurred in Lulehe area, corresponding to the Indo-Asian collision and plateau tectonic uplift from Cenozoic in 53.5~2.9Ma. The rapid uplift of southern Qilian, which happened at ca. 50.1~46.6Ma, responded to the propagation of initial continental collision. The uplift of Tibetan Plateau with crustal vertical growth and thrust structure caused top erosion of Saibei thrust and provenance transformation event in Lulehe in Eocene(44.5Ma). Both of Saishiteng and Qilian Mountain supplied sediments at the end of Oligocene(22.6Ma)when different regions in plateau were raised synchronously. The findings will provide new crucial sedimentary data for deep understanding of evolutionary history of whole Tibetan Plateau and distant effect of the continental collision.