ABSTRACT

The exhumation history of the Central Tibetan Mountain Range (CTMR) in the Qiangtang terrane is important for establishing the boundary conditions prior to the India-Asia collision. Previous studies suggest that the CTMR is a significant provenance for Jurassic sediments in the Qiangtang terrane. The Middle Jurassic sediments north of the CTMR provide crucial information to constrain the timing of exhumation in the source area. Here we present detailed stratigraphic sections and detrital zircon U-Pb geochronology in the northern Qiangtang basin. Sedimentary facies analyses indicate that the Early-Middle Jurassic Quemoco Formation is mainly deposited in the deltaic system and carbonate-platform environment. Upsection, the Middle Jurassic Xiali Formation was deposited in a prodelta environment. Combined analyses of palaeocurrent indicators, conglomerate clast composition and U-Pb age spectra suggest that the CTMR is the main provenance for the Quemoco and Xialai formations; while the Triassic southern Qiangtang strata and Jinsha suture are the secondary source areas. The changes in the specific position of detrital zircon U-Pb age peaks around 500 Ma indicate evolving source terranes. Detrital zircon U-Pb geochronological data from the base of the Quemoco Formation and top of the Xiali Formation constrain the conservative maximum depositional ages to be 174.8 ± 1.0 and 161.7 ± 2.3 Ma, respectively. Combined with previous geochronology data, structural geology, and provenance studies across the Qiangtang terrane, the CTMR experienced rapid exhumation during Middle Jurassic and Late Cretaceous and slow exhumation since Eocene. The Jurassic uplift and exhumation of the CTMR were accompanied by the uplift of the southern Qiangtang terrane. The deformation and exhumation history is in favour of the hypothesis that plateau growth in the south-central Qiangtang terrane initiated during the Mesozoic, which is an important initial condition to quantify Cenozoic growth of the Tibetan Plateau.

摘要

羌塘地体中藏中山脉（CTMR）的折返历史对于确定印亚碰撞前的边界条件具有重要意义。以往的研究表明，CTMR是羌塘地体侏罗系沉积物的重要物源。CTMR 以北的中侏罗统沉积物提供了重要信息，以限制源区挖掘的时间。在这里，我们展示了羌塘盆地北部的详细地层剖面和碎屑锆石 U-Pb 年代学。沉积相分析表明早-中侏罗世克莫科组主要沉积于三角洲体系和碳酸盐岩台地环境。上段，中侏罗统夏利组沉积于前三角洲环境。古流指标综合分析，砾岩碎屑组成和 U-Pb 年龄谱表明 CTMR 是 Quemoco 组和夏来组的主要物源；三叠系南羌塘地层和金沙缝合带为次生源区。500 Ma 附近碎屑锆石 U-Pb 年龄峰具体位置的变化表明源地体的演化。Quemoco组底部和夏利组顶部碎屑锆石U-Pb年代学数据将保守的最大沉积年龄分别约束为174.8±1.0和161.7±2.3 Ma。结合之前羌塘地体的年代学数据、构造地质学和物源研究，CTMR在中侏罗世和晚白垩世经历了快速折返和始新世以来缓慢折返。CTMR侏罗系的隆升和剥露伴随着羌塘地体南部的隆升。变形和折返历史支持羌塘地体中南部的高原生长始于中生代的假设，这是量化青藏高原新生代生长的重要初始条件。