可可西里盆地新生代沉积演化历史重建

Reconstruction of Depositional History of the Cenozoic Hoh Xil Basin

青藏高原北部可可西里盆地是高原腹地最大的第三纪沉积盆地,分布着厚度达5737.5m的新生代沉积。本文根据遍布整个盆地的野外实测剖面和地质观察点资料,采用典型剖面精确古地磁测年为基础的时间框架,开展沉积层序、岩性特征、沉积环境和古水流变化综合对比研究,将可可西里盆地新生代(约56Ma至约16Ma)划分为7个演化阶段,其中在30Ma至约23Ma期间盆地经历抬升变形,没有沉积作用发生。结果显示,前6个阶段(约56Ma至30Ma),盆地沉积中心逐渐向北、向东迁移,盆地南缘和西缘的构造逆冲作用逐步加强,而且在晚渐新世发生强烈南北向地壳缩短,反映青藏高原腹地早期隆升过程是依靠南北向地壳缩短和北东向逆冲扩展作用来实现的。在早中新世(约23Ma至约16Ma),盆地沉积物遭受低度变形,表明此期间高原以差异隆升为主。

The Hoh Xil basin with Cenozoic sediments as thick as 5737. 5 m is the largest Cenozoic sedimentary basin in the hinterland of the Qinghai-Tibet Plateau. This paper presents the reconstruction of a seven-stage deposi-tional history of the Cenozoic Hoh Xil basin from 56 to 16 Ma, except a sedimentary hiatus between 30 and 23 Ma, when there was no occurrence of sedimentation because the basin was uplifted and deformed. The study is based on comprehensive correlation of sedimentary sequences, lithologic characteristics, depositional environments and palaeocurrent directions, which were derived from many field measured sections and geologic sites distributed in the entire basin. A palaeomagnetostratigraphic dating of the typical sections provides a geologic time outline with lithologic columns. The results show that the depocentre of the Hoh Xil basin migrated northward and eastward during the first six stages (56-30 Ma). The migration could beproduced by intensified tectonic thrusting on the south and west margins of the Hoh Xil basin. In addition, a strong north-southward shortening happened during the late Oligocene. The authors thus deduce that the early uplifting processes of the Qinghai - Tibet Plateau hinterland could be produced by the north-southward shortening and northeastward thrusting growth. During the early Miocene of 23 -16 Ma, only a low-grade deformation happened in the Hoh Xil basin sediments. This could indicate that the uplift of the plateau hinterland was based on the differential u-plift.