Title : Detrital Zircon U-Pb Dating and Geochemistry of the Paleogene-Neogene sediments in the Qaidam Basin (China): Implications for Provenance and Tectonics
Abstract:
Different sediment routing systems merge in the Qaidam Basin, providing an example of the interaction of several source areas with distinct petrographic signatures, recording several stages of exhumation of the surrounding orogenic belts. However, despite decades of studies dealing with the provenance of the Cenozoic sediments in the northern margin of the Qaidam Basin, the source to sink model is still under debate. Published thermochronology data revealed an obvious tectonic-thermal event between 200-300Ma in mountain belts surrounding the Qaidam Basin, which provided the main source composition for Cenozoic sediments. Most Paleozoic and early Mesozoic magmatism bodies are distributed in small sub-basins along the Altyn Tagh and the southern flank of the Qilian Shan in the NE Qaidam Basin. There is still no convincing model with reliable evidence for the sediment sources and migration channels that hinders our understanding of the basin-mountain coupling mechanism.
In this paper, the Cenozoic Paleogene-Neogene sediments of the Qaidam Basin are studied by using the methods of petrological observations, geochemical analysis, and zircon U-Pb dating. The results show that the Paleogene-Neogene sediments mainly derived from felsic parent rocks, and after the Paleogene, they experienced obvious sedimentary recycling. The Chemical Index of Alteration (CIA) is in the range of moderate weathering. The parent rock is in the tectonic setting of the active continental margin and continental island arc. The provenance analysis of the Lulehe Formation indicates that it is mainly derived from the southern Qilian Mountains and the Mesozoic crystallization basement. The direct provenance areas of the Xiaganchaigou Formation and the Shangganchaigou Formation are the Saishiteng, Lvliang, and Aolao Mountains, and the indirect provenances are from the South Qilian Mountains, the Mesozoic crystallization basement, and the underlying Lulehe Formation sediments. In addition, it is concluded that the deformation response of the uplift process of the Qinghai Tibet Plateau in the northern margin of Qaidam Basin develops from west to east and has the characteristics of diachronic.
