CENOZOIC SOURCE TO SINK RELATION BETWEEN THE QAIDAM BASIN AND THE EASTERN KUNLUN SHAN
Résumé
Understanding the source to sink relationship through time between the Eastern Kunlun Shan, one of the major mountain belts in the northern Tibetan Plateau, and the actively deforming Qaidam Basin to the north has important implications for unravelling the growth history of the Tibetan Plateau. In this study, we first carried out a flexural loading modeling to estimate the topography load of the Qilian Shan and Eastern Kunlun Shan during the deposition of the Lulehe Fm. and compared this result with the basin shape which was obtained from shortening restoration and decompaction by using the drill core, seismic profile and isopach data. In addition, U-Pb dating of detrital zircons from 22 sandstone samples collected from four sections within the southwestern Qaidam Basin is combined with provenance analysis and new seismic profile interpretation to investigate the mountain building of the Eastern Kunlun Shan and its effects on the development of the Qaidam Basin. Flexural loading estimate suggests that the single Qilian Shan failed to produce a sufficient load to create the observed Qaidam basin during the deposition of Lulehe Fm. The topographic load generated by both the Eastern Kunlun Shan to the south and the Qilian Shan-Altyn Tagh Range to the north was responsible for the flexural subsidence of the Qaidam basin during the deposition of Lulehe Fm. The U-Pb age distributions of detrital grains from Lulehe Fm. strata are characterized by a major component of Paleozoic to late Proterozoic ages. Carbonate debris containing foraminifera have been recognized in the Lulehe Fm. conglomerate sequences. We suggest that the Eastern Kunlun Shan was exhumed during the deposition of Lulehe Fm. The southward onlaps strata (Lulehe Fm. to Shangganchaigou Fm.) observed on seismic profiles and the appearance of a Mesozoic component in the detrital zircon age spectra of Xiaganchaigou Fm. to Shangganchaigou Fm. strata indicate that the Qaidam Basin was widening southward during that early Cenozoic period. Well-developed growth strata and the increasing proportion of Mesozoic and Paleozoic U-Pb ages in detrital zircon grains from late Neogene strata demonstrate that the relief of the Eastern Kunlun Shan and Altyn Tagh Range increased, leading to isolation and narrowing of the Qaidam Basin, from Miocene to the present.