| The Tibet Plateau was formed by the successive collision of many micro-blocks/massifs at different times,and finally merged at the southern edge of the Eurasian continent.Therefore,its formation and evolution process have a unique role in the spatial and temporal study of global tectonics,specifically,it is an excellent research site for study the evolution of Tethys tectonics,continental collisional orogenic system and basin-mountain coupling.As the northwestern boundary of the Tibetan Plateau,the Altyn strike-slip fault is one of the main control boundary faults on the northern edge of the plateau,and is also the geological boundary between the Tarim Basin and the Qaidam Basin,and is the transition boundary connecting their internal folded and ruptured zones,and is therefore a pivotal and important fault zone within the Asian continent.The Qaidam Basin is an important Middle-Cenozoic terrestrial oil and gas basin in the western part of China,sandwiched between the Kunlun Mountains,Qilian Mountain and Altyn Mountain,with complex basin tectonic deformation,and the western part of the Qaidam Basin is the most strongly deformed area in the basin.The Hongsanhan area is located in the northernmost part of the western part of the Qaidam Basin,adjacent to the Altyn Mountain,and its sedimentary evolution and other geological features are closely related to the uplift of the mountain and the activity of the Alytn strike-slip fault.In this paper,the low temperature thermochronology of apatite fission track（AFT）and detrital mica 40Ar-39Ar dating for the upper and lower Ganchaigou Formation sandstones were studied based on the precise magnetic chronological framework of the Hongsanhan No.1 area in Western Qaidam Basin,and combined with previous researches of framework composition analysis of sandstone in Hongsanhan area and provenance analysis.The main provenance of sediments was determined,the thermal evolution history of the sedimentary basin was inverted,and the uplift history of the Altyn Mountain and the"basin-mountain coupling"relationship of the deposition of Qaidam Basin were discussed.The results of the detrital mica 40Ar-39Ar age of sandstones show that the 307 effective data can be divided into four main age groups:P1:30.5～65 Ma;P2:67～138 Ma;P3:147.9～200.7 Ma;and P4:203～342.1 Ma.Based on the statistics of a large number of previous chronological research data in the Altyn Mountain and the analysis of the sedimentary facies and depositional center changes in the basin,it is suggested that the detrital sediments of the upper and lower Ganchaigou Formation in the study area may mainly come from the near-source sediments of the Altyn Mountain.In addition,the apatite fission track dating shows that the ages are mainly grouped as,P1:～6.1 Ma;P2:11.8～17.9 Ma;P3:40～65.8 Ma;P4:73.5～84.9 Ma;and P5:～145.7Ma component intervals.Moreover,the apatites in the sandstone have been over-annealed.Due to the low closure temperature of apatite,the measured ages are relatively new.It is inferred that the Cenozoic sedimentary history of the section is complicated,and the long span of the component ages also reflects the multi-phase and non-equilibrium of the Altyn uplift in the source area.Based on the above researches and the regional depositional and structural characteristics,the depositional process of Hongsanhan No.1 area in western Qaidam Basin is well coupled with the tectonic uplift of the Altyn Mountain and activities of the Altyn strike-slip fault.It also indicates that the Altyn Mountain has undergone multi-stage,pulse-type uplift and exudation evolution during the uplift and northward extension of the Tibetan Plateau.This study provides evidence to further discuss the uplift and deformation model of the Tibet Plateau. |
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