柴西北晚新生代沉积源区分析:来自碎屑锆石U-Pb年龄及Hf同位素的约束OA

The Qaidam Basin,on the northeastern margin of the Tibetan Plateau,preserves dis-tinctive stratigraphic and sedimentary records of a complex basin-mountain system and multiple provenance sources.In the Dalangtan-Heibei sag of the northwestern basin,a thick Late Cenozoic gravel succession hosts a newly recognized gravel-type potash-bearing brine deposit.In this study,seven sandstone samples from different depths in boreholes CJ-2 and CJ-3 were analyzed for detrital zircon U-Pb geochronology,trace elements,and Lu-Hf isotopes.The detrital zircons are predominantly magmatic in origin,with Th/U ratios of 0.02-1.26 and REE patterns characterized by HREE enrichment,pronounced negative Eu anomalies,and positive Ce anomalies.U-Pb ages range from 213.9 to 3307 Ma and define four main age groups:200-300 Ma,330-510 Ma,740-990 Ma,and 1.1-3.3 Ga.Provenance comparison shows that the Qigequan Formation in borehole CJ-2 was sourced mainly from the East Kunlun-Qimantagh,whereas that in borehole CJ-3 was influenced chiefly by the Altyn Tagh and the northern Qaidam margin.The Shizigou Formation shows stronger multi-source mixing:in borehole CJ-2 it records contributions from the East Kunlun-Qimantagh,northern Qaidam margin,South Qilian Mountains,and Altyn Tagh,whereas in borehole CJ-3 it was derived mainly from the East Kunlun-Qimantagh,with subordinate input from the Altyn Tagh and northern Qaidam margin.These inter-well provenance differences reflect the combined effects of lateral differentiation within the piedmont alluvial-proluvial fan system and intensified Late Cenozoic tectonic activity.The results can provide reliable age evidence for the rapid uplift of the Altun Mountains and the northern margin of the Tibetan Plateau,and offer new age constraints for exploring the gravel type potassium-bearing brine resources in the Dalangtan-Heibei sag of Qaidam Basin.