鄂尔多斯盆地西南缘二叠系上石盒子组碎屑锆石U-Pb年龄与地质意义

U-Pb Age and Geological Significance of Detrital Zircon in the Upper Shihezi Formation Permian System from the Southwestern Margin of Ordos Basin

运用碎屑锆石LA-ICP-MS锆石U-Pb测年方法,结合碎屑锆石矿物特征、阴极发光图像和年龄谱分布特征,对鄂尔多斯盆地西南缘麟游地区二叠系上石盒子砂岩进行了碎屑物源分析。结果表明:碎屑锆石U-Pb年龄分布主要包含3组峰值年龄:1864 Ma、2500 Ma和441 Ma,另外具有一颗3.3 Ga古老的碎屑锆石年龄及一组次级年轻年龄组299~363 Ma。1864 Ma和2500 Ma两组峰值的锆石颗粒约占总体的82.2%,表明二叠纪末上石盒子期华北克拉通为鄂尔多斯盆地西南缘提供主要物源,3.3 Ga年龄的存在也指示其来源于华北克拉通;441 Ma峰值的锆石颗粒约占总数的10.4%,指示其可能来自秦岭-祁连造山带,由于缺少800~1000 Ma的新元古代年龄,表明秦-祁造山带在上石盒子期抬升及剥蚀程度较低;299~363 Ma年龄组指示其可能来源于华北克拉通北缘的兴-蒙造山带岩浆弧。

Combined the characteristics of detrital zircon mineral, cathodoluminescence image and characteristics of the age spectrum distribution, provenance of sandstone in the Upper Shihezi Formation, the Permian system from Linyou area in the southwestern margin of the Ordos Basin were analyzed by LA-ICP-MS U-Pb dating method. Results show that the detrital zircon U-Pb age distribution mainly has three groups peak age, 1864 Ma, 2500 Ma, 441 Ma, and also has an ancient subprime detrital zircon age of 3.3 Ga and a younger age group from 299 to 363 Ma. The two groups peak age of zircon grains accounted for 82.2% of the total, indicating that late Permian stone box on the stage of the North China Craton provides the main source for the southwest margin of the Ordos Basin. The presence of 3.3 Ga age also indicates that it comes from the North China Craton. The 441 Ma peak zircon grains account for 10.4% of the total, indicating that it may come from the Qinling-Qilian orogenic belt, due to the lack of the Neoproterozoic age of 800-1000 Ma, showing that the uplift and denudation extent of Qinling-Qilian orogenic belt on the Upper Shihezi stage is low. The age group 299-363 Ma indicates that it probably comes from the Xing-Meng orogenic belt magmatic arc in the northern margin of the North China Craton.