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中吾农山构造带位于南祁连地块和柴北缘欧龙布鲁克地块之间,其构造特征研究对邻区的构造演化有重要的启示意义。目前关于中吾农山构造带加里东期构造-地层-热事件的研究很少,且对于该构造带及邻区中吾农山群的物质来源和其形成的构造环境仍存在不同观点。本文对中吾农山构造带及邻区中吾农山群开展岩石学、地球化学、碎屑锆石U-Pb年代学及其微区原位Hf同位素分析,结果显示中吾农山群碎屑岩具有较低的化学蚀变指数(CIA<72)和斜长石蚀变指数(PIA=50.26~68.12),较高的成分变异指数(ICV=1.21~1.58),表明成熟度较低,经历了弱-中等的化学风化、不具“沉积再旋回”特征。地球化学指标(La/Sc,Th/Sc,Zr/Sc,Cr/Th,Th/Co等)和判别图解(Zr/Sc-Th/Sc和La/Sc-Co/Th)显示源岩主要为长英质岩石。锆石U-Pb年龄谱存在新元古代(0.8~1.0 Ga)和早古生代(0.4~0.45 Ga)两个主要峰值,对应εHf(t)分别为-9.6~-3.09和-15.87~9.5,而最年轻碎屑锆石年龄为410 Ma。结合前人研究,推测中吾农山群可能形成于晚奥陶世–早泥盆世早期,而柴北缘鱼卡-沙柳河高压-超高压变质带内新元古代花岗片麻岩和早古生代滩间山蛇绿杂岩带内大陆弧型花岗岩为其主要物源,其沉积形成于早古生代活动大陆边缘-大陆岛弧环境下的弧后盆地。
The Zhonggong Nongshan tectonic belt is located between the South Qilian block and the Oulongbuluke block in the northern Qaidam basin. The study of its tectonic characteristics has important implications for the tectonic evolution of its adjacent areas. At present, few studies have been done on the Caledonian tectono-stratigraphy-thermal events in the Nonggongshan tectonic belt in Central China, and there are still different opinions on the material sources and the tectonic environment of the Wugongnongshan Group in the tectonic belt and its adjacent areas. In this paper, petrology, geochemistry, detrital zircon U-Pb chronology and in-situ Hf isotope analysis of the Hegongshan structural belt and its adjacent Nongnongshan group in Zhongwu, The petrofacies have lower chemical alteration index (CIA <72) and plagioclase alteration index (PIA = 50.26 ~ 68.12) and higher compositional variation index (ICV = 1.21-1.58), indicating that the maturity is low, Has experienced a weak - moderate chemical weathering, not “deposition and then cycle back” feature. Geochemical indicators (La / Sc, Th / Sc, Zr / Sc, Cr / Th, Th / Co etc.) and discriminant diagrams (Zr / Sc-Th / Sc and La / Sc- Co / Th) Long British rock. There are two main peaks of Neoproterozoic (0.8-1.0 Ga) and Early Paleozoic (0.4-0.45 Ga) in zircon U-Pb ages, corresponding to -9.6 ~ -3.09 and -15.87 ~ 9.5 for εHf (t) The youngest detrital zircon is 410 Ma. Based on the previous studies, it is speculated that the Nongguoshan Group may be formed in the early Ordovician-Early Devonian, whereas the Neoproterozoic granitic gneiss in the Yuka-Salix High-pressure metamorphic belt in the northern margin of Qaidam Basin The main provenance of continental arc granite in the Paleozoic Shan She ophiolitic complex belt is that its sediments were formed in the back-arc basins under the continental margin of the Early Paleozoic-continental island arc.