关键词: 大别造山带, 新县二长花岗岩, 岩石成因, 锆石U-Pb年龄, 地球化学

Abstract: The Mesozoic intermediate-acid plutons are widespread within the Dabie orogenic belt which is located between the North China Block and the Yangtze Block. This work conducts an integrated study including field geology, zircon U-Pb dating, and elemental and isotopic measurements for the Xinxian batholith, aiming to reveal its geological and geochemical characteristics and to discuss its petrogenesis. The investigation results indicate that the Xinxian pluton consists predominantly of monzogranites. They were crystallized in 133-129 Ma and can be divided into three units based on grain sizes. Paleoproterozoic inherited zircons have been observed from samples of this pluton. The monzogranites are characterized by enrichment of silica and alkaline, depletion in LILEs (e.g., Ba and Sr) and HFSEs (e.g., P and Ti) with indistinct Nb-Ta anomalies on the primitive-mantle normalized spidergrams, and can be grouped into weakly peraluminous high-K calc-alkaline series. The chondrite-normalized REE patterns show strongly enrichment in LREEs, depletion in MREEs, weakly enrichment in HREEs and exhibit distinct negative Eu anomaly. These features indicate that the monzogranites were derived from an amphibole stable zone in an extensional environment of the thickened crust, rather than from a garnet stable zone in the thickened lower crust. The whole-rock εNd(t) values of this pluton range from -20.8 to -18.4, with two-stage Nd model ages of 2.61 to 2.43 Ga, implying that the parent magmas were originated mainly from partial melting of ancient crustal rocks, such as the Kongling and/ or Douling Groups. By comparison the Xinxian monzogranites with the ore-bearing rocks from the Qian’echong and Baoanzhai Mo deposits, it is shown that they have consistent geochemical features, implying that they have closely genetic relationship, and were likely produced from different differentiation stages of the same magma.

Key words: Dabie Orogenic Belt, the Xinxian monzogranite, petrogenesis, zircon U-Pb age, geochemistry