Geochemical characteristics and genesis of Yanshanian granite in the Dabie ultrahigh-pressure (UHP) metamorphic belt

Abstract： According to the rock composition, occurrence, textures, emplacement mechanism and geochemical characteristics, the Yanshanian granitoids in the Dabie UHP metamorphic belt may be classified into two major types： the high-K calc-alkaline series and the normal calc-alkaline series. The high-K calc-alkaline series is represented by the Datong rock body and the early-stage and main-stage Sikongshan rock bodies and composed lithologically of granodiorite-monzogranite. The chemical composition is characterized by SiO2 >56%, Al2O3≥14%, MgO <3%, high Sr and Ba contents, enrichment in LREE, strong depletion in HREE, high Sr/Y and La/Yb ratios (≥30 and ≥39, respectively), low Y(<18×10-6) and Yb (<1.9×10-6) contents, and indistinct Eu and Sr negative anomalies. These characteristics are similar to those of adakite. The normal calc-alkaline series is represented by the Yingshanjian rock body, consisting dominantly of monzogranite. It is characterized by high SiO2 (>70%), low Al2O3 (<14%), low Sr and Ba contents, low Sr/Y （<10） and La/Yb （<10） ratios, high Y (>18×10-6) and Yb (>1.9×10-6) contents, depletion in LREE, enrichment in HREE, and pronounced negative Sr and Eu anomalies. The high-K calc-alkaline granites might be derived by partial melting of the thickened lower crust, while the normal calc-alkalis granites probably originated by anatexis of the normal crust.