Permian High Ba-Sr Granitoids: Geochemistry, Age and Tectonic Implications of Erlangshan Pluton, Urad Zhongqi, Inner Mongolia

Erlangshan Pluton from Urad Zhongqi.central Inner Mongolia,is located in the middle segment of the northern margin of the North China Plate.The rocks consist mainly of diorites with gneissic structure.Petrochemicai characteristics reveal that the diorites belong to metaluminous,high-potassium calc-alkaline series,with chemical signatures of 1-type granites.They are characterized by low SiO2 contents(56.63%-58.53%)and A/CNK(0.90-0.96),high Al2O3 contents(17.30%-17.96%)and Na2O/K2O ratios(1.20-1.70),enrichment in large ion lithophile elements(LILE,e.g.,Ba=556-915ppm,Sr=463-595 ppm),and relative depletion in high field strength elements(HFSE,e.g.,Nb,Ta,Ti)in primitive mantle-normalized spidergram.and right-declined rare earth element patterns with slightly negative Eu anomalies(δEu=0.72-0.90).They have Sr/Y ratios(20-25)evidently less than Kebu Pluton (49-75)to its east.Sensitive high resolution ion micro-probe U-Pb zircon dating of thediOrites has yieldIed an intrnsive a2e of 270±8 Ma.This leads US to conclude that Erlangshan diorites were formed by mixing between the middle or lower crustal.derived magma and minor mantle-derived mafic magnm,followed by fractional crystallization,which was trigged by crustal extension and fault activity in post-coilisional setting.