Characteristics and Their Tectonic Environment of Late Mesoproterozoic Granitoids in the Middle Segment of North Margin of the North China Plate
ZHANG Chen LIU Shuwen HE Guoqi HUANG Baoling (Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing, 100871)
Granitoids in the late stage of the Mesoproterozoic along the north margin of the North China plate, are composed of biotite granites, tonalites, granodiorites and monzonitic granites. They exhibit the features of peraluminous granites, A/CNK1.1, and are characterized by higher SiO2, K2O and low FeO, MgO, CaO, TiO2, also higher Rb, K, Ta, Nd, Hf and low Nb, Sr, P, Ti in trace and minor elements. They have strong differentiation between LREE and HREE (La/Yb)N=6.61-54.63). REE patterns have middle negative Eu anomalies. The granitoid belt is approximately EW-trenging and parallel to Mesoproterozoic island arc belt of Bainaimiao group and Weijiagou rock group and ophiolite mélanges belt of Kaiyuan rock group. The new geochemical data suggest that the Mesoproterozoic granitoids in middle segment of north margin of the North China Plate belong to syn-collisional S-type granitoids.They were produced during processes of subduction and collision between the North China Plate and Xiberia Plate in the late stage of Mesoproterozoic. This collisional event in the North China Plate may provide an essential constraint to the aggregation between the plate and others of supercontinental Rodinia.