The ages and petrogenesis of granite porphyry in Tarqi area, Inner Mongolia

Based on geological characteristics, zircon U-Pb ages and geochemical features, the authors studied the ages and petrogenesis of granite porphyry in Tarqi area. The zircon U-Pb ages (136.5~126.4Ma) indicate that the granite porphyry was formed in Early Cretaceous. An analysis of geochemical data shows that the granite porphyry is characterized by high silica, rich alkali, weakly peraluminous attribute (A/CNK=1.0~1.29) and high differential degree, suggesting high-kcalc-alkaline series. It is also enriched in LILE (Rb, Th, U, K) and LREE, and depleted in HFSE (Nb, Ta, Ti, P). The zircon Hf isotope data indicate that the granite porphyry has ε_Hf(t) values of +7.19~+7.29, and the model ages (T_DM2) of two stages are from 851Ma to 569Ma, which implies that the granite porphyry might be derived from the partial melting of the crustal substance from depleted mantle during Neoproterozoic-Early Palaeozoic. According to the regional geological data, Taerqi granite porphyry and Baiyingaolao volcanic rocks in the study area may be the products of contemporaneous magmatism, and were probably formed in an extensional environment.