Geochemistry and tectonic environment of the Xiongshangou intrusion in the West Qinling

Abstract：On the basis of regional geological survey and integrated research, the authors conducted detailed studies of the petrology, contact relationships, isotope ages and geochemistry of the original Baihua intrusion in the southeastern part of Tianshui, West Qinling, and through the studies they separated the Xiongshangou intrusion from the Baihua intrusion and gained a preliminary knowledge of the characteristics of magmatic activity of this separated intrusion. The rock type of the early-stage Xiongshangou intrusion is plagiogranite, which is petrochemically characterized by a low K2O content with K2O∕Na2O=0.33-0.42 and A∕CNK=1.01-1.05；the rock type formed in the late stage is monzogranite, which is enriched in K2O with K2O∕Na2O=1.01-1.43 and A∕CNK=0.86-1.07, and the rock belongs to the tholeiite-calc-alkaline series. Furthermore, the intrusion shows characteristics of enrichment in the trace elements Th, Hf, Nb and Zr and in LREE and no or unpronounced Eu negative anomalies, with δEu=0.58-0.87 and low δ18O (δ18O=＋3.32‰). The rock has the features of “I”-type granite and the magma was derived from materials of the lower crust and the intrusion formed in a continental arc tectonic environment.