The age of granitic intrusion from Dongliushuquanzi in Urad Zhongqi, Inner Mongolia and its tectonic implications

Abstract

The Dongliushuquanzi magmatism contains two units: granitic intrusion and multiple intrusive dioritic veins. LA‐ICP‐MS zircon dating results have revealed that the magmatism developed in two distinct episodes: the first episode, which occurred in the Late Carboniferous–Early Permian, is characterized by the main granitic intrusion and the Phase I dioritic veins, Phase II dioritic veins developed during the second magmatic episode in the late Early Permian. The analysing results of major and trace elements indicate that the granitic intrusion are enriched in light rare earth elements and large‐ion lithophile elements such as Rb, Ba, K, but depleted in high‐field‐strength elements, such as Nb, Ta, P, and Ti. These geochemical signatures, in addition to their weak negative Eu anomalies, are similar to those of continental arc magmatic rocks. The main body of the granitic intrusion and the Phase I dioritic veins are characterized by negative and inhomogeneous ε Hf (t) values (include ε Hf (t) < −10 and −10 < ε Hf (t) < −5 two subgroups), they were derived from mixture of decompression melting basaltic juvenile lower crustal materials and partial melting ancient materials in middle‐upper crust. Phase II dioritic veins are characterized by positive and homogeneous zircon εHf(t) values (~ + 10), record predominantly juvenile crustal sources, formed by partial melting of basaltic juvenile lower crustal materials. The two magmatic episodes are in response to slab rollback, slab break‐off and final amalgamation of the Palaeo‐Asian Ocean. The ages of inherited zircons record ~499 and ~365 Ma magmatic activity, imply that there also exist Cambrian and Devonian magmatism in the west section of the northern margin of the North China Craton.