Geochemistry and petrogenesis of Permian granitoids in the northwestern margin of the North China Craton: insights from the Dongshengmiao pluton, Inner Mongolia

Abstract

Permian granitoid emplacement represents one of the most important tectonothermal events in the northern margin of the North China Craton (NCC). In this study, we collected geochronological and geochemical data of the regional Permian granitoid in the northwestern margin of the NCC, and investigated the Dongshengmiao pluton, using it as an example to constrain the regional granitoid petrogenesis and its geodynamic settings. The Dongshengmiao pluton contains porphyritic granite and quartz diorite. LA-ICP-MS zircon U-Pb dating results have constrained the granitoid emplacement to be ca. 287‒275 Ma. The Dongshengmiao granitoids have a SiO2 range of 58.4‒76.5%, moderate to high alkali content (Na2O + K2O = 5.16–7.94%), and are rich in large-ion lithophile elements (LILEs; e.g. Rb, Ba) and depleted in high-field strength elements (HFSEs; e.g. Nb, Ta, Ti). The zircons in quartz diorite have εHf(t) values of −15.6 to −11.1 with two-stage Hf model ages (TDM2) of 1997–2281 Ma, suggesting that the magma was derived from partial melting of old continental materials. In contrast, porphyritic granite shows variable Hf isotopic composition with εHf(t) values of −13.7 to −2.6 and TDM2 of 1471–2167 Ma, indicating a heterogeneous magma source. Besides the Dongshengmiao pluton, all the Permian granitoids in the northwestern margin of the NCC exhibit similar geochemical characteristics, including enrichment in LILEs, depletion in Nb and Ta, and enriched Hf isotopic signatures. The comprehensive geochemical data indicate that these Permian granitoids are derived from magma mixing between dominant partial melting of ancient felsic crustal materials and minor juvenile basaltic magma. Tectonically, the Dongshengmiao and other granitoids in the northwestern margin of the NCC may have been formed in a post-collisional extensional setting.