Petrogenesis and Tectonic Significance of the Late Palaeozoic Granitoids in Hazhu Area, Inner Mongolia

The chronology, geochemistry and zircon Hf isotopes of granitoids in Hazhu area of the northern Beishan belt are systematically studied, and the genesis of the plutons and their restrictions on the tectonic magma evolution in Late Paleozoic are discussed. The zircon LA-MC-ICP-MS U-Pb dating results show that the granodiorites and monzogranites formed during the late Late Carboniferous in 298.6±1.7 Ma and 306.0±1.3 Ma, and the alkali-feldspar granites formed in Early Permian 289.3±1.3 Ma. Chemically, the granodiorites and monzogranites are characterized by middle potassium calc alkaline, low Mg# value and middle degree of differentiation (D.I.=79.2-86.9), metaluminum and enriched-magnesium. And alkali-feldspar granites show high contents of silica and alkalis, metaluminum, low abundances of calcium, magnesium and iron, and high degree of differentiation (D.I.=94.4-96.5). All of them are enriched in Rb, Ba, Th, U, La, Ce, and so on, and depleted in high field strength elements, Nb, Ta, P, Ti, Sr, and so on. The εHf(t) values in this paper are all positive. The Hf isotopic crustal model age TDMC is mainly concentrated from 800 Ma to 450 Ma. According to the data obtained in this paper and other regional geological data acquired recently, the subduction plate dehydrated, after then, the subduction fluid entered into the juvenile crust, and induced partial melting of the juvenile crust, forming the granitoids in Late Carboniferous. The extension resulted in the thinning and stretching of the lithosphere due to the post collisional extension in Early Permian, which caused the partial melting of the new crust, and then the alkali-spar granites were formed by a high degree of differentiation and evolution. © 2019, Editorial Department of Earth Science. All right reserved.