Geochronology, Geochemistry and Tectonic Setting of Late Palaeozoic Granites in the Tes Area, Northern Mongolia

ABSTRACT This study presents LA–MC–ICP–MS zircon U–Pb ages, whole‐rock geochemical data and zircon Hf isotope compositions of granitoid rocks from the Tes area of Northern Mongolia in the central CAOB, in order to determine their formation age, source nature, and tectonic setting. Zircons in the granitoids are mostly euhedral to subhedral crystals with well‐developed oscillatory zoning, and their Th/U ratios range from 0.06 to 1.69, consistent with a magmatic origin. Zircon U–Pb dating reveals that the syenogranite, alkali feldspar granite, quartz alkali feldspar syenite, and quartz syenite formed during the Late Carboniferous to Middle Permian (305–269 Ma). These granitoid rocks have SiO 2 = 59.22–75.56 wt.%, Na 2 O/K 2 O = 0.74–1.62, A/CNK = 0.85–1.03. Their REE patterns are right‐inclined and characterised by LREE/HREE = 8.14–18.5, (La/Yb) N = 7.98–27.5, and Eu/Eu* = 0.58–1.05. These granitoids show a remarkable enrichment in LILEs (e.g., Rb, Th, U, and K) relative to HFSEs and LREEs, as well as negative Nb, Ta, P, and Ti anomalies. The zircon ε Hf (t) values of these granites range from +1.20 to +12.1, and the two‐stage Hf model ages ( T DM2 ) range from 634 to 1614 Ma. Collectively, these geochemical and isotopic features indicate that the granitoids are metaluminous to weakly peraluminous, shoshonitic to high‐K calc‐alkaline I‐type granites, and that their primary magma was derived from the partial melting of newly accreted mafic igneous rocks in the deep continental crust. Combined with the coeval igneous rock associations and regional tectonic evolution, we conclude that the Late Carboniferous to Middle Permian granitoid rocks in the Tes area formed in an active continental margin setting related to the subduction of the Mongol‐Okhotsk oceanic plate.