Recognition of Late Carboniferous arc‐related volcanic rocks from Ongniud Banner, southeastern Inner Mongolia: Evidence of southward subduction and implication of closure time for Palaeo‐Asian Ocean

Abstract

Newly recognized Late Carboniferous volcanic rocks occur in Ongniud Banner on the northern margin of the Sino‐Korean palaeoplate, including rhyolite, dacite, and related volcaniclastic. The volcanic rocks have for a long time been considered to form in the Early Permian. Our new LA‐ICP‐MS U–Pb zircon dating of two rhyolite samples and one dacite sample yielded ages of 305.6 ± 1.6 Ma, 312.2 ± 2.3 Ma, and 305.3 ± 1.7 Ma, respectively, corresponding to the Late Carboniferous. The volcanic rocks are enriched in light rare earth elements (LREEs) and large‐ion lithophile elements (LILEs) and depleted in heavy rare earth elements (HREEs) and high‐field‐strength elements (HFSEs, e.g., Nb, Ta). The positive zircon εHf(t) values (+6.64 to +9.49) of the volcanic rocks and the high Mg# values (47.05–51.47) of some samples indicate the contribution of mantle materials to the sources. Integrated with geological, geochemical, and Lu–Hf isotopic studies, it is considered the volcanic rocks formed in a subduction‐related continental margin arc setting. Combined with the studies in the southeastern part of the Central Asian Orogenic Belt on the ophiolitic mélanges, magamatic belts and sedimentary environment of the Late Palaeozoic, collision‐related granites, and so on; it is suggested that the southward subduction for the eastern segment of the Palaeo‐Asian Ocean beneath the northern margin of Sino‐Korean palaeoplate was still occurring in the Late Carboniferous.