The early Permian high-temperature felsic magmatism induced by slab breakoff in Southern Mongolia, Central Asian Orogenic Belt and its tectonic implications

The Central Asian Orogenic Belt (CAOB), characterized by its significant Phanerozoic accretion, develops tremendous post-Carboniferous granites in its southern part and their origins are still unclear, hindering our understanding on the CAOB late-staged evolution, especially its crust growth history. Herein, we presented zircon U-Pb-Hf-O and whole-rock geochemical and Sr—Nd isotopic data for the granitic rocks of early Permian (minor late Carboniferous) from the Khan-Bogd area in southern Mongolia. These early Permian granitic rocks formed at ∼280–290 Ma, together with the coeval previously-studied A-type granites there, are mainly high temperatures (∼800–960 °C) granitic rocks and have contributions of deep substances such as relicts of oceanic slab, lithospheric or asthenospheric mantles, as suggested by their zircon Hf[sbnd]O, and whole-rock Sr[sbnd]Nd isotopes. Similar cases occurred commonly in other areas of southern CAOB and we infer that this is related to a significant shift of the early Permian non-subduction-related magmatism from the earlier arc magmatism. Combined with the accompanying significant contraction of the Paleo- Asian Ocean (PAO), we concur the occurrence of the closure of multiple secondary oceans of the PAO and later accompanying slab-breakoff occurred commonly after the Carboniferous in the southern CAOB. Thus, we propose that the relicts of oceanic slabs, as an important magma origin of these post-Carboniferous granites, were reasonably caused by the commonly-occurred slab breakoff and therefore, it is of great importance for the vertical accretion of the post-Carboniferous evolution of the CAOB, rather than mantle plume and other models.