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

Abstract

<p>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 degrees 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-O, and whole-rock Sr-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.<br></p>