Late Paleozoic Diachronous Subduction Initiation of the SE Paleo-Asian Ocean: Implications for Tectonic Transition From Passive to Active Continental Margin Along Northern North China Craton

Subduction initiation is fundamental to our understanding of plate tectonics. However, the mechanisms and processes of subduction initiation, especially at passive continental margins, are poorly understood due to limited geological records. Here we identify a magmatic sequence resembling the Izu-Bonin-Mariana (IBM) forearc crust in the Mandula area of Inner Mongolia that recorded the subduction initiation of the Paleo-Asian Ocean (PAO) along the northern margin of the North China Craton (NCC). Geochemical analysis indicates that basalts and sheeted diabase dikes originated from partial melting of the upwelling asthenosphere at a forearc spreading center, succeeded by incipient arc volcanic and intrusive rocks, with increasing input of subducted slab-derived hydrous fluids. Zircon U-Pb ages reveal that the magmatic events in the Mandula area have taken place in a relatively short time interval between ∼284 Ma and ~272 Ma, similar to the duration of IBM forearc magmatism. The new results integrated with available data suggest that the southward subduction initiation of the PAO along the northern NCC was diachronous from early Carboniferous to early Permian and propagated from east to west following arc-continent collision. Therefore, our study provides a four-dimensional spatiotemporal perspective for tectonic transition from passive to active continental margin along the northern NCC.