A review of magmatism and deformation history along the NE Asian margin from ca. 95 to 30 Ma: Transition from the Izanagi to Pacific plate subduction in the early Cenozoic

摘要

Previous plate reconstruction in the Paleo-Pacific domain indicates that the Izanagi and Pacific plates influenced the NE Asian continental margin during the Mesozoic and Cenozoic, respectively. However, it remains unclear how and when the transition from Izanagi to Pacific plate subduction occurred, because most evidence came from the oceanic crust. However, the onshore geological records are poorly understood, so in order to solve this problem, we review recently-published data and identify three magmatic episodes, a magma gap and four deformation stages from ca. 95 to 30 Ma. Margin-parallel Izanagi-Pacific ridge subduction is proposed to explain the changing magmatic and deformation signatures and other regional events in the early Cenozoic. From ca. 95 to 65 Ma, the N- or NNW-directed subduction of the Izanagi plate triggered sinistral shearing along the NNE-striking faults. Arc magmas at that time incorporated older crustal materials. From ca. 65 to 55 Ma, the NWW-striking transform faults and ridge segments were subducted, developing small slab windows and facilitating the input of juvenile magmas. Local extension was active above these windows. During ca. 55 to 45 Ma, the ridge was totally subducted, and a margin-wide slab window was opened, resulting in an arc magma gap and extension. Massive asthenosphere upwelling caused the extensive accretion of juvenile materials. From ca. 45-30 Ma, the dextral NNE-trending faults resulted from the W-directed subduction of the Pacific plate. New arc magmas were generated from juvenile materials and thus are isotopically depleted.