A MESOZOIC FLAT-SLAB SUBDUCTION EVENT IN NORTHEAST ASIA FROM TOP TO BOTTOM

The Jurassic-Cretaceous tectonics of East Asia is dominated by the “Paleo-Pacific” subduction. Nevertheless, the nature of the Paleo-Pacific are controversial, because it had been entirely consumed. We use teleseismic tomography models to map the subducted slabs in 3-D and tie them with geologic records on the surface. Two colossal slab remnants are mapped in the lower mantle under East Asia, namely Izanagi and Hunan. The Izanagi slab is a N35E-trending, steeply dipping, 2700-km-wide slab wall at ca. 1100-2100 km depths, and its surface projection spans Khabarovsk and Amur of Far East Russia and the Great Xing’an Range of Northeast China. The Hunan slab is separated by a slab-gap from the Izanagi. It also shows a thick, vertical wall-shaped geometry at >1450-km depths. Projected onto surface, this slab ranges from the Taihang Mountains in North China to the central South China and northern Vietnam. We further integrate 5000+ crystallization ages of the Mesozoic igneous rocks in a GIS database, and examine their spatial-temporal distribution patterns. In Northeast Asia, a 2500-km-wide magmatic front started to sweep westward at ca. 165 Ma and reached ca. 1500 km inboard at 140 Ma, followed by rapid eastward migration and high flux event. In South China, the magmatic front migrated slowly towards the coast from 200 Ma on. A “jog” of the igneous activity at 140 Ma is clearly shown on the map along the Qinling-Dabie Mountains. Based on these observations, we suggest that a giant flat-slab subduction event took place in Northeast Asia during the Izanagi subduction in the Jurassic-Cretaceous. It was separated by a slab tear from the Hunan slab subduction along the South China margin. In addition, the destruction of the eastern North China Craton was caused by the flat-slab subduction.