Origin of Late Mesozoic igneous rocks in Southeastern China: implications for lithosphere subduction and underplating of mafic magmas

On the basis of geological, geochemical and geophysical data of Late Mesozoic igneous rocks in SE China, we suggest that during the period from 180 to 80 Ma, the slab dip angle of Paleo-Pacific plate subduction underneath SE China increased from a very low angle to a median angle. Consequently, magmatic activity of the SE China continental margin migrated oceanward to the southeast. Initially, magmatism was concentrated in the region as far as 800∼1000 km northwest of the ocean-continent boundary zone, which is located in the eastern flank of the Central Ranges, Taiwan. As the slab dip angle increased, this magmatic belt migrated rapidly to the region only 100-200 km away from this boundary zone. During subduction process, various degrees of mantle wedge melting and basaltic underplating provided the necessary heat to cause partial melting of lower- and middle- crust, and generation of voluminous felsic magmas. A combination of these processes is responsible for the formation of the famous Yanshanian granitoids, volcanic rocks and related ore deposits in SE China. Mantle input may have played an important role in sustaining magma fractionation and eventually leads to release of magmatic fluids and formation of world class W, Sn and other types of ore deposits in SE China.