Abstract:

In this article, we expound the relationship between the largescale magmatism and lithosphere thinning, and suggest that the lithosphere thickness is equal to the crust thickness when the asthenospheric mantle contacts the crust directly, namely, the lithosphere being the thinnest (the thickness of lithospheric mantle is equal to 0). The lithosphere in the Eastern China is thick except in the Yanshanian. We have discussed the relationship between the largescale magmatism and the plate subduction in Eastern China, and pointed out that there are no relations between the magma activity and the ancient Pacific Ocean plate in  Eastern China during the Yanshanian. This conclusion is based on the following considerations. (1)  Eastern China does not belong to the CircumPacific Ocean tectonics belt, and is not the Andeantype active continental margin. (2) The basalts are not of the island arc basalt characteristic in the Mesozoic era, and the acid magma activity can not induce an island arc settings. (3) The expanding direction of the ancient Pacific Ocean plate during the Triassic period does not support the view of the plate subduction westwards either. The super mantle plume may have caused the largescale magmatism during the Yanshanian in  Eastern China, and may have been a new type of the large igneous province (LIP). We divided the large igneous province into two types: One is the Btype LIP, which is partially melted in the lithosphere bottom and characterized by the development of basalt. Another is the Gtype LIP, which is partially melted in the crust bottom and characterized by the development of largescale granitoid magma. Five large igneous provinces have been differentiated according to the spacetime distribution of the largescale magmatism in Eastern China. They are the Okhotsk LIP (in the north part of Da Hinggan Mountain), the Zhangguangcai MountainXiao Hinggan Mountains LIP, the North ChinaDa Hinggan Mountain LIP, the South China LIP and the Coast of East China. The lithosphere thinning can cause many effects, and is the most important geodynamics of the crust evolution, and may have had no relation with the crust extension during the Yanshanian. We have reviewed the popular opinions on lithosphere thinning, and consider that the popular opinion of lithosphere thinning, which limits the timing of the lithosphere thinning in the Cenozoic era (lithosphere thickness 80120 km), is a paradox, not a scientific proposal.

Key words: lithosphere thinning; largescale magmatism; super mantle plume; large igneous province; Yanshanian; Eastern China