Geochronology of Yanshanian Magmatism and Metamorphism in the Hinterland of the Dabie Mountains and Their Geologic Implications1

A strong tectono-magmatic thermal event has been revealed by field observations of granitic, migmatitic and metamorphic rocks in the hinterland of the Dabie Mountains. K-Ar, Ar-Ar and Rb-Sr determinations show that the event took place 133-117 Ma ago (Yanshanian) Contemporaneously, a southwestward thrust-type ductile shearing at multiple levels occurred in the lower crust or at even deeper levels, suggesting that the Dabie Mountains region was still under the influence ot strong continent- continent overlapping tectonism of the Yangtze block under the Sino- Korean block at depth. Metamorphic rocks of amphibolite facies, migmatites and deep structural deformations resulting from this tectonothermal event are now exposed to the surface. The present features of the Dabie Mountains thus have appeared only since ca. 100 Ma B.P. The block composed of the Dabie Group is not an uplift or shield which would have undergone a long-continued erosion.