Two episodes of subduction and collision events at the northern foot of Dabie Mountains: Evidence from petrology and structural geology of granitoid rocks

The intrusive bodies studied include Mafan diorites ((462.7 +/-1.5) Ma, Ar- 40/Ar-39 amphibole plateau age), Duhudian granites ((293 +/- 12) Ma, U-Ph z ircon age) and Suxianshi granites ((146.2 +/-0.9) Ma) in Beihuaiyang area a t the northern foot of Dabie Mountains, central China. Petrological studies indicate that all of them belong to I-type granitoid rocks. Among them, th e Mafan and Duhudian stocks were formed by are magmatism, while the Suxians hi pluton is a post-collisional granitic body. Three intrusive bodies have distinctive characteristics of structural deformation. The Mafan stock has a rather complicated structure pattern resulting from polyphase deformation during the Caledonian and Mesozoic, the Duhudian stock has been pronounced ly deformed during the Hercynian-Yanshanian events, while regional foliatio n is not pronounced within the Yanshanian Suxianshi stock. Combination of r egional stratigraphic, regional structural and geochronological data shows that the Yangtze plate has experienced two episodes of subduction northward beneath the North China plate during the Paleozoic and following collision al events. The first phase of collision at about 400 Ma resulted in the for mation of the Beihuaiyang crystalline basement and the Caledonian high-pres sure metamorphism in Dabie orogenic zone, and a late phase of continent-con tinent collision (similar to 230 Ma) is responsible for the Triassic ultrah igh- and high-pressure metamorphism in Dabie Mountains and for orogenic upl ift of the Dabie Mountains. It is suggested that the Beihuaiyang tectonic b elt at the northern foot of the Dabie Mountains is a multicyclic suture.