Tectonic Boundary and Ceasing Time of Amalgamation between the North China Craton and the North Qinling Belt

The Qinling orogenic belt is a composite orogen, consisting of the north and south Qinling belts with different collision ages. The North Qinling belt is composed of several petro-tectonic units, including the Kuanping, Erlangping, Qinling and Danfeng groups with numerous granitoid plutons from Neoproterzoic to Middle Devonian. To the north of the Kuanping Group, a mylonitized granite body in the Luanchuan Group was determined to have the magmatic age of 850 Ma, which is the northernmost Neoprotozoic granite body. The volcanic rocks of the Dahongkou Formation from the Luanchuan Group had the eruptive age of 1 600 Ma, obtained from zircon U-Pb LA-ICP-MS analysis. The detrital zircons in meta-sandstones from the Taowan Group have three populations of 920-1 400, 1 600-2 100, and >2 200 Ma ages, whereas those from the Kuanping Group shows six populations with the peaks of 590, 767, 952, 1 590, 2 485, and 3 200 Ma. These data suggest that the boundary between the North China Craton and the North Qinling belt cannot simply be constrained by using the events determined from zircon U-Pb ages. The granitoid plutons with the magmatic age of 430 Ma were strongly deformed, while those with the magmatic age of 390 Ma show no or less deformation, indicating that the deformation of amalgamation between the North China Craton and the North Qinling belt ceased between 390 and 430 Ma.