GEOCHEMICAL IDENTIFICATION OF THE DEVONIAN FORELAND BASIN IN THE EASTERN QINLING, THE SOUTHERN SHAANXI

The Devonian System of the eastern Qinling,the Southern Shaanxi is distributed in front of the eastern Qinling Suture and developed on the ancient passive margin of the eastern Qinling.This Devonian System can be divided into three belts of north,central and south belts respectively bounded by the Zhengan-Banyanzheng and the Shanyang-Zhashui faults.According to the geochemical and geological studies,it concludes that the Devonian system of the eastern Qinling had developed under the tectonic settings of peripheral foreland basin and the foreland basin can be characterized by the followings:1.The migration of the depocenter of the foreland basin,the depocenter was located ar the flank of the Yangtze Craton during the early Devonian and thereafter,it migrated gradually to the Danfeng-Shangnan obducting slab.2.The contact relationship between the Devonian sequences and the underlying sequence transformed successively from conformity,pseudoc-onformity to unconformity from the Yangtze Craton to the Danfeng-Shangnan obducting slab.3.The sedimentary facies of the system can be classified into lagoon and shore facies for the south Devonian belt,neritic shelf facies for the central belt and neriticfacies for the north belt respectively.4.The detrital sediments of the north belt derived from the ancient suture belt of the Qinling and the northward high land,and those of the central and south belts from the north passive continental margin of the Yangtze Craton.