THE DOULING PALEO-ISLAND ARC AND WUDANG PALEO-BACKARC BASIN IN EAST XINLING AND THEIR GEOLOGICAL SIGNIFICANCE

The Danfeng-Xinyang ophiolitic melange zone is the principal suture zone of the Qinling Dabie collisional orogenic belt and its southern part is the continental margin in the northernpart of the Yangtze plate. The study area,located on the southern side of the East QinlingMountains,is a part of the northern continental margin of the Yangtze plate. （1）In the LateProterozoic-Middle Sinian the northern margin of the Yangtze plate （the East Qinlingsector） was an active continental margin,where the Douling arc and Wudang backarc basindeveloped. （2）During the Late Sinian-Early Paleozoic the northern margin transformed into apassive margin:the Douling arc became a marginal massif and the Wudang backarc basin evolved into a marginal basin. （3）In the late Early Paleozoic the Qinling arc on the southernmargin of the North China plate collided with the Douling massif （paleo-arc）,resulting in theclosing of the Wudang basin （paleo-backarc） and the formation of the Linting foredeep andEryugou foreland basin. （4）The collision did not bring about large-scale uplift in the QinlingDabie area at the end of the Early Paleozoic because of the existence of the Erlangpingbackarc basin and Wudang marginal basin,and the Qinling-Dabie orogenic belt only took itsembryonic form. A large-scale uplift of the Qinling-Dabie area took place in the Early Mesozoic and it was attributed to the intracontinental subduction. The recognition of the Doulingpaleo-arc and Wudang paleo-backarc basin is a key to explain the contradictory phenomenonthat the collision in the Qinling-Dabie area in the Caledonian Stage did not make mountainswhile mountains were created without collision in the indosinian.