INDOSINIAN TURKIC-TYPE OROGEN BORDERING YUNNAN AND GUANGXI：WITH REFERENCE TO COUPLED BASIN EVOLUTION

The Babu-Phu Ngu ocean bordering China and Vietnam separated the Vietbac Block from the Huanan (South China) Subcontinent,with rifting started from the Devonian.The oceanic crust must have been created in Early Carboniferous,evidenced by the Sm-Nd isochron age of 328.3 Ma from the ophiolite,and in the oceanic basin some submarine plateaus occurred on which the shallow marine carbonate rocks deposited during Late Paleozoic.Beginning from the Early Permian the ocean subducted southwestwards,with the magmatic arc migrating toward the ocean.Correspondingly,the passive continental margin migrated northeastwards.The southwestward subduction and arc migration toward the northeast kept on in Early-Middle Triassic,when the passive continental margin inverted to foredeep where flysch formation well developed in areas bordering Guangxi-Guizhou.During the subduction,the carbonate rocks on submarine plateaus,plus the volcano-sedimentary rocks of active continental margins,were accreted onto the Vietbac Block.In Late Triassic,the accreted Vietbac Block collided the Huanan Subcontinent,and the accreted volcano-sedimentary wedges obducted the latter.The molasse deposits (the Erqiao Formation) occurred accompanying with the collision,but now preserved in the central Guizhou only.The stacking up of crustal wedges resulted in the thickening of continental crust,and the orogenic area uplifted and eroded in Juro-Cretaceous.The lithospheric delamination and related collapse rifting might hardly occurred,since the collision did not occur between two lithospheric plates.In short words,the Paleotethysides bordering Yunnan and Guangxi may have been a Turkic-type orogen,which controlled developing of the coupled basins both in continental margins and intracontinental (intracratoi nic) ones.The examples from Guizhou as well as Hunan and east Sichuan revealed that the change of tectonic regime (from sea-floor spreading to oceanic subducting) resulted in a regional compressive stress field and a group of comtemporaneous folds constraining intracratonic sedimentation.Based on analysis of relation between the orogenesis and coupled basin developing,the potential areas for oil-gas exploration are suggested as follows:1) The underthrust and buried marine Upper Paleozoic deposited on the Huanan Subcontinent,especially,to the northeast side of the Youjiang fracture;2) the buried Triassic sediments in the foredeep and foreland basins,as well as the Upper Paleozoic on the South Guizhou Slope.