Triassic Subduction Polarity and Orogenic Process of the Sulu Orogen, East China

The Sulu Orogen, located in East China, has experienced a series of complex Indosinian tectonic processes including subduction of oceanic crust, continent-continent collision, deep continent subduction and intracontinental orogenism. After synthesis of recent researches on tectonics, petrology and paleogeography in the Sulu Orogen, this paper reached the following conclusions that are different from the traditional tectonic models of subduction of the South China Block under the North China Block. 1) In addition to the NW thrusts in the Xu-Huai area, a large number of northwestward thrusts occur in the orogen. 2) The existence of inherited Early Pterozoic zircon and the Sr-Nd-Pb isotopic tracers in the Cretaceous granites in the Sulu Orogen sugest the affinity of the orogen to the North China Block. 3) In the Jiaolai Basin and the Jiaobei Uplift, there is no arc magmatism was recorded from Late Paleozoic to Mesozoic. 4) The southern margin of the North China Block was a passive margin in Triassic. The Shangdan Ocean was subductd southeastward under the Qinling-Dabie Microplate in the Sulu segment, but northward in the Qinling-Dabie segment from Late Paleozoic to Early Triassic, which resuted in the collision of the North China Block and the Qinling-Dabie Microplate. The North China Block indented into the Qinling-Dabie Microplate and thus caused the vertical exhumation of the high-pressure and ultra-high pressure metamorphic rocks. During the Middle-Late Triassic, the northward scissors-type closure of the Mianlue Ocean resulted in an assembly of the South China Block to the Qinling-Dabie Microplate from west to east. The Qinling-Dabie Microplate between the North China and South China blocks was laterally extruded to the west and the north respectively. In the Mesozoic, together with the intracontinental subduction of the North China Block to the South China Block, the Sulu-Dabie Orogen was indented southeastwards by the North China Block. The tectonic setting in the Sulu Orogen and adjacent region was basically formed then.