Evolution of Triassic volcanic-sedimentary basins in the central segment of the Yidun island arc of the Songpan-Garzê orogenic belt, western Sichuan, China

According to a comprehensive study of 83 stratigraphic sections and depositional isopachs, the central segment of the Triassic Yidun island arc is divided into five tectonic-paleogeographic units, i.e.: the Yidun back-arc foreland basin, Yidun volcanic arc, Changtai-Heni interarc basin swarm, Shaluli volcanic magma arc and Xionglongxi-Jinchanggou forearc basin swarm. Of these, the Yidun back basin mainly has the Shangmarong depocenter and Yidun depocenter; the Yidun volcanic arc may be subdivided into the Guode, Genlong, Langge and Hadai volcanic domes; the interarc basin swarm include the Nata, Qudeng, Xiasai and Hari basins; the Shaluli volcanic magma arc is subdivided into the Muhegou and Kounianggongma volcanic domes; and the Xionglongxi-Jinchanggou forearc basin swarm comprises eight volcanic-sedimentary subbasins such as the Xionglongxi, Moba and Jinchanggou basins. It is thought that the evolution of the Yidun island arc was mainly controlled by the evolution of the Litang suture zone and also by the Jinshajiang suture zone. Generally, four stages are proposed for the basin evolution of the Triassic Yidun island arc: a failed aulacogen, an immature island arc, a mature island arc and remnant basins.