The formation and evolution of the Songpan-Garze fore-arc basin, western Sichuan

The Songpan-Garze fold zone, western Sichuan is a triangular tectonic zone located on the junction of the Qaidam landmass and Qiangtang landmass, and bounded by central Kunlun ophiolitic melange zone to the north, Hoh Xil-Jinshajiang suture zone to the south, Longmenshan fault to the east, and extended into the Karakorum Mountains to the west. The megagiant fore-arc fold zone 2500 km long in the EW direction and 150-500 km wide in the NS direction consists dominantly of tremendous (>10 km) Triassic flysch complexes,that are built up of fore-arc basin sedimentary rock series and basement accretionary complexes. It is inferred that the fold zone resulted from the accretion of the Palaeo-Tethys in the areas between active continental marginal arcs and trenches during its collision towards the southern margin of the Qaidam landmass north of it during the Late Carboniferous to the Late Triassic, or may owe its origin to the wedging of the triangular Zoige landmass on northern Gondwanaland and southward migration of the subduction zone. The Songpan-Garze fore-arc tectonic zone has evolved from a narrower fore-arc basin during the Late Carboniferous to the Early Triassic to a broad fore-arc basin during the Middle and Late Triassic.