The discovery of Jurassic accretionary complexes in Duolong area, northern Bangong Co-Nujiang suture zone, Tibet,and its geologic significance

The outcropped accretionary complexes in Duobuza-Bolong ore concentration area of northern Bangong Co-Nujiang metallogenic belt belongs to Non-Smith Strata which are totally disordered but partially ordered and deformed strongly. The bases are Jurassic sand-muddy flysch formation and blocks consisting of basalt, sandstone, silicalite, argillaceous limestone and ultrabasic rocks which differ in size. The accretionary complexes experienced strong tectonic replacement while the bases and blocks were separated by penetrative and unequal extrusion foliations or shearing foliations, suggesting accretionary complexes of a typical orogenic belt. Researches show that the accretionary complexes were derived from the lateral accretion of Jurassic southern Qiangtang massif, which was related to the subduction from Meso-Tethys Bangong Co-Nujiang oceanic crust to Qiangtang massif. Qiangduo magma arc can be described as continental margin volcanic-magmatic arc based on accretionary wedge. This new understanding provides new clues for understanding the geological background of the Duobuza-Bolong superlarge porphyry copper-gold deposit and the evolution of the Bangong Co-Nujiang suture zone.