Crustal deformation of the Gangdese Cretaceous back-arc basin and formation of Proto-plateau, South Tibet

A Cretaceous carbonatite-clasolite-bearing back-arc basin, with a basement of Jurassic volcanic rocks, developed in the south of Gangdese magmatic arc, South Tibet. The basin was featured by a large-scale angular unconformity, overlaid by Linzizong Formation of uppermost Cretaceous-lower Tertiary volcanic-bearing strata, and extensive emplacement of 65 similar to 40Ma granitic plutons. The upper crust deformation in South Gangdese could be mainly expressed as the Gangdese Decollement (GD) of "decollement-fold" structural style, which consists of 1) a main structural plane between Jurassic basement and overlying sediments with a top-to-south shearing sense and 2) overlying Cretaceous sedimentary units with tight folds and listric faults. We suggest the Gangdese Decollement, attributed to the coeval crustal shortening, crustal thickening and orogenesis, was formed due to the northward subduction of Neo-Tethys oceanic lithosphere during 90 similar to 69Ma. The angular unconformity between Linzizong Formation and underlying strata shows as a volcanic drape-style unconformity type, recording the transition from ocean-continent subduction to continental collision, accompanied by regional crustal extension, shortening, orogen uplifting, then denudation and planation. Hence, we propose that an Andes-type South Gangdese Proto-Plateau triggered by northward subduction of Neo-Tethys oceanic lithosphere beneath the southern margin of Asia during the Late Cretaceous, then the whole regional planation occurred before Middle Eocene.