Stratigraphic characteristics and sedimentary environments of the Upper Triassic Rola Kangri Group Complex on the northern margin of North Qiangtang continental block

The Upper Triassic Rola Kangri Group Complex on the northern margin of the North Qiangtang continental block occurs in the Rola Kangri thrust fault sandwiched between the North Qiangtang continental block and Lazhuglung-Jinshajiang suture zone,and consists of sandy and muddy flysch,intermediete,basic and ultrabasic volcanic rocks,and marble associations intercalated with the Late Permian limestone and ophiolite relicts.These rocks are slightly to moderately metamorphosed and highly deformed.The intermediate to basic volcanic rocks in the Rola Kangri Group Complex have an oceanic island and island-arc origin and generated during the southward subduction of the Jinshajiang oceanic basin during the Late Triassic.Abundant Late Triassic fossils including sporopollen,brachiopods and bivalves collected from the Rola Kangri Group Complex and Ar-Ar ages dated 201±4 Ma of basalt indicate that the Rola Kangri Group Complex should be traced back to the Norian(Late Triassic).