Riwanchaka Group in central Qiangtang Basin, the Tibetan Plateau: Evidence from detrital zircons

The Riwanchaka Formation (C1r), a set of carbonate and clastic early Carboniferous strata rich in warm-water fossils, is spread in the Gangmar Co-Riwanchaka area along the central Lungmu Co-Shuanghu-Lancang River suture zone nearly in east-west direction. An analysis of 120 age data of sandstone samples from the Riwanchaka Formation indicates that detrital zircon has six age ranges, which are 325~400Ma, 400~500Ma, 500~600Ma, 950~1100Ma, 1400~1800Ma and >1800Ma, and that the youngest detrital zircon age is 325Ma, which confirms its age of Early Carboniferous. Among these ages, peak ages of 362Ma and 454Ma are the most obvious. They reflect the tectonic magmatic events of the initial arc reduction stage in the Lungmu Co-Shuanghu-Lancang River Ocean and the Caledonian orogeny, implying that the provenance of the clastic rocks was probably the Yangtze Continent. In combination with the information of fossils, the authors hold that the Riwanchaka Formation (C1r) should be Carboniferous sedimentary strata of Eurasia Yangtze type, belonging to the shallow water deposition in an island arc environment.