U-Pb ages of zircon from metamorphic dolomite of the Wuliangshan Rock Group in Nanjian area, western Yunnan, and its tectonic significance

The Wuliangshan Rock Group, which is widely exposed in the Nanjian-Yunxian area of western Yunnan, is a set of low and medium metamorphic sedimentary rocks intercalated with volcanic rocks closely related to the Sanjiang Tethys orogenic belt. Its formation age, sedimentary filling sequence and tectonic attributes have been controversial. The Wuliangshan Rock Group, exposed in Gonglong County and Nanjian County, has a metamorphic ananite intercalation several centimeters thick. The zircon U-Pb LAICP-MS dating of the metamorphic andesite Sample was carried out, and the magmatic crystallization age of 428.7±8.7Ma and the metamorphic age of 338~387Ma, 250.5 ±8.1Ma and 146.0 ±6.0Ma were obtained respectively. It is considered that the original sedimentary rocks of the Wuliangshan Rock Group were formed in Silurian and experienced regional metamorphism in the Palaeozoic arc forming process during the Paleo-Tethys Ocean subduction and thermal metamorphism in the Cretaceous period due to thermal events. At the same time, the single grain ages of 2034±22Ma, 1140±16Ma, 731±15Ma and 469~522Ma were obtained, which can be compared with the Precambrian, Paleozoic tectonic caloric event ages and distribution characteristics obtained from the western margin of the Yangtze block. It underwent the formation and breakup of Columbia, Rodinia and Gondwana supercontinent.