LA-ICP-MS zircon U-Pb age of metamorphic basic volcanic rock in Gongyanghe Group of southern Gaoligong Mountain, western Yunnan Province, and its geological significance

Gongyanghe Group, which was named in 1965, is composed of epimetamorphic sandstone and shale interlayered with small amounts of siliceous rock (or siliceous shale) and limestone and represents a set of turbid flow and bathyal facies sediments with flyschoid rhythm and rare organisms. Its age has been generally considered to be between Sinian and Middle Cambrian, which, however, is not based on the evidence of fossils or accurate dating. In this study, the authors identified the stratigraphic sequence composed of several layers of metamorphic basic volcanic rock in Bangmai Village of Longling County. It is held that its original rock was basalt formed in an intra-continental tension environment and probably related to extension after the Pan-African orogenic period. The authors got for the first time the U-Pb age (499.2Ma±2.1Ma) of zircon from metamorphic basic volcanic rock and thus provided a reliable chronological basis for the division of the Gongyanghe Group and the restriction of the age. This achievement is very important for the further study of the tectonic characteristics and history of the deformed metamorphic belt of the Gaoligong Mountain.