LA-ICP-MS zircon U-Pb dating of the Chongshan Group in the Xiaowan area along the southern section of the Lancang River in western Yunnan and its geological significance

This paper focuses on the LA-ICP-MS U-Pb ages of the zircons of five samples(mylonitization plagioclase leptynite, bio-tite amphibolites, gneiss, mylonitization granitic gneiss, and mylonitization biotite amphibolites)from the Chongshan Group in the Xiaowan area along the southern section of Lancang River of western Yunnan.Cathodoluminescence images of five samples reveal that these zircon crystals generally have oscillatory zoning, implying their magatic genesis.One hundred and two analyses of five sam-ples yielded concordance, with their weighted average ages being 239.4±3.8Ma, 248.4±4.3Ma, 237.1±5.7Ma, 268.7±3.2Ma, and 238.4±5.5Ma.According to geological characteristics and available age data, it is considered that the so-called Chongshan Group in the Xiaowan area is orthometamorphite composed of various parent components with different ages rather than entirely Proterozoic crystalline basement rocks as previously considered.