Abstract: The Youjiang Fold Belt is located in the connection region between Yangtze Block and Cathaysia Block. It is characterized by Late Yanshanian bimodal magmatic activities and consists of basic-ultrabasic dyke swarms and ultra-acid rock veins. In this study, the phlogopite ⁴⁰Ar/³⁹Ar dating of phenocryst and matrix from phlogopite lamproite veins, which are located in the Du' an County of central Guangxi, yielded two plateau ages of 93.6±0.6Ma, 92.9±0.6Ma and two isochron ages of 93.4±0.9Ma, 92.7±0.8Ma, respectively. These ages are interpreted as the emplacement age for phlogopite lamproite veins. The new results obtained by the authors in junction with the coeval magmatic events further reveal that the voluminous Late Cretaceous bimodal magmatic activities occurred in the Youjiang Fold Belt as well as its peripheral regions in response to the Late Yanshanian tectonic transition and subsequent lithospheric thinning and extension in South China.