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The Mesozoic geology of SE China is characterized by intensive and widespread magmatism. However, the tectonic regime that accounted for the Mesozoic magmatism has been an issue with little consensus. A comprehensive study of ₄₀Ar-₃₉Ar dating, geochemistry and Sr-Nd isotopes has been conducted on basalts from southern Hunan and syenite intrusions from eastern Guangxi. Three episodes of Jurassic magmatism, i.e. alkaline basalts of c.175 Ma in age, syenitic intrusions of c.160 Ma and high-Mg basalts of c.150 Ma, are identified. The older, c.175 Ma alkaline basalts are characterized by low Sr (I_Sr = 0.7035–0.7040) and high Nd (ε_Nd(T) = 5 to 6) isotopic compositions and OIB-like trace-element patterns (e.g. Nb/La > 1). In contrast, the younger, c.150 Ma high-Mg basalts have high Sr (I_Sr c.0.7054) and low Nd (ε_Nd(T) c.-2) isotopic compositions and incompatible trace-element patterns of arc affinity …