Elemental and Sr-Nd isotopic systematics of the early Mesozoic volcanic sequence in southern Jiangxi Province, South China: petrogenesis and tectonic implications

Elemental and Sr-Nd isotopic results are presented for the early Mesozoic volcanic sequence (similar to172 Ma) in southern Jiangxi Province, South China. The sequence is voluminously composed of similar to45% subalkaline basaltic rocks (group 1), <5% high-mg andesite-dacites (group 2) and similar to50% rhyolites (group 3). The group 1 rocks are characterized by (La/Yb)(cn) = 3.8-7.2, Eu/Eu* = 0.65-1.15, Nb/La = 0.64-0.99, Sr-87/Sr-86(t) = 0.70602 similar to 0.70822 and epsilon(Nd)(t) = -1.63 to +0.11, similar to those of an EMII-like source. The group 2 rocks have mg = 0.42similar to0.60, SiO2 = 60.24 similar to 66.71%, MgO = 2.65 similar to 5.54%, Ni = 24 similar to 102 ppm and Cr = 84 similar to 266 ppm, classified as high-mg andesitic rocks. These rocks are more enriched in LILEs and LREE with more significant negative Eu anomaly (0.63 similar to 0.79), are more depleted in HFSEs with Nb/La ratios of 0.40-0.56 and have lower epsilon(Nd)(t) (-9.44 to -7.78) and higher Sr-87/Sr-86(t) (0.70985 similar to 0.71016), in comparison with the group 1 rocks. They most likely originated from metasomatised veins in the lithospheric mantle. The origination of the group 1 and group 2 magma suggests the development of a peridotite-plus-vein lithospheric mantle during early Mesozoic era beneath the interior of the Cathaysian block. The group 3 rhyolites are characterized by high SiO2 (72.75 similar to 77.97%), Zr (99 similar to 290 ppm), Hf (3.9similar to9.7 ppm) and Ga/Al (2.76 similar to 3.87) and significant Nb-Ta, Ba-Sr and P-Ti depletions. These rhyolites exhibit Sr-Nd isotopic compositions (Sr-87/Sr-86(t) = 0.70962 similar to 0.71104, epsilon(Nd)(t) = -4.63 to -5.80) similar to the contemporaneous Zhaibei and Pitou A-type granites in the area. Such characteristics suggest that they might be derived from the underplating basaltic magma contaminated by crustal materials. Therefore, an early Mesozoic rifting model in response to intracontinental lithospheric extension is proposed to account for the early Mesozoic volcanism in southern Jiangxi Province, South China.