Geochronology and geochemistry of volcanic rocks in Huaining basin in comparison with other basins in the middle-lower Yangtze region

Abstract：The volcanic rocks in Huaining basin, one of a series of late Mesozoic volcanic basins developed in the Middle-lower Yangtze region, are characterized by high K and rich alkali and mainly belong to typical shoshonitic series. However, bimodal volcanic association appeared at the late stage of volcanism in Huaining basin. The volcanic rocks in the basin are all depleted in high-field-strong-elements (HFSE) such as Nb and Ta, and enriched in strong incompatible elements such as Rb, Th, U and K as well as light rare earth elements (LREE). In this study, the authors used SHRIMP and LA-ICP-MS zircon U-Pb technique to date the samples from Pengjiakou Formation and early volcanism respectively in Huaining basin, and obtained emplacement ages of 129.4±1.6 Ma and 131.6±0.6 Ma respectively. The age of 122.3±0.7 Ma was also obtained by LA-ICP-MS zircon U-Pb technique for rhyolite from Jiangzhen Formation, which is late volcanism in Huaining basin. Based on a comparison with other volcanic basins in the Middle-lower Yangtze region, the authors found that the ages of volcanism in Huaining basin are similar to those of such other volcanic basins in the Middle-lower Yangtze region as Luzong basin and Ningwu basin; nevertheless, the end of volcanism in Huaining basin occurred about 6 Ma later than other volcanic basins. The volcanic rocks in Huaining basin have wider variation range and lower εNd(t) values than other shoshonite volcanic basins in the Middle-lower Yangtze region, which may be related to the fact that their tectonic setting was near the Dabie orogen, and hence more crust materials were added to the magma. The proto magma of Huaining volcanic basin mainly came from partial melting of the enriched mantle, with different degrees of mixture of lower crust materials during the magmatic evolution.