U-Pb age, geochemistry characteristics and tectonic setting of basalt in the Zhilingtou area, Zhejiang Province

In order to deepen the understanding of the Cretaceous tectonic setting in the eastern part of South China, the petrological, geochemical and Sr-Nd-Hf isotope analyzes of the basalt in the Zhilingtou area of Zhejiang Province were carried out.The basalt are massive and porphyritic, and the phenocrysts consist of plagioclase and hornblende.LA-ICP-MS zircon U-Pb dating shows that the age is 101±1 Ma, which is the product of Early Cretaceous magmatic activity.The results of geochemical analyzes show that the basalt has the characteristics of rich alkali, high K₂O/Na₂O ratio, high K₂O+Na₂O value, and high Al₂O₃ content, enrichment in large ion lithophile elements(Rb, Sr)and light rare earth elements, depletion in high field strength elements(Nb, Ta, Ti, Hf).The distribution curve of rare earth elements is generally right-sloping, with a weak positive Eu anomaly, which should belong to potash basalt series, and has experienced a certain degree of fractional crystallization during the magma evolution process.The ratios of Th/La, Th/Ce and Lu/Yb are closer to the ratio of mantle-derived magma.(⁸⁷Sr/⁸⁶Sr)_i=0.70729-0.71029, ε_Nd(t) and ε_Hf(t) values range from -19.7 to -11.8 and -9.7 to -0.8, respectively, indicating that the source area of basalt has the characteristics of EMⅠ-enriched mantle, and a small amount of crustal material is also involved.Structural discriminant diagrams show that basalt was formed in an intraplate extensional environment.In combination with the spatiotemporal distribution and geochemical characteristics of Late Mesozoic basic magma in South China, and with the continuous rollback of the paleo-Pacific plate, South China was a backarc spreading tectonic environment in the Early Cretaceous.The EMⅠ-type enriched mantle formed by fluid metasomatism generated by dehydration of subduction plates partially melted and ejected from the surface to form the basalt in the Zhilingtou area.