Study on the Sr, Nd, Pb and O Isotopes of Basic Dyke Swarms in the Wudang Block and Basic Volcanics of the Yaolinghe Group

摘要

The Sr, Nd and Pb isotopic characteristics of the Wudang basic dyke swarms and basic volcanics of the Yaolinghe Group show that they were derived from the same multi|component mixing source in the mantle. The Wudang basic dyke swarms have ({}+{87}Sr/{}+{86}Sr)-i={0.6905}～{0.7061}, ε-{Nd}(t)={-1.9}～{5.0}, Δ{}+{208}Pb/+{204}Pb={35.49}～{190.26}, Δ{}+{207}Pb/{}+{204}Pb=4～85, low Th/Ta and a wide range of La/Yb ratios; and the basic volcanics of the Yaolinghe Group have ({}+{87}Sr/{}+{86}Sr)-i={0.6487}～{0.7075}, ε-{Nd}(t)={0.11}～{3.94}, Δ{}+{208}Pb/{}+{204}Pb={-81.58}～{219.95}, Δ{}+{207}Pb/{}+{204}Pb={4.44}～{16.68} and higher Th/Ta and La/Yb ratios, indicating that their source is a mixture of DM and EMII, and the basic volcanics of the Yaolinghe Group were contaminated by crust materials en rout to the surface. Based on the geochemical features of continental tholeiitic basalts and being products of different facies derived from the same source, it can be concluded that an important rifting event in the South Qinling basement block occurred during Neoproterozoic, followed by a setting of oceanic basin in the Early Paleozoic.