Trace element and Nd-Sr-Pb isotope studies of Mesozoic and Cenozoic basalts in coastal area of SE China.
中国东南沿海中-新生代玄武岩微量元素和Nd-Sr-Pb同位素研究

Trace element and Nd-Sr-Pb isotopic compositions of mantle xenolith-free Mesozoic basalts and mantle xenolith-bearing Cenozoic basalts in the coastal area of SE China are studied to provide an insight into the nature of their mantle sources and processes. The Mesozoic basalts have negative Ta, Nb and Hf anomalies, low Ce/Pb, Nb/U and high La/Nb ratios, similar to those for island arc volcanics and continental crustal rocks, suggesting a mixing of chemical components of mantle and the continental crust during the generation and ascending of the magma. In contrast, the Cenozoic basalts have positive Ta, Nb anomalies and negative Pb anomalies, high Ce/Pb, Nb/U and low La/Nb ratios, similar to those for oceanic island basalts (OIB); in addition, their Nd-Sr isotopic compositions are similar to those for Hawaiian basalts, so they haven' t been significantly contaminated by crustal components. Furthermore, the negative relationship between 143Nd/144Nd and 206Pb/204Pb, and the positive relationship between 87Sr/86Sr and 206Pb/204Pb suggest that the Cenozoic basalts in the studied area were generated from the intermediate-depleted asthenospheric mantle and EMII component.