Partial Melting of Subducted Sediments Produced Early Mesozoic Calc-alkaline Lamprophyres from Northern Guangxi Province South China

摘要

There is growing agreement that subducted sediments recycled into the deep mantle could make a significant contribution to the generation of various mantle-derived rocks. However, solid evidence and examples to support this view are few, and whether or not the subducted sediments can act as the dominating material source for the magma is unclear. Here, we report a comprehensive geochemical study that demonstrates that the newly identified Early Mesozoic calc-alkaline lamprophyres in the northern Guangxi Province, southeastern Yangtze Block in South China were likely derived in large part from the partial melting of the subducted terrigenous sediments in the deep mantle. The investigated lamprophyres are SiO2-rich minettes, characterized by moderate TFeO and MgO and high Mg^# (>70). The multi-element pattern shows a typical crustal-like signature, such as enrichments in large-ion lithophile elements (LILE) and light rare earth elements (LREE) with troughs in Nb-Ta, Ti and Eu and peaks in Th-U and Pb. These rocks also show sediment-like ratios of Nb/U, Nb/Th and Ce/Pb, together with extremely radiogenic ⁸⁷Sr/⁸⁶Sr (0.71499–0.71919), unradiogenic ¹⁴³Nd/¹⁴⁴Nd (0.51188–0.51195) and radiogenic ²⁰⁷Pb/²⁰⁴Pb (15.701–15.718) isotopic compositions.