Geochemistry and petrogenesis of Quaternary basalts from Weizhou Island, northwestern South China Sea: Evidence for the Hainan plume

Abstract

Weizhou Island, located in the northwestern South China Sea (SCS), is the largest volcanic island in China. Its eruption represents the most recent volcanic activity in and around the SCS. We determined whole-rock major- and trace-element contents and Hf–Sr–Nd–Pb isotope compositions of Quaternary basalts from Weizhou Island to provide insights into the nature of their mantle sources and formation processes. These basalts have SiO2 contents of 48.21 to 50.04 wt% and belong to the alkaline series. The basalts bear the signature of typical ocean-island basalt, being characterized by enrichments in large-ion lithophile and high-field-strength elements, clear differentiation of light rare-earth elements (REEs) from heavy REEs ((La/Yb)N = 15.19–19.29, mean of 16.82), and show no obvious Eu anomalies (Eu/Eu* = 0.98–1.17, mean of 1.04). Hf–Sr–Nd–Pb isotope compositions show that the mantle source of these basalts can be regarded as a mixture of a depleted MORB mantle source and enriched mantle 2 (EM2), with geochemical data supporting an origin of the EM2 end-member from the Hainan mantle plume. Combining the new results with previous findings, we propose that Cenozoic intraplate volcanism in the SCS and surrounding areas is related to the magmatic activity of a large igneous province and that this province is associated with the Hainan mantle plume.