Geochemistry of Cretaceous basalts from the Ontong Java Plateau: Implications for the off-axis plume–ridge interaction

Abstract

Ontong Java Plateau (OJP) is the largest known igneous province preserved on Earth. The hypotheses for the origin of the OJP volcanic activities remain controversial. Here we report new major, trace-element, and Sr–Nd–Pb isotopic compositions from volcanic rocks from Ocean Drilling Program Sites 1183, 1185, 1186, and 1187 of the OJP. Samples from the OJP are tholeiitic in composition and can be divided into low- and high-Ti groups, display flat rare-earth elements (REEs) distributions that are generally similar to normal mid-ocean-ridge basalt (N-MORB) patterns with slightly positive Nb, Ta, Th, U, and Ti anomalies and negative K, Pb, and Sr anomalies. However, OJP samples have significantly enriched 87Sr/86Sr (0.703641–0.704629), 143Nd/144Nd (0.512941–0.512972), and 206Pb/204Pb (18.493–18.940) radiogenic isotopic ratios, indicating that at least three distinct FOZO-type, EM1-type, and HIMU-type enriched components are involved. Combining with the method of principal component analysis, the special geochemical compositions with depleted N-MORB-incompatible elements and enriched isotopes of OJP volcanic samples could be explained by the off-axis ridge–plume interaction model. Due to the influence of strong ridge tensile forces, the off-axis plume magmatic mantle would flow to the ridge axis and undergo decompression melting, resulting in the depletion of the highly incompatible elements but the invariability of the isotopic compositions due to the relatively long half-life of the radiogenic elements. We speculate that these isotopically enriched N-MORB-type basalts may be an exclusive product of an off-axis ridge–plume interaction.