Petrological Characteristics and Genesis of the Central Indian Ocean Basin Basalts

The Central Indian Ocean Basin (CIOB) basalts are plagioclase‐rich, while olivine and pyroxene are very few. The analyses of 41 samples reveal high FeO^T (～10–18 wt%) and TiO₂ (～1.4–2.7 wt%) indicating a ferrobasaltic composition. The basalts have high incompatible elements (Zr 63–228 ppm; Nb ～1–5 ppm; Ba ～15–78 ppm; La ～3–16 ppm), a similar U/Pb (0.02–0.4) ratio as the normal mid‐oceanic basalt (0.16±0.07) but the Ba/Nb (12.5–53) ratio is much larger than that of the normal mid‐oceanic ridge basalt (～5.7) and Primitive Mantle (9.56). Interestingly almost all of the basalts have a significant negative Eu anomaly (Eu/Eu*=0.78–1.00) that may have been a result of the removal of feldspar and pyroxene during crystal fractionation. These compositional variations suggest that the basalts were derived through fractional crystallization together with low partial melting of a shallow seated magma.