Genesis of Central Indian Ocean basin seamounts: morphological, petrological, and geochemical evidence

Abstract

We present the petrological investigation carried out of the seamounts located between water depths of 4300 and 5385 m in the Central Indian Ocean Basin (CIOB). The seamounts have variable shapes (conical and elongated) and heights (625–1200 m). The basalts have a glassy veneer that forms the outer rind, while the holocrystalline interior shows variable textures. The basalts are plagioclase phyric and compositionally have low FeO* (8.0–10.5 wt%) and TiO2 (1.3–2.0 wt%), and variable K2O (0.1–1.0 wt%) contents and are slightly enriched in the light rare-earth elements. These characteristics are similar to the basalts from the CIOB seafloor and the Central Indian and Southeast Indian Ridges. These facts attest to the simultaneous formation of the CIOB seafloor and associated seamounts that shared a common source between 56 and 51 Ma when the spreading (half) rate was 95 mm/year. Similar to the East Pacific Rise (EPR), the source melt was perhaps ferrobasalts which over a period of time fractionated to N-MORB during the emplacement of the seamounts. The production of the seamounts may have involved a periodic tapping of a regularly replenished and shallow seated source melt. These basalts from the older seamounts of the CIOB are analogous to their present-day counterparts that form at the fast-spreading EPR and other locales in the world oceans.