Coexistence of pumice and manganese nodule fields—evidence for submarine silicic volcanism in the Central Indian Basin

Abstract

Pumice, of various shapes and sizes, uncoated or coated by ferromanganese oxides, have been recovered from deeper parts of the Central Indian Basin (CIB). The pumice field covers an area of 600,000 km 2, approximately encompassing one-ninth of the basinal area. Such a large field we believe, has not been reported previously in the world oceans. Pumice occurs as the nucleus for manganese nodules, suggesting that the morphology of pumice decide the shape, size and surface texture of the nodules. First-generation mine-sites of manganese nodules, of high abundance and paramarginal ore grade, seem to be closely related to the pumice field. Circumstantial evidence, i.e. juxtaposed pumice and nodule fields in the vicinity of three major fracture zones (73°E, 75°45′E and 79°E) and a number of seamounts and abyssal hills within and around the fields, suggest a tectonic control on the distribution of pumice. Further, it is speculated that in situ submarine silicic volcanism in the basin was responsible for the huge deposition of pumice. We rule out the possibility of drift pumice from any known sources. Chemical analysis of pumice from the CIB supports such a contention.