Rocks from the Mid-Oceanic Ridge in the Indian Ocean

Abstract

Previous study of rocks from the Mid-Indian Oceanic Ridge has been limited to specimens from dredge hauls taken from a few restricted areas. Those described in this report were recovered exclusively from piston cores taken from thousands of miles apart between 06°50′N, 60° 12′E; and 31° 38′S, 83° 48·5′E and at depths between 2400 and 4300 m. They have an average diameter of about 4 cm and were buried under 20–856 cm of unconsolidated sediment of Pleistocene and younger age.Twenty-four of the thirty-two samples examined are basalts and two are spilites derived from basaltic lava on the Cralsberg Ridge near 02° 50′N; 67° 31′E. Four specimens of pyroclastic glassy sand and vesiculated basalt are a product of aerial volcanism between the islands of Réunion and Mauritius. Two serpentinized periodotites were collected close to the Rodriguez Fracture Zone between 20°S; 61°E and 21°S; 71°E. The basalts and serpentinites of the Mid-Indian Oceanic Ridge are similar to those from the Mid-Atlantic Ridge.Chemical analyses of the Indian Ocean rocks indicates that different petrologic provinces exist along the Mid-Indian Oceanic Ridge. Differentiation processes have concentrated more mafic elements on the Carlsberg Ridge than any other portion of the Ridge investigated, with the exception of high volcanoes which are built up of alkali-basalts.