Arabian-Indian Ridge

a submarine midocean ridge in the northwestern Indian Ocean. It stretches 4,500 km from the Gulf of Aden to Rodriguez Island. It is up to 750 km wide. The prevalent depths over the crest are 2,500–3,000 m; the smallest depths are as little as 1,658 m. The surface of the ridge is strongly dissected and in places is complicated by zones of cross fractures. Narrow rift fissures up to 6,492 m deep are located near the crest. In 1964, Soviet scientists on the ship Vitiaz’ observed the first exposures of ultrabasic rock in a midocean ridge; this rock may be the very little changed substance of the earth’s mantle.