The Indian Ocean is characterized by scattered elevated platforms and ridges which influence
bottom-water circulation and inter-basin communication. The origin of these ridges has been
ascribed to continental fragments, ancient island arcs, and volcanic activity associated with either
fracture zones in the oceanic crust or stationary hot spots. Leg 115 investigated the nature of
basement rocks underlying the Mascarene Plateau and the Chagos-Maldive-Laccadive Ridge, a
system which, with Ninetyeast Ridge, were thought to have formed over hot spots now located near
Reunion and Kerguelen islands, respectively. Drilling results obtained from sites along the proposed
Reunion hot spot track support the hot spot model of increasing age of volcanism northward toward
India. The basalts are derived from mixtures of magmas from both hot-spot and spreading-ridge
melting regions. The hot spot started beneath the Indian Plate, was crossed by that spreading ridge
at about 35 Ma, and has since been under the African Plate. Similarly, the Kerguelen hot spot was
overrun by the Southeast Indian Ridge and separated from its volcanic trail, the Ninetyeast Ridge.
Basalts at the northern end of the lineament in the Maldive archipelago are geochemically similar to
Reunion basalts and were probably formed in an intraplate setting. Paleomagnetic measurements
indicate paleolatitudes of ~28°S at 35 Ma, 7°S of the present-day Reunion hot spot.
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