Mauritius: A Hybrid Island

Like many volcanic islands across the globe, Mauritius, in the Indian Ocean east of Madagascar, was thought to have formed above a hotspot.  In such cases, a mantle plume pushes upward into the oceanic crust, igniting volcanism and the formation of land that gradually emerges from the sea.  If the oceanic plate is moving above the hotspot, a chain of islands is formed (see The Hawaiian Ridge).

The volcanism that produced Mauritius has occurred on and off for about 9 million years.  Recently, however, as reported in the New York Times this week, a geologist has discovered the presence of continental crust beneath the volcanic rock.  In essence, it appears that a hotspot formed adjacent to or beneath the continental fragment or that oceanic crust has been subducting beneath that fragment to produce the volcanism; the latter seems less likely.

The continental fragment itself apparently broke away from Gondwana as it split up to form the Southern Continents (Africa, South America, Antarctica, India and Australia) some 200 million years ago.  The Madagascar-Seychelles platform, north of Mauritius, is also a continental fragment of Gondwana; such fragments move about the globe as oceans open and close and these exotic terranes may eventually fuse to the edge of the major Continents.