A Plateau Below

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Science  26 Jul 2002:
Vol. 297, Issue 5581, pp. 479
DOI: 10.1126/science.297.5581.479c

Volcanic flood basalt provinces have generally been thought to arise within 5 million years, which is a relatively short time scale for geology. The Keguelen Plateau in the South Indian Ocean, one of the largest oceanic plateaus, has been thought to have formed from a large outpouring of basaltic lava and would thus be one of the largest such provinces on Earth. Although it may have been emergent for a considerable part of its history, its remote location (mostly 1 km or more below sea level) has made its origin speculative. A recent oceanic drilling program leg aimed at understanding its origin and history has now provided dating results that imply that major volcanic eruptions commenced about 120 million years ago. Although large volumes of magma erupted near that time, significant volcanic eruptions continued subaerially for about 25 million years, which is much longer than would be expected for the melting of a single plume in the mantle. Parts of the plateau at least are underlain by continental crust that is likely to be fragments of India that were adjacent to the plateau as it began to form. Evidence for crustal contamination is seen in the earlier magmas but not in volcanism on the Plateau after about 20 million years ago. This suggests that a change occurred in the source region at depth in the mantle. — BH

J. Petrol.43, 1109 (2002).

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