Osmium isotopic constraints on the nature of the DUPAL anomaly from Indian mid-ocean-ridge basalts

S. Escrig (), F. Capmas, B. Dupré and C. J. Allègre
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S. Escrig: Institut de Physique du Globe de Paris, Université Denis Diderot (Paris 7)
F. Capmas: Institut de Physique du Globe de Paris, Université Denis Diderot (Paris 7)
B. Dupré: Université Paul Sabatier
C. J. Allègre: Institut de Physique du Globe de Paris, Université Denis Diderot (Paris 7)

Nature, 2004, vol. 431, issue 7004, 59-63

Abstract: Abstract The isotopic compositions of mid-ocean-ridge basalts (MORB) from the Indian Ocean have led to the identification of a large-scale isotopic anomaly relative to Pacific and Atlantic ocean MORB1. Constraining the origin of this so-called DUPAL anomaly2 may lead to a better understanding of the genesis of upper-mantle heterogeneity. Previous isotopic studies3,4,5,6,7,8,9,10 have proposed recycling of ancient subcontinental lithospheric mantle or sediments with oceanic crust to be responsible for the DUPAL signature. Here we report Os, Pb, Sr and Nd isotopic compositions of Indian MORB from the Central Indian ridge, the Rodriguez triple junction and the South West Indian ridge. All measured samples have higher 187Os/188Os ratios than the depleted upper-mantle value11,12 and Pb, Sr and Nd isotopic compositions that imply the involvement of at least two distinct enriched components in the Indian upper-mantle. Using isotopic and geodynamical arguments, we reject both subcontinental lithospheric mantle and recycled sediments with oceanic crust as the cause of the DUPAL anomaly. Instead, we argue that delamination of lower continental crust may explain the DUPAL isotopic signature of Indian MORB.

Date: 2004
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DOI: 10.1038/nature02904

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