Journal Article

Isotopic portrayal of the Earth’s upper mantle flow field

Blichert-Toft, Janne, Humler, Eric, Meyzen, Christine M., Mével, Catherine, Albarède, Francis, Ludden, John N.

2007

Overview

It is now well established that oceanic plates sink into the lower mantle at subduction zones, but the reverse process of replacing lost upper-mantle material is not well constrained. Even whether the return flow is strongly localized as narrow upwellings or more broadly distributed remains uncertain. Here we show that the distribution of long-lived radiogenic isotopes along the world’s mid-ocean ridges can be used to map geochemical domains, which reflect contrasting refilling modes of the upper mantle. New hafnium isotopic data along the Southwest Indian Ridge delineate a sharp transition between an Indian province with a strong lower-mantle isotopic flavour and a South Atlantic province contaminated by advection of upper-mantle material beneath the lithospheric roots of the Archaean African craton. The upper mantle of both domains appears to be refilled through the seismically defined anomaly underlying South Africa and the Afar plume. Because of the viscous drag exerted by the continental keels, refilling of the upper mantle in the Atlantic and Indian domains appears to be slow and confined to localized upwellings. By contrast, in the unencumbered Pacific domain, upwellings seem comparatively much wider and more rapid. The distribution of long-lived radiogenic isotopes along the world's mid-ocean ridges can be used to map geochemical domains, reflecting contrasting refilling modes of the upper mantle. Refilling of the upper mantle in the Atlantic and Indian domains is slow and confined to localized upwellings, whereas in the Pacific, upwellings are comparatively much wider and more rapid.

• Publisher: Nature Publishing Group UK,Nature Publishing,Nature Publishing Group
• Subject: Advection / Cratons / Earth / Earth Sciences / Earth, ocean, space / Exact sciences and technology / Geochemistry / Hafnium / Humanities and Social Sciences / Indian / Internal geophysics / Isotope geochemistry / Isotope geochemistry. Geochronology / Isotopes / Lower mantle / Mantle / Marine / multidisciplinary / Oceanography / Oceans / Plate tectonics / Refilling / Return flow / Ridges / Roots / Science / Sciences of the Universe / Seismic phenomena / Seismology / Solid-earth geophysics, tectonophysics, gravimetry / Upper mantle / Upwelling / Viscous drag