Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.v23e0690m&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #V23E-0690
Physics
1025 Composition Of The Mantle, 1032 Mid-Oceanic Ridge Processes (3614, 8416), 3614 Mid-Oceanic Ridge Processes (1032, 8416), 3619 Magma Genesis And Partial Melting (1037), 8416 Mid-Oceanic Ridge Processes (1032, 3614)
Scientific paper
Isotopic studies of MORB have established the existence of broad isotopic provinces within the underlying asthenosphere, such as in the Indian Ocean (DUPAL). How these features relate to mantle circulation is, however, still unknown. The steepness of the transition between such isotopic provinces will define the geometry of the velocity field in the upper mantle. In this respect, the transition between the Indian and South Atlantic provinces, two domains that are isotopically contrasted, should be readily identifiable over this long ridge segment. Here, we present Hf isotope data for 60 samples dredged along the SWIR between 35° and 69°E. The new Hf isotope data show that the Indian asthenosphere does not spill directly into the South Atlantic upper mantle: the general decreasing southward gradient observed for ^{176}Hf/^{177}Hf down the mid- Atlantic Ridge, and also for Sr isotopes and model Th/U ratios (derived from Pb isotopes), is overprinted by material with radiogenic Sr, unradiogenic Hf and high Th/U. The Indian domain grades into the South Atlantic around Bouvet, while the South Atlantic collides with the Atlantic province around Tristan. We interpret these features to represent fronts between three adjacent isotopic provinces similar to what has been suggested for the Australian-Antarctic Discordance. The common DUPAL signature of MORB and OIB from the Indian province and the geochemistry of Gulf of Aden MORB and the Afar plume suggest that the source of this distinctive mantle component is deep and lies to the north of the province. This is also what the three-dimensional flow field computed by Behn et al. (2004) from shear-wave splitting shows with a major lower mantle upwelling radiating at the base of the asthenosphere under the Afar plume. Lower mantle gushing out from this source flows southward unimpeded along the Indian ridges, whereas it only reaches the South Atlantic ridge after first having been deflected under the deep roots of the South African Archean cratons. Erosion of these roots by the asthenospheric drift confers a distinct continental signature on the source of South Atlantic MORB. This pattern is also consistent with the observation that the lowest He isotope values occur, on average, along the South Atlantic ridge. To some extent, the dynamics of the North Atlantic upper mantle mirrors the Indian situation: the flow field of Behn et al. (2004) shows that the North Atlantic asthenosphere also fills up through deep mantle upwellings, which is consistent with the Dupal-like isotopic signature of the Arctic ridges. M.D. Behn, C.P. Conrad and P.G. Silver (2004), Detection of upper mantle flow associated with the African Superplume, Earth. Planet. Sci. Lett., 224, 259-274.
Albarède Francis
Blichert-Toft Janne
Humler Eric
Ludden John
Mével Catherine
No associations
LandOfFree
The Upper Mantle Flow Field around South-Africa as Reflected by Isotopic Provinciality does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The Upper Mantle Flow Field around South-Africa as Reflected by Isotopic Provinciality, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The Upper Mantle Flow Field around South-Africa as Reflected by Isotopic Provinciality will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-963108