Other
Scientific paper
May 1986
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1986e%26psl..78..104m&link_type=abstract
Earth and Planetary Science Letters, Volume 78, Issue 1, p. 104-114.
Other
57
Scientific paper
Rare earth element abundances and Sr, Nd, Pb isotope compositions have been measured on zero-age dredge samples from the Rodriguez Triple Junction (RTJ) and the South-East Indian Ridge (SEIR), Along the SEIR, the geochemical ``halo'' of the St. Paul hot spot has a half-width of about 400 km and the data may be fairly well accounted for by a binary mixing between an Indian MORB-type component (87Sr/86Sr = 0.7028, 143Nd/144Nd = 0.51304, 206Pb/204Pb = 17.8) and the plume-type St. Paul component (0.7036, 0.5129, and 18.7 respectively). The alignment of the lead isotope data is particularly good with an apparent age of 1.95 +/- 0.13 Ga and Th/U source value of 3.94. One sample dredged on the ridge 60 km southeast of St. Paul bears a definite Kerguelen isotopic signature.
The RTJ has distinctive geochemical properties which contrast with those of the adjacent ridge segments. Low 206Pb/204Pb ratios which plots to the left of the geochron, rather high 208Ph/204Ph and 87Sr/86Sr ratios (17.4, 37.4, and 0.7031 respectively), a striking isotopic homogeneity, and variable LREE/HREE fractionation with (La/SM)N = 0.3-0.8 make this triple junction an anomalous site.
The geochemical properties of the Indian Ocean basalts have been examined using a three-component mantle model involving (a) a normal MORB-type source though to represent the depleted upper mantle matrix, (b) an OIB-type source of uncertain parentage (recycled oceanic crust?), and (c) a component with low μ, low Sm/Nd, high Rb/Sr (time-averaged value) which is tentatively assigned to ancient hydrothermal and abyssal sediments recycled in the mantle. The high 201Ph/204Ph and 87Sr/86Sr ratios typical of the Dupal anomaly are likely due to the widespread distribution of this latter component in the basalt source from this area, including that for MORBs.
Michard Annie
Montigny Raymond
Schlich Roland
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