| Abstract |
Rare earth element abundances and Sr, Nd, Pb isotope compositions have been measured on zero-age dredge sample 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 plus or minus 400 km and the data may be fairly well accounted for by a binary mixing between an Indian MORB-type component ( super(87)Sr/ super(86)Sr = 0.7028, super(143)Nd/ super(144)Nd = 0.51304, super(206)Pb/ super(204)Pb = 17.8) and the plume-type St. Paul component (0.7036, 0.5129, and 18.7 respectively). The RTJ has distinctive geochemical properties which contrast with those of the adjacent ridge segments. Low super(206)Pb/ super(204)Pb ratios which plot to the left of the geochron, rather high super(208)Pb/ super(204)Pb and super(87)Sr/ super(86)Sr ratios (17.4, 37.4, and 0.7031 respectively), a striking isotopic homogeneity, and variable LREE/HREE fractionation with (La/Sm) sub(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. |
