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505483 
Journal Article 
Influence of the Amsterdam/St. Paul hot spot along the Southeast Indian Ridge between 77 degrees and 88 degrees E: Correlations of Sr, Nd, Pb, and He isotopic variations with ridge segmentation 
Nicolaysen, KP; Frey, FA; Mahoney, JJ; Johnson, KTM; Graham, DW 
2007 
Yes 
Geochemistry, Geophysics, Geosystems
ISSN: 1525–2027 
8 
9 
Q09007 
English 
The submarine Amsterdam-St. Paul ( ASP) Plateau, bisected by the Southeast Indian Ridge (SEIR), is a bathymetric high rising similar to 2 km above the surrounding seafloor that includes the islands of Amsterdam and St. Paul; this excess volcanism is attributed to a mantle hot spot. We obtained new Sr, Nd, and Pb (n = 37) and He isotopic ( n = 10) ratios for basalt glasses from 11 SEIR segments on and adjacent to the plateau and from three seamounts on the plateau. The results show systematic spatial variations in these isotopic ratios that correlate with physical segmentation of the ridge. Specifically, lavas from the four ridge segments on the ASP Plateau have higher Pb-208/Pb-204 at a given Pb-206/Pb-204 than SEIR basalts distant from ASP Plateau. Surprisingly, lavas from the ridge segment 100 km north of the ASP Plateau are distinguished by the most radiogenic Pb-206/Pb-204 (up to 19.4) and highest He-3/He-4 ratios (up to 14.1 R-A). These are characteristics of lavas erupted at Amsterdam and St Paul Islands. The isotopic data for SEIR basalts erupted on or adjacent to the ASP Plateau provide equivocal evidence for a mantle component derived from the distant Kerguelen hot spot. Overall, the Pb-Nd-Sr-He isotope variations within this data set are explained well by three mantle end-members: (1) depleted mantle having relatively low Pb-206/Pb-204 and Sr-87/(86) Sr and high Nd-143/Nd-144, which has been variably mixed with (2) material having relatively high Pb-208/Pb-204 and Sr-87/Sr-86 and low Nd-143/Nd-144, a signature commonly ascribed to detached or eroded metasomatized continental lithosphere, and (3) hot spot related mantle having elevated He-3/He-4 and Pb-206/Pb-204 but intermediate Sr-87/Sr-86 and Nd-143/Nd-144, similar to the common or C material observed in hot spots globally. These results suggest either that the ASP hot spot is isotopically heterogeneous or that the shallow mantle or lithosphere beneath the ASP Plateau contains more continentally derived material than the SEIR mantle >= 500 km away. Perhaps, like the 39 degrees-41 degrees E section of the Southwest Indian Ridge, beneath the ASP Plateau there are rafts of continental material stranded within a local "tectonic corridor,'' possibly present since the opening of the Indian Ocean basin. 
Southeast Indian Ridge; DUPAL; hot spot-ridge interaction; Amsterdam-St. Paul; Indian ocean; mantle geochemistry; mid-atlantic ridge; kerguelen archipelago basalts; rodriguez triple; junction; mantle heterogeneity; broken ridge; elan bank; geochemical; characteristics; flood basalts; ocean basalts; island lavas