HR: 1340h
AN: V33A-1169    [Abstracts]
TI: Correlation of Sr, Nd, Pb and He Isotopic Variation With Ridge Segmentation: Interaction Between the Southeast Indian Ridge (77-88°E) and the Amsterdam/St. Paul Hotspot
AU: * Nicolaysen, K E
EM: nicolakp@whitman.edu
AF: Department of Geology, Whitman College, Walla Walla, WA 99362, United States
AU: * Nicolaysen, K E
EM: nicolakp@whitman.edu
AF: Department of Geology, Kansas State University, Manhattan, KS 66506, United States
AU: * Nicolaysen, K E
EM: nicolakp@whitman.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, M.I.T., Cambridge, MA 02139, United States
AU: Frey, F A
EM: fafrey@mit.edu
AF: Department of Earth, Atmospheric and Planetary Sciences, M.I.T., Cambridge, MA 02139, United States
AU: Mahoney, J J
EM: jmahoney@soest.hawaii.edu
AF: School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI 96822, United States
AU: Johnson, K T
EM: kjohnso2@hawaii.edu
AF: School of Ocean and Earth Science and Technology, University of Hawaii, Honolulu, HI 96822, United States
AU: Graham, D W
EM: dgraham@coas.oregonstate.edu
AF: College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, United States
AB: The Southeast Indian Ridge (SEIR) bisects the Amsterdam-St. Paul (ASP) Plateau, which is a submarine, bathymetric high that includes the islands of Amsterdam and St. Paul and which rises two km above the surrounding seafloor. The origin of this volcanic plateau is attributed to a mantle hot spot. We obtained Sr, Nd, and Pb (n=37) and He isotope ratios for basalt glasses from 11 SEIR segments on and adjacent to the plateau and from three plateau seamounts. 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 ²⁰⁸Pb/²⁰⁴Pb at a given ²⁰⁶Pb/²⁰⁴Pb, than SEIR MORB (mid-ocean ridge basalt) distant from ASP. Surprisingly, lavas from the ridge segment 100 km north of the ASP Plateau are distinguished by the most radiogenic ²⁰⁶Pb/²⁰⁴Pb (up to 19.5) and highest ³He/⁴He ratios (up to 14.1 R_Air). These are characteristics of lavas erupted at Amsterdam and St Paul Islands; consequently. Overall, the Pb-Nd-Sr-He isotope variations within this dataset are explained well by the interaction of three mantle end-members: 1) depleted mantle with relatively low ²⁰⁶Pb/²⁰⁴Pb and ⁸⁷Sr/⁸⁶Sr, and high ¹⁴³Nd/¹⁴⁴Nd, which has been variably mixed with 2) material with relatively high ²⁰⁸Pb/²⁰⁴Pb and ⁸⁷Sr/⁸⁶Sr and low ¹⁴³Nd/¹⁴⁴Nd at a given ²⁰⁶Pb/²⁰⁴Pb, a signature commonly ascribed to detached or eroded metasomatized, continental lithosphere, and 3) hotspot-related mantle with elevated ³He/⁴He and ²⁰⁶Pb/²⁰⁴Pb but intermediate ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd, similar to the common or C material observed in hotspots globally. These results suggest either that the ASP hotspot is isotopically heterogeneous or that the lithosphere or shallow asthenosphere beneath the ASP Plateau contains more continentally-derived material than the SEIR mantle > 500 km away. Perhaps rafts of continental material lie stranded within a local °tectonic corridor° beneath the ASP Plateau, possibly since the opening of the Indian Ocean basin.
DE: 1009 Geochemical modeling (3610, 8410)
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 1038 Mantle processes (3621)
DE: 1040 Radiogenic isotope geochemistry
DE: 9340 Indian Ocean
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting