HR: 14:40h
AN: V52D-05    [PDF]
TI: He, Sr, Nd, and Pb isotopic variations in basaltic lavas from Marquesas Archipelago, south-central Pacific
AU: * Castillo, P R
EM: pcastillo@ucsd.edu
AF: Scripps Institution of Oceanography, UCSD, La Jolla, CA 92093-0212 United States
AU: Craig, H
AF: Scripps Institution of Oceanography, UCSD, La Jolla, CA 92093-0212 United States
AU: Scarsi, P
EM: paolo.scarsi@pa.iasf.cnr.it
AF: Scripps Institution of Oceanography, UCSD, La Jolla, CA 92093-0212 United States
AB: The Marquesas Archipelago is one of the proposed hotspot volcanic chains in French Polynesia. Previous studies have suggested that the volcanic chain is being built by melts from two plume end-components originating from deep thermal boundary layers (EM2 and HIMU), and interacting with the oceanic lithospheric mantle (DMM) and/or crust (e.g., Dupuy et al., ESPSL 82, 1987; Desonie et al., JGR 98, 1993; Caroff et al., Lithos 46, 1999). Effects on plume melts of shallow lithosphere and crustal contamination through melting, magma mixing and wall-rock assimilation coupled with AFC processes are most apparent in intermediate lavas. To minimize the signature of the lithosphere mantle and crust on the purported plume-generated lavas, we analyze only high magnesian (MgO = 7 to 37 wt%) basalts, picrites and a gabbro for Sr, Nd and Pb isotopes. Olivine separates from these samples have been previously analyzed for He isotopes by Scarsi \& Scarsi (Nuovo Cimento Della S.I.F. 23, 2000). The basaltic lavas show significant isotopic variations. Although plots of Sr, Nd and Pb isotopic ratios show simple binary relationships, plots of 3He/4He vs. 87Sr/86Sr and 3He/4He vs. 207Pb/204Pb suggest three possible plume end-components. In addition to EM2 and HIMU, which are believed to be recycled crustal materials, there is a trace of a component with high 3He/4He (up to 14.4 R/RA), near bulk-earth 87Sr/86Sr (0.7047) and 143Nd/144Nd (0.51284, e = 3.9) and radiogenic 206Pb/204Pb (19.01). This component points toward the PHEM (FOZO or "C") region in some of the permutations of isotope plots, and thus may provide evidence for the existence of a common, near-primitive mantle source for some hotspot lavas.
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
DE: 1025 Composition of the mantle
DE: 1040 Isotopic composition/chemistry
DE: 1065 Trace elements (3670)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting