HR: 1340h
AN: V13A-1456    [Abstracts]
TI: Slab Devolatilization and Os and Pb Mobility in the Mantle Wedge of the Kamchatka Arc
AU: Saha, A
EM: aniki@earth.rochester.edu
AF: University of Rochester, Department of Earth and Environmental Sciences, Rochester, NY 14627 United States
AU: * Basu, A R
EM: abasu@earth.rochester.edu
AF: University of Rochester, Department of Earth and Environmental Sciences, Rochester, NY 14627 United States
AU: Jacobsen, S B
EM: jacobsen@neodymium.harvard.edu
AF: Harvard University, Department of Earth and Planetary Sciences, Cambridge, MA 02138 United States
AU: Poreda, R J
EM: poreda@earth.rochester.edu
AF: University of Rochester, Department of Earth and Environmental Sciences, Rochester, NY 14627 United States
AU: Yin, Q -
EM: yin@geology.ucdavis.edu
AF: University of California, Davis, Department of Geology, Davis, CA 95616 United States
AU: Yogodzinski, G M
EM: gene@sc.edu
AF: University of South Carolina, Department of Geological Sciences, Columbia, SC 29208 United States
AB: Os-, Nd-, and Pb-isotope measurements were performed on a suite of eleven Kamchatka peridotite mantle xenoliths in andesitic volcanics from the southern (Avachinsky) and central (Sheveluch and Kharchinsky) segments of the Kamchatka peninsula. The peridotite xenoliths studied are mostly wehrlites, harzburgites and dunites. In our previous study of these xenoliths (Basu et al., 2004), petrographic evidence as well as He-, Sr-isotopic, CO$_{2}$ and trace element concentration data were interpreted to indicate that fluids derived from seawater-altered lithosphere moved through the mantle wedge beneath Kamchatka. Peridotites with higher Os content (1.3- 5.2 ppb) show a narrow $^{187}$Os/$^{188}$Os range between 0.1182 and 0.1272 while the xenoliths with lower Os content ($<$ 1 ppb) show a wider variation and more radiogenic $^{187}$Os/$^{188}$Os values (0.1287- 0.1585). $^{187}$Os/$^{188}$Os and $^{3}$He/$^{4}$He (R/Ra) values of the xenoliths indicate that the xenoliths are metasomatized by the slab-derived fluids from the subducting altered oceanic crust. The original Os signature of some of the mantle wedge xenoliths seems to be eradicated and imprinted by the slab fluids from the subducting crust. The Nd-isotopic (+8.7 - +9.3) and Pb-isotopic ratios ($^{206}$Pb/$^{204}$Pb = 18.25- 18.76; $^{207}$Pb/$^{204}$Pb = 15.43- 15.55; $^{208}$Pb/$^{204}$Pb = 37.68- 38.24) of the xenoliths are similar to those of the Pacific MORB. Pb and Ba contents of the xenoliths increase with increasing $^{187}$Os/$^{188}$Os . The Os- and Pb-isotopic data of these xenoliths combined with the He-isotopic data (Basu et al., 2004), indicate that the radiogenic Os-signature and the higher Ba and Pb concentration in these rocks are inherited from the devolatilized altered lithospheric slab. Thus, the mantle-wedge beneath Kamchatka was infiltrated by slab-derived fluids with Os, Pb, and other volatile and fluid-mobile elements.
DE: 1025 Composition of the mantle
DE: 1040 Isotopic composition/chemistry
DE: 1065 Trace elements (3670)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2004 AGU Fall Meeting