HR: 0800h
AN: V21B-0607    [Abstracts]
TI: Constraints on Melting Beneath the Slow-Spreading Kolbeinsey Ridge from 238U, 230Th, and 231Pa Excesses
AU: * Elkins, L J
EM: lelkins@whoi.edu
AF: WHOI, MS#22, Woods Hole, MA 02543,
AU: Sims, K W
EM: ksims@whoi.edu
AF: WHOI, MS#22, Woods Hole, MA 02543,
AU: Prytulak, J
EM: J.Prytulak@bristol.ac.uk
AF: University of Bristol, Dept. Earth Sciences, Bristol, BS8 1RJ, United Kingdom
AU: Mattielli, N
EM: nmattiel@ulb.ac.be
AF: Universite Libre de Bruxelles, Dept. Sciences de la Terre, Brussells, B-1050, Belgium
AU: Elliott, T
EM: tim.elliott@bristol.ac.uk
AF: University of Bristol, Dept. Earth Sciences, Bristol, BS8 1RJ, United Kingdom
AU: Blichert-Toft, J
EM: jblicher@ens-lyon.fr
AF: ENS de Lyon, 46, Allee d'Italie, Lyon, 69364,
AU: Kelemen, P
EM: peterk@ldeo.columbia.edu
AF: Lamont-Doherty Earth Obs., Columbia University, Palisades, NY 10964,
AU: Mertz, D
EM: mertz@uni-mainz.de
AF: Johannes Gutenberg University, Gutenberg-Universitat Mainz, Mainz, 55128, Germany
AU: Devey, C
EM: cdevey@ifm-geomar.de
AF: IFM-GEOMAR, Gebaude Ostufer, Wischhofstrasse 1-3, Kiel, 24148, Germany
AB: We report measurements of U-Th and U-Pa disequilibria, radiogenic isotopes, and major and trace element compositions for young basalts (<10 ka) from the slow-spreading Kolbeinsey Ridge north of Iceland (u_1/2~1 cm/yr; 67°05'- 70°26'N). These basalts display both (²³⁰Th/²³⁸U)<1 and (²³⁰Th/²³⁸U)>1. While the (²³⁰Th/²³²Th) in the samples are essentially constant, there is a large range in (²³⁸U/²³²Th), generating a horizontal array on a (²³⁰Th/²³²Th) - (²³⁸U/²³²Th) isochron plot. Kolbeinsey rocks have highly depleted incompatible element abundances and ratios and (²³¹Pa/²³⁵U)>1. Samples with ²³⁸U excesses have the lowest Th concentrations, consistent with either shallow mantle melting or shallow mantle-melt rock reaction. Nd, Hf, and Sr isotopic compositions of these samples are not correlated with (²³⁰Th/²³⁸U) and fall into two groups relative to their proximity to Iceland: samples south of the Spar Fracture Zone (nearer to the Iceland hotspot) generally are isotopically enriched, while samples north of the Spar FZ are isotopically depleted, reflecting a change in mantle source composition north and south of the fracture zone. Southern Kolbeinsey samples also tend to have higher (²³¹Pa/²³⁵U) values than those from north of the Spar FZ, which could reflect source heterogeneity, differences in the melting process, or a combination thereof.
DE: 8410 Geochemical modeling (1009, 3610)
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
DE: 8427 Subaqueous volcanism
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting