HR: 0800h
AN: U21B-0415    [Abstracts]
TI: Carbonate-rich Sediments in the Hawaiian Plume: Evidence from Mahukona Volcano
AU: * Huang, S
EM: huang@magnet.fsu.edu
AF: National High Magnetic Field Laboratory and Department of Geological Sciences, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, FL 32310, United States
AU: Abouchami, W
EM: wafa@mpch-mainz.mpg.de
AF: Max-Planck-Institut für Chemie, Postfach 3060, Mainz, 55020, Germany
AU: Blichert-Toft, J
EM: jblicher@ens-lyon.fr
AF: Ecole Normale Supérieure de Lyon, 46, Allée d'Italie, Lyon Cedex 7, 69364, France
AU: Clague, D A
EM: clague@mbari.org
AF: Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039, United States
AU: Cousens, B
EM: brian_cousens@carleton.ca
AF: Carleton University, 1125 Colonel By Drive, Ottawa, ON K1S5B, Canada
AU: Frey, F A
EM: fafrey@mit.edu
AF: Massachusetts Institute of Technology, 77 Mass. Ave., Cambridge, MA 02139, United States
AU: Humayun, M
EM: humayun@magnet.fsu.edu
AF: National High Magnetic Field Laboratory and Department of Geological Sciences, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, FL 32310, United States
AB: Hawaiian shield lavas exhibit considerable heterogeneity in Sr-Nd-Hf-Pb isotope space, as well as in their major and trace element abundances. Some of these geochemical features are attributed to recycled oceanic crust, including sediments. Here we report major and trace element concentrations, and Sr-Nd-Hf-Pb isotopic compositions for shield lavas from Mahukona Seamount, Hawaii. Using these data, we identify a carbonate-rich sedimentary source component in the Mahukona lavas. Specifically, within Mahukona lavas, Nd-Hf-Pb isotopic ratios are highly correlated with each other, while ⁸⁷Sr/⁸⁶Sr is decoupled. Since the isotopic compositions were obtained on strongly acid-leached residues, the discordance of ⁸⁷Sr/⁸⁶Sr is not inferred to be alteration-related. Moreover, ⁸⁷Sr/⁸⁶Sr is positively correlated with Sr/Ce and negatively correlated with Rb/Sr and Ba/Sr. Because the Mahukona lavas are tholeiitic to transitional basalts, their Sr/Ce, Rb/Sr and Ba/Sr reflect their source values. We infer that one of the Mahukona source components has high Sr/Ce (>16) and 87Sr/86Sr (>0.7038), and low Rb/Sr (<0.015) and Ba/Sr (<0.15). Such a composition cannot be generated through mantle metasomatism, because high ⁸⁷Sr/⁸⁶Sr requires high Rb/Sr. We rather propose recycled ancient carbonate-rich sediment as a possible component in the Mahukona source. Carbonate-rich sediments, in general, have high Sr/Ce, and low Rb/Sr and Ba/Sr. Furthermore, ancient carbonate-rich sediments would have inherited their ⁸⁷Sr/⁸⁶Sr from seawater, which had ⁸⁷Sr/⁸⁶Sr greater than 0.7040 at 2 Ga. Since a carbonate-rich sedimentary component has very high Sr/X (X=Nd, Hf, Pb), sampling it would affect only ⁸⁷Sr/⁸⁶Sr and leave the Nd-Hf-Pb isotopic ratios unchanged.
DE: 1025 Composition of the mantle
DE: 1033 Intra-plate processes (3615, 8415)
DE: 1038 Mantle processes (3621)
DE: 1040 Radiogenic isotope geochemistry
DE: 1065 Major and trace element geochemistry
SC: Union [U]
MN: 2007 Fall Meeting