HR: 0800h
AN: V41C-1460    [Abstracts]
TI: The Pacific-Antarctic Ridge Axis Between 41 and 51° : First Sampling and Geochemical Data
AU: * Hamelin, C
EM: cedric.hamelin@sdt.univ-brest.fr
AF: Universite de Bretagne Occidentale, I.U.E.M. Domaines Oceaniques Place Nicolas Copernic, Plouzane, 29280 France
AU: Dosso, L
EM: laure.dosso@univ-brest.fr
AF: C.N.R.S., UMR6538 Domaines Oceaniques IFREMER BP70, Plouzane, 29280 France
AU: Hanan, B B
EM: bhanan@mail.sdsu.edu
AF: Department of Geological Sciences, San Diego State University 5500 Campanile Drive, San Diego, CA 92182 United States
AU: Moreira, M
EM: moreira@ipgp.jussieu.fr
AF: Institut de Physique du Globe, Laboratoire de Geochimie et Cosmochimie 4 Place Jussieu, Paris, 75005 France
AU: Klingelhoefer, F
EM: Frauke.Klingelhoefer@ifremer.fr
AF: IFREMER, BP 70, Plouzane, 29280 France
AU: Barrat, J
EM: barrat@univ-brest.fr
AF: Universite de Bretagne Occidentale, I.U.E.M. Domaines Oceaniques Place Nicolas Copernic, Plouzane, 29280 France
AU: Ondreas, H
EM: Helene.Ondreas@ifremer.fr
AF: IFREMER, BP 70, Plouzane, 29280 France
AB: In 1998, following 2 cruises which sampled the Pacific Antarctic Ridge between 53 and 66°, geochemical data showed evidence of a large-scale chemical and thermal division of the Pacific mantle. The boundary was identified at the latitude of the Easter island microplate. However those conclusions were drawn from an incomplete data set as the ridge section between 51 and 41°S had not yet been sampled. This, therefore became the main objective of the PACANTARCTIC 2 cruise which took place during the austral summer 2004-05. This 1300 km-long ridge section is characterized by a dome shape axis. It is segmented by the Menard major transform fault near 50° and by small overlapping spreading centers. 24 dredges were collected along axis at regular intervals. Preliminary geochemical data show that the great majority of samples are depleted with (Nb/Zr)N <0.5. Within each segment, the most depleted sample is found at its northern end where the ridge becomes less robust. At the studied section scale, a general decrease in (Nb/Zr)N ratios towards the north is observed. It is accompanied by a decrease in bathymetry from 2500 to 2300 m. South of Easter Island, considering available data from 66° to 41°, all geochemical parameters including He and Hf isotopes indicate a mantle source more enriched to the north of the Eltanin fracture zone system than to the south. The variability of the data is less north of Eltanin FZ than south of it. At the South Pacific ocean scale, the new Sr-Nd data confirms the evidence of two mantle domains limited by the Easter microplate.
DE: 1025 Composition of the mantle
DE: 1032 Mid-oceanic ridge processes (3614, 8416)
DE: 1037 Magma genesis and partial melting (3619)
DE: 1038 Mantle processes (3621)
DE: 1040 Radiogenic isotope geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005