HR: 15:10h
AN: V22F-07    [PDF]
TI: High H$_{2}$O in MORB From Gakkel Ridge
AU: * Michael, P J
EM: pjm@utulsa.edu
AF: The University of Tulsa, 600 S. College Ave., Tulsa, OK 74104 United States
AU: Matzen, A K
EM: andrew-matzen@utulsa.edu
AF: The University of Tulsa, 600 S. College Ave., Tulsa, OK 74104 United States
AU: Langmuir, C H
EM: langmuir@eps.harvard.edu
AF: Harvard University, 20 Oxford St, Cambridge, MA 02138 United States
AU: Goldstein, S L
EM: steveg@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia Univ., Rt. 9W, Palisades, NY 10964 United States
AU: Soffer, G
EM: gsoffer@ldeo.columbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia Univ., Rt. 9W, Palisades, NY 10964 United States
AU: Schmieder, P
EM: schmied@ldeo.cilumbia.edu
AF: The University of Tulsa, 600 S. College Ave., Tulsa, OK 74104 United States
AU: Schmieder, P
EM: schmied@ldeo.cilumbia.edu
AF: Lamont-Doherty Earth Observatory of Columbia Univ., Rt. 9W, Palisades, NY 10964 United States
AU: Graham, D W
EM: dgraham@coas.oregonstate.edu
AF: Oregon State University, COAS, Corvallis, OR 97331
AB: Enriched and depleted mid-ocean ridge basalts (MORB) from western Gakkel Ridge (GR) in the Arctic Ocean have distinctive trace element and volatile characteristics compared to MORB globally. They are enriched in H$_{2}$O and large ion lithophile (LIL) relative to rare earth elements (REE), so have high H$_{2}$O/Ce and Ba/La. To a lesser degree, they are enriched in REE relative to HFS (e.g., high La/Nb). The order of enrichment is H$_{2}$O $>$Ba$>$Rb$>$K$>$La and is similar to the subduction zone signature displayed by some back-arc basin basalts. There has been about 200 km of shortening in this region as Greenland converged with the Arctic Basin during the Cenozoic (Brozena et al, 2003) but true subduction is less likely. The enrichment pattern also has some similarity with continental lithosphere, which may be present in the source region since continental rifting was relatively recent in this region. Continental involvement was suggested for Knipovich R. (Schilling et al., 1999). The geographic extent of the distinctive enrichment should help constrain its origin, since an anomaly associated with Greenland convergence should be localized to western GR. H$_{2}$O/Ce and Ba/La both diminish toward the eastern GR, where basalts resemble Pacific MORB.However, H$_{2}$O/Ce remains high toward the North Atlantic along Knipovich, Mohns, Kolbeinsey and Reykjanes Ridges, suggesting a much larger region, perhaps related to a larger and more ancient subduction event. The extent of the high Ba/La in the northernmost Atlantic is not clear from current data. Isotopic data from Gakkel ridge MORB should provide additional constraints on the nature of the high- H$_{2}$O component on GR. When MORB are considered globally, there are no consistent associations between H$_{2}$O/Ce and other trace element and isotopic characteristics. Some MORB with high Ba/Nb and high $^{87}$Sr/$^{86}$Sr relative to $^{206}$Pb/$^{204}$Pb have high H$_{2}$O (SEIR) whereas others (southern MAR) have distinctive low H$_{2}$O (Dixon et al; 2002; Michael and Kamenetsky, 2002). This might reflect very different high-Ba components, or it could reflect different behavior of H$_{2}$O within the high Ba component compared to the normal peridotite. Brozena et al. (2003) Geology Dixon et al., (2002) Nature 420, 385-389 Schilling et al., (1999) JGR 104, 10543-10569
DE: 1025 Composition of the mantle
DE: 3035 Midocean ridge processes
DE: 3670 Minor and trace element composition
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting