HR: 1340h
AN: V33B-1388    [Abstracts]
TI: Water in Arctic Mid-Ocean Ridge Basalts: Evidence for a Wet Recycled Crustal Component in the Jan Mayen Plume
AU: * Rau, C
EM: dolphina93@aol.com
AF: University of Miami, GSC/P.O. Box 249176, Coral Gables, FL 33124-9176, United States
AU: Monsalve, M L
EM: mmonsalve@rsmas.miami.edu
AF: University of Miami, GSC/P.O. Box 249176, Coral Gables, FL 33124-9176, United States
AU: Dixon, J E
EM: j.dixon@miami.edu
AF: University of Miami, GSC/P.O. Box 249176, Coral Gables, FL 33124-9176, United States
AU: Kingsley, R
EM: kingsley@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, United States
AU: Schilling, J
EM: jgs@gso.uri.edu
AF: Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, United States
AB: We present H₂O concentrations in fresh mid-ocean ridge basalt (MORB) glasses dredged from 3 contiguous Arctic MAR ridge segments (Kolbeinsey, Mohns, and Knipovich Ridges) to determine the volatile content of the Jan Mayen plume end-member within this low ³He/⁴He region. Water concentrations (0.15-1.30 wt%) correlate with other indicators of mantle enrichment. H₂O/Ce ratios vary from 208 to 428, consistent with high H₂O/Ce of North Atlantic basalts (regional means of 240-280±50; Michael, EPSL, 131, 1995), but extend to values higher than previously reported. Previous Pb-Sr-Nd-Hf-H isotope studies of basalts from the Mohns Ridge confirm a strong binary mixing relationship along this ridge segment, grading from the Jan Mayen platform (enriched) eastward to the Greenland FZ where the Mohns Ridge meets the more depleted Knipovich Ridge. We model trace element concentrations in these basalts as binary mixing between depleted mantle and an enriched Jan Mayen component, followed by 7% batch melting of the mixed source using variable mineralogies. Depleted compositions are consistent with melting of a spinel lherzolite mantle, whereas the most enriched Jan Mayen lavas are best modeled by deeper melting of a mantle assemblage richer in clinopyroxene (>50%) and garnet suggesting involvement of a recycled crustal (eclogite) component. Moderately enriched lavas require intermediate mineralogies. Involvement of a recycled crustal component is consistent with the positive Nb and Ta and negative Pb anomalies in enriched samples. Water concentration in the Jan Mayen mantle component is estimated to be ~3000 ppm, significantly higher than previous estimates of water in other mantle plumes. The H₂O/Ce of melts derived from melting of this component is ~300. A possible origin for the enriched component is subducted oceanic lithosphere retained in the shallow mantle during formation of the Caledonian suture at ~410-410 Ma as proposed for Iceland by Foulger and others (JVGR, 141, 2005). While high ³He/⁴He values in Icelandic basalts would appear to preclude such a model for Iceland, the Arctic ridges are characterized by low ³He/⁴He values, and thus could have a foundered slab source with little or no lower mantle involvement. A foundered slab may have a less dehydrated composition (~88% dehydrated) than those that subduct into deeper mantle (Dixon et al., Nature, 2002). Variable contributions of this "wet" crustal component into North Atlantic mantle may account for the high water concentrations in this region.
DE: 1025 Composition of the mantle
DE: 1065 Major and trace element geochemistry
DE: 3614 Mid-oceanic ridge processes (1032, 8416)
DE: 3621 Mantle processes (1038)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting