HR: 0800h
AN: V41D-1489    [Abstracts]
TI: Geochemistry of NE Atlantic non-rifting zones, Iceland and Jan Mayen
AU: * Tronnes, R G
V41D-1489 AF: Nordic Volcanol. Centre, IES, Univ Iceland, Reykjavik, 101 Iceland
AU: * Tronnes, R G
V41D-1489 AF: Natural Hist. Museum, Univ Oslo, Oslo, 0318 Norway
AU: Waight, T
V41D-1489 AF: Geological Inst., Univ Copenhagen, Copenhagen, 1350 Denmark
AB: The fertile components of the NE Atlantic mantle are sampled preferentially by alkaline basalts in the volcanic flank zones of Iceland and in the Jan Mayen and Vesteris seamount areas. Our data from primitive flank zone lavas from Iceland and Jan Mayen demonstrate a HIMU-affinity with enrichment of HFSE, U/Pb, Th/U and Nb/Th. In PM-normalized spider diagrams the least enriched samples have weakly positive Sr-anomalies, whereas the most enriched samples have negative Sr-anomalies. The entire sample suite shows negative Sr-Nd-isotope correlation, whereas the samples of each volcanic system or flank zone generally lack such a correlation. Our data confirm the anomalously high 87/86Sr of the Orafajokull volcanic system in the eastern flank zone. The results are consistent with existing data for other primitive flank zone basalts from Iceland and Jan Mayen. Common geochemical features linking alkaline flank zone basalts and high-degree tholeiitic melts include high 87/86Sr (and probably 176/177Hf) for a given 143/144Nd, negative delta-207Pb (except for Orafajokull) and positive delta-Nb. Alkaline flank zone basalts have generally higher 87/86Sr, 206/204Pb and 18/16O and lower 143/144Nd, 187/188Os and 3/4He than rift zone tholeiites. The different 18/16O ratios in flank and rift zone basalts are consistent with seafloor hydrothermal alteration of the upper and lower parts of recycled oceanic lithosphere, respectively. Olivine-melt fractionation may contribute to the difference. Indications of lower 187/188Os in alkaline basalts compared to nearby rift zone tholeiites could be caused by subduction zone loss of Re from the upper part of recycled slabs. The partial melting and volcanic sampling of the fertile mantle components under Iceland and the NE Atlantic is governed by the crustal structure and geometry of the Icelandic volcanic zones and the lateral deflection of the upwelling heterogeneous mantle source originating under central Iceland. Based on the pattern of V-shaped ridges along the Kolbeinsey ridge, the lateral mantle flow from central Iceland may well extend beyond Jan Mayen. The geochemical similarities between the enriched basalts of the Icelandic flank zones and Jan Mayen support this contention, although a minor separate plume under JM is a possibility.
DE: 1025 Composition of the mantle
DE: 1037 Magma genesis and partial melting (3619)
DE: 1038 Mantle processes (3621)
DE: 1040 Radiogenic isotope geochemistry
DE: 1041 Stable isotope geochemistry (0454, 4870)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005