HR: 0800h
AN: V31C-0637    [Abstracts]
TI: Differences in Composition of Arc Volcanic Rocks in Central America and Kamchatka Reflect Differences in Input and Tectonic Processes
AU: Hoernle, K
EM: khoernle@ifm-geomar.de
AF: IFM-GEOMAR Research Center, Wischhofstr. 1-3, Kiel, 24148 Germany
AU: Hoernle, K
EM: khoernle@ifm-geomar.de
AF: SFB574, University of Kiel, Kiel, 24148 Germany
AU: * Sadofsky, S
EM: ssadofsky@ifm-geomar.de
AF: SFB574, University of Kiel, Kiel, 24148 Germany
AU: Portnyagin, M
EM: mportnyagin@ifm-geomar.de
AF: IFM-GEOMAR Research Center, Wischhofstr. 1-3, Kiel, 24148 Germany
AB: Differences in the composition of arc lavas in Central America and Kamchatka reflect differences in the composition of the subducting slab and in tectonic processes occurring in the forearc (erosion versus accretion). Concentrations of water in Kamchatkan and Central American arc magmas, measured in primitive undegassed melt inclusions in olivine phenocrysts, range up to ~5 wt. % and correlate negatively with concentrations of mantle-derived incompatible elements (e.g. Ti). These correlations reflect water-fluxed melting beneath arcs where more hydrated mantle is melted to larger extents. Water contents in the mantle source (calculated from the Ti content of the magmas) show a systematic decrease from up to 1 % in some volcanic front magmas to much lower concentrations in the back-arc in both regions, consistent with continuous metamorphic dehydration producing progressively less water as the subducting plate sinks. Water-rich fluids/melts transport fluid-mobile elements from the slab to the mantle wedge where they trigger melting. Central American and Kamchatkan melts show strikingly different behavior when comparing Ba/Th, Sr/Th, and B/Nb with H2O/La (a proxy of source H2O). Central American melts display a positive correlation of H2O/La with Ba/Th and Sr/Th and no correlation with B/Nb, whereas the Kamchatkan melts show no correlation of H2O/La with Ba/Th and Sr/Th but a positive correlation with B/Nb. Carbonate sediments subducting beneath the erosive Central American margin have high Ba and Sr and low B and could be the primary source for the trace element enrichment beneath Central America. In Kamchatka, the margin appears to be accretionary. Here the slab fluids are likely derived from the Ba and Sr-poor but B-rich altered oceanic crust and/or serpentinites.
DE: 1000 GEOCHEMISTRY
DE: 1030 Geochemical cycles (0330)
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 1043 Fluid and melt inclusion geochemistry
DE: 1065 Major and trace element geochemistry
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005