Stable Isotopic Evidence for Fluid-Rock Interactions in the Ivrea Zone, Italy |
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| Authors: | BAKER A J |
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| Institution: | Grant Institute of Geology West Mains Road, Edinburgh EH9 3JW, ScotlandScottish Universities Reactor and Research Centre East Kilbride Glasgow G75 OQU, Scotland |
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| Abstract: | Stable isotope compositions of Ivrea Zone marbles and associatedlithologies are in general heterogeneous. The oxygen isotopecomposition of quartz in pelites ranges from  18O  +9 to + 17(SMOW) and does not vary systematically with metamorphic grade.Peridotites retain oxygen isotope signatures close to mantlevalues. Marble calcites vary in isotopic composition from 13C + 2(PDB),180 +24(SMOW)to 13C –6(PDB), 18O + 13 (SMOW).Depletions in 18O and 13C may be explained dominantly by interactionwith fluids derived from within the observed metasedimentarysequence during prograde metamorphism. 18O and 13C show gradients of greater than 5/m across marblemargins and within marbles. The preservation of such isotopicgradients is not consistent with the long-term presence of grain-boundary-scaleinterconnected fluid films in and around marbles. There is ageneral lowering of 18O within individual marble bodies althoughlarge carbon and oxygen isotopic gradients are present. Calcitein marbles may attain oxygen isotope equilibrium, but rarelycarbon isotope equilibrium, with surrounding metapelites. Infiltrationof marbles must involve a component of channelized fluid flow. The general lack of isotopic equilibration within the sequencerequires channelized fluid flow and limited fluid-rock ratios.Large pervasive mantle to crust fluid fluxes are not consistentwith the observations.
*Present address: Natural Environment Research Council, Polaris House, North Star Avenue, Swindon SN2 1EU, England |
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