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Fluid–rock interaction at a carbonatite-gneiss contact, Alnö, Sweden
Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Geologi.
Stockholm University, Faculty of Science, Department of Geology and Geochemistry. Geologi.
2007 (Swedish)In: Contributions to Mineralogy and Petrology, Vol. 154, 75-90 p.Article in journal (Refereed) Published
Abstract [sv]

We evaluate balanced metasomatic reactions

and model coupled reactive and isotopic transport

at a carbonatite-gneiss contact at Alno, Sweden.

We interpret structurally channelled fluid flow along

the carbonatite-gneiss contact at ~640C. This caused

(1) metasomatism of the gneiss, by the reaction:

biotite + quartz + oligoclase + K2O + Na2O +/- CaO +/-

MgO +/- FeO = albite + K-feldspar + arfvedsonite +

aegirene-augite + H2O + SiO2, (2) metasomatism of

carbonatite by the reaction: calcite + SiO2 = wollastonite

+ CO2, and (3) isotopic homogenization of the

metasomatised region. We suggest that reactive

weakening caused the metasomatised region to widen

and that the metasomatic reactions are chemically

(and possibly mechanically) coupled. Spatial separation

of reaction and isotope fronts in the carbonatite

conforms to a chromatographic model which assumes

local calcite–fluid equilibrium, yields a timescale of

10^2–10^4 years for fluid–rock interaction and confirms

that chemical transport towards the carbonatite

interior was mainly by diffusion. We conclude that

most silicate phases present in the studied carbonatite

were acquired by corrosion and assimilation of ijolite, as a reactive by-product of this process and by

metasomatism. The carbonatite was thus a relatively

pure calcite–H2O–CO2–salt melt or fluid.

Keywords Carbonatite, Fluid flow, Metasomatism, Alno

Place, publisher, year, edition, pages
2007. Vol. 154, 75-90 p.
URN: urn:nbn:se:su:diva-19471DOI: doi:10.1007/s00410-007-0180-1ISI: 000247210700005OAI: diva2:185995
Available from: 2007-11-12 Created: 2007-11-12 Last updated: 2011-01-11Bibliographically approved

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