We report Alpine metamorphic evolution and fluid inclusion data of a rodingite exposed in the Bellecombe antigorite serpentinite, Piemonte Zone, Aosta Valley, Italian Western Alps. A fine-grained rodingite, derived from a basaltic dyke protolith, is cross-cut by a network of at least six vein generations consisting of chlorite, diopside, and grossular-rich garnet (Type I), andradite-grossular garnet + diopside (Type II), andradite garnet + chlorite (Type III), grossular-rich garnet (Type IV), vesuvianite (Type V), and chlorite (Type VI), respectively. The fine-grained rodingite and the associated rodingitic veins reveal a tectono-metamorphic history similar to that recognized in the hosting serpentinite and characterized by an earlier HP metamorphism followed by a decompression, with re-equilibration under greenschist-facies conditions, and by a further cooling. Primary fluid inclusions in vesuvianite from type V veins, and secondary fluid inclusions in andraditic garnet from type III veins revealed that CH <sub>4</sub>-H <sub>2</sub> bearing brines (X <sub>H2O</sub> = 0.988; X <sub>H2</sub>=0.01 X <sub>CH4</sub> =0.002; salinity 6 wt % CaCl <sub>2</sub> + 6 wt % NaCl) were introduced into the rock at 0.22 GPa and 400°C. This fluid has a composition compatible with the Ca-rich H<sub>2</sub>–bearing reducing aqueous solutions present at the serpentinization front. These data testify for an important event of rodingitization during the late greenschist-facies Alpine evolution, probably triggered by serpentinization of metamorphic olivine.

Late Alpine rodingitization in the Bellecombe meta-ophiolites (Aosta Valley, Italian Westen Alps): evidence from mineral assemblages and serpentinization-derived H2-bearing brine

FERRANDO, Simona;COMPAGNONI, Roberto
2009-01-01

Abstract

We report Alpine metamorphic evolution and fluid inclusion data of a rodingite exposed in the Bellecombe antigorite serpentinite, Piemonte Zone, Aosta Valley, Italian Western Alps. A fine-grained rodingite, derived from a basaltic dyke protolith, is cross-cut by a network of at least six vein generations consisting of chlorite, diopside, and grossular-rich garnet (Type I), andradite-grossular garnet + diopside (Type II), andradite garnet + chlorite (Type III), grossular-rich garnet (Type IV), vesuvianite (Type V), and chlorite (Type VI), respectively. The fine-grained rodingite and the associated rodingitic veins reveal a tectono-metamorphic history similar to that recognized in the hosting serpentinite and characterized by an earlier HP metamorphism followed by a decompression, with re-equilibration under greenschist-facies conditions, and by a further cooling. Primary fluid inclusions in vesuvianite from type V veins, and secondary fluid inclusions in andraditic garnet from type III veins revealed that CH 4-H 2 bearing brines (X H2O = 0.988; X H2=0.01 X CH4 =0.002; salinity 6 wt % CaCl 2 + 6 wt % NaCl) were introduced into the rock at 0.22 GPa and 400°C. This fluid has a composition compatible with the Ca-rich H2–bearing reducing aqueous solutions present at the serpentinization front. These data testify for an important event of rodingitization during the late greenschist-facies Alpine evolution, probably triggered by serpentinization of metamorphic olivine.
2009
Geoitalia 2009, VII Forum Italiano di Scienze della Terra
Rimini
9-11 Settembre 2009
3
198
198
metasomatism; rodingite; fluid inclusion study
FERRANDO S.; FREZZOTTI M.L.; ORIONE P.; CONTE R.; COMPAGNONI R.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2318/132867
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