Fluid-mineral equilibria in prehnite-pumpellyite to greenschist facies metabasites near Flin Flon, Manitoba, Canada: implications for petrogenetic grids |
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Authors: | S. DIGEL E. D. GHENT |
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Affiliation: | Department of Geology and Geophysics, The University of Calgary, Calgary, Alberta, Canada, T2N 1N4 |
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Abstract: | A sequence of regional metamorphic isograds indicating a range from prehnite-pumpellyite to lower amphibolite facies was mapped in metabasites near Flin Flon, Manitoba. The lowest grade rocks contain prehnite + pumpellyite and are cut by younger brittle faults containing epidote + chlorite + calcite. Isobaric temperature- X CO2 and pressure-temperature (constant X CO2) diagrams were calculated to quantify the effects of CO2 in the metamorphic fluid on the stability of prehnite-pumpellyite facies minerals in metabasites containing excess quartz and chlorite. Prehnite and, to a lesser extent, pumpellyite are stable only in fluids with X co2 <0.002. For X co2>0.002, epidote + chlorite + calcite assemblages are stable. Our calculated phase relations are consistent with regional metamorphism in the Flin Flon area in the presence of an H2O-rich fluid and a more CO2-rich fluid in the later fault zones. We believe that the potential effects of small amounts of CO2 in the metamorphic fluid should be assessed when considering the pressure-temperature implications of mineral assemblages in low-grade metabasites. |
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Keywords: | CO2 fluids prehnite-pumpellyite facies regional metamorphism |
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