Geometry and pressure-temperature significance of the kyanite-sillimanite isograd in the Mica Creek area,British Columbia |
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Authors: | Edward D Ghent Philip S Simony Clifford C Knitter |
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Institution: | (1) Department of Geology and Geophysics, University of Calgary, T2N 1N4 Calgary, Alberta, Canada |
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Abstract: | Late Precambrian and Lower Paleozoic metapelitic rocks near Mica Creek, British Columbia, range in metamorphic grade from biotite zone to sillimanite zone. The kyanite-sillimanite isograd was established after phase 2 folding but was deformed by phase 3 folding. Topographic relief of about 2 km, combined with phase 3 folding, permits reasonably precise determination of the geometry of the isogradic surfaces. The effects of phase 3 folding have been accounted for and the isobaric surfaces at the time of metamorphism are inferred to have been dipping gently. Using the kyanite-sillimanite experimental phase diagram, intersection of the isobars and the isograd permits estimates of differences in temperature and pressure along a cross section. These estimates are about 400 bars and 20° C. Mineral geothermometry (garnet-biotite) and geobarometry (garnetplagioclase-Al 2SiO5-quartz) does not provide a fine enough resolution to detect these predicted differences. |
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