Geometry and pressure-temperature significance of the kyanite-sillimanite isograd in the Mica Creek area, British Columbia
✍ Scribed by Edward D. Ghent; Philip S. Simony; Clifford C. Knitter
- Publisher
- Springer
- Year
- 1980
- Tongue
- English
- Weight
- 643 KB
- Volume
- 74
- Category
- Article
- ISSN
- 0010-7999
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✦ Synopsis
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-AleSiOs-quartz) does not provide a fine enough resolution to detect these predicted differences.