Geometry and pressure-temperature significance of the kyanite-sillimanite isograd in the Mica Creek area, British Columbia

摘要: 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 deformed by 3 folding. Topographic relief of about km, combined with folding, permits reasonably precise determination the geometry isogradic surfaces. effects have been accounted for isobaric surfaces at time metamorphism are inferred dipping gently. Using experimental diagram, intersection isobars estimates differences temperature pressure along a cross section. These 400 bars 20° C. Mineral geothermometry (garnet-biotite) geobarometry (garnetplagioclase-Al 2SiO5-quartz) does not provide fine enough resolution detect these predicted differences.