Fig. 2

Photomicrographs and backscatter electron (BSE) images illustrating minerals and microstructures in metapelite sample BS 10. Scale bars are 1 mm. Mineral abbreviations are according to Kretz (1983). a Larger grains of garnet, cordierite (partly altered), K-feldspar and quartz are relics of the original high-T paragenesis and are embedded in a fine-grained retrograde matrix consisting mainly of quartz, plagioclase and micas (photomicrograph; crossed polarizers). b, c Details from a (BSE images) showing the marginal replacement of garnet by biotite, and the pseudomorphic replacement of cordierite by biotite and muscovite. Arrows indicate fresh cordierite relics. d Sillimanite and An-rich plagioclase (Pl I) also belong to the peak paragenesis. Pl I (~An₇₅) is replaced and overgrown by a younger plagioclase (Pl II) with lower An content (BSE image). e Close-up of the zoned plagioclase from d, showing that the An-rich core zone (Pl I) encloses needles of sillimanite (photomicrograph; plane light). f Andalusite grains in quartz–mica matrix (BSE image)