P–T pseudosection and selected compositional isopleths calculated in the model system MnNCKFMASHTO for a local bulk composition of a part of the sample measured by SEM. Coloured fields highlight the stability of the M1 assemblage with epidote, epidote-kyanite and kyanite. The arbitrary large amount of H₂O ensures that all the subsolidus assemblages are saturated in aqueous fluid.