a P–T pseudosection calculated for the Pengguan migmatite (16YX-1-1) in the MnNKCFMASH system (Quartz and H2O in excess). Internally consistent thermodynamic dataset of Holland and Powell42 was used. Mineral assemblage in the thin green belt along the solidus is consistent with the mineral composition and field observations of sample 16YX-1-1. The predicted Si isopleths content in muscovite (3.06–3.18, in molar per formula unit) are shown by the white dotted lines. Gt–garnet, Bi–biotite, Mus–muscovite, Pl–plagioclase, Fsp–K-feldspar, Ilm–ilmenite, sil–sillimanite, ky–kyanite, Sp–spinel, Crd–cordierite. b P-T conditions of the Pengguan migmatite formation (green line) projected on geothermal gradients in various geologic settings (modified after Rothstein and Manning25, Hopkins et al.43 and Peacock23).