Mixtures of synthetic muscovite with synthetic sanidine or natural , with and without water, were reacted in piston-cylinder apparatus between 10 and 35 kb; metastable corundum persisted in runs not seeded with sillimanite kyanite. Phases produced include muscovite (Ms), KAlSi_3O_8 • H_2O (OrH), sanidine (Or), kyanite (Ky), sillimanite (Si), quartz (Qz), coesite (Ct), liquid (L), and (V). Melting reactions determined include: (A) Ms + Qz ⇔ Or + Ky + L, (B) Ms + Qz + V ⇔ Ky + L, (C) Or + Qz + V ⇔ L, and (D) OrH + Ct + V ⇔ L. 30 kb, the vapor-absent melling reaction (A) is about 140°C higher than the reaction (B) with excess vapor. Melting reactions (A) and (B) extrapolate to meet the invariant point for the assemblage Ms + Or + Qz + Si + L + V at 5.8 kb and 730°C, as defined by Storre and Karotke (1972). This lies just below melting reaction (C). This invariant point is the high pressure for the subsolidus dehydration reaction: Ms + Qz ⇔ Or + Si + V, and its facilitates selection from among the varied dehydration reactions previously . These results are combined with published results for melting reactions muscovite without quartz, to provide a P-T projection of muscovite melting and reactions in the quaternary system. By analogy with the system K_2O-Al_2O_3-SiO_2-H_2O, a similar diagram for paragonite dehydration and melting reactions obtained by combining published paragonite dehydration reactions with albite-quartz-water melting reactions. Comparison of these mineral stability grids with estimates of temperature distribution in subducted lithosphere slabs suggests muscovite in metamorphosed subducted sediment dissociates or melts at shallow depths, and it seems unlikely that muscovite can contribute water magmatic processes much beyond the arc-trench gap or influence chemical variations lavas across an arc complex.
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Huang et al. (1974) studied this question.