Phlogopite enstatite

Wood B. J. (1976a). The reaction phlogopite + quartz = enstatite + sanidine + H2O. In Progress in Experimental Petrology, G. M. Biggar, ed. Natural Environment. Res. Coun-cihPubl. series D. 

Sato K., Katsura T., and Ito E. (1997) Phase relations of natural phlogopite with and without enstatite up to 8 GPa implications for mantle metasomatism. Earth Planet. Sci. Lett. 146, 511-526. 

Aranovich L. Y. and Newton R. C. (1998) Reversed determination of the reaction Phlogopite -I- quartz = enstatite 4- potassium feltspar -I- H2O in the ranges 750-875 °C and 2-12 kbar at low H2O activity with concentrated KCl solutions. Am. Mineral. 127, 261-271. 

At low HO pressures, phlogopite and quartz react to form sanidine, enstatite, and an H 0-rich gas. This reaction terminates between 830 C and 850 C and 400 bars and 500 bars at an invariant point, (Tr ), involving silicate melt. Luth (1967) discussed the topology of this invariant point which is reproduced here schematically in Figure 1. The chemography of the solid phases and melt is projecfed from the H O apex onto the three components... 

Qz) lies between 830 C and 840 C at 500 bars. Its high temperature termination is the invariant point phlogopite-sanidine-enstatite-forsterite-liquid-gas, as described by Luth (1967). Schairer (1954) indicated that the solubility of MgO in KAlSi303-Si02 melts was very small. Curves (Ph) and (En) are assumed to be identical to the curve sanidine-quartz-liquid-gas described by Shaw (1963). The data in Table 3 indicate that this is the case for (En) within the uncertainties of this body of data. 

Abbreviations of phases En, enstatite Gl, glass, Ph, phlogopite Qz, quartz Sa, sanidine ... 

Stability of Phlogopite, Quartz and Diopside Superposing Boyd s (1959) curve for the reaction Ca2Mg5Si70s022(0H)2 2CaMgSi205 + 3MgSi03 + Si02 + H2O (Ph,Sa,L) tremolite diopside enstatite quartz gas... 

The low value of (dP/dT) for the reaction (L) is due to the very large volume term involving HO for this reaction. The activity of SiO has a profound effect on the stability of phlogopite as has been pointed out by Luth (1967) and Yoder and Kushiro (1969). A whole series of stability curves exist for phlogopite in which the activity of SiO is successively buffered by quartz, enstatite-forsterite, leucite-sanidine, and leucite-kalsilite. 

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