P-T Stability of Phlogopite, K-Richterite and Phengite, as a Source of Potassium in the Mantle - Origin of Potassium-rich Silica-deficient Igneous Rocks - page 359

Fig. 12.11 P-T projection of phase relations involving phlogopite, enstatite, forsterite, magnesite,
sanidine, kalsilite, leucite, liquid, and vapour in the system KAlSiO 4 - MgO - SiO 2 - H 2 O - CO 2 .
Dashed lines at low pressure are reactions in the H 2 O-saturated join (quaternary). The results for
I 10 are from Yoder and Kushiro (1969) and those for I 11 ,I 12 , and I 13 are from Luth (1967). Light
and solid lines are reactions in the CO 2 -saturated join (quaternary) and volatile-absent subsolidus
reactions that are discussed in Wendlandt and Eggler (1980a). Heavy solid lines are univariant
reactions in the H 2 O - CO 2 join (quinary). The reaction leucite → sanidine + kalsilite is from
Lindsley (1966) and the reaction enstatite + magnesite → forsterite + CO 2 is from Newton and
Sharp (1975). Pyrope is observed as a reaction product at 4.0 GPa and higher. Although kalsilite is
a predicted reaction product at pressures above I 9 , it was not observed in run products.
Abbreviations are same as Fig. 12.4 and additionally, En: enstatite, Mag: magnesite; Pyr: pyrope.
(after Wendlandt and Eggler 1980b)
According to Wendlandt and Eggler (1980), small percentage of melting of
phlogopite-bearing upper mantle between 2.0 and 3.0 GPa will result in the gen-
eration of a potassium-rich silica-undersaturated melt corresponding to a olivine
leucitite or a basanite.