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 358

12.4 Investigation of the System KAlSiO 4 - Mg 2 SiO 4 - SiO 2

in Presence of H 2 O and CO 2 up to 2 GPa

Wendlandt and Eggler (1980) studied the compositional join)KAlSiO 4 - MgO -

SiO 2 - H 2 O - CO 2 at high pressures and high temperatures. They emphasised the

signi cance of the following reactions:

(1) phlogopite + kalsilite + leucite forsterite + liquid (Yoder and Kushiro

⇌

1969),
(2) phlogopite

forsterite + liquid,
(3) phlogopite + vapour

⇌

forsterite + liquid,
(4) phlogopite + kalsilite + leucite + vapour

⇌

forsterite + liquid,

⇌

(5) phlogopite + sanidine + vapour forsterite + leucite + liquid,

(6) phlogopite + enstatite + sanidine + vapour

⇌

forsterite + liquid,

⇌

(7) phlogopite + sanidine + quartz + vapour enstatite + liquid,

→

(8) phlogopite + sanidine + leucite + vapour forsterite + liquid,

→

forsterite + liquid,
(10) phlogopite + forsterite + sanidine + vapour

(9) phlogopite + sanidine + vapour

→

liquid,

→

(11) phlogopite + sanidine + vapour liquid,

(12) phlogopite + enstatite + forsterite + sanidine + vapour

→

liquid,

→

(13) phlogopite + enstatite + sanidine + vapour liquid,

→

(14) phlogopite + forsterite + sanidine + vapour enstatite + liquid,

⇌

(15) phlogopite + sanidine + vapour enstatite + liquid,

→

(16) kalsilite + sanidine 2 leucite,

(17) phlogopite + kalsilite + sanidine + vapour

→

→ forsterite + liquid,

(18) kalsilite + 4 enstatite,

(19) phlogopite + enstatite + kalsilite + vapour

sanidine + 2 forsterite →

→ forsterite + liquid,

(20) phlogopite + enstatite + magnesite → forsterite + kalsilite + vapour,

(21) enstatite + magnesite + liquid,

(22) phlogopite + enstatite + magnesite

forsterite + kalsilite + vapour

→

forsterite + kalsilite + liquid,
(23) phlogopite + enstatite + magnesite + vapour → forsterite + liquid, and
(24) phlogopite + kalsilite + vapour

→

enstatite + magnesite + liquid.

→

The P-T projection of phase relations involving phlogopite, enstatite, forsterite,
magnesite, sanidine, kalsilite, leucite, liquid and vapour in the compositional join
KAlSiO 4 -

CO 2 , as determined by Wendlandt and Eggler is
shown in Fig. 12.11 . Dash lines at low pressure are reaction in the H 2 O-saturated
quaternary join. Wendlandt and Eggler obtained the results related to I 10 are from
Yoder and Kushiro (1969) and those for I 11 ,I 12 and I 13 are from Luth (1967). In
Fig. 12.11 , light solid lines are related to reactions in the CO 2 -saturated quaternary
joins and volatile-absent subsolidus reactions are already discussed in the preceding
sections. The reaction, enstatite + magnesite

MgO SiO 2 - H 2 O

- -

forsterite + CO 2 is from Newton
and Sharp. The reaction related to the breakdown of leucite to form sanidine and
kalsilite is from Lindsley (1966).

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