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 352

The reactions considered by Wendlandt and Eggler (1980) are as follows:

(3) kalsilite + leucite liquid,

(4) kalsilite + leucite + vapour

→

liquid,

→

(5) leucite + forsterite liquid,

→

(6) leucite + forsterite + sanidine liquid,

→

(7) sanidine + liquid,

(8) kalsilite + leucite + forsterite

leucite + forsterite

→

liquid,

→

(9) sanidine + enstatite leucite + liquid,

→

(10) leucite + enstatite forsterite + liquid,

→

(11) sanidine + forsterite leucite + 2 enstatite,

→

(12) plagioclase + olivine nepheline + pyroxene, and albite + 2 forste-

→

rite nepheline + 4 enstatite.

→

The reactions 12 and 13 have been suggested by Shand (1933) and Barth (1936),
respectively. The other reactions studied by Wendlandt and Eggler (1980) are as
follows:

(13) sanidine + enstatite → forsterite + liquid,

(14) sanidine + forsterite → leucite + liquid,

(15) sanidine + leucite + forsterite → liquid,

(16) sanidine + forsterite liquid,

→

(17) sanidine + enstatite + forsterite → liquid,

(18) sanidine + enstatite liquid,

→

(19) sanidine + forsterite enstatite + liquid,

→

(20) sanidine + liquid,

(21) kalsilite + forsterite + sanidine

leucite + forsterite

→

liquid, and

→

(22) 4 enstatite + kalsilite sanidine + 2 forsterite.

→

The P-T projection of all these reactions studied by Wendlandt and Eggler
(1980), and the two reactions 1 and 2 investigated respectively by Lindsley (1966)
and Scarf et al. (1966) are included in Fig. 12.5 . Details of reactions associated with
singular points S 3 ,S 4 and S 5 are shown in Fig. 12.6 . The

figures show that leucite
and enstatite coexist in equilibrium over a limited P-T range i.e. between 980 ° C and

one bar and the singular point I 5 (1205 ° C and 0.65 GPa). Wendlandt and Eggler

studied the join KAlSiO 4 - SiO 2 up to 3.0 GPa in presence of CO 2 . The P-

T projection of the reactions investigated in this join is shown in Fig. 12.7 . The
details of reactions associated with singular points S 9 ,S 10 and S 11 are shown in
Fig. 12.8 . It is noted that phase relation in the CO 2 -bearing system mimic those in
the volatile-absent system, at pressures less than about 2.0 GPa, except for that
reactions which occur at lower pressure. At pressures above I 14 (Fig. 12.7 ), phase
relations are not equivalent to the CO 2 -free system. Reactions resulting from I 14 ,
pass through 3 singular points S 18 -

Mg 2 SiO 4 -

S 20 (inset Fig. 12.7 ) and mark the rapid passage
of liquid toward silica-poor magnesia-rich composition as the kalsilite-enstatite-
vapour, and kalsilite-forsterite-vapour joins are pierced (Fig. 12.7 ). They noted that
at I 8 , liquid in equilibrium with forsterite + enstatite + kalsilite + vapour also attains
equilibrium with magnesite; but at higher pressure forsterite does not appear in the