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 365

minimum at high pressure (kalsilite + sanidine + forsterite + liquid or
leucite + sanidine + forsterite + liquid).

12.6 Phase Relations in the System KALSiO 4 - Mg 2 SiO 4 -
SiO 2 at 2.8 GPa in Presence of Fluorine

Fluorine concentration in potassium-rich lamproites is high and it shows positive
correlation with potassium content (Aoki et al. 1981). The possible importance of

fluorine in the petrogenesis of lamproites has been emphasised by Jaques et al.
(1984), who suggested that at higher P-T condition,

fluor-mica is more stable than
hydroxy-mica. Foley et al. (1986) therefore, studied phase relationship in the join
kalsilite quartz at 2.0 GPa with approximately 4 wt% F added to the

system. Figure 12.14 shows the liquidus phase relations at 2.8 GPa with 4 wt%
(F 2 O) − 1 .
The results presented in Fig. 12.14 for 4 % (F 2 O) − 1 have been projected by
Foley et al. (1986), onto the kalsilite-forsterite

forsterite

- -

- quartz base from the corresponding

figure therefore, represents a
prismatic projection along the F 2 O − 1 exchange vector from a plane within the
prism, because of the addition of

fluorine end members, KAlSiF 8 - Mg 2 SiF 8 - SiF 4 . This

fluorine by direct substitution. According to Foley

Olz

Olz

10

8

9

San

En

2

5

En

7 3

Phl

4

Ks

1

Fo

6

Phl

Ks Fo

Fig. 12.14 Liquidus phase fields for the join kalsilite-forsterite-SiO 2 at 2.8 GPa in presence of
4%F 2 O − 1 . Numbers mark starting compositions. Ks kalsilite, San Sanidine, Phl phlogopite, Qtz
quartz, En enstatite. (after Foley et al. 1986)