Experimental Studies on K-Rich Rocks - Origin of Potassium-rich Silica-deficient Igneous Rocks - page 405

suppresses the phologopite stability as suggested by Ryabchikov and Green (1978).
The clinopyroxenes are found to be calcic ½ Ca/Ca + Mg) 0.46 and olivines are

[

forsteritic Mg ½ = ð Mg þ Ca Þ ¼ 0 : 83 0 : 89 . Orthopyroxene is rich in MgSiO 3

molecule Mg ½ = ð Mg þ Fe Þ ¼ 0 : 76 0 : 85 and garnets are pyrope-rich as expected.

Mica is phlogopitic Mg ½ = ð Mg þ Fe Þ ¼ 0 : 85 and appears to be the main source of

K 2 O in the mantle.

13.2.10 Experimental Investigation on a Phlogopite-Bearing
Minette

Experimental study was made on a phlogopite minette from Buell Park, Alizona by
Esperanca and Holloway (1987). Chemical analysis of the rock is given in
Table 13.2 . The minette was studied under oxygen fugacities equivalent to that
maintained by iron-wustite-graphite (IWG) and quartz-magnatite-fayalite (FMQ)
buffers at pressures between 1.0 and 2.0 GPa. Their results are summarized in
Fig. 13.19 , where comparison between experimental products obtained under these
two buffer conditions are shown. Their results demonstrate that olivine together with
clinopyroxene appears as the primary phase followed by precipitation of phlogopite.

2.0

IWG

Phl

Oliv Cpx

Glass

Liq + Cpx
+ Phl

QFM

Ol Phl

Cpx

Pilm

Glass

1.5

Liq +
Ol +
Cpx

Liq +
Cpx +
Phl + Ol

Liq

1.0

1050 1100 1150 1200 1250

T o

Fig. 13.19 Liquidus phase diagram for Buell Park minette sample. Phase boundaries are drawn
based on models for IGW (iron-wustite-graphie experiments), “ Picroilmenite out ” curve (Pilm out)
extrapolated from QFM (quartz-fayalite-magnetite) buffer experiment. Filled parts represent
coexisting near liquidus phase counter clockwise from the bottom, glass, clinopyroxene, phlogopite,
olivine, picroilmenite. Boundaries were approximate (after Esperanca and Holloway 1987)