Melilite- and Leucite-Bearing Systems - Origin of Potassium-rich Silica-deficient Igneous Rocks - page 313

Fig. 10.8 Course of
crystallization of liquid
in the join diopside -
nepheline - leucite (after Gupta
and Lidiak 1973)

1275 ± 5 C

o

Fo
Di

Ne
Lc

1194 ±5 o

Lc

Fo

o
(Ne-Lc-Fo-Mel)

1180 ± 5 C

1257±5 C

o

Fo
Di
Lc

Ne
Lc
Fo

(Fo-Di-Lc-Mel)

Mel Mel

(1168C -1100C)

o o

(Fo-Di-Lc-Mel-Ne)

o o

(Fo out, 1135 C -1060 C)

Mel
Ne
Lc
Di

Fig. 10.9 Rock-
nomenclature diagram,
corresponding to Fig. 10.8
(after Gupta and Lidiak
(1973)

1275 ±5 o

1194 ±5 o

1180±5 o 1257±5 o

Olivine-Melilite-
Nepheline Leucitite o o

(1168C-1100C)

buffer conditions in a furnace, where oxygen fugacity was maintained by passing a
mixture of gases having compositions, CO 2 :95.25%andCO:4.75%.Theystudied19
compositions to determine phase relations and course of crystallization of an oliv-
ine

leucitite and a katungite liquid. They concluded that both the two
magma types yield an olivine

nepheline

- -

Cunder
atmospheric pressure and under QFM buffer condition. They noted a reaction rela-
tionship between olivine and liquid, and found that olivine

melilite nepheline leucitite liquid at 1,090 °

- -

finally disappears at around

1,053 C. The course of crystallization of liquid as established by Gee and Sack (1988)

is similar to what was predicted by Gupta et al. (1973; Figs. 10.8 and 10.9 ).
They found cotectic crystallization of leucite + nepheline + spinel

°

± meli-

lite ± high calcium pyroxene ± olivine ( ± whitlockite ± perovskite) in equilibrium

with liquid at 1 atm (fO 2 * QFM) over the temperature range, 1,050 - 1,110 ° C.