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Fig. 6.3 High pressure study
on melting of sanidine
(modi
ed after Lindsley
1966)
1600
LIQUID
1500
1400
LEUCITE + LIQUID
1300
HIGH SANIDINE
1200
1100
0
1
2
3
4
Pressure (GPa)
6.1.2 Melilite Stability
Melilite is often present in association with leucite in ultrapotassic rocks Lower
Austria, Rift valley of East Africa, Roman Province (Italy) and Alto Paranaiba
province of Brazil. The P-T
T stability of melilite is therefore, important to know the
condition of formation of ultrapotassic rocks containing melilite.
Yoder (1973) studied the stability of pure akermanite in presence of excess water
pressure, and established that between 680
-
C and 0.63 GPa,
akermanite breaks down to wollastonite, monticellite and vapour
°
C and 1 bar, and 750
°
(Fig.
6.4
).
Fig. 6.4 Akermanite
H
2
O
system under variable P-T
-
T
conditions (modi
ed after
Yoder 1973)
-
diopside + liquid + gas
1.1
B
1.0
Diopside
+
+
gas
merwinite
0.9
0.8
liquid + gas
0.7
A
0.6
wollastonite
monticellite
+
gas
+
0.5
0.4
akermanite + gas
0.3
0.2
0.1
600
700
800
900
1000
1100 1200
1300 1400
Temperature ( C)
°
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