Geology Reference
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1526±2
1500
1500
1400
1391±5
1400
L
Cg +L
ss
Ol+Mel+L
1300
1300
Di +L
ss
1258
Cg +Ne +L
1260±5
ss
ss
Ne +L
Di +Ol+L
ss
ss
1193
Ol+L
1200
Ne +Ol+L
ss
Ne +Ol+Mel+L
ss
1200
Di+ Ol + M e l+ L
ss
Di +Ol+Mel+Ne +L
ss
Ne + Ol+ M el +D i +L
ss
ss
1100
ss
1100
Di +Mel+Ne +L
ss
ss
1000
1000
Ne +Mel+Di
ss
ss
900
900
Nepheline
10
20
30
40
50
60
70
80
90
Diopside
(CaMgSi O )
2
(NaAlSiO )
4
(Weight percent)
6
Fig. 6.6 Phase relation in the system diopside
nepheline under one atmospheric pressure (after
-
Schairer et al. 1962)
The presence of melilite and olivine in K-rich nephelinites can be explained by
the following reaction (Yoder and Kushiro 1972):
3CaMgSi 2 O 6 þ
2NaAlSiO 4 ð
Ca 2 MgSi 2 O 7 þ
diopside
nepheline
akermanite
CaNaAlSi 2 O 7 Þþ
Mg 2 SiO 4 þ
NaAlSi 3 O 8
sodamelilite
forsterite
albite
nepheline (Bowen 1928; Schairer
et al. 1962). It is possible that it remains as a dissolved species in the melt at high
temperatures, and at low temperature it is included in nepheline as solid solution.
Singh et al. (2000) studied the join diopside
Albite did not appear in the system diopside
-
nepheline at variable pressures and
temperatures, and established that the reaction of diopside and nepheline to produce
olivine and melilite is eliminated at 1.9
-
0.3 GPa, and above this pressure melilite
and olivine did not appear. Phase relations of the diopside
±
nepheline join studied
under 2.8 GPa is shown in Fig. 6.7 , which shows complete disappearance of
melilite, and presence of only diopside ss and nepheline ss in the subsolidus region.
Singh and Gupta (1992) and Sing et al.
-
(2000)
studied the system
diopside
nepheline at 1.0 GPa (Fig. 6.8 ) and variable temperatures in presence of
excess water. They noted that under hydrous condition subsolidus assemblage is
-
 
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