Geology Reference
In-Depth Information
10.3.2 The Join Forsterite
Diopside
Leucite at 0.1 GPa
-
-
[
P
(H
2
O) =
P
(Total)]
Gupta (1972) studied this join under atmospheric pressure (Fig.
10.2
), but the same
join was studied by Nag et al. (2007) under 0.1 GPa [P(H
2
O) = P(Total)] at variable
temperatures to learn about the effect of H
2
O on phase relationships. These experi-
mental results are summarised in Fig.
10.15
. The pseudo-eutectic point for the join
Fo
Lc in presence of excess water has been estimated to be Fo
17
Lc
83
(
'
B
'
in
-
Fig.
10.15
) from Luth (1967), who studied the system Mg
2
SiO
4
-
KAlSiO
4
-
SiO
2
-
H
2
O at 0.1 Gpa [P(H
2
O) = P(Total).
The join Fo
Lc in presence of excess water has been estimated to be Fo
17
Lc
83
-
(
'
B
'
in Fig.
10.15
)
from Luth (1967), who studied the system Mg
2
SiO
4
-
KAlSiO
4
-
SiO
2
-
H
2
O at 0.1 Gpa [P(H
2
O) = P(Total)]. The pseudoeutectic point for
the join Fo
Di was estimated to be at Fo
16.5
Di
83.5
(C, by Nag et al. 2007). From the
study of the starting materials within the Fo
-
Di
Lc join, the pseudo-eutectic point
-
-
(
Lc join was determined by Nag et al. (2007) and was found to
occur at Di
49.5
Lc
50.5
at 885
'
D
'
) for the Di
-
±
5
°
C. The
five-phase point for the join Fo
Di
Lc
-
-
occurs at
C, where forsterite
ss
, Diopside
ss
and
leucite
ss
are in equilibrium with liquid and vapour.
With reference to the study of the same join under 1 atmospheric pressure by
Gupta (1972) (Fig.
10.2
), it is observed that in the presence of water the coexistence
of Fo
ss
+Di
ss
+Lc
ss
+ Liq occurs at 880
'
A
'
(Fo
3
Di
50
Lc
47
) and 880
±
5
°
°
C (Fig.
10.15
) which contrasts the
presence of the same assemblage at 1,296
±
5
°
C. (Fig.
10.2
) under one atmospheric
pressure. The data show a drop of about 416
°
C in the temperature of coexistence
for
five-phase Point
(Fo
ss
+Di
ss
+Lc
ss
+ Liq + V) moves closer towards leucite, since such ma
these four phases.
In presence of excess water
the
c phases
Fig. 10.15 Phase relations in the join Fo
Lc studied under 0.1 GPa [P(H
2
O) = P(Total)] (after
Nag et al. 2007). The bold line with squares is a projected path of the liquid as determined from the
composition of glasses in equilibrium with crystalline phases
Di
-
-
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