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M
1175
0
R
(Di-Ne-Lc)
N
Fo
ss
Di
ss
Ne
ss
Lc
ss
(?)
Fo
ss
1150
0
(Ne-Ak-Lc)
Mel
Ne
ss
Lc
ss
Fo
ss
Fo
ss
Di
ss
I
Mel
Di
ss
Ne
ss
Q
1105
0
0
1135
0
Mel
1258 C
B.M.1075
0
(Di-Ne-Ak)
P
Lc
ss
(Di-Ne-Lc)
Di
ss
Mel
Ne
ss
Lc
ss
Fo
-Mel-Di
-Ne
-Lc
ss
ss
ss
ss
(Di Ak Ne )-Lc
100-x
38
3
59
x
J
Fig. 10.12 Flowsheet diagram of the system diopside
nepheline
akermanite
leucite (after Gupta
-
-
-
et al. 1973)
crystallization, the
five phase assemblage of forsterite
ss
+ diopside
ss
+ leucite
ss
+ meli-
lite + liquid is reached at 1,258
C. The above assemblage is represented by point P
of Fig.
10.12
. At B (Fig.
10.7
), forsterite
ss
, nepheline
ss
and leucite
ss
coexist with
liquid, but as the temperature drops melilite appears at 1,175
±
5
°
C. The assemblage of
forsterite
ss
+ nepheline
ss
+ leucite
ss
+ melilite + liquid, is shown by point M
(Fig.
10.12
). In the join nepheline
°
leucite (Fig.
10.10
), nepheline
ss
,
melilite, leucite
ss
and liquid are in equilibrium at point S at 1,170
akermanite
-
-
C. As crystalli-
zation, continues the same assemblage of point M is reached at 1,150
°
°
C (N,
Fig.
10.12
). Onuma and Yagi (1967) found that in the join diopside
nepheline
ak-
-
-
ermanite, the
five phase assemblage of diopside
ss
+ nepheline
ss
+ forsterite
ss
+ meli-
lite + liquid is reached at 1,135
C, which is represented by point Q (Fig.
10.12
). The
six phase invariant assemblage at I implies the possible existence of a
°
ve-phase
piercing point within the system nepheline
SiO
2
, where diop-
side
ss
, nepheline
ss
, leucite
ss
, forsterite
ss
and liquid, coexist. The join, which contains
this piercing point is unknown. The temperature of the six-phase assemblage at I is
obtained from the pseudobinary system. After the disappearance of forsterite
ss
, liquid
moves from this point towards an invariant point of unknown composition. The
disappearance of forsterite
ss
kalsilite
CaO
MgO
-
-
-
-
C
(Fig.
10.12
). A rock nomenclature diagramcorresponding to Fig.
10.12
is presented in
Fig.
10.13
.
Paragenetic relationship based on the
takes place over a temperature range of 30
°
c
and ultramafic lavas is not clear. However, on the basis of the phase equilibria
studies on the join diopside
field occurrences of potassium-rich ma
leucite, some suggestions on
the genetic relationship between various rock types can be made.
Holmes (1950) described close association of such rock types as katungite (1),
olivine
nepheline
akermanite
-
-
-
melilite leucitite (2), melilite leucitite (3),
leucite ankaratrite (4) and
-
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