Geology Reference
In-Depth Information
10.4.2 The Join Forsterite
Leucite Studied
under 2.3 GPa at Variable Temperatures
Diopside
-
-
With reference to Fig.
10.16
b, the experimental study suggests that from a liquid
of composition
'
'
'
'
A
(Fo
20
Di
30
Lc
50
) forsterite
ss
crystallises
rst near
b
(melt
composition
, Fig.
10.16
), phlogopite
ss
starts to precipitate in addition to for-
sterite
ss
. The composition of liquid then moves long a multi-saturation line
'
l
'
'
b-B
'
to
'
), where diopside
ss
co-precipitates with forsterite
ss
and phlogopite
ss.
With the lowering of temperature further, K-feldspar
ss
appears at
985
B
'
(near melt composition
'
3
'
final assemblage comprises forsterite
ss
+ phlogo-
pite
ss
+ diopside
ss
+ K-feldspar
ss
and liquid. The assemblage along
±
10
°
C. Thus,
the
corre-
sponds to a madupite, a type locality of which is Pilot Butte at Leucite Hills. The
assemblage forsterite
ss
+ phlogopite
ss
+clinopyroxene corresponds to missourite or
kazanite. The
'
b-B
'
final crystalline product comprising phlogopite
ss
, diopside
ss
, forste-
rie
ss
and K-feldspar
ss
similar to a phenocrystal assemblage of olivine
pyroxene
-
minette.
Makhotkin et al. (1989) described lamproites comprising olivine, phlogopite
and diopside from Khani (57
°
54
′
N, 120
°
46
′
E) and Ryabinovaya (57
°
40
′
N, 125
°
51
E) of Aldan alkaline province of Russia. This assemblage corresponds to that
of the
′
(Fig.
10.16
b). The lamproite of Rayabinovaya is
associated with a phlogopite-bearing minette. There is also a brecciated pipe
(600
five-phase point
'
B
'
700 m long) at Kaila of the same petrographic province of Aldan. The pipe
is constituted of olivine, diopside and phlogopite phenocrysts with clinopyroxene,
phlogopite and K-feldspar occurring in the groundmass, as is the near solidus
assemblage (point
-
Brien et al. (1991) described
olivine minettes from Highwood)Mountains, Montana, USA, which have the
seriate porphyritic texture with phenocrysts of phlogopite, clinopyroxene and
forsteritic olivine (Fo
87
-
92
) in a matrix of sanidine, clinopyroxene, phlogopite and
glass.
From a liquid of composition (Fo
3
Di
60
Lc
37
) (Fig.
10.16
b), diopside
ss
precipitates
'
X
'
in Fig.
10.18
). Similarly, O
'
rst at 1,010
°
C, followed by K-feldspar as the second phase at
'
e
'
, then phlogopite
appears at 990
) as the third phase. The assemblage diop-
side
ss
+ liquid corresponds to K-rich pyroxenite, whereas the assemblage at
°
C (at point
'
C
'
'
(Di
ss
+Kf
ss
+ Liq) correrponds to pyroxene-bearing syenite, and the assemblage
at
'
e-C
(Di
ss
+Kf
ss
+Ph
ss
+ Liq) corresponds to pyroxene-bearing minette.
With further lowering of temperature, the
'
C
'
final assemblage comprises diopside
ss
K-feldspar
ss
, phlogopite
ss
, kalsilite
ss
, and liquid. This assemblage corresponds to
kalsilite
pyroxene minette magma ascends upward
quickly, leucite should appear at shallower depth before K-feldspar
ss
and kalsilite
ss
completely disappear (Fig.
10.16
a). Bhowmik (2000) described diopsidite veinlets
in association with rocks comprising K-feldpsar, kalsilite, phlogopite, leucite, and
diopsidic pyroxene from the ductile shear zones of Borra near Visakapatnam, south
India. Such Kalsilite
pyroxene minette. If a kalsilite
-
-
Kfeldspar-bearing rocks have also been reported from the
Punalur locality of southern India (Sandifored and Santosh 1991). This assemblage
-
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