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(a)
(b)
2
1
Fo
Fo
En
2
1
En
10
Ok
Ok
14
20
Lc
Lc
Or
12
26
18
Q
27
Q
24
Ph
Or
Ok
Lc
Or
Q
(c)
(d)
5
7
4
6
Ph
Fo
Ph
Fo
Ph
Ok
En
Ok
En
7
11
20
11
20
26
27
Q
Lc
Lc
14
14
Q
27
26
Or
Or
(e)
(f)
5
6
7
5
6
Fo
Ph
Fo
Ph
Ok
En
Ok
20
En
15
16
20
15
16
11
7
27
11
Ph
Lc
27
26
Q
Or
Lc
Or
26
Q
(g)
(h)
5
6
7
Fo
Ph
Ok
En
20
11
27
Q
Lc
Ph
Lc
En
14
14
21
Q
24
Or
26
h
Or
g
(i)
(j)
3000
f
6
5
Fo
e
Ok
7
20
i
11
En
Lc
Ph
2000
Q
d
14
27
Or
26
c
1000
b
a
0
800
1000
1200
1400
o
T ( C)
Fig. 12.2 a
j Inferred phase relations on the saturation surface. Projection of the saturation surface
on to the anhydrous base of the tetrahedron from the H
2
O apex. a. Isobaric-polythermal, 500 bars
(a of Fig.
12.2
j). b. Isobaric- polythermal, 1,000 bars (b of Fig.
12.2
j). c. Isobaric-polythermal,
1,500 bars (c of Fig.122j). d. Isobaric-polythermal, 2,000 bars (d of Fig.
12.2
). e. Isobaric-
polythermal 2,500 bars (e of Fig.
12.2
j). f. Isobaric-polythermal 3,000 bars (f of Fig.
12.2
j).
g. Polybaric-polythermal (g of Fig.
12.2
j). h. Polybaric-isothermal, 900
°
C (h of Fig.
12.2
j).
i Polybaric polythermal (i of Fig.
12.2
j). j Pressure-temperature orientation for Fig.
12.2
a
-
i. (after
Luth 1967)
-
leucite-bearing rocks, although K-feldspar is an accompanying phase enstatite
is absent.
On the basis of Fig.
12.2
, Luth (1967) considered that a magma at depth initially
precipitating olivine should be resorbed to form mica and then pyroxene. These
early differentiates should be present as xenoliths and react with liquid. He referred
to the existence of phlogopite-bearing ultrama
c xenoliths in the potassium-rich
lavas of the Bufumbira region (Holmes and Harwood 1937), to support his con-
clusion. Luth also considered that the magmas of this region cooled for a long
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