Mineralogy and geochemistry of
K-rich basalts of the central part of the
Babansky A., Solovova I.
Institute of
The potassium-rich igneous suite of the Tigil
anticlinorium in
Table 1. Chemical compositions
of phenocrysts from the alkaline rocks, wt %
|
1 |
2 |
3 |
4 |
5 |
6 |
7 |
SiO2 |
41.79 |
38.55 |
51.92 |
54.29 |
51.75 |
55.94 |
67.42 |
TiO2 |
- |
- |
0.64 |
0.26 |
0.46 |
0.08 |
0.00 |
Al2O3 |
- |
- |
3.59 |
0.65 |
1.49 |
27.03 |
19.74 |
FeO |
22.08 |
29.52 |
5.80 |
16.34 |
8.06 |
0.81 |
0.33 |
MnO |
|
|
|
1.19 |
0.57 |
0.04 |
0.00 |
MgO |
39.38 |
44.95 |
14.80 |
26.85 |
15.67 |
0.06 |
0.00 |
CaO |
0.28 |
0.08 |
22.62 |
1.28 |
21.15 |
9.69 |
0.28 |
Na2O |
- |
- |
0.32 |
- |
0.45 |
5.73 |
3.65 |
K2O |
- |
- |
- |
- |
- |
0.51 |
11.02 |
SrO |
- |
- |
- |
- |
- |
0.21 |
0.00 |
BaO |
- |
- |
- |
- |
- |
0.04 |
0.33 |
mg |
0.76 |
0.67 |
- |
- |
- |
- |
- |
Wo |
- |
- |
46.5 |
- |
45.4 |
- |
- |
En |
- |
- |
44.3 |
75 |
46.8 |
- |
- |
Fs |
- |
- |
9.3 |
25 |
7.7 |
- |
- |
An |
- |
- |
- |
- |
- |
47 |
1 |
Ab |
- |
- |
- |
- |
- |
50 |
33 |
Or |
- |
- |
- |
- |
- |
3 |
66 |
Note. Anmanna River: (1) olivine from sample
7039, (2) olivine from sample 7042, (3) clinopyroxene from
sample 7039. Uksichan caldera: (4) orthopyroxene,
(5) clinopyroxene
xenocryst, (6) plagioclase, (7) K-feldspar.
The olivine-free
alkaline basaltoids of the Uksichan caldera contain abundant phenocrysts of
Mn-bearing orthopyroxene (up to 2 wt % Mn๏, mg-number
of 0.700.75) and feldspars, plagioclase (An47Ab50Or3)
and alkali feldspar (An1Ab33Or66) (Table 1).
In addition, there are amphibole and FeTi oxide phenocrysts.
The initial magma of the basaltoids is alkali-rich
(up to 9 wt % Na2O + K2O at K/Na up to 1.6) and shows
high contents of volatile components (up to 0.2 wt % Cl and F), ๒2O5 (up to 2 wt %), and ๎2๏. The bulk analyses
of the shonkinites contain up to 4 wt % H2O. The magmas of the
Uksichan caldera were probably F-rich, which is indicated by the F-rich
composition of apatite (up to 6% wt % F). Also noteworthy are high contents of
some incompatible trace elements, especially Ba and Sr, which were detected in
substantial amounts in feldspar compositions. Heating experiments with the melt
inclusions showed that the melt began crystallizing at relatively low
temperatures, no higher than
Table 2. Chemical compositions of rocks (Anmanna River) and melt
inclusions in olivine and clinopyroxene, wt %
|
1 |
2 |
3 |
4 |
5 |
6 |
7 |
8 |
9 |
Sample |
7042 |
7039 |
7021 |
7039 |
7039 |
7039 |
7042 |
7039 |
7021 |
SiO2 |
51.17 |
52.76 |
55.26 |
50.18 |
54.07 |
55.07 |
48.1 |
45.5 |
48.9 |
TiO2 |
1.73 |
1.15 |
1.44 |
2.3 |
0.85 |
0.83 |
0.68 |
0.95 |
0.64 |
Al2O3 |
15.2 |
17.31 |
19.21 |
15.36 |
14.29 |
14.28 |
15.98 |
13.28 |
12.86 |
FeO |
11.4 |
9.62 |
5.1 |
6.29 |
6.32 |
6.08 |
7.256 |
8.723 |
6.77 |
MnO |
- |
- |
- |
- |
- |
- |
0.16 |
0.19 |
0.17 |
MgO |
5.31 |
4.87 |
3.27 |
5.76 |
5.32 |
5.17 |
8.59 |
12.33 |
12 |
CaO |
6.66 |
6.36 |
4.91 |
11.06 |
8.8 |
8.77 |
8.02 |
7.22 |
5.41 |
Na2O |
3.09 |
3.39 |
3.2 |
3 |
2.27 |
3.08 |
2.92 |
2.55 |
2.71 |
K2O |
4.13 |
5.56 |
7.16 |
3.68 |
5.16 |
5.27 |
3.09 |
2.52 |
3.44 |
Total |
98.69 |
101.0 |
99.55 |
97.63 |
97.08 |
98.55 |
94.79 |
93.26 |
92.90 |
K2O+Na2O |
7.22 |
8.95 |
10.36 |
6.68 |
7.43 |
8.35 |
9.1 |
7.59 |
9.59 |
๔, C |
1160 |
1160 |
1115 |
1135 |
1165 |
1165 |
- |
- |
- |
Note. (13) Inclusions in olivine, (46) inclusions in clinopyroxene,
and (79) bulk rock compositions. T is the homogenization temperature of
melt inclusions.