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70
Ba (ppm)
SiO
2
5000
LSC 288
60
3000
50
1000
90
20
Ce (ppm)
Al
23
50
10
Nb (ppm)
20
10
FeO
10
5
0
0
5
(634)
Rb (ppm)
CaO
12
3
8
4
1
0
Y (ppm)
10
KO
2
20
5
10
0
Zr (ppm)
200
P
25
0.8
100
0.4
0
0
24
20
16
12
8
4
20
16
12
8
4
0
MgO (Wt.%)
MgO (Wt.%)
Fig. 5.14 MgO variation diagram for selected major and trace elements. The solid line is an
olivine-clinopyroxene control, calculated by combining them in 4:1 ratio. The core composition of
olivine (Fo
93
) and diopside (Ca
45
Mg
46
Fe
9
) in high K-minettes are after Macdonald et al. (1992)
Interpretation of Turi and Taylor (1976) was however, based on determination of
oxygen isotope content of more evolved rocks. The studies of Rogers et al. (1985)
and Holm and Munksgaard (1982) provide data relative to more primitive K-rich
lavas (magnesian leucitites and leucite basanites), which might have been in
equilibrium with a K-rich mantle source. The data of Roger et al. suggest that
primary Vulsini high K-series lavas were characterized by following oxygen and Sr
isotopic ratios, respectively:
0.7088 and the values of
143
Nd/
144
Nd ratios
range between 0.51209 and 0.51228.5.5. The trace element and REE abundance of
K-rich silica de
8 and
*
≥
cient Rocks of Bearpaw Mountains are shown in Fig.
5.14
.
It was shown by Macdonald et al. (1992) that some of the highly magnesium-
rich minettes have high Ni and Cr contents (700 and 1,200 ppm) and their high
potassic character is re
ected by their high Ba (up to 5,491 ppm), Rb (283 ppm), Cs
(54 ppm) and Sr (2,291 ppm) content. They found that the Bearpaw rocks are more
enriched in Rb contents compared to K in highly potassic minettes. The K/Rb ratio
in these rocks range from 122 to 291 (mean 221). The Zr values are up to 163 ppm
and Nb 20 ppm. Thus, LILE/HFSE ratio is high, which is typical of K-rich rocks
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