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116 SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES
10
FIGURE 9.—Microprobe step-scan for Fe and Mg across an
orthopyroxene grain in section 8. Grain center at left, boundary
towards feldspar at right. Fe increase between the grains
is caused by thin vein of iron oxide formed by terrestrial
weathering.
1.5+
1.0-
0.5-•
%CaO
6.1 •
6.2 o
4.0 5.0 % FeO
FIGURE 10.—CaO vs FeO in orthopyroxene from inclusion 6.
%CaO
0.9 +
0.8-
0.7-
%FeO
40 45 50
FIGURE 11.—CaO vs FeO, average values of orthopyroxenes
from different sections.
This is an important test to determine whether or
not the chemical differences between different
inclusions, as shown in the values of Table 8, are
due to sample inhomogeneities or are real. These
variations are already evident from the variations
in modal composition of inclusions 4 and 5 (Table
1). In Table 8 an average composition for the
inclusions 1 to 5 has been calculated, although it
seems doubtful that such an average gives meaningful
values.
A consistent feature of the inclusions is the lower
FeO-content compared to chondrites, which is
caused by the lower FeO-content of the mafic minerals.
In Table 9, therefore, the silicate composition
Grain Ifo.
38
43
44
45
51
55
79
81
Mean
TABLE 6.—FeO content (weight percent) of olivines
in inclusion 8
Center
4.18
3.83
4.09
4.28
4.35
4.39
4.39
4.34
4.23
Rim
3.71
3.45
3.80
3.79
3.98
3.62
3.91
4.00
3.78