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NUMBER 19 111 FIGURE 7.—Graphite flakes in silicate area of inclusion 3, reflected light. (Width of image = 280 microns.) inclusions, and the spread within any one inclusion is larger than for the olivines. Compared to the mafic minerals, the plagioclase is very constant in composition at about 3.0% CaO, except for inclusion 6 with 3.4% CaO and inclusion 8, which shows the largest spread in An content of the feldspar (Table 5). The outer rim of the mafic minerals is lower in FeO content than the central part. Table 6 gives FeO values for several olivine centers and rims of inclusion 8. In Figure 9 the results of microprobe step-scans across several olivine and pyroxene grains are plotted. The large amounts of Fe just outside the grains are due either to a thin rim of iron oxide (formed by terrestrial weathering) or to troilite adjacent to the silicate grain. The drop in iron measured at the grain boundary, despite the steep rise just next to it, shows that this is a real effect, since any overlapping effect of the electron beam at the grain boundary should have raised the iron reading, not lowered it. Mg is plotted together with iron to show that the measured points are still in the silicate grain. The rise in MgO content compensating the drop in FeO (Table 6) is not visible here, because it is too small relative to the Mg level. In orthopyroxene Ca shows higher values in the grain centers and lower ones towards the rim. There is also a general tendency in the orthopyroxene for high Fe grains to also have high Ca contents, as shown in the CaO/FeO plot in TABLE 2.—Composition of silicate minerals from inclusion 8, determined by electron microprobe (numbers in parentheses give number of grains analyzed) Constituent SiO2 . . . AI2O3 • • MgO . . . FeO . . . CaO . . . TiO2 . . CT2O3 • • MnO . . . Na2O . . K2O . . . Total Orthopyroxene (65) 58.9 0.25 35.2 4.37 0.79 0.20 0.37 0.39 100.4 Olivine (63) 42.00 53.8 4.00 0.04 0.02 0.33 100.2 Diopside (33) 55.2 0.74 17.9 1.81 21.6 0.60 1.24 0.34 0.83 100.3 Plagioclase (53) 64.9 22.4 0.15 3.24 10.0 0.57 101.2 K-Feldspar (2) 64.0 19.8 0.52 1.17 1.0 14.7 101.2
112 15 10 32 3.6 40 44 48 •fl-r Olivine 3.2 3.6 40 44 48 Olivine 32 3.6 40 UU Olivine Inclusion 1 Section 2 Inclusion 2 Section 4 Inclusion 2 Section 9.1 9.2 3.2 36 40 44 48 5.2 %FeO Pyroxene S\ 3.6 40 4.4 48 5.2 Pyroxene 3.6 40 l*U 48 5.2 Pyroxene % FeO SMITHSONIAN CONTRIBUTIONS TO THE EARTH SCIENCES 5- 10- 3.2 3.6 40 44 Olivine u 3.6 40 4.4 Olivine % FeO 22 3.6 40 44 Olivine Inclusion 2 Section 3.1 3.2 Inclusion 2 Section 7 Inclusion 3 Section 1 n 3.6 40 44 48 5.2 Pyroxene % FeO 3.6 40 4.4 48 5.2 % FeO Pyroxene 36 40 44 48 5.2 %FeO Pyroxene FIGURE 8.—<strong>Hi</strong>stograms of microprobe FeO values of different inclusions. (The suffix ".1" or ".2" following a section number means that grains in two different areas were measured; results from 1 are hatched except for inclusion 12.) Figure 10. The same is true for the average Fe and Ca contents of the orthopyroxenes in different inclusions, higher FeO being accompanied by higher CaO values (Figure 11).
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SMITHSONIAN CONTRIBUTIONS TO THE EA
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Contents MINERALOGY COMPOSITION OF
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Constituent SiO TiO Al 0 fl 2 3 Cr
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PER CENT CBLCIUM FIGURE 3.—The ca
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Constituent TiO,, 2 2 3 FeO* MnO Mg
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20 Cfl 40 .60 SMITHSONIAN CONTRIBUT
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35'50' I L 6.. 3.. 2.. r FOKT DEFIA
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12 SMITHSONIAN CONTRIBUTIONS TO THE
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14 20 SMITHSONIAN CONTRIBUTIONS TO
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16 Constituent Si0 2 TiO2 A12O3 Cr
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18 20 40 £0 SMITHSONIAN CONTRIBUTI
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20 40 20 SMITHSONIAN CONTRIBUTIONS
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Abyssal Basaltic Glasses as Indicat
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24 Electron-M icroprobe Analysis An
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30 Hill in the NE Atlantic, and fro
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32 cores the arrangement is stratig
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36 ATLANTIC OCEAN LAT. LONG. DEPTH
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