Rit (Vísindafélag Íslendinga) - 01.06.1984, Page 230
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PÁLL IMSLAND
TABLE 36 Sector zoning in apatites
Analyses on basal sectors Analyses on prismatic sectors
Wt. % C1 F h2o C1 F h2o
1. grain 0.51 0.91 1.21 0.90 0.92 1.19
2. grain 0.48 0.93 1.20 0.77 1.26 0.97
3. grain 0.58 1.27 1.01 0.93 1.42 0.85
4. grain 0.47 1.21 1.17 0.66 1.31 0.97
5. grain 0.56 1.30 1.00 0.72 1.23 1.00
Average 0.520 1.124 1.118 0.796 1.228 0.996
Number of ions
1. grain 0.146 0.487 1.364 0.263 0.501 1.236
2. grain 0.141 0.508 1.351 0.224 0.685 1.090
3. grain 0.170 0.693 1.137 0.272 0.774 0.954
4. grain 0.137 0.660 1.203 0.193 0.714 1.093
5. grain 0.165 0.713 1.122 0.210 0.670 1.119
Average 0.152 0.612 1.235 0.232 0.669 1.098
Concentrations of analysed C1 and F and calculated H2O on basal and prismatic
sectors of five euhedral apatite grains in a hydrous mineral xenolith (Jan 329)
showing the sector zoning of volatiles in these grains.
Si, Sr, Fe, Mn and Mg. In one grain of a basalt sample (Jan 69), Ti, Al, Cr,
Na and K were determined as well. Of these AI2O3 and Cr203 were not
detected (i.e. <0.005 wt. per cent) but Ti02 amounts to 0.04 per cent. The
alkalies are low as well, Na20=0.05 and K20=0.02 wt. per cent. Where
these elements are reported in apatite analyses they generally show such low
concentrations as here, except for slightly higher values reported by Nash
(1972) for Na and K from the Shonkin Sag laccolith apatites.
Si02 (Fig. 115) was detected in all the analysed grains and the range oí
concentration is from 0.14 to 0.97 wt. per cent Si02, with an average of0.39
per cent. The Si02 concentrations obtained by Nash (1976) in the apatites
of the tholeiitic Skaergaard intrusion rocks show slightly higher average
values (range=0.29—0.73, average 0.50 wt. per cent) than those of Jan
Mayen. The same holds true for the apatites of the Shonkin Sag laccolith
(Nash, 1972), where the difference is still greater (r=0.45—0.81, av=0.61
wt. per cent). The apatites of the Leucite Hills volcanic rocks, analysed by
Carmichael (1967), similarily show slightly higher values (r=0.50—1.10,
av=0.73 wt. per cent). Silica is thus apparently generally present in apatites
of igneous rocks in amounts up to ~1 wt. per cent, as Si02. In the Jan