Rit (Vísindafélag Íslendinga) - 01.06.1984, Síða 113
mineral chemistry and relationships
109
TABLE 17 (continued)
87—B 65—A 10—A 15—B 87—E 89—B 152 —E 57—E 63 —D 168—B
sío2 40.32 37.89 38.87 38.55 37.48 37.68 36.05 35.03 35.83 34.48
tío2 0.03 0.00 0.00 0.05 0.03 0.05 0.06 0.05 0.07 0.02
Al^os 0.05 0.05 0.09 0.05 0.03 0.06 0.05 0.03 0.04 0.00
Cr203 0.03 0.00 0.00 0.01 0.00 0.00 0.03 0.00 0.04 0.02
FeO' 15.26 18.74 20.49 23.01 25.21 25.87 29.97 33.36 35.48 39.34
MnO 0.22 0.28 0.34 0.39 0.60 0.67 0.83 1.02 0.93 2.59
MgO 43.34 42.13 39.62 36.43 35.10 35.11 32.98 30.48 28.20 23.41
CaO 0.26 0.24 0.55 0.39 0.30 0.19 0.33 0.35 0.41 0.17
NiO 0.14 0.00 0.16 0.01 0.00 0.09 0.03 0.00 0.05 0.00
Total 99.65 99.33 100.12 98.89 98.75 99.72 100.33 100.32 101.05 100.03
Number of cations on basis of 4 oxygens
Si 1.021 0.972 1.004 1.024 1.006 1.002 0.970 0.958 0.986 0.991
Ti 0.001 0.000 0.000 0.001 0.001 0.001 0.001 0.001 0.002 0.000
A1 0.002 0.002 0.003 0.002 0.001 0.002 0.002 0.001 0.002 0.000
Cr 0.001 0.000 0.000 0.000 0.000 0.000 0.001 0.000 0.001 0.000
Fe 0.323 0.402 0.442 0.511 0.565 0.576 0.674 0.763 0.817 0.946
Mn 0.005 0.006 0.008 0.009 0.014 0.015 0.019 0.024 0.022 0.063
Mg 1.637 1.611 1.525 1.442 1.404 1.392 1.322 1.243 1.157 1.003
Ca 0.007 0.007 0.015 0.011 0.009 0.005 0.010 0.010 0.012 0.005
Ni 0.003 0.000 0.003 0.000 0.000 0.002 0.001 0.000 0.001 0.000
Fo 83.5 80.0 77.5 73.8 71.3 70.8 66.2 62.0 58.6 51.5
Numbers above analyses are rock sample numbers. A=kink-banded olivines, B=
unstressed phenocrysts, C=wehrlite olivine, D=microphenocrysts, E=groundmass
crystals. Nr. 12, 30, 65 & 10 are ankaramites; nr. 80, 87, 26, 15, 152, 57, & 63 are
basalts; nr. 151 is a wehrlite; nr. 89 is a basaltic tristanite; nr. 168 is a trachyte. n.d.=
not determined.
tion is in agreement with the values obtained for the olivines of the lavas and
the gabbro xenolith of Jan Mayen as is obvious from Fig. 73, but the
wehrlite xenolith olivines contain between 0.3 and 0.4 wt. per cent CaO,
which is within the Ca range of the phenocrysts of the same Fo content. This
is far higher than the generally low Ca contents found in olivines of
ultramafic plutonic rocks reported by Ross et al. (1954), White (op.cit.) and
Simkin & Smith (op.cit.). While the reasons for this discrepancy between
the observed behaviour pattern of Ca in olivines are not obvious, it does
nevertheless indicate that the Ca content of olivines is controlled by other,
perhaps more complicated factors, than control the Mn and Ni content of
olivines, which seem to be independent of the crystallization environment.