Jökull - 01.12.1977, Blaðsíða 18

TABLE III (continued)
Bb 465 N = 4 X ± Bb 480b N = 5 X ± Bb 483 N = 4 xT ± Bb 483 N = 8 X ± Bb 483x N = 4 X ±
SÍ02 49.00 1.04 49.86 .37 50.20 .62 76.24 1.76 49.50 1.00
ALOa 13.79 .22 13.53 .12 13.65 .10 11.97 .50 13.32 .21
TiOo 1.75 .11 1.52 .04 1.82 .06 .30 .06 3.00 .24
FeO* 12.44 .46 11.41 .38 12.36 .10 2.85 .45 14.02 .40
MnO .20 .01 .20 .05 .23 .05 .08 .07 .25 .07
MgO 6.52 .48 8.46 .23 7.79 .13 .17 .08 6.21 .24
CaO 12.18 1.20 12.16 .19 11.46 .32 1.41 .23 9.86 .54
Na20 2.51 .45 2.56 .11 2.56 .13 .88 .30 2.77 .17
KoO .26 .12 .24 .02 .23 .04 1.64 .18 .46 .03
P2O5 .18 .05 .18 .03 .18 .07 .06 .05 .31 .06
98.83 100.12 100.48 95.60 99.70
Bb 483x N = 3 X ± Bb N = X 484 = 4 S.D. Bb N = X 486 = 6 Bb 490 N = 4 X ± Bb 492 N = 6 X ±
Si02 50.56 .70 51.03 .82 49.23 1.02 49.50 .44 48.95 .55
AI2O3 13.93 .20 14.37 .20 13.56 .29 13.56 .38 13.58 .40
TiOo 1.80 .06 1.66 .03 1.71 .10 1.69 .05 1.69 .06
FeO* 12.60 .20 12.26 .35 12.04 .52 12.07 1.45 12.31 .26
MnO .21 .02 .20 .02 .22 .06 .24 .04 .26 .23
MgO 7.74 .10 6.69 .44 6.67 .13 6.37 .47 6.71 .14
CaO 11.36 .19 11.23 .75 12.04 .10 11.65 .78 12.04 .23
Na20 2.61 .07 2.61 .10 2.40 .11 2.34 .09 2.36 .06
K»0 .23 .03 .18 .08 .25 .03 .24 .06 .26 .06
P2O5 .20 .04 .13 .03 .17 .02 .16 .04 .18 .02
101.24 100.36 98.29 97.82 98.34
may be íormed in eruptions hitherto unrecord-
ed, in the regions west to northeast o£ Bárdar-
bunga. However, in view o£ the Kv? 1477 ana-
lysis (Table II, no. 12) it seems likely that some
of the tephras £rom the period between 1650
and 1730 may be front Kverkfjöll.
The next few years will see much new chemi-
cal clata on known tephras in Iceland, procured
with the microprobe, but so far little work has
Ireen done along these lines beyond that pre-
sented here. One aspect, which has to be tested,
] 6 JÖKULL 27. ÁR
is the question of the homogeneity (or other-
wise) of the products of the various volcanoes.
Finally, in Table II, 12 analyses are given
for comparison representing known volcanoes
that cover the range in chemical characteristics
observed in the Bárdarbunga samples. The ana-
lyr.es are plotted for comparison in Fig. 6. Clear-
ly tlie 12 analyses sliow greater scatter than do
tlic microprobe glass analyses — it is as if they
represent various mixtures of the “pure compon-
ents”.