Rit (Vísindafélag Íslendinga) - 01.06.1984, Blaðsíða 218

214
PÁI.I, IMSI.AND
TABLE 33
1 2 3 4 5 6 7 8 9 10
Si02 44.19 42.93 47.73 45.60 42.43 45.70 48.59 49.28 49.52 52.01
tío2 2.75 3.73 3.30 2.42 4.11 3.65 2.82 3.27 3.18 2.11
ai2o3 13.26 12.05 15.53 15.36 14.15 16.70 16.84 15.53 17.72 18.76
Fe203 2.82 5.58 2.02 2.44 5.84 3.73 3.29 2.16 2.55 2.46
FeO 8.79 8.27 8.95 8.89 8.48 7.28 7.03 10.25 5.66 5.99
MnO 0.18 0.16 0.14 0.15 0.17 0.17 0.19 0.22 0.18 0.05
MgO 10.30 10.28 8.37 7.36 6.71 4.89 4.58 3.54 3.42 3.11
CaO 8.77 12.58 8.71 8.99 11.91 9.91 8.75 8.78 7.58 6.60
Na20 3.71 2.36 2.89 3.13 2.77 3.96 4.35 3.72 4.94 4.34
k2o 2.02 1.47 1.70 1.68 2.04 3.10 2.06 1.60 3.88 3.38
p2o5 0.97 0.59 0.29 0.80 0.58 0.84 0.72 0.92 1.09 0.44
h2o 1.12 0.26 0.24 3.65 0.78 0.21 0.76 0.33 0.44 0.48
Total 98.91 100.26 99.87 100.47 99.97 100.14 99.97 99.60 100.16 99.73
Fe203' 12.58 14.77 11.96 12.31 15.26 11.82 11.10 13.54 8.83 9.11
Liquidus temperature in °C
Plag 1125 1145 1130 1165 1170 1150 1156 1140 1145 1170
Composition ofalkaline rocks which closely resemble thejan Mayen rocks and their
first appearance plagioclase temperature. 1) AJI 2164 (Arculus, 1975), Basanite,
Victoria, Australia. 2) 114 (Baker et al., 1964), Ankaramite, Tristan da Cunha. 3) G
111 (Le Maitre, 1962), Porph. ol. basalt, Gough Island. 4) (Tilley et al., 1967),
Alkali ol. basalt, N.S. Wales. 5) 6 (Baker et al., 1964), Olivine basalt, Tristan da
Cunha. 6) 364 (Baker et al., 1964), Trachybasalt, Tristan da Cunha. 7) AJ 175
(Thompson & Flower, 1971), Alkalic basalt, Anjouan Island. 8) SNS 9 (Steinthors-
son, unpubl.), Alkalic basalt, Snaefellsnes, Iceland. 9) 125 (Baker et al., 1964),
Trachybasalt, Tristan da Cunha. 10) G 95 (Le Maitre, 1962), Porph. trachybasalt,
Gough Island. The temperature determinations of the Tristan rocks were made by
Tilley et al. (1965) and of the Gough rocks by Tilley et al. (1967). The temperature is
determined at 1 atm pressure except for No. 1, which is at 10 kb.
resorption and after build-up of volatile separation and thus coincide with
the microphenocryst crystallization.
If known, the depth of the volatile release of the magma would put
restrictions on the pressure under which the microphenocryst crystallization
started and the resorption stopped. This depth is diflicult to determine and
it is probably different from one magma to another, depending, i.a., on the
amount ofvolatiles in the magmas. Moore (1970) found the amount ofwater
and other volatiles in basic magmas of deep sea pillow lavas to increase with
increasing alkalinity of the magmas. The solubility of water in magmas