Rit (Vísindafélag Íslendinga) - 01.06.1984, Page 160
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PÁLI, IMSLAND
TABLE 22
Olivine Spinels Temperature
Fog0 (Mg62 Fe2+38) (Cr54 Al39 Fe3+07) 1510°C
Fo9] JJ JJ 1389°C
Fog2 JJ JJ 1273°C
►D O to 0 (Mg7, Fe2+29) (Cr56 Al33 Fe3+, 1) 2394°C
Fo91 JJ JJ 2132°C
F092 J J J J 1897°C
F090 (Mg67 Fe2+33) (Cr57 Al32 Fe3+n) 2030°C
JJ (Mg60 Fe2+40) 1581°C
J J (Mg53 Fe2+47) 1293°C
Fo90 (Mg67Fe2+33) (Cr57Al32Fe3+,i) 2030°C
JJ (Cr50 Al39 Fe3+,,) 1804°C
” (Cr43 Al46 Fe3+,,) 1598°C
O t£> O (Mg67 Fe2+33) (Cr57 Al32 Fe3+,,) 2030°C
JJ (Cr52 Al29 Fe3+,9) 2220°C
” (Cr48 Al27 Fe3+25) 2400°C
Effect of changing mineral composition on the equilibrium temperature of olivine
and spinel. In the last example the Cr/Al ratio is constant.
phenocrysts attached to these silicate phenocrysts. The composition of the
olivine is around F090 (average of the 53 analysed early olivines of the
ankaramites is Fo8g 6 with a range from Fo80-9i.8). If these olivines and the
early spinels represent equilibrium crystallization pairs then equlibrium
temperature is around and over 2000°C, according to Jackson’s equation.
These are similar temperatures to those obtained by Evans & Wright
(op.cit.) for the Kilauea case. Some of these samples, however, have
crystallized a chromian diopside before the olivine crystallized, as shown
previously. These early spinels are found as inclusions in the clinopyroxenes
as well as in the olivine, which would indicate that the spinel has in some
cases, at least, crystallized before the olivine. In such instances the olivine
and the spinel are not equilibrium pairs. It has been shown previously that
the crystallization temperature of the early chromian diopside was most
probably around or slightly above 1350°C. In the cases where spinel has
crystallized prior to the clinopyroxene it may be supposed to have crystal-
lized at around 1350—1400°C. The olivines, which these early spinels of the
ankaramites would be in equilibrium with at 1400°C, have the composition
F091.7-94.5. Such an olivine would crystallize out of a liquid with a MgO/FeO