DISTRIBUTION OF FE3-SPINELS AND BASALT MELTS IN TERMS OF COMPOSITION,TEMPERATURE AND OXYGEN FUGACITY( AND FE2+ BETWEEN CHR OME)

An empirical equation describing the dependence of Fe3+/Fe2+ ratio in spinel (Sp) on the temperature, oxygen fugacity as well as Fe3+/Fe2+ a nd Al/(Al + Na + K) ratios in mafic melts (L) has been developed as a result of multiple linear regression analysis applied to a set of 112 ''most equilibrium'' coexisting Sp and L compositions: ln(Fe3+/Fe2+)(S p) = 58107/T + 2,007lgf(O2) -3,026ln(Fe3+/Fe2+)(L) - 3,648 ln[Al/(Al Na + K)](L) - 30,623. On the basis of the regression parameters, expe rimental temperatures for the set of compositions were calculated with an accuracy of 9 degrees C (if given lgf(O2)), whereas lgf(O2) values were reproduced with an accuracy of 0.1 log. unit. It was shown, that during petrologic calculations dealing with natural olivine-spinel-me lt equilibria, when the equilibrium temperatures and (Fe3+/Fe2+)(L) ra tios were initially unknown, but may be calculated from olivine-melt h eothermometers and Sack et al. (1980) equation, the accuracy of the es timates of lgf(O2) is about 0.5 log. unit.