Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 99. (Budapest 2007)

Embey-Isztin, A. ; Dobosi, G.: Composition of olivines in the young alkali basalts and their peridotite xenoliths from the Pannonian Basin

In an ideal case the calculated and the measured composition of olivines do not differ much from each other. However, there can be a difference if the already crystallized olivines establish a new equilibrium with a fractionated melt phase through diffusion, and also if we have failed to find the most primitive olivine composition in a given rock sample. In both cases the measured olivines will be somewhat more iron-rich than the calculated equilibrium composition. Greater differences can occasionally occur, but these are already signs of major, less common genetic and magma evolution processes. In Fig. 10 we can see the connection between the Fe

2+

/Mg ratio of the most primitive olivines and that of the whole rocks and their positions relative to the calculated equilibrium line. Fig. 8. Relationship between the Fe/Mg ratio of olivine and that of the host basalt. (A) samples in which the composition of early crystallised olivines approach the equilibrium composition, (B) samples with early crystallised olivines that are more evolved than the equilibrium composition, (C) samples containing more magnesian early crystallised olivines relative to the equilibrium value, (D) is a magnified portion of subset (C)