Although illite crystallinity can be used as an empirical parameter to characterize incipient metamorphism of sedimentary rocks not containing facies or zone-indicative mineral assemblages, the variations in half-width of the 10 A basal reflection of illite are caused by the superimposition of various factors. The effects of illite crystallinity on the average size of coherently diffracting domains in the c-axis direction and of the lattice distortion were distinguished. In the NE Hungary metamorphic sequences from the deep diagenetic zone to the epizone, the effect of domain size on illite crystallinity is significant. In the diagenetic and anchizones parallel with the increasing grade of metamorphism, the domain size increases while the lattice distortion decreases. In the epizone the considerable rise in domain size is not accompanied by a further drop of lattice distortion. With increasing metamorphic grade (decreasing illite crystallinity) there is a decrease in mixed- layer 14-15 A structures and an increase of the K content of the micas.-R.A.H.
|Number of pages||18|
|Journal||Acta Geologica Hungarica|
|Publication status||Published - Jan 1 1983|
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