Diagenetic-metamorphic zones

Diagenetic zone (or more precisely, diagenetic illite crystallinity zone) after Kibler (1964, 1968), the diagenetic zone is a pre-metamorphic stage defined by illite crystallinity (IC) valu es greater than 0.42 A°20 as measured on the <2 gm fraction of clay-rich, normal clastic rocks under conditions that correspond to the recommendations on sample preparation, X-ray diffraction settings and interlaboratory standardization as summarized by Kisch (1991). 

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