X-ray diffraction parameters in very low-grade metamorphism seen in the “light” of TEM

TL;DRAbstract

Methods based on X-ray diffraction commonly used to decipher diagenetic / lowgrade metamorphic conditions are revised and evaluated according to our current knowledge of related geological processes obtained via transmission electron microscopy. A lack of evident qualitative changes in phyllosilicates, including their mineral chemistry, from deep diagenetic to low-epizone conditions explains the scarcity of valid grade criteria. Throughout this range of diagenetic-metamorphic conditions a progressive increase in the crystalline domain size together with a decrease in the number of defects are the only significant changes to be observed. Therefore indices related to crystallinity still remain the most successful methods based on the crystalchemical characteristics of phyllosilicates.

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