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THE STEP FROM DIAGENESIS TO METAMORPHISM IN PELITIC ROCKS DURING ALPINE OROGENESIS
Author(s) -
FREY M.
Publication year - 1970
Publication title -
sedimentology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.494
H-Index - 108
eISSN - 1365-3091
pISSN - 0037-0746
DOI - 10.1111/j.1365-3091.1970.tb02189.x
Subject(s) - illite , geology , geochemistry , greenschist , phengite , metamorphism , diagenesis , chlorite , authigenic , metamorphic facies , metamorphic rock , mineralogy , petrology , facies , clay minerals , geomorphology , quartz , paleontology , eclogite , structural basin , subduction , tectonics
Summary Pelitic rocks were followed from unmetamorphosed clays and marls of Upper Triassic and Lower Liassic to anchimetamorphosed phyllites of the Alpine border region in Switzerland. Phengite and Al‐rich chlorite formed from mixed‐layer illite/montmorillonite; pyrophyllite from kaolinite. For the formation of paragonite, the following sequence is proposed: irregular mixed‐layer illite/montmorillonite → regular mixed‐layer mica/montmorillonite → mixed‐layer paragonite/phengite → paragonite. Besides the formation of new minerals in the transition zone (anchizone) between diagenesis and greenschist facies, other changes with increasing metamorphic grade are: the crystallinity of illite (in the sense of K ubler , 1967) increases, the intensity ratio 002/001 of the illite basal reflexions increases, 1M d illite changes to 2M 1 phengite; the slates change colour from red to pink; the mean density increases; and textural changes due to reactions between clastic quartz and clay cement occur.