The relationship of phyllosilicate orientation, X-ray diffraction intensity ratios, and c/b fissility ratios in metasedimentary rocks of the Helveticzone of the Swiss Alps and the Caledonides of Jamtland, central western Sweden

Phyllosilicate preferred orientations, X-ray diffraction intensify ratios, and c/b fissility ratios were determined from 23 metasedimentary rocks from the Helvetic zone of the Swiss Alps and from the Caledonides of Jamtland, Sweden. The relationships between these parameters of phyllosilicate orient ation depend strongly on the lithology and the cleavage morphology. Differe nces in orientation direction and in degree of preferred orientation reflec t both deformation intensities and lithologies. Whereas polyphase deformed. fine-grained samples generally have phyllosilicates that are oriented para llel to cleavage showing high orientation intensities, phyllosilicates in l ess deformed and/or coarse-grained rucks are oriented parallel to bedding w ith low orientation intensities. Weak orientation intensities in samples wi th phyllosilicates that are oriented parallel to bedding reflect compaction strain, The higher strain in samples with micas and chlorites that are par allel to cleavage is a combination of compaction and tectonic strain due to the development of crenulation cleavage. (C) 2000 Elsevier Science Ltd. Al l rights reserved.