Quartz deformation mechanisms in metasediments from Prins Karls Forland, Svalbard

Abstract

Quartzites and phyllites of presumed Precambrian-Cambrian age in western Spitsbergen were deformed and metamorphosed at middle to lower greenschist facies conditions. They exhibit a wide variation in quartz content with less variable quartz grain sizes. Quartz microstructures and lattice orientations in these rocks are used to infer which deformation mechanisms were dominant in the different lithologies. Three variable factors in the quartzites and phyllites may have influenced the way in which quartz deformed. These are: 1. (1) quartz content, 2. (2) average quartz grain size, 3. (3) the distribution of accessory phases (particularly the micaceous minerals) between the quartz grains. Generally, in a rock with a high quartz content, a coarse average quartz grain size, and/or poorly distributed accessory phases, quartz exhibits microstructures and lattice orientations which suggest that intracrystalline mechanisms dominated during deformation. On the other hand, in a rock with a low quartz content, a fine average quartz grain size, and/or evenly distributed accessory phases, quartz exhibits microstructures and lattice orientations which suggest that it deformed by means of intercrystalline mechanisms.