A Note on Deformation Bands in Quartz

HARA Ikuo

Journal of science of the Hiroshima University. Series C, Geology and mineralogy

Variation in width of deformation bands in quartz in four specimens collected from the Sangun crystalline schist of the Nakase district, Hyôgo Pref., and the Sambagawa crystalline schist of the Kôtsu district, Shikoku, has been examined. The band width is considerably variable. Within a restricted domain (e. g. each specimen), however, it is fairly constant, showing a single marked maximum (the most frequent width) in the variation diagram of the band width for each specimen. Both the most frequent width and the maximun width are different between four specimens, and the former is proportional to the latter, that is, the former increases with increase in the latter. The band width does not appear to be always dependent upon the grain size. The band width may be dependent upon the rate and temperature of deformation, that is, it may increase with increase in temperature and decrease in strain rate, as is the case of creep deformation of metalic crystals. The present knowledges of some other properties of the deformation bands in quartz are also briefly described and discussed.
Three types of syntectonic recrystallization of quartz which are also referred to three types of paracrysta-lline deformation of quartz have been distinguished as follows: 1) Type I － it is shown by poly-gonization of bending lattice (e.g. band-boundaries)and formation of new grains which do not show preferred lattice and dimensional orientation. 2) Type II － the shapes of recrystallized quartz grains are strongly elongated parallel to the direction of mass elongation of the system concerned but the reorientation of the c-axes (lattice) of those grains are scarcely induced. And 3) Type III － the formation of preferred lattice and dimensional orientation. Deformation bands do not appear to be formed in quartz grains giving rise to the syntectonic recrystallization of Types II and III.

英語

HIROSHIMA UNIVERSITY

[ISSN] 0075-4374

[NCID] AA00706718