Skalenie serii metamorficznej Gór Bialskich i Złotych w Sudetach
Abstract
Feldspars from the metamorphic series of the Góry Bialskie and Góry Złote ranges in the Sudetes
Abstract
By means of optical, X-ray and chemical methods, an analysis has been made of feldspars from two rock complexes occurring together and derived from analogous series of sedimentary origin: the gneiss Góry Bialskie complex developed under conditions of the amphibolite facies, and the granulite Góry Złote complex formed under conditions of the granulite facies. The feldspars of these two complexes differ in composition, development and structural features. After examining the bearing of temperature and pressure on the composition and development of the feldspars it is supposed that pressure was the factor mainly responsible for the differentiation of feldspars in the complexes here considered. Two chief stages may be distinguished in the development of feldspars in the gneiss complex. In the earlier stage, under conditions of directional pressure, the increasing temperature was the predominant factor of metamorphism. In the final phase it attained the lower limit of temperatures prevalent in the granulite complex. In the later stage, under conditions of very slight variability of temperature fitting into the lower temperature limit of the granulite complex, pressure underwent a change, with the disappearance of directional pressure. The present development of the feldspars from the granulite complex most likely took place under fairly stabilised physical conditions, no essential role being played by the directional pressure. The investigation of the feldspars has led to the conclusion that the conditions of metamorphosis in the rock complexes correspond to the high pressure and to the low temperature ranges in the field of the amphibolite and granulite facies, the boundary between these facies occurring at a temperature of c. 500°C, with the pressure at 7.4 kb. The above data as well as those obtained from the literature permitted tentatively to determine the amphibolite-granulite facies boundary in the temperature-pressure field.