Pumpellyite - actinolite facies quartzites from the eastern cover of the Zulova pluton (NE Bohemian Massif)

摘要

Detrital and metamorphic minerals occur in the feldspar-rich quartzites occurring in the eastern cover of the Zulova granitic pluton (northern part of the Moravo-Silesian Zone of the Bohemian Massif). The detrital minerals comprise quartz, K-feldspar, plagioclase (An 23-48) and scarce biotite. The metamorphic mineral assemblage consists of albitic plagioclase, pumpellyite, actinolite/ferroactinolite, clinozoisite, chlorite, muscovite, titanite, graphite and optically isotropic "allophane" representing chemically a mixture of silica, alumina and iron oxides/hydroxides. The crushing of detrital plagioclase grains triggered their decomposition into pumpellyite, clinozoisite, albitic plagioclase and, in places, muscovite. The plagioclase decomposition products are associated with actinolite/ferroactinolite and chlorite. The metamorphic mineral assemblage indicates sub-greenschist pumpellyite-actinolite facies; rocks belonging to this facies were not described up to now from the Moravo-Silesian Zone. The pumpellyite-actinolite metamorphism was of prograde character with pressure probably exceeding 4 kbar.