Pumpellyite-prehnite mineral assemblage in Tatric basement and its relation to the Central Western Carpathian units

摘要

Pumpellyite ± prehnite-bearing secondary mineral assemblage has been found in several basement rocks of the Tatric Unit. Quartz-free rocks, ranging from amphibolic schists to calc--silicate hornfelses, represent the most appropriate lithology for the pumpellyite forming reactions. Growth and composition of pumpellyite are widely influenced by the type of mineral precursor and fluid infiltration. Besides of tiny veinlets, pumpellyite formed predominantly at the expense of pre--Mesozoic diopside, amphibole, biotite, garnet and fine-grained groundmass. Prehnite replaced mainly An-rich plagioclase. Pumpellyite is represented mostly by Al-type; pumpellyite-(Mg) or lower thermal pumpellyite-(Fe) developed only locally. Based on investigated mineral assemblages and chlorite geothermometric estimations, metamorphic overprint in the Tatric basement-rocks is constrained by pumpellyite-prehnite fades conditions. Alpine tectono-metamorphism is preferred as the main forming process of studied mineral assemblages. The Hronic Unit is envisaged as integral nappe-unit involved in the Alpine (Cretaceous) collision tectonics of the Central Western Carpathians. Based on pumpellyite and/or actinolite occurrences, there is outlined a tentative zonation of the Alpine metamorphism in the Central Western Carpathians.