Distribution of radioactive elements in three progressively metamorphosed pelite series of the Bohemian Massif

Abstract

The variations of the content of radioactive elements in pelitic rocks in dependence on the grade of metamorphism were studied in three regions of the Bohemian Massif with a different character and age of metamorphism. The concentrations of Th, U and K were determined by gammaspectrometric method, the major elements Si, Ti, Al, Fe, Mn, Ca, K, P by the X-ray fluorescence method. An increasing mobility of radioactive elements was found with the help of variation diagrams in the higher stages of metamorphism, the migration being apparent especially for Th and usually starting in the garnet or biotite zone. A significant negative correlation of both Th and U content with the content of SiO2 was determined. It was found that the behaviour of Th and U during the metamorphic processes reflect a different character of metamorphism. In agreement with[1] the decreasing tendency of Th and U during progressive metamorphism was confirmed in the metamorphic sequences of the Barrovian type, whereas an opposite trend in sequence of periplutonic character was found.