Element mobility and fluid path ways during feldspar alteration: textural evidence from cathodoluminescence and electron microprobe study of an example from tonalites (High Tatra, Poland-Slowakia)

Abstract

Infiltration of aqueous or CO2 rich fluids into plutonic rocks cause strong redistribution of the major elements within individual feldspar grains. This paper documents these features, using cathodoluminescence and electron microprobe analyses, on an example from a tonalite (High Tatra). An-rich plagioclase with small inclusions of K-feldspar decomposed under the influence of H2O fluids into albite, white mica, prehnite and quartz . This reaction leads to separation of alkalies from Ca and migration of alkalies and Ca over a distance of around 200 micrometers within the grain. Redistribution of Al is less affected by this reaction. Infiltration of H2O + CO2 -rich fluids through the An-rich plagioclase with minor orthoclase component produces calcite together with prehnite, albite and white mica. Reactions preferably affect the An-rich domains in plagioclase, Ab-rich domains remain unaffected, and the presence of K-feldspar in plagioclase either as inclusion or as a solid solution component facilitates the reactions.