Abstract
Study of melt-rock interaction in open system.
Gneisses and migmatites of the Gföhl unit (Moldanubian Zone, Bohemian Massif) range from banded mylonitic orthogneiss with recrystallized monomineralic bands, through stromatic (metatexite) and schlieren (inhomogeneous diatexite) migmatite, to isotropic nebulite (homogeneous diatexite). This sequence was classically attributed to increasing degree of anatexis. Under the microscope, the evolution is characterized by progressive destruction of the monomineralic banding that characterizes the original mylonitic orthogneiss. Throughout, the mineral assemblage is biotite-K-feldspar-plagioclase-quartz +- garnet +- sillimanite, but the mineral compositions exhibit systematic changes with progressive disintegration of the layering. From banded orthogneiss to nebulite, the garnet composition changes systematically,