The granite system near Betliar village (Gemeric Superunit, Western Carpathians): Evolution of a composite silicic reservoir

Abstract

Boron- and fluorine-rich highly evolved granites in the Betliar area (Gemeric Unit, Western Carpathians) represent composite intrusion that formed probably during two distinct magmatic episodes. During the first stage, evolved granitic magma originating from an underlying volatile-rich reservoir intruded into an open fault system in the form of sill-like bodies and crystallized as equigranular or medium- to fine-grained rocks. The subsequent volatile flux enhanced postmagmatic alterations of the solidified granites and led to the formation of greisens with elevated amounts of tourmaline and Nb-Ta-W-Th phases. During the second stage, magma from a deeper magmatic reservoir intruded as a mush containing K-feldspar, albite, mica and quartz phenocrysts and gave rise to porphyritic granites. Partial dissolution and corrosion of the phenocrysts was enhanced by a pressure drop during emplacement of the porphyritic granites into middle-crustal level where the volatile-rich residual melt rapidly crystallized and is now preserved as quartz-albite-K-feldspar matrix with tourmaline and other accessories. Monazite and zircon geochronology indicates that the process occurred during Middle and Late Permian, and possibly extended to Early Triassic.