International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

THE BREAKDOWN OF MONAZITE IN THE WEST-CARPATHIAN VEPORIC ORTHOGNEISSES AND TATRIC GRANITES

Pages: 161 - 167

Authors: IGOR BROSKA, PAVOL SIMAN

Abstract: The complete breakdown of monazite was observed in metagranites of the Veporic Superunit while only slight alteration of monazite occurs in unmetamorphosed Tatric granitoids (Tribec Mts., Mala Fatra and Strazovske vrchy Mts.). Monazite breakdown is probably a result of the reaction monazite+annite+anorthite+quartz+fluids giving apatite+allanite+muscovite. During monazite breakdown its margins are replaced outward by apatite corona, allanite rim and REE-rich epidote. In extreme cases monazite cores are fully consumed by apatite which occupies the place of the former monazite. The result of such breakdown is grains with apatite cores and the allanite-REE epidote rims. The monazite breakdown in the Veporic Superunit occured under conditions of amphibolite facies during an Alpine metamorphic event, although the process of breakdown had probably already started during the Variscan metamorphosis. In the case of monazite from Tatric granites initial breakdown of monazite was found in the context of Variscan subsolidus granite alteration. Only restricted mobility of the REE is supposed during the breakdown of monazite.

Keywords: Alpine metamorphism, REE mobility, monazite, allanite, granite, metagranite

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