Nitrogen-bearing fluids, brines and carbonate liquids in Variscan migmatites of the Tatra Mountains, Western Carpathians - heritage of high-pressure metamorphism
Hurai, Vratislav; Janak, Marian; Ludhova, Livia; Horn, Elfrun-Erika; Thomas, Rainer; Majzlan, Jura
European Journal of Mineralogy Volume 12 Number 6 (2000), p. 1283 - 1300
published: Nov 17, 2000
manuscript accepted: Jun 23, 2000
manuscript received: Jan 17, 2000
ArtNo. ESP147051206015, Price: 29.00 €
Abstract Gaseous inclusions in migmatites of the Tatra Mountains contain 5-100 mol. % nitrogen, contrasting with essentially the nitrogen-absent, mostly CO2-CH4 composition of fluid inclusions in other migmatites. While CO2 predominates in the Tatra metapelite migmatites, pure nitrogen inclusions are typical of the associated metabasite migmatites. CaCl2-rich brines (>30 wt.% NaCI eq.), halite, graphite and carbonate globules are the additional phases accompanying the nitrogen-rich fluids in the migmatite Ieucosomes. Monophase, crack-bound carbonate inclusions, consisting of calcite in metabasites and of Mg-bearing siderite in Fe-rich metapelites, are believed to represent a carbonate liquid, coexisting with and ex solving from the CO2-N2-brine fluid at temperatures between 550-700 0c. Compositions and densities of the N2-CO2 fluids and associated brines are similar to those in highpressure granulites and eclogites. Therefore, these volatiles are interpreted to have been inherited from a high-pressure stage, pre-dating the migmatisation. Together with mineral textures and assemblages, the fluidinclusion record is indicative of a substantial crustal thickening in the Western Carpathians during the Variscan orogeny. Essentially pure CO2-N2, graphite-saturated fluids in metapelites have been generated at dry conditions (XH2O = 0.2-0.25), resembling those of typical granulite-facies metamorphism.