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

PRESSURE-TEMPERATURE CONDITIONS OF HIGH-GRADE METAMORPHISM AND MIGMATITIZATION IN THE MALA FATRA CRYSTALLINE COMPLEX, THE WESTERN CARPATHIANS

Pages: 287 - 302

Authors: MARIAN JANAK, BRANISLAV LUPTAK

Abstract: Pressure-temperature conditions of metamorphism and migmatitization were investigated in the Mala Fatra crystalline complex, representing one of the deepest segments of the Variscan basement in the Western Carpathians. Field observations together with structural data document close relationships between migmatitization and deformation. The penetrative, syn- to post-metamorphic Variscan deformation with generally top-to-the south-southeast sense of shearing has been documented. Thermobarometric data obtained by conventional and internally consistent (TWEEQU) methods indicate the attainment of ca. 700–750 °C and 6 kbar in metapelitic migmatites and 700–750 °C and 8–10 kbar in garnet-clinopyroxene amphibolites. Migmatitization took place by partial melting during decompression, producing granitic leucosome in metapelites and tonalitic-trondhjemitic leucosome in the metabasites. Initial high-pressure stage and a "clockwise" P-T path is inferred from a) kyanite-sillimanite transformation in metapelites and b) kelyphitic and symplectitic textures in garnet-clinopyroxene metabasites, indicating the breakdown of eclogites reequilibrated at upper-amphibolite to granulite facies conditions. The proposed metamorphic evolution is consistent with considerable crustal thickening and extension of the West-Carpathian crystalline basement during the Variscan orogeny.

Keywords: Western Carpathians, Mala Fatra, Variscan orogeny, high-grade metamorphism, thermobarometry, deformation, migmatites

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