Textural and age relations of polymetamorphic rocks in the HP Meliata Unit (Western Carpathians)

Slices and tectonic blocks of amphibolite facies crustal rocks overprinted by blueschist facies metamorphism occur in the Middle-Jurassic Meliata high-pressure unit of the Western Carpathians. The Early Paleozoic age for relic muscovite is known from some micaschists with blueschist facies overpint in the eastern sector of the Meliata unit. Based on lithology, some amphibolite facies rocks are comparable with the Early Paleozoic basement rocks in the Gemeric unit. In this work, we present results of petrology and Ar–Ar and Rb–Sr geochronology from blueschist facies rocks with relicts of hornblende, muscovite, garnet, and rutile. The older amphibolite facies metamorphism was followed by retrogression prior to the blueschist facies overprint. The blueschist facies metamorphic minerals are Ca-rich garnet, glaucophane, phengite, and albite. The coarse-grained relict muscovite indicates an Early Paleozoic age using the Ar–Ar method and a Middle-Jurassic age using the Rb–Sr technique. The presence of amphibolite facies rocks within the Meliata unit is interpreted as involvment of Variscan/Pre-Variscan basement-unit rocks in the Middle-Jurassic subduction of the Meliata-Hallstatt oceanic basin.

► Mineral textures and age dating in metasediments record two metamorphic processes.
► Variscan amphibolite facies assemblages are overprinted by Jurassic blueschist facies minerals.
► The micaschists support involvement of basement units in the Jurassic subduction.