Magnetic fabric overprints in multi-deformed polymetamorphic rocks of the Gemeric Unit (Western Carpathians) and its tectonic implications

Abstract

In the Gemeric Unit of the Central West Carpathians, the magnetic fabric was investigated in Early Palaeozoic metasediments and metavolcanics, Permian to Early Triassic granites, and Late Palaeozoic (molasse) metasediments. In addition to Variscan greenschist facies metamorphism in the Early Palaeozoic basement, all rocks underwent Cretaceous (Alpine) low-grade metamorphism, which significantly modified their mineral composition and fabric; original magnetic minerals were destroyed at least partially and new, mostly paramagnetic, minerals were created.In the Early Palaeozoic metasediments, the magnetic fabric is entirely metamorphic/deformational in origin. In metavolcanics, the magnetic foliations are partly parallel to the Alpine metamorphic foliations developed in relatively incompetent lithologies such as tuffs and tuffites and partly to disjunctive foliations developed in competent rhyolites and its subvolcanic members. Their magnetic fabrics probably represent gradual transition from Variscan to Alpine fabrics. In the Permian granites, the magnetic foliations are near the Alpine mesoscopic disjunctive foliations crosscutting metamorphic schistosity in contact aureoles of granite. In the Late Palaeozoic (molasse) metasediments, the magnetic foliations are near the Alpine metamorphic foliations that are mostly parallel to the original bedding. On regional scale, the magnetic fabrics show curved pattern indicating complex interactions between the Gemeric and underlain Veporic units in the final stages of intendation and collision.The magnetic fabric pattern in the Gemeric Unit roughly resembles that in the Veporic Unit. This results from similar tectonic movements operating at least during Cretaceous collision in both the units. This tectonic process occurred subsequent to the closure of the Meliata ocean and was responsible for creation of the final structure of the Central Western Carpathians. Nevertheless, in contrast to the Veporic unit, where dominantly Alpine type of magnetic fabrics is present, in the Gemeric Unit the Alpine overprint had variable degrees of modification of AMS fabrics ranging from relatively weak to totally obliterated.