The Alpine overprints of the magnetic fabrics in the basement and cover rocks of the Veporic Unit (Western Carpathians, Slovakia)

Abstract

In the Veporic Unit building up the central areas of the Western Carpathians, the magnetic fabrics are more or less coplanar and coaxial in metamorphic (Early Palaeozoic in age), granitic (Early to Late Palaeozoic in age) and sedimentary cover rocks (Permian/Triassic in age). The magnetic fabrics in metamorphic and granitoid basement rocks, as well as in sedimentary (-volcanic) cover rocks, appear to reflect a very wide P– T conditions of Cretaceous (originally Variscan) basement reactivation connected with a prograde metamorphism of the sedimentary cover rocks in lower greenschist (in the North-Veporic area) or the upper greenschist to lower amphibolite facies (in the South-Veporic area) during collisional burial in a collisional wedge. In addition, there are deformation zones where the magnetic fabrics formed due to a ductile deformation associated with extensional exhumation along (sinistral) lateral strike slip and normal faults. The late open folds did not principally change the former magnetic fabrics. The magnetic fabrics in sedimentary cover rocks of the North-Veporic area are either related to still recognizable bedding planes (in competent layers) with parallel superimposed metamorphic schistosity, or they are conformable to subparallel or oblique metamorphic cleavages. In the South-Veporic area, they are undoubtedly related to the metamorphic–mylonitic fabrics of the basement granitoids and their metamorphic mantle rocks. The magnetic fabrics in granitoid rocks of the South-Veporic area (S of the Pohorelá sinistral strike-slip fault) are influenced with micromechanisms of dominated low-temperature ductile deformation and partial dynamic recrystallization. We ascribe the observed coaxial magnetic fabrics in metamorphic, granitic and sedimentary rocks to an Alpine collision (110–95 Ma; P max∼8–9 kbar, T max∼530 °C) and extension tectonometamorphic events (95–80 Ma; up to P∼4–5 kbar, T∼300 °C) of Cretaceous age. The magnetic fabrics seem not to be strongly dependent on temperatures until the medium part of the amphibolite facies (as in this example), but they are strongly following simultaneous deformational low-temperature to medium-temperature meso- and microfabrics.