Distinct metasomatic events and their relation to a crustal-scaledeformation zone (Gemer-Vepor Contact Zone, CentralWesternCarpathians)

International audienceNumerous talc, magnesite and siderite ore deposits occur in the Central Western Carpathians (Slovakia) along theso-called Gemer-Vepor Contact Zone, which marks the contact between two major blocks of Variscan basement,the Vepor and Gemer units. During the polyphase deformation of Cretaceous age, the Gemer Unit was first thrustover the Vepor Unit. This is well documented by the development of subhorizontal and prograde metamorphic foliationreaching up to amphibolite facies conditions in the Vepor and by the development of subvertical greenschistfacies cleavages in the Gemer Unit. The subsequent exhumation of the Vepor Unit along large-scale detachmentzone is documented by the development of subhorizontal lower grade cleavage in the Vepor Unit. Finally, the ongoingnorthward propagating convergence with the Gemer Unit led to the development of the sinistral transpressionalTrans-Gemer Shear zone. Two types of shear zones with contrasting metasomatic record have been recognized inthe Vepor Unit. Mg-enriched shear zones heterogeneously develop within the Carboniferous granitoids resulting information of Mg-chlorite–muscovite–quartz phyllonites as well as Mg-chlorite–kyanite-bearing schists. Comparedto the composition of granitoids, these mylonites-phyllonites are depleted in alkalies and enriched in magnesium,iron and manganese, which is most likely related to the influx of fluids along the shear zones. The equilibriummineral assemblage chlorite, kyanite, muscovite, rutile and quartz corresponds to 420C at 4 kbar. In contrast,the second type of shear zones developed within chloritoid-kyanite schists of the Veporic Permian cover. Theseshear zones display metasomatic alteration characterized by a strong Fe-enrichment resulting in formation of Fechlorite-muscovite-quartz phyllonite. The unusual enrichment in either Mg or Fe suggests either heterogenous fluidcomposition or two separate metasomatic events in the studied area. Indeed, the two types of shear zones are associatedwith two distinct deformation events. The Mg-enriched first type shear zones are associated with progrademetamorphic evolution related to burial of the Vepor Unit whereas the Fe-enriched second type shear zones arerelated to the Vepor exhumation. Therefore, the formation of these metasomatic rocks reflects different stages ofthe polyphase Cretaceous evolution, rather than heterogenous composition of fluids. The sources of metasomaticfluids are discussed in relation to the nearby ore deposits