Petrology and palaeotectonic setting of Cretaceous alkaline basaltic volcanismin the Pieniny Klippen Belt (Western Carpathians, Slovakia)

Abstract

Occurrences of mafic alkaline volcanics are scattered all around Europe, being mostly related to anorogenic, extensional tectonic environments. While the widespread Cenozoic alkaline basalts have been intensively studied and are comparatively well-known, their Cretaceous precursors were often associated with the Alpine-Carpathian orogenic zones, and so their genesis and geodynamic setting are partially obscured by superimposed deformation and alteration. We describe a newly discovered body of melanephelionites inserted within the Upper Cretaceous deep-marine pelagic succession of the Pieniny Klippen Belt in Western Slovakia. The body consists of hyaloclastic lavas of nephelinitic composition. The mineralogical composition and geochemical features of the Vršatec volcanites correspond to melanephelinites. Reconstruction of the geodynamic setting of the Cretaceous mafic alkaline volcanism in the Alpine-Carpathian-Pannonian realm infers a general extensional/rifting tectonic regime that ultimately led to the opening of Penninic oceanic rift arms. However, this rifting started as basically passive and non-volcanic. Only during the later, post-breakup extension phases did the slow-spreading oceanic ridges develop, which are characterized by the MORB-type (mid-ocean-ridge basin) basaltic volcanism. Alkaline volcanic provinces have a linear character and appear to follow passive continental margins of Penninic oceanic arms opened during the Jurassic and Early Cretaceous. We infer that alkaline volcanism resulted from heating and partial melting of the subcontinental mantle lithosphere on the peripheries of asthenospheric upwellings confined to slow-spreading ridges of the Alpine Tethys. Consequently, regarding the debate about the plume vs. non-plume origin of the Cretaceous alkaline volcanism, the geological data from this area rather support the latter affinity