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 rather well known, their Cretaceous precursors are often involved in the Alpine-Carpathian orogenic zones, therefore their genesis and geodynamic setting are partially obscured by superimposed deformation and alteration. We describe a newly discovered body of alkaline basalts in the central part of the Pieniny Klippen Belt – Vršatec, then, farther to the east, dike bodies of Hanigovce and in the Ukrainian part of the klippen belt, alkaline basalts of Velikij Kamenec. The basalt at Vršatec is lying within the mid-Cretaceous deep-marine pelagic sediments of the Pieniny Klippen Belt in western Slovakia. The body consists of hyaloclastic lavas of basanitic composition. There is not revealed any direct contact of the Hanigovce bodies with the surrounding sediments; however, due to missing signs of contact metamorphosis in their close environment – sediments of the Proč, and/or Proč-Jarmuta layers, we consider them olistoliths. Macroscopically they are homogenous very fine-grained rocks with visible phenocrysts of olivine, clinopyroxene and rarely amphibole. The matrix is made from devitrified glass, tiny albites, clinopyroxene and amphibole microliths and zeolites. Olivine is wholly altered and superimposed by a mixture of chlorite and serpentinite minerals. The basalts from Velikij Kamenec have similar mineral and chemical composition. The mineral composition (Cpx – high contents of Ti, Na, K; amphibole – kaersutite etc.) points to alkaline character of the rocks, which is also evidenced by the presence of partly resorbed leucite/analcime.
The chemical composition of volcanics is rather specific. Generally, these rocks are characterized by low SiO2 contents (ca 41.0 weight %), enhanced contents of TiO2 and P2O5 (3.3, and/or 1,5 weight %) and elevated contents of incompatible elements such as Ba (1300 ppm), Sr (1100 ppm) and LREE, as well as those of Nb (217 ppm), V (161 ppm) and Zr (1050 ppm). For various discrimination diagrams these volcanics correspond to OIA (oceanic island alkali basalts) or WPA (within-plate alkali basalts) fields. Similarly, the course of the normalized REE curve is clearly declined in the direction of low HREE contents without a considerable Eu-anomaly. Such a course of normalized curve is typical for ocean island (OIB), Cretaceous basalt from the Jarmuta Formation or continental alkaline volcanic suites of central and Western Europe, as well as for Mesozoic alkaline rocks from various parts of Europe.
Reconstruction of the geodynamic setting of the Cretaceous mafic alkaline volcanism in the Alpine-Carpathian-Pannonian realm infers the 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 the slow-spreading oceanic ridges developed, which are characterized by the MORB-type basaltic volcanism. Alkaline volcanic provinces have 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 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 opportunity.