Metabasic rocks from the Zemplinic crystalline basement (Western Carpathians, Slovakia): Metamorphic evolution and igneous protolith

Abstract

: The Zemplinic pre-Alpine crystalline basement occur within a northwest-southeast striking tectonic horst, uplifted from the basement of the Cenozoic fill of the East Slovakian Basin. Its tectonic affiliation has not yet been clearly resolved, therefore, this either represents a continuation of the Western Carpathians crystalline basement units to the east or belongs to another tectonic unit. The Zemplinic metabasic rocks are represented by typical amphibolites, which are dark-coloured with strong to weakly foliated or lineated structures. The results of geothermobarometry and constructed phase diagrams indicate a P–T interval of an amphibolite facies with conditions of 610–730 °C at 0.58–0.76 GPa. Their critical mineral association Hbl + Pl + Cpx corresponds to the climax of the orogenic metamorphism of the Zemplinic crystalline basement. Based on their chemical composition, the protolith of metabasic rocks corresponds to two volcanic groups: the sub-alkali basalt (Nb/Y = 0.05–0.31) and the alkali basalt (Nb/Y = 0.90–1.85). The Nb N / Th N values (= 0.04–0.19) exhibit “arc” signatures for the sub-alkali metabasalts. The sub-alkali metabasalt group, which is shown in the incompatible element’s diagrams, indicates that it normalized to N-MORB and E-MORB and inclines to E-MORB basalts, with evidence of Zr–Hf, Ti, Y, and Nb depletion. On the other hand, the group of alkali metabasalts tends to be more transitional to the OIB basalts, with evidence of higher enrichment in LREE and MREE, as well as in Th, U, Nb, Zr, Ti, and Y. The Zemplinic metabasic rocks comprise a variety of enriched basalts, running from intra-oceanic towards within-plate or towards intra-oceanic- and island-arc field accord with the extensional supra-subduction regime of back-arc basins. From the point of view of tectonic development, we consider the Zemplinic Unit to be a continuation of the Inner Western Carpathians.