The 40Ar-39Ar dating and geochemistry of the Carpathian C1 obsidians (Zemplin, Slovakia)

In situ 40Ar-39Ar UV laser ablation dating of the Carpathian C1 obsidians from the Slovakian part of the Zemplin - Tokaj area yielded new 40Ar-39Ar obsidian glass ages that fall in a narrow time interval of 12.07 +/- 0.37 to 11.44 +/- 0.39 Ma. This indicate that most of the Zemplin obsidian findings come from one short-time monogenic volcano, forming part of a long-lasting volcanism over the 15-10 Ma period. Chemical compositions of the Carpathian C1 obsidians clearly indicate common similarities between all examined localities (Brehov, Cejkov, Hran, and Vinicky). Geochemically, these obsidians belong to the silica-rich, peraluminous, high-potassium, calc-alkaline rhyolite series volcanic rocks of ferroan character. They were derived by multi-stage magmatic processes, from mixed mantle and crustal sources, and generated during subduction in a volcanic arc tectonic setting. The primary basaltic magma formed from the melting of the lower crustal source at the mantle/crust boundary. Subsequent formation of melt reservoirs in the middle and upper crust, accompanied by secondary melting of the surrounding rocks with continual addition of ascending melt, and repeated processes of assimilation and fractionation produced rhyolitic rocks with obsidians in the Zemplinske vrchy Mts.