Mid-Triassic rhyolitic lavas and ignimbrites as markers of Eoalpine high-pressure metamorphism and large-scale lateral extrusion of Adria derived units at the edge of the European Alps

Abstract. Middle Triassic felsic volcanic rocks exposed at Margečan and in the Kjumberk area, located along the Periadriatic Fault System and the Mid-Hungarian Shear Zone, have long been assigned to the Southern Alpine domain and interpreted mainly in terms of their magmatic affinity. This study demonstrates that ignimbritic rhyolites from the Margečan area record a previously unrecognized high-pressure, low-temperature metamorphic overprint reaching blueschist-facies conditions. Phengitic muscovite compositions indicate peak pressures of ~1.1–1.2 GPa at temperatures around 300 °C, providing the first evidence that these felsic volcanic rocks were involved in Eoalpine subduction-related metamorphism and represent a part of the Austroalpine units. In contrast, felsic volcanic rocks from the nearby Kjumberk area, although compositionally and temporally similar, show no evidence of overprint and retain their Southern Alpine affinity, thus outlining a first order tectonic boundary between the two areas. U–Pb zircon ages constrain felsic volcanism to the late Anisian–early Ladinian (~244–242 Ma). Whole-rock geochemistry and Nd isotopic compositions indicate derivation from a subduction-modified mantle source with substantial crustal contribution, consistent with Triassic calc-alkaline magmatism along the Adriatic margin. These petrogenetic characteristics provide a framework for regional correlations but do not explain the contrasting metamorphic overprint. The recognition of Cretaceous Eoalpine blueschist-facies metamorphism in the Margečan ignimbrites therefore revises the tectonic interpretation of this sector of the Adriatic margin and implies large-scale eastward extrusion of the Austroalpine units into the Carpathian embayment, accommodated by high-offset right-lateral strike-slip faults.