40Ar/39Ar ages of glaucophane and phengitic muscovite from the Mt. Medvednica blueschists (NW Croatia): Evidence for Middle–Late Jurassic subduction in the northwestern Neotethys

In the northwesternmost part of the Dinarides, which is a part of the southwestern segment of the Zagorje–Mid-Transdanubian Zone within the Mt. Medvednica area, localized occurrences of blueschists with an OIB-type protolith affinity preserve evidence of vestiges of high-pressure, low-temperature metamorphism. New 40Ar/39Ar ages from glaucophane (160.0 ± 1.5 to 164.9 ± 1.0 Ma) and phengitic muscovite (154.4 ± 1.0 Ma), obtained from phengite–ferroglaucophane and glaucophane–Mg-riebeckite schists, constrain the metamorphism to the Middle to Late Jurassic (Callovian to Kimmeridgian). This indicates the formation of the analysed rocks within an accretionary prism above an intra-oceanic subduction zone in the northwestern Neotethys. In a regional context, these data are consistent with a diachronous, northeast-dipping subduction system operating across parts of the western Neotethys. Metamorphic soles in the Dinaridic Ophiolite Belt, dated at 174 to 157 Ma, mark the onset of early hot subduction, whereas Jurassic to Early Cretaceous HP/LT assemblages in Pelagonia and Mt. Fruška Gora record continued convergence and progressive cooling at comparable depths. Coeval HP/LT rocks in the Western Carpathians broadly document comparable subduction depths and thermal gradients farther northeast. Mt. Medvednica occupies a temporally and structurally-intermediate position within this regional framework and preserves the northwesternmost record of Middle to Late Jurassic HP/LT metamorphism in the Dinarides. Together, these observations suggest regionally distributed and diachronous subduction-related processes, with ridge-proximal subduction initiating in the Bajocian, maturing during the Callovian to Kimmeridgian, and progressively shifting southeastward in response to trench retreat across the Dinaridic–Vardar realm.