Late Jurassic blueschist facies pebbles from the Western Carpathian orogenic wedge and paleostructural implications for Western Tethys evolution

In spite of the absence of ophiolitic slices at the surface, some traces of the lost Tethys ocean are recorded along the Pieniny Klippen Belt (PKB), a narrow d\ue9collement thrust system sutured at the transpressive boundary between the Outer and Inner Carpathians. The enigmatic precollisional evolution of Western Carpathians can be deciphered from some late Albian to Campanian flysch conglomerates which display chrome spinel grains, ophiolitic detritus and pebbles of blueschist facies tholeiitic metabasalts yielding a 40Ar/39Ar plateau age of 155.4\ub10.6 Ma. Other detrital components are represented by extrabasinal pebbles of limestones, arc volcanics, and igneous to metamorphic basement rocks from southern sources. Our results suggest a markedly northward extension of the sublongitudinal Triassic Vardar (Meliata) Ocean and its subduction since the late Middle Jurassic, supposedly balanced westward by coeval spreading in the Ligurian\u2010Piedmont basin of the Apennine\u2010Western Alpine Tethys. A lateral kinematic connection between these diachronous and roughly parallel Tethys branches was provided on the north by a left\u2010lateral east\u2010west trending shear zone running from the Swiss\u2010Austrian Penninic domain to the Northern Carpathians. This reconstruction replaces the classic model of two paired North Penninic and South Penninic oceanic basins and eastern homologues with the Brian\ue7onnais\u2010Hochstegen and Czorstin microcontinents in between. The Late Jurassic\u2010Early Cretaceous evolution of the Carpathian active margin was characterized by subduction metamorphism and accretion of a wide orogenic wedge; in this time, the shallowing to deeply subsiding basins inferred from facies analyses on the sedimentary units of the PKB were likely floored by individual sections of the growing wedge. Later, some exhuming blueschist ophiolitic units of the wedge were uplifted to the surface and functioned in the Albian\u2010Campanian as an \u201cexotic ridge\u201d supplying clasts to the forearc basin. Finally, the colliding wedge became a cryptic paleostructure when, since the latest Cretaceous, it disappeared beneath the Inner Carpathian orogenic lid and was incorporated within the eastward moving infrastructure of the Carpathian oroclin