Triassic evolution of the western Neotethys: constraints from microfabrics and U-Pb detrital zircon ages of the Plattenkalk Unit (External Hellenides, Greece)

The Plattenkalk Unit forms the structurally deepest nappe of the External Hellenides and plays a key role for the reconstruction of Triassic paleogeography in the western Tethyan realm. To shed light on the provenance of the Plattenkalk Unit, we present microfabrics and U-Pb detrital zircon data obtained from quartzite and metaconglomerate of its basal part (Kastania and Transitional Beds exposed on the southern Peloponnesus). A Minoan-type age spectrum of detrital zircons, together with inherited deformation microfabrics of detrital components, points to a very low- to low-grade metamorphic basement as source rock that was situated along the northern passive margin of Apulia facing the Neotethys in the north. The siliciclastic rocks of the Kastania Beds reflect the late Permian/early Triassic opening of the Neotethys, whereas the Transitional Beds indicate the late Triassic facies change toward the Pantokrator-type dolomite, which is a characteristic rock of late Triassic Tethyan carbonate platforms. Dolomite and evaporites of the Trypali Unit, on the other hand, were deposited vis-a-vis along the southern passive margin of Cimmeria. This Triassic configuration of Tethyan basins fits well with the S/SW-directed transport and the recent vertical succession of the Hellenic nappes. The proposed Triassic position of the Plattenkalk basin implies that the Apulian microplate was not part of the Cimmerian block since Permian times. The separation of the Apulian microplate from Gondwana is attributed to the Jurassic breakup of Pangea resulting in the opening of the Mesogean ocean, the relics of which are undergoing subduction beneath the Aegean microplate still today.