Early Cretaceous contraction in the SW Tisza as a result of Adria-Europe collision? Structural and stratigraphic evidence from Papuk Mt. in East Croatia

The Tisza Unit represents a continental microplate of European affinity, today sandwiched between the European and Adriatic plates. Its southwesternmost exposures crop out in the Slavonian Mountains of Croatia, where they occur in close proximity to rocks of the Adriatic Plate and the Sava Suture Zone separating them. Papuk Mountain consists of a Variscan crystalline basement and an overlying Permo–Mesozoic sedimentary cover and is considered as part of the Bihor Nappe within the Tisza nappe stack. We present structural and stratigraphic evidence constraining E-vergent structures, possibly related to the Early Cretaceous nappe stacking within the Tisza and Dacia Mega-Units.

Shallow-marine Permian to Upper Triassic siliciclastic sandstones and carbonates were deposited on top of Variscan high-grade metamorphic series and granites. These deposits are continuously overlain by Lower Jurassic to lowermost Cretaceous (Berriasian) pelagic carbonates, marking the onset of the separation of Tisza from European plate. Structural mapping of the study area revealed a meter to kilometer scale superposed folding that is particularly well expressed within the Permian to lowermost Cretaceous succession. Older E-vergent tight overturned folds were subsequently refolded by a younger folding phase with a compression axis subparallel to the fold axes of the older folds, resulting in a characteristic arrowhead interference pattern. Considering that Upper Miocene strata are involved in the younger deformation, the age of younger folding event is constrained to the Late Miocene to Recent. Until recently, the age of the older folding event was only broadly constrained between the earliest Cretaceous and the Late Miocene. However, our recent discovery of an Upper Cretaceous Gosau-type transgressive succession unconformably overlaying the deformed Permian to lowermost Cretaceous sequence significantly refines this constraint. The unconformity indicates that folding occurred within a relatively short time interval between the deposition of the youngest pre-deformation sediments (Berriasian) and the deposition of transgressive post-deformation Gosau-type sediments (late Santonian).

This Early Cretaceous folding and thrusting(?) event coincides with an Early Cretaceous metamorphic overprint previously recognized in Papuk Mountain (commonly referred to as “Alpine metamorphism”), recorded under conditions of 340–460 °C and 3.5–6.0 kbar in the Paleozoic units and 250–300 °C in the Mesozoic sedimentary succession. It also overlaps with zircon fission-track ages of 135 ± 8 Ma obtained from Variscan basement granites. The short time interval between the deposition of Berriasian pelagic limestones and their subsequent folding and metamorphic overprint, followed by rapid exhumation to the surface levels, indicates rapid and intense Early Cretaceous crustal shortening. We corelate this compressional deformation with Early Cretaceous “Austrian” phase documented in the Eastern Carpathians and Apuseni Mountains, and broadly coeval Eoalpine orogenic stage in the Eastern Alps.

Presented research was conducted in the scope of the internal research project PAPUKRON at the Croatian Geological Survey, funded by the National Recovery and Resilience Plan 2021–2026 of the European Union – NextGenerationEU, and monitored by the Ministry of Science and Education of the Republic of Croatia.