New insights into the building of the Variscan Belt in Eastern Europe (Romania, Serbia, Bulgaria)

The basement of the Alpine Upper Danubian/Balkan nappe, dismembered between Romania, Serbia and Bulgaria, contains evidence of the Variscan orogenic evolution (Lower Devonian Balkan–Carpathian ophiolite, Carboniferous granites). Our study presents a new tectono-metamorphic interpretation of this basement and documents two main deformation phases, D₁ and D₂. D₁ is a right-lateral thrust recorded in the metagabbroic rocks at the base of the ophiolitic nappe that also affects the underlying units. This phase is related to the ophiolite emplacement on a northerly margin with a top-to-the-palaeo-WNW (Variscan coordinates) at c. 360 Ma. D₂ records a collisional event in a sinistral transpressive regime. In a zone of sheared folds, it juxtaposed low- (Eşelniţa metasediments) to high-grade metamorphic rocks (Corbu rocks: 600°C/ 5.2 kbar). Syntectonic granitic intrusions later heated these rocks locally before their final cooling, still during the D₂ phase, and with localized circulation of fluids. The sinistral transpressive regime would prevail after the docking of the Balkans and the Sredna Gora terranes separating the Balkan–Carpathian oceanic basin and could correspond to left-lateral escape due to large-scale readjustments between both terranes during the Carboniferous. The Upper Danubian/Balkan basement appears to be located more northerly in the Variscan Belt than the other intra-Alpine basements (Getic, Western Carpathians, Eastern Alps, Western Alps).