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, D-1 and D-2. D-1 is a right-lateral thrust recorded in the meta-gabbroic 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. D-2 records a collisional event in a sinistral transpressive regime. In a zone of sheared folds, it juxta-posed low- (Eselnita metasediments) to high-grade metamorphic rocks (Corbu rocks: 600 degrees C/5.2 kbar). Syntectonic granitic intrusions later heated these rocks locally before their final cooling, still during the D-2 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).