Petrology, geochemistry and Sm-Nd analyses on the Balkan-Carpathian Ophiolite (BCO – Romania, Serbia, Bulgaria): Remnants of a Devonian back-arc basin in the easternmost part of the Variscan domain

摘要: Abstract The pre-Alpine basement of the Southern Carpathians/Western Balkans contains four ophiolitic massifs dismembered by Alpine tectonics, which define “Balkan-Carpathian Ophiolite” (BCO) for tectonic setting and age formation are still debated (Precambrian or Early Devonian). In this contribution, we demonstrate that, in light a Pre-Alpine restoration, belonged to unique slice very complete, obducted oceanic lithosphere re-evaluate its setting. Large chromitite volumes with Al-rich spinel compositions (Cr# = 0.39–0.48), as well major trace geochemical results on basalts (slightly enriched N-MORBs low negative Nb anomaly associated calk-alkaline BABBs), point back-arc basin. Mantle composition (Cr# = 0.49–0.51) melting modeling indicate mean extents 8.5–11% favouring intermediate spreading rate. New Sm-Nd dating lower gabbroic rocks give whole rock isochron, interpreted BCO crust at 409 ± 38 Ma, thus confirming an Devonian crust. previous ∼563 Ma U-Pb zircon can be casual inheritance indicating proximity old continental lithosphere. Taking into account lithological evidences paleocontinental affinities two recognized terranes separated BC basin (Balkans Sredna Gora) analogy other Variscan ophiolites Western/Central Europe, suggest that ophiolite belong ∼400 Ma group between West East Galatia belonging southern suture. However, is only one north not involved Lower Allochthon/ophiolite/Upper Allochthon thrust pile, likely explaining exceptional preservation. Finally, tentatively propose new unifying model where different terrane drift rates highly oblique displacements create Rheic branches, “Rheic” “Galicia-Brittany-Massif Central”.