In the Balkans, the Serbo-Macedonian Unit (SMU), Serbia, is thrust bounded by the composite Tethyan Vardar Zone and the Carpatho-Balkanides. The SMU actually emerges from beneath the Neoalpine Miocene–Pliocene deposits. Both provenance and geodynamic position of the SMU are poorly known and still debated. This paper reviews the data hitherto published and includes some new field data interpretations. The SMU is composed of a Neoproterozoic–Cambrian high-grade (para- and ortho-) gneiss with peraluminous magmatic arc components (560–470 Ma). The SMU is in the contact with Neoproterozoic upper Ordovician–Carboniferous low-grade metasedimentary succession of an accretionary wedge assembly represented by the Supragetic basement. The SMU basement became folded, sheared and metamorphosed around 490–450 Ma. Paleomagnetic data point to high southern latitudes and a peri-Gondwanan position of the SMU at that time, which concurs with glaciomarine evidence recorded from the upper Ordovician sediments at the base of an accretionary wedge succession. Based on the published data and field survey in the Stalać region, we correlate the SMU with the pre-Mesozoic gneiss terrane exposed in the Strona-Ceneri zone of the Alps. This terrane, identified as the Cenerian orogen of the Alaskan subduction type, developed at an active margin of Gondwana during middle Ordovician times. The SMU basement, with augen and migmatitic gneisses and arc-related peraluminous magmatic bodies, developed at this margin as part of the Cenerian belt or its equivalent. Such an orogenic edifice proved transient and in the earliest Silurian the SMU fragments drifted away being bound for Baltica (amalgamated Moesian microplate and Danubian terrane) to which they became accreted in the Carboniferous and included in the southern European branch of the Variscan orogen (Marginal Dacides/Carpatho-Balkanides). Despite considerable Variscan and Alpine reworking, the pre-Variscan, Cenerian-type crustal assembly along with an inferred boundary between the magmatic arc and the accretionary wedge, accompanied by back-arc/forearc deposits, are still decipherable in the Western Balkan countries.

This paper attempts to allocate a segment of the Paleozoic Ocean situated in what is now Southeastern Europe (SEE) into a regional geological and paleotectonic synthesis connecting the sedimentary, metamorphic and igneous records associated with the ocean’s cycle. The Supragetic basement (external section of the Carpatho-Balkan arch) represents a tectonically reworked basement vestige of the Neoproterozoic–Lower Paleozoic oceanic floor system recrystallized under regional low temperature greenschist-facies conditions. The regional geological constraints associated with this low-grade basement are integrated with information from the overlying Silurian, Devonian and Lower Carboniferous cap-rocks of the “Kučaj Unit” to demonstrate the presence of a major Paleozoic ocean crossing this segment of SEE. In connection with the Lower Paleozoic north Gondwanan Pan- African processes, the low-grade Supragetic basement (including its Devonian cover) is in a complex relationship with the occasionally anchimetamorphic Silurian, Devonian, and Lower Carboniferous deep-water record of the polymetamorphic “Kučaj Unit”. The Upper Devonian–Lower Carboniferous flysch and molasse of the “Kučaj Unit” are interposed with the Neoproterozic–Lower Paleozoic oceanic vestige or with the Supragetic basement with the corresponding Devonian Balkan-Carpathian back-arc ophiolite-bearing lithosphere and its carrier (Danubian Unit). This regional-scale synthesis demonstrates that a segment of the Rheic Ocean referred to as the Saxo-Thuringian seaway and its suture lay to the east, underneath the Permian red-bed overstepping sequence and to the west of the Danubian aggregation. Unlike many of the high-pressure rocks characterizing the segment of the Rheic suture in the Central European Variscides, the SEE zone described here has only a mild overprint.