The early-Middle Palaeozoic oceanic events along the southern European margin: The Deli Jovan Ophiolite Massif (NE Serbia) and palaeo-oceanic zones of the Great Caucasus

Abstract

The paper deals with the Middle Palaeozoic oceanic events on the northern margin of the Eastern Mediterranean Hercynides. The Balkan-Carpathian Ophiolite Belt (BCO) and palaeo-oceanic zones of the Great Caucasus, all framing the East European Platform from the south, are correlated. The BCO palaeo-oceanic complex was widely thought to be a Late Precambrian-earliest Cambrian oceanic thrust sheet (563±5 Ma), a part of the South European Palaeooceanic Suture. The geochronological studies carried out on gabbroic series of the Deli Jovan Massif (BCO, NE Serbia), showed, however, that they are of much younger (Early Devonian) age: (a) Sm-Nd mineral isochron age of 406±24 Ma, εNdT= 8.32±0.39; 87Sr/86Srinit= 0.702592±0.000160; and (b) U-Pb SHRIMP zircon age, 405.0±2.6 Ma. All the studied gabbroic rocks represent high-alumina (19-24.5% Al2O3) gabbro-troctolites, originating from shallow level (≤ 2 kb) crystallization of low-K (< 0.3% K2O) tholeiitic basaltic melts (T= 1190-1350°C). Geochemical and isotopic data for the Balkan-Carpathian ophiolites fit well a MORB-type setting. Thus, the presence of Middle Palaeozoic oceanic events is evident in the BCO, which is important for the evolution of the European Palaeomargin. Data for Lower-Middle Palaeozoic palaeo-oceanic thrust sheets of the Hercynides of the Great Caucasus are also reviewed. The most significant outcrops are located in the Crystalline Core Zone and in the Front Range Zone of the Great Caucasus. These mafic basement complexes in both zones correspond to metamorphosed accretionary wedges consisting, predominantly, of metamorphosed palaeo-oceanic fragments, associated with tonalite-gneisses, plagiogneisses and metasediments. The ophiolite allochthon consists of depleted spinel harzburgites, ultrabasic and basic cumulates, sheeted dykes, volcanics and a volcano-sedimentary series. Unlike the BCO almost all the Palaeozoic oceanic series of the Great Caucasus show a clear SSZ imprint. It is assumed that the Middle Palaeozoic oceanic complexes of the Eastern Mediterranean Hercynides apparently correspond to a uniform system of Palaeo-Tethyan marginal basins. © TÜBİTAK.