Early Paleozoic formations within pre-Alpine fragments incorporated into the Internal Dinarides

Abstract

The Internal Dinarides include ten larger allochthonous pre-Alpine complexes, similar in many respects to those in the Eastern Alps, Carpathians and Rhodopes. The Dinaride Paleozoic complexes consist mainly of Devonian to Permian formations and are commonly associated with abundant Triassic sediments. In addition, the largest Paleozoic complexes contain subordinate Cambrian-Ordovician formations. The best developed Early Paleozoic complex, which occurs in western Macedonia, is composed of fossiliferous Cambrian metasediments with ophiolites and fossiliferous Ordovician metasediments, interlayered with subordinate metavolcanics and intruded by coeval Ordovician granitoids (461-465 Ma) that were overprinted during the Variscan and Alpine tectonogeneses. It is underthrust by Variscan formations and overthrust by Neoproterozoic Pelagonide formations. Parts of the Paleozoic Drina-Ivanjica complex are composed of fossiliferous Cambrian-Ordovician metasediments containing metamafics and metatuff that were overprinted by Early Cretaceous metamorphism. In the Mid-Bosnian Schist Mts, formations of presumed Cambrian- Ordovician age characteristically consist of gneiss and amphibolite, which can be compared to the Oetztal complexes of the Eastern Alps. Dinaridic Cambrian-Ordovician formations from all three areas were metamorphosed during the late Ordovician deformation under P-T conditions of greenschist and, to a lesser extent, epidote-amphibolite facies (400-500 °C and 4-5 Kbar). Based on geochemical data, Ordovician bimodal volcanics and granitoids indicate a geotectonic setting comparable to recent back-arc basins.