GEODYNAMIC AND PETROGENETIC EVOLUTION OF ALPINE OPHIOLITES FROM THE CENTRAL AND NW DINARIDES: AN OVERVIEW

Abstract

Dismembered ophiolites occur in the Dinaride Ophiolite Zone (DOZ) that is related to the open-ocean Tethyan realm, whereas highly dismembered ophiolites occur in the Vardar Zone (VZ) related to a back-arc basin. The ophiolites of DOZ are associated with a Jurassic olistostrome mélange (DOZM), the youngest component of which are Tithonian limestone exotics and with the Mesozoic bed-to-bed Radiolarite Formation. Late Jurassic/Early Cretaceous to Late Cretaceous clastic sequences, comprising redeposited fragments of ophiolites, disconformably overlie the DOZM. Ophiolites of VZ are associated with tectonized ophiolite mélange (VZM), the youngest component of which are Late Cretaceous–Paleogene limestone exotics. The VZM is associated with the Late Cretaceous–Paleogene flysch formation. Ophiolites of both the DOZ and the VZ are predominantly peridotite tectonites, represented mainly by fertile spinel lherzolite in the western and central part of DOZ and VZ, and by depleted harzburgites in their southeastern parts. Cumulate ultramafics and gabbros are subordinate and are in some places overlain by massive or sheeted dyke complexes, capped by metabasaltic pillow lavas. Metamorphic soles of ophiolites are represented by varieties of amphibolites with subordinate pyroxenite schists and scarce eclogites with ultramafic interlayers, which were progressively metamorphosed under P–T conditions of eclogite (?), granulite, amphibolite and greenschist facies. The according protoliths are cumulate gabbros in the DOZ, medium-grade bimineralic epidote–amphibolite facies amphibolites derived from diabase–dolerites, and low- to medium-grade metapelites and metapsammites. K–Ar and Sm–Nd measurements yield ages of 174±14–136±15 Ma on ophiolites from DOZ and 109.6±6.6–62.2±2.5 Ma on ophiolites from VZ. Basic petrological and geochemical features for all Dinaridic ophiolites and associated amphibolites are correlatively presented both for DOZ and VZ. Dinaridic ophiolites were generated in the Dinaridic Tethys over the period of about 150 Ma. The bulk of oceanic crust was generated during the Late Triassic to pre-Late Jurassic/Early Cretaceous when oceanic subduction processes, accompanied by DOZ ophiolite obduction onto the Apulian margin, started. Generation of the oceanic crust continued during the Cretaceous–Early Paleogene in a reduced Dinaridic Tethys under back-arc setting. Eocene closure of the Dinaridic Tethys was accompanied by the second emplacement of VZ ophiolites and the final structuration of the Dinarides and their uplift. At the end, geological and petrological similarities and dissimilarities of ophiolites from both DOZ and VZ are presented.