The Upper Cretaceous ophiolite of North Kozara – remnants of an anomalous mid-ocean ridge segment of the Neotethys?

Abstract

Abstract This study sheds new light on the origin and evolution of the north Kozara ophiolite, a part of the Sava-Vardar Zone. The Sava-Vardar Zone is regarded as a relict of the youngest Tethyan realm in the present-day Balkan Peninsula. The north Kozara ophiolite consists of a bimodal igneous association comprising isotropic to layered gabbros, diabase dykes and basaltic pillow lavas (basic suite), as well as relicts of predominantly rhyodacite lava flows and analogous shallow intrusions (acid suite). The rocks of the basic suite show relatively flat to moderately light-REE enriched patterns with no or weak negative Eu-anomaly, whereas those of the acid suite exhibit steeper patterns and have distinctively more pronounced Eu- and Sr- negative anomalies. Compared to the known intra-ophiolitic granitoids from the Eastern Vardar Zone, the acid suite rocks are most similar to those considered to be oceanic plagiogranites. The new geochemical data suggest that the basic suite rocks are similar to enriched mid-ocean ridge basalts. The geochemical characteristics of the acid suite rocks indicate that their primary magmas most probably originated via partial melting of gabbros from the lower oceanic crust. Our study confirms the oceanic nature of the north Kozara Mts rock assemblage, and suggests that it may have formed within an anomalous ridge setting similar to present-day Iceland.