Age constraints on the igneous and metamorphic evolution of the Hellenic-Dinaric ophiolites

Abstract

Summary The available age data from Greek and Yugoslavian ophiolites and related rocks are reviewed and, where necessary, have been corrected using the decay constants of Steiger & Jäger (1977). In addition, new K-Ar ages are presented from igneous mineral phases from the Guevgueli ophiolite and Fanos granitoid. Rb-Sr ages are also presented for the Furka and Stip granitoids of the Vardar Zone. Igneous ages of the dated ophiolites are approximately 160–180 Ma, although data from the Guevgueli Complex indicate that associated basic igneous activity also occurred during the Upper Jurassic. Granitoids yield ages ranging between 150 to 174 Ma. When compared with dates obtained from metamorphic soles beneath the Greek and Yugoslavian ophiolties (160–180 Ma), it is apparent that both sub-ophiolite metamorphism and granitoid intrusion closely followed ophiolite formation at a spreading centre. This indicates that the initial obduction movements occurred when the ophiolites were both young and hot and capable of forming basal dynamothermal soles mainly by the effects of their residual heat. When these ages are integrated with the field evidence for the period of final ophiolite emplacement in the Hellenides and Dinarides (Late Jurassic to Early Cretaceous), it is possible to reconstruct a simplified igneous, metamorphic and emplacement history for these displaced fragments of oceanic crust and upper mantle.