Interplay between tectonics and magmatism in the internal Dinarides

The Sava suture zone that runs across the Balkan peninsula contains Maastrichtian trench-fill sediments, termed Sava flysch, that record the closure of the northern branch of the Neotethys. Subsequent collision between Adria-derived thrust sheets and blocks of European affinity in Latest Cretaceous to Paleogene times culminated in the formation of the Dinarides fold-andthrust-belt. The suture zone hosts numerous plutons of I-type granitic composition of Oligocene age. Many of these intrusions are located in the center of metamorphic core complexes (MCCs) that were exhumed in early Miocene times. This phase of post-collisional extension was concomitant with the opening of the northerly adjacent Pannonian Basin and associated with granitic S-type magmatism. The processes responsible for extensional deformation and magmatic activity in the internal Dinarides are still a matter of debate. The data of the present study shows an asynchronous extensional reactivation of formerly contractional structures that gave rise to these core complexes as low-angle detachments in the early Miocene. This is indicated by a variation in deformation ages of 3 Ma, obtained by Ar-Ar in-situ dating of white mica from deformed rocks of the respective shear zones. While Motajica MCC was exhumed from within the Sava zone during E-W extension at approximately 20 Ma, Cer MCC was exhumed as part of the underlying Adriatic basement during N-S extension between 17-16 Ma. For the Cer MCC, a concordia age of 17.6±0.1 Ma (2σ) obtained by U-Pb LA-ICP-MS on zircons from a structurally and petrographically well constrained and undeformed S-type granite in combination with an Ar-Ar inverse isochron age of 16.6±0.2 Ma (2σ) obtained on white mica from the same sample, indicate a cooling rate of approximately 400°C/Ma. The results of this study contribute to the idea of rapid exhumation of mid-crustal material in the form of MCCs in response to the opening of the Pannonian Basin.