The Zvornik “suture” in the Internal Dinarides: A key to understanding regional strike-slip structures in the Balkans

Sedimentary basins that develop in convergent tectonic settings are excellent archives for evidence of the tectonic processes active during orogen formation. A representative example of this basin type occurs in the Internal Dinarides, at the boundary between the two most distal tectonic units of Adria - the Jadar-Kopaonik and Drina-Ivanjica units. This sedimentary basin possesses unique characteristics not described elsewhere in the Dinarides: it contains an “olistostrome mélange” formation, which Milorad Dimitrijevic (1973) interpreted as a mélange produced by subduction and/or underthrusting of the Drina-Ivanjica element beneath the Jadar block. The type locality where this unit was first described is in the vicinity of town Zvornik, while the tectonic structure along which subduction was postulated was subsequently named the “Zvornik suture”. In this study we focus on another locality where the Upper Cretaceous “olistostrome mélange” has been mapped - the Jelica Mts. near the town of Cacak. By applying structural-geological mapping and detailed study of magmatic rocks and sedimentary successions across the broader Jelica Mts. area, we aimed to determine the principal properties of the tectonic structures related to activity along the Zvornik Fault, and to assess the potential geodynamic significance of this Upper Cretaceous “mélange”. Our results suggest that the volcano-sedimentary series of the Jelica Mts. represents deposition within a wedge-top basin that developed due to the oblique thrust of the Jadar-Kopaonik Unit. The pronounced dextral horizontal component along this thrust could have created transtensional domains in which partial melting of the upper mantle produced basalts which in this study are determined at 87.4 ± 0.96 Ma. Based on our findings, we conclude that the Zvornik Fault represents the front of the Jadar-Kopaonik thrust, which in recent stress field accommodate a significant dextral strike-slip component.