Structural and geochronological constraints from the Drina-Ivanjica thrust sheet (Western Serbia): implications for the Cretaceous–Paleogene tectonics of the Internal Dinarides

Abstract

We have investigated successive episodes of ocean-continent and continent–continent convergence in Western Serbia (Drina-Ivanjica thrust sheet). The coupled application of structural and petrological analyses with Illite Crystallinity measurements and K/Ar dating has revealed the timing and structural characteristics of multiple regional deformation phases, and allowed us to revise the origin of the different Triassic units outcropping in the study area. D 1 tectonic burial was characterized by anchizonal metamorphism, dominantly WNW-verging isoclinal folding (F 1 ), and related axial planar cleavage (S 1 ) formation in the Paleozoic basement and the stratigraphic cover of the Drina-Ivanjica thrust sheet exposed along the northern rim of this thrust sheet. The timing of D 1 deformation is constrained by K/Ar ages suggesting 135–150 Ma tectonic burial for the Drina-Ivanjica thrust sheet. D 1 deformation and metamorphism is correlated with the closure of the Vardar ocean by top-W to NW ophiolite obduction and the underthrusting of the Adriatic distal passive margin below the oceanic upper plate. Since D 1 structures are lacking in the southern occurrences of Triassic rocks within the study area it is proposed that this Triassic is may not be the original sedimentary cover of the Drina-Ivanjica Paleozoic basement. We propose that this southern Triassic originated from a more external Dinaridic thrust sheet and was transported to its present-day position by a top-NE backthrust presumably during late Early Cretaceous–Paleogene times. Map-scale, NW–SE striking D 2 thrust faults and abundant NW–SE trending F 2 folds observed in all units correspond to the general trend of the Dinaridic orogen and are attributed to the latest Cretaceous–Paleogene collision between Adria and Europe. Regional Latest Cretaceous–Paleogene shortening was followed by strike-slip tectonics (N–S shortening and perpendicular extension) and subsequent Miocene normal faulting in both orogen-parallel and orogen-perpendicular directions driven by slab rollback processes of the Carpathian-Dinaridic realm.