Torn Between Two Plates: Exhumation of the Cer Massif (Internal Dinarides) as a Far‐Field Effect of Carpathian Slab Rollback Inferred From 40Ar/39Ar Dating and Cross Section Balancing

Abstract

AbstractExtension across the southern Pannonian Basin and the internal Dinarides is characterized by Oligo‐Miocene metamorphic core complexes (MCCs) exhumed along mylonitic low‐angle extensional shear zones. Cer MCC at the transition between Dinarides and Pannonian Basin occupies a structural position within the distal‐most Adriatic thrust sheet and originates from two different tectonic processes: Late Cretaceous‐Paleogene nappe‐stacking during a continent‐continent collision with Adria in a lower plate position, and exhumation related to Miocene extension driven by the Carpathian slab‐rollback. Structural data and a balanced cross section across the Cer massif show linking of the exhuming shear zone to a breakaway fault, which reactivated the early Late Cretaceous most internal nappe contact. Paleozoic greenschist‐to amphibolite‐grade lithologies surround a polyphase intrusion composed of I‐ and S‐type granites and were exhumed along a shear zone characterized by top‐N transport. Thermobarometric analyses indicate an intrusion depth of 7–8 km of the Oligocene I‐type granite; cooling below ∼500°C occurred at 25.4 ± 0.6 Ma (1σ) yielded by 40Ar/39Ar dating of hornblende. Biotite and white mica from this intrusion as well as from the mylonitic shear zone yield 40Ar/39Ar cooling ages of 17–18 Ma independent of the used techniques (in situ laser ablation, single‐grain total fusion, single‐grain step heating, and multi‐grain step heating). White mica from the S‐type granite yield an 40Ar/39Ar cooling age of 16.7 ± 0.1 Ma (1σ). Associated dikes intruding the shear zone were also affected by N‐S extension resulting in the exhumation of the MCC, which was triggered by the opening of the Pannonian back‐arc basin in response to the Carpathian slab‐rollback.