Meso-Cenozoic evolution of the external Dinaride-Albanide-Hellenide orogen and the role of the Shkoder-Peja transverse zone: An updated paleomagnetic perspective

The Dinaride-Albanide-Hellenides form a remarkably continuous chain facing the E margin of Adria and the Ionian oceanic basin. Paleogeography and nappe assemblage change significantly from Dinarides to Albano-Hellenides, as well as age and magnitude of nappe rotation synchronous with thrust emplacement since Miocene times. Although it is well-established that the external zones of the Albano-Hellenides underwent a ~40° post-Oligocene clockwise (CW) rotation relative to Africa/Adria, the rotation timing remains debated. Previous models mainly suggested either two Miocene and Plio–Pleistocene rotation episodes, or a single post mid-Miocene rotation accelerating along time. Uncertainties reflect the contribution from local thrust tectonics and/or strike-slip faults biasing the regional rotational trend. Here we present new paleomagnetic data from 41 sites in the continuous Eocene-Upper Pliocene sedimentary sequence of the Tragjasi thrust sheet (Ionian zone, SW Albania). Sampled layers lie on the backlimb of a 50 km-long anticline subparallel to the regional orogenic trend and away from major strike-slip faults. Twenty-eight sites yielded reliable paleomagnetic directions carried by magnetite. The dataset includes 15 normal, 11 reverse and 2 mixed-polarity sites, yielding positive fold and reversal tests. Eocene to Lower Pliocene sediments consistently record a 37°±9° CW rotation, demonstrating that rotation in the external Albanides began not earlier than the late Early Pliocene (~4 Ma). By assuming rigid orogen rotations, we get post-4 Ma displacements reaching ~100 km at Vlore and ~150 km in Crete, corresponding to trench-retreat rates of ~3 to ~4 cm/yr. We interpret this rapid, recent rotation as driven by enhanced Ionian slab pull, slab tearing beneath the Albanides, crust coupling across the Kefalonia-Lefkada Transform Fault, and ultimately westward propagation of the North Anatolian Fault. The boundary between Dinarides and Albano-Hellenides is traditionally acknowledged to occur along the Shkoder‐Peja transverse zone (SPTZ) of Northern Albania, characterized by a ∼100 km SW‐ward shift of the ophiolitic nappe front. The SPTZ has been variably interpreted as a paleogeographic inheritance, a dextral strike‐slip fault, the hinge of the clockwise (CW) rotating Albano‐Hellenides, and a Miocene normal fault. We studied the paleomagnetism of 23 Triassic‐Cretaceous sites from the Krasta‐Cukali and Albanian Alps domains, located both within and north of the SPTZ. We found both pre‐and post‐tilt paleomagnetic directions that consistently yielded a∼70° CW rotation with respect to Adria/Africa, except 9 sites from the Koman zone at the boundary with the ophiolitic nappe, which record a 38°±15° CW rotation. Thus, the well‐known regional CW rotation of the Albano‐Hellenides extends northward in the southern Dinarides, and the SPTZ is not a rotation boundary as previously assumed. The∼70° CW rotation is interpreted as the sum of a 30° rotation associated with Late Oligocene‐Aquitanian thrusting of the Krasta‐Cukali nappe over the Kruja zone, plus the 40° post-4 Ma rotation that we have now constrained in the external Ionian zone of Albania. We suggest that the SPTZ is the heritage of a Lower‐Middle Triassic transform fault of the Maliac Tethyan Ocean, later overprinted by the Lower Cretaceous obduction of the Vardar Ocean that rejuvenated Maliac Ocean since the Middle Jurassic.