Coupled Crust-Mantle Response to Slab Tearing, Bending, and Rollback Along the Dinaride-Hellenide Orogen

Abstract

We integrate structural, geophysical, and geodetic studies showing that the Dinarides-Hellenides orogen along the Adria-Europe plate boundary in the Western Balkan peninsula has experienced clockwise oroclinal bending since Eocene-Oligocene time. Rotation of the Hellenic segment of this orogen has accelerated since the middle Miocene and is associated with a north-to-south increase in shortening along the orogenic front. Within the Paleogene nappe pile, bending was accommodated by orogen-parallel extension, clockwise block rotation, and thrusting in the hanging wall of the Skhoder-Peja Normal Fault (SPNF). The SPNF and related faults cut the older Skhoder-Peja Transfer Zone with its pre-Neogene dextral offset of the West Vardar ophiolite nappe. Rotation of the SPNF hanging wall involved Miocene-to-recent, out-of-sequence thrusting that was transferred to the Hellenic orogenic front via lateral ramps on dextral transfer zones. Along strike of the Dinarides-Hellenides and coincident with the southward increase in Neogene shortening, the depth of the Adriatic slab increases from ~160 km north of the SPNF to ~200 km just to the south thereof, to several hundreds of kilometers to the south of the Kefalonia Transfer Zone. The geodynamic driver of tectonics since the early Miocene has been enhanced rollback of the Hellenic segment of the Adriatic slab in the aftermath of Eocene-Oligocene slab tearing and breakoff beneath the Dinarides, which focused slab pull in the south. The SW-retreating Hellenic slab segment induced clockwise bending of the southern Dinarides and northern Hellenides, including their Adriatic foreland, about a rotation pole in the vicinity of the Mid-Adriatic Ridge.