Tertiary geodynamic evolution of the Southern Adria microplate

The southern Adria microplate is the common foreland for the Hellenide and Southern Apennine thrust belts. The Apulian Platform dominates the microplate; outcrop, well. and seismic data allow us to trace the carbonate platform edge, whilst structural analysis, geophysical and palaeomagnetic data provide important clues to the geodynamic evolution of the region. The present structural fabric of Apulia is dominated by several E-W lineaments that divide the region into different blocks (Rospo Plateau, Gargano Promontory, Murge Ridge, Salento Peninsula, Apulian Plateau). One such lineament (the Pescara Dubrovnik 'Line', a prominent feature traversing the Adriatic Sea between central Italy and southern Croatia) has been active since the early Mesozoic, when it acted as a major transform fault controlling sedimentation along the northern margin of Southern Adria. During the Cenozoic the Pescara-Dubrovnik underwent predominantly vertical and oblique movement due to a differential flexural response of the platform and the adjacent pelagic sequences to the thrust belt loading. In Tertiary time the Southern Adria microplate was partly involved in Hellenide collision. The Apulian platform can be considered as an area of thicker crust more resistant to underthrusting than the surrounding basins. During the orogenic events it acted as a passive rigid indentor, causing local distortion of the most external Hellenide structures. The dextral transpressive activity recorded along the south-east margin of this indentor (Kephallinia line) can be interpreted as the result of the oblique collision between the margin of the thick Apulian Platform (in this zone NNE-SSW striking) and the NW-SE striking Hellenic thrust belt. Horizontal stress generated during the collision was partly transmitted to the rigid foreland re-activating palaeo E-W faults within the south Adria microplate in a dextral strike-slip sense. The clockwise rotation recorded in the Salento Peninsula can be explained by the rotation of several NW-SE striking faulted blocks. The rotation was accompanied by the opening of small transtensional basins between blocks. This block rotation was caused by the dextral shear that is expressed along the North and the South Salento Fault Zones.