Post-20 Ma Motion of the Adriatic Plate: New Constraints From Surrounding Orogens and Implications for Crust-Mantle Decoupling

摘要

A new kinematic reconstruction that incorporates estimates of post-20 Ma shortening and extension in the Apennines, Alps, Dinarides, and Sicily Channel Rift Zone (SCRZ) reveals that the Adriatic microplate (Adria) rotated counterclockwise as it subducted beneath the European Plate to the west and to the east, while indenting the Alps to the north. Minimum and maximum amounts of rotation are derived by using, respectively, estimates of crustal extension along the SCRZ (minimum of 30 km) combined with crustal shortening in the Eastern Alps (minimum of 115 km) and a maximum amount (140 km) of convergence between Adria and Moesia across the southern Dinarides and Carpatho-Balkan orogens. When combined with Neogene convergence in the Western Alps, the best fit of available structural data constrains Adria to have moved 113 km to the NW (azimuth 325 degrees) while rotating 5 +/- 3 degrees counterclockwise relative to Europe since 20 Ma. Amounts of plate convergence predicted by our new model exceed Neogene shortening estimates of several tens of kilometers in both the Apennines and Dinarides. We attribute this difference to crust-mantle decoupling (delamination) during rollback in the Apennines and to distributed deformation related to the northward motion of the Dacia Unit between the southern Dinarides and Europe (Moesia). Neogene motion of Adria resulted from a combination of Africa pushing from the south, the Adriatic-Hellenides slab pulling to the northeast, and crustal wedging in the Western Alps, which acted as a pivot and stopped farther northwestward motion of Adria relative to Europe.