Fragmentation of the Adriatic Promontory: New Chronological Constraints From Neogene Shortening Rates Across the Southern Alps (NE Italy)
Résumé
Key-points Folded alluvial surfaces and balanced cross-section constrain post-LGM and Neogene shortening-rates Decrease in shortening-rate and change in compression direction are inferred at 1-2 Ma Kinematic reorganization is best explained by a shift from Nubia-driven to Adria-driven convergence Abstract The eastern Southern Alps are located at the northern tip of the Adria microplate, which imposes 2.0-2.5-mm/yr of N-S-convergence relative to stable Eurasia. We map surface evidence of recent folding/faulting in this area from a 5-m-DEM. In the eastern part of the belt, observations reveal a 30-km-wide zone of active folding composed of at least five growing anticlines. The most recent ones warped the post-glacial alluvial surface by <10m. Combining these findings with published geological and geophysical data allows us to infer that active thrusting occurs along a single deeply rooted thrust, which accommodates the indentation of the Adriatic crust. Resolving the observed pattern of uplift on the inferred fault geometry indicates that NNE-SSW-shortening across the eastern Southern Alps has occurred at a rate of about 1.5 mm/yr over the post-glacial period. On the other hand, a balanced cross-section for the eastern Southern Alps at the scale of the upper crust constrains a minimum of 43 km of finite shortening over the last 14Ma, yielding a shortening-rate of about 3 mm/yr, which is two times higher than the post-glacial shortening-rate. This decrease in the shortening-rate is associated to the Pleistocene activation of new thrusts that is compatible with a change in the direction of compression. The inferred local change in the kinematics of thrusting during the Pleistocene is consistent with a change from Nubia-imposed to Adria-imposed convergence indicating that the fragmentation of the Adriatic promontory could have occurred 1-2 Ma ago.
Origine : Fichiers produits par l'(les) auteur(s)