Eocene rotation of Sardinia, and the paleogeography of the western Mediterranean region

- First paleomagnetic data from Cretaceous and Paleogene rocks from Sardinia.
- Sardinia-Corsica experienced a ∼40° counterclockwise rotation in the Eocene.
- The first phase of rotation of Sardinia-Corsica postdated the rotation of Iberia.
- Sardinia-Corsica is an independent microcontinent, separated from Iberia by a fault.
- Rotation of Sardinia-Corsica coincided with the Alpine Briançonnais collision.

Key to understanding the complex Mediterranean subduction history is the kinematic reconstruction of its paleogeography after Jurassic extension between Iberia, Eurasia, and Africa. While post-Eocene Liguro-Provençal back-arc extension, and associated Miocene ∼50° counterclockwise (ccw) rotation of Sardinia-Corsica have been well documented, pre-Oligocene reconstructions suffer uncertainties related to the position of Sardinia-Corsica with respect to Iberia. If a previously constrained major post-middle Jurassic, pre-Oligocene rotation of Sardinia-Corsica can be quantified in time, we can test the hypothesis that Sardinia-Corsica was (or was not) part of Iberia, which underwent a ∼35° ccw during the Aptian (121-112 Ma). Here, we present new paleomagnetic results from Triassic, Jurassic, Upper Cretaceous and Lower Eocene carbonate rocks from Sardinia. Our results show a consistent well constrained post-early Eocene to pre-Oligocene ∼45° ccw rotation of Sardinia-Corsica relative to Eurasia. This rotation postdated the Iberian rotation, and unambiguously shows that the two domains must have been separated by a (transform) plate boundary. The Eocene rotation of Sardinia-Corsica was synchronous with and likely responsible for documented N-S shortening in the Provence and the incorporation of the Briançonnais continental domain, likely connected to Corsica, into the western Alps. We argue that this rotation resulted from the interplay between a southward 'Alpine' subduction zone at Corsica, retreating northward, and a northward subduction zone below Sardinia, remaining relatively stationary versus Eurasia.