Messinian-Early Pliocene crustal shortening along the Tyrrhenian margin of Tuscany, Italy

Federico Sani(1), Marco Bonini(2), Andrea Cerrina Feroni(3), Francesco Mazzarini(4), Giovanna Moratti(2), Giovanni Musumeci(5), Giacomo Corti(2), Federica Iatta(1) & Alessandro Ellero(3)
(1) Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Via G. La Pira, 4 - 50121 Florence, Italy, fsani@geo.unifi.it. (2) CNR, Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse, U.O. Firenze, Via G. La Pira, 4 - 50121 Florence, Italy. (3) CNR, Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse, Via Moruzzi, 1 - 56124 Pisa, Italy. (4) INGV, Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, Via della Faggiola, 32 - 56126 Pisa, Italy. (5) Dipartimento di Scienze della Terra, Università degli Studi di Pisa, Via S. Maria, 53 - 56126 Pisa, Italy.

This paper illustrates the results of structural studies carried out in the western margin of Tuscany along a major crustal structure. Surface deformation of sediments filling different basins aligned on top of this major structure (from north to south: the Fine Basin, the Sassa-Guardistallo basin, the Rio Guardigiano area in the Lustignano basin) allow us to date its tectonic activity to the Messinian-Early Pliocene. In these areas, structures such as reverse and strike-slip faults and mesoscopic folds are widely developed. Structural analysis determined a compressive stress field with the σ1 oriented from E-W to NE-SW active from Messinian to Early Pliocene. At the southern end of this crustal structure, the Gavorrano antiform and the granitic pluton (radiometric age of granite ∼4.4 Ma) coring this fold correlate with a thrust ramp anticline at depth, and thus constrain thrust activity to the Early Pliocene. These data document a Messinian-Early Pliocene compressive activity that contrasts with models invoking continuous extensional tectonics affecting the hinterland since the Late Oligocene-Middle Miocene in the frame of a back-arc-slab retreating process. The results presented therefore raise the question of which geodynamical model could account for such a complex structural evolution of Northern Apennines hinterland.

Northern Apennines, hinterland areas, structural analysis, pluton emplacement.