Quaternary tectonics in Sardinia

The Sardinia-Corsica lithospheric block played a key role in the Cenozoic tectonic evolution of the Western Mediterranean, since Miocene drifting from the southern European margin and opening of the Algero-Provençal Basin to the Plio-Quaternary evolution of the Tyrrhenian Basin. Following the structuring of the eastern Sardinian margin, extensional deformation progressively migrated eastward driven by retreat of the Tethyan slab, leading to the formation of the Vavilov Basin during the Pliocene and the Marsili basin during Pleistocene. In Sardinia, Quaternary tectonics has traditionally interpreted has the westernmost expression of this extensional regime, mainly testified by the structuring of the Campidano graben and contemporaneous intra-plate volcanic activity.

Here we present geological, geophysical and geomorphological evidence indicating that tectonic activity in Sardinia persisted throughout the Quaternary and cannot be entirely explained by the evolution of the Tyrrhenian extensional system. The data suggest that an additional geodynamic process has controlled the recent deformation of the island.

The Campidano graben, filled by more than 1 km of Pleistocene-Holocene continental deposits, represents the main Quaternary tectonic structure in Sardinia. Seismic reflection data and field observation document the occurrence of Upper Pleistocene-?Holocene normal faults affecting both the basin fill and the western footwall of the graben. Low-magnitude seismicity is concentrated along the main Cenozoic fault systems, including the Campidano Graben, with hypocentres generally shallower than 10 km. Geothermal springs aligned along these fault zones indicate that they remain permeable and provide pathways for deep fluid circulation. In addition, GNSS measurements reveal vertical crustal motions of few mm per year, despite the limited seismic activity. Recent uplift is also supported by geomorphic evidence, including deep river valleys and widespread relief rejuvenation.

The Upper Pleistocene-Holocene age of the deformation suggests that the observed tectonic activity postdates the main extensional phases that affected the western Tyrrhenian Basin. During the Late Quaternary, active deformation was largely restricted to the Marsili sector, whereas no evidence of active deformation is recognized in the Vavilov Basin, between Sardinia and Marsili. Consequently, the recent tectonic activity in Sardinia is unlikely to be directly related to the present evolution of the Tyrrhenian Basin.

We propose that the observed deformation reflects regional uplift associated with the anomalous lithospheric structure beneath Sardinia, characterized by a relatively thin lithospheric mantle beneath a crust of approximately normal thickness. The origin of this lithospheric thinning remains uncertain but may be related to mantle processes inherited from Tethyan subduction, such as the presence of a stagnant slab and/or small-scale mantle convection, promoting asthenospheric upwelling, thermal erosion of the lithosphere, and long-lived surface uplift.