From stretching to mantle exhumation in a triangular backarc basin (Vavilov basin, Tyrrhenian Sea, Western Mediterranean)

In this study, we describe the mode of extension of the Vavilov, a fossil backarc basin, triangle-shaped (approximately240 km-wide and 200 km-long), located between Sardinia margin to the west and Campania margin tothe east.We combine the analysis of recent geophysical and geological data, in order to investigate the relationshipbetween the crustal/sedimentary structure and the tectonic evolution of both apex and bathyal parts of thebasin. With this aim,we interpret a large data set of multichannel seismic reflection profiles and severalwell logs.We observe that the apex basin corresponds to a sediment-balanced basin, with a sedimentary infill recordingthe episodes of basin evolution. In contrast, the distal basin corresponds to an underfilled basin, characterizedby localized volcanic activity and a thin sedimentary succession that covers the exhumed mantle. The basin architecturereveals the occurrence of rift and supradetachment basins in the Vavilov rift zone. We find that therifting of the Vavilov triangular basin was synchronous from the apex to distal regions around a single Eulerpole located in Latium, between 5.1 and 1.8 Ma. The kinematic evolution of the Vavilov basin occurred in twostages: initial pure shear mode (5.1–4.0 Ma) that produced high-angle normal faults and syn-sedimentarywedges, followed by simple shear mode (4.0–1.8Ma) that caused supradetachment basins filled by a Transgressive-Regressive succession that documents high subsidence rates (1.22mm/y) in the apex region. The final stageof extension in the distal region led to: (i) complete embrittlement of the crust; (ii) direct continuation of crustalfaults to uppermantle depth; (iii) serpentinization andmantle exhumation. Based on constraints on the presentdaycrustal structure of the Vavilov basin, we obtain a stretching value (β=3.5) and extension rates (3 cm/y) inthe bathyal zone analogous to those reported for magma-poor rifted margins.