Mapping the Moho Geometry around the exhumated mantle in the Tyrrhenian Sea: A Synthesis of Multi-vintage Seismic Data and DSDP/ODP/IODP Drilling Results

The Tyrrhenian Sea is a young back-arc basin that began to open in the Langhian/Serravallian (15.97-13.82 Ma). Its formation was driven by the eastward roll-back of the Apennine-Maghrebide subduction system, leading to the exhumation of the mantle in the Vavilov Basin. The spatio-temporal evolution of this exhumation occurred just after the Messinian Salinity Crisis (MSC). Consequently, the distribution and thickness of Messinian evaporites (5.97–5.33 Ma) provide a chronostratigraphic marker to constrain the transition from continental rifting to mantle exhumation. Within this framework, the present study aims to reconstruct a refined 3D Moho topography to reveal the relationship between crustal thinning and mantle exhumation.

In the Tyrrhenian Sea, we analysed a comprehensive suite of legacy seismic lines, including the SITHERE (1985), CS (1989), CROP (1995), and MEDOC and CHIANTI (2010 and 2015) surveys. We then converted Two-Way Travel time (TWT) into depth, integrating a robust velocity-depth model generated from five 2D seismic reflection profiles with coincident refraction data collected during the Spanish Survey MEDOC/CHIANTI. The resulting Moho geometry and the boundaries of mantle exhumation are validated and constrained by a synthesis of borehole data from DSDP, ODP (Sites 651 and 655), and the recent IODP Expedition 402 (Sites U1612, U1615, and U1616).

Our mapping reveals that a prominent, high-amplitude reflector is consistently observed across the region, typically occurring around 7s TWT. Once converted into depth, this interface deepens toward the continental margins and shallows toward the basin centres. In the Vavilov Basin, where mantle exhumation has been confirmed by drilling (U1614, U1616, and 651), we have identified reflectors within the exhumed basement. Notably, as imaged by the MEDOC-9 seismic profile crossing the heterogeneous exhumed domain at IODP Site U1612, one of these reflectors is sub-horizontal and truncates a set of rotated reflectors, suggesting a possible complex fault-like feature within the mantle.

The identified reflectors occurring within the mantle may be either a tectonic or hydrothermal boundary, such as a serpentinization front or a major detachment fault within the exhumed domains. Spatial correlations between Moho shallowing and the thinning of Messinian units indicate that the most intense phase of crustal thinning and mantle exhumation in the Vavilov Basin occurred shortly after the Messinian. Our new 3D Moho contour map provides a refined geodynamic framework for constraining the timing and magnitude of lithospheric extension in this back-arc region and for guiding future geodynamic modelling.