A combined MCS and WAS experiment reveals the complex crustal transition between the Central and Northern Tyrrhenian basin

Abstract

The Tyrrhenian back-arc basin formed as a result of the migration of subduction fronts towards the east and southeast during the Neogene. The complex evolution of this subduction system caused differences concerning the degree of back-arc extension from north to south: while the northern region suffered a moderate amount of rifting, full continental break up occurred in the central and southern regions. In 2010, the MEDOC experiment was carried out with the collaboration of the Spanish B/O Sarimiento de Gamboa, the Italian R/V Urania, and several land teams to investigate the crustal structure of the basin and provide new insights on the formation processes of rifted continental margins. During the survey, multichannel seismic (MCS) and wide-angle seismic (WAS) data were acquired across the Tyrrhenian basin along five coincident transects, together with gravimetric, bathymetric, and hydrographic data. Here we present WAS, MCS, and gravity MEDOC data acquired along two of these transects: E-F (~400 km-long) and G-H (~450 km-long), both crossing the central basin from Sardinia to Campania. WAS data along transect G-H were recorded by 5 Land stations (LS), and 26 Ocean Bottom Seismometers and Hydrophones (OBS/H). Similarly, line E-F WAS data were recorded by 5 LSs and 28 OBS/H. The coincident MCS data along these two lines were acquired using a 276-channel, 3450 m-long streamer. Travel-times of first arrivals and Moho reflections were manually tracked from the OBS/H recordings and modelled using the tomo2d joint refraction and reflection travel-time inversion method to obtain the corresponding 2D P-wave velocity models. MCS data were processed to obtain two post-stack time migrated profiles. Integration of these results together with a rigorous velocity uncertainty analysis and a Vp-derived density modelling reveal that regions previously interpreted as extended continental crust present velocities and densities consistent with those expected for magmatic rocks, whereas basement properties in other regions previously interpreted as oceanic crust are better explained by exhumed mantle rocks