Rifting in the Northern Tyrrhenian Sea: Results from a combined wide-angle and multichannel seismic study

Extension in the continental lithosphere leads to the formation of rift basins or finally to passive continental margins where plates fully broke apart. The extensional processes at basins and passive margins are still not fully understood. One of the reasons is that the observed amount of crustal thinning is often much higher than the horizontal extension in the brittle upper crust that can be accounted by faulting. Regarding this objective we present an analysis of two W-E striking depth-migrated multichannel- and wide-angle seismic sections from the Northern Tyrrhenian Sea. The new data were acquired onboard the Spanish R/V Sarmiento de Gamboa and Italian R/V Uraniain spring 2010, within the framework of the MEDOC project. The lines cross the basin from the Corsica and Sardinia margins towards the conjugated Latium/Campania margins (Italy). Along the transects we found two distinct domains distinguishable in tectonic style, heat-flow and crustal thickness: 1) The deep sedimentary Corsica and Sardinia basins in the West which formation started in the Oligocene (~30 Ma) and reveal a fan-shaped sedimentary infill with the Messinian erosional unconformity on top (~5-7 Ma) and 2) rifted crystalline continental crust expressed by horst and graben structures towards the East. These two domains are separated by a deep reaching (~10 km) and westward dipping fault/thrust complex. To quantify the amount of horizontal extension we identified pre-, syn-, and post-tectonic sedimentary units in the northern line A-B (Figure 1), calculated the relative extension factor by large faults as well as balancing the length of the pre-tectonic basement. The Messinian reflector can be well identified throughout the complete section and is therefore an excellent time-marker within the syn-tectonic sequence. The syn-tectonic sequence is limited by a reflector of Pliocene age. The above lying Pleistocene to Quaternary sediments are undisturbed and identified as the post-tectonic sequence. Tomography of first arrivals obtained from refraction and wide-angle seismic data reveals the crustal architecture and thickness of 18 km ± 1 km along the northern profile. We found that the eastern domain is horizontally stretched by >= 30 % and thinned vertically by 40 %. However, we believe that many faults are overlooked due to the partly complexity of Messinian-Tortonian syn-tectonic sequences and that in this young stage of (back-arc) basin evolution the crust evolves in a uniform manner. In this work, we will present these combined seismic data sets and compare them with the C-D transect, which is located ~80 km further south and shows larger stretching factors. Map of the Northern Tyrrehnian Sea and locations of seismic transects.