Early-stage rifting of the northern Tyrrhenian Sea Basin: Results from a combined wide-angle and multichannel seismic study

[1] Extension of the continental lithosphere leads to the formation of rift basins and ultimately may create passive continental margins. The mechanisms that operate during the early stage of crustal extension are still intensely debated. We present the results from coincident multichannel seismic and wide-angle seismic profiles that transect across the northern Tyrrhenian Sea Basin. The profiles cross the Corsica Basin (France) to the Latium Margin (Italy) where the early-rift stage of the basin is well preserved. We found two domains, each with a distinct tectonic style, heat flow and crustal thickness. One domain is the Corsica Basin in the west that formed before the main rift phase of the northern Tyrrhenian Sea opening ( 8–4 Ma). The second domain is rifted continental crust characterized by tilted blocks and half-graben structures in the central region and at the Latium Margin. These two domains are separated by a deep ( 10 km) sedimentary complex of the eastern portion of the Corsica Basin. Travel-time tomography of wide-angle seismic data reveals the crustal architecture and a subhorizontal 15–176 1 km deep Moho discontinuity under the basin. To estimate the amount of horizontal extension we have identified the pre-, syn-, and post-tectonic sedimentary units and calculated the relative displacement of faults. We found that major faults initiated at angles of 45 –50 and that the rifted domain is horizontally stretched by a factor of 1.3 ( 8–10 mm/a). The crust has been thinned from 24 to 17 km indicating a similar amount of extension ( 30%). The transect represents one of the best imaged early rifts and implies that the formation of crustal-scale detachments, or long-lived low-angle normal faults, is not a general feature that controls the rift initiation of continental crust. Other young rift basins, like the Gulf of Corinth, the Suez Rift or Lake Baikal, display features resembling the northern Tyrrhenian Basin, suggesting that half-graben formations and distributed homogeneous crustal thinning are a common feature during rift initiation.