Zooming into the early stages of the exhumation process in the Tyrrhenian Basin by IODP Exp. 402

The International Ocean Discovery Program Expedition 402 in the Tyrrhenian Sea was conducted from February 9 to April 8, 2024. The Tyrrhenian is the youngest basin in the western Mediterranean Sea. It formed from the Middle Miocene to the Recent by lithospheric thinning associated with slab rollback and with the east-southeast to southeast retreat of the Apennine subduction system. Continental breakup was followed by mantle exhumation in the Vavilov Basin after Messinian (5.33 Ma ago), central Tyrrhenian. Mantle exhumation was not followed by seafloor spreading, providing an exceptional opportunity to zoom in on the early stages of the exhumation process.

The samples and data collected during Exp. 402 provide an extensive new data set to constrain the geometry and timing of the deformation that led to mantle exhumation and elucidate the processes that unroofed the deep mantle forming the continent-ocean transition. Sediments collected at the basement contact constrain the minimum age of emplacement of mantle rocks, which occurred in the Pliocene. Drilling has provided conclusive evidence that the basement of the Magnaghi-Vavilov Basin consists of serpentinized upper mantle peridotites and that mantle exhumation was not followed by the formation of a magmatic oceanic crust. The oldest sediments above the basement were biostratigraphically dated to 2.82-3.56 Ma at Site U1612 and 3.56-3.85 Ma at Site U1616. The oldest biostratigraphic dates at Site U1614 were younger, 1.71-1.95 Ma. This information, placed in the context of knowledge of the basin, will allow us to reconstruct the geometry of the Tyrrhenian basin before, during, and after crustal extension and to follow its kinematic evolution over time until mantle exhumation.