Tethys Rifting in the Valencia Trough Basin

The basins of the western Mediterranean are thought to have formed during Tertiary times related to the rollback of subducting slabs from the Thethys ocean. New seismic images support that a large part of the Valencia Trough Basin (east of Iberia) is characterized by thin continental crust filled by dominantly Mesozoic syn-rift sediment. The Mesozoic basin displays marked lateral changes in basement thickness, delineating several sub-basins. The offshore Mesozoic Valencia Trough Basin contains Triassic sediment in the lower units, with Keuper facies producing diapiric structures. Younger possibly early Jurassic infill can be interpreted to develop along the same structural trends and is locally overlain by an unconformable probably Cretaceous unit. Early Jurassic sediment cropping out in the Balearic Island located to the east indicate deep water deposition. Thus, we interpret that the Mesozoic Valencia Trough Basin is part of the Thethys rift system that has been preserved during the Tertiary structuration of the western Mediterranean arcs and basins. The basin is in a position between moderately thinned crust of the Iberian Range and -yet subducted- oceanic crust that separated Iberia from Africa in Jurassic times, as kinematic reconstructions indicate. Crustal thickness, measured as changes in crystalline basement (based on available wide-angle seismic data) indicates that abrupt thinning from >20 to 3 km occurs over short distances of a few tens of km. This extreme thinning was produced by a combination of steep strike-slip faulting and related normal faulting, without the participation of large-scale detachment faulting. The basin is to our knowledge the only large-scale example of an undeformed structure of a Thetys basin in the region. The analysis supports that the basin structure developed largely by by strike-slip tectonics in a transcurrent geodynamic setting and it is possibly representative of other Tethyan basins formed during the translation of Iberia with respect to the Africa and Eurasian plates. Seismic images support that stretching stop thinning close to crustal break up with apparently little associated synrift magmatism and therefore the structure and evolution are possibly significant to understand magma-poor Tethyan rifting.