Modes of stepwise eastwardmigration of the northern Tyrrhenian Sea back-arc extension: Evidences from the northern Latium offshore (Italy)

The structural architecture of a portion of the eastern side of the Tyrrhenian Sea back-arc basin has been defined reinterpreting a public data set made up by seismic reflection profiles. A detailed reconstruction of the extensional front migration trough time across the area has been achieved. Migration has been defined by identifying the generation of unconformities in the graben-like basins developed in the area, as due to the activation and deactivation of normal faults. Such phenomena are part of a tectonic process that also involved blocks rotation, crustal thinning, and stretching. Syn-rift extension affected the area since the early to middle Miocene (our estimate), principally interesting the north-westernmost sectors. During late Miocene and throughout the Plio-Quaternary the extensional front moved stepwise toward the southeastern and eastern sectors. Widespread postrift conditions established over the whole area since the late Pliocene to early Pleistocene. Since the Quaternary, the locus of active extension further migrated toward the present onshore area, where a pronounced volcanic phase developed. In this evolutionary framework the rates of observed migration could be correlated with the acceleration of Calabrian slab rollback since Pliocene. Furthermore, direct evidences of magmatism were not recognized in the offshore. Although the observed crustal thinning, the absence of volcanic bodies in the study area could be related to normal faults which were unable to sufficiently extend the crust, in association with lower crust and mantle processes unable to produce melts.