REVISITING THE INTERNAL LIGURIAN UNITS OF THE ANTESSIO AREA (LIGURIAN APENNINES, ITALY): INSIGHTS INTO THE OCEANIC LITHOSPHERE OF THE LIGURIAN-PIEDMONT BASIN

Tectonic setting of Antessio area (Ligurian Apennines, Italy)

Abstract

This paper presents a complete stratigraphic, tectonic, and structural dataset of the Internal Ligurian Units outcropping in the Antessio area, based on new geological mapping and micro- and mesoscale analyses. A stack of three Internal Ligurian Units, namely, from top to the bottom, the Gottero, Bracco-Val Graveglia and Colli-Tavarone Units, has been recognized. The general stratigraphic characteristics of these units indicate that they are derived from a dismembering of a sequence derived from a Ligurian-Piedmont oceanic basin. This sequence includes Middle to Late Jurassic ophiolites, Late Jurassic to Late Cretaceous pelagic deposits, Late Cretaceous to Early Tertiary turbidites and Early Tertiary mass-transport deposits. This sequence is interpreted to have developed during the progressive trench-ward motion of a segment belonging to the inner part of the Ligurian-Piedmont oceanic basin. In the Antessio area, the deformation history of the Internal Ligurian Units includes two deformation phases, whose features support the involvement of these units in a subduction-related accretionary wedge zone by coherent underplating followed by exhumation. This picture suggests a close correlation between the Internal Ligurian Units of the Antessio area and those of the Bracco Massif, as well as those of the Graveglia and Vara Valleys.