Continental gabbros in the Dent Blanche Tectonic System (Western Alps): from the pre-Alpine crustal structure of the Adriatic palaeomargin to the geometry of an alleged subduction interface
Résumé
Several Permian gabbro bodies are known in the continental-derived Dent Blanche Tectonic System (Western Alps).A new gabbroic complex, the Berrio Gabbro, is described in this paper, and compared with the other gabbro bodies of theAdriatic palaeomargin, as well as of the Tsaté Unit, a remnant of the Piemonte–Liguria ocean, immediately underlying the DentBlanche Tectonic System. The Berrio Gabbro comprises ultramafic cumulates (clinopyroxenite, wehrlite and hornblendite) andmafic rocks (leucocratic and mesocratic gabbros). Ultramafic (serpentinite) and mafic rocks (gabbro) are also present in theoceanic Tsaté Unit of the Combin Zone. The ultramafic–mafic rocks of the Dent Blanche and the Tsaté are clearly distinguishedby their mineralogy and their geochemistry. In addition, their behaviour during the Alpine deformation is distinct. Detailedmapping associated with geochemical characterization of the protoliths allows us to infer the structure of the Adriatic crustduring the Permian extension and refute a model of mixing between oceanic and continental material along the hypothesizedsubduction interface.