The Sesia Nappe is a Salassic tectonic unit located between the Canavese Fault to the east and the Upper Penninic units to the west. It is composed of three units of crystalline basement characterized by different lithological associations. The Gneiss Minuti Unit consists mainly of orthogneisses, derived from granitoid of probable Permian age and interbedded with more mafic layers. High-pressure metamorphism of this unit was largely obliterated by the later greenschist-facies metamorphism. The Eclogitic Micaschist Unit comprises mostly paragneisses with minor mafic rocks, orthogneisses and calcitic marbles. Eclogitic mineral assemblages are well preserved, rarely overprinted by the subsequent greenschist-facies metamorphism. The unit referred to as Second Dioritic-Kinzigitic Zone (2DK) consists of kilometer-scale slices of micaschists, characterized by well-preserved pre-Alpine amphibolite to granulite-facies mineral assemblages as well as minor amphibolites and marbles, locally overprinted by the early Alpine high-pressure metamorphism.

Couverture monométamorphique de la nappe de Sesia.

Gneise, Metabasite und Marmore der Sesia-Decke, mit einer charakteristischen spätvariszischen granulitfaziellen Metamorphose.

Interne Einheit der Sesia-Zone, mit alpidische eklogitfazielle Metamorphose: pelitische Glimmerschiefer (mit Jadeit, Granat, Phengit, Quarz), Eklogite, Marmore, sowie Orthogneise und leukokrate Gänge.

Externe Einheit der Sesia-Zone, vorwiegend mit grünschieferfaziellen Paragenesen (nur vereinzelten Relikten einer Hochdruckmetamorphose): Metagranodiorite, Metagranitoide, sowie gebänderte Paragneise, Prasinite une Amphibolite.