Vogogna Castle

Near Vogogna Castle, phyllonites are exposed; these are highly foliated rocks resulting from the plastic deformation of pre-metamorphic rocks along faults. The phyllonites form a belt along the Canavese Line, the western part of the Insubric Line, a fault that separates the Alpine domain proper (to the north) from the southern Alpine domain, which was not affected by Alpine orogenesis.

The Insubric Line also marks the suture zone of the collision between Europe and Africa that gave rise to the Alps. Along the Canavese Line, from south to north, the phyllonites derive from Ivrea-Verbano milonites, milonitised Permian–Mesozoic cover rocks (Canavese) and milonites derived from the Sesia Zone (in this outcrop, from Sesia-Lanzo orthogneisses). Here, the phyllonites have a greenish colour due to the presence of chlorite, a mineral that remains stable at temperatures below 500 °C.