Crevola–Varallo

The outcrop reveals what is normally found at a depth of around 15 km within the Earth’s crust, at the contact between the Basic Complex and the crustal rocks into which it has intruded. These rocks, which are heavily deformed, with chaotic folds and structures known as ‘boudinage’, bear evidence of stretching.

The intense heat released by the Basic Complex caused the crustal rocks to melt partially, giving rise to light-coloured portions (neosome) intercalated with the unmelted residue of the pre-existing, darker-coloured rocks (paeosome). These lighter-coloured parts are precisely the result of the partial melting of the crust and have a granitic composition. These molten materials, having migrated upwards, gave rise to the granites found in the upper crust – as can be seen at the Agnona geosite – and triggered the eruption of the supervolcano.