Sesia zone

The outcrop in the southern part of the Aosta Valley is bounded to the south by the Insubric line.

The unit shows traces of high-grade metamorphism in the form of eclogite and blueschist relicts.

This greenschist metamorphic grade is seen as a late (Meso-Alpine) overprint, most researchers think the whole Sesia zone or at least part of it has been in eclogite or blueschist conditions during Paleogene subduction.

When the continents Europe and Africa were divided by a rift zone in the Jurassic period, Apulia and the Austroalpine are supposed to have rifted apart from Africa (just like for example the present day British Isles, which are separated from the rest of Europe by the North Sea basin).

When the plates converged again in the Paleogene, many small pieces of continental crust, like the Austroalpine microcontinent, became incorporated in the nappe stacks of the Alps.