Sesia unit
From Wikipedia, the free encyclopedia
| Geology of the Alps |
|---|
 |
| Tectonic subdivision |
| Penninic nappes |
| Austroalpine nappes |
| Southern Alps |
| Formations & rocks |
| Geological structures |
|
Aarmassif | Dent Blanche klippe | Engadine window | Flysch zone | Giudicárie line | Greywacke zone | Hohe Tauern window | Molasse basin | Penninic thrustfront | Periadriatic Seam | Ivrea zone | Lepontin dome | Rechnitz window | Rhône-Simplon line | Sesia unit |
| Paleogeografic terminology |
| Briançonnais microcontinent |
| Piemont-Liguria Ocean |
| Apulian or Adriatic plate |
The Sesia unit or Sesia nappe, also called the Sesia-Dent Blanche unit is a tectonic unit or terrane in the Swiss and Italian Alps. The unit is located around the Dent Blanche group in the Pennine Alps and in the southern part of the Aosta Valley. The unit is at the first locality sometimes seen as an independent nappe and then called Dent Blanche nappe or unit.
Today the Sesia unit is often seen as part of the Austroalpine nappes, though the metamorphic history of the unit is different from rocks from those nappes.
The unit consists of high-grade metamorphic rocks, but the metamorphic grade is not as high as in the Penninic nappes, which are in the tectonic sequence of the Alps positioned below it.
The part of the Sesia unit that crops out around the Dent Blanche forms a large klippe (Dent Blanche klippe). The outcrop in the southern part of the Aosta Valley is bounded to the south by the Insubric line, a fault zone that is part of the Periadriatic Seam. The other side of this fault zone is called the Ivrea zone here and is a part of the Southern Alps.
The Sesia unit is considered to have been (just like the Austroalpine nappes) originally part of the continental margin of the Apulian plate. When the continents Europe and Africa were divided by a rift zone in the Jurassic period, the Sesia unit is supposed to have been rifted off the Apulian plate a bit (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 collided in the Eocene, this small piece of continental crust became incorporated in the nappe stacks of the Alps.
