The Tethys Ocean itself is sometimes considered to have begun east of the Apulian and African plates, but normally the Alpine Tethys is regarded as part of it. The Piemont-Liguria Ocean and the Valais Ocean are, together with some other small oceanic basins, called Alpine Tethys Ocean or Western Tethys Ocean. From the Cretaceous onward the oceanic crust of the Piemont-Liguria ocean subducted at these trenches beneath the Apulian plate.
rocks from the former European continental margin that were subducted and obducted again.
Subdivision in the Western Alps įour paleogeographic domains can be recognized in the Penninic nappes of the Western Alps: Upper Penninic nappes include the Zermatt-Saas and Tsaté, of oceanic origin and the Dentīlanche nappe ( Austroalpine), of African origin. Middle Penninic nappes include the Monte Rosa, Mont Fort, Siviez-Mischabel, Cimes Blanches and Frilihorn, of European origin. They are characteristically ophiolite sequences and deep marine sediments, metamorphosed to phyllites, schists and amphibolites. They were deposited as sediments on the crust that existed between the European and Apulian plates before the Alps were formed. They contain high grade metamorphic rocks of different paleogeographic origins. Of the three nappe stacks the Penninic nappes have the highest metamorphic grade. The name Penninic is derived from the Pennine Alps, an area in which rocks from the Penninic nappes are abundant. In the western Alps the Penninic nappes are more obviously present than in the eastern Alps (in Austria), where they crop out as a narrow band. The Penninic nappes or the Penninicum, commonly abbreviated as Penninic, are one of three nappe stacks and geological zones in which the Alps can be divided.
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