Penninic

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. 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 name Penninic is derived from the Pennine Alps, an area in which rocks from the Penninic nappes are abundant. Of the three nappe stacks the Penninic nappes have the highest metamorphic grade. They contain high grade metamorphic rocks of different paleogeographic origins. They were deposited as sediments on the crust that existed between the European and Apulian plates before the Alps were formed. They are characteristically ophiolite sequences and deep marine sediments, metamorphosed to phyllites, schists and amphibolites. Middle Penninic nappes include the Monte Rosa, Mont Fort, Siviez-Mischabel, Cimes Blanches and Frilihorn, of European origin. Upper Penninic nappes include the Zermatt-Saas and Tsaté, of oceanic origin and the Dent Blanche nappe (Austroalpine), of African origin. Four paleogeographic domains can be recognized in the Penninic nappes of the Western Alps: rocks from the former European continental margin that were subducted and obducted again. rocks from the continental crust of the Valais Ocean, metamorphosed ophiolites and other sedimentary rocks from this disappeared oceanic basin. The occurrence of eclogite lenses shows these rocks were subducted to great depths in the Earth's mantle. Valais sedimentary rocks include thin Cretaceous limestones (now marbles) and Tertiary flysch which is now turned into (mica-) schists. rocks from the former Briançonnais microcontinent. These are rocks from the lower continental crust deformed and intruded by Variscan granites, but also metamorphosed sedimentary rocks: graphite-bearing Carboniferous rocks, red sandstones from the Permian period, Triassic evaporites and thin limestones of the Jurassic and lower Cretaceous.