The Penninic Ocean fully closed and subducted 50 million years ago, although sections of orogenic rock were thrust onto the Helvetic Shelf. Nappes in the South Alpine Superunit formed as the unstable Adriatic Plate shifted northward into the Helvetic Shelf. The building of the Alps continued, as some units subsided 60 kilometers below the surface, metamorphosing under high pressure. Eclogite and blueschist in the Sub-Penninic Superunit and Penninic Superunit are seen as evidence of the extent of metamorphism.
