Lepontin dome

The Alps north of the Periadriatic Seam are usually divided into three large nappe complexes.

The same counts for the region west of the dome, if the Sesia unit is seen as part of the Austroalpine nappes.

The dome itself however only shows Penninic and Helvetic (the boundary between the two is still disputed) rocks.

Apparently the uplift of the dome caused the upper Austroalpine material to be totally eroded away.

The creation of the dome was caused by a phase of east-west directed extension in the Miocene that occurred throughout the Eastern and Central Alps.