Fig. 9

Schematic sketch, showing simplified evolution of the Western Alps in the time interval from 160 to 35 Ma. Two Ocean basins existed, the Valais and the Piemonte-Liguria Ocean. a After the opening of the Piemonte-Liguria Ocean, the TGU (yellow star) was part of the passive margin of the Cervinia microcontinent. b The Briançonnais terrane was separated from the European continent by rifting of the Valais Ocean in the Late Jurassic–Early Cretaceous. Subduction startet around 70 Ma at the latest. c TGU was subducted and accreted while other units of the Zermatt Saas Zone were still near the surface. d Subduction propagated continuously to the NW, while the Lago di Cignana Unit (white stars) was subducted to UHP depth. The process lasted until the arrival of the Briançonnais microcontinent which blocked the subduction zone and the subduction of the Valais Ocean started. e Between 44 and 35 Ma, the western Alpine nappe stack was formed and the exhumation of the ZSZ and associated “Austroalpine outliers” took place. Exhumation was accompanied by thrusting along the Combin fault. In this model, the Internal Crystalline Massives are located at the European margin (Gebauer 1999; Froitzheim 2001). Sketches are not to scale