Fig. 1

a Map of Alpine belt (after Von Raumer et al. 2013) with high-lighted pre-Mesozoic basement units for which Ordovician orthogneisses and large-scale Schlingen folds are reported. b Geological map of the Strona-Ceneri Zone (after Boriani et al. 1990). The types of orthogneisses are defined in Table 1. (Abbreviations: C: Cannobio, F: Ponte Falmenta, E: location of eclogite sample from Franz and Romer (2007), SBS: San Bartolomeo Schlinge, MGS: Monte Giove Schlinge, GS: Gambarogno Schlinge). c Road profile of Molinetto (Villa Elisabeth, c. 1.5 km south of Cannobio, Italy). Sample Z135 (Swiss coordinates: 2ʹ698ʹ055/1ʹ100ʹ650) is a meta-Spn-Hbl-Bt tonalite (Zurbriggen 1996); sample Z137 (Swiss coordinates: 2ʹ697ʹ980/1ʹ100ʹ380) is a banded amphibolite (Zurbriggen 1996). d Typical banded amphibolite (Swiss coordinates: 2ʹ698ʹ074/1ʹ100ʹ083)