Fig. 8

Cooling ages and rates of the Lepontine gneiss dome (A–A’ on Fig. 1) modified after Fig. 12 in Steck and Hunziker (1994; Campani 2011), completed by U–Pb zircon dating of Liati et al. (2009) and Rubatto et al. (2009). (1) High temperature crystallisation (resetting) of zircon in the Adula nappe (Liati et al. 2009). (2) Crystallisation of zircon in Tertiary migmatite leucosome from Bellizona (20 km to the south of profile A–A’; Rubatto et al. 2009). Note that the progressive cooling below 500 °C started during and after Lower Penninic nappe emplacement some 38 Ma ago at the western and eastern border of the Lepontine dome and was followed by the rapid cooling some 26 Ma ago of the Verzasca F4 anticline (Hurford 1986). 32 Ma zircon U–Pb resetting in the Adula nappe and 32–22 Ma zircon crystallisation in the southern steep belt testify of temperatures of over 650 °C until 22 Ma (Rubatto et al. 2009). Accelerated cooling continued by uplift and erosion of 50 °C/Ma between 23 and 18 Ma of the Ticino dome to the E and followed by the rapid cooling of the Toce dome to the W, with phases of accelerated cooling by detachment on the Rhone–Simplon low angle normal fault of 37.5 °C/Ma between 18–15 and 12–10 Ma and 40 °C/Ma since 4 Ma. The U–Pb monazite ages obtained by Köppel et al. (1981) suggest a cooling (resetting?) temperature of ~450 ± 50 °C (Steck and Hunziker 1994). The Antigorio and Simano nappes are distinguished in red and orange–yellow colour on the cross-section A–A’. They occur in the same tectonic position in the Alpine nappe stack, but the structural relation of the two units is still problematic