Fig. 1

a Tectonic map showing location of the Malenco unit and Margna–Sella nappes and the surrounding Austroalpine and South Penninic nappes, in the SE of Switzerland and northern Italy. The Malenco unit is located below the Lunghin–Mortirolo movement zone (Mohn et al. 2011). The location and ages of geochronological data from literature is provided; we distinguish authors (shape; Hunziker et al. 1992; Handy et al. 1996; Bachmann et al. 2009; Price et al. 2018), from geochronological methods (colour). The red star shows emplacement of studied area. b The brecciated material is in red, at the boundary between the Margna and Malenco nappes. The entire region is folded and the mantle outcrops as a tectonic window. Locally ophicalcites in Malenco serpentinized peridotites attest that these rocks cropped out at the seafloor before Alpine deformation