Fig. 7

Paleogeographic reconstruction and cross sections from Handy et. al. (2010), depicting the main stages of fissure formation in association with extensional exhumation following nappe stacking during the Cretaceous and Cenozoic at 94 Ma, 35 Ma and 20 Ma. Open fissure form typically at 450–550 °C and 0.3–0.6 GPa or below (Mullis et al. 1994; Poty et al. 2007, 2018). The situation at 94 Ma is associated with exhumation of the Koralpe-Saualpe region. The situation at 35 Ma depicts the early exhumation of the high-pressure units in the future Western Alps, following the subduction of the Penninic units. Open fissures are NW striking and vertical in orientation. The reconstruction at 20 Ma shows the situation during early exhumation of the Tauern and Lepontine metamorphic and structural domes and of the external massifs. Open fissure forming until ~ 12 Ma are vertical in orientation and “N–S” oriented in the metamorphic domes (Fig. 4). Open fissure in the external massifs are horizontal in orientation (Fig. 4) and caused by reverse faulting (vertical foliation and down-dip lineation)