The East Variscan Shear Zone: a structural and geochronological review for improving paleogeographic reconstruction of the southern Variscides

Matteo Simonetti (1)
(1) Dipartimento per il Servizio Geologico d'Italia, ISPRA, 00144 Roma, Italy Corresponding author e-mail: matteo.simonetti@isprambiente.it

The Alpine orogenesis partially overprinted the Southern European Variscan Belt complicating paleogeographic reconstructions. A main debate concerns the extension and the tectonic significance of the regional-scale East Variscan Shear Zone (EVSZ). This work reviews the data obtained thanks to a systematic and multidisciplinary study of the Ferriere-Mollières shear zone in the Argentera Massif, the Emosson-Bèrard shear zone in the Aiguilles Rouge Massif and the Cavalaire Fault in the Maures Massif. A pure shear-dominated transpression with a a variable component of simple shear is recognized in the studied shear zones. Syn-kinematic paragenesis, microstructures and quartz c-axis fabrics revealed syn- shear decreasing temperature starting from amphibolite-facies. Petrochronology constrained the timing of deformation. Ages range between ~340-330 Ma and ~320 Ma. Older ages are interpreted as the beginning of the activity of the EVSZ along its older branches (Ferriere-Mollières shear zone) while ages of ~320 Ma, obtained in all the shear zones, demonstrate that they were active at the same time. The data revealed a similar tectono-metamorphic evolution of the shear zones and highlights that transpressional deformation affected the European Variscan Belt after the metamorphic peak linked to the initial collisional stage. The review constrains the extension, the kinematics and the timing the EVSZ.

East Variscan Shear Zone, Argentera Massif, Aiguilles Rouge Massif, Maures Massif, Structural Analysis.