A ductile shear zone terminating a brittle strike-slip fault: The gypsum- dominated Paluzza-Comeglians shear zone as western extension of the Fella- Save fault, Southern Alps

Compressive and extensive horsetails are common structures on the lateral termination of brittle strike-slip faults, which forms within the shallow continental crust. Here we report another possibility, the lateral termination of a brittle strike-slip fault in a formation-parallel low-temperature ductile shear zone within sulphatic, gypsum-dominated evaporites. In the Southern Alps, over a distance of ca. 35 km, a steeply to gently S-dipping foliation, a subhorizontal stretching lineation and pure shear-dominated porphyroclast systems developed within the S-dipping Lower Bellerophon Formation of uppermost Permian age. Subordinate σ-clasts indicate dextral shear. The main-stage foliation is often overprinted by shear band structures, which also consistently indicate dextral shear along the shear zone. Open to tight faults form at several stages during shear zone development, and mainly refold the mylonitic foliation. Open folds are sometimes associated with reverse faults indicating final N-S shortening. Together, the structures within the Paluzza-Comeglians shear zone indicate transpression, which accommodated dextral displacement of the Fella-Save fault in the east.