The Meran-Mauls Fault: Tectonic switching from compression to transpression along a restraining bend of the Periadriatic Fault

The WSW-ENE Meran-Mauls Fault (MMF) represents a break in the broadly E-W trending Periadriatic Fault (PAF), separating the Southern Alps from the N-verging wedge of the European Alps. Understanding the MMF evolution is mandatory to reconstruct the role of the entire PAF during the evolution of the belt since the late Cenozoic. Structural and microstructural analyses and paleostress calculations based on fault-slip data suggest the occurrence of four evolutionary stages for the MMF: 1) top-to-the-SE mylonites; 2) top-to-the-SE brittle faulting; 3) dextral faulting with re-activation of previous structures; 4) N–S compression associated with conjugate sets of mainly strike-slip fault systems. Paleostress reconstructions point to a σ2-σ3 permutation from stage 2 to stage 3, resulting in the switch from pure thrusting to strike-slip, followed by an anticlockwise rotation of the principal stress axes during stage 4, in a strike-slip regime related to N–S compression. Geochronological and thermochronological data point to 39-22 Ma age for stage 1, 22-17 Ma for stage 2, less than 17 Ma for stage 3. Our reconstruction strongly supports the interpretation of the MMF as a restraining bend of the PAF, which was weakly reactivated along its eastern portion as a dextral fault and later displaced by NNE-SSW left-lateral faults.