Time constraints and fault kinematic evolution of the Periadriatic Fault System along the Meran-Mauls segment (N Italy)

Abstract

<p>The Periadriatic Fault System (PFS) is one of the most important tectonic element in the Alps, separating the Europe-verging collisional wedge from the S-verging Southern Alps. The PFS developed in a dextral transpressional regime during the Cenozoic, following the Adria-Europe collision. The area between the Passeier and the Eisack rivers (Meran, NE Italy) is a key area for the understanding of the interactions among the PFS, the Giudicarie Fault and the fault network here active in the middle to late Cenozoic. Here the elsewhere E-W trending PFS rotates to a NE-SW trend, impliying significant changes in the fault kinematics and evolution.</p><p>The NE-SW strand of the PFS, known as the Meran-Mauls fault, is connected to the North Giudicarie Fault to the west and to the Pustertal segment of the PFS to the east. A general evolution from the ductile to brittle deformation regime has been recognized on the base of field-based structural analysis and microstructural analysis of fault rocks. Pseudotachylytes occur all along the fault zone, testifying to the seismic activity of the Meran-Mauls fault. <sup>40</sup>Ar-<sup>39</sup>Ar dating of pseudotachylytes provided ages in the 32-22 Ma time interval, indicating that the PFS experienced a prolonged seismic activity during middle Cenozoic times. Several pseudotachylytes veins show a re-activation as cm-thick ductile shear zones, indicating that the plastic-brittle transition was not sharp in time.</p><p>Combining the structural analysis of the PFS with other adjacent faults connected in space and time (Passeier fault, Faltleis fault, Val Nova fault and other minor faults) we reconstructed a marked reverse dip-slip kinematics of the Meran-Mauls Fault during a progressive transition across the plastic-brittle regime, followed in time by a dextral transpression. Paleostress reconstructions performed on these faults populations indicate a progressive switch of the main direction of compression from NW-SE to N-S. This switch likely occurred when the Meran-Mauls segment of the PFS definitively passed to a brittle deformation regime.</p><p> </p>