Geochronological constraints on the evolution of the Periadriatic Fault System (Alps)

Fault rocks from various segments of the Periadriatic fault system (PAF; Al ps) have been directly dated using texturally controlled Rb-Sr microsamplin g dating applied to mylonites, and both stepwise-heating and laser-ablation Ar-40/Ar-39 dating applied to pseudotachylytes. The new fault ages place b etter constraints on tectonic models proposed for the PAF, particularly in its central sector. Along the North Giudicarie fault, Oligocene (E)SE-direc ted thrusting (29-32 Ma) is currently best explained as accommodation acros s a cogenetic restraining bend within the Oligocene dextral Tonale-Pusterta l fault system. In this case, the limited jump in metamorphic grade observe d across the North Giudicarie fault restricts the dextral displacement alon g the kinematically linked Tonale fault to similar to 30 km. Dextral displa cement between the Tonale and Pustertal faults cannot be transferred via th e Peio fault because of both Late Cretaceous fault ages (74-67 Ma) and sini stral transtensive fault kinematics. In combination with other pseudotachyl yte ages (62-58 Ma), widespread Late Cretaceous-Paleocene extension is esta blished within the Austroalpine unit, coeval with sedimentation of Gosau Gr oup sediments. Early Miocene pseudotachylyte ages (22-16 Ma) from the Tonal e, Pustertal, Jaufen and Passeier faults argue for a period of enhanced fau lt activity contemporaneous with lateral extrusion of the Eastern Alps. Thi s event coincides with exhumation of the Penninic units and contemporaneous sedimentation within fault-bound basins.