Neogene kinematics of the Giudicarie fault (Central-Eastern Alps, Italy): new apatite fission-track data

The Neogene kinematics of the Giudicarie fault (part of Periadriatic lineament, NE Italy) have been re-examined using apatite fission-track analysis. Twenty samples were collected along two geological sections; the first one crossing the Tertiary Corno Alto pluton (Adamello batholith) and the Variscan basement (Southalpine domain) adjacent to the South Giudicarie fault, the second one close to the North Giudicarie fault, in the Variscan basement of the Tonale nappe (Austroalpine system). Samples from the southern section show short tracks and ages between 14.7±1.2 Myr and 22.5±2.2 Myr along 1570 m of the profile; samples from the northern profile present long tracks and ages between 11.3±1.3 Myr and 14.7±3.4 Myr along 1225 m of the vertical profile. In the former, the presence of short tracks might indicate either a long permanence of the rocks in the apatite partial annealing zone, or a more complex thermal history; in the latter case we are dealing with rocks which experienced more rapid cooling.
  The two differing segments of the Giudicarie fault can be explained either as two completely independent tectonic features or, more likely, by hypothesizing a single fault active in its southern and northern parts at different times. Fission track data support a first exhumation of this single fault c. 15 Ma along the North Giudicarie, with a final exhumation towards the south, in the Adamello area, at c. 8–10 Ma (Mid Tortonian). This age fits with the so-called 'Giudicarie' phase, during which σ₁ in the stress field was orientated N280–290°.