Description: This study concentrates on small intrusions along two important faults of the Giudicarie fault system, the Northern Giudicarie and the Meran-Mauls fault, summarised under the term tonalitic lamellae. Magnetic fabric analyses in combination with structural field data indicate dextral strike slip deformation along the NE–SW striking northern part of the Giudicarie fault system, the Meran-Mauls fault, overprinted by younger thrusting. The regional stressfield was oriented approximately NNW–SSE during Tertiary times. The distinctive change in deformation along the Meran-Mauls fault from dextral strike slip to top-SE thrusting may be caused by a rotation or bending of the fault after the intrusion of the tonalites and the formation of their horizontal magnetic foliation. Based on the assumption of a preliminary straight Periadriatic lineament bent by the NNW-wards advancement of the Southalpine indenter, the tonalitic lamellae may be interpreted as lenses sheared off from the Adamello batholith during indentation. New U/Pb data on zircon show that some of the lamellae are of Oligocene (Rupelian), others of Late Eocene (Priabonian) age. An amphibole-gabbro lens occurring on the Meran-Mauls fault provides a Middle Eocene (Bartonian) age. Among the major Periadriatic plutons, only the southern units of the Adamello batholith also intruded in the Eocene that suggests a strong correlation between the tonalitic lamellae and the Adamello batholith. The analyses of the remanent magnetisation and the Curie point determinations argue for magnetite as the main carrier of a viscous magnetisation blocked at relatively low temperatures. This indicates slow cooling of the investigated intrusions along the Giudicarie fault system down to approximately 300°C, which is in contrast to the fast cooling determined for the Adamello intrusion units currently at the surface. The new zircon fission track data also show later cooling of the tonalites along the Giudicarie fault system when compared with the Adamello batholith in the south and the Mauls lamellae in the north, indicating that this area contains magmatic bodies exhumed from a deeper structural level than in the Adamello and the Mauls region. This may be due to important top-SE thrusting and transpressive faulting in the footwall of the Northern Giudicarie fault and the Meran-Mauls fault.

Description: Quartz veins in the Eastern Tonale mylonite zone (Italian Alps) were deformed in strike-slip shear. Due to the synkinematic emplacement of the Adamello Pluton, a temperature gradient between 280°C and 700°C was effected across this fault zone. The resulting dynamic recrystallization microstructures are characteristic of bulging recrystallization, subgrain rotation recrystallization and grain boundary migration recrystallization. The transitions in recrystallization mechanisms are marked by discrete changes of grain size dependence on temperature. Differential stresses are calculated from the recrystallized grain size data using paleopiezometric relationships. Deformation temperatures are obtained from metamorphic reactions in the deformed host rock. Flow stresses and deformation temperatures are used to determine the strain rate of the Tonale mylonites through integration with several published flow laws yielding an average rate of approximately 10−14s−1 to 10−12s−1. The deformation conditions of the natural fault rocks are compared and correlated with three experimental dislocation creep regimes of quartz of Hirth & Tullis. Linking the microstructures of the naturally and experimentally deformed quartz rocks, a recrystallization mechanism map is presented. This map permits the derivation of temperature and strain rate for mylonitic fault rocks once the recrystallization mechanism is known.