6th Swiss Geoscience Meeting, Lugano 2008 The Giudicarie Fault System at the transition between Southern and Eastern Alps (Northern Italy) A new structural analysis Pomella Hannah*, Fügenschuh Bernhard*, Stipp Michael** * Institute of Geology and Paleontology, University of Innsbruck. Innrain 52, A-6020 Innsbruck Hannah.Pomella@uibk.ac.at, Bernhard.Fuegenschuh@uibk.ac.at ** IFM-GEOMAR, Leibniz Institute of Marine Sciences. Wischhofstr. 1-3, D-24148 Kiel email@example.com The NNE-SSW striking Guidicarie Fault System (composed of the Northern and Southern Giudicarie Fault and the Meran-Mauls Fault) represents a distinctive bend in the Periadriatic Fault System (PFS). It terminates the E-W striking Tonale Fault Zone to the east and the ESE-WNW striking Pustertal-Gailtal Fault to the west. The apparent sinistral offset between these two dextral strike-slip faults amounts to about 80 km realized by the 290/40-60 oriented Northern Giudicarie Fault and its northeastern prolongation the Meran-Mauls Fault (320/40-60). The NNE-SSW striking Southern Giudicarie Fault is located south of the conjunction Tonale Fault Zone – Northern Giudicarie Fault and delimits the Oligocene Adamello Pluton to the east. Two end member models are generally discussed concerning the Cenozoic evolution of the Guidicarie Fault System as part of the Periadriatic Fault System: an originally straight Periadriatic Fault System, dissected and sinistrally offset in the Miocene (e.g. Laubscher, 1971; Frisch et al., 1998; Stipp et al., 2004) or Neogene compressional inversions of an inherited Early Permian to Lower Liassic NE-SW trending horst and graben structure (e.g. Viola et al., 2001; Castellarin et al., 2006). At the easternmost end of the Tonale Fault Zone the mylonitic foliation of the Adamello Pluton bends from an E-W into a NE-SW trending orientation close to the intersection with the Guidicarie Fault System whereas the stretching lineation remains still nearly horizontal. Also along the NE-SW striking Meran- Mauls Fault a nearly horizontal stretching lineation with a dextral sense of shear can be observed, overprinted by a clearly younger steep dipping lineation, revealing top ESE to SE thrusting. We interpret these NE-SW oriented mylonites with horizontal stretching lineations as boudinaged elements of the Tonale mylonites which formed during dextral strike slip movements along the PFS in the Oligocene. In case of an originally curved Periadriatic Fault System transpression along the NE-SW trending sections of the Periadriatic Fault System should not allow for subhorizontal stretching lineations. Along the Guidicarie Fault System Oligocene tonalitic bodies occur, subsumed under the term “Oligocene Tonalitic lamellae”. Along the southern part of the Northern Giudicarie Fault only a few less then 50 m thick and 200 m long lenses crop out, often strongly affected by brittle deformation. So far no tonalitic bodies have been found between the locality Rumo in the Val di Non and Pawigl south of the city of Meran, i.e. for some 20 km. From Pawigl to the NE the lenses are more continuous, up to 150 m thick and less affected by brittle deformation. 6th Swiss Geoscience Meeting, Lugano 2008 Near Pawigl on the northern end of the Northern Giudicarie Fault tonalites display a mylonitic foliation parallel to the foliation of the overlying Austroalpine Paragneisses (325/40). The ductile fault is dissected and sinistrally offset by brittle NNE-SSW striking strike-slip faults with offsets of ~50 m. Similar faults are observed along the “Falschauer” river located a few hundred meters south of the fault (see figure 1). Towards NE a cumulative sinistral offset of about 4,5 km along one or several NNE-SSW trending sinistral strike-slip faults is necessary in order to connect the Giudicarie Fault System near Pawigl with the Meran-Mauls Fault north of Meran. The NNE-SSW trending south-western sinistral strike slip faults can be interpreted as a younger fault system related to the late Miocene Passeier Fault (Viola et al. 2001). For structural reasons the outcrops near Pawigl are interpreted to represent the southernmost part of the Meran-Mauls Fault dissected by the Miocene Passeier fault which belongs to the late sinistral offset along the Giudcarie fault. We propose that the Meran-Mauls Fault belonged initially to the dextral transpressive segments of the PFS, ie. Tonale and Pustertal-Gailtal Fault. Afterwards it was presumably rotated and evidently reactivated as SE-directed (back)thrust. Finally, Tonale Fault (e.g. Stipp et al. 2004) and Meran-Mauls Fault were sinistrally offset by Passeier and Giudicarie strike slip faulting. REFERENCES Castellarin, A. et al. 2006: The Alpine evolution of the Southern Alps around the Giudicarie faults: A Late Cretaceous to Early Eocene transfer zone – Tectonophysics, 414, 203-223. Frisch, W. et al. 1998: Palinspastic reconstruction and topographic evolution of the Eastern Alps during late Tertiary tectonic extrusion – Tectonophysics, 297, 1– 15. Laubscher, H.P. 1971: Geologische Rundschau, 60, 710-718. Stipp et al. 2004: Contemporaneous plutonism and strike-slip faulting - Tectonics, 23, TC3004 Viola, G. et al. 2001: Late Oligocene-Neogene evolution of Europe-Adria collision – Tectonics, 20, 999-1020.
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