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					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

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.

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.