Open Session - SWISS GEOSCIENCE MEETINGs

1.
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 (mstipp@ifm-geomar.de)
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.
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.
Symposium 1: Structural Geology, Tectonics and Geodynamics