The Northern Giudicarie and the Meran-Mauls fault (Alps,Northern Italy) in the light of new paleomagnetic and geochronological data from boudinaged Eo-/Oligocene tonalites |
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| Authors: | Hannah Pomella Urs Klötzli Robert Scholger Michael Stipp Bernhard Fügenschuh |
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| Institution: | 1.DOC-fFORTE-fellowship of the Austrian Academy of Sciences at the Institute of Geology and Paleontology,University of Innsbruck,Innsbruck,Austria;2.Department of Lithospheric Research,University of Vienna,Vienna,Austria;3.Paleomagnetic Laboratory Gams, Chair of Geophysics,University of Leoben,Frohnleiten,Austria;4.Leibniz-Institute of Marine Sciences,Kiel,Germany;5.Institute of Geology and Paleontology,University of Innsbruck,Innsbruck,Austria |
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| Abstract: | 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. |
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