Preliminary results of the Swiss National Map, sheet Osogna (no.1293, 1:25’000)

Schenker, Filippo and Ambrosi, Christian and Scapozza, Cristian and Maino, Matteo (2015) Preliminary results of the Swiss National Map, sheet Osogna (no.1293, 1:25’000). In: Geo Alp 2015, Fortezza. (Unpublished)

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We present the geological map of the Osogna sheet, (Swiss National Map no. 1293,1:25’000). The area extends S-N from Claro to Biasca and W-E from Lavertezzo to the Pizzo di Claro, respectively. From bottom-to-top, the mapped area includes the subpenninic gneissic nappes of the Leventina, Simano, Adula/Cima-Lunga and Maggia. These nappes derive from the same post-Variscan gneissic crust complicating their lithological distinction. In particular, the boundary between the Leventina and the Simano gneisses is not clear. Generally, the boundary was traced within leucogneisses by joining quartzite, amphibolite or paragneiss lenses. Nevertheless, we could not find any quartzite and the amphibolite and paragneisses lenses are vertically distributed in the tectonostratigraphy and do not form a single folded horizon. Furthermore, no significant strain gradient related to top-to-the-foreland shearing has been observed between these two units, also when paragneisses and amphibolites were present. Therefore, we present evidence that the top-to-the-foreland deformation between the Leventina and the Simano units was more distributed that commonly assumed, questioning the allochthonous character of the Simano unit.

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