Rotondo Granite

The Rotondo Granite is a late Variscan granitic intrusion located in the Saint-Gotthard Massif in the Swiss Alps. Its name comes from the Pizzo Rotondo.

Ridge made of Rotondo Granite.

Description

It shows as a fine to medium-grained granite. Unlike other granitic intrusions present in the Gotthard Massif (Gamsboden Granite and Fibbia Granite), the foliation is only very weakly developed[1] and is mostly visible in ductile shear zones. Radiometric dating showed an age of 294 Ma.[2] On surface, it outcrops over an area of 20–25 km2.[3]

The Rotondo Granite forms at least part of Monte Prosa.[4]

Significance
Fresh Rotondo Granite surface in the Bedretto Tunnel.

The Bedretto Underground Laboratory for Geoenergies which is located in the Bedretto Tunnel (in German "Bedretto-Fenster"), is performing research on deep geothermal energy in the Rotondo Granite. The site was selected, among other reasons, because of the similarities that this rock shows with basement rocks that are expected to be encountered at a depth of 4–5 km below the Swiss Plateau.

References
  1. Lützenkirchen, V., & Loew, S. (2011). Late Alpine brittle faulting in the Rotondo granite (Switzerland): deformation mechanisms and fault evolution. Swiss Journal of Geosciences, 104(1), 31-54.
  2. Sergeev, S. A., & Steiger, R. H. (1995). Caledonian and Variscan granitoids of the Gotthard massif: new geochronological and geochemical results, Schweizerische Mineralogische und Petrographische Mitteilungen, 75, 315-316.
  3. Labhart, T. (2005). Erläuterungen Zum Geologischen Atlas Des Schweiz 1:25000, Val Bedretto, Atlasblatt 68. ed. Bundesamt für Wasser und Geologie.
  4. Hafner, Stefan S.; Loida, Andreas (1980). "Origin and variation of the microcline triclinicity in granitic bodies of the Central Alps". Eclogae Geologicae Helvetiae. 73 (2): 563.
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