Scientific article
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Metamorphose niedrigst temperierten Grades in den Westalpen

Published inFortschritte der Mineralogie, vol. 47, no. 1, p. 52-64
Publication date1970-08

It seems now certain that Alpine regional metamorphism extended outside the classical domain of the Pennine Nappes. The main proof of this extension lies in the transformation into the zeolitic facies of the Taveyanne sandstones of the Helvetic zone. These graywackes with up to 90% of andesitic fragments show the typical mineral association of the Taringatura section in New Zealand. Three main types of graywackes can be distinguished: the laumontite type, the prehnite-pumpellyite type and the "green" type characterised by the non-diagnostic association of albite and chlorite. In a few cases the primary calcic plagioclase has escaped the general albitisation process. On the other hand near the root zone of the Helvetic nappes some Taveyanne sandstones have been submitted to a more intense rnetamorphism (actinolite-pumpellyite subfacies). lt is likely that the presence of stilpnomelane, the crystallinity of illite in pelitic sediments, the nature of serpentine mineral in ultramafics of the ophiolite group could be used to detect the effects of light metamorphism. The existence of the zeolitic facies in the Helvetic zone has two important consequences. First, in order to have a sufficient load, the piling up of Nappes in the external parts of the Alpine arc had to be thicker than is admitted in classical papers on alpine tectonics. In the second place we are loosing the main arguments in favor of the primary origin of alpine spilites; we can no more say that they are in zones lying outside the domain of alpine metamorphism and, in the "green" graywacke type, fragments showing the albite chlorite association without any structural deformation show us that this association typical of many spilites can be the result of a metamorphic process.

Citation (ISO format)
MARTINI, Jacques, VUAGNAT, Marc. Metamorphose niedrigst temperierten Grades in den Westalpen. In: Fortschritte der Mineralogie, 1970, vol. 47, n° 1, p. 52–64.
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Article (Published version)
  • PID : unige:159112
ISSN of the journal0015-8186

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