Very low-grade metamorphism in the para-autochtonous sedimentary cover of the Pelvoux massif (Western Alps, France) - Archive ouverte HAL
Article Dans Une Revue Swiss Journal of Geosciences Année : 2012

Very low-grade metamorphism in the para-autochtonous sedimentary cover of the Pelvoux massif (Western Alps, France)

Résumé

The metamorphic grade from the para-autochtonous cover of the Pelvoux Massif (PM, western Alps, France) was investigated in Priabonian metamarls, through mineral assemblages, simultaneous measurements of illite and chlorite "crystallinity", K-white mica b cell dimension and K-white mica polytypes content. Kübler (KI) and Árkai (ÁI) indexes display values characteristic for uppermost diagenetic to low anchizonal conditions. These results are supported by the incomplete transformation of K-white mica polytypes from 1M d to 2M 1 and are in line with the not annealed status of zircon fission tracks in the southeast zone of the Pelvoux Massif (Seward et al. 1999). Our findings differ from previous results, which suggested epizonal conditions at several places in the northern part of our field area, but are coherent with the temperature estimation suggested by the mineral assemblage described in the literature. These results are further supported by temperature values deduced from fluid inclusion investigations. A small decrease of KI and ÁI values is observed within the basal decollement level of the Priabonian cover, when going from the least deformed zones to the most deformed ones. K-white mica b cell dimensions in micas of the area are in the range 9.000-9.040 Å, which corresponds to an inferred geothermal gradient of 25-35°C/Km, similar to the values found further north in the Dauphinois domain (Ceriani et al. 2003). Based on Ferreiro Mählmann (2001), this can supposed a long stady state heat flow corresponding to a long term metamorphic event like in the eastern Alps.
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Dates et versions

hal-03683486 , version 1 (31-05-2022)

Identifiants

Citer

Sébastien Potel, Ghislain Trullenque. Very low-grade metamorphism in the para-autochtonous sedimentary cover of the Pelvoux massif (Western Alps, France). Swiss Journal of Geosciences, 2012, 105 (2), pp.235-247. ⟨10.1007/s00015-012-0102-8⟩. ⟨hal-03683486⟩
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