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Fig. 11 | Swiss Journal of Geosciences

Fig. 11

From: A step towards unraveling the paleogeographic attribution of pre-Mesozoic basement complexes in the Western Alps based on U–Pb geochronology of Permian magmatism

Fig. 11

Simplified metamorphic map of the SW Alps. Colours refer to both metamorphic grade (in terms of metamorphic facies), and ages. This map is based on Bearth (1962), Bocquet (1971), Bousquet et al. (2004), Michard et al. (2004), Bousquet et al. (2008), Beltrando et al. (2010), Groppo et al. (2019), and our own observations. The distribution of lawsonite (red lozenges) is only shown in the External Briançonnais. Further east, lawsonite becomes widespread in the meta-ophiolites and meta-sediments of the Piemonte-Liguria Ocean (e.g. Caron 1974; Lefeuvre et al. 2020; Vitale Brovarone et al. 2020). Key references for the age of the peak-pressure metamorphism are found in Manzotti et al. (2014) and refs therein for the Sesia-Zone; Rubatto et al. (2008) for the Lanzo peridotites; Monié and Phillipot (1989), Rubatto and Hermann (2003), Rubatto and Angiboust (2015) and Garber et al. (2020) for the Viso; Agard et al. (2002) for the Queyras; and Rubatto and Hermann (2001), Gauthiez-Putallaz et al. (2016) and Chen et al. (2017) for the Brossasco-Isasca Unit. The two studied samples from the Zone Houillère (Guillestre and Briançon) belong to units displaying low-grade parageneses (lawsonite-albite), while their equivalents in the Pinerolo Unit are characterised by garnet-blueschist facies assemblages. Despite identity of the pre-Alpine history i.e. Carboniferous sedimentation (Manzotti et al. 2016) and early Permian magmatism (this study), their fate during the Alpine orogeny is very different

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