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Fig. 2 | Swiss Journal of Geosciences

Fig. 2

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. 2

Simplified cross-section of the Briançonnais Domain along the Guil valley. The colour code is the same as in Fig. 1. The upper part (i.e. above sea-level) of the section closely follows Debelmas et al. (1966) and Kerckhove et al. (2005). The lower part (i.e. below sea-level) is intended to display a potential geometry of the nappe stack at depth. The normal fault displacement along the Durance Fault, which offsets the basal Briançonnais Thrust, is drawn according to Debelmas (1955) and Tricart et al. (1996), and may have been accompanied by a strike-slip displacement. The pre-Triassic basement, made of Carboniferous sediments and Permian volcanics, is only poorly exposed west of the Durance Fault, but preserved north of the section considered here. Permian sediments, formerly considered as a granite (Kerckhove and Piboule 1999; Kerckhove et al. 2005), occur in a narrow fault-bounded slice along the Durance Fault (Plan-de-Phazy). The largest outcrop of Permian andesites studied here is located in the Lower Unit of the External Briançonnais (Fig. 3). Note that backfolding and backthrusting inverted the original nappe stack, bringing the units of the Internal Briançonnais over calcschists and minor ophiolites derived from the Piemonte-Liguria Ocean

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