Rock types and structures of Val du Haut Boréon: a: foliated chilled margin and vesicle-rich layers running parallel to melanocratic appinite dyke walls (coin for scale); b: the 10-metre-thick mafic dyke of Lacs Bessons and its symmetrical structure; c: appinite enclaves mingled in leuco-appinite at core of the main mafic dykes of Lacs Bessons. Appinite and leuco-appinite may be pervasively replaced by granoblastic aggregates of epidote and chlorite, i.e. at the left margin (coin for scale); d: comb layered appinite with phenocrysts of amphibole of centimetre-size. Amphibole phenocrysts are perpendicularly oriented with respect to the dyke walls. The fine-grained matrix is locally replaced by greenish aggregates of epidote and chlorite (coin for scale); e: disrupted fragments of melanocratic spessartite into appinite and leuco-appinite groundmass; leucocratic veins crosscut the edges of the fragments (hammer for scale); f: leucocratic veins within melanocratic spessartite characterised by layers of vesicles; at bottom, the central leucocratic vein is widely replaced by epidote and chlorite (coin for scale); g: mylonitic shear zone of Alpine age crosscutting the dyke of Lacs Bessons. The mafic dyke is affected by a composite foliation where S and C surfaces are mainly supported by biotite and chlorite; S-C structure geometry are consistent with the sense of displacement of the dyke (cf. Fig. 5) (chisel for scale); h: S-C structures suggesting sinistral sense of shear along the wall of a spessartite dyke (pencil for scale).