Late pervasive crustal-scale extension in the south Armorican Hercynian belt (Vendée, France)

The coast of Vendée, in the southern Hercynian Armorican Massif, shows a complete Barrovian metamorphic section, from upper-crustal low-grade metasediments, down to high-grade partially molten rocks. The bottom of the pile is intruded by numerous synkinematic granitic dykes. The pattern of the dyke array shows that syn-emplacement deformation combined coaxial sub-vertical shortening and sub-horizontal shearing. Strain estimates using dykes and deformed metamorphic isogrades suggest a maximum amount of bulk shortening in the range of 80%. Results are consistent with extensional tectonics mainly accommodated by large pervasive thinning, rather than by strain localisation along a detachment zone.