A Paleozoic history of Armorica recounted through anorogenic to vaugneritic magmatism

The Plouaret-Commana-Huelgoat (PCH) vaugnerite-granite complex, emplaced at around 315 Ma on both sides of the North Armorican Shear Zone (NASZ) in the Armorican Massif (France), can be regarded as the “axial pivot” around which a large part of the history of the Armorican magmatism was revolving. Indeed, four main magmatic cycles can be distinguished in the Ordovician/Early Permian time-span over much of the considered areas, i.e. North and Central Armorican Domains (N/CAD): (1) several anorogenic mafic complexes (plutons, dykes and/or lavas) were successively emplaced from the Ordovician to Early Carboniferous; (2) near the Bashkirian/Moscovian time-boundary, when the N/CAD started to record the effects of the Variscan collision, magmatism became predominantly lamprophyric/vaugneritic (K-rich West-Armorican kersantites and PCH vaugnerites), prior to (3) the generalized granitic peak during the Moscovian-Kasimovian ages, in turn followed by (4) a K-rich intermediate magmatic activity, including again vaugnerites and the last granitic intrusions, during the late-/post-collision stages in the upper Pennsylvanian-Early Permian time-period. The sharp geochemical break evidenced in the present work between an early anorogenic magmatic group and a syn- to post-collisional system in the N/CAD emphasizes the original magmatic history recorded by part of Armorica, including probably the Central Iberian Zone (CIZ), during the nearly entire Paleozoic era compared to those commonly applied to the rest of the European Variscan orogen. This evolution is assumed to result from: (1) large-scale asthenospheric upheavals due to the downward straightening and retreat of variously plunging slabs during the Paleozoic times, (2) partial melting of metasomatized lithospheric/asthenospheric mantle due to fluid release from fragments of buried continental crust, and (3) crustal anatexis.