Kersantites and associated intrusives from the type locality (Kersanton), Variscan Belt of Western Armorica (France)

Kersantite is the international designation for hypabyssal lamprophyres essentially made up of dark micas and plagioclase. Kersantites from type locality (Kersanton hamlet) W-Armorican surrounding area are Serpukhovian/Bashkirian in age. They systematically associated field with microgranodiorites, both types being intruded synchronously as syn-compressional magmatic bodies that postdated pre-tectonic Tournaisian/Visean dolerites. The kersantitic amphibole compositions can be used to constrain crystallization pressures oxygen fugacities (redox conditions much more oxidizing than Ni-NiO buffer). oscillatory zoning observed clinopyroxene phenocysts consistent a magma chamber repeatedly refilled by mafic liquid. melting source kersantites corresponded lithospheric mantle located spinel-garnet transition zone (75–85 km depth), highly metasomatized fluids probably released subducted sediment-bearing slab. Microgranodiorites could result intimate mixing between mantle- crust-derived magmas, cordierite possibly phase. emplacement dolerites anorogenic geochemical signature prior kersantites/microgranodiorites implies upwelling asthenospheric relatively high level, an extension induced either roll back slab or delamination overriding plate. heat input long-lasted asthenosphere rise have favored (1) formation early 347 330 Ma; then, (2) genesis microgranodiorites 310 Ma, once overlying was fluids. This sequence marked beginning Avalonia-Armorica collision, just main Variscan compressional event this at c. 315 Ma.