CONTINENTAL THOLEIITIC MAGMATISM ASSOCIAT ED WITH THE HERCYNIAN OROGENY - THE KERROCH-VISEAN VOLCANISM, ARMORICAN MASSIF (FRANCE)

The Visean volcanism of the Kerroc'h formation, located near the north ern edge of the Chateaulin Basin (Armorican Massif) is typically bimod al: continental tholeiitic basalts, whose composition is close to thos e of oceanic island tholeiites (OIT), alternate with andesitic breccia s and metarhyolites. These lavas were emplaced within a pull-apart bas in controlled by dextral strike-slip faults. The Kerroc'h basalts are likely derived from an enriched mantle source and the associated acid rocks might represent melting products from the continental crust of t he Armorican Massif. We relate anorogenic volcanism to a crustal fract uration event contemporaneous with a major phase of Hercynian intra-co ntinental convergence.