Magmatisme alcalin «intra-plaque» en contexte d'arc insulaire : le massif plutonique d'Ashizuri (Japon SO)

During the Middle Miocene, the geology for the Shimanto belt in the outer zone of southwestern Japan is marked by a diversified magmatic episode. The latter consists of plutono-volcanic complexes, generally reported to I- or S-type granite, E-MORB basalts, arc tholeiites, and finally a within-plate alkaline plutonic complex, exposed at Ashizuri. Our petrological and geochemical data show that the Ashizuri complex genesis involves the contribution of an OIB type mantle source. Occurrence of such a source is unusual in an island-arc environment and its related accretionary prism. Possible geodynamic models include a slab window in the subducted plate, or the ascent and partial melting of the asthenospheric mantle during a collisional tectonic event