ABSTRACT

The Kinan Seamount Chain lies close to the extinct spreading center of the Shikoku Basin, one of the largest marginal basins in the western Pacific region. Geochemical and isotopic analyses reveal that basalts from the Kinan Seamount Chain have the following characteristics that differ from the Shikoku Basin tholeiite: 1) more incompatible emelent enriched compositions, 2) lower abundance of the heavy rare earth elements (HREE), and 3) higher ⁸⁷Sr/⁸⁶Sr and lower ¹⁴³Nd/¹⁴⁴Nd ratios. These results indicate: 1) a more enriched mantle source for basalts from the Kinan Seamount Chain, 2) existence of clinopyroxene and/or amphibole in their residual mantle, and 3) mixing of magmas from a normal MORB source with the EMI signature and an ocean-island basalt (OIB) source with the EMII signature; and 4) the latter has a more significant contribution to the Kinan Seamount Chain basalts than the Shikoku Basin tholeiite.