Petrological and geochemical characteristics of lithospheric mantle and magmatism related to its evolution at the Southwest Japan arc

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Ultramafic xenoliths from Kurose, Southwest Japan represent fragments of the lithospheric mantle beneath the back-arc of the active Southwest Japan volcano-tectonic arc. We divided the Kurose peridotite xenoliths into three types, on the basis of the Sr-Nd isotopic and trace element compositions of the clinopyroxenes in the 13 ultramafic xenoliths,(1) Japan-Sea basalt type which shows depletion of incompatible elements and similar variation of Sr-Nd isotopic compositions of Japan-Sea basalts,(2) EM I type which has similar Sr-Nd isotopic compositional range of Cenozoic balasts of Kyushu and(3) EM II type with enriched Sr-Nd isotopic composition and incompathible elements. These xenoliths would have experienced the following events ;(1) open-system partial melting of the continental lithosphere with influx of an asthenospheric melt with MORB-like isotopic composition during the back arc basin the Japan Sea opening,(2) metasomatism with the asthenospheric melt related to the Kyushu basalts.