Role and chemical characteristics of magmatic fluid on material recycling process between earth's crust and upper mantle at subduction zone.

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Representative low-alkali tholeiitic rock samples are collected from Iwate, Minami-Zao and Adatara volcanoes at volcanic front and also from Akita-Komagatake at inner side from the volcanic front in northeastern Japan arc. Basic concept of this research is that the characteristics of slab-derived fluid must be inferred from the heterogeneity postulated in magma source mantle beneath a single volcano. Such mantle heterogeneity should be revealed through petrochemical investigations trying to make clear the diversity of parental magmas and evorutionary processes for the tholeiitic magma batch systems that is believed to originate in mantle.Five tholeiitic magma batch systems are recognized at Iwate volcano, and each batch has distind parental magma and evolutionary process. Similarly, 3 co-genetic magma suites are distinguished among the tholeiitic series at Minami-Zao volcano. As for the Akita-Komagatake volcano, at least 4 suites of tholeiitic magmas exist in its post-caldera stage.Based on distinctive chemical characteristics among the tholeiitic parental magmas within a single volcano, the magma source region beneath the volcanic front may be enriched in Rb and K but not Ba through matasomatism by slab-derived fluid. Further, difference in LIL/HFS between tholeiitic and calc-alkaline magma suites coexisting at the volcanic front may reflect such heterogeneity in magma source region. In addition, it is revealed that the fractional crystallization is not always the main evorutionary process in the tholeiitic series ; magmatic mixing or assimialation may be the main