Temporal variation in primary magma compositions in the northeast Japan Arc |
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| Authors: | Shigeru Yamashita Yoshiyljki Tatsump Susumu Nohda |
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| Institution: | Institute for Study of the Earth's Interior, Okayama University, Misasa, Tottori 682-01, Japan;School of Earth Sciences, IHS, Kyoto University, Kyoto 606-01, Japan;Kyoto Sangyo lJnicersity, Kyoto 603, Japan |
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| Abstract: | Abstract A remarkable temporal variation in primary magma compositions has been found in the Northeast Japan arc. The trench-side magmas have become more enriched in FeO* and the backarc-side magmas have become more depleted in FeO* while retaining almost constant SiO, levels for the last ～20 million years. In order to understand the origin of the temporal variation, FeO* and SiO, contents in partial melts are modeled for an adiabatically-rising mantle as a function of potential temperature and original composition of the mantle material. The result demonstrates that the primary magmas that are more depleted in FeO* were derived from the mantle materials either at lower potential temperatures or with compositions more depleted in basaltic components. A possible mechanism for the inferred primary magma variability is the change in depth intervals with time of magma production in a compositionally-layered mantle wedge; greater degrees of depletion at a greater depth is reconciled with a probable thermal regime in the mantle wedge. |
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| Keywords: | Northeast Japan arc primary magma temporal variation |
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