東北日本弧, 二ノ目潟かんらん岩捕獲岩および本質噴出物について [in Japanese] Peridotite xenoliths and essential ejecta from the Ninomegata crater, the Northeastern Japan arc [in Japanese]
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Peridotite xenoliths and essential ejecta from the Ninomegata crater of the Megata volcano, Northeast Japan arc, were described in detail. The peridotites have a wide spread of Cr # (=Cr/(Cr+Al) atomic ratio) of chromian spinel, from 0.10 to 0.45, almost comparable with but slightly lower than that of the Ichinomegata peridotites. They often have a secondary hydrous mineral, pargasite, replacing primary minerals. One of lherzolites has several small veinlets of hornblendite. The amount of pargasite is far smaller than that from the Ichinomegata peridotites. The Ninomegata peridotite xenoliths, therefore, preserve characteristics of primary mantle restite; they are in the olivine-spinel mantle array and the Fe<sup>3+</sup>/(Cr+Al+Fe<sup>3+</sup>) atomic ratio of chromian spinel is not high (<0.05).<br> Petrographical and/or chemical variety of peridotite xenoliths decreases from Ichinomegata to Sannomegata through Ninomegata within the Megata volcano.<br> The essential ejecta from the Ninomegata crater has almost the same characteristics as those from Ichinomegata in terms of petrography and bulk chemistry.
- Journal of Mineralogical and Petrological Sciences
Journal of Mineralogical and Petrological Sciences 90(2), 41-49, 1995-02-05
Japan Association of Mineralogical Sciences