日本地球惑星科学連合2019年大会

講演情報

[E] ポスター発表

セッション記号 S (固体地球科学) » S-MP 岩石学・鉱物学

[S-MP30] 地殻-マントル・コネクション

2019年5月28日(火) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:田村 芳彦(海洋研究開発機構 海域地震火山部門)、石塚 治(産業技術総合研究所活断層火山研究部門)、Chris Conway(Geological Survey of Japan)

[SMP30-P03] Origin of variable CaO/Al2O3 in olivine-hosted melt inclusions from Kibblewhite Volcano, Kermadec Arc

*平井 康裕1田村 芳彦2Kaj Hoernle3Christian Timm4Folkmar Hauff3Reinhard Werner3羽生 毅2Bogdan Vaglarov2常 青2宮崎 隆2木村 純一2 (1.金沢大学大学院 自然科学研究科、2.海洋研究開発機構、3.ゲオマール海洋研究所、4.GNSサイエンス)

キーワード:Subduction zone、Kermadec Arc、Kibblewhite Volcano、SO-255、Olivine-hosted melt inclusion

During R/V SONNE expedition SO-255 mafic basaltic to magnesian andesitic lavas containing melt inclusion hosting forsteritic olivines (Fo90.3–92.4) were recovered from Kibblewhite Volcano, southern Kermadec Arc. The re-homogenized melt inclusions have compositions similar to primitive basalt (49.6–52.0 wt.% SiO2; 12.7–15.9 wt.% MgO). Their CaO/Al2O3 values, however, range from 0.9 to 1.6, which cannot be explained by melting of lherzolite. Moreover, CaO/Al2O3 values in the melt inclusions correlate negatively with Ni contents of their host olivines suggesting that the high CaO/Al2O3 values result from interaction between mafic melts and subarc lithospheric mantle. Prior to the interaction the mafic magma must have had high Ni contents and low CaO/Al2O3 values, thus they crystallized high Ni olivines trapping low CaO/Al2O3 melt inclusions. During the interaction the olivines crystallized from the mafic magmas and its latent heat assimilated pyroxenes from the surrounding lithospheric mantle. This assimilation of pyroxenes allowed the Ni content of the melt to decrease and CaO/Al2O3 to increase while buffering the the Mg-number of the mafic magmas during the ascent. Thus, magmas during and after the interaction could crystallize low Ni olivines bearing high CaO/Al2O3 melt inclusions.