日本地球惑星科学連合2014年大会

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セッション記号 S (固体地球科学) » S-IT 地球内部科学・地球惑星テクトニクス

[S-IT02_29PM1] Aqueous fluids and melts in subduction zones: Experiment, modeling, and geophysical observations

2014年4月29日(火) 14:15 〜 15:30 211 (2F)

コンビーナ:*Mysen Bjorn(Geophysical Laboratory, Carnegie Inst. Washington)、Junichi Nakajima(Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan)、Eiji OHTANI(Graduate School of Science Tohoku University 6-3 Aoba, Aramaki, Aoba-ku Sendai 980-8578)、座長:大谷 栄治(東北大学大学院理学研究科地学専攻)、中島 淳一(東北大学大学院理学研究科附属地震・噴火予知研究観測センター)

15:00 〜 15:15

[SIT02-04] 西南日本における高温スラブ沈み込みによる様々なマグマの生成:フォワードモデルによる検討

*木村 純一1ギル ジェームズ2 (1.海洋研究開発機構、2.カリフォルニア大学サンタクルツ校)

キーワード:西南日本, 火山岩, 地球化学, フォワードモデル

In response to the subduction of the young Shikoku Basin of the Philippine Sea Plate, arc magmas erupted in SW Japan throughout the late Cenozoic. Many magma types are present including ocean island basalt (OIB), shoshonite (SHO), arc-type alkali basalt (AB), typical sub-alkalic arc basalt (SAB), high-Mg andesite (HMA), and adakite (ADK). OIB erupted since the Japan Sea back-arc basin opened, whereas subsequent arc magmas accompanied subduction of the Shikoku Basin. However, there the origin of the magmas in relation to hot subduction is debated. Using new major and trace element and Sr-Nd-Pb-Hf isotope analyses of 324 lava samples from seven Quaternary volcanoes, we investigated the genetic conditions of the magma suites using a geochemical mass balance model, Arc Basalt Simulator version 4 (ABS4), that uses these data to solve for the parameters such as pressure/temperature of slab dehydration/melting and slab flux fraction, pressure, and temperature of mantle melting. The calculations suggest that those magmas originated from slab melts that induced flux-melting of mantle peridotite. The suites differ mostly in the mass fraction of slab melt flux, increasing from SHO through AB, SAB, HMA, to ADK. The pressure and temperature of mantle melting decreases in the same order. The suites differ secondarily in the ratio of altered oceanic crust to sediment in the source of the slab melt. The atypical suites associated with hot subduction result from unusually large mass fractions of slab melt and unusually cool mantle temperatures.