日本地球惑星科学連合2015年大会

講演情報

口頭発表

セッション記号 S (固体地球科学) » S-MP 岩石学・鉱物学

[S-MP43] 変形岩・変成岩とテクトニクス

2015年5月24日(日) 16:15 〜 18:00 A03 (アパホテル&リゾート 東京ベイ幕張)

コンビーナ:*石井 和彦(大阪府立大学大学院理学系研究科物理科学専攻)、河上 哲生(京都大学大学院理学研究科)、座長:宮崎 一博(産業技術総合研究所 地質情報研究部門 地殻岩石研究グループ)、遠藤 俊祐(産業技術総合研究所地質情報研究部門)

17:27 〜 17:30

[SMP43-P05] スリランカのarrestedチャーノッカイトの形成:全岩化学組成と物質移動

ポスター講演3分口頭発表枠

*山崎 由貴子1池田 剛1本吉 洋一2廣井 美邦3プレーム バーナード4角替 敏昭5 (1.九州大・院・理、2.国立極地研究所、3.千葉大・院・理、4.スリランカ地質調査所、5.筑波大・生命環境)

キーワード:スリランカ, アレステッドチャーノッカイト, 普通角閃石-黒雲母片麻岩, 物質移動, シュードセクション

Arrested charnockite, that represents granulite facies mineral assemblage, occurs in several decimeters scale within amphibolite facies gneisses. The gneissosity in the gneiss becomes, in general, obscure toward center of charnockite. This suggests that the gneiss was metamorphosed into charnockite in local scale. The local charnockitization may be caused by fluid influx and/or partial melting or difference of local bulk composition (e.g. Newton et al., 1980; Hiroi et al., 1990; Burton and O'Nions, 1990; Ravindra Kumar, 2004; Endo et al., 2012, 2013). This study described mode of occurrence of arrested charnockite in Sri Lanka, and reveals cause of metamorphic formation of arrested charnockite. Mass transformation during charnockitization was also discussed.
Arrested charnockite in Sri Lanka occurs as a number of patches in Hbl-Bt gneiss. The modal abundance of minerals in both rocks indicates that the elements transformed between melanocratic and leucocratic parts. The elements constituent of Bt in leucocratic part moves to melanocratic part, and those of Pl, Ksp and Qtz of melanocratic part, instead, move to leucocratic part. The modal abundance of Bt of leucocratic part in Hbl-Bt gneiss decreases into the charnockite near the boundary. This suggests that mass transformation also be caused across the boundary.
The formation of Opx can be described by the following two reactions,
Ti-rich Bt + Qtz = Ti-poor Bt + opx + Ilm + Ksp + H2O and
Ti-rich Hbl + Qtzz = Ti-poor Hbl + Opx + Ilm + An + Ab + Ksp + H2O.
These reactions suggest the possibility that the fluid influx and/or the partial melting produced arrested charnockite. However, similar chemical composition of apatite in both rocks implies that there is no positive evidence to support the above possibility. The pseudosection modeling of mineral assemblage in NCKFMASHTO system shows that the local difference of bulk composition is responsible for the local charnockitization.