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Genesis of Quaternary volcanism of high-Mg andesitic rocks in the northeast Kamchatka Peninsula

Nishizawa Tatsuji, Nakamura Hitomi, Churikova T., Gordeychik B., Ishizuka Osamu, Iwamori Hikaru (2016) Genesis of Quaternary volcanism of high-Mg andesitic rocks in the northeast Kamchatka Peninsula // Japan Geoscience Union Meeting, 22-26 May 2016, Makuhari, Messe. pp. SVC48-02.

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Arc magmatism is a product of subduction factory, involving thermal and chemical interactions between a subducted slab as a material input and mantle wedge as a processing factory. In turn, the compositions of arc magma provide invaluable information concerning the material input and the interactions. The northeast Kamchatka Peninsula is an ideal field to examine such interactions and relationships, being characterized by (1) subduction of the Emperor Seamount Chain (Davaille and Lees, 2004), and (2) possible material and thermal interaction among the subducted slab, the overlying mantle wedge and the sub-slab mantle via the edge of subducted Pacific slab (Portnyagin and Manea, 2008). Within this area, a monogenetic volcanic group occurs along the east coast, including high-Mg andesitic rocks and relatively primitive basalts (East Cones, EC (Fedorenko, 1969)). We have conducted geochemical studies of the EC lavas, with bulk rock major and trace elements, and K-Ar and Ar-Ar ages, based on which a possible contribution of subducted seamounts and its relation to the tectonic setting are discussed. The elemental compositions indicate that the lavas from individual cones have distinct mantle sources with different amounts and/or compositions of slab-derived fluids. Based on mass balance, water content and melting phase relations, we estimate the melting P-T conditions to bet ~1200 ℃ at 1.5 GPa, while the slab surface temperature is 620 –730 ℃ (at 50-80 km depth). Compared with the southern part of Kamchatka, the slab surface temperature beneath EC seems to be high due to the thinner Pacific slab associated with the seamount chain and/or the plate rejuvenation from a mantle plume impact (Davaille and Lees, 2004; Manea and Manea, 2007). The K-Ar and Ar-Ar ages of the Middle Pleistocene are consistent with the tephrochronological study (Uspensky and Shapiro, 1984) and the present tectonic setting after 2 Ma (Lander and Shapiro, 2007). The high-Mg andesite with the highest SiO2 content in the EC lavas shows the oldest age (0.73 ±0.06 Ma) within not only EC but also the northeast part of Kamchatka (e.g., Churikova et al., 2015, IAVCEI). On the other hand, the rest of EC lava samples show relatively younger ages to 0.18 ±0.07 Ma. These results suggest that the EC lavas including high-Mg andesite and basalt were generated by mantle flux-melting induced by dehydration of a subducted seamount inheriting a local thermal anomaly (Nishizawa et al., 2014, JpGU; 2015, JpGU).

Abstract (translation)

島弧火成活動はサブダクションファクトリーの産物で, それは沈み込んだスラブ(物質のインプット)-マン トルウェッジ(加工工場)間の熱的・物質的相互作用を含む. 島弧マグマの組成は, その物質インプットと相 互作用について非常に貴重な情報をもたらす. カムチャツカ半島北東部はそのような相互作用と関係性を調べ るうえで理想的な場所である, それは次のような特徴を有する為だ(1)天皇海山列の沈み込み(Davaille and Lees, 2004)(2)沈み込んだスラブ, マントルウェッジと太平洋スラブエッジにかけてのサブスラブマントル との物質的・熱的相互作用の可能性(Portnyagin and Manea, 2008). この地域の東海岸沿いに, 高-Mg安山岩 と比較的初生的な玄武岩を産出する単成火山群が確認されている(East Cones, EC(Fedorenko, 1969)). 我々はこのEC溶岩について全岩主要-微量元素組成分析とK-Ar, Ar-Ar年代測定を含む地球化学的研究を行い, 沈み込んだ海山からの寄与の可能性とテクトニックセッティングとの関係について議論する. EC溶岩の組成は, 火山ごとに独立したソースに由来しており, そのソースの違いはスラブ起源流体の量および またはその組成の違いによることを示す. マスバランス, 含水量, 相関係に基づき, 我々は溶融温度-圧力条 件を推定した, 溶融温度・圧力~1200℃, 1.5 GPa, スラブ表面温度 620-730℃(深度50-80 km). カム チャツカ南部に沈み込むスラブ表面温度と比較すると, EC直下のスラブ表面温度は高く, これは天皇海山列に 沿ったプレートの薄化およびまたは沈み込む直前のプルームからの熱的効果による若返り効果によるものと考 えられる(Davaille and Lees, 2004; Manea and Manea, 2007). K-Ar, Ar-Ar年代測定値は中期更新世で, これはテフラ層序学からの推定年代と一致し(Uspensky and Shapiro, 1984), 2Ma以降現在のテクトニックセッティングに変化したこととも矛盾しない(Lander and Shapiro, 2007). 最もSiO2含有量が高い高Mg安山岩は最古の年代を示し(0.73 ±0.06 Ma), これはECのみな らずカムチャツカ北東部においても最も古いとみられる(e.g., Churikova et al., 2015, IAVCEI). 一方他 のECはより若い年代を示す(~0.18 ±0.07 Ma). これらの結果は以下のことを示す: 高Mg安山岩, 玄武岩を 含むEC溶岩は沈み込んだ海山による局所的な温度異常がスラブ起源流体の脱水を強めそれによって生じたフ ラックス溶融によりもたらされた(西澤他, 2014, JpGU; 2015, JpGU).
Item Type: Conference Item (Thesis) conference proceedings
Title: Genesis of Quaternary volcanism of high-Mg andesitic rocks in the northeast Kamchatka Peninsula
Title (translation): カムチャツカ半島北東部における高Mg安山岩を産出した第四紀火山の起源
Language: English
Subjects: 3 State scientific and technical information rubricator (ГРНТИ) > 38 ГЕОЛОГИЯ > 38.37 Петрография > 38.37.25 Вулканология
Depositing User: Надежда Егорова
Date Deposited: 29 Mar 2017 05:49
Last Modified: 29 Mar 2017 05:49

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