著者

平賀 岳彦

出版者

Tokyo Geographical Society

雑誌

地学雑誌 (ISSN:0022135X)

巻号頁・発行日

vol.108, no.2, pp.110-121, 1999-04-25 (Released:2009-11-12)

参考文献数

27

被引用文献数

3 3

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Grain boundaries in metamorphic rocks were obsereved by high-resolution transmission electron microscopy. Most of the boundaries have no distinct secondary phases at a nanometer scale. Not only between the same kind of minerals but also between different minerals, mineral grains are directly connected at their boundaries, showing that the structual width of the grain boundaries is less than 0.5nm. Grain boundaries with spheroidal voids are observed in the boundaries. It can be concluded that this type of grain boundary is formed by the healing of microcracks. Low-index plane boundaries are well-developed, showing that this type of boundary has low grain boundary energy. Local structural modification, indicating the segregation of impurities, in grain boundaries is observed. The present results show that the actual width of the grain boundary in rocks is too small for the grain boundary diffusion to be as the dominant transport mechanism.

著者

平賀 岳彦

出版者

一般社団法人 日本地質学会

雑誌

地質学雑誌 (ISSN:00167630)

巻号頁・発行日

vol.123, no.6, pp.379-390, 2017-06-15 (Released:2017-07-25)

参考文献数

37

被引用文献数

2

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ファインセラミックス合成とその物性を参考にした,岩石を模擬した人工ファイン岩石を用いた研究を総括する.まず,天然の岩石とファインセラミックスの粒界において,共通な構造と偏析が存在していることが示される.また,その粒界の移動した結果(粒成長)生じる,相(鉱物)間の粒径の関係,ゼナー則が成り立っていることが分かった.初期条件(化学組成等)や形成条件(時間,圧力等)が極めて異なる両者において,その微細構造は相似の関係が成り立っている.人工ファイン岩石の超塑性の発現とその変形微細構造が,マイロナイトやマントル岩を含む変成岩の構造と比較され,粒界すべりに伴う,同相粒子集合化構造,変形誘起粒成長および結晶軸選択配向が議論される.ファインセラミックスと岩石のアナロジーの本質は,「共通な」粒界による「共通な」粒界現象にある.決定的に知るのが困難な岩石形成プロセスの理解において,今後も人工ファイン岩石を用いた実験的研究の重要性は増すだろう.

著者

平賀 岳彦 渡部 泰史 宮崎 智詞

出版者

一般社団法人日本地球化学会

雑誌

地球化学 (ISSN:03864073)

巻号頁・発行日

vol.46, no.4, pp.231-242, 2012-12-31 (Released:2017-02-20)

参考文献数

39

被引用文献数

1

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Investigation of intergranular regions of fine-grained metamorphic rocks using various electron microscopy reveals the presence of intergranular pores previously filled with an aqueous fluid. Such intergranular fluid inclusions exhibit a characteristic shape which minimizes interfacial energy at intergranular regions. The distribution of the inclusions indicates that they were formed from fluid filled intergranular microcracks that ovulated into inclusions due to the initially unstable form of a fluid film at grain boundaries. A simple calculation of interfacial stresses produced by anisotropic thermal contraction of quartz grains during cooling of the quartz aggregate demonstrates that most grain boundaries in crustal rocks experience intense intergranular cracking accompanied by infiltration of fluids. Presence of the fluid filled cracks might explain the observations of low electrical resistivity and seismic wave speeds at middle to shallow crustal depths. The inhibition of the crack formation due to the interfacial stress relaxation in ductile crustal regions results in higher electrical resistivity and seismic wave speeds at greater deep. Intergranular chemical components in mantle rocks are ubiquitously found in mantle xenoliths. We can attribute these components to intergranular melts which were present in the mantle.