Problems Concerning the Explanation for the Variety of Igneous Rocks Dealt with in High School Education

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  • 高校地学で扱われる火成岩とその多様性の説明に関する問題点
  • 教育実践論文 高校地学で扱われる火成岩とその多様性の説明に関する問題点 : 北海道有珠火山を題材とした学習プログラム
  • キョウイク ジッセン ロンブン コウコウ チガク デ アツカワレル カセイガン ト ソノ タヨウセイ ノ セツメイ ニ カンスル モンダイテン : ホッカイドウ ウス カザン オ ダイザイ ト シタ ガクシュウ プログラム
  • ―北海道有珠火山を題材とした学習プログラム―
  • —A Practical Educational Program Using Volcanic Rocks of Usu Volcano, Hokkaido—

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Abstract

<p>High school earth sciences deal with the crystallization differentiation model as the main reason for the variety of igneous rocks. Recent igneous petrology, however, indicates that magma mixing and the partial melting of crust material are more important factors than previously though in producing the island arc igneous rocks. In this paper, we propose a practical educational program for verification of crystallization differentiation and magma-mixing models by using variable igneous rocks of Usu Volcano, Hokkaido. A small amount, less than 20% in weight, of felsic magma is expected from the differentiation model of basaltic primary magma. Mass balance calculations of individual igneous rock from Usu Volcano are conducted using a topographic map and a geologic map. Usu Volcano consists of a large amount of felsic rocks ～65%, which means there is an inconsistency with the simple crystallization differentiation model. An observation program for thin sections of felsic rocks using a polarization-microscope tells us much about the evidence of the magma-mixing model, such as basic inclusions in the felsic rocks, and resorption morphology of plagioclase phenocrysts.</p>

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