造山帯中の緑色岩からみた海洋地域の火成活動 : みかぶ帯の火成岩の岩石学的特徴と火成年代

概要

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Accreted greenstones in orogenic belts were originally formed by ancient igneous activities in oceanic area. Petrological and geochlonogical studies on those greenstones should provide constraints for reconstructing oceanic volcanism through earth history. The Mikabu belt, in the outer belt of southwest Japan, is mainly composed of basic volcanics and related mafic-ultramafic cumulates and its lateral length is comparable to occanic plateau or seamount chain. Trace elements and isotope compositions of the igneous rocks from the Mikabu belt are similar to those of MORB. However, major element compositions and order of crystallization indicate their different petrogenesis from MORB. K-Ar dating of igneous origin amphibole indicates the volcanism of the Mikabu belt occurred at 200 Ma and 150 Ma. This variation of age suggests that the origin of the Mikabu belt may not be an oceanic plateau but a seamount chain.
特定非営利活動法人日本火山学会の論文
1997-04-25