美濃・丹波帯緑色岩の岩石学的研究 : 特に超苦鉄質火山岩について

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The ultramafic volcanic rocks (meimechite and ferropicrite) and the related rocks in the Jurassic Mino-Tamba accretionary complex were geologically and petrologically studied to reveal the ancient igneous activities in the Permian ocean. The ultramafic volcanic rocks intruded into the Middle Permian chert and the Early Permian nappe-basal basalt (greenstone), and their fractionation product (basalt) erupted on the Middle Permian chert. Chemistry of the ultramafic volcanic rocks suggests that they were generated by the low-degree partial melting of peridotitic mantle with subducted oceanic crust component at high pressures (up to 5 GPa). The komatiitic basalt associated with the ferropicrite shows conspicuous olivine spinifex texture, which is the evidence for the high temperature, ultramafic parental magma. Ultramafic volcanic rocks such as meimechite and ferropicrite are rare on the Earth, but characteristically occur in LIPs (Large Igneous Provinces) such as Siberia and Ontong Java. The presence of the ultramafic volcanic rocks in the Mino-Tamba belt suggests that the greenstone in the Mino-Tamba belt is the fragments of the oceanic plateau formed in the Permian paleo-Pacific ocean, which was derived from large scale mantle plume (superplume).
2009-01-30