<研究報告>アパタイト中のフッ素と塩素の定量, 東南極ナピア岩体トナー島産の変成超苦鉄質岩中のアパタイトの起源

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The Napier Complex, East Antarctica is one of the oldest Archaean terrane in the world. Tonagh Island is located in the southern end of Amundsen Bay. Mafic gneisses and meta-ultramafic rocks are exposed on Tonagh Island. The meta-ultramafic rock that is located at the northeastern part of the island cuts the layers or foliations of neighboring quartzo-feldspathic gneisses, suggesting that the meta-ultramafic rock was originally intrusive rock. The meta-ultramafic rock consists mainly of olivine, clinopyroxene, orthopyroxene and hornblede. Subhedral apatite is included in olivine. Major and trace element compositions of the meta-ultramafic rock resemble those of komatiitic rocks from the Archaean greenstone belts. Chondrite normalized REE pattern for the meta-ultramafic rock shows enrichment in LREE. Quantitative analyses of F and Cl were done for the apatite in the meta-ultramafic rock. F and Cl contents of the apatite revealed that the apatite was directly crystallized from komatiitic melt. An apatite is regareded as a main container for LREE in the upper mantle. Both LREE-enriched and -depleted types of komatiitic rocks are exposed on the Archaean continents. Therefore, an apatite component may play an important role to understand the petrogenesis of Archaean komatiitic rocks.
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