LREE-enriched mafic gneiss and meta-ultramafic rock from Tonagh Island in the Napier Complex, East Antarctica

• Main Authors: Owada,Masaaki, Osanai,Yasuhito, Tsunogae,Toshiaki, Toyoshima,Tsuyoshi, Hokada, Tomokazu, Crowe,Warwick A.
• Format: Report
• Language: English
• Published: Department of Earth Sciences, Yamaguchi University/Department of Earth Sciences, Okayama University/Department of Earth Sciences, Shimane University/Graduate School of Science and Technology, Niigata University/National Institute of Polar Research/Department of Geology and Geophysics, University of Western Australia 2000
• Subjects: Archaean; Napier Complex; mafic gneiss and meta-ultramafic rock; REE geochemistry; source mantle; East Antarctica; Riiser-Larsen; Napier; Tonagh Island; Antarc*; Antarctica; Polar geoscience
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=3067; http://id.nii.ac.jp/1291/00003067/; https://nipr.repo.nii.ac.jp/?action=repository_action_common_download&item_id=3067&item_no=1&attribute_id=18&file_no=1

Mafic gneisses and meta-ultramafic rocks are exposed on Tonagh Island These rocks are high-Mg composition and have undergone ultrahigh-temperature metamorphism Most of the mafic gneisses and the meta-ultramafic rocks occur as intercalated layers or lenses within the quartzo-feldspathic gneisses Some of the mafic gneisses and the meta-ultramafic rocks locally cut the layers or foliations of neighboring quartzo-feldspathic gneisses, suggesting that these mafic gneisses and meta-ultramafic rocks were originally intrusive rocks Major and trace element compositions of the mafic gneisses and the meta-ultramafic rocks resemble those of komatiitic basalt to komatiite from the Archaean greenstone belt Light REE-enriched and flat patterns are recognized in the mafic gneisses and meta-ultramafic rocks although the REE pattern of the deformed sample is convex upward In the Mt Riiser-Larsen region situated 40 km northeast from Tonagh Island, it has been found in a previous study that the LREE-enriched mafic gneisses and meta-ultramafic rocks have been derived from komatiitic rocks whose chemical trends show magmatic variations Therefore, the LREE-enriched patterns of mafic gneisses and ultramafic rocks on Tonagh Island and in the Mt Riiser-Larsen region could be inherited from the chemical nature of original rocks prior to undergoing ultrahigh-temperature metamorphism The LREE-enriched pattern cannot be explained by interaction between an LREE-flat parental magma and an LREE-enriched crustal material m terms of geochemical constraints Hence, the LREE-enriched and flat types of the mafic gneisses and the meta-ultramafic rocks on Tonagh Island would have been derived from different source mantles with respect to LREE signatures