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タイトル: パンアフリカン造山帯の構造と衝突テクトニクス : ゴンドワナ超大陸トランセクトの意義
その他のタイトル: Structure and collision tectonics of Pan-African orogenic belt : Scientific significance of the geotransect for a supercontinent : Gondwanaland
著者: 石川, 正弘
金尾, 政紀
著者(別言語): Ishikawa, Masahiro
Kanao, Masaki
キーワード: lithospheric structure
laboratory rock velocities
Lutzow-Holm Complex
Pan-African orogeny
collision tectonics of Gondwanaland
発行日: 2003年1月31日
出版者: 東京大学地震研究所
掲載誌情報: 東京大学地震研究所彙報. 第77冊第3号, 2003.1.31, pp. 287-302
抄録: A combination of rock velocities with seismic structures have presented clues to understanding the structure and the evolution of the continental crust. However, most works addressed continental crusts of the northern hemisphere such as North America and Europe. Only a few studies focused on Gondwanaland. Here, we present a tectonic model of the Pan-African orogeny by comparing the laboratory velocities of granulite/gneiss with geophysical data of the Lutzow-Holm region, East Antarctica. The "Structure and Evolution of the East Antarctic Lithosphere (SEAL)" project has been carried out under the framework of the Japanese Antarctic Research Expedition in recent years. Several geophysical studies including deep seismic refraction/wide angle reflection surveys have been conducted at the Lutzow-Holm region. Velocity models and reflection sections of the crust are given by both active source seismic surveys and passive analyses for teleseismic receiver functions. From laboratory measurements, rock velocities revealed that the lower crust (6.9 km/s) consists of pyroxene granulite. Moreover, middle crustal velocity is equivalent to the velocity of mixture of pyroxene granulite (20%) and felsic gneiss (80%). The ratio of pyroxene granulite is similar to that geologically observed as meta-mafic sills, which were probably related to mafic magma underplating at Archean. The idea is also supported by model calculations of acoustic impedance, which show middle and lower crustal laminations. This evidence demonstrates that the East Gondwanaland (Napier Complex) lies under the Pan-African orogenic belt (Lutzow-Holm Complex) and was subducted westward. Because it is pointed out that West Gondwanaland descended eastward under the Pan-African belt, the coalescence of both Gondwanalands, i.e. formation process of Gondwana supercontinent is regarded as collision tectonics along with symmetrical subductions where late Proterozoic island arcs and ophiolites were put between East Gondwanaland and West Gondwanaland. The lithospheric structure of the Pan-African belt will be clarified by making deep seismic surveys to cross over the continental segments in the southern hemisphere that once were fragments of Gondwanaland. Deep seismic profiling in the LEGENDS (Lithospheric Evolution of Gondwana East iNterdisciplinary Deep Surveys) project will reveal the architecture and the evolution of the lithosphere of these regions. The "SEAL" transect has also been carried out as the chief contribution to LEGENDS, to delineate a whole crustal section in different geological terrains from Western Enderby Land to Eastern Dronning Maud Land, East Antarctica.
URI: http://hdl.handle.net/2261/13257
ISSN: 00408972


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