Structure and collision tectonics of Pan-African orogenic belt : Scientific significance of the geotransect for a supercontinent : Gondwanaland

• Main Authors: 石川, 正弘, 125958, 金尾, 政紀, 125959
• Language: Japanese
• Published: 東京大学地震研究所 2003
• Subjects: 453; lithospheric structure; laboratory rock velocities; Lutzow-Holm Complex; Pan-African orogeny; collision tectonics of Gondwanaland; Antarctic; East Antarctica; Napier; Antarc*; Antarctica
• Online Access: https://repository.dl.itc.u-tokyo.ac.jp/record/32584/files/ji0773007.pdf

application/pdf 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. ...