著者

松沢 勲

出版者

日本アフリカ学会

雑誌

アフリカ研究 (ISSN:00654140)

巻号頁・発行日

vol.1967, no.4, pp.1-24, 1967-04-15 (Released:2010-04-30)

参考文献数

32

被引用文献数

1

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The African rift valley, one of the most outstanding topographic and geologic features of the earth's crust, is also accompanied with many peculiar geophysical phenomena, that is, anomalies of gravity, heat flow, and geomagnetism, which suggest the connection to the earth's interior. Based upon many studies hithertio made, the hypothesis of mantle convection can most adequately elucidate the peculiarities of the rift valley.As it is well known, unit cell of the convective current causes a horizontal tensional stress at the bottom of the crust situated on the lateral flow, and a compressional stress at that on the downward flow. Therefore, if it is permissible to consider that the rift valley has been torn away by the lateral tension attributed to the mantle convection, the genetical relationship to the compressional area should be clarified.Judging from the geohistorical studies, the African rift valley commenced with the gentle up-doming movement in the Mesozoic era. It followed the rifting with volcanic actions at the Tertiary period, which feebly continued up to the recent. Namely, it coincides with the Alpine orogenic cycle in age. The problem is thus focused on the point that although the Alpine orogenic belt, which is undoubted compressional zone at that time, is oriented in E-W direction from the Mediterranean coast to the Himalayan undulation, the tensional zone of the African rift valley has N-S trend on the whole.Judged by the geotectonic studies, the crustal framework of the Africa is composed of three continental cores implying the oldest Precambrian rock in the world, such as west Africa, Congo, anb Kalahari cratons, which are joined with the latest Precambrian—earliest Palaeozoic Mozambique belt. All of them consist of metamorphic rocks, however, the rocks of continental cores may be harder and stiffer than those of the Mozambique belt. Furthermore, the extention of the belt is trending nearly N-S direction in East Africa, and the interior structure of the belt also takes the same direction in general.It is of the present writer's opinion that these factors, tectonic elongation, interior structure, and less hardness of rocks of the Mozambique belt controlled the disharmonic trend and location of the African rift valley against the Alpine orogenic belt.