Abstract
The Afar depression (Ethiopia and Gibuti area) is the site of the junction of three major rift zones: two oceanic (Red Sea and Gulf of Aden) and a continental one (East African rift). Approaching Afar some modifications are observed in the structure as well as in the petrology of each rift branch. Gulf of Aden is characterized by WNW spreading segments offset by ENE transform faults; approaching Afar the ridge-transform system leaves the place to “en echelon” disposed narrow rift valleys. The central trough of the Red Sea progressively looses its morphological expression between Jebel at Tair and Hanish islands, the latter being formed by eruptions through fissures transverse to the Red Sea axis. These two spreading rifts are characterized by typically oceanic basalts (light REE depleted, low-K tholeiites). An increase of the alkalinity of basalts is observed in the southernmost part of the Red Sea. The East African rift is the site of continental lithosphere attenuation marked by normal faulting, open fissures and associated volcanism. Volcanologically the main difference with respect to the oceanic rifts is the frequent development of huge central volcanoes and the abundance of salic alkaline and peralkaline products, which occur also in fissural eruptions.
Approaching Afar the most recent activity tends to concentrate along en echelon disposed sets of faults, where basalts become more abundant and show a progressively less alkalic affinity.
Similar contrasting structural and magmatic situations occur within Afar evolving both in time and space. Short oceanic spreading segments (“axial ranges”), surface expressions of transform faults and fracture zones are recognized and allow the reconstruction of a complex plate geometry within Afar and its evolution with time. Structural as well as petrological and geochemical data are used for a discussion of the plate tectonics and mantle plume models.
This work has been supported by CNR (Contract n. 76.00148.05) and CNRS (RCP 341)
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© 1978 D. Reidel Publishing Company, Dordrecht, Holland
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Barberi, F., Varet, J. (1978). The Afar Rift Junction. In: Neumann, ER., Ramberg, I.B. (eds) Petrology and Geochemistry of Continental Rifts. NATO Advanced Study Institutes Series, vol 36. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-9803-2_6
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DOI: https://doi.org/10.1007/978-94-009-9803-2_6
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