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Geology of the Comores Archipelago, Western Indian Ocean

  • J. Esson (a1), M. F. J. Flower (a2), D. F. Strong (a3), B. G. J. Upton (a4) and W. J. Wadsworth (a1)...

Summary

The Comores Archipelago comprises four principal islands, lying in a WNW–ESE line at the northern end of the Mozambique Channel. The Islands are almost entirely volcanic and show a simple age progression from Grande Comore, with its active shield volcano Kharthala (2650m), east-south-eastwards through Mohéli and Anjouan, which are quite deeply dissected, to Mayotte, which is in an advanced stage of erosion and subsidence, and is encircled by a barrier reef. There is also evidence of minor volcanic rejuvenation in relatively recent times in Mayotte, and perhaps Anjouan and Mohéli. The lavas of Kharthala, and the neighbouring extinct shield volcano (Massif de la Grille) on Grande Comore are all basaltic, ranging from oceanitic and ankaramitic to aphyric types. Numerous tuff cones occur, especially on the flanks of Massif de la Grille. Basaltic lavas, similar to those of Grande Comore, form the bulk of the dissected volcanic shields of Mohéli and Anjouan, but there is also evidence of differentiation towards alkalic under-saturated end products, both as lavas and as intrusive bodies. Lherzolitic and gabbroic nodules are locally abundant on each of the islands, while xenoliths of sandstone and quartzite have been found on the three westernmost islands. Petrochemical data are presented for a considerable variety of Comores rocks, and the volcanic activity is discussed in terms of the major structural features of the Madagascar-Mozambique region.

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Bauer, M. 1911. Gesteinsproben der Wittu Insel, von Zanzibar, Archipel von den Comoren, Madagascar, Ceylon etc. pp. 1751 in Voeltzkow, A: Reise in Ost-Afrika in den Jahren 1903–1905, Bd. 1, Absteil II.
Guilcher, A. 1965. Coral reefs and lagoons of Mayotte Island, Comoro Archipelago, Indian Ocean, and of New Caledonia, Pacific Ocean. In Whittard, W. F. & Bradshaw, R. (Eds.): Submarine Geology and Geophysics, Butterworth Press, London.
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1922a. La constitution lithologique de l'Archipel des Comores. C.R. XIII ième Congrès International Géologique, fasc. 2, 949979, Brussels.
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1958. Le volcan actif de l'Ile de la Réunion et celui de la Grande Comore. Gauthier-Villiers, Paris.
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Saint Ours, J. de. 1960. Etudes géologiques dans l'extreme nord de Madagascar et L'Archipel des Comores. Service Géologique, Tananarive.
Strong, D. F. & Flower, M. F. J. 1969. The significance of sandstone inclusions in lavas of the Comores Archipelage. Earth Planet, Sci. Letters 7, 4750.
Voeltzkow, A. 1906. Die Comoren. Zeitschrift der Gesellschaft für Erdkunde, Berlin, 606630.

Geology of the Comores Archipelago, Western Indian Ocean

  • J. Esson (a1), M. F. J. Flower (a2), D. F. Strong (a3), B. G. J. Upton (a4) and W. J. Wadsworth (a1)...

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