Over a large area extending from the vicinity of Tadjoura, on the Gulf of Tadjoura, northwards to the Ethiopian border a sequence of thick rhyolitic flows, domes, dykes and pyroclastic rocks, known as the Mablas (Mabla) series, is predominantly of peralkaline composition, but some 30% of the seq
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Djibouti occupies the eastern part of the Afar Depression and as such is an integral part of that volcanic-dominated feature, much of which is described under Ethiopia. The 1:500,000 'Geological map of Central and southern Afar' (Varet, 1978) covers the whole of Djibouti and the following localities are all distinguished on that map. The greater proportion of the country is occupied by basalts, mostly tholeiitic, but there are also extensive areas of rhyolite much of which is peralkaline.
Babba Olou is a large silicic volcanic centre essentially comprising rhyolitic flows which are probably peralkaline but details of which have not been found.
This is a small area of Mablas peralkaline rhyolites located near the south coast of the Gulf of Tadjoura (Varet, 1978). The Mablas rhyolites are described under the North Tadjoura area (No. 2).
The Ali Sabieh-Aysha horst extends southwards into Ethiopia and along its northwestern and eastern margins are rhyolitic rocks which are correlated with the Mablas rhyolites of the North Tadjura area (No. 2) (Varet, 1978).
This volcanic centre straddles the border with Ethiopia and is described under that country (No. 9).