Geological map of the Republic of Djibouti

Geological map of the Republic of Djibouti

Despite its modest size, close to that of Brittany, the Republic of Djibouti has the privilege of hosting one of the world's most iconic geological sites - the Asal Rift. Avec ses entablements de laves basaltiques, découpés en lanières par des réseaux de failles, le fossé d’Asal, dont le plancher se situe à – 150 m sous le niveau de la mer du Ghoubbet, est l’aboutissement d’un étirement et d’un amincissement de la lithosphère continentale, à l’avant de la ride océanique d’Aden séparant les plaques Arabie et Somalie. Ces processus géodynamiques de premier ordre, proches du stade de la déchirure continentale, sont exceptionnellement exposés à Djibouti, mais, paradoxalement, aucun document cartographique ne rendait compte à ce jour de leur contexte géologique régional.

Cette lacune est maintenant comblée par la Geological map of the Republic of Djibouti at a scale of 1:200 000 (edited by the Commission of the Geological Map of the World) established between 2011 and 2015 under the coordination of Bernard Le Gall (UMR/CNRS 6538) and in close collaboration between scientists from the 'Domaines Océaniques' laboratory in Brest (René Maury and Joël Rolet) and the CERD in Djibouti.

A synthesis of ten existing 1:100,000 maps, combined with newly acquired data from the field and satellite imagery, this original document highlights the main components of the Afar system in Djibouti, namely :

- the preponderance of synrift volcanism whose basic and acidic lavas, emitted for about 30 million years (Ma) in the context of the Afar mantle plume, cover more than 70 % of Djibouti's territory.

- the importance of very young (< 3 Ma) fault networks, markers of crustal extension and responsible for a morphology of tilted blocks and large subsiding troughs, such as that of Asal.

- the heterogeneity of sedimentary deposits, whether of continental origin, such as the terrigenous filling of ditches, or marine, such as the evaporites of Asal and the reef limestones bordering the Gulf of Tadjourah.

- the existence of ante-rift bedrock represented by the Mesozoic sandstones and limestones of the Ali Sabieh sector. Their antiform structure is attributed to the intrusion of a laccolith at the early stage of rifting.

- The marine geology of Ghoubbet, the Gulf of Tadjourah and the approaches to Bab el Mandeb incorporates the fault networks and submarine volcanoes identified on the available bathymetric records.

Geological map of the Republic of Djibouti