The Cenozoic volcanic province of Tibesti Sahara

Authors: C Deniel P M Vincent A Beauvilain A Gourgaud

Publish Date: 2015/08/08

Volume: 77, Issue: 9, Pages: 74-

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Abstract

Using both field relationships and some absolute ages the sequence of volcanic units in the Cenozoic Tibesti Volcanic Province TVP Chad is established as follows 1 plateau volcanism between at least 17 and 8 Ma consisting of flood basalts and silicic lava plugs with intercalated ignimbritic sheets in the upper basalt succession increasing in amount upwards Ages decrease from NE to SW following the migration of the small NWSE flexures concentrating the feeding dike swarms 2 Late Miocene large central composite volcanoes exhibiting diverse and original structures Some of them Tarso Toon Ehi Oyé and Tarso Yéga are located along a major NNE fault representing the main tectonic direction in Tibesti since Precambrian times 3 construction of three large ignimbritic volcanoes associated with significant updoming of the basement ending with the collapse of large calderas Voon about 5–7 Ma Emi Koussi 24–133 Ma and Yirrigué 043 Ma 4 basaltic activity starting at about 5–7 Ma and essentially consisting of cinder cones and associated lava flows Tarso Tôh Tarso Ahon and Tarso Emi Chi and 5 final volcanic activity represented by postYirrigué caldera activity in the Tarso Toussidé Volcanic Complex and especially Ehi Toussidé the only active volcano in Tibesti plus Ehi Timi and Ehi Mousgou volcanoes similar to Ehi Toussidé The two tectonic directions controlling some volcanic features of the province correspond to the major old lithospheric structures delimiting the volcanic province namely the great NWSE Tassilian flexure to the SW and a major NENNE fault zone to the E Unusual conditions of uplift and erosion in the TVP enable exceptional exposure of the internal structure of its volcanoesField work in the 1990s was made possible mainly thanks to the Chadian Ministry of National Education and Research CNAR the Ministry of Mines and Energy DRGM the army and local authorities plus the French Foreign Office Mission de Coopération et d’Action Culturelle the United Nations’ Programme for the Development PNUD and the French Air Force Opération “Epervier” CD is grateful to J Maley for fruitful email exchanges and some field photographs Fig 8a b and to K Suchorski and P Boivin for their teaching and advice about Illustrator and Photoshop softwares We are grateful to C Pin and P Boivin for helpful discussions comments and suggestions and to JP Liégeois R McDonald and Editor S Self for their careful and insightful reviews which greatly improved this paper

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