A major dyke swarm in the Ogaden region south of Afar and the early evolution of the Afar triple junction

• DOI: 10.1144/sp420.7
• Publication Date: 2015-05-13T01:31:20Z
• Authors: D. Mège; P. Purcell; A. Bézos; F. Jourdan; C. La
• Keywords: Triple junction

Abstract Geological mapping in the Ogaden region of SE Ethiopia, integrated with aeromagnetic data, has revealed a large dyke swarm extending SSE more than 600 km from southern Afar margin across Somali Plate to Ethiopia–Somalia border. 40 Ar/ 39 Ar age dating shows that emplacement occurred at 24–27 Ma, contemporaneous early rifting and dyking Red Sea. Slab-pull forces generated Zagros subduction zone strained lithosphere Afro-Arabian plate, began extend south Sea c. 27 Afar, fed by plume-related magma source, rather rift-related source prevailing along Immediately margin, system was emplaced Precambrian Marda Fault Zone, continuation may have been controlled lithospheric weakness associated splay Fault. We suggest Dyke Swarm is crustal dilation continuing trend Horn Africa constituting original third ‘arm’ triple junction. Geochemical geochronological analyses indicate basaltic outpourings flowed least as far east border emanated same Ethiopian flood basalts, which had erupted earlier 30 Ma. Dykes are emergent only occasionally marked surface linear sand-filled troughs varying 2 20 m deep caused tensional collapse above tip. Magnetic anomalies dykes vary width up 1 likely identify zones. Supplementary material: map Zone surroundings; argon analytical protocol isotopic data corrected baseline; petrographic description representative samples used for geochemistry available http://www.geolsoc.org.uk/SUP18829 .