Large-scale flexuring and antithetic extensional faulting along a nascent plate boundary in the SE Afar rift

Abstract : New structural data from the SE Afar margin in Djibouti lead us to discriminate two recent (<1 Ma) extensional fault networks between the Afar accreted crust, and the South Danakil block to the east. Emphasis is placed on the N-S-oriented Makarassou fault system which dissects the prominent westward-(riftward-)facing topographic flexure between the two structural domains. The most striking characteristic of the Makarassou fault belt is a closely spaced network of continentward-dipping extensional faults, bounding domino blocks of 3-1 Ma tilted lavas of the Stratoid series. The Makarassou fault-flexure system is interpreted as an extensional faulted monocline that developed in response to differential subsidence and crustal downwarping of the Afar magmatically accreted transitional crust. Large-scale flexuring and associated structures along the eastern flank of the Asal-Manda-Inakir incipient plate boundary are regarded as indicative of a nascent volcanic rifted margin in SE Afar.