Rifting Processes at a Continent-Ocean Transition Rift Revealed by Fault Analysis: Example of Dabbahu-Manda-Hararo Rift (Ethiopia)

Stephanie Dumont (1, 2) , Yann Klinger (1) , Anne Socquet (3, 4) , Javier Escartin (1) , R. Grandin (1) , E. Jacques (1) , S. Medynski (5, 6) , C Doubre (7)

1 IPGP - Institut de Physique du Globe de Paris
2 UBI - University of Beira Interior [Portugal]
3 ISTerre - Institut des Sciences de la Terre
4 IFSTTAR - Institut Français des Sciences et Technologies des Transports, de l'Aménagement et des Réseaux
5 CRPG - Centre de Recherches Pétrographiques et Géochimiques
6 Cerema - Centre d'Etudes et d'Expertise sur les Risques, l'Environnement, la Mobilité et l'Aménagement
7 IPGS - Institut de physique du globe de Strasbourg

Analyses of fault attributes have contributed to unraveling fault growth processes in diverse tectonic settings. By integrating such analysis at the scale of a fault population, we propose to investigate the characteristics of a rift that has evolved up to a stage typical of a continent-ocean transition. We address this problem by considering Dabbahu-Manda-Hararo (DMH) rift segment (Central Afar, Ethiopia), recognized for being in a late rifting stage. We quantify fault azimuth, length, and throw attributes for 668 normal faults. Along DMH rift, the mean fault density is 0.87 ± 0.7 km/km 2 and the median tectonic strain ranges from 1.8% to 3.1% assuming a fault dip of 60°and 45°, respectively. Maximum tectonic strain (>10%) is found where the rift azimuth changes. Along-rift variations in fault azimuth, length, and scaling relationships suggest a different stage of rifting in the northern part of the rift. We show that this difference can be attributed to the influence of the Dabbahu volcano located at the northern tip of the rift, which captured the propagating Manda-Hararo rift in the last~100 kyr. The morpho-tectonic analysis reveals numerous common features with slow-spreading ridge segments, such as the Lucky Strike segment located along the Mid-Atlantic ridge (segment length, spreading rate, associated magmatic system) but also with intermediate and fast ones (axial valley, fault throws, and diking). This study reveals that a rift at the continent-ocean transition may be characterized by a transient and evolutionary behavior that shares features with oceanic ridges from slow-to fast-spreading rates.

Domaines: Tectonique

Stephanie Dumont, Yann Klinger, Anne Socquet, Javier Escartin, R. Grandin, et al.. Rifting Processes at a Continent-Ocean Transition Rift Revealed by Fault Analysis: Example of Dabbahu-Manda-Hararo Rift (Ethiopia). Tectonics, 2019, 38 (1), pp.190-214. ⟨10.1029/2018TC005141⟩. ⟨hal-02324058⟩