Quantitative Analysis of Faulting in the Danakil Depression Rift of Afar: The Importance of Faulting in the Final Stages of Magma-Rich Rifting

Abstract

Magmatic intrusion and faulting both accommodate crustal extension in magma-rich rifts. However, quantitative constraints on the contribution of faulting to total extension and along-rift variations of faulting during the final stages of break-up are lacking. We targeted the Danakil Depression (Afar, Ethiopia) to conduct a quantitative, high-resolution study of fault activity and interaction in a magma-rich rift near break-up. Quantitative analysis of >500 rift axis faults, identified using remote sensing data (satellite imagery, DEMs), shows an increase in fault density, length and connectivity away from magmatic segments. Kinematic and earthquake focal mechanism data demonstrate a transition from transtensional opening in the northern and central sub-regions of the rift to oblique opening in the southern Giulietti Plain and Tat-Ali sub-regions. Oblique opening is attributed to the along-axis step between the Erta-Ale and Harak sub-regions. Integration of seismic reflection and borehole data with the mapped faults shows that extension is primarily accommodated by magmatism within the rift center, with faulting more significant toward the ends of the rift. ∼30% of crustal extension is accommodated by axial faulting in areas of low magmatism, highlighting the importance of faulting even in the final stages of magma-rich rifting. Comparing our findings with spreading ridge morphology and structure, relevant due to the rift maturity and extensive magmatism, we conclude that the Danakil Depression is in a transitional stage between continental rifting and seafloor spreading. Spatial changes in the importance of faulting and magmatism in accommodating extension, alongside rift morphology, resemble the relationships observed along spreading ridges.