207-2 ARISE: Afar Rift Integrated Seismic Experiment – A Tribute to Mohamed G. Abdelsalam

Session: Honoring the Late Professor Mohamed Abdelsalam: Outstanding Researcher, Generous Colleague, Legendary Mentor, and Ambassador for the Geosciences In Africa

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The Main Ethiopian Rift-Red Sea-Gulf of Aden rift triple junction is the type example of continental rifting, and the Afar portion of this system is the most evolved toward formation of new oceanic lithosphere. Evolution of the Tendaho, Dobi, and Immino grabens within the last ~2 Ma suggests they are extensively intruded by mafic magmas within highly-extended crust, and bounded by relatively unextended continental crust on the flanks of the rift axis. Constraints on crustal thickness from passive-source seismology suggest significant disparities between the locus of crustal thinning and these shallow rift segments; the thinnest crust (18 km) lies ~50 km west of the central axis of the Tendaho graben, and the Immino graben sits within 30-km thick crust of the Danakil block. These relationships imply a spatial discrepancy between the expression of extension in the upper crust and in the lower crust/upper mantle, requiring a structural detachment within the crust. This study will evaluate two competing models: (1) a subhorizontal zone of mid-crustal detachment, or (2) a lithosphere-scale low-angle extensional system linking upper crustal extension laterally to lower crust/upper mantle extension. In addition, development of these rift segments within the southern extent of the Red Sea Propagator has resulted in isolation of the continental Danakil block (30 km thick) within the extensional system. Such continental ribbons are predicted by recent models of continental extension from passive continental margins, involving lithosphere-scale detachment faults.

When funded, the ARISE (Afar Rift Integrated Seismic Experiment) effort will result in the collection of multi-component, controlled-source, seismological data at variable scales (shallow-crustal to lithospheric), to image the structure of the most evolved and active continental rift on Earth along a ~200-km transect within the Afar Depression of Ethiopia. Sensors will be deployed simultaneously for (1) 3-component refraction/wide-angle reflection, (2) long-record (60 s) near-vertical reflection, and (3) shallow, high-resolution imaging of rift segment boundaries along the entire profile. These data, integrated with extant geological and geophysical data, will provide the first systemic 2-D image, as well as P- and S-wave velocity structure, from the shallow crust to the mantle lithosphere of the nascent transition from continental to oceanic lithosphere, and reconcile current disparities in estimates for extensional strain at these differing scales and lithospheric depths.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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