303-3 How do Propagating Rifts Breach Cratons? Insights from the Northwestern Branch of the East African Rift.

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

Poster Booth No.: 178

Presenting Author:

Andrew Katumwehe

Authors:

Katumwehe, Andrew B.¹, Atekwana, Estella A.², Abdelsalam, Mohamed G.³, Mickus, Kevin Lee⁴, Goussi, Jeannot Francois⁵, Kolawole, Folarin⁶

(1) Oklahoma State University, Wichita Fals, TX, USA, (2) UC Davis, Davis, CA, USA, (3) Boone Pickens School of Geology, Stillwater, OK, USA, (4) Missouri State Univ Geology, Springfield, MO, USA, (5) Oklahoma City Community College, Oklahoma, OK, USA, (6) Columbia University, Earth and Environmental Sciences, Palisades, NY, USA,

Abstract:

We investigated how continental rifts initiate and propagate across cratons by exploring the crustal structure of the northwestern tip of the East African Rift System (EARS), which hosts the volcanic-rich Edward-George and non-volcanic Albertine-Rhino rifts, and their termination at the Precambrian Aswa Shear Zone. We conducted a derivative analysis of magnetic data, utilized power spectral analyses, and implemented a two-dimensional (2D) forward modeling of gravity data constrained by the seismic results obtained from the region. A magnetic derivative map indicates that the border faults of the Albertine Rift, at a regional scale, trend parallel to the Mesoproterozoic Madi-Igisi fold belt (MIFB) structures, representing the suture zone between two Archean microcratons.

Our results show a pronounced thinned crust (~24 - 30 km) beneath the southern segments of the rift zone, particularly the Edward-George rift, the Rwenzori Mountains, and the southern Albertine graben, consistent with previous seismic studies. In general, we observe that: 1) the rift system follows the boundary between a broadly thinner crust (21 - 41 km) to the southeast in Uganda, and thick crust (34 - 41 km) to the northwest in Congo, and 2) within the rifts, the crustal thickness along the axes exhibits a strong gradient that attenuates northwards beneath the Albertine-Rhino graben. We supplement the geophysical results with field observations of an exhumed Permian ‘Karoo’ rift (Entebbe Graben) in central Uganda, indicating the possible source of inherited thinner crust to the southeast of the Albertine-Rhino Rift. We propose that the northwestern tip of the EARS exploited a cratonic crustal thickness gradient, assisted by structural inheritance from crustal metamorphic fabrics, and potentially, thermo-mechanical weakening of the deeper crust by partial melts beneath some of the rift segments.

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

doi: 10.1130/abs/2025AM-7601

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