33-9 Lithospheric Thermal Structure of the Southwestern Branch of the East African Rift: Implications for a Southwestward Transition from Mantle to Crustal Processes in Rifting

Session: Going with the Shear - New Insights into Lithospheric Extensional and Strike-Slip Systems (Posters)

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Abstract:

To better understand rift initiation processes, we investigate the lithospheric thermal structure of the Southwestern Branch (SWB) of the East African Rift, which consists of incipient rifts. We analyze Bouguer anomalies from the World Gravity Map 2012 using the power spectrum technique to estimate the crustal and lithospheric thickness beneath the SWB. We apply similar techniques on aeromagnetic data to estimate the Curie Point Depth (CPD) and heat flow. We find: (1) thin crust (30–35 km) beneath rifts in the SWB and thicker crust (35–42 km) beneath surrounding cratons; (2) thinner lithosphere (~148–175 km) occurs beneath the northern portion of the SWB; (3) thicker lithosphere (~175–220 km) occurs beneath the southern portion and surrounding cratons; (4) the mobile belts show shallow CPDs (16–24 km) and high heat flow (65–90 mW/m²); and (5) the surrounding cratons show deeper CPDs (24–32 km), and lower heat flow (36–65 mW/m²). We interpret that the SWB is characterized by decoupling of crust-lithospheric mantle extension with preferential thinning in the lithospheric mantle at its northern portion. The younger southern portion of the SWB exhibits preferential thinning in the crust, which elevates the heat flow. We conclude that the northern portion of the SWB is experiencing asthenospheric upwelling in response to the lithospheric thinning, generating dynamic topography beneath the Central African Plateau. Rift initiation at the southern portions involves remobilization of preexisting structures in the crust, suggesting a southwestward transition from mantle to crustal processes in the SWB.

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

doi: 10.1130/abs/2025AM-5750

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