Influence of Lateral Plume Channel on the Evolution of Rift Arms of the Afar Triple Junction: Constraints From 3‐D Gravity Interpretation

• Published in: Journal of geophysical research. Solid earth Vol. 128; no. 8
• Main Authors: Sreenidhi, K. S., Betts, P. G., Radhakrishna, M., Armit, R.
• Format: Journal Article
• Language: English
• Published: 01.08.2023
• Subjects: Afar mantle plume; Afar Triple Junction; crustal thickness; mantle plume channel; Red Sea; upper mantle gravity
• ISSN: 2169-9313; 2169-9356
• DOI: 10.1029/2023JB026791

The Afar region presents a unique example of a juvenile R‐R‐R triple junction with the arms evolved to various stages of maturity. The lithosphere in this area has been modified heterogeneously by the nearby Afar mantle plume. To gain a comprehensive and consistent understanding of the link between crustal geometry and geodynamics of the region and facilitate comparisons across different tectonic elements, we developed a high‐resolution crustal thickness map of the region that resolves major tectonic features. The calculation involved a well‐constrained 3‐D inversion of upper mantle‐corrected crustal Bouguer gravity anomalies computed with the help of tomography‐derived densities. Our results match earlier localized crustal thickness estimates, illustrating the method's efficacy. A thinner crust (∼20–26 km) is revealed in the Afar compared to adjacent continental regions. The Main Ethiopian Rift has the thickest crust in the central part of the rift (∼38–40 km) and thinner to the north (∼30 km) and south (∼35 km). The crustal thickness along the Gulf of Aden changes from east (∼5 km) to west (∼17 km) in the west, consistent with a westward transition from seafloor spreading to continental rifting. The southern Red Sea is characterized by asymmetric crustal thickness, with a thicker crust (∼17 km) on the eastern flank compared to the western flank (∼11 km), which we attribute to the influence of a sub‐lithospheric channel from the Afar mantle plume. We propose a model describing the channel leading to asymmetric features of the southern Red Sea, such as crustal accretion, marginal topography, and volcanism. Plain Language Summary The Afar region is a divergent triple junction where the Main Ethiopian Rift, the Red Sea, and the Gulf of Aden converge and is the site of impingement of the Afar mantle plume on the lithosphere. We have developed a high‐resolution crustal thickness map using gravity inversion techniques to study how deep geodynamics affect the rifting process and crustal geometry of the region. We isolated the gravity signals caused by shallow geological features by removing the deeper components. These shallow signals and crustal thickness data provide insights into the evolution of the triple junction arms and the influence of the mantle plume. We found a transition from seafloor spreading to continental rifting in the Gulf of Aden. There is discontinuous crustal accretion in the central Red Sea and continuous accretion in the south. Moreover, the computed crustal thickness suggests that crustal accretion is not symmetric in the southern Red Sea. We suggest seafloor spreading in the southern Red Sea occurs above a lateral sub‐lithospheric channel from the Afar plume, which may also cause crustal thickness asymmetry, uneven rift margin topography, and volcanism in the region. Key Points Crustal thickness asymmetry in the southern Red Sea reveals differential crustal accretion under the influence of the Afar plume channel Custal gravity anomalies reveal the heterogeneous nature of the Red Sea and the westward spreading‐rifting transition in the Gulf of Aden Proposed a model linking the horizontal plume channel with the observed asymmetry around the southern Red Sea