3D Mapping of Upper Mantle Density and Thermal Characteristics in the NE Arabian Shield Through Integrated Approach

Abstract

The central portion of the Red Sea Rift (RSR) experiences passive rifting and represents a major geological structure shaped by the divergence of the Arabian and African plates. Its rifting processes are influenced by mantle upwelling and lithospheric extension. This study integrates seismic tomography and 3D density modeling to develop a comprehensive model of upper mantle density and thermal characteristics in the northeastern Arabian Shield. Gravity anomaly inversion, constrained by seismic tomography, was employed to construct the model. Terrain and crustal gravity effects were removed from the EIGEN-6C4 gravity field to obtain the residual mantle gravity anomaly (RMGA).The results show significant density variations in the upper mantle, with high-density anomalies thickening eastward and westward before diminishing at depths of 300 km in regions such as Afar, related to the tectonics of the Red Sea. However, low-density anomalies are observed in the northern Red Sea and eastern Sudan, particularly along plate boundaries and collision zones, suggesting elevated temperatures and dominant mantle upwelling. In addition, a low-density zone around the Arabian Shield and eastern Sudan dominates the lithosphere beneath the fault belt. A thinner, high-density layer beneath the southwest of the Sea may be related to older oceanic lithospheric fragments.Furthermore, seismic tomography highlights extensive low-velocity zones in the upper mantle, indicating high temperatures and potential partial melting beneath the rift. The RF analysis uses raw data comprised of three-component broadband velocity seismograms from earthquakes with magnitudes greater than Mw 5.8 and epicentral distances ranging from 30° to 90°. Therefore, the thermal structure along the rift axis is not uniform, with hotter mantle material ascending beneath the central and southern portions of the RSR. Additionally, seismic velocities between 1.5 and 4.9 km/s align with sedimentary layers in grabens, reinforcing evidence of lithospheric thinning.These findings enhance our understanding of the region's geodynamic evolution by refining the upper mantle density model. However, the thermal regime remains insufficiently explored, emphasizing the need for further geophysical studies to fully elucidate the Red Sea Rift’s tectonic processes.