Abstract The incipient Okavango rift zone (ORZ) in the southern end of the East African rift system is one of the youngest rift zones on Earth. Knowledge of the lithospheric structure of the ORZ is crucial to understanding the early-stage rifting processes of the rift system and even the mechanisms leading to the breakup of ancient continents. In this study, we construct a 3D lithospheric shear-wave velocity model beneath the ORZ by jointly inverting Rayleigh-wave phase velocity dispersion and receiver functions using a nonlinear Bayesian Monte Carlo algorithm. The model exhibits velocity structure from the surface to 160 km depth, and several lithospheric features associated with the continental stretching are revealed. Within the crust, low velocities are found beneath the ORZ, which could be caused by the presence of melts. We also observe four low-velocity anomalies in the upper mantle. Two of these anomalies are located at the two ends of the ORZ, probably related to decompression melting caused by the stretching of the continent. The third one is observed directly beneath the rift, which starts from ∼110 km depth and extends deeper. We postulate the anomaly is attributable to the presence of a small volume of melts and/or high temperatures of the region that may be caused by hot fluids from greater depths. These three anomalies may act as melt reservoirs feeding the crust. Another low-velocity anomaly is imaged beneath the boundary between the Limpopo belt and Kaapvaal craton. Unlike the others, this feature is likely related to the compositional changes due to the reduction of Mg# in the lithospheric mantle associated the Precambrian magmatic events. As such, it may not serve as a melt reservoir in the current tectonic setting.
Wang et al. (Fri,) studied this question.