Unraveling the Upper Mantle Heterogeneities of the South African Cratonic Region Using Seismic and Gravity Data

Seismic tomography provides critical insights into the Earth’s interior, yet seismic velocity perturbations are largely influenced by tem perature variations. Integrating seismic data with gravity anomalies enables a more comprehensive understanding by incorporating compositional variations in the upper mantle of Precambrian cratons. The South African cratonic region, encompassing the Kaapvaal and Zimbabwe cratons, exhibits significant upper mantle heterogeneity in both temperature and composition. To unravel these variations and their corresponding density anomalies, we employ an integrative approach that jointly interprets seismic tomography and gravity data. Our method combines a global surface seismic tomography model with an embedded regional model, derived from teleseismic S-body wave inversion using data from the Southern African Seismic Experiment. Initially, we invert the seismic model for temperature, assuming a refertilized upper mantle composition. Through an iterative process, we adjust both temperature and composition by progressively increasing iron depletion to match the residual density derived from joint inversion of residual gravity and topography data. The GOCE gravity gradients are also incorporated to increase the robustness of the method. Our results reveal that the most depleted lithosphere is found in the Southeastern Terrane of the Kaapvaal Craton and the central region of the Zimbabwe Craton at depths shallower than 100 km. These areas exhibit temperatures exceeding 150 °C relative to a refertilized lithosphere, providing key insights into the thermochemical evolution of the South African cratonic region