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Abstract:
Earlier studies revealed the effect of different degrees of depletion on lateral/vertical velocity and density variations in the upper mantle of the Precambrian cratons. The South Africa cratonic region includes the Kaapvaal and Zimbabwe craton, whose deep and fast lithospheric roots are likely depleted in heavy constituents. In contrast, there exist regions, such as the Limpopo belt and Bushveld Complex, which are characterized by negative velocity anomalies in the upper mantle, likely indicating a more fertile composition. To unravel the origin of these anomalies and link them to the tectonic history of the area, we apply an integrative technique based on a joint interpretation of the seismic tomography and gravity data, which can discern temperature and compositional variations. For this purpose, we combine the global surface seismic tomography model [1] with the embedded regional model [2], derived from teleseismic tomographic inversion of the S-body wave dataset recorded by the Southern African Seismic Experiment. The combined seismic model is inverted for temperature, assuming an initial fertile composition based on the xenolith data [3], using a mineral physics approach [4]. The composition and temperature of the upper mantle are iteratively changed to fit the residual density, obtained from the joint inversion of the residual gravity and residual topography. The key results show different structures and properties of the upper mantle, improving our understanding of the South African cratonic lithosphere.
References
[1] Schaeffer and Lebedev, 2013. https://doi.org/10.1093/gji/ggt095
[2] Youssof et al., 2015. http://dx.doi.org/10.1016/j.epsl.2015.01.034
[3] Griffin et al., 2004. doi:10.1016/j.chemgeo.2004.04.007
[4] Conolly, 2005. doi:10.1016/j.epsl.2005.04.033
