3D Density Heterogeneity of the Crust beneath Botswana and its Tectonic Implications

By: Chikondi Chisenga,

Abstract

I present the first information on the 3-D crustal density structure across Botswana obtained from 3D tesseroid inversion of Bouguer anomaly data. Crustal density structure provides important information for understanding tectonic and geodynamic processes in Botswana. I applied the inversion algorithm in spherical coordinates and included constraints consistent with the geological information for Botswana. The results show that density values in Botswana are inhomogeneous, varying from 2650 kg/m3 to 3000 kg/m3 . Greater variation is noticed in the upper 20 km while the lower crust has a mostly uniform density of ~ 2850 kg/m3 . A combination of density, published Curie point depth, and Moho depth data shows that cratonic regions are mostly characterized by homogenous density values, with presence of mafic intrusions. On the other hand, mobile belts and sedimentary basin exhibit greater density variation, with the presence of > 2800 kg/m3 density in some of the crustal scale elements. The study further maps possible edges of tectonic terranes. Furthermore, the northern end of Nosop basin indicates possible magnetization in the lower crust, which could be the result of serpentinization.