A crustal thickness map of Africa derived from a global gravity field model using Euler deconvolution

Abstract

We develop a new continental scale crustal model for Africa by modelling the free-air gravity anomaly EIGEN-GL04C, which was developed from 30 months of GRACE Level 1B data covering the period from 2003 February to 2005 July, and surface gravity data from seven different sources. From this gravity model, crustal thickness is estimated using 3-D Euler deconvolution, a method that does not rely on a priori depth and density constraints. The results are in good agreement (i.e. within 5 km) of seismically determined Moho depth estimates from across the continent, except for narrow tectonic regions, such as rift valleys, and areas where seismic velocity models of the crust indicate a gradational Moho. The results show that crustal thickness is fairly homogeneous, with an average crustal thickness for the whole continent of 39 ± 2(SD) km. The average Moho depth for most terrains is within 5 km of the continental average, and there is little variability between terrains of different age. The average thickness for Archean, Proterozoic and Palaeozoic crust is 39, 39 and 41 km, respectively. Crustal thickness in sedimentary basins across northern and central Africa varies between 33 and 36 km. Through comparison with global averages for similar-aged terrains, we find that African crustal thickness does not deviate significantly from the thickness of crust in other parts of the world