Satellite gravity data for mapping lithospheric structure of Precambrian tectonic blocks in Africa: The advantages and limitations

In this study, we use the Precambrian tectonic blocks in southern Africa to examine the utility of satellite gravity data in mapping the lithospheric structure beneath the Precambrian terrains in Africa. For this, we focus on the Archean – Paleoproterozoic Congo – Tanzania – Bangweulu, Zimbabwe – Kaapvaal – Niassa cratons, Paleoproterozoic – Neoproterozoic Trans-Southern Africa orogen, the Neoproterozoic early Cambrian Lufilian arc, and Paleoproterozoic – Neoproterozoic Irumide metacraton. We use the Bouguer gravity anomalies of the World Gravity Model 2012 (WGM 2012). Our goal is to estimate the thickness of the lithosphere (hence the depth to lithosphere – asthenosphere boundary (LAB)) beneath these Precambrian tectonic blocks. We use two approaches including the two-dimensional (2D) radially averaged power spectral analysis (henceforth the spectral analysis), and 2D forward gravity modeling (henceforth the 2D forward gravity model). Using the spectral analysis, we are able, to a large extent, image the Congo – Tanzania – Bangweulu craton, as been underlain by thick lithosphere with the LAB depth of ∼250 km. Differently, using this method, we find no anomalously thick lithosphere beneath the Zimbabwe – Kaapvaal craton, although some of the 2D forward gravity models show relatively thick lithosphere beneath this craton. The only segment of the Trans-Southern Africa orogen we find to have thinner lithosphere (∼150 km) using the spectral analysis is the Mesoproterozoic – Neoproterozoic Damara – Ghanzi – Chobe orogen. We find the “system” limitations in using satellite gravity data for imaging Precambrian lithospheric structure to be the selection of linear segments in the spectral curves, selection of the size of sub-windows during the analysis, and selection of density values during the 2D forward gravity modeling. We find the “environmental” limitations to be the modification of Precambrian lithospheric structure by younger tectonic events.