Geodynamic processes inferred from Moho and Curie depths in Central and Southern African Archean Cratons

Abstract

Central and Southern Africa is home to major Archean Cratons, flanked by Proterozoic mobile belts. The region is characterized by anomalously high topography and shallow Curie depth (Zb). Factors controlling topography and Zb anomalies in old continental crusts remain poorly understood. In this study, we present high-resolution Moho undulation (Zm) derived with gravity spectral technique. Archean Cratons and Proterozoic belts are mostly characterized by deep Moho (>36 km), whereas the Moho depths in Mozambique belts is mostly shallow (~26 to 41 km). Extremely shallow Zb (<10 km) is dominant in Archean Cratons, whereas intermediate Zb (10–25 km) is prevalent in the mobile belts. The Curie points are mostly above the Moho. Low surface heat flow (Qs) in Archean Cratons indicate that Zb is not correlated with thermal perturbation. Shallow Zb are mostly found in areas with low Vp/Vs ratio, predominantly felsic lower crust and sharp Moho. Shallow Zb also correlate with intense metasomatism and mineral enrichment, as well as depletion in basaltic components and geochemical overprinting by multiple episodes of melt and fluid infiltration. Crustal composition is the main factor that controls shallow Zb in Central and Southern Africa Archean Cratons. The regional elevated topography is not due to thermal perturbation as mostly argued by mantle plume hypothesis, but may be caused by regional thermo-chemical mantle upwelling dominated by composition.