Global gravity gradient inversion reveals variability of cratonic crust

In this contribution, we present a global estimate of crustal thickness with emphasis to cratons. In an inverse scheme, satellite gravity gradient data are inverted for the Moho depth, exploiting laterally variable density contrasts based on seismic tomography. Our results are constrained by an active source seismic data base, as well as a tectonic regionalization map, derived from seismic tomography. For the global analysis, we implement a moving window approach to perform the gravity inversion, followed by interpolating the estimated density contrasts of common tectonic units with a flood-fill algorithm.

The estimated Moho depth and density contrasts are especially interesting for the cratons of the Earth. Our results reveal a surprising variability of patterns with average Moho depth between 32-42 km, reflecting an individual tectonic history of each craton. Statistical patterns of Moho depth and density contrasts are discussed for the individual cratons and linked to their stabilization age. For example, Australia shows the lowest average Moho depth (32.7 km), indicating early stabilization in the Archean and removal of a dense lower protocrust. This observation matches well with receiver function studies. The globally inverted Moho depth is validated by gridded seismic Moho depth information, which shows that for many cratons the inverted Moho depth is within expected uncertainties of the seismic Moho depth. In addition, the formerly connected cratons of South America and Africa are analyzed and discussed in a Gondwana reconstruction. Here, the once-connected West African and Amazonian Cratons have a shallow Moho depth, indicating that only little tectonic activity occurred during the Phanerozoic. The tectonically-linked Congo and Sao Francisco Cratons have intermediate Moho depths, with the Congo Craton having a slightly shallower Moho depth. This could reflect dynamic support of the upper mantle on the African side.