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Thermo-compositional models of the West Gondwana cratons

When Western Gondwana broke apart into the South American and African continents ⁓ 120 Ma ago, some of its cratons were broken apart as well. Following the isopycnic hypothesis, their long-term stability and often neutral to positive buoyancy can be explained by the counteracting effects of cooling (density increase) and iron depletion (density decrease). To separate these effects, we created the presented models following an iterative integrated approach using mainly seismic and gravity data. In the first step, seismic models of Depth to the Moho were created to allow correction of the gravity field and calculation of the residual topography. Second, based on mineral physics and S-wave tomography, we assessed temperature variations in the uppermost mantle and subtracted their effects from both residual gravity and topography. Afterwards, a joint inversion enables determination of potential compositional variations. Adapting the initially juvenile mantle composition leads to a change of thermal effects, thus the process was repeated iteratively until convergence. In result, we obtained self-consistent models of temperature, thermal and compositional density variations, and #Mg, a measure of iron depletion. Our results show deep depleted cratonic roots under the Amazonas, São Francisco, Paranapanema (South America), West African, Northern to Central Congo and Zimbabwe Cratons (Africa). Depletion appears to be mostly absent in the Rio de la Plata Craton of South America and its proposed African counterpart, the Southern Congo Craton as well as the Kaapvaal Craton below 100 km depth and the Tanzania and Uganda Cratons.


Nils-Peter Finger1,2, Mikhail K. Kaban1,3, Magdala Tesauro4,5, Walter D. Mooney6, Maik Thomas1,2
1GFZ Potsdam, Germany; 2Free University Berlin, Germany; 3Schmidt Institute of Physics of the Earth, RAS, Moscow, Russia; 4University of Trieste, Trieste, Italy.; 5University of Utrecht, Utrecht, Netherlands; 6US Geological Survey, Menlo Park, USA.
GeoKarlsruhe 2021