Processing and interpretation of satellite and terrestrial gravity data for the lithospheric structure of Egypt and the Saharan Metacraton

We model the variations of the crustal and lithospheric thicknesses as well as the variation in temperature, composition, S-wave seismic velocity and density of the lithosphere beneath the Saharan Metacraton (SMC) using three-dimensional (3D) modelling. The SMC was once an intact Archean-Paleoproterozoic craton, but was remobilized (metacratonized) during the Neoproterozoic due to partial loss of its sub-continental lithospheric mantle (SCLM) during collisions along its margin. The partial loss of the SCLM might have permitted the preservation of the cratonic remnants within the metacraton. We discuss the possible preserved cratonic remnants within the SMC exploiting integrated modelling using geophysical, petrological, and geological information for the crust and the lithospheric mantle. The cratonic remnants are overlain by Paleozoic-Mesozoic sedimentary basins and they are surrounded and separated by topographic swells with known Cenozoic volcanism including the Hoggar Swell (HS), the Tibesti Massif (TM), and the Darfur Dome (DD). We find that the three cratonic remnants are underlain by a relatively thicker lithosphere (the thickest being beneath Al-Kufra reaching ~ 200 km) compared to the surrounding SMC, which has an average lithospheric thickness of ~ 150 km. We also find that the SCLM of the cratonic remnants to be relatively colder and denser, as seen by faster S-wave velocities compared to the surrounding SMC. Our preferred models are approached considering different lithospheric thicknesses beneath the SMC with a uniform moderately depleted composition (Proterozoic SCLM composition). We suggest that the presence of a relatively thinner lithosphere beneath the SMC, outside the cratonic remnants, was due to a combination of Precambrian events (partial SCLM delamination during the Neoproterozoic) and Phanerozoic events (Mesozoic-Cenozoic rifting and Cenozoic mantle volcanism).


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