“Until now, it was believed that everything happened 100 million years ago. But we knew something was wrong with the existing theories, explains Gilles Chazot, professor at the University of Western Brittany who led the study. In fact, they assumed that the structure was formed in a single step. However, this contains two types of magmatic rocks, the establishment of which could not have taken place at the same time. On the one hand we have the two rings of gabbros, magmatic rocks poor in silica, and dikes (veins) which have a very particular composition, these are carbonatites. The latter are not made up of silica like most volcanic rocks, but of carbonates. These are quite rare rocks, whose installation is incompatible with that of the gabbros rings”. On site, in the Sahara, samples of gabbros were taken by El Houssein Abdeina, a Mauritanian doctoral student, then sent to Australia where they were dated by Fred Jourdain, a French researcher stationed at the University of Perth, a world-renowned specialist. potassium/argon dating. And the verdict is in: it turns out that they were formed 200 million years ago, well before the carbonatites.
The theory is once again confirmed by the analysis of their chemical composition. “It corresponds exactly to that of the magmatic rocks of a major event which took place 200 M years ago, that of the formation of the magmatic province of the central Atlantic, underlines Gilles Chazot. This event is the equivalent of the Deccan traps formed 65 million years ago by the stacking of lava layers which caused the disappearance of the dinosaurs.. One hundred million years later, the injection of carbonatites will lift the horizontal strata to give them their dome shape. All that will remain is for erosion to do its meticulous work for another 100 million years for the eye of Africa to finally open.
