Tectonic link between the Neoproterozoic dextral shear fabrics and Cenozoic extension structures of the Mekelle basin, Northern Ethiopia
Résumé
The Mekelle basin (area ~ 5500 km2) is located at the immediate western margin of the Afar Depression, which has a history of collision, subsidence, uplift, magmatism and now rifting. The evolution of such small to medium size basins as the Mekelle in a complicated geodynamic set-up is a subject of debate, because several different mechanisms of basin formation could apply. To address the possible basin evolution scenarios, we combine structural and dynamic analyses of northern Ethiopia, with strong emphasis on the basin and basin bounding basement rocks. The northern basin bounding block is uplifted by about 1500 m compared with the western and southwestern basin-bounding blocks. In the basin, superposition of large-scale orthogonal brittle shear fabrics and the development of young, parallel to subparallel extensional fractures and domino faulting have produced a total of ~ 2200 m vertical displacement. These observations, coupled with the absence of gradual roll-down of the internal basin (i.e., absence of bending/folding of an elastic beam supported at both ends), imply that Mekelle basin is not an IntraCONtinental Sags (ICONS) or plate interior basin, as previously described, but is instead a multi-tectonic triggered basin. Integrated satellite images using ground-controlled measurements and deep borehole data were used to decipher the entire evolution of the basin starting from the late-collisional deformation through the regional up-doming to the sills/dikes injection and basin formation.