The ophiolite-decorated Allaqi-Heiani suture zone along the Egypt-Sudan border is a key tectonic feature in the Arabian-Nubian Shield, and is considered as the northern extension of the East African Orogen (EAO). This zone is commonly interpreted as a fold-and-thrust belt in which southward-vergent thrust segments of allochthonous ophiolites tectonically overlie medium-grade metamorphosed island arc rocks. Formation of this belt was attributed to collision between the SE Desert and Gabgaba arc terranes and N-S shortening at ca. 750-720 Ma. Discrete NW-trending stretching lineations, asymmetric tails and rolling structures along the thrust planes indicate a left-lateral sense of shear obscured in places by crenulation cleavage and rootless NNW-trending folds. The geometry of the crenulation cleavage and association with 100s km-long wrench zones with common pull apart basins and swelling centers may express the accretion of the Arabian-Nubian Shield with the Saharan Metacraton in the west, which occurred concurrent with Gondwana assembly through progressive oblique convergence (640-580 Ma). Clear superimposition of older and younger structures are difficult to observe, but NW-SE foliation deflection and nucleation of NNW –trending foliation through C-S structure is very likely. Based on the microstructure of the foliated rocks along the thrust planes of the Allaqi-Heinai suture, we assume that these two foliations resulted from the same oblique convergence tectonics and preclude the early N-S accretion phase. Therefore, the East-West Gondwana collision should have started earlier than previously thought by at least 100 Ma. |
