Late Proterozoic extensional collapse in the ArabianNubian Shield

A structural and petrological study of the Late Proterozoic rocks in the Wadi Kid area, Sinai, Egypt indicates the presence of an extensional metamorphic core complex in the northern ArabianNubian Shield. Gneissic domes throughout the ArabianNubian Shield resemble the core complex of the Wadi Kid area and as a result, they are interpreted as extensional metamorphic core complexes. The presence of a widespread phase of extension at the end of the PanAfrican period in the ArabianNubian Shield requires a new interpretation of the tectonic history of this shield. Three main tectonic phases are recognized in the Late Proterozoic of the ArabianNubian Shield. Ophiolites and islandarc remnants are relicts of an oceanic phase, the oldest one. This phase was followed by arcaccretion, well established in the ArabianNubian Shield from the presence of individual terranes bordered by sutures, which was responsible for lithospheric thickening. The Late Proterozoic ended with widespread NWSE extension. The metamorphic core complexes, lateorogenic extensional basins and large strike slip zones were formed during this phase. Similarity of the tectonic evolution of the ArabianNubian Shield with the Mesozoic and Early Cenozoic evolution of western North America lead us to conclude that gravitational instability at the final stages of the arcaccretion phase caused the collapse and resulted in extension at the latest stages of the PanAfrican orogeny in the ArabianNubian Shield.