Abstract

The Hamisana shear zone (HSZ) is a broad zone of deformation, approximately 50 km wide and at least 300 km long, making it one of the largest basement structures in NE Africa. It has been interpreted as a Precambrian suture, as a zone of strike-slip displacement, or as a zone of crustal shortening. The results of new Rb-Sr and U-Pb zircon geochronological studies indicate that the northern HSZ was thermally active during the Pan-African event until c. 550 Mg ago; initiation of the structure may have begun 40–110 Ma earlier. All units have low initial 87Sr/86Sr ratios, indicating juvenile derivation. The timing of activity in the HSZ is 50–150 Ma younger than collisional suturing and terrane assembly in the Arabian-Nubian Shield but is similar to the 655–540 Ma Najd fault system of Egypt and Arabia. Deformation and metamorphism along the HSZ clearly post-date terrane accretion and probably are closely related to the Najd tectonic cycle. The most important deformation of the HSZ is unrelated to suturing, and at least one late Precambrian suture must extend west from Arabia into the interior of N. Africa.

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