Notes on some shear zones of northern Somalia

Low-angle thrusts, displaying a well developed, stretching lineation, and west to south-west vergence, are reported from the basement of northern Somalia, and interpreted as the extreme evolution of a (Upper Proterozoic) phase of folding. This is seen as a late event, roughly coeval with gabbro emplacement, and later than the main metamorphism of the basement complex. Thrusting took place when the gabbros were still at a high temperature, as shown by ‘hot’ metamorphic assemblages within the zones of ductile shear. Development of abundant pegmatite and of some muscovite granite also took place, probably triggered by gabbro emplacement.

Tectonic style suggests that here we may be dealing with the continuation of the collision zone with the East Gondwana Plate, recently recognized by some researchers near the eastern margin of the Saudi Arabian shield.