STRUCTURE OF THE LATE PROTEROZOIC NAKASIB SUTURE, SUDAN

The Nakasib suture is a prominent structural belt in the central Red S ea Hills, Sudan. It is one of the ophiolite-decorated sutures along wh ich the late Proterozoic (Pan-African) island arc/back are terranes an d continental micro-plates of the Arabian-Nubian Shield were welded to gether. It juxtaposes the 900-800 Ma Haya terrane in the south with th e 830-700 Ma Gebeit terrane to the north. New structural data from the Nakasib suture show that the suture had evolved through three phases of deformation which gave rise to a fold and thrust belt. During the e arly two phases of deformation, SE-verging tight folds and thrusts wer e developed. The third phase of deformation refolded the earlier struc tures into NE-trending, upright, and horizontal antiforms and synforms and culminated in the development of NW-verging thrusts. The structur al data are used, together with previous stratigraphic and geochemical data, to suggest a tectonic model for the evolution of the Nakasib su ture. The suture followed a Wilson Cycle. This started with rifting of the Haya terrane, extrusion of rift volcanics and deposition of passi ve margin sediments, and development of a NW-dipping subduction zone o ver which the are volcanics of the Gebeit terrane erupted. The closing of the oceanic basin gave rise to the Nakasib suture with the present structural configuration. The structural styles of other sutures of t he Arabian-Nubian Shield are examined in light of structural data from the Nakasib suture. These sutures show a common feature of steepening of the early subhorizontal ophiolite-obduction structures during a la te event of upright folding which may be related to collision between terranes.