Terrane Amalgamation and the Late Proterozoic Growth of the Eastern Arabian Shield PDF

Keywords

Arabian Shield, geology, Proterozoic growth

Abstract

Some attempts were made in the past to subdivide the Arabian Shield into a number of tectonostratigraphic terranes that were accreted onto the eastern margin of the African Craton towards the end of the Proterozoic. The eastern half of the shield in particular appeared to be a classic example of such a process, as it contained well-defined sutures dotted with genuine ophiolitic assemblages. The most popular terrane scheme for this part of the shield recognizes two blocks (Ar Rayn and Afif Terranes) of continental affinity separated from the western oceanic terranes by the major Nabitah Suture. Closer inspection, however, using recent geochemical and radiometric age data reveals that the Ar Rayn block is merely a rifted fragment of the Afif microcontinent. and should accordingly be considered as a parautochthonous terrane. The Hail structural province in the northern extremity of the Nabitah Belt contains a much more varied assemblage of magmatic rocks than is typical of the Nabitah Suture, as well as having a number of thick, slightly metamorphosed, sedimentary units that are restricted in their outcrop to this region of the shield. All of this, combined with the fact that all the contacts of this province with the rest of the shield are marked by major fault zones, some of which are ophiolite-bearing makes it reasonable to elevate it to full terrane status.