Ras Ed Dom

The 61 km2 Ras ed Dom complex displays a remarkable series of semi-circular migrating intrusive centres. It is emplaced into Precambrian biotite gneisses and quartzo-feldspathic granulites and is in contact with the Sultaniyat complex (No. 155-00-039). Although, by analogy with adjacent complexes e.g. Sultaniyat, it is likely that there was a substantial volcanic pile at Ras ed Dom, this is now represented only by minor rafts and xenoliths of acid tuffs and lavas. Eight intrusive centres have been recognised within the complex encompassing 24 separate units. Each centre commenced with the emplacement of ferrohedenbergite syenite, the centres moving eastwards with time and becoming progressively smaller. Individual intrusions vary from sub-circular stocks and nested plutons to numerous crescentic sheets and swarms of cone-sheets. O'Halloran (1985b) divides the rocks into two main groups: the first includes metaluminous syenites containing relict fayalite and ferrohedenbergite mantled by ferroedenite, with prominent apatite and Fe-Ti oxides; quartz is minor. They range texturally from feldsparphyric trachyte dyke rocks to coarse syenites but comprise only some 6% of the complex. The second group consists of peralkaline quartz syenites and granites with ferrorichterite zoned to arfvedsonite and mantled and replaced by aegirine; zircon and riebeckite are minor. There are 18 individual peralkaline syenite bodies occupying 54% of the area and three granites covering 40%. Ras Abu Siba is a 1x1.5 km intrusion of peralkaline felsite lying four kilometres to the north of Ras ed Dom. Analyses of feldspar, amphibole and pyroxene are given and discussed in detail by O'Halloran (1985b) who also gives a range of rock analyses, including some RE and other trace elements.