Geometry, structure and emplacement of mafic dykes in the Red Sea Hills, Sudan

Abstract

The volcano-tectonic evolution of the Red Sea area prior to the initiation of continental stretching (since 35 Ma) and sea-floor spreading (since 5 Ma) is still poorly known. Here we present results of a study of more than 2000, mostly mafic and fresh, dykes from the Haya area, located at the west margin of the Red Sea in the Red Sea Hills of Sudan. The dykes belong to two main age groups, one emplaced at around 130–140 Ma and the other at around 600–700 Ma. The dykes were studied in the field as well as from Landsat ETM and SPOT images. The results show that although the dykes trend in various directions, there is noticeable group of ENE-trending dykes whereas the NNW-trending dykes dominate. The length and thickness distributions of dykes are statistical laws with negative exponents. Using the aspect (trace length/thickness) ratios of the dykes, the magmatic overpressure at their time of emplacement is estimated. Most values obtained indicate overpressure between around 2 and 20 MPa. A plot of dyke strike versus thickness shows that only those dykes that trend north–northwest reach thicknesses in excess of 4 m. Because most of the dykes formed in a direction perpendicular to the minimum compressive principal stress, these results indicate that the time-averaged direction of the minimum compressive stress during dyke emplacement was ENE–WSW. This direction coincides roughly with that of the spreading vector associated with the opening of the Red Sea during the past 5 Ma, suggesting that the regional stress field in this area has been relatively stable since at least 130–140 Ma.