Geophysical studies on early tectonic controls on Red Sea rifting, opening and segmentation

Abstract

Seismic, gravity and magnetic data are combined with results of structural geology to elucidate the earliest stages of rifting in the Red Sea. The abrupt continent- ocean transition at the Egyptian and Sudanese Red Sea, compared to other margins, suggests that it was created as a transform margin. Following a major plate kinematic re-orientation around 22 Ma, the transform plate boundary became extensional and the Red Sea basin started to open. Formation of oceanic crust by sea-floor spreading is not restricted to the bathymetrically defined axial graben and deeps, but may have started at spreading rates below 5 mm/year, as early as 10–12 Ma. The geometry of the initial rift line is the result of the regional stress field interfering with older lithospheric lineaments that acted as stress guides. The rift follows the path of least resistance by jumping from one available zone of structural weakness to another. This minimizes the energy needed for break-up of the continents. Harmonization of local variations of spreading ridge orientation with the overall regional extension thus determines the original rift geometry. Such a control of old continental lineaments over the segmentation pattern of a developing spreading ridge has probably not only occurred in the Red Sea, but, in a much broader sense, can be applied to the segmentation of mid-ocean ridges in general.