Magnetic and Gravity Fields over the Red Sea

Strong magnetic anomalies associated with the axial trough of the Red Sea are considered to be related to a second phase of opening. Lack of magnetic expression of the first and wider separation is attributed to initial thinning and necking of the continental crust and, possibly, to a slow rate of spreading. The rise of the mantle during this first stage is reflected in the positive Bouguer gravity anomaly which extends over the whole Sea. A displacement of the magnetic anomaly pattern and a grouping of earthquake epicentres at latitude 19$\frac{1}{2}$ degrees N delineates a transform fault. Futher offsets in the anomaly pattern between 19$\frac{1}{2}$ degrees N and 23 degrees N may be related to other transform faults presently inactive. If Sinai is treated as a separate block then the two-stage clockwise rotation of Africa to open the Red Sea leads to the southerly displacements of this block required by the geology. Negative gravity anomalies in the Gulf of Aqaba support the idea of a shear. A separate rotation of the Horn of Africa is believed to have contributed to the opening of the Gulf of Aden.