A total intensity magnetic anomaly map of the Red Sea and its interpretation

Abstract

All available total intensity magnetic field data have been used to prepare a total intensity magnetic anomaly map of the Red Sea at a scale of 1:2,000,000. These include airborne surveys at various elevations and numerous sea surveys. The data have been digitised at approximately one kilometre intervals and the International Geomagnetic Reference Field (IGRF epoch 1965.0) removed. The resulting values have been upward continued to a common height of 1.83 km (6000 ft), transferred to a base map and contoured at 100 nT intervals. The map is published in colour by the United States Geological Survey - Saudi Arabian Project. The map reveals three distinct zones: (1) large amplitude (approximately 800 nT), short wavelength (15 km peak to trough) anomalies over the axial trough which form lineations roughly parallel to the coastlines, (2) smaller amplitude (approximately 300 nT), longer wavelength (30 km) anomalies over the main trough and shelves which also form lineations parallel to the coastlines, and (3) very variable amplitude (100 to 400 nT), short wavelength (5 to 30 km) anomalies over the shield areas on both sides of the Red Sea. The large, linear anomalies terminate in the north at about 23 °N and in the south at about 15 N. The anomalies over the main trough and shelves converge south of approximately 15.5 N. Several NE trending magnetic features offset the linear, axial anomalies. Such features are confined to zones (1) and (2) and are thought to indicate leaky transform faults. The interpretation of the magnetic data is presented in three parts: the northern Red Sea (north of 24°N), the central Red Sea (18°N to 24°N) and the southern Red S ea (south of 18 N). For each part, there is a discussion of the extent of oceanic crust, the seafloor spreading history, the possible location of transform faults and the relationship of the magnetic anomalies to the deep holes. In Chapter 7, the results are brought together and their significance for Red Sea floor spreading, transforms and plate geometry discussed. The problems of the brine deeps are briefly discussed in Chapter 8.