Depth: 32 km
The available magnetic data provide a great deal of information about the geology of the central and western areas of the Kingdom of Saudi Arabia and the areas bounding the Red Sea (Fig. 8). The structural elements are shown, such as fractures, shear zones, the Daraz between the Precambrian topography and dikes, in addition to the intrusive rocks.
The major geologic structures of the Arabian Shield correlates with the magnetic anomalies. The magnetic anomalies also revealed new structures that were not recognized in the field.
The change in the texture noticeable in some maps of the Cenozoic basalts is due to the increased altitude of the aircrafts used during the survey of the Harrat (2,000–2,500 m). This, in turn, resulted in the loss of details.
Other noticeable features are shown in the anomalies that are within the range of strong negative frequencies (blue). It is expected that the magnetic anomalies are positive (red) due to the amplification of the current magnetic field of earth. Negative anomalies probably exist intensively due to the remaining magnetization in the reverse direction of the current field. This characteristic is known as the Al Haya Al Adasiya rocks existing along the shear zones in the Arabian Shield.
As a general principle, the magnetic field in the Arabian Shield is governed by the magnetic properties of the rocks which underlie the Shield in the western area of the Kingdom of Saudi Arabia and the Phanerozoic rocks in the central part of the Kingdom. The sedimentary rocks were originally transparent(?) and magnetic, but at the scale of the map shown here, magnetic anomalies are not registered. So, the magnetic field in this eastern part of the Shield indicates that the underlying rock formations belong to the Precambrian rocks, and are designated as the magnetic base.