Spectral Analysis of Aeromagnetic Data Over the Precambrian Shield and Phanerozoic Cover Rocks, Kingdom of Saudi Arabia

SGS-TR-2007-2 Ian C.F. Stewart and Peter R. Johnson
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The aeromagnetic data over the Saudi Arabian shield, Phanerozoic cover rocks and central Red Sea has been completely reprocessed and merged to produce a high-quality total magnetic intensity (TMI) grid suitable for use in regional structural studies.   The reduced-to-the-pole (RTP) grid derived from the TMI grid has been used here in a systematic study of the depth to magnetic sources across the whole map area.  Two-dimensional spectral analysis using automated methods has been used with window sizes varying from 50 km to 400 km to estimate source depths at 10 km intervals.  This has enabled magnetic sources from the near surface down to the base of the crust to be imaged.  Using the smallest spectral windows the basement surface under the cover rocks increases to depths of about 4 to 5 km at distances of 200 km from the shield, with depths down to about 7 km in the far north of the map area.  For the larger spectral windows source depths at mid-crustal levels are calculated.  Although some depths towards the base of the crust are found, the analysis has not enabled any layer in the lower crust that could unambiguously be correlated with the Curie point to be identified.  It is possible that the longer wavelengths in the RTP are of too low amplitude to enable the analysis to determine the Curie depth consistently across the grid, especially in the presence of high amplitude and short wavelength anomalies over much of the area.  One interpretation of the present results is that the Curie temperature is unusually shallow over much of the map area, in the mid crust at about 20 km depth.  There are several regions of limited extent where greater depths are observed, such as the northward extension of the Ad Dawadimi zone in the eastern shield.



Stewart, I.C.F. and Johnson, P.R., 2007,  Spectral analysis of aeromagnetic data over the Precambrian shield and Phanerozoic cover rocks, Kingdom of Saudi Arabia: Saudi Geological Survey Technical Report SGS-TR-2007-2, 33 p., 26 figs.