Aeromagnetic-Anomaly Maps of Central and Western Saudi Arabia
Hani M. Zahran, Ian C.F. Stewart, Peter R. Johnson, and Mabrouk H. Basahel
Regional geophysical surveys have been conducted in central and western Saudi Arabia for more than four decades. They were mainly done under the auspices of the Deputy Ministry for Mineral Resources and the results are now archived for safekeeping and further processing by the Saudi Geological Survey. The acquisition of regional aeromagnetic data commenced with 11 surveys flown in 1962 over mineral prospecting areas in the Precambrian rocks of the Arabian shield followed in 1965-66 by a comprehensive survey of the remaining parts of the shield (fig. 1 and table 1). These surveys used terrain clearances of 150 m and 300 m, a line spacing of mostly 800 m although, in detail, the spacing varied between 500 m and 2000 m, and analog recording methods. Small areas of the shield and coastal plain, including areas covered by Tertiary flood basalt (harrats), were filled in by separate surveys flown at various times between 1976 and early 1983, at a line spacing of 2500 m and terrain clearance of 300m, and the central Red Sea was covered in 1976 by a survey commissioned by the Saudi-Sudanese Commission. Phanerozoic rocks in a zone about 200 km wide flanking the shield (the “cover rock survey”) encompassing an area of about 450,000 km2, were flown in 1982 and 1983, at a terrain clearance of 120 m and, line spacing of 2 km, using digital data recording methods. For the shield, the regional magnetic data were compiled by the individual contractors into contour maps at various scales between 1:50,000 and 1:1,000,000, using optimum methods at the time of processing. Georgel and others (1990) digitized the early analog data and produced TMI (total magnetic intensity) and RTP (reduced to the pole) maps, in which the data were continued upward to 800 m above ground level. These maps give a useful indication of the regional variations in the magnetic anomaly field, although they tend to lack fine detail. Analyses of the shield magnetic data were done by Hase (1970) and Blank and Andreasen (1991), and an overall analysis of the magnetic patterns in the shield was carried out by Johnson and Vranas (1992). The cover rock survey data were analyzed, at a regional scale, by Phoenix Corporation (1985), and locally in greater detail (e.g. Griscom, 1982). An early interpretation of magnetic data over the Red Sea was given by Hall (1979). Some of the early shield magnetic maps suffered from a pronounced north-south gradient due to poor definition of the International Geomagnetic Reference Field (IGRF), which was rectified in later compilations. For the purpose of this Open-File report, the magnetic survey data for the shield, Phanerozoic rocks, and Red Sea were reprocessed from the line data, yielding considerable improvement in data quality, great reduction in noise, and consequent enhancement of detail. Optimum techniques were employed to merge the data to give the grids used as the bases for the maps displayed here.
Zahran, H.M., Stewart, I.C.F., Johnson, P.R., and Basahel, M.H., 2003, Aeromagnetic-anomaly maps of central and western Saudi Arabia: Saudi Geological Survey Open-File Report SGS-OF-2002-8, 4 p., 1 fig., 1 table, 4 plates.