THE USE OF GRAVITY AND MAGNETIC DATA TO DETERMINE THE STRUCTURAL MAKEUP OF BASINS WITHIN THE WESTERN DESERT, IRAQ

The Western Desert of Iraq is part of the northern Arabian Platform, where relatively thin Phanerozoic sediments cover the Precambrian fractured basement complex. The platform is divided into two parts: a stable part which includes the western portion of the Western Desert and an unstable part to north and east of the stable part. The stable part was been unaffected by deformation since the Late Cretaceous as Paleozoic deformation formed a series of basins that vary in depth between 3.5 and 11.5 km. Fault systems within the basins have only been identified by using Landsat TM data due to the lack of seismic reflection and well data. In order to help identify the structure makeup of the basins, an analysis of available gravity and magnetic was undertaken. An isostatic residual gravity anomaly map shows three prominent gravity minima including an north-trending low in the west, a circular low caused by an intrusion or salt diapir in the central Western Desert and a northwest-trending low amplitude low in the eastern Western Desert. These gravity lows that are thought to be the main basins and are separated by a series of NNW-SSE gravity maxima. These reduced to the pole magnetic map in general agrees with the gravity interpretation, however there are some differences related to the magnetic susceptibility variations within the basement.

To further understand the tectonic and the structural makeup of the basins, a derivative and CET (Centre for Exploration Targeting) analysis was applied to the gravity and aeromagnetic data. The CET method is supposed to provide unbiased lineament results, but to test the CET results, a variety of derivative methods (e.g., total horizontal, theta, analytic signal, local phase and local wavenumber) were applied. Lineaments which be related to faulting were determined using maximum values for total horizontal, analytic signal, local wavenumber and zero contours for local phase derivatives. Four sets of lineaments were determined using the CET grid and derivative analysis. These lineaments are thought to be related to the formation of the basins in the Western Desert.