GRAVITY AND GROUND MAGNETIC FOLLOW-UP OF AEROMAGNETIC ANOMALY WEST Al-GHAR'RAF RIVER, SOUTH IRAQ

Abstract

A more detailed gravity and ground magnetic surveys have been executed in a mostly agricultural area, which covers (28 × 40) Km and lies between Al-Nasiriya and Al-Kut Governorates, close to Al-Gharraf River and towards west. The surveys aim to determine deep structures within the sedimentary cover, by following-up a deep source anomaly, which appears in aeromagnetic and Unified Bouguer gravity maps. A net of polygons, including 868 gravity and magnetic stations with spacing interval of 0.5 Km, has been measured. Bouguer anomaly and total magnetic intensity (TMI) maps are constructed. Filters for enhancing shallow and deep source anomalies and high gradient areas were applied to Bouguer anomaly and TMI maps. The Bouguer anomaly map shows a prominent gravity high in ENE – WSW direction. In addition, residual anomalies that may reflect antiforms and synforms or faults are pointed out on this map. Gravity profiles across the gravity high and some residual positive anomalies are plotted. On the other hand, the TMI map shows a magnetic high, which has the same direction, extension, length and location of the gravity high. The magnetic high is, essentially, related to a basement intrusion, and it may be a causative source for the gravity high. Two magnetic profiles across and along this high are displayed. The study of depth maps of four seismic reflectors showed no anomalous structures down to the Permian surface (~ 6000 m deep), while it shows considerable paleostructures on this surface. Moreover, the magnetic high (the intrusion) is older than the Permian, which is (6000 – 9000) m deep. However, local magnetic anomalies (LMA) related to Quaternary gray sand sediments, can easily be recognized throughout the area. The LMA tend to disturb the earth’s magnetic field. However, upward continuation filter is applied to remove the effect of these anomalies.