Abstract
The aim of this study is analysis of gravity and magnetic data to delineate the tectonic features of Concession 6, which located in the central part of Sirt Basin of Libya. The data that used in this study is about 8871 gravity values were made available from Libyan Petroleum Institute (LPI). The magnetic data made available from Magnetic Mapping Project (AMMP) by Libyan Petroleum Institute. The international Geomagnetic Reference Field (IGRF) was removed from the original data using Geosoft Package software. Based on analysis of the Bouguer gravity map, it showed numerous anomalies varying from high gravity anomaly expression in the north (Al Jahamah Platform) with the maximum value 9.4 mGal to low gravity expression in the Maradah trough with minimum value -32 mGal. The most structural features in the study area are characterized by NW-SE trend directions, which related to the Late Cretaceous rift that affect the entire of the Sirt basin. The Total Magnetic Intensity (TMI) map reflects high magnetic anomaly with value of 115 nT in north part of study area (Al Jahamah Platform) and reflects low magnetic anomaly with value -50 nT in the Maradah trough. Both the Reduction to magnetic Pole and Pseudogravity anomalies maps generally reflects structural trend NW-SE direction. Several techniques were applied to the Bouguer gravity and total magnetic intensity to delineate subsurface structures. Total horizontal derivative for gravity and magnetic data, upward continuation to different levels, regional gravity and residual maps were obtained, while magnetic maps were obtained Reduction to the pole and pseudogravity maps. The total horizontal derivative maps of gravity and magnetic data show faults lineaments can be interpreted as structural trends. High gradient values delineate NNE-SSW and N-S lineament occurs over the southern part of study area that is well indicated by the total horizontal derivative. Upward continuation was applied to the Bouguer gravity anomaly in order to enhance the deep seated features (regional gravity map) by using various of cutoff-wave numbers 10,15,20,25,50,75 km. Finally, it had found that the best cutoff-wave number is 25 km. The residual gravity anomaly is calculated by separated the regional anomaly from Bouguer anomaly. The residual gravity anomaly was characterized by positive anomaly in the northern part dominant NW-SE trend, and also the trends in southern and central part were orientation NW-SE trending anomalies. A strong N-S trend was in the southern part of the study area which reflects to the Hagfa trough (Maradah Trough). Reduction to the Pole (RTP) map was characterized by low and high frequencies anomalies. The elongated negative anomalies with values between -28 to -135 nT where observed over Zaltan Platform. These anomalies were characterized by high frequency and high amplitude. Pseudogravity anomaly is obtained from TMI used a density contrast 1 g/cc and magnetization was 0.5 gauss such that transformation makes the TMI behaves like gravity data.. Further investigation is recommended by using such as gravity and magnetic modeling, well logging data, seismic, …..etc.