Magnetic Data for Delineating Subsurface Structures and Estimating Magnetic Sources Depth of Magnetic Intrusive in Farigh Area, Sirt Basin

Abstract

The studied area is characterized by having complex structures that trend mainly in the NW–SE, 
and E–W directions. Magnetic data is used to delineate the subsurface structures and to estimate the magnetic 
sources depth of the selected area in Farigh area, Sirt basin Libya. Power spectrum analysis, Horizontal gradient 
technique, Analytic Signal and 3D Euler deconvolution technique using standard deviation filters have been 
applied in order to achieve the above mentioned goals. Interpretation of the onshore magnetic anomaly of this 
area, suggests that the high total magnetization may be caused by an intrusive body. Analysis of the magnetic 
power spectra indicates the presence of four sub-anomalies at depths of 350 m, 1400 m, and 2525 m which 
probably related to the igneous rocks. The presence of igneous rock as basement at depth of 4740 m was 
confirmed by drilling J1-12. Assuming that all rock magnetization in the area is caused by induction in the 
present geomagnetic field, it strongly suggests that the causative structure has a remnant magnetization of 
declination D= 2.322o
 and inclination (I) = 41.579o
. Based on magnetic data, the total Horizontal derivative 
map shows high gradient values in E-W trends related to the structures in the eastern part of the Sirte basin. 
An analytic signal method was applied to the aeromagnetic data to estimate locations and the minimum depths 
to the contact. The depth values for profiles 1,2,3,4,5 respectively 1400m,1430m, 2744m,2190m and 1415m. 
The depth from well J1-12 is 1400m matched to the depth results from profile 5 (1415m). The 3D Euler 
deconvolution map derived from magnetic data clearly indicates the location of igneous body in the study area 
as well as its tectonic trends and depth, which is estimated at 350 m to 1400 m below the surface. Depth of 
magnetic anomalies at 1400 m to 2525 m is considered as anomalies in between shallow and deep. Anomaly at 
depth of approximately 4740 m below the surface is interpreted as basement rock. Geologically, the magnetic 
survey shows that the source of anomaly is a mafic igneous rock of Early Cretaceous in age. The study also 
discovered a left-lateral sheared fault zone along the NW-SE of Hercynian in age which was believed to be 
reactivated during Early Cretaceous.