A GEOPHYSICAL STUDY OF SOME GEOLOGICAL STRUCTURES IN THE LOW FOLDED ZONE, NORTH IRAQ
The study area, which is characterized by numerous surface and subsurface structures of NW – SE dominating trend, is located in the Low Folded Zone of Iraq. The gravity responses of these structures are studied. The study is further extended to include the vertical and horizontal variations in density derived from seismic reflection data of two seismic profiles across Jambur structure. Such variations may be helpful in clarifying the sources of some gravity anomalies and also in theoretical modeling.
There are three aims of the present study; the first is to consider these responses, which reflect the effect on the gravity field due to the continuous compression of the Alpine stresses, taking into account that these stresses also have regional effects on the gravity field. Then, the total effects may be removed to obtain a new “corrected field”. The second is to estimate the maximum thickness of the sedimentary cover affected by the Alpine stresses, which might probably be observed in the gravity field “affected depth”, and the third aim is to calculate the gravity response of Jambur anticline from the available seismic data.
The results show that the gravity field responses are observed on the Bouguer map as gravity highs, lows and high gradients. The gravity highs coincide perfectly with the surface anticlines; however, some gravity highs show subsurface extensions. The gravity highs are elongate and narrow ellipsoidal or nose-shaped, whereas their magnitudes range from 1.2 to 8.0 mGal. The gravity lows can be divided into two groups according to their “origin”; the first has good matching with the synclines, while the second may be related to depressions. The shapes of these lows are either elongated and ellipsoidal running parallel to the gravity highs or broad circular shaped. The gravity value of those lows is close to – 2.0 mGal. Some gravity highs and lows are not reflected in the geologic map.
The results also show that the maximum thickness of the sedimentary cover where the Alpine stresses may be observed in the gravity field is about seven kilometers. In addition, two dimensional models of Jambur anticline show that the structure has a residual positive gravity value ranging between 8.0 and 9.0 mGal.