Interpretation of Magnetic Anomalies of Salt Range of Pakistan

Abstract

The analysis of the magnetic maps shows that study area is divided into positive and negative strips/belts extending northeast-southwest. These strips/belts seem to be defining the fault pattern. The distribution of magnetic anomalies in these features points out an extensive diapiric activity in the area. This activity coupled with the thrusting of the sedimentary wedge towards south on the ductile Salt Range formation developed several anticlinal and synclinal features which are marked respectively by the positive and negative anomalies in the study area. The proven anticlinal features of Lilla, Khewra, Warnali, and Vasnal are associated with positive residual magnetic anomalies and Dhariala, Kallar Kahar, Bhadrar, Chakri and area southwest of Pail are associated with negative magnetic anomalies. The differentiation in this case, lies within the proportional thickness of paramagnetic and diamagnetic lithologies. It is one of the conclusion that negative anomalies are representing the anticlinal/domal structures having the greater proportional thickness of Salt Range formation and Nilawahan group which are behaving as diamagnetic lithologies. The anticlinal/domal structures with positive magnetic anomalies would be associated with relatively greater thickness of Siwalik and Jhelum groups behaving as paramagnetic lithologies. Residual anomaly map has also shown clearly the Salt Range frontal fault, continuation of Diljaba thrust to Nilawahan fault and the character of Kallar Kahar fault. The two anomalous zones in the south western half, north of Khushab and around Katha Sughral, apparently seems to be local features, however, the depths of these features categorize them the basement features, as the supra-basement and intra-basement anomalies respectively.