Ideal body analysis of the Pomerania Gravity Low (northern Poland)

Abstract

The large negative residual Bouguer gravity anomaly in northern Poland called the Pomerania Gravity Low (PGL) was analysed using Parker’s ideal body theory. A residual gravity anomaly along the profile was inverted to find bounds on the density contrast, depth, and minimum thickness of its sources. As the ideal body reaches the surface, the greatest maximum negative density contrast is –0.038 g/cm3, while the body itself has a thickness of 52 km. If 8 km is taken as a depth to the source body top, the density contrast must correspond to at least –0.092 g/cm3, with a maximum allowable thickness of 18 km. The ideal body inversions show that the depth to the body top cannot exceed 15 km. Assuming a geologically reasonable maximum density contrast as small as –0.2 g/cm3, the source body top can be no deeper than 11.5 km, and its thickness greater than or equal to 6 km, assuming it extends up to the Earth surface, or greater than or equal to 7 km, when its top is below 8 km depth. It can be hypothesized that the main source of the negative gravity anomaly is related to a predominance of felsic rocks in the Paleoproterozoic Dobrzyń Domain of the East European Platform basement.