Effect of erosion on gravity and magnettic signatures of complex impact structures: Geophysical modeling and applications

The changes in the gravity and magnetic anomalies of meteorite impact structures as a function of erosion have been investigated. The model structure represents a typical midsize, complex impact crater in the Precambrian target rocks, with a diameter of 30 km and a height of the central uplift of 1.5 km. We used a three-dimensional forward modeling technique. Six erosional levels from 1 to 6 km which successively followed the crater formation time, were modeled from the time of primary erosional leveling of the surface to the time when the structure was completely eroded. In the gravity field, the major effect of erosion is a pronounced decrease in the amplitude of the negative anomaly, with only minor change in its diameter (or half-width), making the gravity anomaly to appear progressively more flat. The amplitude of the central positive anomaly due to the structural uplift also decreases with erosion but not as rapidly as the main anomaly. The diameter of the central gravity anomaly is unaffected by erosion. The model agrees with observations of gravity amplitudes and erosion levels of thirteen impact structures with diameter ranges of 20-40 km. The magnetic anomalies also change during erosion but in a more complex way than the gravity anomalies. Moreover, the shape and amplitudes of magnetic anomalies and their changes due to erosion are latitude-dependent. Therefore, the magnetic data and modeling results presented in this chapter are valid only for Fennoscandia.