Suppression of dominant topographic overprints in gravity data by adaptive filtering: southern Wyoming Province

Abstract

In areas of the world with a protracted tectonic history, the gravity field may be dominated by anomalies due to individual structural features developed during the latest tectonic event. These individual tectonic features often have a topographic expression. Adaptive filtering techniques can be used to suppress the gravity effects of such features. Iterative space domain techniques are particularly well suited to these types of problems. One such technique, the stochastic gradient algorithm, allows easy updating of filter coefficients at each spatial step through the data. This approach eliminates windowing and spectral estimation problems associated with cross-spectral admittance schemes. In this study, adaptive filtering of Bouguer gravity and topography in the southern Wyoming Province was successful in suppressing gravity signatures of Laramide structural features. The regional gravity trends due to isostatic effects were significantly absent from the residual anomaly map. A large, continuous, positive gravity anomaly stretching from the southern Wind River Range to the northern end of the Laramie Range was another outstanding feature observed in the residual anomaly. This positive anomaly is about the same magnitude, size and shape as anomalies due to greenstone belts observed in other Archean cratonal areas. Scattered occurrences of greenstone lithologies are known throughout the area of the anomaly, but a continuous feature is absent in outcrop. Due to the unusual structural history of the area, it is possible that such a continuous belt does exist, but was buried at shallow crustal levels by Laramide thrusting, or later collapse of a Laramide uplift due to a change in the regional stress field.