Gravity anomaly maps of the Arctic (free-air, Bouguer, isostatic and enhanced isostatic)

Abstract

Free-air, Bouguer and isostatic gravity anomalies of the Arctic regions, derived from 350,000 irregularly distributed gravity observations, were gridded at a 10 km interval and plotted against rock-equivalent topography. All of these anomalies show various degrees of correlation with topography, depending on the type of anomaly, which tend to mask the geological source of the anomalies. As an aid to gravity interpretation, a new type of gravity anomaly, the enhanced isostatic anomaly (EIA), was developed. The EIA emphasizes anomalies related to local geological structures while reducing the regional effects of topography and bathymetry, of crust-mantle interfaces, of continent-ocean boundaries, of glacial loading and of abnormal thermal conditions within the lithosphere. The use of the EIA as an interpretative tool is shown in an example from the Queen Elizabeth Islands. Colour maps illustrate the four different types of gravity anomaly fields of the Arctic regions. Areas of positive EIA are suggested to be associated with relatively young (Late Cretaceous or younger) crust characterized by higher seismicity and heat flow values, and areas of negative EIA with older, more stable crust. On continents, young mountain formations, volcanic areas, and areas with uncompensated sedimentary deposits are characterized by positive EIA, while unmetamorphosed sedimentary basins tend to be located in areas with negative EIA