Moving-window Poisson analysis of gravity and magnetic data from the Penokean orogen, east-central Minnesota

Analytical correlation of gravity and magnetic data through moving-window application of Poisson's theorem is useful in studying the complex Precambrian geology of central Minnesota. Linear regression between the two data sets at each window position yields correlation, intercept, and slope parameters that quantitatively describe the relationship between the gravity and magnetic data and, in the case of the slope parameter, are often accurate estimates of magnetization-to-density ratios (MDR) of anomalous sources. In this study, gridded gravity and magnetic data from a 217.6 x 217.6 km area in central Minnesota were analyzed using a 8.5 x 8.5 km window. The study area includes part of the Early Proterozoic Penokean orogen and an Archean greenstone-granite terrane of the Superior Province. The parameters derived by the moving-window analysis show striking relationships to many geologic features, and many of the MDR estimates agree with rock property data. Inversely related gravity and magnetic anomalies are a characteristic trait of the Superior Province, but moving-window analysis reveals that direct relationships occur locally. In the Penokean fold-and-thrust belt, gravity and magnetic highs over the Cuyuna range produce a prominent belt of large MDR estimates, which reflect highly deformed troughs of iron-formation and other supracrustal rocks. This belt can be traced northeastward to sources that are buried by 3-5 km of Early Proterozoic strata in the Animikie basin. This configuration, in conjunction with recent geologic studies, indicates that the Animikie strata, which may represent foreland basin deposits associated with the Penokean orogen, uncoformably overlie parts of the fold-and-thrust belt, and that earlier stratigraphic correlations between Cuyuna and Animikie strata are wrong. The results of this study indicate that moving-window Poisson analysis is useful in the study of Precambrian terranes.