GEOPHYSICAL AND PETROLOGIC INVESTIGATIONS OF INVERSELY CORRELATED AEROMAGNETIC AND BOUGUER GRAVITY ANOMALIES WITHIN PRECAMBRIAN GNEISS TERRANE NEAR GARVIN, SOUTHWESTERN MINNESOTA

Abstract

Geophysical models and petrologic inferences presented here are consistent with a buried gabbroic to noritic intrusion as the principal source of two geographically coincident, kilometer-scale, inversely correlated gravity and magnetic anomalies (the Garvin anomalies) located within Archean continental crust near the present-day southern margin of the Superior Craton in Minnesota. Two-dimensional profiles modeled from the total magnetic anomaly, reduced to pole, and the Bouguer gravity anomaly, upward-continued to 2 kilometers, are fit to geologically reasonable distributions of source rocks that have density and magnetic susceptibility values within the ranges reported for gabbro or norite intrusions.