Crustal magnetization and long-wavelength aeromagnetic anomalies of the Minto block, Quebec

Abstract

Measured susceptibilities of >3500 samples from a 500×500 km area of the Minto block, Superior province, Quebec, have an average value of ∼0.03 SI (equivalent to induced magnetizations of ∼1.5 A/m). Charnockitic lithologies (igneous orthopyroxene-bearing granodiorite, granite, diorite), that constitute large parts of the Minto region, yield the highest susceptibilities. The variations in susceptibility show a good correlation with the variations in the observed magnetic field, including those at long wavelengths (>100 km), suggesting that charnockitic and related granitoid rocks could be responsible for the long-wavelength anomalies. Modeling of a magnetic profile perpendicular to the strike of mapped lithotectonic subprovinces in the Minto block supports this contention. Charnockitic lithologies are not usually considered a possible sources of long-wavelength anomalies: mafic rock types are generally favored. The dominant Minto lithologies are more felsic but are more efficient in the production of magnetite from the available iron. Copyright 1999 by the American Geophysical Union.