Long-wavelength aeromagnetic anomalies and deep crustal magnetization in Manitoba and Northwestern Ontario, Canada

Abstract

A new type of aeromagnetic anomaly map (a long-wavelength anomaly map with anomaly widths in the range 60 km < λ < 4000 km) is presented for the area. It is believed that this group of anomalies represents a physically distinct field. This field shows considerable correlation with the broad features of deep crustal structure as derived from seismic sounding; linear relationships were found between the field and depths to the bottom of the crust and to the boundary between the upper and the lower crustal layers, as well as to the thickness of the lower crustal layer. A theoretical relationship connecting structure on magnetized layers to magnetic anomalies is given showing that the linear relationships are to be expected. It is shown that the lower crustal layer is the most likely source of the anomalies, with an intensity of magnetization of 5.3 X 10^-3 emu/cc. It is also indicated that the upper crustal layer could also be the source, but that a shallow plate of magnetization could not explain the anomalies. Thus deep crustal magnetization must (on all interpretations made in the present paper), be responsible for the long-wavelength anomalies. Also, these anomalies are strongly related to major features in surface geology.

          ARK: https://n2t.net/ark:/88439/y012135

Permalink: https://geophysicsjournal.com/article/171