Abstract
A traverse across Precambrian rocks of the Superior Province in central Manitoba provided 56 samples for magnetic study from the Pikwitonei granulite domain and the adjacent Cross Lake subprovince. These rocks represent a cross section of the continental crust presently exposed at the surface. Thirty-one samples are dominantly paramagnetic, and three contain pyrrhotite. Twenty-two samples from silicic plutonic rocks, which make up about 80% of the section by volume, contain nearly pure magnetite and have susceptibilities that are almost constant between room temperature and 540°C, averaging about 1 × 10 −2 SI units. The mafic supracrustal rocks, with much higher iron content, are about an order of magnitude less magnetic because they contain little or no magnetite. Susceptibility is generally independent of metamorphic grade or apparent depth in the crust. The discrepancy between induced magnetizations of measured lower crustal rocks and the source requirements of long-wavelength magnetic anomalies may be due to a high-temperature viscous magnetization in the deep crust.
Published Version
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