Proterozoic Geology: Selected Papers from an International Proterozoic Symposium
Proterozoic magnetic overprinting and tectonics of the Laurentian Shield
Published:January 01, 1983
David J. Dunlop, Larry D. Schutts, 1983. "Proterozoic magnetic overprinting and tectonics of the Laurentian Shield", Proterozoic Geology: Selected Papers from an International Proterozoic Symposium, L. G. Medaris, Jr., C. W. Byers, D. M. Mickelson, W. C. Shanks
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The NRM (natural remanent magnetization) of a metamorphic rock is the vector sum of primary NRM and one or more secondary overprints. Magnetic overprinting is a thermal or chemical effect resulting from (1) burial and uplift (regional heating), (2) intrusive activity (local heating), or (3) hydrothermal supercritical solutions (local heating and/or alteration. We present a number of examples drawn from the Proterozoic of North America illustrating how paleomagnetists decipher magnetic overprints and use them to date and interpret tectonic events. Granites from the western Superior Province record the 2600 Ma Kenoran orogeny and an event at 1250 Ma, perhaps related...