Abstract

The Thessalon basalts outcrop in Ontario on the north shore of Lake Huron near the base of the Huronian Supergroup in the Southern tectonic province. After alternating field and thermal demagnetization on 230 specimens from 23 sites, a stable high coercivity remanence in titanomagnetite was isolated giving a direction of 304°, 54° (α95 −7°). The pole position of 169°W, 47°N (7°, 9°) corresponds to the primary age of 2375 ± 75 Ma based on geologic evidence and radiometric data from other units. Thus, the magnetite remanence predates the reset Rb–Sr isochron age of 2040 ± 50 Ma determined for the basalts. Viscous remanence directions confirm the petrologic evidence that the basalts have not been metamorphosed much above lowest greenschist facies. Existing North American Paleoaphebian paleomagnetic data are critically evaluated and a conservative apparent polar wander path drawn. The Thessalon volcanics were extruded at a middle paleolatitude of 35° indicating that the contemporaneous Blind River – Elliot Lake uranium deposits were formed in a warm temperate climate.

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