In this first dating study of the Thanet gabbro complex from the Hastings Basin area we have obtained K–Ar evidence to support the geological contention that this pluton (and, by inference, others nearby) has escaped the severity of the Grenvillian metamorphic overprint. Specifically, a reliable date of 1200 Ma for a hornblende demonstrates that this body was emplaced at least 100 Ma earlier than the peak of metamorphism in the adjacent Haliburton Highlands.From considerations of possible cooling histories and a proposed Grenville apparent polar wander (APW) curve we deduce that only the Thanet magnetization component with the lowest laboratory blocking temperatures (Th3) was likely acquired as a thermoremanent magnetization, whereas the other two components were probably acquired as low-temperature chemical remanent magnetizations. Furthermore, the Th3 component was likely set before 1.0 Ga, consistent with our earlier proposed Grenville Loop.

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