A redetermination of the age of the Otto stock by the whole-rock Rb–Sr isochron method indicates an age of 2160 ± 80 m.y., a figure that is substantially greater, by about 450 m.y., than the previously quoted value. This age, which is almost identical to the generally accepted value for the Nipissing diabase, appears to be consistent with both geological and palaeomagnetic observations.

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