Abstract

The significance of Grenville poles and the validity of some of the models that have been postulated to explain their apparent incompatibility with the North American apparent polar path are examined. Different models are briefly reviewed in terms of the Grenville St-Urbain pole (StU) which simply falls in its expected location on the most probable North American path. The StU pole derived from a hematite remanence is associated more closely with magnetite poles than hematite poles and this poses serious objections to some of the models reviewed. A few problems inherent to the study of multicomponent remanences are discussed: the recognition of all components, the sequence of remanence acquisition of the components, the absolute age and origin of each component, and most importantly the clear separation of the components. As they can be isolated by thermal treatment. hematite remanences are usually more accurate indicators of the magnetizing field than magnetite remanences which may be biased by an underlying hematite remanence. Furthermore, magnetite remanences obtained from limited experimental work may not be the initial remanences. Of much interest in the discussion of some models is the resolution that can be expected from paleomagnetic data, and which is not expressed statistically. The relatively simple (single remanence) St-Urbain results are inspected in some detail and used to demonstrate the inaccuracies in pole determination that may evolve from dual polarity remanences. They also raise questions about the validity of closely spaced sequential poles. The St-Urbain and other recent results from Interior Laurentia show that most of the Grenville poles can be explained without necessitating any special modelling. At the present, only the most southerly Grenville poles cannot be accounted for and it is suggested they may belong to a segment of a yet incomplete North American apparent polar path.

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