Abstract
An anistropy of magnetic susceptibility (AMS) study of the relatively fresh Mealy diabase dyke swarm indicates a correlation between the AMS and the deformational effects in the rocks. Several AMS components were revealed during experimental work on 211 samples that had been heated to 640°C during a paleomagnetic study and 22 fresh samples progressively treated in alternating fields. Seventeen sites with slight or no deformation have a magnetic fabric composed of two major components. The stable component, attributed to a primary shape anisotropy, has minimum and maximum principal susceptibility directions preferentially oriented vertically and along dyke strike (≈N 60°E), respectively. This configuration is consistent with an origin due to a post‐emplacement stress field, whereby horizontal extension acted on a vertical sheet of partially crystallized magma. The orientation of this component with respect to the present horizontal suggests that the dykes have not been tilted since their emplacement. The unstable component, removed by fields up to 250 mT, is attributed to induced (domain) anisotropy produced by mild tectonic stress during the Grenville Orogeny. The approximate orientation of its principal components, as found by the method of substitutional ellipsoids, suggests an east‐west‐directed maximum stress. Four other sites with noticeable deformation have magnetic fabric that could not be reliably analyzed, but which may be largely composed of domain and stress‐induced anisotropies developed during the Grenville Orogeny.
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