Abstract

At Cobalt the Nipissing diabase intrusive occurs as a 1000 ft (~305 m) thick undulating sheet exposed in a series of basin and arch structures from which 112 specimens were collected at 14 sites. Paleomagnetic analysis of the cleaned natural remanence directions from the 11 acceptable sites suggests that these structures are dominantly primary. Minor post-solidification compression associated with the NW–SE trending faults may have amplified the primary NE–SW axial trends of the structures. Significant folding adjacent to the faults does not appear probable. The origin of the narrow argentiferous veins is probably related to minor local differential movements of large blocks of diabase or to cooling-contraction of the sheet. A revised pole position of 91.9 °E, 19.4 °N (dp = 3.9°; dm = 6.5°) is given for the 2140 m.y. old Nipissing diabase.

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