David A. Baker HBSc thesis abstract

A Paleomagnetic Study of the Logan Sills, Northwestern Ontario

David A. Baker - 2001

A total of 74 oriented samples were collected from the Proterozoic Logan Sills of Northwestern Ontario.  The anisotropy of magnetic susceptibility (AMS) of 207 cores drilled from the 74 oriented samples was measured.  The magnetic foliation which defines the average magmatic flow plane shows that the flow was subhorizontal with flow axes varying between sample locations; however a NE-SW flow axes dominates.  This is approximately perpendicular to the Nipigon Rift.

The natural remnant magnetism (NRM) was used to determine the Koningsberger ratio of all 74 samples.  The average value is 1.060 " 0.166, with a standard deviation of 13.856.  This advocates great caution in the interpretation of aeromagnetic or ground magnetic surveys, because remanent magnetization may mask the induced magnetization due to the present geomagnetic field.

Progressive thermal demagnetization of 74 oriented samples in 10 steps from 100°C to 560°C revealed stable components by principal Component Analysis (PCA).  These sample show both upward and downward primary remanence directions, as well as a downward secondary.  Some, but not all of the principal components correspond to the Proterozoic apparent polar wander path (APWP) for North America.  The anomalous principal components have yet to be explained.