France Lagroix HBSc thesis abstract

The Rainy Lake - Bad Vermilion Lake anorthosite intrusion, is found in the Rainy Lake Wrench Zone (RLWZ) of the Quetico belt, in the Superior Province of the Canadian Shield.  It has a sigmoidal NE-SW to E-W orientation and dips steeply to the northwest.  The sigmoidal form cuts across the width of the RLWZ.

Anisotropy of magnetic susceptibility (AMS) fabric is controlled by paramagnetic chlorite and biotite, while anisotropy of anhysteretic remanence magnetism (AARM) fabric is controlled by ferromagnetic pyrrhotite and magnetite.  On the southern boundary of the RLWZ, AMS fabric is offset anticlockwise with respect to AARM fabric, consistent with dextral shearing.  In the interior, the AMS fabric is offset clockwise with respect to AARM fabric, suggesting the existence of conjugate faults with sinistral motion within the interior of the RLWZ.

Thermal demagnetization uncovered two meaningful components.  Principal component analysis (PCA) defined an A - component with a mean orientation of 318°/-29° and a B -component with a mean orientation of 004°/67°.  The orientations are consistent with a progressive northward tilting of the intrusion through time.  Coupled with smeared demagnetization curves, indicating syn-rotational magnetization, northward tilting is compatible with northward subduction.