Perry A. Sarvas HBSc thesis abstract

Immediately north of Thunder Bay, Ontairo, Archean rocks of the Western Superior structural province are exposed.  Near the small community of Lappe, in the present study area, well stratified metasedimentary rocks are in contact with metavolcanic rocks.

The metasedimentary rocks consist of greywackes, siltstones, mudstones and turbidites.  The metavolcanic rocks are predominantly massive flows of basic to intermediate composition.  Both major rock types have been affected by a low grade metamorphism.  Graded bedding and flame structures in the metasedimentary rock exposures are generally well preserved, but the directions of younging and bedding orientations of the metavolcanic sequences could not be determined.

A variably developed cleavage is present in exposures of both major rock types.  The cleavage is shown to be axial planar to dominant, sideways-closing folds in the region.  Reversals in structural facing directions indicate that the cleavage developed in previously deformed rocks.

Structural facing also indicates that the stratigraphy, as a whole, becomes younger to the southwest or northeast.  In parts of the study area, the metavolcanic rocks appar to stratigraphically underlie metasedimentary rocks, while in other parts of the area, the metavolcanic and metasedimentary rocks appear to be interlayered.  Elsewhere, the stratigraphic relationship is not clear.  In any case, it is quite possible that deformation events affected both metavolcanic and metasedimentary rocks.  Evidence of polyphase deformation indicates that the contact between the two major rock types is complex.