Ruby Reid-Sharp HBSc thesis abstract

New expansion along Highway 11/17 east of Thunder Bay, Ontario exposes faults and damage zones that cut through and displace the Gunflint Formation of the Animikie Group, the underlying Archean basement rock, and the basal unconformity between them.  Observations and stereographic projections were used to characterize outcrop-scale deformation along a curved road-cut on a hill approximately 1km long and covering an increase in elevation from west to east (where the unconformity is exposed) of about 65m.  The Highway 11/17 road-cut exposes a fault zone network that has accommodated a minimum of 60m of vertical displacement and unknown horizontal displacement.  Two sets of well-preserved slickenlines record normal oblique sense movement on the fault zone.  A void-filling calcite vein system is exposed in conjunction with the fault systems and is associated with brecciation.

Calcite crystals reach up to 10cm in diameter where larger voids are filled.  At least two major fault zones with damage zones at least 1m wide are exposed at the study site and are seen at the far east and far west of the road-cut.  The Eastern Fault Zone (EFZ) has an average strike and dip of 071°/72° cutting through both Archean basement rock and Gunflint Formation.  The Western Fault Zone (WFZ) average strike and dip is 067°/65° and cuts through Gunflint Formation rocks.  Two relatively minor reverse faults strike 345° and dipping 48° to 58° cut through the Gunflint Formation about 80m southwest of where the WFZ first appears.  The relationship between EFZ and WFZ is obscured by an oblique fault cutting through Archean rock between them with an average strike and dip of 040° and 60°.

The site is a potentially important study location for understanding fault/fluid interactions and how extensional faulting can accommodate fluid transportation.  All major extensional features in the study area have a roughly northeast strike which aligns well with the orientation of the Mid-Continent Rift to the southeast suggesting that this fault zone is associated with extension ca.  1Ga.