Abstract:
Rocks correlated with the Hough Lake and Quirke Lake Groups of the Huronian
Supergroup form part of a northeasterly trending corridor that separates 1750 Ma granitic
intrusive rocks of the Chief Lake batholith from the 1850 Ma mafic intrusive rocks of the
Sudbury Igneous Complex. This corridor is dissected by two major structural features; the
Murray Fault Zone (MFZ) and the Long Lake Fault (LLF). Detailed structural mapping and
microstructural analysis indicates that the LLF, which has juxtaposed Huronian rocks of
different deformation style and metamorphism grade, was a more significant plane of
dislocation than the MFZ. The sense of displacement along the LLF is high angle reverse in
which rocks to the southeast have been raised relative to those in the northwest. South of the
LLF Huronian rocks underwent ductile defonnation at amphibolite facies conditions. The
strain was constrictional, defined by a triaxial strain ellipsoid in which X > Y > z.
Calculations of a regional k value were approximately 1.3. Penetrative ductile defonnation
resulted in the development of a preferred crystallographic orientation in quartz as well as the
elongation of quartz grains to fonn a regional southeast-northwest trending, subvertical
lineation. Similar lithologies north of the LLF underwent dominantly brittle deformation
under greenschist facies conditions. Deformation north of the LLF is characterized by the
thrusting of structural blocks to form angular discordances in bedding orientation which were
previously interpreted as folds. Ductile deformation occurred between 1750 and 1238 Ma and
is correlated with a regional period of south over north reverse faulting that effected much
of the southern Sudbury region.
Post dating the reverse faulting event was a period of sedimentation as a conglomerate
unit was deposited on vertically bedded Huronian rocks. Rocks in the study area were
intruded by both mafic and felsic dykes. The 1238 Ma mafic dykes appear to have been
offset during a period of dextral strike slip displacement along the major fault'). Indirect
evidence indicates that this event occurred after the thrusting at 950 to 1100 Ma associated
with the Grenvillian Orogeny.
