Regional variations of deformation mechanisms in the Lorrain Quartzite near Whitefish Falls, Ontario, Canada /
Abstract
The quartzite microfabric found in the Lorrain Formation was studied across the La
Cloche syncline, along a regional north-south transect along highway 6, near Whitefish
Falls, Ontario. The complete stratigraphic sequence across the syncline is preserved, and
is present on each fold limb. The lithostratigraphic units with the smallest grains size and
lowest mica content are located close to the core of the fold, while coarser grained mica
and feldspar rich units are situated at the northern and southern most extent of the
transect. Deformation mechanisms vary with lithology and with position across the fold.
Pressure solution appears to be the dominant deformation mechanism in the feldspathic,
micaceous and ferruginous units. In the finer grained, mica poor white medium grained
and cherty sandstone units, grain boundary migration (GBM) characteristics show
dominance over those of pressure solution and show high amounts of fracturing which
cut migrated boundaries and therefore post date GBM. All samples across the fold
display a preferred orientation of quartz c-axes. The senses of asymmetry of fabrics are
found to be similar across the syncline, with the exception of the ferruginous sandstone
unit. Formation of these similar fabrics synmietries can not be the result of strain related
to first order folding. The mica content appears to be related to the percentage of quartz
lost due to pressure solution as a result of strain; the more mica present, the less quartz
was lost. Calculations based on the shape of initial grains suggest that conservatively
30% of the quartz volume has been dissolved out of the Lorrain quartzite, and potentially
migrated hundreds of meters to other members of the Huronian Supergroup as there was
no meso or macroscopic evidence observed in outcrop.