Abstract:
The Paint Lake Deformation Zone (PLDZ), located within
the Superior Province of Canada, demarcates a major structural
and lithological break between the Onaman-Tashota Terrane to
the north and the Beardmore-Geraldton Belt to the south. The
PLDZ is an east-west trending lineament, approximately 50 km
in length and up to 1 km in width, comprised of an early
ductile component termed the Paint Lake Shear Zone and a late
brittle component known as the Paint Lake Fault.
Structures associated with PLDZ development including S-,
C- and C'-fabrics, stretching lineations, slickensides, C-C'
intersection lineations, Z-folds and kinkbands indicate that
simple shear deformation dominated during a NW-SE
compressional event. Movement along the PLDZ was in a dextral
sense consisting of an early differential motion with southside-
down and a later strike-slip motion.
Although the locus of the PLDZ may in part be
lithologically controlled, mylonitization which accompanied
shear zone development is not dependent on the lithological
type. Conglomerate, intermediate and mafic volcanic units
exhibit similar mesoscopic and microscopic structures where
transected by the PLDZ.
Field mapping, supported by thin section analysis,
defines five strain domains increasing in intensity of
deformation from shear zone boundary to centre. A change in
the dominant microstructural deformation mechanism from
dislocation creep to diffusion creep is
observed with
increasing strain during mylonitization. C'-fabric development
is temporally associated with this change. A decrease in the
angular relationship between C- and C'-fabrics is observed
upon attaining maximum strain intensity.
Strain profiling of the PLDZ demonstrates the presence of
an outer primary strain gradient which exhibits a simple
profile and an inner secondary strain gradient which exhibits
a more complex profile. Regionally metamorphosed lithologies
of lower greenschist facies outside the PLDZ were subjected to
retrograde metamorphism during deformation within the PLDZ.
