by trains of quartz crystals and by moderately anasta-
mosing selvages now filled with fine opague material, seri-
cite and muscovite. Some of the mylonite has aligned
micas distributed randomly throughout the matrix of fine
grained recrystallized quartz. These mylonitic features are
developed to some degree in most rocks of the Snowshoe
Group. They are, however, gradational with flow features
related to folding and therefore their regional extent
depends upon a somewhat arbitrary division of the
gradation.

The age of the mylonitization is confined between the
age of the Snowshoe Group (pre-Permian) and the uncon-
formably overlying Quaternary deposits. It can be further
constrained through various assumptions and inferences.
The youngest part of the Snowshoe Group may be Paleo-
zoic and therefore shearing may be post-Cambrian. The
peak of metamorphism mainly postdates the shear fabric.
The time of freezing of the metamorphic minerals is not
known but regionally is considered to be Jurassic. Locally
garnet is involved in the shear, but it is not known
whether this is due to younger superimposed shear or if
the freezing of the garnet was a protracted event cover-
ing a considerable period. The most precise age of the
mylonite is determined by first assuming it was the result
of the emplacement of the Crooked Ampibolite and sec-
ondly, by correlating the Crooked Amphibolite with the
Antler Formation. The Antler Formation was thrust over
the Barkerville and Cariboo terranes after the Permian
and prior to the Upper Cretaceous.

The shearing event responsible for the mylonitization
may be responsible for the development of a regional
bedding-cleavage within the Snowshoe Group. These
features are the first phase of the structural sequence of
the Snowshoe Group structural package.

Bedding-parallel cleavage

Bedding-parallel cleavage occurs in almost all rocks of
the Snowshoe Group and was recognized by all previous
workers. It is folded and crosscut by spaced crenulation
cleavages. Locally within the Ramos succession near
Keithley Creek and Sovereign Mountain there are fold
hinges with no bedding-parallel cleavage.

The bedding cleavage may be the regional conse-
quence of the shearing event as portrayed by the mylo-
nite concentrated at the contacts with the Crooked and
Island Mountain amphibolites. Such a structural system
would likely have isoclinal recumbent nappe-like folds,
however, the size of those folds is unconstrained.

Rootless isoclinal folds

Campbell et al. (1973) and Sutherland Brown (1957) sug-
gested the bedding cleavage was the consequence of inter-
bed slip and that it had no associated isoclinal folds.
Rootless hand-size isoclinal folds lie parallel to the bed-
ding cleavage and some of them may have formed in the
early stages of cleavage development. Known reactiva-

68

tion of the bedding cleavage surfaces leaves some doubt
that all rootless isoclinal folds were formed early. Meso-
scopic isoclines with the bedding cleavage as axial sur-
faces exist locally. Regional isoclinal folds associated with
the cleavage are not unequivocally known (see Struik,
1982a). Shear structures are the first phase of the cleav-
age and fold progression of the structural package of the
Snowshoe Group.

Ductile shortening

Cleavage, folds and faults included in this category repre-
sent a period of ductile shortening superimposed on the
bedding-parallel cleavage and in part on the shear fabric.
The shear fabric itself is a consequence of ductile shor-
tening and the two categories in this way are intermeshed
and transitional.

Cleavage and folds

Two or more sets of cleavage and folds are formed under
conditions of ductile flow. The earlier, relatively more
ductile set may include undifferentiated earlier cleavage
and folds. Folds of both sets are asymmetric with mod-
erately to shallowly dipping cleavages. The folds lean
towards and the cleavage dips away from an axis (the
Lightning Creek Anticlinorium, Fig. 49) that traverses
the area from northwest to southeast. The folds are simi-
lar, range from open to isoclinal, and trend mostly north-
west. Deviations from the northwest trend are most pre-
valent southwest of the Lightning Creek Anticlinorium
(Fig. 50). The highest grade of metamorphism is recorded
in, and partly overprints, the cleavage of the first set.
Cleavage everywhere is defined by muscovite, although
locally it coexists with chlorite or biotite.

Set 1 cleavage. This set is defined everywhere by musco-
vite and locally by biotite. Garnet grew approximately
at the same time as the biotite, and together they repre-
sent the highest grade of metamorphism recorded in the
area. The cleavage overprints the earlier shear foliation
where they are parallel or nearly so. In the hinges of
related folds it is a very closely spaced crenulation of the
bedding cleavage. Locally it is more widely spaced and
less well developed, especially in pure quartzite.

Isoclinal to tight folds are superimposed onto the
shear fabric. Their characteristics vary according to the
composition of the host rock. Quartzite supports more
concentric folds than does pelite although all of this gen-
eration are flow folds (similar; see Fig. 36).

These folds and their cleavage represent ductile (rela-
tively low viscosity) deformation during early stages of
orogenesis.

Set 2 cleavage. The second set is predominantly a widely
spaced crenulation in pelite and is poorly to undeveloped
in quartzite. It dips steeply and crosscuts the previous
generations in areas of chlorite zone metamorphism.
Muscovite is partly parallel to the cleavage selvages which