| dc.description.abstract | A supracrustal sequence of rocks near Manitouwadge, Ontario
consists of metavolcanlc rocks, Including pillow lavas, banded iron
formation, amphibolite, and a quartzofe1dspathic hornblende-blotite
gneiss. This rock has been given the name bladed gneiss to reflect
the blade-like appearance of its mafic components. Results of a
detailed geological investigation of the entire supracrustal
sequence suggests that the apparent fragmental appearance of the
gneiss, and to a lesser degree the other rock types, is not a
primary feature, but rather, the product of deformation. The rocks
were initially part of a layered sequence which became variably
fragmented. The blades are in part the result of the transposition
of layers and the variations in blade morphology are attributable
to the response of the layers to strain during folding.
Individual layers deform by the development of cuspate-1obate
folds, buckle folds, and boudinage. The extent of fragmentation
during deformation is controlled by competency contrasts between
adjacent layers, absolute and relative layer thickness, and layer
orientation with respect to principal finite strain directions.
Planar and linear structural elements in the metasedimentary
and metavolcanic rocks suggest a defomational history which
Includes two episodes of folding accompanied by medium grade
metamorphism and recrystallization. Similarities in lithology and
structural elements between the rocks of the study area and those
of the nearby Manitouwadge synform suggest that parent rock
assemblages were closely related and that structures present in both locations developed contemporaneously in response to regional
tectonic activity. "Mobilist" tectonic models for the development
of the Superior Province entail northward directed subduction and
accretion, and are popular with many workers. The recumbent nature
of Fi folds, the shallow plunging hinge lines of Fa folds, and
their coaxial relationship may be related to low angle thrust
faults and nappe structures which would be likely consequences in
the proposed subduction model.
Many workers have attempted to map subprovince boundaries. In
the region of the present study, the boundary between the Wawa and
Quetico Subprovinces is traditionally placed a few miles north of
Man 11ouwadge. If this is correct, the rocks studied form part of
the Wawa Subprovince. Results of this Investigation suggest that,
on the basis of lithology and structure, such a placement of the
boundary is inappropriate. It appears more appropriate to suggest
that the terrain discussed in this thesis, as well as the rocks of
the Manitouwadge synform, is best considered to form a zone of
transition between the two subprovinces. | |
