| dc.description.abstract | The Quetico subprovince is a northeast-southwest striking
linear belt of migmatites, gneisses, and metasedimentary rocks.
These Archean rocks form part of the southern Superior Province-
This study involves an examination of variations in metamorphic
grade along cross-strike transects in an area north of Thunder Bay,
Ontario.
The rocks of the Quetico subprovince include metasedimentary
rocks with well preserved primary structures, knotted schists,
gneisses, migmatites, and anatectic granitic rocks. Metamorphic
porphyroblasts include muscovite, biotite, garnet, staurolite,
cordierite, andalusite, and sillimanite. Chemical analyses of
garnets, geothermobarometry, and mineral assemblage data were used
to determine variations in metamorphic grade in transects across
the subprovince.
Mineral assemblages characteristic of low to high grade
metamorphism are exposed along an across-strike transect.
Metamorphic grade rises gradually from low grade (521°C) to high
grade (714°C) northwards along Highway 527. North of the peak
conditions, the grade drops off sharply. Garnet-biotite
geothermometry confirms this pattern. Maximum pressure reached in
the study area is approximately 5 kbar.
The model proposed to account for the distribution of
metamorphic assemblages and minerals involves transpression of the
Quetico accretionary prism between the Wabigoon volcanic cratonic
margin to the north and the docking Wawa volcanic complex to the
south. Buckling and folding of the sedimentary rocks was
accompanied by thrusting. Erosion has exposed high grade
migmatitic and anatectic rocks within the Quetico fold belt which
developed as a result of thermal relaxation of depressed isotherms.
The boundaries between metavolcanic and metasedimentary terranes
are structurally complex. Boundaries may be best described as
geometrically complex zones up to several kilometres in extent in
which various rock types representative of the adjacent terranes
have been folded, faulted, and intruded. | |
