rock magnetic and structural investigation of the moss lake stock and local area : western shebandowan belt
abstract
the thesis area is located 120 km west of the city of thunder
bay, ontario, straddling the contact of the quetico and wawa
subprovinces of the archean superior province.
metasedimentary rocks of the quetico subprovince with basic and
granitic intrusions occupy the northwestern portion of the study
area and are in contact to the southeast with metamorphosed mafic
and felsic metavolcanic rocks of the wawa subprovince.
tectonic compression has shortened the metasedimentary rock
layers a minimum of 80%. bedding dips steeply to the northwest and
a later cleavage, developed by transpression, is sub-parallel to
bedding. graded beds young predominantly to the northwest. some
graded beds young to the southeast and may represent pre-cleavage
folding. no large-scale folds are present. metamorphic grade
increases northwest from greenschist to amphibolite facies over a
distance of about 10 km.
magnetite is the predominant magnetic component of the moss
lake stock; hematite is present in trace amounts. magnetic
susceptibility of the stock is high ( 12,000 x10-6 si), making the
intrusion amenable to anisotropy of magnetic susceptibility (ams)
work.
ams study of the moss lake stock shows that individual
directions of maximum susceptibility have been reoriented, in most
cases sub-parallel to the local planar fabric strike of the quetico
subprovince. magnetic fabric parameters show that the rock magnetic
fabric of the intrusion is deformed. vestiges of original magmatic
fabric are evidenced by prolate (constricted) magnetic fabric
associated with the central long axis of the stock but magnetic
fabric parameters confirm that the intrusion margin is more
deformed than the interior. the predominant oblate (flattened)
magnetic fabric of the moss lake stock is the product of northwestsoutheast
tectonic compression.
alternating field and thermal demagnetization of oriented rock
specimens confirm that the moss lake stock is deformed by tectonic
compression. separation of magnetite and hematite magnetic
contributions, by blocking temperature, reveals that primary
natural remanent magnetization (nrm) orientations from hematite are
parallel to the local planar fabric strike of the quetico
subprovince. minor preservation of primary magmatic fabric is
indicated by the mean principal component analysis (pca)
orientation for magnetite which corresponds closely in trend to the
mean ~ e orientation for the region, obtained by previous
investigators. original moss lake stock magnetic fabric is
overprinted by compression and shearing.
comparison of magnetic studies (ams and nrm) of the moss lake
stock to structural data of country rocks argues in favor of a
common tectonic control.
collections
- retrospective theses [1604]