Download Data Collection: Recording Metamorphism and Lithology at the

Data Collection: Recording Metamorphism and Lithology at the
Grenville Front along the Georgian Bay
Michelle M. LaBelle
1Department
of Earth Sciences, University of South Alabama, Mobile, AL;
2Geology Program, University of South Alabama, Mobile, AL
Abstract
Methods
During the Mesoproterozoic, the first supercontinent, Rodinia, was formed. The
result was a major mountain-building event that occurred due to the collision of
the Laurentian and South American plate. That long lived event was the
Grenville Orogeny. A field study was organized to collect and catalog data
pertaining to the country rock and metamorphic composition as well as the
tectonic environment that shaped the study area within the Grenville Front Zone.
Lithology and deformation of crust within the Grenville tectonic zone from the
area of Parry Sound tracing the Georgian Bay to Killarney was recorded using a
cluster analysis based on access. Limited tectonic activity in the area allowed
for a more accurate study of the Grenville metamorphism. The most recent
glacial recession had exposed the existing bedrock of the orogeny in the study
area. The study of this area provided a base compilation of data for future
studies. Initial analysis has found granitic samples with a low percentage of
potassium feldspar in a localized area (Grundy Lake). This suggests
hydrothermal processes in the area. Several Sturgeon Bay site samples showed
boudinage characteristics that may indicate post orogenic deformation. The
literary research gathered herein is to provide a basic knowledge regarding this
study, and a basis in which to compare this study’s findings.
Data collection was based on cluster samples tracing the Georgian Bay from
Parry Sound to Killarney, Ontario. Samples chosen for data collection were
part of the exposed bedrock and maintained the alignment of the source
bedrock. Each specimen was recorded with north facing alignment, angle of
dip, and elevation. Specimens were separated from the bedrock by utilizing
pre-existing cracks in the bedrock. A hand lens evaluation of each specimen
was made to determine a mineral assemblage, and each specimen was
photographed against a white background on site with markers illustrating the
azimuth and dip. The specimens chosen for study were based on access,
study area representation, and duration of field work. Equipment used to
collect data on the specimens were a pocket transit with level, tape measure,
hand lens, GPS handheld device, a magnet, paper denoting north facing, and
camera. Specimens suspected of having a carbonate composition were tested
with diluted HCl. Specimens were assigned a designation based on the camp
location in the vicinity (i.e. C1S03 = Campsite 1, Specimen 03).
A photographic and written observation of the surrounding bedrock was
recorded to compare the specimen analysis with the overall topographic
formation. A photographic record was made of the exposed outcrops along
highway 401 from the Sudbury District moving southeasterly to the suspected
suture zone at kilometer marker 152.
The latitude and longitude of each specimen was plotted on Google Earth to
demonstrate the cluster areas that were studied. Any specimen in which
identification of assemblage was uncertain was examined by Dr. David Allison
through photographs of specimens and locations.
Figure 1. Drawing of the supercontinent
Rodinia. The Grenville Orogeny is
represented by the shaded area that spans
across Rodinia.
The North American land mass (Laurentia) is
shown here positioned against the South
American land mass (Amazonia). Prior to this
continental collision, exotic terrain of possible
volcanic arc origin impacted the Laurentian
continental margin. (Levin, 2013)
The Grenville Orogeny
Glaciation
During the Pleistocene Epoch, the last glaciation, the Wisconsinan Glaciation,
(0.08 to 0.02 MA) receded. The northward moving glaciers removed the
sediments that covered the Grenville Front in the Georgian Bay area. The
bedrock was scrapped clean and scored as the glaciers retreated. (Rutter et al,
2012) Rocks broken from the bedrock were transported great distances and
redeposited hundreds of miles away. The weight of the continental ice sheet
depressed the surrounding area and created the great lake region. Thousands
of bedrock micro islands exist in the Georgian Bay area that show the roots of
the ancient orogenic event.
Abundant mafic intrusions and mineral assemblages identified within the
tectonic zone show evidence of possible subduction of a mafic composition
plate, or impact with a volcanic island arc system along the ancient Laurentian
continental margin. Evidence of exotic terrain of intermediate composition
suggests that the Grundy Lake area (site 3) may have been from the exotic
terrain overriding the Laurentian land mass.
It is suggested by this author that the amount of mafic deposits are a result of
the thickening of the felsic composition land mass that allows the magmatic
intrusions to have a more mafic composition, and thus contain more favorable
resources.
Figure 4. Folded and tilted banded iron formations at Parry Sound show strong
deformation in high pressure and temperature conditions.
Figure 5. Mafic dike intrusions in white quartzite bedrock. The photograph was taken
in Lake George.
Background
Between 1.2 and 1.0 billion years ago a long lasting mountain building event
occurred along the eastern coast of North America (Laurentia)and the western
South America (Amazonia). It was part of the assemblage of the first
supercontinent, Rodinia (Fig 1). (Levin, 2013) . The continental margin
impacted the eastern edge of the continent with an unknown exotic terrain.
Widespread deformation and metamorphism of the margin created large
regions of amphibolite to granulite facies. Deep plastic deformation at the front
as well as substantial faulting has been mapped extensively within the study
area by Brett. Brett’s study examines the zones along the Georgian Bay to
Quebec (Brett, 1960).
Ancient Proterozoic rocks were thrust up into a vast mountain range. Evidence
suggests additional metamorphism occurred after the Grenville Orogeny at this
margin during the expansion of the front as a result of the breakup of Rodinia.
(Streepey et al., 2004) Over millions of years the mountains that were up thrust
by tectonic and magmatic influences eroded away down to their roots. Both
basement rocks and sedimentary rocks underwent intense metamorphism and
deformation due to the heat and pressure from the collision. Magmatic
intrusions of primarily magnesium and iron-rich lava formed dikes that cut
through the pre-existing rock. Whole-rock rubidium – strontium and uranium –
lead dating suggest that these events first began occurring around 2.4 billion
years ago. (Seyfert, Sirkin, 1973) The temperatures at the tectonic zone of this
collision were estimated to be approximately 850 degrees at central Grenville
Province. (Rivers et al, 2002) The Parry Sound area was estimated to have
temperatures up to 800 degrees and decreasing to 650 in the Sudbury district.
Pressure changes from the 11 kb to 4 kb exist along the front area though there
are small areas of discontinuity regarding pressure-temperature. (Anovitz,
Essene, 1990)
Hypothesis
Conclusions
• The Grundy Lake Cluster collection shows indications of hydrothermal
Figure 2. Google Earth image showing the locations of the cluster studies. The
data collection sites followed along the Georgian Bay in Ontario, Canada from
Parry Sound, in the southeast, to Killarney in the northwest. The information
derived from these sites were performed on site. (Google Earth) Figure 3. The
general lithology of the study area (Culshaw et al., 2004)
Results
Using available outcrops and exposed areas of rock along highway 400 in
Ontario, it was noted that there was a visible change in lithology around km
marker 152 in which the southeast general lithology appeared to be andesitic in
nature; whereas the northwest lithology appeared to contain substantial granite
gneisses with abundant mafic dike intrusions.
The felsic bedrocks within 50 km to the north west of km marker 152
demonstrated joint frost weathering as well as sheeting. The Parry Sound (C1)
site showed amphibolites with calsilicate lenses, foliated granites, boudinage
quartzites with magnetite crossbedding, and mafic source rocks. The Rose
Trail site (C2)was found to have foliated granites, amphibolites, and megacrystic
granites. At Grundy Lake (C3) there was a noticeable absence of k-feldspar in
the phaneritic rock. Specimens that were studied at this site were identified as
diorite, amphibolite, and possibly tronjamite. George Lake and Killarney (C4 and
C5) showed signs of a fault zone by the presence of mylonite specimens and
boudinage prophyroclast containing quartzite. Banded iron formations
containing magnetite along bedded planes indicated a metasediment
environment. Mafic dikes also showed metamorphism as greenstones.
Much of the specimens that were studied had iron staining. A specimen was
observed in the Sudbury District. It was identified as a mafic gabbro containing
olivine and sodium plagioclase.
36 specimens were studied, recorded, and photographed . Their locations,
lithology, and alignment have been recorded on a data sheet and will be used in
future research.
processes due to the lack of potassium feldspar in the bedrock composition.
•Extension deformation is suspected at the Sturgeon Bay site. Several of the
specimens studied had boudinage characteristics that could indicate the second
deformation after the orogeny.
•The number four and five sites (Lake George and Killarney) show less folding;
however, mafic dike intrusions and mid-grade metamorphism are prevalent.
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Grenville Province of Ontario*. Oxford University Press. 1990. Abs.
Brett, Brian Dudley. The Grenville Front of Ontario and Quebec. McGill University, Montreal. 1960. Pp.
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Culshaw, N.G., Corrigan, D., Ketchum, J.W.F., Wallace, P., Wodicka, N. and Easton, R.M. 2004.
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