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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. Literature Cited Anovitz, Lawrence and Essene, Eric J. Thermobarometry and Pressure-Temperature Paths in the Grenville Province of Ontario*. Oxford University Press. 1990. Abs. Brett, Brian Dudley. The Grenville Front of Ontario and Quebec. McGill University, Montreal. 1960. Pp. 1-113. Culshaw, N.G., Corrigan, D., Ketchum, J.W.F., Wallace, P., Wodicka, N. and Easton, R.M. 2004. Georgian Bay geological synthesis, Grenville Province: Explanatory notes for Preliminary Maps P.3548 to P.3552; Ontario Geological Survey, Open File Report 6143, 28p. Levin, Harold L. The Earth Through Time, Tenth Edition. Courier Kenallville. 2013. p.258-260. Marshak, Stephen. Essentials of Geology, fourth edition. W.W.Norton * Company. 2013. p.335. Postlethwaite, Ben. Seismic velocities and composition of the Canadian crust. B.Sc., The University of British Columbia, 2014. Rivers, T. et al. "Assembly and Preservation of lower, mid, and upper orogenic crust in the Grenville Province-Implications for the evolution of large hot long-duration orogens". Precambrian Research 167 (3–4). 2008. p 237–259. Rivers, Toby, Ketchumb, John, Indares, Aphrodite, and Hynes, Andrew. The High Pressure belt in the Greenville Province: architecture, timing, and exhumation. NRC Canada. 2002. Abs. Rivers, T. Testing and refining a tectonic model for the Grenville orogeny. Geophysical Research Abstracts Vol. 15, EGU2013-3455, 2013. EGU General Assembly 2013. Seyfert, Carl K. and Sirkin, Leslie A. Earth History and Plate Tectonics: An Introduction to Geology. Harper & Row, Publishers, Inc. 1973. p.149-150 Streepey, M.M., Lithgow-Bertelloni, C., van der Pluijm, B.A., Essene, E.J., and Magloughlin, J.F., 2004, Exhumation of a collisional orogen: A perspective from the North American Grenville Province, in Tollo, R.P., Corriveau, L., McLelland, J., and Bartholomew, M.J., eds., Proterozoic tectonic evolution of the Grenville orogen in North America: Boulder, Colorado, Geological Society of America Memoir 197, p. 391–410. 2004. Woodruff,Lauren G., Nicholson, Suzanne W., and Fey, David L. A Deposit Model for Magmatic IronTitanium-Oxide Deposits Related to Proterozoic Massif Anorthosite Plutonic Suites. Chapter K of Mineral Deposit Models for Resource Assessment Scientific Investigations Report 2010–5070–K. U.S. Department of the Interior U.S. Geological Survey. 2013. Nat Rutter, Andrea Coronato, Karin Helmens, Jorge Rabassa, Marcelo Zárate. Glaciations in North and South America from the Miocene to the Last Glacial Maximum: Comparisons, Linkages and Uncertainties. Springer Science & Business Media, Jun 30, 2012. P.55