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EESA06H3 (540)
Nick Eyles (472)
Lecture 10

Lecture 10: Canada's Geologic Journey

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University of Toronto Scarborough
Environmental Science
Nick Eyles

EESA06 Lecture 10 Page 1 EESA06 Lecture 10 Canada’s Geologic Journey: The Last 4 Billion Years 1. Continents grow through time by obduction 2. North American continent shows 5 growth stages: a) Arctica (2.7 Ga) – oldest Giganum (Billion) b) Columbia (1.8 Ga) c) Rodinia (1.0 Ga) - a + b +c = Canadian Shield (the craton) – the old hard core rocks, rigid d) Pangea assembly (350 Ma): Maritime Canada is added during Appalachians Orogeny (Appalachian Mountains) – added sedimentary + highly fossil rocks e) Pangea breakup (<200 Ma): British Columbia is added during Cordilleran Orogeny (e.g. Rockies) Geology of North America known for 100 years but what put it together? - Brown – old hard core ( Ontario+ Quebec area) - Blue – Appalachian belt – maritime Canada Zircons: - 2.7 billion year old zircons – Uranium + Lead dating - Age rings, amount of lead in the crystals - Tom crow – expert on dating rocks - Detrital – Secondary, having be derived from something else - Detritous - Garbage Acasta Gneiss (NWT): - 4 billion years old – near Yellowknife - The oldest continental crust found so far? - Zircons: from igneous rocks, weathered, zircons released, become sedimentary rock then metamorphosed into a gneiss Continents grow thru time – similar to Swiss roll – older stuff in the middle Deconstructing North America: 1) The original NA continent, Arctica which started to form about 2.5 billion years ago from smaller continents and was completed by about 1.9 billion years ado when old Archean cratons (ex: Slave, Nain provinces) were welded together by the Trans-Hudson Orogen and others 2) Added to the North American continent during the formation of Nena about 1.8 billion years ago after the Penokean Orogeny 3) Added During the Formation of Rodinia about 1.3 billion years ago during the Grenville Orogeny 4) Added during the formation of Pangea about 600 million-300 million years ago – Appalachian Mt 5) Added after the breakup of Pangea about 250 million years ago – Corillera EESA06 Lecture 10 Page 2 Provinces – not politics, rocks that stretch over large areas fairly similar in appearance, have very sharp boundaries (ex: Superior Province, Hern Province, Nain Province) Orogen – the rocks that result from orogeny, highly deformed rocks (ex: most common = gneiss) - Provinces seem to be separated by orogens (ex: Himalaya) Green stone belts – metamorphosed old ocean rocks Slave Province – true core of Canadian shield, Yellowknife area, oldest part of North American continent - Greenland – broke of about 80million years ago, separated by a failed rift Craton – old rocks that make up the rigid interior of the continent Lithoprobe – dancing elephants, has a large plate which create strong vibrations to mimic earthquakes - Help reconstruct earth’s surface up to 70km - Seismic Transsects – cross-sections of shield over long distances Canadian Shield – peneplain (almost a plain/flat), no mountains, has been eroded Labrador is added to Canada - Cartoons - Ancient earth behaved similar to present day - Confirms uniformitarianism - Might have been faster in past – earth was warmer, hotter mantle Political Unificiation of the Provinces 1867 to 1949 - Driving the “Golden spike” November 1885 – Canadian Pacific Railroad - An analog for welding of geological “provinces” through geologic time Cratonization: the building of cratons/shields - Obduction: The Accretionary Process that builds continents from smaller crustal blocks Greenstone Belt – green rocks, metamorphosed basalt – amphibolites - Superior Craton – a lot of mineral wealth - Hydrothermal processes – near mid-ocean ridges Great thickness of Pillowed Basalts between blocks of continental crust – at Yellowknife (a lot of Gold) - Simple bacterial filaments at c. 3.3 Ga - Australia - Gunflint Chert (oldest bacteria in Ontario) c. 1.1 Ga - Stromatolites – bacterial colonies, like hypersaline lagoons, no predators, Shark Bay Western Australia Sudbury Meterorite Crater 2 billion years ago – Nickel rich - Big depression in the surface of the shield nd - Once thought to be volcanic but actually is a product of a large meteorite strike (2 largest) – 10km diameter - Largest is in South Africa - Oval – has been squeezed by oduction during the Grenville Orogeny - Fractures are softer rocks – caused by many things - Wanapikei Lake – younger meteorite crater, 37 million year old EESA06 Lecture 10 Page 3 Sudbury - Cone structures – shatter corners - Surround the crater, record intense impact stresses created by the meteorite strike Ontario 1 billion years ago: the Greenville mountains, very high - Group of seven – painted the current shield, peneplain - South America that was colliding with North America = Grenville Orogeny
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