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EESA06H3 (234)
Nick Eyles (205)
Chapter 20

Chapter 20 - Geological History of Canada.docx

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Environmental Science
Nick Eyles

Chapter 20: Geological History of Canada Canada: A Young Nation, But an Old Country - Acasta Gneiss (4 Ma)- North West Territories, which forms part of the Slave Province of the Canadian Shield - North America was essentially complete by 65 million years ago - Last ice sheet – 12,000 years ago left southern parts of country, 6,000 years ago finally melted in Labrador - Baffin Island – remnants of this vast ice sheet still survive on Baffin Island as Penny and Barnes Ice Caps What are the main geological “Building Blocks” of North America? Geologic Jigsaw - Craton – the ancient core of North America, composed of a complex assemblage of several distinct geologic provinces - Geologic provinces – broad regions of similar rocks, with characteristics that differ significantly from rock types present in adjacent areas o Sub-Provinces – fault-bounded units containing similar rocks types, structures and mineral deposits - Terranes – provinces + subprovinces, discrete fragments of oceanic or continental material that have been added to a craton at an active margin by accretion (material is added to a landmass) The North American Craton versus the Canadian Shield - North American Craton – a large, continent-sized block of distinct geology aking up the basement of much of North America (and Greenland) - Canadian Shield – exposed part of the craton, and consists of a gently undulating surface that rises inconspicuously, almost like an arch, in its center (peneplain) o consists predominantly of very old, Archean and Proterozoic rocks (age 1-4 Ga years old, lack fossils) - Peneplain – “almost plain”, caused by erosion and beveling o Margins of Shield are buried below younger sedimentary rocks, ancient peneplain surface now forms an unconformity between the craton below and younger rocks above o Grand Canyon in Arizona –unconformity separates metamorphic rocks of the craton from overlying Paleozoic cover rocks - Cover strata – younger sedimentary strata that bury the more ancient craton around its margins o Deposited when the outer margins of the craton were depressed and flooded by shallow seas – occurred during orogenies , collision of other landmasses with the craton o Cover rocks – thicker than 10km The Geologic Jigsaw of the North American Craton - Geological provinces (Sir William Logan) – areas of the shield with distinctive geological characteristics 20.1 The Sudbury Impact Structure: Collision of an Ancient Meteorite - Oval shape crater – squeezed by Penokean Orogeny, o depth of 35km, rich in nickel, copper and platinum ores - Shatter Cones – V-shaped cones that form when rocks are struck violently during a meteorite impact event - Breccia (Pseudotachylite Glass) – formed by disintegration and mixing of rock when hit by a large meteorite and broken into angular fragmentsSlave Omogon Wyoming Province Yavapai 2 Mazatzal Otogin trogen Southem Naga augioadan Orogen Nain Province Gremile orogon 600 Slave Omogon Wyoming Province Yavapai 2 Mazatzal Otogin trogen Southem Naga augioadan Orogen Nain Province Gremile orogon 600Deconstructing 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 ago 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 How Did the North American Continent Evolve? (5) Stages in the Evolution of the North American Continent - Orogens – consists of crushed and deformed rocks that represent the remains of mountain belts or volcanic arcs formed during collision (ex: Trongat and Wopmay) - Wilson cycle – process of repeated continental aggradation and breakup forms supercontinents - Supercontinents – a giant conglomerate of all the continents on Earth Stage 1: Arctica – North America in the Archean Era (4-2.5 Ga) - Arctica – The original North American continent, begun to form 2.5 Ga years ago , finally assembly 2 Ga years ago, included present-day Siberia o Slave Province (3.96 – 4.05 Ga) – oldest rocks on Earth found in Acasta Gneiss of the Northwest Territories, diamonds in kimberlite pipelines o Superior Province – mineral wealth (gold, zinc, copper, silver) - Subprovince –fault-bounded subdivisions of a geological province that contain similar rock types, structure and mineral deposits, subprovinces within Superior Province record clear evidence of the operation of plate tectonics in the ancient past o Plutonic subprovinces – composed of granite and record the intrusion of giant plutons into the Superior Province o Greenstone subprovinces – consisted of metamorphosed sea-floor volcanic rocks (basalt) originally formed on the floor of ancient Achean oceans, contain BIFs, and records the first large-scale production of oxygen by single-celled cyanobacteria o Metasedimentary subprovinces – consists of deep-sea Archean ocean sediments, - Gowganda glaciations (2.4 Ga)– a major glaciations at the southern continental margin of Arctica o Form part of the Huronian Supergroup of Ontario, famous for uranium deposits near Elliot Lake Stage 2: Nena and Rodinia – North America in the Proterozoic Era (2.5 Ga – 570 Ma) - Nena (North Europe and North America) - A supercontinent that existed between 1.9 and 1.3 Ga years ago recorded by the Penokean Orogeny o Southern Province, Yavapai and Mazatzal Orogenies added to Arctica around 1.9 Ga o Penokean Orogeny - created a major Himalayan-type mountain, now eroded but remain as the Penokean Fold Belt along the northern border of Lake Huron OntarioStage 3: The Grenville Orogeny and Formation of Rodinia - Grenville Orogeny – the result of a long-lived collision between ancestral South and North America between 1.3 and 1 billion years ago o Formed current day southern Greenland to Northern Mexico, accretion of smaller land masses created Rodinia - Rodinia – A supercontinent that formed about 1,000 million years ago o The accreted and deformed rocks now underlie much of Southern Ontario and Quebec extending thru the Maritimes and into Newfoundland - Grenville orogenic belt (Grenville Province or Gren vill Orgen) – dominated by banded gneisses, highly metamorphosed sediments, and igneous rocks o Eroded to peneplain 800 million years ago, now forms the exposed Canadian Shield o Made up of smaller terranes: highly deformed remnants of island arcs, microcontinents, pieces of ocean floor that were not subducted, welded together by the intrusion of granite pluton and dikes Rodinia Breaks Apart (750 Ma – 570 Ma) - Triple junction – consists of interlinked grabens the eventually grow and widen into a new ocean basin (failed grabens are called aulacogens) - Panthalassic Ocean – ancestral Pacific Ocean, the first break: Antarctica + Australia broke from western margin of North America - Iapetus Ocean – ancestral Atlantic Ocean, last break: Europe + Africa broke from eastern margin of North America - Cambrian Explosion – proliferation of early life forms such as those of Burgess Shale and the Mistaken Point Formation Stage 4: Pangea – North America in the Later Paleozoic and Some of the Mesoic - Baltica – modern Europe - Laurentia – modern North America - Laurasia = Baltica + Laurentia - Taconic Orogeny (Caledonian Orogeny) – formed mountains in Wales, Scotland, Scandinavia similar to Andes’ Mountains (arc of volcanic islands rose above an active subduction zone and andesitic volcanoes) off the eastern coast of North America o Marker horizons – ash beds, within thick sedimentary strata that cover the outer margins of the North American craton o Bentonite – weathered ash that can be fingerprinted o Intracratonic basins – form on the craton and are underlain by continential crust rather than oceanic crust (ex: Appalachian Basin has more than 10km of Paleozoic sediments) - Queenston Delta – drained the North Slopes of Taconic Mountains and spread fossiliferous sediment inland, across outer margins of the North American craton o Delta - a body of sediment deposited at the mouth of a river when the river velocity decreases
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