Textbook Notes (368,720)
Canada (162,105)
EESA06H3 (234)
Nick Eyles (205)
Chapter 20

Chapter 20

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Environmental Science
Nick Eyles

Chapter 20: Geological History of Canada Canada: A Young Nation, But an Old Country Canada has been in existence since 1867 as a nation Act of Confederation (British North America Act) brought together provinces of Ontario, New Brunswick, Nova Scotia, Quebec Construction of North America began at least 4000 million years ago with the formation of the Acasta Gneiss of the Northwest Territories, which now forms part of Slave Province of the Canadian Shield The building of North America was essentially complete by 65 million years ago, although the modern landscape is the result of geologically recent glaciations that have occurred in the last 2.5 million years o The last ice sheet left southern portions of country only 12 000 years ago, and finally melted in Labrador 6000 years ago What Are the Main Geological Building Blocks of North America? A geological jigsaw Northern part of continent, in Canada, is underlain by the exposed part of the ancient core (craton) of North America o Exposed part called Canadian Shield that consists mostly of very old, Archean and Proterozoic rocks Craton composed of complex assemblage of several distinct geologic provinces o Geologic provinces are broad regions of similar rocks, usually covering many thousands of square kilometres Individual geologic provinces have been subdivided into smaller units called subprovinces, which are fault-bounded units containing similar rock types, structures, mineral deposits Provinces and subprovinces are now widely recognized to be terranes o Terranes are discrete fragments of oceanic or continental material that have been added to a craton at an active margin by accretion o Likely originated as small continents and remnants of ocean-floor crust North American craton is largest in world and extends from Atlantic seaboard, west beneath the Rocky Mountains, and south as far as Texas o Greenland also consists of a detached mass of same craton that broke off from NA during opening of northern North Atlantic Ocean 80 million years ago The North American craton versus the Canadian Shield North American craton is a large, continent-sized block of distinct geology making up the basement of much of NA Shield is the exposed part of the craton and consists of a gently undulating surface that rises inconspicuously, almost like an arch in its centre Shield is a large landform called a peneplain, which is a surface of low relief and great areal extent and age o Erosion and bevelling of ancient rocks of craton had created peneplain 800 million years ago Cover rocks that bury outer margins of North American craton are fossiliferous sedimentary strata of Paleozoic and Mesozoic age o Sedimentary rocks deposited when the outer margins of craton were depressed and flooded by shallow seas Occurs primarily during mountain-building episodes (orogenies) that resulted from collision of other land masses with craton The geological jigsaw of the North American craton Rocks got younger as one travelled away from geographic interior of NA to its coasts Some of earliest gold mines in Nova Scotia www.notesolution.com
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