Textbook Notes (369,205)
Canada (162,462)
EESA06H3 (234)
Nick Eyles (205)
Chapter 20

Chapter 20 Textbook Notes.odt

7 Pages

Environmental Science
Course Code
Nick Eyles

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Chapter 20 ➢ Canada's economic well being is dependent on geological resources and the finding and use of new mineral and energy deposites, such as oil and gas, requires new generations of geoscientists ➢ Growing dependence on geology due to urbanization ➢ Adetailed understanding of Canadian geology is required for  Safe disposal of wastes  Design of foundations for buildings  Roads  Location of sufficient quantities of construction materials such as sand and gravel  The assessment of earthquake risk all require a detailed understanding of Canadian geology ➢ Canada:AYoung Nation, ButAn Old Country  Been a nation since 1867  Act of Confederation brought together provinces of Ontario, New Brunswick, Nova Scotia, and Quebec to create a larger and more powerful political entity  Welded together by a railway  Last province to join was Newfoundland  North American continent (almost in the same fashion) was assembled by plate tectonic processes that brought together many smaller land masses  Process of CONTINENTAL BUILDING has taken more than 4 BILLION YEARS to accomplish  Construction of North America began at least 4 000 million years ago (4 billion) with the formation of the Acasta Gneiss of the Northwest Territories, which now forms part of the Slave Province of the Canadian Shield  Acasta Gneiss – Located in Yellowknife, oldest known crustal fragment on earth  Important in establishing the early history of continental crust  Building of North America completed 65 million years ago!  Last ice sheet melted in Labrador 6 000 years ago. ➢ WHATARE THE MAIN GEOLOGICAL BUILDING BLOCKS OF NORTHAMERICA  Craton  Northern part of the continent in canada, is underlain by the exposed part of the ancient core or craton of north america  This exposed part is called the canadian shield and consists predominantly of very old Archean and Proterozoic rocks  Rocks range from 4 billion to 1 billion years old and have no fossils  Cratons composed of assemblage of geologic provinces  Geologic provinces: broad regions of similar rocks, usually covering many thousands of square kilometres, with characteristics that differ significantly from rock types present in adjacent areas  Further subdivided into sub-provinces = fault-bounded units containing similar rock types, structures, and mineral deposits  Terranes  New name given to provinces and subprovinces  Discrete fragments of oceanic or continental material that have been added to a craton at an active margin by accretion ➢ NORTH AMERICAN CRATON VERSUS THE CANADIAN SHIELD  Difference between NorthAmerican craton and the Canadian Shield  North American craton:  Acraton is formed through the assembly of geological provinces and makes up the core of the NorthAmerican continent • “Alarge continent sized block of distinct geology making up the basement of much of North America”  Underlying rock: metamorphic  Overlying rock: cover strata = sedimentary rock that are fossiliferous from Paleozoic and Meseozoic • These bury the outermost margins of the craton  It is the largest craton in the world – assembled btwn 1 and 4 billion yrs ago  Greenland contains a portion of it as it was once part of NorthAmerica beforeAtlantic Ocean opened up in between  Burying of outer margins explained by: • Flooding by shallow seas and mountain-building episodes (orogenies) • depressed by the weight of mountain belts and their thick piles of sediment  Many other continents on Earth show the same basic anatomy of a central, ancient craton created by the fusion of many separate geological provinces (microcontinents), buried around its margins by younger sedimentary cover strata .  Building of North America • 5 principle building blocks • Original North American continent called =Arctica • Appalachian mountains were added during the formation of Pangea • etc.  The Shield   Is the exposed part of the craton and consists of a gently undulating surface that rises like an arch, in its centre  Canadian Shield forms one of the most extensive and ancient landforms in the world and is remarkable because geologists have little detailed knowledge of how such a landscape formed.  Peneplain  Canadian Shield is a large landform called a peneplain  Asurface of low relief and great areal extent and age  Created 800 million years ago by erosion and bevelling of craton ancient rocks  Forms the unconformity btwn craton below and younger surface rocks above  Unconformity can be seen in the Grand Canyon (Arizona, US) • Separating metamorphic rocks of craton from overlying Paleozoic rock ➢ THE GEOLOGIC JIGSAW OF THE NORTHAMERICAN CRATON  Before plate tectonics people knew of the term “geological province”  Province was used to decribe the many distinct blocks of geology they discovered within the Canadian Shield  Sir William Logan  First to write of “geological provinces” - in 1860  Term is still used to describe areas of the shield  Geological provinces are broad areas/regions of similar rock types that cover thousands of square kilometers and differ significantly from adjacent areas of different rock types  Geological Survey of Canada (1840s)  Systematic study of the Geology of Canada by professional geologists started with this  Atime when few topographic maps existed  Aneed to better understand Canada's geological resources; mostly, coal  First director: William Logan  Alot of coal in Nova Scotia  Logan's map of Geology of Canada published in 1869 (parts of Manitoba, Ontario & Quebec) and a major achievement  Even today, much of the Canadian Shielf remains to be mapped in detail  Plate tectonics and studies of sea floor provided key to origin of Canadian Shield  Plate tectonics is responsible for bringing together the various geological provinces of Canada  Uniformitarianism = using modern world processes to explain evolution of NorthAmerican craton ➢ HOW DID THE NORTH AMERICAN CONTINENT EVOLVE?  Stages in the Evolution  Geological provinces (within craton) are rimmed by intensely deformed rocks that form ancient orogens  In other worlds, geological provinces can be regarded as the remains of individual continents that collided  Orogens consist of crushed and deformed rocks that represent the remainsof mountain belts or volcanic arcs formed during collision  Wilson Cycle • Growth of NorthAmerica has 5 stages = each characterized by collision of breakage from other lands • This process of repeated continental aggradation and breakup is known as the Wilson Cycle and has resulted in the development of supercontinents • This explains why present day continents have a broadly similar geologic history  Early stages of Canada's geological history is preliminary = still more to learn.  Strage 1 –Arctica: North America in theArchae
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