EESA06H3 Chapter Notes - Chapter 20: Elliot Lake, Fits, Acadian Orogeny

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26 Jan 2013
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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
A detailed 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: A Young Nation, But An 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.
WHAT ARE THE MAIN GEOLOGICAL BUILDING BLOCKS OF NORTH AMERICA
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
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NORTH AMERICAN CRATON VERSUS THE CANADIAN SHIELD
Difference between North American craton and the Canadian Shield
North American craton:
A craton is formed through the assembly of geological provinces and makes up the core
of the North American continent
“A large 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 North America before Atlantic
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
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