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EESA06H3 (240)
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Chapter 20

Chapter 20

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Department
Environmental Science
Course Code
EESA06H3
Professor
Nick Eyles

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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
oThe 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
oExposed part called Canadian Shield that consists mostly of very old, Archean and Proterozoic
rocks
Craton composed of complex assemblage of several distinct geologic provinces
oGeologic 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
oTerranes are discrete fragments of oceanic or continental material that have been added to a
craton at an active margin by accretion
oLikely 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
oGreenland 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
oErosion 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
oSedimentary 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
Processes operating in modern world are being used to explain evolution of ancient North American
craton, a working principle known as uniformitarianism
How Did the North American Continent Evolve?
Stages in the evolution of the North American continents
Geologic provinces can be regarded as remains of individual continents that collided
Orogens consist of crushed and deformed rocks that represent the remains of mountain belts or volcanic
arcs formed during collision
Some suggest that growth of NA can be broken down into 5 different stages
oEach stage is characterized by a major plate tectonics event, when ancestral AM either collided
with or ripped apart from other land masses
Process of repeated continental aggradation and breakup is known as Wilson Cycle and result in
development of supercontinents at certain times in Earths history
Each of present-day continents has a broadly similar geologic history
Stage 1- Arctica: North America in the Archean
Formation of central part of NA spans the entire Archean Era (4-2.5 billion years ago)
Some of oldest rocks so far dated on Earth are found in Slave Province and thought to be 3.96 and 4.05
billion years old
Rocks formed part of ancient continent that some have named Arctica
Slave Province is today the focus of much mineral-exploration activity, especially for diamonds that
occur in kimberlite pipers penetrating the ancient shield rocks
Superior Province, which is also formed part of Arctica is of great importance because of its mineral
wealth
Detailed mapping of ancient rocks of Superior Province reveals smaller subprovinces composed of
distinct rock types that record particular geologic events
oPlutonic subprovinces are composed of granites and record the intrusion of giant plutons into the
Superior Province
Greenstone subprovinces consist of metamorphosed sea-floor volcanic rocks, such as basalts, originally
formed on floor of ancient Archean oceans
oSubprovinces contain thick banded iron deposits that form major source of world’s iron and
record the first large-scale production of oxygen by single-celled cyanobacteria on Earth
Metasedimentary subprovinces consist of deep-sea Archean ocean sediments
Southern continental margin of Arctica was sit of major glaciations (Gowganda glaciation)
oOne of oldest glaciations recorded- 2.4 billion years ago
oGlacial deposits of Gowganda Formation form part of Huronian Supergroup of Ontario, famous
for uranium deposits found near Elliot Lake
Stage 2- Nena and Rodinia: North America in the Proterozoic
Span the entire Proterozoic Era (2.5 billion to 570 million years ago)
Southern part of Canadian Shield, including Southern Province and Yavapai and Mazatzal Orogenics
added to Arctica about 1.9 billion years ago and shortly formed larger land mass called Nena
Final assembly of Nena recorded in Ontario by Penokean Orogeny
oCreated major Himalayan-type mountain range near Lake Huron
Stage 3- The Grenville Orogeny and formation of Rodinia
Grenville Orogenny was result of long-lived collision between ancestral South and North America
between 1.3 and 1 billion years ago
Result of collision, huge supercontinent called Rodinia was created
Rocks accreted and deformed during orogeny underlie much of southern Ontario and Quebec, extending
through Maritimes and into Newfoundland
Grenville orogenic belt (Grenville Province or Grenville Orogen) is dominated by beautifully banded
gneisses, highly metamorphosed sediments, and igneous rocks
www.notesolution.com

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Description
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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