EESA06H3 Lecture Notes - Lecture 10: Superior Craton, Euramerica, West Antarctic Rift

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21 Apr 2012
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EESA06 Lecture 10 Page 1
EESA06 Lecture 10
Canada’s Geologic Journey: The Last 4 Billion Years
1. Continents grow through time by obduction
2. North American continent shows 5 growth stages:
a) Arctica (2.7 Ga) oldest Giganum (Billion)
b) Columbia (1.8 Ga)
c) Rodinia (1.0 Ga)
- a + b +c = Canadian Shield (the craton) the old hard core rocks, rigid
d) Pangea assembly (350 Ma): Maritime Canada is added during Appalachians Orogeny (Appalachian
Mountains) added sedimentary + highly fossil rocks
e) Pangea breakup (<200 Ma): British Columbia is added during Cordilleran Orogeny (e.g. Rockies)
Geology of North America known for 100 years but what put it together?
- Brown old hard core ( Ontario+ Quebec area)
- Blue Appalachian belt maritime Canada
Zircons:
- 2.7 billion year old zircons Uranium + Lead dating
- Age rings, amount of lead in the crystals
- Tom crow expert on dating rocks
- Detrital Secondary, having be derived from
something else
- Detritous - Garbage
Acasta Gneiss (NWT):
- 4 billion years old near Yellowknife
- The oldest continental crust found so far?
- Zircons: from igneous rocks, weathered, zircons
released, become sedimentary rock then
metamorphosed into a gneiss
Continents grow thru time similar to Swiss roll older stuff in the middle
Deconstructing 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 ado 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
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EESA06 Lecture 10 Page 2
Provinces not politics, rocks that stretch over large areas fairly similar in appearance, have very sharp
boundaries (ex: Superior Province, Hern Province, Nain Province)
Orogen the rocks that result from orogeny, highly deformed rocks (ex: most common = gneiss)
- Provinces seem to be separated by orogens (ex: Himalaya)
Green stone belts metamorphosed old ocean rocks
Slave Province true core of Canadian shield, Yellowknife area, oldest part of North American continent
- Greenland broke of about 80million years ago, separated by a failed rift
Craton old rocks that make up the rigid interior of the continent
Lithoprobe dancing elephants, has a large plate which create strong vibrations to mimic earthquakes
- Help reconstruct earth’s surface up to 70km
- Seismic Transsects cross-sections of shield over long distances
Canadian Shield peneplain (almost a plain/flat), no mountains, has been eroded
Labrador is added to Canada
- Cartoons
- Ancient earth behaved similar to present day
- Confirms uniformitarianism
- Might have been faster in past earth was warmer,
hotter mantle
Political Unificiation of the Provinces 1867 to 1949
- Driving the “Golden spike” November 1885
Canadian Pacific Railroad
- An analog for welding of geological “provinces
through geologic time
Cratonization: the building of cratons/shields
- Obduction: The Accretionary Process that builds
continents from smaller crustal blocks
Greenstone Belt green rocks, metamorphosed basalt
amphibolites
- Superior Craton a lot of mineral wealth
- Hydrothermal processes near mid-ocean ridges
Great thickness of Pillowed Basalts between blocks of
continental crust at Yellowknife (a lot of Gold)
- Simple bacterial filaments at c. 3.3 Ga - Australia
- Gunflint Chert (oldest bacteria in Ontario) c. 1.1 Ga
- Stromatolites bacterial colonies, like hypersaline lagoons, no predators, Shark Bay Western
Australia
Sudbury Meterorite Crater 2 billion years ago Nickel rich
- Big depression in the surface of the shield
- Once thought to be volcanic but actually is a product of a large meteorite strike (2nd largest)
10km diameter
- Largest is in South Africa
- Oval has been squeezed by oduction during the Grenville Orogeny
- Fractures are softer rocks caused by many things
- Wanapikei Lake younger meteorite crater, 37 million year old
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