lectures 18/19: tectonics - south alabama
TRANSCRIPT
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GY 112: Earth History
The Proterozoic Part 1 Lectures 18/19: Tectonics
Instructor: Dr. Douglas W. Haywick
UNIVERSITY OF SOUTH ALABAMA
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Last Time
1) The Early Atmosphere 2) The Oceans and Hydrosphere 3) The Change
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Earth’s Early Atmosphere
4.1 GA: N2; HCl; SO2; CO2; CH4; NH3; NO2; H2O
No…. O2
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Earth’s Hydrosphere • All water on, in and over the Earth is recycled via the
hydrologic cycle
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Ozone UV radiation in the upper atmosphere makes ozone 2H2O + UV → H2 + O2
2O2 + UV → O3 + O
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Oxygen
Cyanobacteria (e.g., the microorganisms comprising stromatolites) and photosynthesis made oxygen starting at least 3.865 GA ago..
6CO2 + 6H2O → C6H12O6 (“sugar”) + 6O2
Photosynthesis
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Oxygen
The atmosphere became oxidizing by 1.8 GA and reached near current levels by the Ordovician.
http://www.biologie.uni-hamburg.de/b-online/ge42/01.jpg
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Today’s Agenda
Proterozoic Part 1: Tectonics 1) The Proterozoic time frame 2) Paleogeography 3) Tectonics (Wopmay Orogeny) 4) The Wilson cycle 5) The Trans-Hudson Orogenic Belt 6) The Grenville Orogeny
(Web Lectures 18 and 19)
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The Proterozoic Eon
Eon Time Phanerozoic 550 MA to 0 MA Proterozoic 2.5 GA to 550 MA Archean 4.1 GA to 2.5 GA Hadean 4.6 GA to 4.1 GA
Platform: younger (550 MA-2.5 GA) sedimentary rocks
http://mmsd1.mms.nrcan.gc.ca/efab/images/slide1canMap_e.gif
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The Proterozoic Eon
Eon Time Phanerozoic 550 MA to 0 MA Proterozoic 2.5 GA to 550 MA Archean 4.1 GA to 2.5 GA Hadean 4.6 GA to 4.1 GA
Division (ERA) Age Neoproterozoic 900 MA to 550 MA Mesoproterozoic 1.6 GA to 900 MA Paleoproterozoic 2.5 GA to 1.6 GA
• Paleo- old • Meso-middle • Neo-new
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• This is about as far back as we can go with detailed paleogeography
Proterozoic Paleogeography
Neoproterozoic 650 MA
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• But we can “guestimate” back to about 1 GA
Proterozoic Paleogeography
Rodinia (the first supercontinent)
The Earth 1.0 GA
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Archean Tectonics
Recall: Archean Tectonics involved differentiation of the Earth’s crust. Volcanoes, plutons and stretching of the crust, but possibly limited to no “rifting”
• Translation: As far as we can tell, there was no modern plate tectonics during the Archean.
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• 7 major lithospheric plates
Modern Plate Tectonics
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• Rigid lithospheric plates “float” atop ductile asthenosphere
Modern Plate Tectonics
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• Where they make contact, you get serious geology (earthquakes, volcanoes, mountain building)
Modern Plate Tectonics
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• But this type of tectonics may not have always occurred
• The first evidence of
divergent and convergent plate tectonics was during the Paleoproterozoic (2.1 GA) in the Slave Province of the Canadian Shield
Proterozoic Tectonics
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Proterozoic Tectonics
• But this type of tectonics may not have always occurred
• The first evidence of
divergent and convergent plate tectonics was during the Paleoproterozoic (2.1 GA) in the Slave Province of the Canadian Shield
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Proterozoic Tectonics
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Proterozoic Tectonics
• Coronation Geosyncline
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Proterozoic Tectonics
• Coronation Geosyncline • Wopmay Orogen
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Proterozoic Tectonics
• Coronation Geosyncline • Wopmay Orogen • Bathurst Aulocogen
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Proterozoic Tectonics
• Coronation Geosyncline • Wopmay Orogen • Bathurst Aulocogen • Athapuscow Aulocogen
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Proterozoic Tectonics
• A paleogeographic reconstruction of the Coronation Geosyncline 2.1 GA would look like this:
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Proterozoic Tectonics
• Which indicates that the Earth’s crust “rifted”, flooded with seawater and deepened over time
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• The Coronation Geosyncline therefore represents the opening of an ocean basin (i.e., a new ocean formed). But…
Proterozoic Tectonics
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Proterozoic Tectonics
• Linear trenches also opened up.
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Proterozoic Tectonics
• Linear trenches also opened up.
• They were mostly filled with coarse gravel and breccia (phase 1 fill in the Coronation Geosyncline)
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Proterozoic Tectonics
• Linear trenches also opened up.
• They were mostly filled with coarse gravel and breccia (phase 1 fill in the Coronation Geosyncline)
• Ternary rifting patterns Triple Junction
Chalk board
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• In any triple junction, one of the “arms” will become a failed rift or an Aulcogen. Two will continue to spread into an ocean
Proterozoic Tectonics
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• The best modern example of a “failed arm” is the East African Rift
Proterozoic Tectonics
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Proterozoic Tectonics
• But the Coronation Geosyncline ocean did not last a long time.
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Proterozoic Tectonics
• But the Coronation Geosyncline ocean did not last a long time.
• Granite was emplaced along the western side around 1.8 GA…
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Proterozoic Tectonics
• But the Coronation Geosyncline ocean did not last a long time.
• Granite was emplaced along the western side around 1.8 GA…
…indicating a plate collision with another continent.
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Proterozoic Tectonics
• This mountain-building event is called the Wopmay Orogeny
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Proterozoic Tectonics
So what hit us?
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Proterozoic Tectonics
So what hit us?
• The culprit was Australia seen here fleeing the scene of the accident about 500 MA after the incident
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• Oceans are created when plate tectonics results in rifting
The Wilson Cycle
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• But the Wopmay Orogeny demonstrates that not only do ocean open up, they can also close back up again (Subduction)
The Wilson Cycle
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• And sometimes they repeat this cycle more than once (e.g., the Atlantic Ocean)
The Wilson Cycle
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• This is now called the Wilson Cycle in honor of J. Tuzo Wilson who first suggested it for the Atlantic Ocean
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Other Proterozoic Orogenies
Orogeny: A mountain building event (mostly collision and subduction, occasionally transform motion, but doesn’t require continent-continent collisions) Note: Most mountain building episodes (regardless of the actual process are given specific names) e.g.: the Wopmay Orogeny
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Other Proterozoic Orogenies
Starting in the Paleoproterzoic, orogenies became very common around the world.
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Trans-Hudson Orogeny 2.0-1.8 GA
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Trans-Hudson Orogeny Modern Island Arcs
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Grenville Orogeny 1.0 GA
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Grenville Orogeny 1.0 GA
Section Line
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Grenville Orogeny 1.0 GA
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Grenville Orogeny 1.0 GA
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Grenville Orogeny
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Today’s Homework 1. Time line version 1 due NOW
2. Study for Lecture test 2 (March 23, Tuesday after spring break)
Next Time 1. Proterozoic climate (a “cool” lecture)
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GY 112: Earth History
Lectures 18/19: Proterozoic Tectonics
Instructor: Dr. Doug Haywick [email protected]
This is a free open access lecture, but not for commercial purposes. For personal use only.