Canada's Geologic Journey- The Last 4 Billion Years
Outline of lecture: (Read Chapter 20)
continents grow through time by obduction
North American continent shows 5 groth stages
Arctica 2.7 Ga
Columbia 1.8 Ga
Rodinia 1.0 Ga
Arctica, Columbia and Rodinia make up the Canadian Shield (the Craton)
Pangea assembly 350 Ma: Maratime Canada is dur ing Appalachian Orogeny (Appalachian
Pangea Breakup <200 Ma: British Columbia is added during Cordilleran Orogeny (eg.
The Canadian shield is the core of Canada
The breakthrough has been our ability to date things.
Tom Krogh was an expert on dating rocks.
Acasta Gniess (NWT) is over 4.1 billion years old and are the oldest rocks found in Canada.
However technically it is not bec ause it has gone through metamor phosis therefore there was
once an older rock
Detrital- is related to detritus which is basically garbage. Detrital means having been derived
from something else.
Deconstructing North A merica: (refers to image in slideshow slide #9)
1. The or iginal North American continent, Arctic a, which started to for m about 2.5 billion years
ago from smaller continents and was completed by about 1.9 billion years ago when old
Archean cratons were welded together by the Trans-Hudson Orogen and others.
2. Added to the North American continent during the for mation of Nena about 1.9 billion years
ago after the Penokean Orogeny
3. Added dur ing t he for mation of Rodinia about 1.3 billion years ago dur ing the Grenville Orogeny
4. Added dur ing t he for mation of Pangea about 600-300 million years ago
5. Added after the break up of Pangea about 250 million years ago.
Lithoprobe- literally means probing rocks. There are vehicles that are meant to mimic
earthquakes, that produce energy that goes down and reflects back up which allows us to
reconstruc t what is down in the earth. The pur pose of Lit hoprobe is to better understand the
shield, and how the shield was put together.
Transects- Are cross sections created by the lithoprobe.
The Canadian shield is a Peneplain it means literally almost a plain, generally speaking the
shield is f lat from years of erosion wiping out most of the mountains.
Political unification of the provinces 1867-1949 is an analog for welding of geolog ical
'provinces' through geologic time
Obduction: The accretionary process that builds continents from small crustal blocks
The building of cratons is called cratonization, it is also the building of shields.
In each individual province you can see the process of obduction and how it has built the