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EESA06H3 (563)
Nick Eyles (495)
Lecture 10

Lecture 10 notes

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Environmental Science
Nick Eyles

EESA06 Lecture 10 Canadas Geologic Journey: The Last 4 Billion Years 1 We will look at how North America was constructed The process we will follow is one on deconstruction taking something apart and seeing how it was made with continents Plate tectonics is the tool of understanding how North America got built 2 Skipped 3 Continents grow through time by obduction (ex. India colliding with Asia) North American continent shows 5 growth stages: o Arctica (2.7 Ga) oldest, Ga means billions of years o Columbia (1.8 Ga) o Rodinia (1.0 Ga) really IMPORTANT because life evolves at this time ARCTICA + COLUMBIA + RODINIA = CANADIAN SHIELD which is very old and hard rock, later softer sedimentary rocks were added on eastern and western Canada A + b + c = Canadian Shield (the craton the core of north America and we have added eastern north America (Maritime) and them we add the west, Maritime is added when Pangea is forming and then western Canada is added after Pangea breaks up) Pangea assembly (350 Ma): Maritime Canada is added during Appalachians Orogeny (Appalachian Mountains) Pangea breakup (<200 Ma): British Columbia is added during Cordilleran Orogeny (e.g. Rockies) 4 Geology of North America known for more than a 100 years The Canadian shield in the picture are the brown rocks The shield (A+B+C) is the old core of North America Then we can see the green and blue rocks which is rapped around that core The blue area on the right hand side is the Appalachian Belt Only until the plate tectonic theory in the late 60s about the oceans closing and the continents moving that this complex picture could begin to be interpreted 5 These are zircons which we use for uranium lead dating Uranium lead age dating using Zircons is one of the break through methods 6 Tom Crow didnt invent the technique but he got it to the stage where it could be used, expert on dating various rocks Need to find out how much lead is in the crystal because that will tell us how long that crystal has been sitting there and the radio active uranium has been breaking down 7 The oldest continental crust found so far in Canada (yellow knife) is Acasta Gneiss (NWT) that is 4.1 billion years old However its hard to know the oldest rock in the world because any country that has a shield have very old rocks Why is it not correct to say that the Acasta Gneiss is the oldest rock? o Ans. Because it has been metamorphose so there must have been a pre-existing rock. And if we look at the Zircons in here they are what we call Detritals means they are secondary and they have been eroded from something else and are old, garbage, they have been derived from something else Ex. The Zircons originate in igneous rocks, they then get weathered and then become a part of a sedimentary rock and metamorphose to a gneiss 8 The pattern in this map is center, its sort of a Swiss roll pattern The oldest stuff is in the middle and as you come out it gets younger and younger Its not a perfect pattern but the conclusion we can draw is that continents have grown through time Old rocks embedded in the interiors of continents 9 DECONSTRUCTING NORTH AMERICA Province a old term used by geologist to identify rocks in a large area which are pretty similar in appearancegeology with sharp boundaries
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