EESA06H3 Lecture Notes - Lecture 9: Canadian Pacific Railway, Cambrian Explosion, Gneiss
15 Oct 2015
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Lecture 9: the oldest rocks are in the middle, and younger rocks get accreted around the core (craton, north american continent has grown in 5 stages, arctica (2. 7 ga, nena (1. 8 ga, rodinia (1. 0 ga) 1 + 2 + 3 = canadian shield ( the craton ). Canadian shield is the heartland of north america: pangea assembly (350 ma)- maritime canada is added during appalachians. Orogeny is the active process of collision, and orogen is the result of the collision: pangea breakup (<200 ma) - the last stage, young rocks. British columbia is added during cordilleran orogeny (e. g. rockies): zircon crystals- 2. 7 billion years old. Very small (need a microscope to see them). They are very useful because when they are formed, their parent host rock contains an unstable of isotope of uranium. And the uranium will break down, and it will ultimately produce lead. Uranium lead decay series, uranium decays to form lead for billions of years.
