GSC 111 Lecture Notes - Lecture 12: Grenville Orogeny, Oceanic Basin, Oceanic Crust
13 Jan 2017
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Proterozoic Environments
1. Proterozoic paleogeography
a. Archean
i. Bulk of Earth was oceanic crust or lithosphere
ii. Small number of microcontinents
1. These protocontinents are scattered around our modern continents
iii. First happened in greenstone belts
1. Small, felsic microcontinents separated by metamorphic
greenstone belts
iv. 2.8-2.5 bya- got larger continents
v. Wopmay orogen
1. A 2 bya mountain building event in the Precambrian rocks of
Canada
2. Have evidence of suturing of two isolated Precambrian continents
coming together
3. Metamorphic belt
4. Gives way to fold and thrust belt where there is less metamorphism
5. We get reverse faulting and thrust faulting (long and pointing
upward) of these sediments
6. Deposition of sediments
a. Archean base
b. Sediment and igneous rocks: quartz, dolomite, sandstone
c. Transitional sediments followed by flych (deposits of mud
that are weathering off of an uplifted mountain belt)
d. Transport shifts from east to the west because of
weathering from uplifted mountains that occur on the
mountain
i. This is the point where the two microcontinents
started to collide
e. Molasses- filled up all the space to sea level, have rivers
and terrestrial sediments being deposited on top
b. If we zoom in on North America, we can go in and radiometrically date different
Precambrian rocks of North America and they correlate with different time
periods
c. Evidence that there was one point where our continent almost rifted apart
i. Keweenawan supergroup
1. Canada, Great Lakes
2. Primarily volcanic dikes and basalts
3. Represents when Laurentia started to diverge
a. Was going to break up and form an ocean basin, but it
stopped
d. Grenville Orogeny
i. Mountain building event on the Eastern coast of North America
ii. Collision
iii. This could have stopped the Keweenawan from rifting
e. 1 bya
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