EESB15H3 Lecture Notes - Lecture 12: Back-Arc Region, Superior Craton, Canadian Shield
4 Nov 2017
School
Department
Course
Professor
Document Summary
Slow pumping of oxygen into the atmosphere. Figure 1: geologic eons as a proportion of geologic time. A salty ocean because of enhanced chemical weathering. Sodium and chloride don"t precipitate easily into rocks and remain in the water. Rudimentary plate tectonics with sea-floor spreading and subduction. Zircons indicated the formation of continental crust. 3. 8 bya at the end of heavy bombardment. Meteor impacts were accreting the earth"s volume. Figure 2: production of continental crust at subduction zones. Ophiolites: are slivers of ancient oceanic crust that are obducted onto the continental margin in an accretionary complex. Archean oceanic crust was less dense due to high temperature, allowing for more ophiolites formations. Figure 4: continental crust formations in the archean. Backarc basins form from extension in the continental crust. Granulites: are highly metamorphoses gneisses from either igneous or sedimentary protolith. Greenstones: are metamorphosed basalts and shales formed as pillow basalts.
