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Lecture 2

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University of Toronto Scarborough

Lecture 2: Plate Tectonics -Jack Tuzo Wilson in 1965 explained that places where crust isn’t spreading apart or coming together and getting recycled but rather moving past each other. Paleomagnetism, sometimes, Earth’s magnetic field flips. -The Theory of Plate Tectonics hold that the Earth’s lithosphere is divided into plates that move relative to one another, and relative to the underlying asthenosphere. As plates move, their interiors remain relatively intact, while their boundaries undergo deformation. Striping on ocean floor occurs because magma rises as ridge opens wider. Reversal in magnetic pole, then normal polarity. -The Wilson Cycle: 1. A continent rifts when it breaks up. 2.As spreading continues, an ocean opens. A passive margin cools and sediments accumulate. 3. Convergence begins, an oceanic plate subducts, creating a volcanic chain at an active margin. 4.Terraine accretion from the sedimentary wedge welds material to the continent. 5. As two continents collide, orogeny thickens crust. 6.Continent erodes, thinning crust. -What drives plate tectonics? Natural Sources of heat in earth, cooling down from heat of formation. Natural minerals decaying and emitting heat. Material in mantle heats and wants to rise (convection currents). Lecture 7. Geologic Time, Fossils, and Evolution -Uniformatarianism is the concept that all things that happen today have happened in the past too. It was developed by James Hutton. This contrasts with catastrophism which holds that small things happen all the time to make changes, not just big catastrophes. -An unconformity is missing information; gap in geologic record. Rocks lost to erosion or no rocks deposited for many years, new rocks on top. -Body Fossils are direct evidence of bones and shells while trace fossils are indirect evidence; footprints and burrows. Index fossils are used to identify relative age of strata and gaps (unconformities). To be a good index fossil, creature must be short lived, and have lived over large area. If it didn’t live long, it would only be found in 1 layer of rocks. The law of faunal succession states that fossils can be used to tell how old layers are relative to each other. -Relative age is the generalization while absolute age is exactly to the point. Arthur Holmes figured out how to find absolute age through isotopes. Same protons, different number of neutrons. Relative age dating was done through uniformatarianism, original horizontality, original continuity, and cross cutting relations. The law of continuity says that something is continuous over large area. Layer 1 rocks, Gneiss and medisedimentary=subjected to a lot of pressure. Formed by plate tectonic collisions. -Arthur Holmes contributed to geologic time by creating isotopic age dating.Lord Kevin provided an estimate of the earth’s age by calculating how long it took to get from the temperature it was at to current temperature. Didn’t know about radioactive decay and the heat being generated in the planet. Henri bacquerel discovered radioactivity, and realized radioactive isotopes go under radioactive decay which changes them. geological time: the time of the physical formation and development of the earth (especially prior to human history). Stratigraphy was concerned with the order and relative position of strata and their relationship to the geological time scale. -When iron rusts due to oxygen, BIFF is created at ocean bottom. Lecture 8 Economic Resources -The two unconformities are “The Great Unconformity” as well as “The Big Gap”. Hutton first discovered the Great unconformity at Siccar Point. It is between layer 1 and 2 and the Big Gap is between layers 3 and 4. -Most layer 1 rocks are metamorphic because of old mountains that don’t exist. Roots of mountains (Gneiss) is layer 1. (Coal was found in Eastern Canada by Logan) It is rich in economic resources, ie Gold, highly metamorphosed. -All VMS ( @ MOR) (volcanic massive sulphides) deposits in Canada show evidence of formation close to black smokers like MOR. Sea water into cracks gets heated. It picks up iron, sulfur, copper, zinc. Water comes back into cold sea, and can’t hold on to minerals because it cools at which point they precipitate out (sulfide mineral). When mining sulfide, if exposed to water it is acidic. Magnetite, Quartz and hematite are BIFs. -Turbidity is underwater landslide which remobilizes droplets. Rusted iron exposed to oxygen builds up, is remobilized and re deposits after turbidity. -To be economically worth mining (an ore) you must satisfy economic and political wishes and rich enough in concentration. The Sudbury impact crator used to be round, but plate tectonics compressed it. Meteor caused it, liquefied some rock, nickel is rich here. -Layer 2 rocks are sedimentary. Heavy oil is stuck to sand in Canada. Nat gas is less dense than oil and will cool on top of it. There will be impermeable trap rock to trap oil and gas. Oil shales are deeply buried farther south, but north they are at the surface. If you keep removing oil without putting anything in it, the ground will collapse. Salt is an evaporate deposit. Water evaporates from sea, salt stays. Resources include: coal, oil and salt. Coal is used for coke, fuel. -Hydrothermal ore deposits- Groundwater gets heated by magma source. It moves through rocks and leeches elements from the rocks around it. As water cycles, it cools down and elements precipitate out and solidify. Come out as deposits. Eg. Copper. Magmatic Ore Deposits- Magma cools in magma chamber and minerals crystallize once they reach a certain temp. Solids can float, they can sink to the bottom and form layers or crystallize on the walls. Sedimentary Ore Deposits- Evaporite deposits from when lake water or seawater evaporates and leaves its dissolved mineral behind. (baking soda). Placer Ore Deposits-Originated elsewhere, and transported by water. Residual Ore De
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