Lecture 5: Plate Tectonics Flashcards
Plate tectonics
Description of the movements of pieces of Earth’s lithosphere on less rigid mantle rocks and the effects caused by plate motion and plate formation
Theory that explains the global distribution of earthquakes and active volcanoes, mountains, and other large features by the movement of large fragments of the Earth’s crust on less rigid mantle rocks.
Convection
Caused by systematic heating and cooling (changing of density) of minerals in outer core and mantle
Sweated out low density elements to form continental crust
Subduction
When the leading edge of a moving place of oceanic lithosphere collides with another place, the denser plate turns downwards and pulled by gravity into the asthenosphere
Arc volcanoes
A curved chain of volcanoes in the overriding tectonic plate of a subduction zone. Volcanic arcs form as the result of rising magma formed by the melting of the downgoing plate. They are curved because of the curvature of the Earth
Ocean islands
Volcanic eruptions in the middle of tectonic plates, far from any volcanically-active plate boundaries, have created many of the thousands of ocean islands and seamounts that cover Earth’s ocean floors
Accreted terranes
Fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or “sutured” to crust lying on another plate
Plate boundary
Three main types
Convergent, divergent and transform
Layers of the earth (3)
- Core
- Mantle
- Crust
Core
Inner and outer
Outer core
Convection currents responsible for generating magnetic field
Mantle
Lower and upper mantle
Upper mantle
Lithosphere
Asthenosphere
Crust
Continental crust
Oceanic crust
Developing theory of plate tectonics
- Observation of EQ, volcanoes, geomagnetic stripping
- Models hindcasted and hypotheses tested
- Predictions came true
Magnetic field reversal
Occurs over less than 12 thousand years
Geomagnetic stripping
New lava formation from Mid-Atlantic ridge
As lava cools past Curie point, atoms point towards magnetic pole
Can plot layers by age and magnetic polarities, building timescale of magnetic polarities
Ocean floor is striped with parallel bands of magnetized rock that should alternate polarities (seafloor pushed away from ocean ridges)
Nazca plate
Moving towards SA plate
Made of iron and other dense elements
Will subduct under continental plates because its more dense
Pacific plate
Biggest intact plate
Moving in 2 directions due to curvature of the Earth
Subducting under NA plate
EQ from transform boundary at San Andreas Fault
South American Plate
Moving away from mid-Atlantic ridge towards Nazca plate
Evidence for plate tectonics
- Magnetic field
- Seafloor spreading
- Subduction and EQ depth
Mesosphere
Extends from core-mantle boundary to 360km below surface
Flow in convection cells
Stiff-plastic solid
Asthensphere
Surrounding mesosphere
Flow in convection cells
Sold plastic
Lithosphere
Outer layer of earth
Rigid
Broken into plates
Ranging from few km to 100km under continents
Boundary between lithosphere and asthenosphere is more important strength boundary
Seafloor spreading
Divergent zones
Magma rises out of cracks to build volcanoes
Down-dropped linear rift valley becomes filled with ocean and becomes a new sea
Earthquake, January 23
7.9-8.2 earthquake this morning near Alaska ~5:30
