Lecture 4: Plate Tectonics Flashcards
What is a tectonic plate?
Large subdivisions in the crust of the planet, which are
generally in motion over long geological time scales
What are the two main types of tectonic plates?
Oceanic crust and continental crust
What is the difference between oceanic and continental crust
Oceanic is more dense, uniform and thin, rich in iron and magnesium.
Continental is less dense, thicker and varying, rich in silicates.
How do tectonic plates move?
Asthenosphere: region below upper mantle where rocks are liquid: colder denser rock sinks and hotter less dense rocks rise, which droves a convection current.
What are the three common patterns in plate interactions?
Divergent boundaries
Convergent boundaries
Transform boundaries
What are ridges and subduction zones?
When tectonic plates are pushed together, the ridge is formed by the plate that slides on top and the subduction zone is formed by the plate that slides below.
What are divergent boundaries?
When new oceanic crust is formed via the rising of hot liquid rock, tectonic plates move apart to create a difergent boundary, allowing the new crust to form.
What are hydrothermal sea vents?
weak points in the sea floor where heated water and minerals enter the ocean (usually found along divergent boundaries).
How does a magnetic pole reversal occur?
When rocks solidify, magnetized minerals become locked in one orientation (which is the current magnetic field). However, as these rocks are disrupted and melted, the earth’s magnetic field can reverse and change direction (~ every 300,000 years).
What is a convergent boundary?
Two plates moving directly towards each other - one is forced under the other
What is a subduction zone?
The area where one plate is forced under second plate.
What happens when oceanic crust meets continental crust?
Ocean crust is denser is always subducted below continental which forms an oceanic trench.
What happens when oceanic crust meets ocean crust?
One still subducts under the other forming an oceanic trench. The subducted crust melts and produces volcanoes.
What happens when continental crust meets continental crust?
one continental cannot easily dubduct under the other into the asthenosphere due its low density. Therefore, one crust is usually forced upwards into new mountain ranges.
Sidenote: if there is some oceanic crust in the mix it can be moved to mountaintops! (ex: marine fossils found in the Himalayas)
What is a transform boundary?
When two plates slide past each other.
What is the elastic rebound theory?
Earthquakes occur because plates at transform boundaries cannot move continuously –> Energy and pressure builds up until it is released all at once.
Which are older: oceanic or continental crust?
Oceanic is 280 MYA
Continental is 3 GYA (billion years)
How can we test the age of oceanic crusts?
Radiometric dating: if C-14 and N-14 isotopes are in equal abundance, one half-life has passed and the specimen is 5,730 years.
How do plate tectonics affect the deep carbon cycle?
As plates shift, new rock and magma/lava are released which leads to volcanic outgassing and inreased weathering, meaning more carbon is released from below the earth’s crust.
