Oceans and Continents
Explain the relationship between crustal thickness and elevation.
Thicker crust = higher elevation
thinner crust = lower elevation
What physical property determines which plate is subducted and which plate is the overriding plate?
Density!
Name a divergent plate boundary on Earth today.
Mid-Atlantic Ridge, East Pacific Rise, East African Rift.
How might we distinguish a hotspot from other types of geothermal activity?
- Isolated volcanism (middle of a plate)
- Cluster of earthquakes different from typical plate boundaries
- Seamount chain
Give an example of evidence that supports the plate tectonic theory.
Many answers (faunal assemblages, APW, bathymetry, seismic velocities, coastline puzzle, etc.)
Which is denser: oceanic crust or continental crust?
Name a volcano that occurs along a subduction zone.
There's many many correct answers!!
What is the most common rock type in oceanic crust?
Basalt (MORBs)
Name a place formed by hotspot volcanism.
Hawaii, Iceland, Yellowstone
Why doesn't the moon have plate tectonics?
The moon's mantle is too cold to drive convection.
About how thick is continental crust? Oceanic?
continental ~ 40 km
oceanic ~5 km
What is the most common rock type in continental crust?
Granite
Why do we call it a mid-ocean ridge or mid-ocean rise?
The elevation at the divergent boundary is slightly higher due to rising mantle convection currents.
How might we tell the relative age between islands in a seamount chain? (not using geochemical methods of dating)
If we know plate motion, we know which direction the "newest" islands will form in. (younger islands in the opposite direction of plate motion)
In which tectonic setting do you find the deepest earthquakes?
Convergent plate margins/ subduction zones.
How do we define the bottom of the crust? (distinction between lower crust and upper mantle)
Seismic velocity discontinuity (Moho boundary)
Why does volcanism occur at subduction zones?
Will accept either or both:
- Introduction of volatiles (freezing point depression)
- mantle/slab interactions
What type of faulting is associated with divergent plate boundaries?
Normal! (will take transform also)
Why is Hawaii made up of several small islands and not one large island?
The Pacific plate moves over the hotspot through time, where the hotspot (source of volcanism) stays relatively fixed.
When was continental crust first formed on Earth?
(probably) the Archean. Will accept 3-4.4 billion years.
Why is continental crust above sea level?
It's less dense and thicker, floats higher in the mantle (isostasy)
What geographic region has the thickest crust on Earth?
The Tibetan Plateau! (fresh continent-continent collision & orogeny)
What is the common name for the hottest hydrothermal vent system? (often found at mid ocean ridges and home to diverse thermophile microorganisms)
Black smokers
Give one possible explanation for the formation of hotspots.
- Mantle plume via thermal diapir
- LLSVPs at the mantle-core boundary
- Glacial unloading/ decompression melting
Name another planet that has active plate tectonics.
Trick question!!! There are none. One possible candidate for active plate tectonics is the Jovian moon, Europa.