Plate Tectonics Flashcards
What evidence supports the theory of continental drift?
the breakup of the supercontinent Pangea
- the fit of continents
- location of glaciations
- fossils
- rock types and structural similarities
- paleoclimates preserved in rocks
What is paleomagnetism?
study of the record of the Earth’s magnetic field in rocks, sediment, or archeological materials
Why can’t you use the polarity of the Earth to determine where the continents have drifted from?
Earth’s polarity is not set, it “wanders” and “true north” changes
What is bathymetry? And when was it used in the oceans?
the measurement of depth of water in oceans, seas, or lakes
Mapping during ww2 for submarines to be able to navigate
How are the continents moving?
The oceanic crust is being pushed below continental crust because it is more dense
What is the deepest part of the ocean?
Mariana trench
What are mid ocean ridges?
Area where new sea floor is being created by the splitting of two plates moving apart
linear mountain ranges in the ocean basins
Where are deep ocean trenches found?
border of volcanic arcs
Where is heat flow greatest?
mid-ocean ridge axis (where the sea floor is spreading and making new material)
How/where are volcanos formed?
at the meeting of the two plates under extreme pressure the volcano forms. molten lava is created from the pressure and immense heat
What are seamount chains?
Underwater mountains (usually dormant volcanos) that might have land above them from when they were active
What are guyots?
an underwater mountain with a flat top (used to be above the water level but worn down by waves over time to form the flat top)
What are volcanic arc islands?
long chains of active volcanoes with intense seismic activity found along convergent tectonic plate boundaries
ring of fire
What is the difference between seamount chains and volcanic arc islands?
both are in chains but only one island (at the end of the chain) remains capable of
erupting
How are islands formed (such as hawaii)
A seamount volcano erupts and the stuff settles on top of the volcano/mountain on the water. Then over time the tectonic plates shift and the volcano is exposed over water again
What is the oceanic crust made of?
Basalt
What is sediment?
a layer of sediment on the ocean floor
overlying crustal rock thickens away from mid-ocean ridges
weathering, erosion
Where do earthquakes most commonly occur?
oceanic earthquakes occur along belts
belts coincide with trenches, ridges and
fracture zones
What are bathymetric features?
places where the crust is moving
What are two things that support sea floor spreading?
- magnetic anomaly
- sediment thickness
What is magnetic anomaly equation?
(expected strength of Earth’s main dipole at a certain location) - (actual measured strength of magnetic field at that location)
Why is the sea floor striped with magnetic anomalies (section pointing to true north, the next to south)?
“True north” wanders and even switches to point “north” to south. The stripes show the direction change
(magnetic reversal)
What is the difference between positive and negative anomolies?
Positive anomalies show normal polarity crust, negative anomalies are reversed and point south
What two theories make up the plate tectonic theory?
Wegener (continental drift) + Hess (sea-floor spreading) = Plate Tectonic Theory
What is the lithosphere?
“Crust” that the 20 plates make up
Bends into the asthenosphere when loaded
What is the asthenosphere?
Layer underneath the lithosphere
What are the two types of lithosphere?
Continental
Oceanic
What is the difference between active and passive margins?
- margins near plate boundaries are “active”
- margins far from a plate boundary are “passive”
What are the three types of plate boundaries?
Divergent
Convergent
Transform
What is a divergent plate boundary?
tectonic plates move apart and material is created
mid atlantic ridge
What is a convergent plate boundary?
tectonic plates move together and one is consumed by the other (subduction)
ring of fire
What is a transform plate (transform fault) boundary?
tectonic plates slide past one another
plate material is neither created nor destroyed
san andreas fault
what is low basalt?
magma quenched at sea floor
what are dikes?
preserved magma channels
what is gabbro?
deeper magma
What are black smokers and how do they work?
vents in the ocean with black “smoke”
water entering fractured rock is heated my magma
- hot water dissolves minerals and cycles back out
of the rock
- when water reaches the sea, minerals precipitate
quickly
How does Earth maintain a constant circumference?
subduction of ocean basalt crust balances out the creation of new crust at mid ocean ridges
What happens to subducted plates?
Once they start going down, it goes down like an anchor on a rope (steeper over time) (slab pull)
The plates go deeper into the asthenosphere until it melts
What are accretionary prisms?
sediments are scraped off of subducting plates and thrusts sediment onto overriding plate
contorted prism can be pushed above sea-level
Taiwan
What are back arc basins?
a marginal sea between an accretionary prism or island arc and a continent
What are triple junctions?
places where 3 plate boundaries coincide
What are hot spots?
Area perforated in the plate where magma can bubble up, usually volcanic
forms chains of volcanos and islands as plates move
hawaii
What are continental rifts?
spreading on continents that eventually forms oceans between them
great rift valley in east africa
