plate margins

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What rock type will you find at a conservative plate boundary and is used in paleomnagnetic studies?
Basalt
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What happens to the edge of oceanic crust as you move away from a mid ocean ridge?
It gets older
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What method would you use to age the oceanic plate?
Radiometric dating
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What is the origin of basaltic magma?
The partial melting of the ultra mafic rock in the upper mantle
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What is the mineral composition of basalt?
Calcium rich Plagioclase feldspar and pyroxene
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What is the texture of basalt?
It's fine grained and it has random orientation
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How are pillow lavas formed?
Underwater eruption, the magma rapidly cools from contact with the sea water causing a skin to form.
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What is normal polarity?
Alignment of magnetite with present day polarity
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Two characteristics of the core thought to be generating the magnetic field
The iron in the core is a liquid. It's a self exciting dynamo.
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Explain how lavas can contain a record of the earths magnetic field at the time of their formation
The iron minerals are magnetized permanently to the earths magnetic field at the time of their alignment, they become fixed when solidified at the curie temperature. The alignment is irreversible
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Why are the stripes found at a divergent plate boundary irregular?
The time spans of chrons are not equal
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What is reversed polarity?
Magnetic fiels in the 'opposite orentation' to the present day
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Why are there stripes on the ocean floor?
Evidence of past magnetism. The stripes show normal and reversed polarity
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What is a geomagnetic reversal?
A change in the Earths magnetic field such that the positions of magnetic North and magnetic South are interchanged
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Describe the earthquakes found at divergent plate boundaries?
Transform faults, low magnitude shallow focus concentrated below ridge
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Why do divergent plate boundaries occur?
They occur because of rising convection currents. The convection current will push on the bottom of the lithosphere lifting it and flowing laterally beneath it, this causes the plate to move as well.
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Why do earthquakes occur along conservative plate margins?
Platesmove in opposite directions past eachother, stress builds up and then the stress release causes an earthquake
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What is a strike -slip fault?
A type of fault whose relative motion is predominantly horizontal in either left or right direction
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What are the two types of transform faults?
Two oceanic plates or continental fault
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What is the origin of andesic magma?
Subduction of oceanic mafic crust under the continental crust, sub-ducted slab becomes partially melted and contaminate
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How might the height of a mountain range change over time?
Increase as collision is still happening and weathering and erosion could cause it to become smaller
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Where would you find earthquake foci located along a subduction zone?
All along the subduction zone until 700km
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Why are there no earthquake foci deeper than 700km at a convergent plate boundary?
Plate is too ductile as it is melted, there is a lack of friction/stress
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At a convergent (collision) plate boundary why is there no subduction?
The plates are equal density, they're both continental and the plates are too thick
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What is an orogeny?
Mountain building
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Why are there earthquakes all long the subduction zone?
The friction of the sub-ducted plate moving against the non sub-ducting plate there's then a release of pressure and volcanic activity
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How do mountains form at a convergent plate boundary?
Two continental plates collide the lithosphere then thickens to form fold mountains
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Why is there a subduction zone when oceanic and oceanic crust meet at a convergent plate boundary?
On plate (the oldest) is cooler an therefore is sub-ducted
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Other cards in this set

Card 2

Front

What happens to the edge of oceanic crust as you move away from a mid ocean ridge?

Back

It gets older

Card 3

Front

What method would you use to age the oceanic plate?

Back

Preview of the front of card 3

Card 4

Front

What is the origin of basaltic magma?

Back

Preview of the front of card 4

Card 5

Front

What is the mineral composition of basalt?

Back

Preview of the front of card 5
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