MID OCEAN RIDGES Flashcards
1
Q
MOR evidence - satellites
A
Show the location of MORs and GPS can measure movement
2
Q
MOR evidence - seismic imagery
A
side scanned sonar
- uses a tow fish just above seabed
- shows detailed shape of sea floor along the MOR
multi-beam echo sounders
- shows overall layout of the MOR
- fan shape from above
3
Q
MOR evidence - surveys
A
magnetic survey
- uses magnetometers
- weakened magnetic field strength at MOR suggests hot rock
gravity survery
- uses gravimeters
- shows light, buoyant, hot rock below the MOR
4
Q
MOR evidence - seismic topography
A
- shows seismic waves are retarded by >10% as they travel through hot rock below the MOR
5
Q
MOR evidence - ophiolites
A
- where the ocean crust (lithosphere) has been obducted rather than subducted
- model for processes at a MOR
- mafic/ultramafic lavas
6
Q
MOR - effects of rate of spreading
A
rate of spreading effects:
- how much heat is carried upwards by magma
- how quickly heat is lost from the top of the chamber
Increased activity causes sea water to be displaced
- MOR takes up space in sea
- global sea levels rise
- E.G Atlantic opened quickly during cretaceous
7
Q
MOR - slow spreading
A
Mid Atlantic Ridge 2-4 cm/year
- cool discontinuous magma chamber (shallow)
- produces occasional lava
- lots of faulting (rift valley)
- rough/jagged
diagram 1
8
Q
MOR - fast spreading
A
East Pacific Rise 16cm/year
- hot continuous magma chamber (deep)
- lots of lavas with few breaks
- little amount of rifting
- smooth dome
diagram 1
9
Q
MOR - adiabatic change
A
A change in temperature due to a change in pressure
Mantle rises –> pressure drops –> material expands –> mantle cools
diagram 2
10
Q
MOR - decompression melting
A
making a rock start to melt by dropping the pressure
diagram 2
