Back-arc spreading Flashcards
Where can seafloor spread occur?
It turns out that the sea floor spreading occurs in many active back arc basins (BABs), such as at the active Lau BAB or the Marina BAB.
How many methods are there to explain back-arc spreading?
Four methods because it is not clear what the main cause is
What is back-arc spreading?
Back-arc spreading is a distinct from ‘normal’ mid-ocean ridge systems as sea floor spreading is asymmetric with respect to the spreading axis (spreading is faster in one direction compared to the other- the ARC spread on figure below is 3 times faster than the other movement)
What is the first model?
Active diapirism model
What happens?
Where you have a subduction zone, the sediments and water which is being subducted causes lower temperature in mantle wedge which can create liquid magma which will tend to rise and fuel spreading in the back arc region which will split the overriding plate open
Arc will move one way
Back-arc will move in the opposite direction
Diapir due to frictional heating or fluids released from the dehydrating slab.
Rising diapir splits the arc and sustains seafloor spreading in the back arc region
What is the second model?
Passive diapirism model
What do you need to know to understand second model?
Slab rollback and subsidiary convection
What is slab roll back?
When the subduction gets steeper overtime
What does this create?
Creates subsidiary convection in the mantle wedge
What happens as the slab rolls back?
As the slab rolls back, the region where convection is, the mantle wedge gets pulled with the overriding plate which pulls it apart
What are the two stresses?
Regional extensional stresses and extensional stresses
What does extensional stress arise from and what does extensional stress lead to?
Regional extensional stresses arise in the asthenosphere from roll-back and downgoing slab due to trench suction
Extensional stresses lead to strain in the asthenosphere, allowing melt pockets to connect with each other, releasing melt into the lithosphere above
What is the third model?
Convection-driven model
What does convection do?
Convection that develops could drag the overriding plate as the slab moves back which also helps to push the plate further downwards
What does it also help with?
Convection could also help to push the magma to the surface and fuel back-arc spreading
