Volcanism at destructive plate margins Flashcards
Give three examples of destructive plate margin volcanic settings.
Island arcs, continental arcs, volcanic arcs.
What type of melting occurs at destructive plate margins?
Hydrous (flux) melting.
Describe the position of the geotherm and solidus at destructive plate margins.
The solidus is pushed to the left, crossing over the geotherm.
Describe hydrous melting.
The melting point of mantle peridotite is lowered by the addition of water.
Where does the water needed for hydrous melting come from?
Subducting slab
Describe the subducting slab.
Comprised of ocean crust and lithosphere with minerals that have been altered by hydrothermal circulation and interaction with the seafloor.
Give three examples of the water-bearing minerals contained in the subducting slab.
Serpentine, chlorine, actinolite.
Describe the three phases of the dehydration of the subducting slab.
1: Pore water is released by the scraping off of sediments.
2: The oceanic crust is dehydrated (doesn’t contain much water).
3: Hydrous minerals start to breakdown from heating and pressurisation (common in serpentine).
Where is the water from the slab released into?
The mantle wedge
What is the mantle wedge?
The mantle that overlays the subducting slab.
What happens to the mantle wedge when water is released into it?
The solidus is lowered.
What does the action of subduction result in?
Drags newly hydrated peridotite deeper and rereleasing some water. This is repeated until there is enough water for partial melting.
Where does the subducting slab get heat from?
The mantle wedge. The subducting slab has to be young and warm to be able to heat enough.
What are subduction zoom volcanoes fed by?
Hydrous melted peridotite from the mantle wedge.
What type of melt does wet peridotite produce?
Primary basaltic melts.
