Mariana Trench Flashcards
What can happen if an accretionary prism doesnt form?
You get a Mariana Trench
What is formed when subducting plates bend and crack open?
When the subducting plate bends, it cracks open which creates ‘Horst’ and ‘Graben’ structures.
What are they?
Graben is the valley bit and horst is the hilly bit
What happens to the hilly sections?
Hilly sections will get scraped off into the valley sections and this will ultimately drag the sediment into the subduction zone. It gets subducted with the subduction movement of the plate
What is a thrust fault?
Thrust fault is a shallow angle, reverse fault is where you shove one block over another
What does bending of plate cause?
Bending causes the underside of the plate to compress
What rocks transition?
There is an important transition from amphibolite to eclogite- temperature does not change too much but pressure and depth does
How does it happen?
When amphibolite is put under more pressure it will form into eclogite
When you reach enough depth with enough pressure, the amphibolite turns into eclogite
Occurs at roughly the same temperature by taking the lighter component out, which is water.
What happens to the water?
The water is being chemically extracted at ~100km depth below the upper surface of the plate where pressure is higher. This depth may vary
When the water is extracted, it is added to the mantle wedge which will chemically react with it, this lowers the melting temperature of the mantle wedge which creates liquid magma which will rise.
As it starts to rise, it will break through the crust and create island arc tholeiite series and volcanic activity essentially.
Why do subduction zones tend to form arcs?
Because the earth is a sphere. Imagine pressing your thumb into a tennis ball, making a dent. This would create an arc around your thumb- and subducting a plate into the earth is the same effect
