Question

Suggest how specific characteristics of convergent plate boundaries and/or oceanic crust may influence the angle of subduction, in particular specific aspects of crustal properties that may lead to a steep or shallow angle of subduction.

(A strong answer will discuss how specific characteristics of oceanic crust may influence the angle at which oceanic crust subducts, preferably by citing examples of the behavior of crust at ocean-ocean or other convergent plate boundaries.)

Answer 1

Nature of subductiong plate plays an important role in angle of subduction.

Many factors affects the angle of subsidence such as

• Age of subducting plate
• Density of subducting plate
• Temperature of subduction plate

On the basis of this factor subductiong can be classified as

1. High stress type subduction
2. Low stress type subduction

1. High stress type subduction (Arc under compression):-

In this type of subduction the undergoing plate is young,thin,hot and bouyant lithospheric plate so due to this bouyancy the undergoing plate subducts at the lower angle.

Shallow Benoiff Zone forms.

Here rate of convergence of plate is greater than rate of subduction so arc is under compression

Example of this type of subduction is Peru-Chile subduction.

Figure :- Schematic of High Stress type subduction

2. Low stress type subduction :-

In this type of subduction the undergoing plate is old,thick,cold and less bouyant lithospheric plate so due to this bouyancy the undergoing plate subducts at the higher angle.

Deep Benoiff Zone forms with absences of accretionary prism.

Here rate of convergence of plate is less than rate of subduction so arc is under tension

Example of this type of subduction is Marina subduction.

Figure :- Schematic of low Stress type subduction