Science Olympiad Dynamic Planet Practice Test

How does the presence of a subducting slab affect the crust in a backarc basin?

1. It leads to the formation of a rift valley

2. It causes crustal compression

3. It initiates extension or rifting of the arc crust

4. It prevents the deposition of sediments

The correct answer is: It initiates extension or rifting of the arc crust

The presence of a subducting slab in a backarc basin initiates extension or rifting of the arc crust due to the dynamics of plate tectonics in that region. When an oceanic plate subducts beneath a continental or another oceanic plate, it generates significant geological forces that alter the stress regime in the overlying crust. In a backarc basin specifically, the retreat of the subducting slab can lower the pressure on the overlying plate, which leads to extension. This extension creates a rifting effect, lowering the lithostatic pressure and allowing for development of normal faults and basin formation. The extension causes the crust to thin and can result in volcanic activity as the mantle is decompressed, leading to melting and the rise of magma to the surface. Overall, this rifting effect in the backarc is crucial for the formation of features associated with extension, such as basins, valleys, and volcanic arcs. Understanding this process enhances our knowledge of how tectonic activity shapes geological features and the evolution of plate boundaries.