In geology, subduction is a process that occurs at certain regions, called destructive plate boundaries, where a tectonic plate moves under another tectonic plate. This process can lead to a kind of slab movement called slab rollback.
Slab rollback refers to the process that involves an older oceanic crust, which is colder and more dense than other slabs, subducting at a steep angle. As the older slab collapses into the asthenosphere, it can "roll back" through the mantle. Slab rollback can pull the upper plate with it, causing an extension in the overlying plate, and possibly resulting in backarc spreading.
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Backarc spreading is a process caused by the sinking of a subducting plate. If this plate sinks and slides under the overriding plate faster than the overriding plate moves forward, rifting can occur.
Slab rollback can cause the overriding plate in the subduction zone to become stretched until it rifts. Rifting results in extensional tectonics or a process where the lithosphere and the Earth's crust pull apart. This stretching enables magma to rise into the gap created by the rift.