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How does back-arc spreading form oceanic crust behind island arcs?

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Earth's lithosphere and upper mantle — oceanic crust A cross section of Earth's outer layers, from the crust through the lower mantle.

Back-arc spreading is a geological process that creates new oceanic crust behind an island arc at convergent plate margins.12

The process is primarily driven by the subduction of an older, denser oceanic plate beneath another. As the subducting slab descends into the asthenosphere, it may undergo "trench roll-back," a phenomenon where the subducting plate retreats oceanward. This movement creates extensional forces in the overlying plate, causing it to thin and rift.213

As the crust thins, the decompression of the underlying mantle triggers melting, producing magma that rises to the surface. This magma exploits the rifts in the crust, leading to the development of spreading centres. Through seafloor-spreading processes similar to those at mid-ocean ridges, new basaltic crust is generated, widening the back-arc basin and expanding the seafloor behind the volcanic arc. These regions are significant sites of hydrothermal activity and provide critical insights into tectonic evolution.124