Knowra Island arc Island arc An island arc is a curved chain of volcanic islands formed above an oceanic subduction zone, where water released by the descending slab helps generate magma in the mantle wedge.
Subduction : The descent of one tectonic plate beneath another into the mantle. The sinking oceanic plate supplies the water and tectonic setting that produce an island arc.
Oceanic crust : The relatively thin, dense crust that forms the ocean floors, mainly from basaltic rocks. Island arcs rise on oceanic crust rather than the thicker continental crust typical of continental arcs.
Aleutian Islands : An island chain in the North Pacific formed above the subduction of the Pacific Plate beneath the North American Plate. The Aleutians are a classic example of a volcanic island arc above oceanic subduction.
Continental arc : A volcanic chain formed above a subduction zone on continental crust. Unlike an island arc, it is built on a continent and commonly interacts with thick continental crust.
Arc magma : Magma generated in a volcanic arc above a subduction zone, commonly enriched by slab-derived materials. Its composition records interactions among the slab, mantle wedge, and overriding plate.
Flux melting : Melting caused when added substances, especially water, lower the melting point of mantle rock. Water released from the slab lowers the mantle wedge’s melting temperature.
Lithosphere : Earth’s rigid outer layer, comprising the crust and the uppermost mantle. Its moving plates create the convergent boundaries on which island arcs form.
Mariana Islands : A volcanic island chain in the western Pacific associated with the Mariana subduction system. The Marianas sit above exceptionally deep subduction and are paired with an active back-arc basin.
Hotspot volcanism : Volcanism caused by localized mantle upwelling, commonly producing chains as a plate moves over the source. Hotspot chains can curve or form islands, but they do not require a subduction zone.
Andesite : A volcanic rock with intermediate silica content, common in many subduction-related volcanic arcs. Its prevalence in arcs raises questions about how mantle-derived magma acquires intermediate compositions.
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