Insights Into the Causes of Arc Rifting From 2‐D Dynamic Models of Subduction

• Published in: Geophysical research letters Vol. 44; no. 21; pp. 10,948 - 10,957
• Main Author: Billen, Magali I.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.11.2017
• Subjects: adakite; arc rifting; boninite; Buoyancy; Computational fluid dynamics; Dynamic models; Fluids; Forces (mechanics); Heating; Instability; Lava; Lithosphere; Magma; Mantle; mantle wedge; Ocean circulation; Plate tectonics; Rifting; Sinking; Spreading; Stability; Subduction; subduction dynamics; Subduction zones; Trenches (pipelines); Two dimensional models; Upwelling; Viscosity; Volcanic activity; Volcanism; Volcanoes; Wedges
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1002/2017GL075061

Back‐arc spreading centers initiate as fore‐arc or arc rifting events when extensional forces localize within lithosphere weakened by hydrous fluids or melting. Two models have been proposed for triggering fore‐arc/arc rifting: rollback of the subducting plate causing trench retreat or motion of the overriding plate away from the subduction zone. This paper demonstrates that there is a third mechanism caused by an in situ instability that occurs when the thin high‐viscosity boundary, which separates the weak fore arc from the hot buoyant mantle wedge, is removed. Buoyant upwelling mantle causes arc rifting, drives the overriding plate away from the subducting plate, and there is sufficient heating of the subducting plate crust and overriding plate lithosphere to form adakite or boninite volcanism. For spontaneous fore‐arc/arc rifting to occur a broad region of weak material must be present and one of the plates must be free to respond to the upwelling forces. Plain Language Summary Oceanic spreading centers are commonly found in the region above sinking plates. These spreading centers are known to form as the result of extension and breaking apart of the arc of volcanoes that form close to where the sinking plate enters the mantle. Here we show that the rifting of a volcanic arc can occur spontaneously and is driven by the buoyancy of the hot mantle wedge material. This result is different from existing models for arc rifting, which argue that external changes in the motion of the sinking or overriding plate are required to cause arc rifting. Key Points Spontaneous fore‐arc/arc rifting can occur when there is a broad region of weak material in the overriding plate Positive buoyancy of hot, mantle wedge material drives rifting and can change overriding or subducting plate motion Heating of the subducting crust and overriding plate lithosphere could produce adakites or boninites during rifting