Amagmatic Subduction Produced by Mantle Serpentinization and Oceanic Crust Delamination.

Recycling of oceanic lithosphere and serpentinized peridotites into the mantle leads to dehydration melting and volcanic arcs. However, the mechanism of the occurrence of long‐term volcanic gap in subduction zones remains poorly understood. Two‐dimensional thermomechanical numerical models focusing on resisting the transport of the major hosts of hydrous minerals to mantle depths, show that thin oceanic crust together with rheologically weak and buoyant serpentinized mantle could result in hydrated lithologies piling up in the accretionary wedge and no or sparse occurrence of arc magmatism. This scenario may occur during subduction of oceanic lithosphere formed at (ultra)slow‐spreading margins characterized by thin crust and extensive mantle serpentinization, which is a plausible explanation for the "arc gaps" in the Alps and southern Tibet. Plain Language Summary: Volcanic arcs in subduction zones are widespread and are mainly attributed to slab dehydration and subsequent mantle hydrous melting. However, the magmatic history of the Alps and southern Tibet is characterized by two periods of "arc gap" (i.e., no volcanism) that lasted for 40–50 Myr and 10–30 Myr, respectively, with no or only very sparse magmatism and simultaneous exhumation of serpentinized mantle slivers. Our numerical models indicate that thin oceanic crust, such as that formed at (ultra)slow‐spreading centers, together with an extensively serpentinized lithosphere facilitates the removal of the subducting crust at shallow depths resulting in limited arc magmatism. Key Points: The influence of abyssal and slab‐bending serpentinites on magmatism in subduction zones are numerically investigatedAmagmatic subduction zones may occur where abyssal serpentinites are abundantModel results can explain sparse magmatism during subduction in the Alps and southern Tibet [ABSTRACT FROM AUTHOR]