Numerical modeling of intraplate and petit-spot volcanism originating from hydrous mantle transition zone

Abstract:

Most magmatism occurring on Earth is conventionally attributed to passive mantle upwelling at mid-ocean ridges, slab devolatilization at subduction zones, and mantle plumes. However, the widespread Cenozoic intraplate volcanism in northeast China, locate more than 1000 km westward of the Japan Trench, and the young alkaline petit-spot volcanoes eastward of the trench, are not associated with any of these mechanisms. Globally, Cenozoic non-hotspot intraplate volcanism is widely distributed in Europe, northeast Africa, east Australia, west US and east Asia (Conrad et al., 2011; Long et al., 2019), which is generally attributed to small-scale convection (e.g., Elkins-Tanton, 2007), asthenospheric shear (Conrad et al., 2010; Davies & Rawlinson, 2014), deep slab dehydration (Zhao et al., 2009), slab fragmentation (Liu & Stegman, 2012; Zhou et al., 2018), and subduction-induced upwelling (Faccenna et al., 2010). Nevertheless, none of those mechanisms can simultaneously explain the off-shore and on-shore volcanoes of Japan Trench.

We noticed anomalous low velocity zones (LVZs) above and below the mantle transition zone (MTZ) in Japan from seismic tomography images. And these two different volcanoes are coincidently sitting above the LVZs, which sparks us to link their relationship. We show that most if not all the intraplate and petit-spot volcanism and LVZs present around the Japanese subduction zone can be explained by the Cenozoic interaction of the subducting Pacific slab with a hydrous transition zone. Numerical modelling results indicate that 0.2-0.3 wt.% H₂O dissolved in mantle minerals which are driven out from the transition zone in response to subduction and retreat of a stagnant plate, causing partial melting above and below the MTZ, is sufficient to reproduce the observations.

Conrad et al., 2010. https://doi.org/10.1016/j.pepi.2009.10.001

Davies & Rawlinson, 2014. https://doi.org/10.1130/G36093.1

Elkins-Tanton, 2007. https://doi.org/10.1029/2005JB004072

Faccenna et al., 2010. https://doi.org/10.1016/j.epsl.2010.08.012

Liu & Stegman, 2012. https://doi.org/10.1038/nature10749

Long et al., 2019. https://doi.org/10.1029/2019GC008591

Zhao et al., 2009. https://doi.org/10.1016/j.pepi.2008.11.009

Zhou et al., 2018. https://doi.org/10.1038/s41561-017-0035-y