Numerical modeling of the formation of extensive intraplate volcanism

The occurrence of mantle melting is generally attributed to high temperature, decreased pressure, and/or the presence of volatiles such as water. Volcanism away from plate boundaries is ascribed to intraplate or anorogenic volcanism, which may reveal important dynamics of the deep mantle. Two of the most striking intraplate volcanism are oceanic plateaus (OPs) and large igneous provinces (LIPs), which often have an extremely thick crust and vast areas. However, the origin of the extremely thick crust is debated, and several mechanisms are proposed: cataclysmic melting of a thermal plume (Richards et al., 1998; Larson, 1991); shallow asthenospheric melting during plate separation (Anderson et al., 1992); melting of the fertile or primitive mantle (Korenaga, 2005; Kerr & Mahoney, 2007); and asteroid impact (Rogers, 1982). Although mantle plume theory is widely accepted and is also often invoked to explain the formation of the OPs and LIPs. However, another school of people interrogates the deep mantle plume origin, which requires extremely high mantle temperature and a wide plume head. In contrast, recent numerical models provide a novel mechanism by linking a hydrous mantle transition zone (MTZ) and a retreating subducting plate for the formation of intraplate volcanism in northeast China and petit-spot volcanism offshore Japan (Yang & Faccenda, 2020). Such a mechanism has been applied to many other present-day and fossil subduction zones. Here we use 2D thermomechanical numerical models to investigate mantle melting and melt extraction processes leading to the formation of large volumes of basaltic crust. Two groups of models have been tested: a purely thermal plume model and a hydrous plume model. Our model results show that an excess mantle potential temperature of 200-300 ^oC likely produces >20 km thick crust if the lithosphere is <80 km. While the presence of >0.5-1 wt% water in a cold plume can result in similar thickness. Our models may explain some oceanic plateaus and large igneous provinces as related to the melting of volatile-rich domains from mid-mantle.

 

References

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