Influence of Mantle Rheology on Plume Dynamics and Periodicities

Many hotspots worldwide display evidence of fluctuating magmatic activities that may be linked to time-dependent variations in melt production within mantle plumes. These periodicities are observed globally on Earth, ranging from 1 Myr to 20 Myr [Morrow and Mittelstaedt, 2021 ; Sokolov et al., 2025]. Remarkably, the Réunion hotspot exhibits short magmatic pulsations with a periodicity of ~400 kyr [Famin et al., in rev.]. Given the ~230 km separation between La Réunion and Mauritius, the synchronous short-period pulsations observed at the Réunion hotspot imply that they originate from deeper plume dynamics.

 

Understanding the physical controls behind these pulsations could establish links between mantle convection, plume dynamics, and surface volcanism. Previous studies suggest that plume behavior is sensitive to mantle rheology. Plume pulsations with periods of ~1-10 Myr have indeed been reported in numerical experiments and can stem from thermochemical instabilities due to the interaction of plumes with small-scale convection in the asthenosphere [Ballmer et al., 2009], thermal instabilities in sufficiently vigorous convection (Rayleigh number > 5×10⁶), buoyancy changes due to mineralogical phase transitions [Trubitsyn and Evseev, 2018], horizontal shearing caused by plate motions over an asthenosphere dominated by dislocation creep, leading to unstable tilted plume conduits [Neuharth and Mittelstaedt, 2023].

 

Here, we seek to investigate how mantle rheology can favour short-period pulses of plume activity and aim to identify the core physical mechanisms that control plume dynamics. We thus run 3D regional convection models in spherical cap geometry with plate-like behavior (viscoplastic rheology) at the surface using the StagYY code [Tackley, 2000]. We developed an automated algorithm to detect and track plumes in space and time, by  defining plumes as the highest percentiles of the upwards vertical advective heat transport . The morphology and dynamics of plumes are then quantified using various parameters such as the buoyancy flux, heat flux, angle of inclination, along with their associated uncertainties. Our study explores the effects of surface yield stress (ranging 10-100 MPa), radiogenic heat production (3-15 pW/kg), a 30 to 100 fold viscosity jump at the transition zone, and of compressibility and phase transitions (especially the post-spinel transition at ~660 km depth that works as an accelerator of upwellings plumes and thus favors dynamic instabilities [Faccenda and Dal ZIlio 2016]) on plume dynamics as well as on plate tectonics. We aim to understand how these parameters control the generation of periodic activity and short-period term plume pulses and ultimately to estimate  melt production variations at the surface in order to compare it with geological observations of magmatic products at the Réunion hotspot. Preliminary results indicate that surface yield stress and radiogenic heat production primarily affect plate tectonics, whereas a viscosity jump across the transition zone promotes periodic (~2 Myr) plume behavior.