Phase Transitions Control Plume Layering During Earth’s Secular Cooling

Earth’s mantle convects, cooling the planet and shaping both its internal structure and surface tectonic regimes. While models and observations provide reasonable constraints on present-day mantle flow, it remains an open question how patterns of mantle convection have evolved throughout Earth’s history. A key factor is temperature. Petrological studies (e.g., Herzberg et al., 2010) estimate mantle cooling rates of up to ~100 K/Gyr, suggesting that the Archean mantle could have been about 300 K hotter than today. A hotter mantle would likely have been less viscous and hosted different mineral phase assemblages and transitions (Figure 1, comparing the different lines). Because endothermic phase transitions can hinder mantle flow and promote layering, it is important to understand how variations in these phase transitions affect mantle dynamics, including the degree of convective layering, the behavior of plumes and subducted slabs, and the material exchange between the upper and lower mantle.

In our recent study (Li et al., 2025), we investigated how varying phase transitions affect convection styles using numerical models. We present a series of 2D cylindrical annulus simulations covering a wide range of core–mantle boundary temperatures and initial mantle adiabats, representing Earth at different stages of cooling. The models evolve forward in time and include plastic deformation to generate plate-like subduction. We use the community code ASPECT (Heister et al., 2017) with the entropy method (Dannberg et al., 2022), which captures the full dynamic effects of phase transitions. To incorporate realistic material behavior, we use a look-up table generated by the thermodynamic software HeFESTo (Stixrude and Lithgow-Bertelloni, 2011), which includes complex phase relations through their variations in physical properties. By solving the energy equation for entropy instead of temperature, we fully include latent heat and avoid numerical instabilities, allowing us to model realistically sharp transitions and their impact on mantle dynamics.

Our models show that when the mantle potential temperature exceeds 1800 K (following the orange or yellow adiabat in Figure 1), the endothermic wadsleyite ⇔ garnet (majorite) + ferropericlase transition (boxed by a dot-dashed line in the right panel) occurs and significantly affects plume behavior. Unlike the widely-studied ringwoodite ⇔ bridgmanite + ferropericlase transition at 660 km, this wadsleyite transition (occurring between 450 and 590 km depth and over the 2000–2500 K temperature range) has received little attention before this work. In our hotter-mantle models (bottom panel in Figure 2), plumes are often trapped by this phase transition near transition-zone depths (500–650 km), forming a global hot layer and producing a variety of stalled plume shapes. This layering effect can reduce vertical plume transport between the lower and upper mantle by nearly 100%. Although slabs continue to sink through the transition and thus convection is not fully layered, the strong impedance of plumes may still influence Earth’s cooling history and the return of deep material to the surface through mantle upwellings. In addition, numerous secondary plumes rise from this hot layer, potentially affecting surface volcanism and plume-driven tectonic motion.

Summarizing the story (Figure 3), the wadsleyite ⇔ garnet (majorite) + ferropericlase transition may have dominated mantle dynamics in early Earth, causing strong plume layering until the mantle cooled below ~1750 K. This was likely followed by a transitional regime in which the effect weakened gradually and the hot layer diffused away. Although today’s mantle is too cool for this transition to occur, it may have played an important role in the past, and could still be dynamically significant on hotter terrestrial planets.

Contributed by: Ranpeng Li, Juliane Dannberg, Rene Gassmöller (GEOMAR Helmholtz Centre for Ocean Research Kiel); Carolina Lithgow-Bertelloni, Lars Stixrude (Earth, Planetary, and Space Sciences, University of California, Los Angeles)

Acknowledgements

This work was supported by NSF award EAR-1925677 and by Helmholtz funding EBP-01-08. University of Florida Research Computing has provided computational resources and support that have contributed to the research results reported in this publication.

References

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