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1. Water transport to the core–mantle boundary

   https://doi.org/10.1093/nsr/nwab007  

   Walter, Michael J (January 2021, National Science Review)

   null (Ed.)

   Abstract Water is transported to Earth's interior in lithospheric slabs at subduction zones. Shallow dehydration fuels hydrous island arc magmatism but some water is transported deeper in cool slab mantle. Further dehydration at ∼700 km may limit deeper transport but hydrated phases in slab crust have considerable capacity for transporting water to the core-mantle boundary. Quantifying how much remains the challenge. 

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2. Plume‐Driven Subduction Termination in 3‐D Mantle Convection Models

   https://doi.org/10.1029/2024GC011523  

   Heilman, Erin; Becker, Thorsten W (July 2024, Geochemistry, Geophysics, Geosystems)

   Abstract The effect of mantle plumes is secondary to that of subducting slabs for modern plate tectonics when considering plate driving forces. However, the impact of plumes on tectonics and planetary surface evolution may nonetheless have been significant. We use numerical mantle convection models in a 3‐D spherical chunk geometry with damage rheology to study some of the dynamics of plume‐slab interactions. Substantiating our earlier 2‐D results, we observe a range of interaction scenarios, and that the plume‐driven subduction terminations we had identified earlier persist in more realistic convective flow. We analyze the dynamics of plume affected subduction, including in terms of their geometry, frequency, and the overall effect of plumes on surface dynamics as a function of the fraction of internal to bottom heating. Some versions of such plume‐slab interplay may be relevant for geologic events, for example, for the inferred ∼183 Ma Karoo large igneous province formation and associated slab disruption. More recent examples may include the impingement of the Afar plume underneath Africa leading to disruption of the Hellenic slab, and the current complex structure imaged for the subduction of the Nazca plate under South America. Our results imply that plumes may play a significant role not just in kick‐starting plate tectonics, but also in major modifications of slab‐driven plate motions, including for the present‐day mantle. 

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3. Analysis of Shear Wave Splitting Patterns in Alaska: Evidence for Strong Intra‐Slab Anisotropy

   https://doi.org/10.1029/2025GL116411  

   Appini, Sharmila; Zheng, Yingcai; Wu, Jonny; Mooney, Walter D (October 2025, Geophysical Research Letters)

   Abstract Shear wave splitting (SWS) patterns at subduction zones are often interpreted by complex mantle flow above or below the slab. However, our recent previous work shows dipping anisotropic slabs can explain observed patterns in Japan. Here, we extend this analysis to the Alaska subduction zone, using 2,567 high‐quality teleseismic SWS measurements from 195 broadband stations. As was found in Japan, the observed SWS patterns in Alaska depend on earthquake backazimuth. The fast‐S polarization directions are either trench parallel or perpendicular in southeastern Alaska and form a prominent circular pattern in central Alaska. We found that a dipping anisotropic slab following the Slab 2.0 geometry, with 30% shear anisotropy, and exhibiting tilted transverse isotropy with a symmetry axis normal to the slab interface, predicts both the fast‐S polarizations and delay times (δt = 1.0–1.5 s). This suggests that intra‐slab anisotropy can be the primary control on SWS, without requiring complex mantle flow. 

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4. Constraining Earth’s nonlinear mantle viscosity using plate-boundary resolving global inversions

   https://doi.org/10.1073/pnas.2318706121  

   Hu, Jiashun; Rudi, Johann; Gurnis, Michael; Stadler, Georg (July 2024, Proceedings of the National Academy of Sciences)

   Variable viscosity in Earth’s mantle exerts a fundamental control on mantle convection and plate tectonics, yet rigorously constraining the underlying parameters has remained a challenge. Inverse methods have not been sufficiently robust to handle the severe viscosity gradients and nonlinearities (arising from dislocation creep and plastic failure) while simultaneously resolving the megathrust and bending slabs globally. Using global plate motions as constraints, we overcome these challenges by combining a scalable nonlinear Stokes solver that resolves the key tectonic features with an adjoint-based Bayesian approach. Assuming plate cooling, variations in the thickness of continental lithosphere, slabs, and broad scale lower mantle structure as well as a constant grain size through the bulk of the upper mantle, a good fit to global plate motions is found with a nonlinear upper mantle stress exponent of 2.43 $\pm$0.25 (mean $\pm$SD). A relatively low yield stress of 151 $\pm$19 MPa is required for slabs to bend during subduction and transmit a slab pull that generates asymmetrical subduction. The recovered long-term strength of megathrusts (plate interfaces) varies between different subduction zones, with South America having a larger strength and Vanuatu and Central America having lower values with important implications for the stresses driving megathrust earthquakes. 

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5. A Limited Effect of Continents on Subduction Initiation for Convection With Grain‐Damage

   https://doi.org/10.1029/2024JB029136  

   Choi, H; Foley, B J (October 2024, Journal of Geophysical Research: Solid Earth)

   Abstract Despite significant study, when and how plate tectonics initiated on Earth remains contentious. Geologic evidence from some of Earth's earliest cratons has been interpreted as reflecting the formation of initial continental blocks by non‐subduction processes, which then trigger subduction initiation at their margins. Numerical models of mantle convection with a plastic yield stress rheology have shown this scenario is plausible. However, whether continents can trigger subduction initiation has not been tested with other rheologies. We, therefore, use numerical models of mantle convection with an imposed continental block to test whether continents facilitate subduction initiation with a grain‐damage mechanism, where weak shear zones form by grain size reduction. Our results show that continents modestly enhance stresses in the lithosphere, but not enough to significantly impact lithospheric damage or subduction initiation: continents have minimal influence on lithospheric damage or plate speed, nor does subduction preferentially initiate at the continental margin. A new regime diagram that includes continental blocks shows only a small shift in the boundary between the mobile‐lid and stagnant‐lid regimes when continents are added. However, as we do find that stresses are modestly enhanced at the continental margin in our models, we develop a scaling law for this stress enhancement to more fully test whether continents could trigger subduction initiation on early Earth. We find that lithospheric stresses supplied by continents are not sufficient to initiate subduction on the early Earth on their own with grain‐damage rheology; instead, additional factors would be required. 

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