More Like this

1. An introductory review of the thermal structure of subduction zones: I—motivation and selected examples

   https://doi.org/10.1186/s40645-023-00573-z  

   van_Keken, Peter E; Wilson, Cian R (December 2023, Progress in Earth and Planetary Science)

   Tada, R (Ed.)

   The thermal structure of subduction zones is fundamental to our understanding of physical and chemical processes that occur at active convergent plate margins. These include magma generation and related arc volcanism, shallow and deep seismicity, and metamorphic reactions that can release fluids. Computational models can predict the thermal structure to great numerical precision when models are fully described but this does not guarantee accuracy or applicability. In a trio of companion papers, the construction of thermal subduction zone models, their use in subduction zone studies, and their link to geophysical and geochemical observations are explored. In part I, the motivation to understand the thermal structure is presented based on experimental and observational studies. This is followed by a description of a selection of thermal models for the Japanese subduction zones. 

   more » « less
2. An introductory review of the thermal structure of subduction zones: II—numerical approach and validation

   https://doi.org/10.1186/s40645-023-00588-6  

   Wilson, Cian R.; van Keken, Peter E. (November 2023, Progress in Earth and Planetary Science)

   Abstract The thermal structure of subduction zones is fundamental to our understanding of the physical and chemical processes that occur at active convergent plate margins. These include magma generation and related arc volcanism, shallow and deep seismicity, and metamorphic reactions that can release fluids. Computational models can predict the thermal structure to great numerical precision when models are fully described but this does not guarantee accuracy or applicability. In a trio of companion papers, the construction of thermal subduction zone models, their use in subduction zone studies, and their link to geophysical and geochemical observations are explored. In this part II, the finite element techniques that can be used to predict thermal structure are discussed in an introductory fashion along with their verification and validation. Steady-state thermal structure for the updated subduction zone benchmark. a) Temperature predicted by TF for case 1; b) temperature difference between TF and Sepran using the penalty function (PF) method for case 1 at f_m=1 where f_mrepresents the smallest element sizes in the finite element grids near the coupling point; c) slab top temperature comparison for case 1; and d)–f) as a)–c) but now for case 2. The star indicates the position or temperature conditions at the coupling point. 

   more » « less
3. Evolving Subduction Zone Thermal Structure Drives Extensive Forearc Mantle Wedge Hydration

   https://doi.org/10.1029/2023AV001121  

   Epstein, G S; Condit, C B; Stoner, R K; Holt, A F; Guevara, V E (August 2024, AGU Advances)

   Hydration of the subduction zone forearc mantle wedge influences the downdip distribution of seismicity, the availability of fluids for arc magmatism, and Earth's long term water cycle. Reconstructions of present‐day subduction zone thermal structures using time‐invariant geodynamic models indicate relatively minor hydration, in contrast to many geophysical and geologic observations. We pair a dynamic, time‐evolving thermal model of subduction with phase equilibria modeling to investigate how variations in slab and forearc temperatures from subduction infancy through to maturity contribute to mantle wedge hydration. We find that thermal state during the intermediate period of subduction, as the slab freely descends through the upper mantle, promotes extensive forearc wedge hydration. In contrast, during early subduction the forearc is too hot to stabilize hydrous minerals in the mantle wedge, while during mature subduction, slab dehydration dominantly occurs beyond forearc depths. In our models, maximum wedge hydration during the intermediate phase is 60%–70% and falls to 20%–40% as quasi‐steady state conditions are approached during maturity. Comparison to global forearc H₂O capacities reveals that consideration of thermal evolution leads to an order of magnitude increase in estimates for current extents of wedge hydration and provides better agreement with geophysical observations. This suggests that hydration of the forearc mantle wedge represents a potential vast reservoir of H₂O, on the order of 3.4–5.9 × 10²¹ g globally. These results provide novel insights into the subduction zone water cycle, new constraints on the mantle wedge as a fluid reservoir and are useful to better understand geologic processes at plate margins. 

   more » « less
4. Constraining Solid Dynamics, Interface Rheology, and Slab Hydration in the Hikurangi Subduction Zone Using 3‐Dimensional Fully Dynamic Models

   https://doi.org/10.1029/2024GC011824  

   Douglas, D; Naliboff, J; Fraters, M_R T; Dannberg, J; Eberhart‐Phillips, D; Ellis, S (June 2025, Geochemistry, Geophysics, Geosystems)

   Abstract Simulating present‐day solid Earth deformation and volatile cycling requires integrating diverse geophysical data sets and advanced numerical techniques to model complex multiphysics processes at high resolutions. Subduction zone modeling is particularly challenging due to the large geographic extent, localized deformation zones, and the strong feedbacks between reactive fluid transport and solid deformation. Here, we develop new workflows for simulating 3‐dimensional thermal‐mechanical subduction and patterns of volatile dehydration at convergent margins, adaptable to include reactive fluid transport. We apply these workflows to the Hikurangi margin, where recent geophysical investigations have offered unprecedented insight into the structure and processes coupling fluid transport and solid deformation across broad spatiotemporal scales. Geophysical data sets constraining the downgoing and overriding plate structure are collated with the Geodynamic World Builder, which provides the initial conditions for forward simulations using the open‐source geodynamic modeling software code ASPECT. We systematically examine how plate interface rheology and hydration of the downgoing plate and upper mantle influence Pacific–Australian convergence and seismic anisotropy. Models prescribing a plate boundary viscosity of Pa s best reproduce observed plate velocities, and changing the configuration of the Pacific–Australia plate boundary directly influences the modeled plate motions. Models considering hydrated olivine fabrics best reproduce observations of seismic anisotropy. Predicted patterns of slab dehydration and mantle melting correlate well with observations of seismic attenuation and arc volcanism. These results suggest that hydration‐related rheological heterogeneity and related fluid weakening may strongly influence slab dynamics. Future investigations integrating coupled fluid transport and global mantle flow will provide insight into the feedbacks between subduction dynamics, fluid pathways, and arc volcanism. 

   more » « less
5. A Coupled Geochemical‐Geodynamic Approach for Predicting Mantle Melting in Space and Time

   https://doi.org/10.1029/2022GC010421  

   Ball, P_W; Duvernay, T.; Davies, D_R (April 2022, Geochemistry, Geophysics, Geosystems)

   Abstract Geodynamic simulations underpin our understanding of upper‐mantle processes, but their predictions require validation against observational data. Widely used geophysical datasets provide limited constraints on dynamic processes into the geological past, whereas under‐exploited geochemical observations from volcanic lavas at Earth's surface constitute a valuable record of mantle processes back in time. Here, we describe a new peridotite‐melting parameterization, BDD21, that can predict the incompatible‐element concentrations of melts within geodynamic simulations, thereby providing a means to validate these simulations against geochemical datasets. Here, BDD21's functionality is illustrated using the Fluidity computational modeling framework, although it is designed so that it can be integrated with other geodynamic software. To validate our melting parameterization and coupled geochemical‐geodynamic approach, we develop 2‐D single‐phase flow simulations of melting associated with passive upwelling beneath mid‐oceanic ridges and edge‐driven convection adjacent to lithospheric steps. We find that melt volumes and compositions calculated for mid‐oceanic ridges at a range of mantle temperatures and plate spreading rates closely match those observed at present‐day ridges with the same conditions. Our lithospheric step simulations predict spatial and temporal melting trends that are consistent with those recorded at intraplate volcanic provinces in similar geologic settings. Taken together, these results suggest that our coupled geochemical‐geodynamic approach can accurately predict a suite of present‐day geochemical observations. Since our results are sensitive to small changes in upper‐mantle thermal and compositional structure, this novel approach provides a means to improve our understanding of the mantle's thermo‐chemical structure and flow regime into the geological past. 

   more » « less