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https://doi.org/10.5194/egusphere-2025-5615
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/egusphere-2025-5615
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
26 Nov 2025
| 26 Nov 2025
Status: this preprint is open for discussion and under review for Solid Earth (SE).
From Strong Plates to Weak Boundaries: Strain Localization in the Lithospheric Mantle with Low- to High-Temperature Dislocation Creep
Abstract. Plate-like behavior may be reproduced in numerical experiments of mantle convection if rheology combines a temperature-dependent viscosity capped with a low yield stress. Other processes limiting the mantle ductile strength have been proposed, among which low-temperature plasticity. We propose to investigate how such a rheology can promote deformation localization at the lithospheric scale. We design a 2-D thermo-mechanical model of plate extension to compare the modes of strain localization as a function of the rheological parameterization. Various experimental flow laws for olivine (diffusion creep and dislocation creep at low- and/or high- temperature) are tested, sometimes combined with a yield-stress formulation. We quantify the evolution of the deformation pattern throughout the lithosphere, and define new diagnostics to assess whether the decrease in plate viscosity is due to an increase in strain rate ('mechanical weakening') and/or in temperature ('thermal weakening'). Deformation localization leads to a new extensional plate boundary in two successive stages: (i) narrowing of the deforming zone, (ii) rapid thinning of the highly deformed lithosphere. Here, a rheology combining diffusion creep and yield stress results in a mantle weakening that is either fully mechanical, respectively fully thermal, for temperatures lower, respectively higher, than ~1300 K. Accounting for dislocation creep enables additional feedbacks between mechanical and thermal weakening within the deforming plate, thereby enhancing the efficiency of strain localization. We demonstrate the consistency of using a yield-stress approximation to cap the mantle strength for temperature below ~1000 K. We also show that dislocation creep and yield-stress are not interchangeable for most of the lithospheric mantle (1000–1500 K), and using only the latter may overestimate the duration of plate break-up. Finally, we discuss how our results compare to natural continental rifting cases.
How to cite. Van Broeck, E., Garel, F., Thoraval, C., Arcay, D., and Davies, D. R.: From Strong Plates to Weak Boundaries: Strain Localization in the Lithospheric Mantle with Low- to High-Temperature Dislocation Creep, EGUsphere [preprint], https://doi.org/10.5194/egusphere-2025-5615, 2025.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
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Status: open (until 09 Jan 2026)
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
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- RC1: 'Comment on egusphere-2025-5615', Antonio Manjon Cabeza Cordoba, 02 Jan 2026 reply
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RC2: 'Comment on egusphere-2025-5615', Vojtěch Patočka, 05 Jan 2026
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General comments:
The manuscript by Van Broeck et al. studies the effects of rheological parameterization on the efficiency of strain localization in models of plate extension. Systematic tests of several rheological parameterizations are performed, particularly also the low-temperature dislocation creep is included (Gouriet et al., 2019), and the relative importance of yielding, dislocation, and diffusion creep is quantified during a plate boundary formation. Despite the vast existing literature on numerical models of extensional tectonics, it seems like a useful task: There is a well known discrepancy between the yield stress values adopted in geodynamical models with plate tectonics-like behavior and the laboratory-derived values. The discrepancy stems from the simplifications that need to be adopted when brittle deformation is modelled at large spatial and temporal scales, but the yield stress values are often tuned ad hoc, while the present manuscript clarifies the interplay between dislocation creep parameters and the adopted yield stress values.
The manuscript is well written and the figures are clear. However, there is a certain discrepancy between Introduction and Results (see the first two Specific comments below) and the Results section is a bit exhaustive, with too many observables describing essentially quite similar behavior. The results report a robust, two-stage process of plate-boundary formation, obtained in nearly all models with plastic yielding. My main objection is that, in all the performed simulations, the extension is driven by a prescribed velocity that mimics Couette flow, computed for a vertical viscosity profile following only the diffusion creep rheology (Appendix A). As a result, mechanical weakening below the plate is restricted near the vertical boundaries of the box (velocity is prescribed there), probably narrowing the range of extensional scenarios that are obtained (and limiting the feedback between surface plate velocity and the amount of below-plate mechanical weakening, Patočka et al., 2024). Given the Discussion (lines 520-525 and 555-560), the manuscript would benefit from testing also a constant tectonic force at the vertical sides, acting on the plate under extension.
In summary, the manuscript is a contribution to the literature, providing a diagnostic tool for quantifying the relative amount of thermal and mechanical weakening, and demonstrating that dislocation creep and plastic yielding result in different efficiency of strain localization (although the obtained overall patterns of deformation are similar). The model set-up is a bit simplistic (2D, no shear heating, single-composition material, pressure approximated by the lithostatic pressure), but given the general focus of the study it can be justified. Nevertheless, the employed simplifications should be discussed in a more quantitative manner - for instance, the amount of shear heating and thus thermal weakening can be estimated from the obtained strain rates and viscosities; dynamic pressure can be compared to the lithostatic one. The role of boundary conditions at the vertical sides should be investigated more thoroughly and it should be clarified why a crustal layer is missing.Specific comments:The term intra-plate deformation is used in Introduction in the context of distributed deformation occurring outside plate boundaries. Later, when discussing the performed 2D models, "intra-plate" is used to describe deformation within certain depths of the plate (lines 380-385). Are these two phenomena linked? Generally, a stronger link between Introduction and the obtained results would help, Section 5.4 is mostly providing comparison to numerical studies rather than to natural observations, and in many ways the paragraphs there describe further "limitations of the present study" rather than "comparison with natural cases". Also, the Introduction mentions depth-dependent yield stress as the common modeling approach (line 37) and then a depth-constant yield stress is assumed.Lines 45-55 indicate that low-temperature dislocation creep is an important mechanism that will have a significant effect on the obtained results. However, from Table 3 it seems that the opposite is true and that yielding mostly overrules the low-temperature dislocation creep (see particularly the comparison of models D-d_HT-Y_500 vs ref-1; both models seem to perform nearly identically). If I read that correctly, the effect of including LT-HT is smaller than anticipated (a negative result) and it should be admitted in the Introduction (or Abstract). See also lines 290-291, where a model without LT-HT is present in group 2, and where dislocation creep is found responsible only for the strain localization speed rather than the overall style of extension.The upper boundary is a free surface, but viscoelasticity is neglected. As shown in a different tectonic context, including a free surface while neglecting elasticity leads to a significant overestimation of shallow stresses (Patočka et al., 2019). In a compressional setting, the effects of viscoelasticity were demonstrated by Jaquet et al., 2016. In an extensional setting, the effect of neglecting viscoelasticity is probably not so dramatic, assuming the resulting topography is small, but it should be discussed.Line 79, the boundary condition for the central inflow at the base of the model domain should be given. Even in Appendix B, it only says that the velocity is "left free to adjust", but since it is not one of the basic boundary conditions, the governing equation should be formulated.Similarly, in Section 2.2.2, Eq. C3 should be included to make the rheological description complete. Also, in Eq. 6, the total strain-rate is denoted as edot_creep, but later, in Eq. 7 and 13, it is labeled simply as edot. I assume that only one total strain-rate is involved, this being attributed either fully to yielding or to creeping, with the distinction being based on whether eta_creep or eta_yield is bigger (Eq. 8 and line 131). These details should be clarified. Note also that, generally, edot is not a very good label for strain-rate. Although widely used in geodynamical literature, it is not used in mathematical literature, because the symmetric part of the velocity gradient (i.e. strain-rate) is not the material derivative of any standard measure of strain (such a relation is only approximative, valid in the linearized theory of deformations).Line 139: Defining 500 MPa as "the upper bound for the validity of the LT-HT dislocation creep" is not very clear. This value is larger than the typical values needed to obtain plate-like behavior in geodynamical models, and so it is promising that localized plate boundaries are obtained with this parameterization, but the motivation behind the particular value could be elaborated a bit more (given that most of the presented results employ this value).Lines 195-200: It would help to clarify how Eq. 11 is related to the traction acting on the vertical boundary and why the employed stresses are evaluated 100 km away from the boundary.If I understand it correctly, Fig. 9 is computed not from the performed simulations, but solely from the rheological equations (i.e. from the viscosity as a function of temperature and strain-rate). This should be stated in the text and not only in the figure caption. It is not fully clear how the time-derivative of temperature and strain-rate is determined in that figure (i.e. what exactly is meant by the employed 50 to 20 Myr plate age scenario, over what time is this change prescribed?).Line 448-450: The nearly identical behavior in models that differ only in the dislocation creep parameters does not imply that "Low-temperature dislocation creep and yield stress seem to play analogous roles in reducing the high lithospheric strength in the temperature range 800-1100K". Instead, it indicates that the low-temperature dislocation creep does not get activated very much, perhaps because yield stress dominates the region, or am I missing something? The sentence would be true if yield stress was not included in the d_LT-HT simulation, but it is.Given the extensive discussion of the absence of a crustal layer (lines 505-535), why isn't a crustal layer prescribed in the simulations? Is it because Fluidity does not allow it, or because it was desired to reduce the number of tested parameters (with crustal rheology introducing new ones)? This should be clarified.Technical comments:Line 3: among which low-temperature plasticity... a verb seems to be missing.Table 1: Volumic mass, isn't it more common to simply say density?Table 2: Activation volume, not energy (in the third rows)Line 221: the word "homogeneous" is often incorrectly used where "uniform" should be used instead.Line 236: "Highly deformed zone" is used for regions with strain-rate amplification > 1. But that is not a very strict criterion, if the number is not at least 2, calling the zone highly deformed may be misleading.Line 250: Why depth-invariance of the weakening rate results in small lateral viscosity contrast is not clear to me.Fig. 4 caption: We represent only values where >60% ... but the color maps seem full, so it is not clear what this sentence is referring to.Line 265: superimposed boundaries? Perhaps reformulate simply as "The dominant def. mech. are delimited by the dashed dark blue lines..."Fig. 5b: The initial evolution (<1 Myr) is not commented on. Is it perhaps an effect of the imposed BCs?Fig 6 caption: White regions represent hardening?Line 318: even if -> even thoughLine 355: The relative change in the width of the deformed zone does not seem so small, so perhaps giving rough numbers would help.Line 535: Two @ symbolsReferences:Patočka, V., Čížková, H., Tackley, P. (2019): Do elasticity and a free surface affect lithospheric stresses caused by upper mantle convection?, Geophys. J. Int., 216(3), 1740-1760.Jaquet Y., Duretz T., Schmalholz S.M. (2016): Dramatic effect of elasticity on thermal softening and strain localization during lithospheric shortening, Geophys. J. Int., 204(2), 780–784.Citation: https://doi.org/10.5194/egusphere-2025-5615-RC2
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From Strong Plates to Weak Boundaries: Strain Localization in the Lithospheric Mantle with Low- to High-Temperature Dislocation Creep - Data set Etienne Van Broeck et al. https://zenodo.org/records/17606932
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Etienne Van Broeck
CORRESPONDING AUTHOR
Géosciences Montpellier, Université de Montpellier, CNRS, Montpellier, France
Géosciences Montpellier, Université de Montpellier, CNRS, Montpellier, France
Catherine Thoraval
Géosciences Montpellier, Université de Montpellier, CNRS, Montpellier, France
Diane Arcay
Géosciences Montpellier, Université de Montpellier, CNRS, Montpellier, France
D. Rhodri Davies
Research School of Earth Sciences, The Australian National University, Canberra, ACT, Australia
Short summary
Earth’s solid shell is made of stiff tectonic plates which can break apart to form new weak plate boundaries. We use numerical models of plate extension to investigate how mechanical properties control the concentration of deformation leading to such a boundary as hot mantle rises underneath. We highlight feedbacks, and quantify how and why, under various deformation mechanisms, the plate weakens as temperature and strain rate increase. We compare the model predictions to natural rifting cases.
Earth’s solid shell is made of stiff tectonic plates which can break apart to form new weak...
Dear editor,
this technical paper presents a series of numerical experiments to address the role of rheology on deformation localization during extensional tectonics. While several detailed models of extension and rifting exist, evaluation of localization and adequate rheological mechanism is mostly absent in modern literature. In addition, they add the role of low-temperature plasticity, a continuation of their own work (Gouriet 2019; Garel 2020)
They show that considering multiple rheological mechanisms, in particular non-linear rheologies, is important to reproduce localization processes as we imagine them on Earth. They could specify a bit more on whether this was ever called into question, or what are the consequences of ignoring one rheology or the other, not just for their models, but for the wider community that will be forced to take simplifying assumptions regardless.
The manuscript is quite technical but the methodology is well explained. I have little to say there. Because Solid Earth has a wide focus - inasmuch as the deep Earth can be called a wide field – the article would benefit for a slightly more careful contextualization (e.g. what advances or new evidence motivate this study? How does this work compare with other studies? What are the implications for other geophysicists/geologists? etc). But this is not a criticism of the science of the manuscript itself.
Overall, I have few important comments to make and the majority of them are oriented to increase the reader interest on the manuscript rather than a criticism of the science of the manuscript. As a matter of taste, I find that they describe too many details of their results; these are simplified far-from-reality numerical experiments, and describing too many details may have little relevance. Perhaps summarizing a bit would improve the manuscript (i.e. in some sections there are some details that would be obvious to most people, like with faster extension comes faster thinning).
Attached, you can find the main comments to be addressed by the authors, then you can find a series of minor suggestions that the authors are free to address or not, or even ignore during review/reply process.