Nitrogen (N) is the most abundant element in Earth's modern atmosphere, but is extremely depleted in the silicate crust and mantle. The volatile inventory of the bulk silicate Earth shows a well-established N deficit compared to CI chondrites, the primitive meteorites representative of the solar composition. However, it remains unclear whether the formation of the iron-rich core, early atmospheric loss, or a combination of both was responsible for this depletion, partly due to the large extrapolation from low-pressure experiments. Here, we study the effect of core formation on the inventory of nitrogen in a terrestrial magma ocean using laser-heated diamond anvil cells. Under core-forming conditions relevant to Earth-sized planets, we find that N is siderophile (iron-loving), making the core its largest reservoir, notwithstanding that the simultaneous dissolution of oxygen in the core lowers that of nitrogen. A combined core-mantle-atmosphere coevolution model, however, cannot account for the observed N anomaly in the silicate Earth via its core sequestration and/or atmospheric loss during accretion, unless Earth's building blocks had experienced vaporisation processes akin to those accountable for the volatile signatures found in CV-CO chondrites. The terrestrial volatile pattern requires severe N depletion (>99%) on precursor bodies but limited atmospheric loss (<5%), prior and posterior to their accretion to the proto-Earth. We argue that early vapour loss/depletion on Earth's building blocks is the key to establishing our planet's volatile budget.

How to cite: Huang, D., Siebert, J., Sossi, P., Kubik, E., Avice, G., and Murakami, M.: Provenance of Earth’s volatile building blocks inferred from the behaviour of nitrogen during core formation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8161, https://doi.org/10.5194/egusphere-egu25-8161, 2025.

During a later stage of Earth's accretion, approximately 4.5 billion years ago, impacts of Mars-sized bodies created a deep terrestrial magma ocean of global extent on proto-Earth. Once core formation is complete, the magma ocean begins to solidify. However, the solidification mechanism and the location where crystallization initiates remain unclear and are subjects of debate. One widely accepted model posits that solidification begins at the bottom of the magma ocean (e.g., [1]). Contrarily, laboratory experiments conducted under high-pressure and temperature conditions suggest two alternate scenarios: Solidification may also commence at the top of the magma ocean (e.g., [2]) or at mid-depth (e.g., [3,4]). The latter might yield a deep molten layer, referred to as a basal magma ocean, at the core-mantle boundary, which could potentially endure chemically and thermally isolated from the remaining mantle for an extended period [5].

We model these three distinct solidification styles (bottom-up, top-down, mid-depth) and examine their impact on the dynamics and temporal evolution of a convecting magma ocean through computational simulations. Determining whether the magma ocean solidifies from the bottom up, top-down, or in a mid-outward manner holds paramount significance for Earth's evolution, influencing factors such as the level of differentiation and the initial conditions governing the advent of plate tectonics. Furthermore, the dominant mechanism and its timing could bear crucial implications for the ensuing evolution of the mantle and the distribution of geochemical trace elements.

References:
[1] Andrault et al. (2011) EPSL, 304(1), 251–259.
[2] Mosenfelder et al. (2007) JGR: Solid Earth, 112(B6).
[3] Stixrude et al. (2009) EPSL, 278(3), 226–232.
[4] Boukaré et al. (2015) JGR: Solid Earth, 120(9), 6085–6101.
[5] Labrosse et al. (2007) Nature, 450(7171), 866–869.

How to cite: Maas, C. and Hansen, U.: Influence of solidification mechanism on magma ocean dynamics and evolution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15172, https://doi.org/10.5194/egusphere-egu25-15172, 2025.

The magma ocean (MO) phase typically describes the early stage of rocky planets, during which the entire planet is molten due to heat generated by accretion processes. In the case of short-period exoplanets inside the runaway greenhouse limit, this phase may last Gyrs, until the inventory of major greenhouse gasses, such as H2O and H2, is exhausted. The internal evolution of these planets is influenced by various factors, including the exchange of volatiles between the molten planetary interior and the atmosphere. This exchange significantly impacts planetary climate, exoplanet bulk densities, surface conditions, and long-term geodynamic activity by controlling greenhouse effects, surface water stability, and atmospheric composition. This research focuses on modeling this interaction under different redox conditions. Using a coupled computational framework of the planetary interior and atmosphere, we study the detailed evolution of the magma ocean phase, aiming to understand the crystallization sequence and the atmospheric composition in equilibrium with long-lived magma ocean. 

How to cite: Sastre, M., Lichtenberg, T., Bower, D., Nicholls, H., and Kamp, I.: Impact of varying redox states on crystallization and atmospheric composition of rocky exoplanets., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-459, https://doi.org/10.5194/egusphere-egu25-459, 2025.

As Earth’s magma ocean solidified, chemical fractionation and physical separation of silicate melt and crystal produced chemical heterogeneity, potentially resulting in the compositional stratification of Earth’s deep mantle. A stratified deep mantle would have prevented advective flux of heat or material between the deep Earth (basal magma ocean (BMO) and core) and the shallow mantle. Therefore, the thermochemical evolution of the Earth hinges on the evolution of the stratified deep mantle. How does this region evolve, especially considering that it is likely underlaid by a radioactively heated BMO and a cooling core? To what extent and in what form would heterogeneity introduced by magma ocean differentiation be preserved in Earth’s mantle over time?

We explored these questions through numerical experiments simulating the evolution of a compositionally stratified, initially solid layer underlaid by a volumetrically heated liquid layer. We model percolation as well as convection driven by density perturbations related to thermal expansion, composition (iron), and melt fraction, using pressure-dependent melting temperatures and density perturbations appropriate for Earth’s deep mantle. We explore a variety of heating rates, stratifications, and material properties.

We find that the evolution of a stratified deep mantle may proceed in two regimes, depending on the competition between the timescales of (1) melt segregation and (2) mantle stirring driven by thermochemical convection.

If stirring is efficient relative to melt segregation, bottom-heating will drive homogenization of a stratified region as heat added to deep material leads to density reduction through partial melting. In this regime, the timescale of homogenization is determined by the time it takes to deliver the energy necessary to reduce the density of the entire deep mantle to match that at the top of the stratified region. Density reduction can be achieved either by thermal expansion or melting; homogenization driven by melting-related density decrease will occur much more rapidly than homogenization driven by thermal expansion. The Earth’s solid mantle following deep mantle homogenization likely had multiple compositionally distinct layers (not including any BMO), which then would have proceeded to mix by entrainment.

If melt segregation is efficient relative to stirring, bottom-heating will still produce partial melt, which will be dense due to the incompatibility of iron and will percolate to the BMO. This process drains incompatible components from the deep mantle to the BMO, with the depleted low-density residue rising in diapirs until the deep mantle is homogenized through depletion. In this case, the Earth is left with a mantle which is more uniform and more depleted than in the stirring-dominated regime, and a thicker BMO.

How to cite: Lark, L., Boukaré, C.-E., Badro, J., and Samuel, H.: Homogenization of Earth’s mantle after magma ocean solidification, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8385, https://doi.org/10.5194/egusphere-egu25-8385, 2025.

Recent impact simulations show that a planet’s iron core can be greatly heated by a giant impact – indeed , by more than the mantle above it (Zhou et al., 2024). This has been proposed to result in long-term influences on mantle evolution in Venus (Marchi et al., 2023), although previous works have shown that for an Earth-like planet, cases with different initial core temperature tend to converge to the same evolutionary path (Nakagawa and Tackley, 2010). Here, the evolution of the coupled mantle and core after giant impact heating of the core is examined using a 2D mantle model coupled to a 1D core model using the StagYY modelling framework.

If the outer core becomes hotter than the liquidus of mantle rock then it 100% melts the bottom of the mantle, with the molten mantle at the same potential temperature as the outer core. The melt front propagates rapidly upwards due to heat supplied by vigorous outer core & molten mantle convection (a Stefan problem) at the same time cooling the outer core rapidly. This phase of rapid mantle melting + core cooling continues until the bottom of the mantle has cooled to the rheological transition (~40% melt fraction). Depending on the temperature, the resulting very hot material at the base of the mantle tends to rise quickly in the form of plumes, causing a pulse of magmatism at the surface (in addition to any magmatism caused by impact heating of the mantle). At the bottom, melt-solid segregation upwards or downwards may result in further complexities including an iron-rich somewhat molten silicate layer. In any case, results show that impact heating of the core leads to transient phenomena rather than long-term dynamical effects.

Marchi, S., Rufu, R. & Korenaga, J. Long-lived volcanic resurfacing of Venus driven by early collisions. Nat Astron 7, 1180–1187 (2023). https://doi.org/10.1038/s41550-023-02037-2

Nakagawa, T. and P. J. Tackley (2010) Influence of initial CMB temperature and other parameters on the thermal evolution of Earth's core resulting from thermo-chemical spherical mantle convection, Geochem. Geophys. Geosys. 11, Q06001, 16 pp., doi:10.1029/2010GC003031.

Zhou, Y., Driscoll, P.E., Zhang, M., Reinhardt, C., Meier, T. (2024) A Scaling Relation for Core Heating by Giant Impacts and Implications for Dynamo Onset, Journal of Geophysical Research: Planets2024, 129(5), e2023JE008163

How to cite: Tackley, P.: Impact-induced core heating has only short-term effects of planetary evolution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17231, https://doi.org/10.5194/egusphere-egu25-17231, 2025.

Grain size is one of the primary influencing factors for mantle viscosity. Larger grains lead to increased diffusion creep viscosity and vice-versa. Grain size is a thermally activated process, so with higher temperature grains grow. Increasing temperature lowers the mantle viscosity but the associated grain size would potentially increase the viscosity.  The net result of this counterbalancing effect of grain size evolution and temperature in the lower mantle remains limited. In this study, we use the self-consistent two-dimensional finite volume StagYY to investigate the evolving grain size and its impact on average mantle viscosity. We compare a model with constant grain size to models with evolving grain size along with dynamic recrystallization and analyze the effect of grain size. 

Using grain size evolution parameters for olivine in the upper mantle and bridgmanite-ferropericlase in the lower mantle shows comparable results with previous literature. In this model, the upper mantle primarily undergoes deformation through dislocation creep, while the lower mantle is dominated by diffusion creep. Despite this, the average viscosity of the lower mantle calculated using the evolving grain size model does not significantly differ from that of a constant grain size model. This suggests that grain size variations exert a limited impact on the average viscosity of the lower mantle, which is predominantly influenced by temperature. This limitation arises because of the slow grain growth of the bridgmanite-ferropericlase assemblage due to Zenner pinning. Such slow grain growth is insufficient to counteract the temperature-dependent viscosity effects. In the early Earth, the Zenner pinning effect could be absent due to single phase crystallization from the magma ocean. Without a secondary phase, bridgmanite could grow significantly larger grains. To investigate the impact of faster grain growth, we applied olivine grain growth parameters to the lower mantle. This hypothetical scenario resulted in the formation of exceptionally large grains (~10,000 μm) and delayed the onset of lid-breaking events in our models. It is possible that in the early Earth, the lid-breaking event was delayed due to strong grain size dependent viscosity. However, once whole-mantle convection began, increased lower mantle stress promoted dislocation creep in the presence of these large grains. In such cases, the lower mantle becomes largely independent of grain size, particularly in the present-day Earth scenario.

How to cite: Golabek, G. J., Paul, J., Rozel, A. B., Tackley, P. J., Katsura, T., and Fei, H.: Importance of grain size-dependent viscosity for the early and present-day Earth, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4197, https://doi.org/10.5194/egusphere-egu25-4197, 2025.

Ocean on the Earth is a key feature, which is likely responsible for the onset and further operation of plate tectonics as well as for the origin of life. Geochemical data suggests that ocean existed on the Earth already since at least the middle Hadean time. Recent studies also infer that after the solidification of the magma ocean, mean concentration of water in the Earth’s mantle could have been up to few 1000 ppm and that extraction of part of it formed the surface ocean. However, a clear understanding of this process is still lacking.

Here, we report results of modelling of Earth’s evolution during its first 1.5 Gyr with a focus on water cycle and generation of the continental crust. We use geodynamic code StagYY in 2D spherical annulus geometry that generates both basaltic and felsic melts, includes cooling of the core and uses an advanced treatment of water. We also included the effect of water on density of crustal and mantle materials based on experimental data and thermodynamic calculations.

Our models start just after solidification of magma ocean with assumed initial mantle potential temperature of 1900K and core temperature of 5000K. We run models with different initial mean water content in the mantle reaching up to 1500 ppm. In all the models, most of the water is initially concentrated in the mantle transition zone (MTZ), because of its higher water storage capacity. Due to the lower density of the water-containing materials, this leads to Rayleigh–Taylor instabilities and hot and “wet” mantle plumes rapidly rise to the surface. As a result, a large amount of mantle water is outgassed forming the surface ocean in just a few million years. Simultaneously, a significant amount of continental crust is produced. Masses of the produced ocean and continental crust depend on the initial concentration of water in the mantle. For instance, for the initial mean water concentration of 1000 ppm, ocean mass of about 1.5 times recent ocean masses (OM) and continental crust of about 0.7 times present-day continental crust mass (CCM) is produced during 7 Myr. Water outgassing from the mantle dominates during the first 100 Myr till ocean mass reaches about 2 OM. Afterwards, the outgassing by plumes and in-gassing by subduction are mostly balanced with a tendency of the surface ocean mass to decrease with time during the 1.5 Gyr.

Interestingly, in all models, MTZ behaves as a buffer for water cycle and despite it’s high water storage capacity, it’s mean water content mostly remains below 400 ppm, rising to up to 1500 ppm only for the short time periods when a number of cold slabs are resting in MTZ. We will show results from a set of models and compare the model-predicted trace elements ratios with the recent geochemical data.

How to cite: Sobolev, S. and Jain, C.: Models of water cycle and continental crust formation on Earth during Hadean and Eo-Archean, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5969, https://doi.org/10.5194/egusphere-egu25-5969, 2025.

Mineral phase transitions can either hinder or accelerate mantle flow. In the present day Earth, the formation of the bridgmanite + ferropericlase assemblage from ringwoodite at 660 km depth has been found to cause weak and intermittent layering of mantle convection. However, for the higher temperatures in Earth’s past or on other planets, different phase transitions might have governed mantle dynamics and shaped mantle structure. 

Here, we apply a recently developed entropy formulation in mantle convection models with plate-like behavior to investigate the effect of phase transitions on changes in convection style throughout Earth's history. We have extended this method to include chemical heterogeneity, and we have implemented and tested the approach in the geodynamics software ASPECT. Our benchmark results show that this multicomponent entropy averaging method effectively captures the system's thermodynamic effects. Furthermore, we apply the entropy formulation in 2-D and 3-D geodynamic models, incorporating thermodynamic properties computed by HeFESTo. Our models reveal the impact of the endothermic transition from wadsleyite to garnet (majorite) and ferropericlase (occurring between 420–600 km depth and over the 2000–2500 K temperature range) in a mantle with potential temperatures hotter than 1700 K, which impedes rising mantle plumes. 

When encountering this phase transition, the plume conduits tilt significantly, and the plume heads spread out laterally. This change in plume morphology accumulates hot material in the transition zone, spawning secondary plumes.  Partial melt generated within these hot, stalling plumes may lead to chemical differentiation as plume material spreads laterally. On a larger scale, the phase transition can reduce the mass flux of plumes by ~90%. The stalling of plumes creates a long-lasting global hot layer and impedes mass exchange between lower and upper mantle, resulting in global thermal and chemical heterogeneity.

Our models reveal a systematic change in convection style during planetary secular cooling. The wadsleyite to garnet (majorite) + ferropericlase phase transformation only occurs at high temperatures and therefore layering of plumes becomes less frequent and eventually stops as the mantle cools down. This indicates that mantle convection may have been partially layered early in Earth's history, or may be layered today in terrestrial planets with a hotter mantle. As the mantle potential temperature decreases and layering ceases, we observe an increase of surface mobility, suggesting that such a change in convection patterns also affects plate tectonics.

How to cite: Li, R., Dannberg, J., Gassmöller, R., Lithgow-Bertelloni, C., Stixrude, L., and Myhill, R.: How Phase Transitions Impact Changes in Mantle Convection Style Throughout Earth’s History: From Stalled Plumes to Surface Dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6598, https://doi.org/10.5194/egusphere-egu25-6598, 2025.

The ¹⁸²Hf-¹⁸²W (half-life = 8.9 Myr) and ¹⁴⁶Sm-¹⁴²Nd (half-life = 103 Myr) isotope systems offer valuable insights into Earth's early differentiation and evolution. Active during the first ~50 and ~500 million years of solar system history, respectively, these systems preserve evidence of primordial fractionation processes, and for Hf-W system, possible imprints from the late accretion and Earth’s core-mantle interaction. Differences in W and Nd isotope ratios between Archean mantle and modern mantle suggest the long-term mixing of early-formed geochemical reservoirs within the silicate Earth over the Hadean and Archean. The absence of a direct correlation between ¹⁸²W and ¹⁴²Nd ratios in Archean rocks implies that silicate differentiation may not be the only significant process influencing the evolution of these isotopic systems.

Our study uses the global geodynamic model StagYY to track the evolution of the ¹⁸²Hf-¹⁸²W and ¹⁴⁶Sm-¹⁴²Nd isotope systems through mantle convection. With models start at 60 Myr after CAI formation, corresponding to an earlier estimated time of the Moon-forming impact, we investigate changes of isotopic ratios in basaltic material over time due to melting, magmatic crust formation, mantle mixing, and possible external inputs such as core-mantle interaction. Our model results demonstrate that (1) if Earth’s mantle was fully homogenized during the magma ocean period, the ¹⁸²Hf-¹⁸²W and ¹⁴⁶Sm-¹⁴²Nd systems would be naturally decoupled due to the low abundance of ¹⁸²Hf in Earth’s mantle at 60 Myr, and (2) the chemical mixing within the mantle is strongly affected by mantle depletion: models indicate that the early-depleted mantle could remain in the lower mantle for billions of years but rarely resurface and be erupted, while early-formed basaltic crust could also stay at the core-mantle boundary for billions of years due to its high intrinsic density and influence the isotopic ratios of newly-formed crust through model time. These findings provide new insights into the processes shaping Earth's early geochemical evolution and highlight the importance of using thermo-chemical models in studying Earth's early history.

How to cite: Tian, J., Tackley, P., and Elliott, T.: Modelling the evolution of the short-lived Hf-W and Sm-Nd isotope systems in mantle convection models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16831, https://doi.org/10.5194/egusphere-egu25-16831, 2025.

Even though surface water is essential for Earth's habitability, the estimates of total amount of water (at the surface and in the deep interior) throughout Earth's evolution vary from 5-15 ocean masses (OM) based on magma ocean solidification models [Hamano et al., 2013] to 1.2-3.3 OM based on petrological studies [Hirschmann, 2006]. Previous numerical models of coupled surface-mantle system have estimated a lower bound of 9-12 OM [Nakagawa et al., 2018]. Experiments have shown that water lowers the melting temperature, density and viscosity of rocks and it is also required for the generation of felsic magmas. In this work, we use global convection models [Tackley, 2008] spanning the age of the Earth to elucidate the effect of water on mantle dynamics in terms of planetary cooling, surface mobility and production of continental crust.

Our models self-consistently generate oceanic and continental (Archean TTGs) crust while considering both plutonic and volcanic magmatism and incorporate a composite rheology for the upper mantle. Pressure-, temperature-, and composition-dependent water solubility maps calculated with Perple_X [Connolly, 2009] control the ingassing and outgassing of water between the mantle and the surface [Jain et al., 2022]. Irrespective of the initial water content used, our models exhibit mobile-lid regime (high surface mobility with subduction) throughout the 4.5 Gyr with episodes of short-lived plutonic-squishy-lid regime (low surface mobility with delamination or dripping) in the Hadean. These models are also consistent with the cooling history of the Earth inferred from petrological observations [Herzberg et al., 2010]. A strong positive correlation is observed between continental crust production and the total amount of water available, with the former's cumulative mass increasing by roughly three times when water in the planetary system is raised from 1 OM to 10 OM.

Models that consider a reduction in the density of crustal and mantle materials in the presence of water exhibit mobile-lid regime for the initial 200 Myr. Afterwards, the mobility stays low as the hydrated oceanic crust is less dense and does not subduct. It thickens over time and eventually collapses as global resurfacing events. Mantle stays comparatively warm and a much lower amount of continental crust is produced. This motivated us to make the following improvements to achieve more realistic models. First, mantle minerals only in the top 5 km of the computational domain (as opposed to 10 km considered previously) are ingassed with water. Second, instead of fully saturating the rocks based on their solubility maps, they are partially saturated to control the input of surface water into the lithosphere. Third, different partition coefficients for water are considered: 0.01 for pyrolite to basalt melting and 0.25 for basalt to TTG melting. These changes help in increasing the surface mobility, cooling down the planet and producing more continental crust. These trends are further amplified in models that additionally consider a viscosity reduction of mantle materials in the presence of water.

How to cite: Jain, C. and Sobolev, S.: Influence of water on global mantle dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5822, https://doi.org/10.5194/egusphere-egu25-5822, 2025.

The amount and distribution of water within Earth’s mantle remain uncertain, largely due to limited observational constraints and the only moderately constrained water capacities of primary lower mantle minerals. Recent advances in experimental and theoretical determinations of H₂O solubilities, however, now enable a more direct integration of these constraints into geodynamic models, offering new insights into Earth’s deep water cycle. Here, we employ Gibbs free energy minimization over a broad range of pressure–temperature conditions, combined with published H₂O solubility measurements, to generate mineral-bound mantle H₂O storage capacity maps as a function of phase equilibria. These maps—along with tables documenting density variations in nominally anhydrous minerals arising from water incorporation—are accessible through a customizable and parallelized Julia script.

Incorporating these storage capacity maps into a 2D mantle convection model (StagYY) yields outcomes consistent with existing literature. The simulations suggest that, throughout Earth’s history, the transition zone harbors a heterogeneous 0.2–0.5 wt% water content. Deeper in the mantle, water transport is controlled by the presence of dense hydrous magnesium silicates in subducting slabs. In their absence, descending material quickly dehydrates while exiting the wadsleyite–ringwoodite stability field, before H₂O solubility increases again under CaCl₂-type stishovite conditions (~50–60 GPa). Nevertheless, slow mantle convection and weak diffusivity enable any deeply emplaced water to persist at great depths. Over 4.5 Gyr of Earth-like evolution, an aquaplanet simulation retains roughly four to five ocean masses of water in the planetary interior, depending on the efficiency of water migration within the mantle. Simplified 3D models coupled with plate reconstructions further elucidate the dynamic balance of water influx and efflux over the Phanerozoic, providing an integrated view of the mantle’s evolving water budget.

How to cite: Moccetti Bardi, N. and Tackley, P.: Mineral-bound H2O solubility maps applied to Earth-like global mantle convection models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11135, https://doi.org/10.5194/egusphere-egu25-11135, 2025.

Earth’s interior plays an important role in the long-term evolution of the surface, climate and biosphere. Rheology is the cornerstone of mantle convection and tectonics, and constraining mantle viscosity has been a priority in the geodynamic community. In this study, we employ fully self-consistent and three-dimensional Earth-like mantle convection models^[1]. The mantle rheology is temperature-, pressure- and stress-dependent. Plate-like behaviour in global mantle models can be obtained using a pseudo-plastic rheology^[2]. Rheology in some of our models also depends on phase and creep mechanism. As in previous work^[3], this is implemented by using laboratory values for activation energy and activation volume for the upper mantle and an analytical fit to experimental data for the lower mantle. The novelty of this work lies in employing a composite rheology with “realistic” rheological parameters in a fully three-dimensional geometry. Using these more realistic models, we aim to improve our understanding of mantle rheology in the context of self-consistent generation of plate-like behaviour. To achieve this, slab sinking rates will be computed that can be compared to estimates based on tomography^[4], which is a relatively new source of constraint^[5]. The tectonic mode depends on the plastic yield stress. In turn, the yield stress parameter space for a plate-like regime depends on whether continents, phase-dependent rheology and dislocation creep are considered. Thus, the yield stress and reference viscosity parameter spaces must first be explored for each rheological model. Generally, we observe that lower yield stresses lead to higher surface mobilities. On top of high surface mobility (deformation), plate-like behaviour asks for localisation of deformation in narrow zones. Plateness is a widely used measure for this, which we find to be high for models with sufficiently low yield stresses. Furthermore, preliminary results show that models with phase-dependent rheology are more likely to be in a plate-like regime compared to models without a viscosity jump between the upper and lower mantle. Lastly, we hypothesise that the slab sinking speed may be highly sensitive to rheology and may be affected by the presence of continents.

^[1] Tackley, P. J. (2008). Modelling compressible mantle convection with large viscosity contrasts in a three-dimensional spherical shell using the yin-yang grid. Physics of the Earth and Planetary Interiors, 171(1–4), Article 1–4.

^[2] Moresi, L., & Solomatov, V. (1998). Mantle convection with a brittle lithosphere: Thoughts on the global tectonic styles of the Earth and Venus. Geophysical Journal International, 133(3), 669–682.

^[3] Tackley, P. J., Ammann, M., Brodholt, J. P., Dobson, D. P., & Valencia, D. (2013). Mantle dynamics in super-Earths: Post-perovskite rheology and self-regulation of viscosity. Icarus, 225(1), 50–61.

^[4] Van der Meer, D. G., Van Hinsbergen, D. J., & Spakman, W. (2018). Atlas of the underworld: Slab remnants in the mantle, their sinking history, and a new outlook on lower mantle viscosity. Tectonophysics, 723, 309-448.

^[5] Van Der Wiel, E., Van Hinsbergen, D. J. J., Thieulot, C., & Spakman, W. (2024). Linking rates of slab sinking to long-term lower mantle flow and mixing. Earth and Planetary Science Letters, 625, 118471.

How to cite: Metternich, M., Tackley, P., and Arnould, M.: Rheological controls on the plate-mantle system using Earth-like mantle models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16834, https://doi.org/10.5194/egusphere-egu25-16834, 2025.

Earth’s tectonic history is punctuated by several cycles of supercontinent assembly and breakup that profoundly influenced the lithospheric structure; however, the roles of the various factors controlling continental strength and deformation during the cycles remain debated. The effective elastic thickness (T_e) reflects the lithosphere’s long-term, depth-integrated strength and is useful for deciphering the complex evolution of continents. In this study, we estimate a new global map of continental T_e projected onto a  grid by inverting the cross-spectral properties (admittance and coherence) between Bouguer gravity and topography data obtained from a continuous wavelet transform. Continental T_e ranges from <5 to ~140 km, with a mean and standard deviation of 50 and 33 km, respectively. Based on a gaussian mixture model-based cluster analysis, we delineate tectonically active provinces, stable Archean cratons and transitional lithosphere. We find an obvious positive correlation between T_e and lithospheric thickness obtained from calibrated upper mantle surface wave tomography models. Further comparing the T_e distribution with orogenic age data shows that T_e exhibits a clear time dependence where the strength is governed by the time since the last orogeny. Based on plate cooling models, we indicate that continental T_e corresponds approximately to the depth of the 300±150℃ isotherm. These results favour a diffusive (cooling) model that considerably influences the strength of the continental lithosphere, despite the complex relation between T_e and the thermal, compositional and rheological structure.

How to cite: Lu, Z., Li, J., Audet, P., and Li, C.-F.: Strength of continental lithosphere governed by the time since the last orogeny, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1455, https://doi.org/10.5194/egusphere-egu25-1455, 2025.

The formation of the continental crust is driven by an igneous process in which mantle-derived magmatism is incorporated into the overlying crust. Continental collision represents a major lithospheric event, where crustal destruction and growth result from balancing continental subduction and orogenic magmatism. Emerging evidence supports a common mantle source for all orogenic, post-collisional magmatic suites. However, the geodynamic triggers behind the metasomatized mantle source of post-collisional magmas remain uncertain, and so does their implication for crustal evolution. In this work we present an integrated thermomechanical–experimental approach to constrain the geodynamic triggers behind orogenic magmatism. Numerical models predict the consistent relamination of deeply subducted continental crust into the orogenic lithosphere during continental collision, owing to the buoyancy-driven detachment of the upper crust. The interaction between the relaminated upper crust and the overlying peridotite is enhanced by protracted brittle-ductile damage of the lithosphere, facilitating the mechanical mixing of crust and mantle peridotite. Our high-pressure experiments confirm that this hybrid interaction generates orogenic magmas, reproducing their natural compositional trends. This crust-mantle interaction has been recorded throughout Earth's history, with magmatism in successive orogenic cycles exhibiting increasingly heterogeneous isotopic signatures. These findings highlight the critical role of deep crustal relamination in shaping Earth's continental crust.

How to cite: Gómez Frutos, D., Castro, A., Balázs, A., and Gerya, T.: Sublithospheric reworking of the continental crust, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11065, https://doi.org/10.5194/egusphere-egu25-11065, 2025.

Thermo-chemical mantle convection models featuring heterogeneous thermal conductivity indicate that heat-producing element (HPE) enrichment in large low shear velocity provinces (LLSVPs) significantly impacts the long-term stability of these regions. Because the rate of internal heating was more significant in the past, thermal conductivity's influence on thermal buoyancy (and bulk erosion) must have also been more substantial. Consequently, their initial volume may have been significantly larger than their present-day volume. Energy balance calculations suggest that a smaller initial mantle volume fraction of LLSVP material supports more HPE enrichment than a larger mantle volume fraction to maintain the mantle's internal heat budget. For example, an initial layer thickness of 160km (~3% mantle volume) implies present-day HPE enrichment factors greater than ~45 times the ambient mantle heating rate (compared with more conservative factors of 10 to 20 for similar initial conditions employed in previous studies of thermo-chemical pile stability). Thus, HPE enrichment may have been significantly underestimated in earlier models of LLSVP evolution. Conversely, and assuming that LLSVPs formed from a much larger reservoir, HPE enrichment may be overestimated based on the present-day LLSVP volume. Our study considers LLSVPs with a primordial geochemical reservoir composition (consistent with an undegassed 4He/3He signature and HPE enrichment). We present thermo-chemical mantle convection models that feature time-dependent internal heating rates and HPE enrichment (implied by initial mantle volume fraction). In this new context, we re-examine, in particular, the impact of a fully heterogeneous lattice thermal conductivity (derived from conductivity measurements of upper and lower mantle minerals). Furthermore, in light of recent developments with radiative conductivity, we also examine the added effect of a strongly temperature-dependent radiative conductivity component on the stability of LLSVPs. Using tomographic filtering on our simulations, with LLSVPs' present-day volume and core-mantle boundary coverage as a constraint, we examine potential initial conditions, heating scenarios, and thermal conductivity for an Earth-like model.

How to cite: Guerrero, J., Deschamps, F., Hsieh, W.-P., and Tackley, P.: Assessing the effects of heat-producing element enrichment and mantle thermal conductivity on the stability of primordial reservoirs, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14052, https://doi.org/10.5194/egusphere-egu25-14052, 2025.

The origin and exact nature of the large low seismic provinces (LLSVPs) located beneath Africa and the Pacific are still open questions and highly debated. As these structures are assumed to be at their respective locations for at least a few hundred million years, a thermochemical nature seems highly likely.
We use a 2D double-diffusive mantle convection model to numerically investigate the temporal and spatial stability of thermochemical piles for various rheological parameters. We compare results of the commonly investigated depth dependence of the viscosity (due to pressure and composition) with the effect of the yield stress and variable thermal expansivity. We find that increasing the top or bottom viscosity yields temporally and spatially more stable piles. Similarly, a decreased thermal expansivity with depth also results in slower entrainment of the high compositional material and thus more stable piles. Additionally, the appropriate combination of parameters can counterbalance destabilizing properties such that, for example, structures containing melt can also be long-lived and spatially stable, which would otherwise be quickly entrained due to the low viscosity of melt.
Furthermore, we studied the effect of rheological parameters on the stability of plumes and investigated the location of plumes with respect to thermochemical piles. Our results show a mutual dependency of the plumes and piles. Typically, large plumes are anchored by piles and located in the pile center. However, strong thermal plumes in the ambient mantle can pull along high compositional material. This can lead to the deformation of piles. During this process, or the merging of piles due to strong slabs, plumes are observed at the edges of piles, existing there for several million years before striving to the center of a pile.

How to cite: Sitte, H. W., Weber, C., Stein, C., and Hansen, U.: Numerical Study on Rheological Parameters Affecting the Stability of Thermochemical Piles and Plumes, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6256, https://doi.org/10.5194/egusphere-egu25-6256, 2025.

Seismic observations have revealed a range of distinct features at the core-mantle boundary of the Earth. To simulate these structures, typically the presence of a primordial layer (a relic of the magma ocean) is assumed. During mantle convection thermochemical structures develop from this layer for which, however, the excess density and mass need to be prescribed ad hoc and are not well constrained.

An alternative origin of the thermochemical structures could be core material penetrating the mantle by various interaction mechanisms. As a potential explanation of the observed tungsten deficits in some ocean island basalts different mechanisms have been proposed by laboratory experiments. To investigate this concept further, we developed a numerical model that incorporates a chemical gradient between the mantle and core to investigate the infiltration of dense material into the chemically depleted mantle.

In our models core material penetrates the mantle by the diffusive chemical influx in regions where slabs spread across the bottom boundary. As a consequence we observe a self-consistently growing dense layer from which thermochemical structures emerge in a similar way as observed in the primordial layer scenario. In the scenario of core-mantle interaction, however, the thermochemical structures are long-lived because of the constant chemical influx. This temporal stability agrees with plate reconstruction models that suggest a stability of the structures in the last 200-500 Ma. We performed a large parameter study in which we analyzed excess density and mass of the primordial layer as well as rheological parameters for both scenarios. Here, we will present our results on the temporal and spatial stability of the structures resulting in the core-mantle scenario and compare these to results from the primordial layer scenario.

How to cite: Stein, C., Sitte, H., and Hansen, U.: Core-mantle interaction as one cause for dense thermochemical structures at the base of the mantle, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12381, https://doi.org/10.5194/egusphere-egu25-12381, 2025.

Heat flux at the Earth’s core-mantle boundary (CMB) partially controls the outer core dynamics and its associated geodynamo. On the mantle side, spatial and temporal variations in this flux are, in turn, controlled by details of mantle convection. Previous simulations of mantle dynamics showed that CMB heat flux may be locally negative, i.e., in these regions heat flows from the mantle to the core. Here, we investigate the conditions needed to generate such patches of negative CMB heat flux. For this, we perform a series of high-resolution numerical simulations of thermo-chemical convection in spherical annulus geometry using the code StagYY. The compositional initial condition consists in a thin basal layer of chemically denser material (alos referred to as primordial material), which subsequently evolves into piles of hot, primordial material, modelling the large low shear-wave velocity provinces (LLSVPs) observed on global seismic tomography maps. We more specifically explore the influence of two key parameters that promote temperature increase within the piles of primordial material: the excess internal heating within these piles ; and the temperature-dependence of thermal conductivity. We quantify the size and amplitude of negative heat flux patches depending on these parameters. As one would expect, a larger internal heating excess and a stronger temperature dependence of thermal conductivity both favor the development of negative heat flux patches within piles of dense material. However, these parameters also alter the piles stability, such that there is no straightforward relationship between them and the size and amplitude of the negative heat flux patches. Finally, we discuss possible consequences of our findings for core dynamics and geodynamo.

How to cite: Deschamps, F., Guerrero, J., and Amit, H.: Local patches of negative core-mantle boundary heat flux : insights from numerical models of thermo-chemical convection, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3892, https://doi.org/10.5194/egusphere-egu25-3892, 2025.

The solid surfaces of airless bodies continuously evolve due to bombardment by objects from space and solar wind.  We see evidence of this evolution in the differences in colour between surfaces known to be younger (such as freshly excavated crater rays) and older surfaces.  In a recent publication [1], we presented a new complete catalogue of the Moon’s rayed craters with diameters of 5 km and greater between ±50 degrees of the equator. In ongoing work, we are creating a catalogue of the rayed craters with diameters 2 km and greater on the asteroid 4Vesta. We use these catalogues and a model of impact gardening to examine how quickly the surfaces of large rocky bodies like the Moon and smaller rocky bodies like the asteroid 4Vesta evolve over timescales of years to billions of years.

Here, we present the results of the quantitative analysis of the maturity and composition of the lunar rayed crater population through the lense of diverse remote sensing datasets. Perhaps unsurprisingly, we find that the most charismatic rays have the least nanophase iron (also denoted ‘npFe’; i.e., they are the least mature). More compelling, however, is that the most charismatic rays include diverse and distinguishable mineralogical contrasts, for example, rays in both plagioclase, olivine, and FeO abundances. Further, regardless of whether the mineralogical contrast is high or low (i.e., a dark or bright ray), maturity is suppressed. As rays degrade, they appear more thermophysically and mineralogically homogenous; however, faint thermophysical and mineralogical contrasts can persist longer than it takes regolith to saturate with nanophase iron and disappear into the optically mature background. We demonstrate that comparative analysis of rayed crater populations can help us distinguish the timescale for various space weathering thresholds, such as the destruction of a thermophysical ray, the saturation of nanophase iron, and the homogenisation of mineralogical contrasts.

[1] Ghent, R. R., Costello, E. S., & Parker, A. H. (2024). The Population of Young Craters on the Moon: New Catalog and Spatial and Temporal Analysis. The Planetary Science Journal, 5(4), 89. 

How to cite: Costello, E., Ghent, R., and Tai Udovicic, C.: Colour and Time: The Evolution of Crater Rays on the Moon and the Asteroid 4Vesta, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4563, https://doi.org/10.5194/egusphere-egu25-4563, 2025.

Globally, the most widespread contractional landforms on Mercury are lobate scarps. Lobate scarps are linear or curvilinear topographic features interpreted as the surface expression of thrust faults, formed as a consequence of planetary cooling and contraction. These features have been studied extensively, from the initial images captured by Mariner-10 to the more recent data acquired by MESSENGER's Mercury Dual Imaging System (MDIS). However, although several works have analyzed the global tectonics of the planet (e.g. Klimckzak et al. 2015; Watters et al., 2015), a comprehensive interpretation of thrust faults geometry and their mechanical behavior on a global scale has not yet been fully constrained. Here we show that the formation and growth of large-scale lobate scarps is facilitated by the presence of a graphite-rich layer(s), acting as fault lubricant. We studied thrust faults from seven different Mercury quadrangles and derived their geometric characteristics (relief height, amount of shortening, detachment depth) considering a fault-propagation geometry for a range of possible dip angles on isolated thrusts. Using a critical taper theory-based model (iterative mechanical model) we then estimated the basal friction coefficient for thrust-belts located in the same quadrangles. The low obtained friction coefficients indicate the presence of a weak material that allows fault slip. Our results demonstrate the crucial role that graphite possibly plays in shaping Mercury’s lithosphere, providing new understanding on thrust faults nucleation and growth and establishing a possible connection between surface deformational processes and Mercury’s early crust composition.

How to cite: Massironi, M., Vergara Sassarini, N. A., Tesei, T., and Bistacchi, A.: The role of graphite in the formation of thrust faults on Mercury, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20096, https://doi.org/10.5194/egusphere-egu25-20096, 2025.

The Marsquake Service (MQS) [1] is finalizing the release of the reference catalogue of Martian seismicity recorded by NASA’s InSight mission. Previous catalogue versions [2] listed over 1300 events classified by their observed frequency content into i) low frequency (LF) and broadband (BB) - the key events for constraining interior structure, ii) 2.4 Hz and high frequency (HF) -  representing the majority of events with weak signals and enigmatic origin,  and iii) very high frequency (VF) events, including several nearby impacts [3].

Since the last release in April 2023, directly following the mission end, MQS has reviewed the entire data set, also using denoised data sets [4,5] to refine phase picks, back azimuths, and ensuring consistency across the catalogue. 

For distance computation, MQS has adopted an updated suite of interior models, now applied to all event types [6, 7]. Previously 2.4 Hz, HF, and VF events were located using constant crustal velocities. However,  new insights from observations of impacts and surface waves [8,9,10] suggest these events propagate through deeper interior layers, leading to significantly larger distances.

MQS has revised the frequency-based event classification, incorporating spectral analysis [11] and other parameters such as distance and seasonality to improve event characterization. Events are grouped into three interpretation types:

• i) Tectonic events, mostly located ~30° east of InSight in Cerberus Fossae and in few other regions with deeper sources, include most LF and BB events with low corner frequencies.
• ii) Swarm events are a subset of HF and 2.4 Hz events clustered in ~44° distance with shallow seasonal sources, though their source region remains speculative; this group has been significantly expanded through deep learning techniques [5].
• iii) Meteorite impacts, characterized by high corner frequencies, encompass VF events, several large BB events, and HF/2.4Hz events located outside of the swarm region.

The reference catalogue includes over 1900 events with improved locations and new interpretation types, providing a more comprehensive view of Martian seismicity observed by InSight.

[1] Clinton et al (2018), 10.1007/s11214-018-0567-5

[2] Ceylan et al. (2022), 10.1016/j.pepi.2022.106943

[3] Garcia et al (2022), 10.1038/s41561-022-01014-0

[4] Scholz et al (2020), 10.1029/2020EA001317

[5] Dahmen et al. (2024), 10.1093/gji/ggae279

[6] Khan et al. (2023), 10.1038/s41586-023-06586-4

[7] Samuel et al. (2023), 10.1038/s41586-023-06601-8

[8] Posiolova et al. (2022), 10.1126/science.abq7704

[9] Panning et al. (2023), 10.1029/2022GL101270

[10] Charalambous et al. (in press)

[11] Stähler et al. (in prep.)

How to cite: Clinton, J., Dahmen, N., Ceylan, S., Stähler, S., Giardini, D., Duran, C., Zenhausern, G., Euchner, F., Horleston, A., Kawamura, T., and Kim, D.: The Marsquake Service Reference Catalogue, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13152, https://doi.org/10.5194/egusphere-egu25-13152, 2025.

The presence of a molten Basal (BML) enriched in iron and in heat-producing elements (HPE) has been suggested just above the Martian core (Samuel et al., 2023; Khan et al., 2023). Such a BML largely affects interior thermal evolution in multiple ways, through the redistribution of HPE between the BML and the mantle, and the likely suppression of core convection. The mode of heat transport from and across the BML itself is also crucial to Mars's thermo-chemical evolution. This, however, is linked to the convective state within the BML, which is yet to be further constrained. In the case of a compositional stratification within the layer, the large amount of heat generated by the HPE-enriched BML can be transferred to the mantle above and the core below via conduction. If compositional stratification is weak or absent, vigorous convection of the liquid-state BML (compared to the timescale of solid-state mantle convection) would allow additional heat loss from this layer.

Here, we consider the scenario where the BML is the product of end-member fractional crystallisation of the initial global magma ocean, followed by the subsequent overturn of the iron- and HPE-enriched component (as described by e.g. Elkins-Tanton et al., 2003). Contrary to the less extreme equilibrium and intermediate crystallisation modes (e.g. Ballmer et al., 2017), this scenario results in a very strong and stable density stratification, strictly preventing the BML to convect (Samuel et al., 2021, 2023). Using the mantle convection code StagYY, we therefore assume in our models that conduction is the only mode of heat transport across the BML; as such, the intrinsic thermal conductivities of the BML and of the mantle are key parameters that may impact the long-term thermal evolution of Mars, while their influence has not yet been thoroughly explored. Varying the intrinsic thermal conductivity as a function of depth, temperature and composition, we report on its effect on observational diagnostics including, but not limited to, mantle temperature and crustal growth history. We further investigate the thermal exchange and feedback between the BML and the core, considering different thermal structures within the core. Our model results assuming a conductive BML and adiabatic core temperature profile are compared with those obtained in Samuel et al. (2023). 

How to cite: Cheng, K. W., Deschamps, F., and Samuel, H.: Influence of intrinsic thermal conductivity of a stably stratified molten silicate layer above Mars's core : insights from mantle convection simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12899, https://doi.org/10.5194/egusphere-egu25-12899, 2025.

Wrinkle ridges (WRs) are among the most prevalent tectonic landforms observed on terrestrial planetary bodies, characterized by highly variable relief. They are interpreted as folds overlying blind thrusts, which can reach reliefs of 100’s meters and widths of several 10’s kilometers. The formation and subsurface characteristics of WRs is still debated with unresolved questions, including: i) geometry and likely structural style of associated blind faults, ii) fault depth, iii) number and role of faults, iv) amount of shortening. Several modelling methods have been proposed, however, none of them completely describe the entire spectrum of observations related to WRs morphometry and kinematics.

In this work, we conduct a 2D to 3D geometrical and kinematic reconstruction of a set of globally distributed WRs by applying Trishear and Fault-Parallel-Flow integrated forward kinematic modelling. The methodology allows to model complex fault geometries by assuming area conservation and plane-strain deformation, to determine the fault geometry and kinematics that best fits the observed topography and the measured outcropping faults dip angles.

Our results demonstrate the reliability of the trishear method to model planetary WRs and provide an improvement in understanding Mars’ lithospheric mechanical stratigraphy and WRs kinematics. We demonstrate how the wrinkly and complex nature of WRs can be related to the presence of multiple faults, which accommodate shortening differently. We suggest the presence of a heterogeneous stratigraphy composed of alternations of weaker and friction detachments which promote fault activity characterized by sequential deformation of backthrusts, synthetic thrusts.

The results of the trishear kinematic modelling indicate correlations of the main morphometric parameters of WRs with the geometry and kinematics of the faults. WRs characterized by a higher relief are driven by larger amounts of horizontal along-fault slip, while the broader the width of the main crest, the deeper and more spaced are the faults below the crest (i.e., master fault and possible backthrust). The location of the hinge zone of the main crest, corresponds to the fault dip change at depth.

How to cite: Carboni, F.: Martian wrinkle ridges morphometry and kinematics correlation from Trishear Forward Modelling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-441, https://doi.org/10.5194/egusphere-egu25-441, 2025.

Venus is believed to be deformed in a stagnant-lid, episodic-lid, or a plutonic-squishy-lid regime with mantle convection occurring beneath a unified lithosphere [1-3]. Its surface age, estimated at 240–800 Ma from impact crater records [4], suggests either a catastrophic resurfacing event involving rapid lithospheric recycling [5] or continuous, regionally tectonic and volcanic processes [6]. Here we raise a key question how strain localization occurs on Venus: do Venusian faults show evidence of multi-stage activation capable of leading to large-scale lithospheric deformation, and is it possible to use this to unravel the tectonic history of Venus?

To address this, we focused our investigation on the equatorial chasmata system in Eastern Aphrodite Terra, Venus, whose origin continues to be a subject of scientific debate. This study documents that the troughs consistently exhibit asymmetric cross-sectional profiles, with steeper slopes intersected by large-scale faults trending subparallel to the trough axis. These shear zones dip at low angles and occasionally form terraces along the slope profile, exposing sections of the shear planes. The shear planes are radar-smooth and exhibit radar emissivities distinct from the adjacent hanging wall and footwall. We propose that these fault planes be coated with melt films, which in some cases display flow features along downslope trajectories.

The formation of these melt films is explored in the context of frictional melting during co-seismic faulting. Frictional melting may be enhanced on Venus due to its elevated ambient temperatures and the likely water-free, mafic composition of its rocks. However, multi-incremental friction-induced melting is unlikely to result in significant strain localization, and the volume of melt generated even under Venusian conditions is insufficient to be resolved in the available SAR imagery. Instead, we hypothesize that the fault planes act as conduits for transporting magma from shallow subsurface reservoirs to the surface. Volcanic centers and edifices near the steep chasmata slopes and within corona interiors are potential sources for shallow subsurface melt reservoirs. Melt veneers along the fault planes may reduce friction coefficients, facilitating normal faulting at shallow dip angles.

The overall morphology of the troughs suggests that the faults were initially formed as thrust faults and later reactivated. Evidence of their youthfulness is provided by fresh hummocky landslide deposits originating from the steep hanging wall scarps, which partially obscure the exposed fault planes. They were likely triggered by fault-induced seismicity, suggesting that faulting on Venus is seismogenic. Seismic moments for the studied shear zones have been calculated to support fault activation.

References

[1] Solomatov, V. S., & Moresi, L. N. (1996). J. Geophys. Res. Planets, 101(E2), 4737–4753. [2] Turcotte, D. L. (1993). J. Geophys. Res. Planets, 98(E9), 17061–17068. [3] Lourenço, D. L., Rozel, A. B., Ballmer, M. D., & Tackley, P. J. (2020). Geochem. Geophys. Geosyst., 21:e2019GC008756. [4] Le Feuvre, M., & Wieczorek, M. A. (2011). Icarus, 214(1), 1–20. [5] Armann, M., & Tackley, P. J. (2012). J. Geophys. Res. Planets, 117(E12), E12003. [6] Bjonnes, E. E., Hansen, V. L., James, B., & Swenson, J. B. (2012). Icarus, 217(2), 451–461.

How to cite: Karagoz, O., Kenkmann, T., and Gurau, M.: Fault-melt interaction and its implications for Venusian Tectonic regimes in Aphrodite Terra, Venus, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-235, https://doi.org/10.5194/egusphere-egu25-235, 2025.

The seismic events from the NASA InSight mission have provided a groundbreaking opportunity to explore the internal structure of Mars, from its crust to core. Events are catalogued by the MarsQuake Service (MQS) into several classes based on their frequency content and signal to noise ratio. This classification has provided a useful framework in which to decode Martian seismicity. In this work we will highlight newly observed features in the P-wave coda of these events to add to this effort.

A prominent feature of event waveforms on Mars is scattering, particularly at high frequencies (above 1 Hz) where the dominant energy of the majority of events is visible. The scattering obfuscates signal polarization, making seismic phase identifications and back azimuth estimations difficult. Although several events have been linked to particular sources, including impacts and tectonic features, the origin of a large number of events remains poorly constrained. Nevertheless, the scattering behaviour within events has offered important clues to the interior structure of Mars and its variation. Here, we present a re-analysis of Martian event envelopes to identify arrival features in the P-wave coda and how these vary across event types and epicentral distances. Using this additional information, we can further constrain MQS distance estimates and subsequently infer the implications for Mars’ internal structure and event origins. This helps open the door to new avenues for processing marsquakes to help place constraints on the seismicity of Mars.

How to cite: Stott, A., Garcia, R., Drilleau, M., Margerin, L., Kim, D., Menina, S., Mimoun, D., Murdoch, N., and Horleston, A.: Examining the P-wave coda features of InSight seismic events, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8985, https://doi.org/10.5194/egusphere-egu25-8985, 2025.

Venus’ geological history holds critical insights into why Venus and Earth, despite their similarities, have followed such divergent evolutionary paths. Recent discoveries have transformed the perception of Venus from a geologically inactive planet to a one characterized by active and diverse geological processes. Mantle convection, lithospheric delamination, and plume-lithosphere (have) create(d) a surface rich with tectonic and volcanic structures, despite the absence of plate tectonics today. Among the most striking tectonic features on Venus are the expansive extensional rift structures, or "chasmata", which can span up to 10,000 km in length and show both unique and familiar features relative to Earth’s extensional tectonics. Many of Venus' rifts exhibit intersecting branches, multiple troughs, and associations with coronae, which are often interpreted as small-scale mantle upwellings.

Here, we present the first 3D geodynamic models of rift tectonics on Venus. With models of uniformly, slowly extending lithosphere, we investigate the impact of crustal rheology (wet vs. dry diabase, i.e., weaker vs. stronger crust) and the thickness of the crust and lithosphere on rift geometry, topography, surface fracturing, and heat flow. We further explore interactions between evolving rift structures and thermal upwellings (plumes) and magmatic intrusions – considered key components of Venus’ geodynamic regime.

We find that rift morphology is highly sensitive to crustal rheology and lithospheric properties, with five modes of rift morphologies predicted: (1) narrow, (2) wide-valley, (3) wide-troughs, (4) multiple, and (5) branching; of which the latter three (see Figure) align most closely with Venus observations. We find that a dry diabase crust -- often assumed likely for Venus -- favors Venus-like rift patterns only when combined with a thin, warm lithosphere, leading to focused faulting and branching rift structures. In contrast, a weaker wet diabase crustal rheology results in broader, less pronounced deformation zones. Underplated thermal plumes induce lower-crustal intrusions and cause localized lithospheric weakening, narrowing the rift regionally.

Importantly, the results show that along-axis rift geometry variations, like multiple offsets and branching, can emerge even in symmetric, uni-axial extension settings. Moreover, the models indicate that if Venus' crust follows a dry diabase rheology, a significantly warm and thin lithosphere is required to reproduce observed rift characteristics. Through comparison to observations, we find that Venus rift morphologies are reproduced by various activity stages of model evolution, commonly under conditions of a thin lithosphere, which supports the possibility that Venus rifts are currently active.

This research was partially conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract (80NM0018D0004) with the National Aeronautics and Space Administration. 

How to cite: Gülcher, A., Gurnis, M., and Smrekar, S.: The Peculiar Case of Extensional Tectonics on Venus: Modes of RIfting and Activity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18383, https://doi.org/10.5194/egusphere-egu25-18383, 2025.

Characterizing the internal composition of exoplanets is an essential part in understanding the diversity of observed exoplanets and the processes that govern their formation and evolution. However, the interior of an exoplanet is inaccessible to observations, and can only be investigated via numerical structure models. Furthermore, interior models are inherently non-unique, because the large number of unknown parameters outweigh the limited amount of observables. One set of observable parameters can correspond to a multitude of possible planet interiors.

Probabilistic inference methods, such as Markov chain Monte Carlo sampling, are a common, but computationally intensive and time-consuming tool to solve this inverse problem and obtain a comprehensive picture of possible planetary interiors, while also taking into account observational uncertainties. This prohibits large-scale characterization of exoplanet populations.

We explore here an alternative approach to interior characterization utilizing ExoMDN, a stand-alone machine-learning model based on mixture density networks (MDNs) that is capable of providing a full probabilistic inference of exoplanet interiors in under a second, without the need for extensive modeling of each exoplanet's interior or even a dedicated interior model. ExoMDN is trained on a large database of 5.6 million precomputed, synthetic interior structures of low mass exoplanets. 

The fast prediction times allow investigations into planetary interiors which were not feasible before. We demonstrate how ExoMDN can be leveraged to perform large-scale interior characterizations across the entire population of low-mass exoplanets. We can show how ExoMDN can be used to comprehensively quantify the effect of measurement uncertainties on the ability to constrain the interior of a planet, and to which accuracy these parameters need to be measured to well characterize a planet’s interior.

How to cite: Baumeister, P., Bahrenberg, J., Tosi, N., and Charly, A.: Exoplanet characterization across the mass-radius space using machine learning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15903, https://doi.org/10.5194/egusphere-egu25-15903, 2025.

The behavior of SiO₂ analogs (GeO₂ and SnO₂) under extreme pressure conditions provides critical insights into the structural evolution of oxide materials in planetary interiors. In this study, we investigate the ramp compression of GeO₂ and SnO₂ to ultra-high pressures exceeding 500 GPa, revealing novel high-pressure phases and structural transitions. Using advanced in situ X-ray diffraction techniques, we characterize these high-pressure phase transformations under conditions relevant to the deep interiors of large rocky planets. Our findings significantly enhance our understanding of the high-pressure behavior of SiO₂ and its analogs, with important implications for modeling the deep interiors of super-Earths and other large rocky planets. Finally, our results underscore the vital role of analog materials in exploring the fundamental physics of oxide systems under extreme conditions.

How to cite: Kim, D.: Dynamic Compression of Planetary Analog Materials: Insights into the Interiors of Large Rocky Planets, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3397, https://doi.org/10.5194/egusphere-egu25-3397, 2025.

For planets to develop narrow, dynamic plate boundaries that resemble Earth’s, the rocks that make up the lithosphere must be able to localize deformation. Decades of field studies have shown that plate boundary deformation manifests as frictional faults at shallow depths and mylonitic ductile shear zones below the brittle-plastic transition, with individual strands as narrow as 10-100s of meters. The physical mechanisms that produce mylonites from a primary lithosphere are of considerable interest since it is presumably impossible to create or sustain Earth-like plate tectonics without them. Experimental studies demonstrate that the characteristic microstructures in mylonites form through the serial processes of dynamic recrystallization and phase mixing.  However, the rapidity with which this occurs depends on temperature, grain-size, and composition, and the volume fraction and viscosity contrast between constituent mineral phases. As such, the mineralogical composition of a rocky planet will determine whether the planet can (a) localize deformation, and (b) initiate and sustain Earth-like plate tectonics. This contribution will review experimental evidence for the onset of mylonitization and show the results of models that predict the time scales (and therefore ease) with which planets of different compositions can localize deformation.  Drawing on data from the Hypatia catalog of exoplanets, these models identify specific stars with exoplanets that may be most amenable to forming Earth-like plate tectonics.

How to cite: Skemer, P., Cross, A., Foley, B., and Putirka, K.: Compositional effects on shear localization in planetary lithospheres, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11284, https://doi.org/10.5194/egusphere-egu25-11284, 2025.

The dynamics of the coupled plate-mantle system control planetary thermal evolution, crustal geology and geo-morphology, dynamo action, as well as atmospheric evolution and habitability. Rocky planets within our solar system display a diverse array of tectonic regimes, despite their similar origins. Among them, Earth is unique in exhibiting plate tectonics, or a “mobile lid”. Several bodies, such as Mars and the Moon, display a tectonically inactive surface, or a “stagnant lid”. An episodic lid or plutonic-squishy lid has been suggested for Venus, and a sluggish lid for early Mars. The conditions that give rise to these regimes and their transitions throughout planetary evolution remain poorly understood.

To address this challenge, we here explore 2D thermochemical mantle-convection models with self-consistent crustal formation and lithospheric yielding. In a broad parameter study, we examine the influence of core-mantle boundary temperature, internal heating rate, upper-mantle activation energy, and effective yield stress on mantle dynamics and surface tectonics. In each model, we analyze the long-term statistics of tectonic characteristics (mobility and plateness) in the statistical steady state in order to quantitatively distinguish between various tectonic regimes. Such an effort that has been previously complicated by the transient nature of planetary evolution. Thereby, we identify a previously unrecognized episodic-squishy lid regime that is characterized by alternating episodes of plutonic-squishy lid and mobile-lid behavior. By systematically exploring the parameter space, we develop a regime diagram that predicts the tectonic evolution of terrestrial planets as they cool over time. Our findings offer a comprehensive framework for understanding the tectonic history of Earth-like planets, shedding light on their surface conditions and interior evolution.

How to cite: Ballmer, M., Lyu, T., Li, Z., Lee, M.-H., Yan, J., Wu, B., and Zhao, G.: Dissecting the puzzle of tectonic lid modes in terrestrial planets, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12196, https://doi.org/10.5194/egusphere-egu25-12196, 2025.

In recent years, there has been a significant increase in the detection of exoplanets, revealing a remarkable diversity of exoplanetary systems that stand in sharp contrast to our Solar System. These systems exhibit a wide range of variations, including size, mass, orbital distance, and host star type. Among them, rocky exoplanets are particularly intriguing because of their potential to harbour life. Tectonic activity is often considered a crucial ingredient in terms of sustaining life-friendly surface conditions.  Therefore, modelling the interior processes of these terrestrial exoplanets is required to understand their tectonic regimes and identify potentially habitable worlds.

Progress made in numerical modelling has greatly enhanced our understanding of tectonically active “mobile lid” and inactive “stagnant lid” tectonic regimes. Alternative tectonic modes, e.g. the episodic lid, sluggish lid, and plutonic-squishy lid, have also been characterised, but are not fully confirmed by observations. In the context of exoplanet discoveries, the question arises whether the mobile lid regime is more or less likely on larger planets, or if alternative surface tectonic regimes become more prevalent. While this is not a completely unexplored topic, previous research yields conflicting results. Moreover, most existing studies overlook factors such as mantle melting, crustal production, and the occurrence of intrusive magmatism.

In this work, we use the mantle convection code StagYY to model generic sub- and super-Earths in 2D spherical annulus geometry, incorporating crustal formation due to extrusive and intrusive magmatism. We focus on determining the trends in tectonic regimes as a function of planet mass (from 0.5 to 2 times that of Earth), surface yield stress, and the ratio of intrusive-to-extrusive magmatism. Our models suggest that the propensity of the mobile lid regime at low surface yield stresses only depends weakly on planet mass. Additionally, the plutonic-squishy lid regime emerges in models with high intrusion efficiency and high yield stresses, whereas the stagnant lid regime occurs at high extrusion efficiency and high yield stresses. Another noteworthy finding is the identification of the episodic-squishy lid regime at intermediate yield stresses, characterised by an alternation between a mobile and a plutonic-squishy lid. Future research will explore the effects of varying surface temperatures within the model. This study holds significant implications for advancing our understanding of planetary thermal and tectonic evolution.

How to cite: Zaharia, E. A., Ballmer, M. D., Brodholt, J. P., Manjón-Cabeza Córdoba, A., and Vočadlo, L.: Tectonic Diversity in Rocky Exoplanets: The Impact of Planet Mass and Magmatism, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13839, https://doi.org/10.5194/egusphere-egu25-13839, 2025.

It is broadly known that magmatic processes play a key role in cooling planetary interiors. While most studies have analyzed the influence of extrusive magmatism (e.g. Armann and Tackley, 2012, Moore and Webb, 2013), recent investigations have shown that intrusive magmatism could also be very efficient for cooling Earth-like planets (e.g. Rozel et al., 2017, Lourenço et al., 2020). Nevertheless, a systematic investigation of the role that the magmatic styles play in the evolution of different terrestrial planets has never been done. We study the effect of the magmatic style on the thermal evolution of Mercury-, Venus-, Mars-, and Moon-like planets, focusing on the magmatism endmembers i.e. ‘fully extrusive’ (Io-like heat pipe model, Moore and Webb, 2013) and the ‘fully intrusive’ (plutonic-squishy lid model, Lourenço et al., 2020).

We use the geodynamical code GAIA in a 2D spherical annulus geometry (Hüttig et al., 2013, Fleury et al., 2024). Our models assume a homogeneous distribution of the heat sources, a depth- and temperature-dependent viscosity (Karato et al., 1986) that follows an Arrhenius law for dry diffusion creep (Karato & Wu, 1993), pressure- and temperature-dependent thermal conductivity and expansivity (Tosi et al., 2013), a time-dependent core cooling (Steinbach & Yuen, 1994), and a melting curve parametrization derived for the Earth’s interior (Stixrude et al., 2009). Apart from surface and core temperature, mantle and core density, planet, and core radius, and initial concentration of radioactive elements, we keep the model parameters similar for all bodies. This choice was made to minimize the differences between models due to the particular conditions of each planet, allowing us to focus our analysis on the influence of intrusive vs. extrusive magmatism rather than each planet’s evolution.

Melting occurs when the mantle temperature exceeds the solidus. For all bodies, we compute partial melting considering latent heat consumption. We extract the melt either to the intrusive melt depth of 50 km for the fully intrusive cases or to the surface for the fully extrusive cases. We delimit the area of buoyant melt from which melts can be extracted by the lithosphere thickness (to avoid re-melting the hot intrusions) and the density crossover at 11 GPa (Ohtani et al., 1995).

For all studied bodies, the convection pattern is characterized by stronger mantle plumes and more vigorous mantle flow for the fully intrusive cases than for the fully extrusive cases. Throughout the evolution of all planet-like models, cases with intrusions present thinner and warmer lithospheres, cooler mantle and CMB temperatures, higher melt production, shallower melting depths with cooler melt temperatures, and higher surface and CMB heat fluxes. Limiting the melt production in the interior by the density crossover greatly impacts the planetary cooling of bodies with high mantle pressures such as Venus, for which an intrusive magmatism style allows for more efficient cooling of the interior while having a warm and thin lithosphere.

Our study provides the first detailed investigation of the effects of intrusive vs. extrusive magmatism on the global evolution of rocky planets, in a comparative planetology sense.

How to cite: Herrera, C., Plesa, A.-C., Maia, J., and Breuer, D.: Effects of magmatic styles on the thermal evolution of planetary interiors, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-862, https://doi.org/10.5194/egusphere-egu25-862, 2025.

The isotopic compositions of lavas from mantle plumes provide evidence for deep mantle heterogeneities and have been associated with primordial mantle material. However, little is understood about how such material formed during the early stages of planetary evolution. Its origin is typically linked to processes such as the sedimentation of iron-rich phases and crystallization in a primordial magma ocean, or, alternatively, to impacts during the later stages of planetary formation. These processes operated under varying temperature and pressure conditions, likely leading to a depth-dependent composition. Regardless of how it originated, this primordial material is thought to contain higher concentrations of radioactive elements compared to the upper mantle. We aim to address a critical question: how does a compositionally stratified mantle evolve over time under convective motions. These motions reshape the boundaries of chemically distinct domains and promote mixing. Therefore, it is crucial to understand the conditions that allow primordial material to persist at the mantle's base over long timescales, particularly in relation to differences in density and heat production between various mantle components.

To investigate this question, we conducted an in-depth experimental study of convection in a stratified system consisting of two fluids with distinct intrinsic densities and heat production rates. We derived scaling laws that connect the dynamical characteristics of convection to the key dimensionless numbers. These scaling laws, coupled with plausible physical parameters, are then applied to extrapolate the results to planetary mantle convection. We illustrate our approach with a diagram relating the effective partitioning coefficients of iron and that of heat producing elements to the lifetime of the stratified mantle.

How to cite: Limare, A. and Boukare, C.-E.: Dynamics of heat producing elements rich domains in rocky planets, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8040, https://doi.org/10.5194/egusphere-egu25-8040, 2025.

Theory and models predict that extremely hot rocky exoplanets (T>850 K) could be covered with lava oceans. However, direct observational evidence of lava oceans remains elusive. Here we show that phase curves can be used to distinguish between planets with smooth, molten surfaces (lava-ocean) versus rough, solid surfaces (Moon- or Mercury-like). To do so, we argue that lava oceans should be smooth enough to exhbit specular reflection, which gives rise to an ocean "glint". We develop both numerical and analytical models which solve for the reflected and emitted light of a surface with specular versus Lambertian reflection. We show that the phase curve of a specular surface is much flatter than the well-known sinusoidal shape of a Lambert surface, and causes the phase curve amplitude to be noticeably smaller than the secondary eclipse depth. Incorporating Fresnel’s law, we predict that two peaks will appear near transit for low-albedo surfaces. Our results suggest that phase curve variations caused by the glint effect can be used to detect smooth, molten surfaces such as lava oceans. This detection method holds promise for characterization of hot rocky exoplanets with thin atmospheres using JWST.

How to cite: Li, H. and Koll, D.: Detecting Lava Oceans on Hot Exoplanets Using the Glint Effect, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19786, https://doi.org/10.5194/egusphere-egu25-19786, 2025.

The discovery of exoplanets has uncovered a vast spectrum of planetary types, from enormous gas giants to smaller, rocky worlds akin to Earth. Among these, super-Earths are prevalent and are believed to exhibit a range of tectonic regimes. A portion of these have ultra-short periods and orbit their stars in mere hours to days, resulting in synchronous rotation with their host star. This establishes a surface temperature dichotomy like that seen on LHS 3844b, a bare-rock super-Earth with a radius approximately 1.3 times that of Earth, where temperatures reach 1040 K at the point receiving the most intense sunlight on the dayside and drop close to 0 K on the nightside.

We use StagYY to model mantle convection on LHS 3844b in a 2D spherical-annulus geometry. Our models incorporate a temperature-dependent yield stress that captures both near-surface and deep lithospheric rheological variations, rather than assuming a fixed effective yield stress as in previous studies. We represent the effects of various temperature-dependent microphysical processes by varying the temperature dependence of the yield stress slope. The yield stress components in our models are systematically varied to examine their impact on tectonic style and mantle dynamics.

Parameterisation of the brittle component is based on the proposition that temperature-dependent frictional weakening plays a factor in the tectonic regimes of Earth and Venus. On Earth, where low surface temperatures create a geothermal gradient that keeps much of the crust below 400°C, frictional heating can reduce the friction coefficient at high slip velocities. In contrast, Venus’ elevated surface temperatures maintain a higher friction coefficient, which helps suppress plate tectonics. In deeper lithospheric regions, elevated temperatures favour ductile deformation, which would normally weaken the lithosphere. However, these higher temperatures can also promote grain growth, counteracting dynamic strain localisation and thereby strengthening the rock.

We find that hemispheric temperature differences strongly influence lithospheric strength and deformation on LHS 3844b: the colder nightside allows brittle failure to persist over greater depths, whilst the hotter dayside promotes ductile flow at shallower depths due to a much thinner lithosphere. Importantly, we find that an increased temperature dependence of the ductile yield stress amplifies the hemispheric contrast in the planet's tectonic behaviour.

How to cite: Zarebski, A., Ballmer, M., Meier, T., and Manjon Cabeza Cordoba, A.: Effects of Temperature-Dependent Lithospheric Yield Stress on Ultra-Short Period super-Earth LHS 3844b, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4391, https://doi.org/10.5194/egusphere-egu25-4391, 2025.