EGU General Assembly 2023  

Plate tectonics is the surface expression of mantle convection, but many aspects of our present-day tectonic setting depend on how the solid Earth system has evolved over time. I touch on work across a range of spatio-temporal scales addressing how convective memory can be used to validate tectonic scenarios to better understand plate boundary evolution. Seismic anisotropy in the upper mantle is one recorder of convective deformation, and the duration over which textures are reworked controls the lifespan of memory. This means that the lithosphere may allow distinguishing between different plate tectonic scenarios over the last ~50 Ma. Uncertainties about those scenarios and slab rheology imply that our understanding of subduction mass transport remains incomplete, leading to ambiguities about the deep mantle record of subduction. One particular issue is how slabs are deformed upon bending in the trench. I discuss results from convection models with rheological memory which affects subduction dynamics and plume-slab interactions. Within global, plate generating convection models, reactivation of damage zones increases the frequency of plate reorganizations, and hence reduces the dominant periods of surface heat loss fluctuations. Inheritance of lithospheric damage dominates surface tectonics over any local boundary stabilizing effects of rheological weakening. Progressive generation of weak zones may counteract any effects of reduced convective vigor throughout planetary cooling, with implications for the frequency of orogeny throughout Wilson cycles. I close by a consideration of the effects of local rheological damage weakening vs. the longest recorder of geological history of all, the continental lithosphere.

How to cite: Becker, T.: On convective memory, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3978, https://doi.org/10.5194/egusphere-egu23-3978, 2023.

When cold and dense oceanic lithosphere sinks into the mantle at subduction zones, it pushes weaker asthenospheric mantle away, creating specific flow patterns. Traditionally mantle flow is divided into two components: trench-perpendicular poloidal flow operating in a vertical plane and 3D toroidal flow around the slab edges. In the past years, we have learned that both poloidal and toroidal mantle flow around slabs effectively connects nearby subduction zones, deforming their slabs and upper plates, and modifying their patterns of volcanism and uplift/subsidence. In turn, the two-way dynamic interaction between the subduction zones also affects the flow pattern, and thus impacts the volcanism, surface uplift and lithospheric deformation (Király et al., 2021).

At present, our best constraints on mantle flow patterns around subduction zones originate from seismic anisotropy observations, which can be interpreted based on 3D geodynamic models. In the mantle, seismic anisotropy originates from crystallographic preferred orientation (CPO), which derives from the anisotropic nature of olivine crystals. Due to olivine’s orthorhombic symmetry and the different strengths of its three slip systems, olivine crystals are anisotropic in their elastic and viscous properties. Hence, when many olivine crystals are aligned within mantle rock (i.e., CPO is developed in an area of the mantle), the mantle will deform anisotropically, both for seismic wave transmission and viscous flow. Since CPO occurs as a response to deformation, seismic anisotropy directions are often read as the recent mantle flow direction in an area. However, there are a few complications to this simple one-to-one interpretation. First, because the CPO depends on the deformation history of the mantle, it might not reflect the current flow orientation if the deformation direction has changed through time (Ribe, 1989). Second, CPO formation depends on stress and on water content (Korenaga and Karato, 2008), which in some cases allows texture to form with a fast axis perpendicular to the deformation direction. Third, the interpretation of seismic anomalies is often difficult because geodynamic models do not incorporate enough complexity to model all the intricacies of the flow. This problem can occur due to complex anisotropic signals from crustal layers, from more complicated geodynamic settings (e.g., multiple slabs), or from a modified flow pattern that arises due to the viscous anisotropy associated with the texture itself.

In this presentation, I will use the Mediterranean area to highlight how including multiple slabs and accounting for viscous anisotropy can eventually help us to interpret the seismic observations from this geodynamically complex region.

References:

Király, Á., Funiciello, F., Capitanio, F.A., and Faccenna, C., 2021, Dynamic interactions between subduction zones: Global and Planetary Change, p. 103501, doi:10.1016/j.gloplacha.2021.103501.

Korenaga, J., and Karato, S., 2008, A new analysis of experimental data on olivine rheology: Journal of Geophysical Research, v. 113, p. 1–23, doi:10.1029/2007JB005100.

Ribe, N.M., 1989, Seismic Anisotropy and Mantle Flow: Journal of Geophysical Research, v. 94, p. 4213–4223.

How to cite: Király, Á.: Mantle flow around subduction zones: evolution through time, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9109, https://doi.org/10.5194/egusphere-egu23-9109, 2023.

Earth's dynamic evolution is controlled by the interplay between mantle convection and plate tectonics. While subducted plates stir the mantle, upwelling plumes can lubricate, push, and break up plates. As the surface expression of upwelling plume dynamics, the plume buoyancy flux is traditionally estimated as the cross-sectional area of the hotspot swell multiplied by plate velocity (for intraplate hotspots) or multiplied by the full-spreading rate (for ridge-centred hotspots).

This classical approach implies two big assumptions: that the swell is fully isostatically compensated by the hot ponding plume material at the base of the lithosphere; and that this plume material spreads at exactly the same speed as the overriding plate moves. However, geophysical observations and numerical models demonstrate that those assumptions are wrong. Hotspot swells are largely dynamically instead of fully isostatically compensated; to some extent, swells are further compensated by sublithospheric erosion [1]. Moreover, at least some plumes spread faster than plate motion [2]. For example, evidence in the North Atlantic from prominent V-shaped ridges, ephemeral landscapes, and off-axis uplift of oceanic gateways suggests that along-axis asthenospheric velocities can be an order of magnitude faster than the full plate-spreading rate near Iceland [3]. Thus, classical estimates for the buoyancy fluxes of deep-seated mantle upwellings may be strongly biased by surface-plate velocities [4]. Alternative estimates of plume buoyancy flux assume a constant swell decay timescale [4] but without any physical underpinning. As detailed estimates of dynamic seafloor topography are now available [5], it is time to revisit the buoyancy fluxes and, thereby, the mass and heat fluxes carried by mantle plumes.

Here, we explore high-resolution regional-scale geodynamic models with a free surface to study plume-ridge interaction and swell compensation. We consider composite diffusion-dislocation creep in our models. We investigate the effects of plume temperature/radius, plate velocity (or spreading rate for ridge-centred hotspots), and mantle rheological parameters on plume-lithosphere interaction and swell support. Preliminary results demonstrate that plume spreading is significantly faster than plate motion for intermediate-to-large plumes at realistic rheological conditions. From this result, we update estimates of plume buoyancy fluxes, showing that the total heat flux carried by plumes across the core-mantle boundary is significantly larger than previously thought.

Reference List

1. Cadio et al., 2012; doi:1016/j.epsl.2012.10.006

2. Ribe & Christensen, 1999; doi:10.1016/S0012-821X(99)00179-X

3. Poore et al., 2011; doi: 10.1038/ngeo1161

4. Hoggard et al., 2020; doi: 10.1016/j.epsl.2020.116317

5. Hoggard et al., 2016; doi: 10.1038/ngeo2709

How to cite: Ma, Z. and Ballmer, M.: New Insights into Global Plume Buoyancy and Heat Fluxes from Numerical Models of Plume-Lithosphere Interaction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-467, https://doi.org/10.5194/egusphere-egu23-467, 2023.

The West Iberian Margin (WIM) was a locus of significant post-rift Late Cretaceous magmatism coeval with multiple intraplate magmatic events on the Central-North Atlantic. The effects of the migration of the Iberian microplate on the location of the distinct magmatic occurrences are here investigated.

At the WIM and within this magmatic cycle, the Sintra, Sines and Monchique intrusive massifs, the Lisbon Volcanic Complex and distinct sill complexes were emplaced on the onshore continental margin. Several coeval oceanic seamounts, are also evaluated in terms of age and location for the assessment of how plausible the combined effects of plate motion and underlying mantle contributions are to their origin.

Using GPlates software we assess the different mantle mechanisms that can explain magmatic upwelling in the region, including: 1) plume, whether static or mobile ones; 2) edge-driven convection; or 3) stationary superplume with secondary plumelets.

The preliminary results suggest that a stationary superplume emitting distinct secondary plumelets is the preferred model for the distinct and diachronous magmatic features that pierced the crust as the Iberian microplate moved along a non-linear path.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) – UIDB/50019/2020- IDL and UIDB/04035/2020- GeoBioTec.

How to cite: Araújo, B., Pereira, R., Duarte, J., and Mata, J.: Resolving Late Cretaceous intra-plate magmatism emplacement models and plate motion on the West Iberian Margin, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-711, https://doi.org/10.5194/egusphere-egu23-711, 2023.

The dynamic behaviour of crystals in convecting fluids determines how magma bodies solidify. In particular, it is often important to estimate how long crystals stay in suspension in the host liquid before being deposited at its bottom (or top, for light crystals and bubbles of volatiles). We perform a systematic 3D numerical study of particle-laden Rayleigh-Benard convection, and derive a robust model for the particle residence time. For Rayleigh numbers higher than 10⁷, inertial particles' trajectories exhibit a monotonic transition from fluid tracer-like to free-fall dynamics, the control parameter being the ratio between particle Stokes velocity and the mean amplitude of the fluid velocity. The average settling rate is proportional to the particle Stokes velocity in both the end-member regimes, but the distribution of residence times differs markedly from one to the other. For lower Rayleigh numbers (<10⁷), an interaction between large-scale circulation and particle motion emerges, increasing the settling rates on average. Nevertheless, the mean residence time does not exceed the terminal time, i.e. the settling time from a quiescent fluid, by a factor larger than four. An exception are simulations with only a slightly super-critical Rayleigh number (~10⁴), for which stationary convection develops and some particles become trapped indefinitely. 2D simulations of the same problem overestimate the flow-particle interaction - and hence the residence time - for both high and low Rayleigh numbers, which stresses the importance of using 3D geometries for simulating particle-laden flows. We outline how our model can be used to explain the depth changes of crystal size distribution in sedimentary layers of magmatic intrusions that are thought to have formed via settling of a crystal cargo, and discuss how the micro-structural observations of solidified intrusions can be used to infer the past convective velocity of magma.

How to cite: Patočka, V., Tosi, N., and Calzavarini, E.: Residence time of crystals in a thermally convecting magma reservoir, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1366, https://doi.org/10.5194/egusphere-egu23-1366, 2023.

Many vertical seismic velocity anomalies originate in the transition zone between the upper and lower mantle (410–660 km) and form so-called secondary plumes. These anomalies are interpreted as the result of thermal effects of large-scale thermal upwelling (primary plume) in the lower mantle and/or deep dehydration of fluid-rich subducting oceanic plates. We present the results of thermo-mechanical modelling to investigate the dynamics of such small-scale thermal and chemical (hydrous) anomalies rising from the lower part of the Earth’s upper mantle. Our goal is to determine the conditions that allow thermo-chemical secondary plumes of moderate size (initial radius of 50 km) to penetrate the overlying lithosphere, as detected in seismo-tomographic studies in such intra-continental areas as the Tengchong volcano in south-western China and the Eifel volcanic fields in north-western Germany. To this end, we investigate the effect of the compositional deficit of the plume density due to the presence of water and hydrous silicate melts. In our models, secondary plumes of purely thermal origin do not penetrate the overlying plate, but flatten at its base, forming “mushroom”-shaped structures at the level of the lithosphere-asthenosphere boundary. On the contrary, plumes with enhanced density contrast due to a chemical (hydrous) component are shown to be able to penetrate upward through the lithospheric mantle to shallow depths near the Moho. Our findings can explain the enigmatic observations of columnar (“finger”-shaped) anomalies in the intraplate lithospheric mantle discovered in Europe and China. We argue that a chemical component is a characteristic feature not only of conventional hydrous plumes developed in the big mantle wedge over presently descending oceanic slabs, but also of upper mantle plumes in other tectonic settings.

How to cite: Cloetingh, S., Koptev, A., Lavecchia, A., Kovács, I., and Beekman, F.: Hydrous secondary plumes: towards understanding the enigmatic «finger» structures in the intraplate lithospheric mantle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2386, https://doi.org/10.5194/egusphere-egu23-2386, 2023.

Although the geoid is usually displayed with respect to the reference ellipsoid, the difference between geoid and the Earth's hydrostatic equilibrium figure is geodynamically more meaningful, and has its deepest low in the Ross Sea area. Nearby in West Antarctica, there is also a residual topography high. This region is characterized by thin lithosphere, and a mantle plume has been suggested beneath. Hence upper mantle viscosity could be regionally reduced, allowing for faster rebound than elsewhere upon melting of the West Antarctic Ice Sheet (WAIS) which is one of the tipping elements of the global climate system. To study the possible causes of the geoid low / topography high combination, we compute the effects of density anomalies with the shape of a cylindrical disk of a given radius and depth range. With a density anomaly of -1% we find that a geoid low of the right size and magnitude can be explained with a disk radius of about 10° of arc and the base of the disk in the lower transition zone or even lower mantle; with a shallower base the amplitude is under-predicted. On the other hand, if in this case the top of the disk is shallower than ~150 km, dynamic topography amplitude is over-predicted. The fact that the residual topography high (more sensitive to density anomalies at shallower depth) is laterally displaced relative to the geoid low (more sensitive to greater depths) could indicate a plume or upwelling that is tilted due to large-scale flow. Alternatively, there may be two separate disks somewhat laterally displaced, one just below the lithosphere and mainly causing a dynamic topography high and one below the transition zone causing the geoid low.
In order to test the feasibility of such density models, we perform computations of a plume that enters at the base of a box corresponding to a 3300 km x 3300 km region in the upper mantle, as well as some whole-mantle plume models, with the Aspect mantle convection code. However, these plume models have typically a narrow conduit (much narrower than ~10° of arc) and the plume tends to only become wider as it spreads beneath the lithosphere, i.e.\ at depths typically shallower than about 300 km, hence it would tend to rather under-predict the amplitude of the geoid compared to dynamic topography. We discuss how to possibly overcome the discrepancy between what is required to explain geoid and dynamic topography, and the outcome of numerical forward models.

How to cite: Steinberger, B.: The deepest geoid low on Earth and its possible relation to the instability of the West Antarctic Ice Sheet, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2410, https://doi.org/10.5194/egusphere-egu23-2410, 2023.

The H₂O incorporation into minerals changes the properties of minerals and rocks and affects the dynamics and evolution of the Earth’s interior. The higher H₂O contents in plume-related magmas than in mid-oceanic ridge magmas suggest that deeper regions store more significant amounts of H₂O than shallower regions in the mantle. Paradoxically, however, the H₂O solubility in the lower-mantle minerals in ultramafic systems is limited. Therefore, we expect basaltic fragments of subducted slabs to store H₂O in the lower mantle. It has been suggested that silica minerals can be H₂O hosts in the basaltic systems under lower-mantle conditions, and alumina incorporation enhances their H₂O solubility. To determine the stability and water solubility of silica minerals under top-most lower-mantle conditions, the current study synthesised silica minerals in the SiO₂-Al₂O₃-H₂O systems at pressures of 24 and 28 GPa and temperatures of 1000 to 2000°C using a multi-anvil press. We identified phases present in the run products using a micro-focused X-ray diffractometer and measured their water solubility using an FT-IR spectrometer.

We found that the Al₂O₃ contents in the silica minerals increased with increasing temperature from 0.7~0.8 wt.% at 1000~1200°C to 10 wt.% at 2000°C. Their H₂O contents also increased with increasing temperature from 0.3 at 1700°C to 1.0~1.1 wt.% at 1900°C. The silica mineral was stishovite at temperatures lower than 1600~1700°C, whereas it was CaCl₂-structured silica, referred to as post-stishovite, at higher temperatures. Thus, post-stishovite contained much more significant amounts of H₂O than stishovite whose water content is consistent with previous reports.

The concomitant increases in H₂O and Al₂O₃ contents suggest that H₂O is incorporated via charge-coupled substitution of Si⁴⁺ — Al³⁺+H⁺ in these silica minerals. The current stability of post-stishovite in H₂O- and Al₂O₃-bearing systems is located at much lower pressures than in pure SiO₂ and H₂O-poor, Al₂O₃-bearing systems. In addition, the OH bands are more intense in the E//[010] direction than in the E//[100] direction. These observations imply that tilting of (Si, Al)O₆ octahedra around the c axis by the hydrogen bonding in the [010] direction may have stabilised poststishovite at lower pressures.

The increases in H₂O solubility in aluminous stishovite and poststishovite with temperature have a tremendous impact on the H₂O storage and transport in the mantle. The H₂O solubility in the other nominally anhydrous minerals decreases with increasing temperature. Dense hydrous magnesium silicates decompose with increasing temperature. Therefore, these minerals cannot be H₂O hosts or carriers in the deep mantle except for cold subduction zones. On the other hand, hydrous stishovite and poststishovite can store and transport H₂O in ambient mantle and even in plumes.

It has been considered that the stishovite-poststishovite transition causes seismic scattering in the mid-mantle. However, many seismic scatterers are located at 700 to 1900 km depths, which are too shallow for the stishovite-poststishovite transition in the pure SiO₂ system. However, we found that the Al₂O₃ and H₂O incorporations lower the transition pressure to 24 GPa, i.e., 700 km depth. Hence, observing the seismic scatterers in the mid-mantle supports significant H₂O storages in aluminous poststishovite.

How to cite: Katsura, T., Ishii, T., Criniti, G., Ohtani, E., Purevjav, N., Fei, H., and Mao, H.: Hydrous aluminous silicas as major water hosts in the lower mantle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2770, https://doi.org/10.5194/egusphere-egu23-2770, 2023.

Geothermal Heat Flow (GHF) is a crucial boundary condition governing ice sheet stability, due to the positive relationship between thermal input into the ice sheet and basal sliding rates. Tectonic history biases the crustal distribution of heat-producing elements, and the pattern of mantle convection influences regional thermal structure, leading to significant intracontinental variations in Antarctic GHF of order 100 mW/m².  However, extensive ice cover across Antarctica severely limits the ability to directly measure GHF or crustal composition. Geophysical proxies are therefore required to access information pertaining to the lateral structure of GHF and its potential impact on ice sheet dynamics.

Previous studies have used geomagnetic data to infer the depth above which ferromagnetic structure is locked in, corresponding to the ~850 K isotherm. Others have relied on the sensitivity of seismic velocity to thermal structure to model local variations in surface temperature gradient. Both approaches require assumptions on crustal properties, which are typically chosen ad-hoc, and may affect GHF estimates in a significant and non-systematic manner. Other studies have used the observed covariation between lithospheric seismic velocity and GHF in regions with high measurement densities (e.g., continental USA) to map Antarctic seismic structure into GHF. This introduces a dependency of inferred Antarctic GHF on the range of tectonic environments sampled by the continental region used to derive the empirical relationship.

Here, we adopt a distinct approach, in which Monte Carlo sampling is used to include crustal conductivity and heat production as free parameters in a numerical modelling procedure that fits theoretical geotherms to new probabilistic seismic inferences of upper mantle temperature structure beneath Antarctica. By integrating empirical constraints on crustal conductivity derived from P-wave velocity data, we are able to build distributions of covarying crustal conductivity, heat production, and GHF. This allows us to generate a model of Antarctic GHF which is complementary to that of other studies, and includes an estimate of lateral uncertainty structure based on the sensitivity of thermal gradients to crustal composition and anelastic deformation at seismic frequencies.

How to cite: Hazzard, J., Richards, F., and Roberts, G.: Refining Estimates of Antarctic Geothermal Heat Flow Using Seismological Constraints on Crustal Composition and Lithospheric Thermal Structure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3400, https://doi.org/10.5194/egusphere-egu23-3400, 2023.

The geodynamic origin of melting anomalies found at the surface, often referred to as hotspots, is classically attributed to mantle plume processes. The coincidence of hotspots and regions of relatively thin lithosphere, however, questions the necessity for mantle plumes in driving hotspot magmatism, especially as the ability of mantle plumes to thin strong mantle lithosphere is disputed. Here, we propose a new mechanism for the self-sustained generation of magmatism at hotspots where the lithosphere-asthenosphere boundary occurs at < ~100 km. By considering the effects of both chemical and thermal density changes during partial melting of the mantle (using appropriate latent heat and depth-dependent thermal expansivity parameters), we find that mantle residues experience an overall instantaneous increase in density when melting occurs at < ~3 GPa. This controversial finding is due to thermal contraction of material during melting, which outweighs chemical buoyancy effects when melting at shallow pressures (where thermal expansivity is high, at ~4.91 x 10^-5 K^-1). These dense mantle residues have a tendency to sink beneath melting regions, driving the return flow of fertile mantle into the melting region and locally increasing magmatic production. This mechanism presents an alternative to the upwelling of hot mantle plumes for the generation of excess melt at hotspots and the genesis of large igneous provinces during continental breakup. We model the development of magma-rich margins using geodynamic numerical models and find a close match between modelled volcanic crustal thicknesses and real-world observations. “Hot”-spots and large igneous provinces, therefore, may not require the elevated temperatures commonly invoked to account for excess melting.

How to cite: Phethean, J. J. J., Papadopoulou, M., Peace, A. L., and van Hunen, J.: Downwelling dense mantle residues and hotspot magmatism, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3846, https://doi.org/10.5194/egusphere-egu23-3846, 2023.

Northeast China is a very typical area for studying intra-plate volcanism in the back-arc setting. It is commonly proposed that the subduction of the Pacific plate has been responsible for widespread Holocene volcanoes in NE China. Yet, how this process drives volcanism remains a topic of vigorous debate. Investigation of seismic anisotropy can provide important evidence for the cause-and-effect relationship between mantle flow, lithospheric deformation and shallow structures. In this study, using seismic data from four networks across NE China and north Korea, we analyze shear wave splitting in converted P- to S-waves at the Moho (Pms), S-waves from the subducted slab interface (local S), and SKS phases. The Pms phases show a relatively weak crustal anisotropy (~0.25 s), with fast polarization directions aligned sub-parallel to major tectonic features. For the local S and SKS phases, fast polarization directions show significant lateral variations. We further perform a quantitative inversion to show that the depth of the anisotropy is ~150 km, thus driven by flow within the asthenosphere associated with Pacific subduction. However, the presence of many null SKS splitting phases, together with scattered local S-wave anisotropy suggests a localized region of vertical flow directly beneath Changbaishan volcano. Such patterns correspond well to regional upper-mantle seismic velocity structure, and suggest that a localized upwelling with a relatively deep origin drives volcanism in the Changbaishan region. Furthermore, we infer that mantle upwelling is deflected to the SW beneath Changbaishan and spreads asymmetrically at the base of the lithosphere, possibly because of the long history of volcanism in the region.

How to cite: Han, C., Hammond, J., and Ballmer, M.: Multi-scale anisotropy in NE China: Implications for intra-plate volcanism, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4570, https://doi.org/10.5194/egusphere-egu23-4570, 2023.

The occurrence of mantle melting is generally attributed to high temperature, decreased pressure, and/or the presence of volatiles such as water. Volcanism away from plate boundaries is ascribed to intraplate or anorogenic volcanism, which may reveal important dynamics of the deep mantle. Two of the most striking intraplate volcanism are oceanic plateaus (OPs) and large igneous provinces (LIPs), which often have an extremely thick crust and vast areas. However, the origin of the extremely thick crust is debated, and several mechanisms are proposed: cataclysmic melting of a thermal plume (Richards et al., 1998; Larson, 1991); shallow asthenospheric melting during plate separation (Anderson et al., 1992); melting of the fertile or primitive mantle (Korenaga, 2005; Kerr & Mahoney, 2007); and asteroid impact (Rogers, 1982). Although mantle plume theory is widely accepted and is also often invoked to explain the formation of the OPs and LIPs. However, another school of people interrogates the deep mantle plume origin, which requires extremely high mantle temperature and a wide plume head. In contrast, recent numerical models provide a novel mechanism by linking a hydrous mantle transition zone (MTZ) and a retreating subducting plate for the formation of intraplate volcanism in northeast China and petit-spot volcanism offshore Japan (Yang & Faccenda, 2020). Such a mechanism has been applied to many other present-day and fossil subduction zones. Here we use 2D thermomechanical numerical models to investigate mantle melting and melt extraction processes leading to the formation of large volumes of basaltic crust. Two groups of models have been tested: a purely thermal plume model and a hydrous plume model. Our model results show that an excess mantle potential temperature of 200-300 ^oC likely produces >20 km thick crust if the lithosphere is <80 km. While the presence of >0.5-1 wt% water in a cold plume can result in similar thickness. Our models may explain some oceanic plateaus and large igneous provinces as related to the melting of volatile-rich domains from mid-mantle.

References

Anderson, D. L., Zhang, Y.-S. & Tanimoto, T., 1992. Plume heads, continental lithosphere, flood basalts and tomography. In: Storey, B.C., Alabaster, T., and Pankhurst, R.J. (eds.) Magmatism and the Causes of Continental Break-up, Geological Society, London, Special Publications, 68, 99-124.

Kerr, A.C., Mahoney, J.J., 2007. Oceanic plateaus: Problematic plumes, potential paradigms. Chemical Geology 241, 332-353.

Korenaga, J., 2005. Why did not the Ontong Java Plateau form subaerially? Earth and Planetary Science Letters 234, 385-399.

Richards, M. A., Duncan, R. A. & Courtillot, V., 1989. Flood basalts and hot-spot tracks: plume heads and tails. Science, 246, 103-107.

Rogers, G.C., 1982. Oceanic plateaus as meteorite impact signatures. Nature 299, 341–342.

Larson, R. L., 1991. Latest pulse of the earth: evidence for a mid-Cretaceous superplume. Geology, 19, 547-550.

Yang, J., Faccenda, M., 2020. Intraplate volcanism originating from upwelling hydrous mantle transition zone. Nature 579, 88-91.

How to cite: Yang, J., Faccenda, M., and Zhao, L.: Numerical modeling of the formation of extensive intraplate volcanism, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5041, https://doi.org/10.5194/egusphere-egu23-5041, 2023.

Physical 1D-average reference models of the Earth offer valuable summaries of the radial variations in rock properties and a reference for geophysical studies. PREM, in particular, has been used widely for >40 years and comprises Vp, Vs, density, radial anisotropy and attenuation profiles, while also fitting the Earth’s mass and moment of inertia. Many of PREM’s features have proven remarkably accurate, despite the limited amount of data used to construct it, but some features are inconsistent with now available data. Also, the upper mantle structure differs so much between Earth’s different tectonic environments that a global average is not quite representative of any of them.  The recent growth in seismic station coverage yields very dense data sampling, globally and over different tectonic environments. Here, we use a large global dataset to construct ten 1D, multi-parameter, reference models of the upper mantle, for the globe and for 9 basic tectonic types: cratons; stable platforms; Phanerozoic continents with normal (<46.5 km) and thick (>46.5 km) crust; rifts and continental hotspots; old oceans; intermediate oceans; young oceans; backarcs.

The dataset comprises Love and Rayleigh-wave phase velocities, measured using waveform inversion and all available data since 1990s; surface heat flow measurements; topography/bathymetry. With tomography-based tectonic regionalization, we identify areas within each tectonic environment and compute average dispersion curves in the 20-30 to 310 s period range, which constrain shear velocity and anisotropy in the entire upper mantle.

We then use computational-petrology-based inversion to calculate 1D physical models for the globe and the 9 basic tectonic types. Our non-linear gradient search converges to true best-fitting models. The main unknowns in the inversion are the depth of the lithosphere-asthenosphere boundary (LAB); the geotherm from the LAB down to 400 km depth; radial anisotropy (0-800 km). The steady-state geotherm in the lithosphere is computed from the LAB depth and the radiogenic heat production and thermal conductivity profiles by solving the conductive heat transfer equation. Rock composition and the geotherm determine the density, seismic velocities and attenuation down to 400 km. Seismic velocities in the crust, transition zone (410-660 km) and shallow lower mantle can vary to fit the data. Density below 410 km and all parameters in the core and most of the lower mantle are from PREM. Like PREM, our reference models honour the Earth's mass and moment of inertia.

Small phase-velocity errors and relative data-synthetic misfits (<~0.1%) are necessary to resolve radial trade-offs in the upper-mantle structure. We achieved this by obtaining very accurate dispersion curves and by meticulously tuning the inversion, its parameterisation and regularisation.

The best-fitting models have slightly depleted lithospheric mantle and fertile asthenosphere for most tectonic types. In Archean and Proterozoic continents, the mantle lithosphere is more depleted. No other compositional heterogeneities are required to fit the data. Isotropic-average seismic velocities decrease monotonically from the Moho to the LAB. The geotherms follow the mantle adiabatic temperature gradient in the asthenosphere. Our results provide useful, accurate new reference models for global and regional seismic imaging and other geophysical studies. 

How to cite: Xu, Y., Lebedev, S., Civiero, C., and Fullea, J.: Global and tectonic-type physical reference models of the upper mantle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5459, https://doi.org/10.5194/egusphere-egu23-5459, 2023.

Mantle shear-wave velocity models derived from seismic full waveform inversion methods reveal a very heterogeneous lithosphere-asthenosphere system beneath intracontinental Western and Central Europe north of the Alps. To better understand the physical state of the upper mantle in this region, we convert shear-wave velocity models to thermodynamically consistent temperature and density configurations using a Gibbs's free energy minimization approach. The inferred physical state of the lithosphere-asthenosphere system is then investigated for its consequences on past and present-day crustal deformation. For instance, a thermal lithosphere-asthenosphere boundary that varies in depth between > 200 km in the southern North Sea and < 80 km close to the Alpine deformation front raises important questions regarding the causes for this thermal disequilibrium and its effects on the thermomechanical stability of the crust. In particular, we will discuss the imaged mantle thermal anomalies in light of the inherited crustal structure and its effects on ongoing deformation (including seismicity) in this intracontinental setting.

How to cite: Bott, J., Scheck-Wenderoth, M., Kumar, A., Cacace, M., Noe, S., and Faleide, J. I.: Relationships between upper mantle thermal structure and crustal deformation in Western and Central Europe – new interpretations of seismic tomography models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6574, https://doi.org/10.5194/egusphere-egu23-6574, 2023.

The mantle transition zone (TZ) is expected to influence vertical mass flow between upper and lower mantle as it hosts a complex set of mineral phase transitions and an increase in viscosity with depth. Still, neither its seismic structure nor its dynamic effects have conclusively been constrained. The seismic discontinuities at around 410 and 660 km depth ('410' and '660') are classically associated with phase transitions between olivine polymorphs, the pressure of which is modulated by lateral temperature variations. Resulting discontinuity topography is seismically visible and can thus potentially provide insight on temperature and phase composition at depth. Besides the olivine phase changes, the disassociation of garnet may additionally impact the 660 at higher temperatures. However, the volume of material affected by this garnet transition and its dynamic implications have not yet been quantified.

This study presents hypothetical realizations of TZ seismic structure and major discontinuities based on the temperature field of a published 3-D mantle circulation model for a range of relevant mineralogies, including pyrolite and mechanical mixtures (MM). Systematic analysis of these models provides a framework for dynamically informed interpretations of seismic observations and gives insights into the potential dynamic behaviour of the TZ. Using our geodynamic-mineralogical approach we can identify which phase transitions induce specific topographic features of 410 and 660 and quantify their relative impact. Areal proportions of the garnet transition at the 660 are ∼3 and ∼1 per cent for pyrolite and MM, respectively. This proportion could be significantly higher (up to ∼39 per cent) in a hotter mantle for pyrolite, but remains low (< 2 per cent) for MM. In pyrolite, both slabs and plumes are found to depress the 660 —with average deflections of 14 and 6 km, respectively— due to the influence of garnet at high temperatures indicating its complex dynamic effects on mantle upwellings. Pronounced differences in model characteristics for pyrolite and MM, particularly their relative garnet proportions and associated topography features, could serve to discriminate between the two scenarios in Earth.

How to cite: Papanagnou, I., Schuberth, B. S. A., and Thomas, C.: Geodynamic-mineralogical predictions of mantle transition zone seismic structure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6820, https://doi.org/10.5194/egusphere-egu23-6820, 2023.

Geophysical methods such as seismology, magnetotellurics and gravity are key to reconstructing the structure of the upper mantle and inferring its composition. However, the relationship between composition and geophysical parameters, e.g. seismic velocity, resistivity or density, is complex and depends on other factors such as temperature, for example. This makes it difficult to untangle the various effects from inversions based on single parameters. Joint inversion establishes quantitative relationships between different geophysical parameters and thus provides additional information that can be interpreted in terms of composition and temperature. I use 3D joint inversion of surface wave, gravity and magnetotelluric data to construct integrated models in a data driven way. The relationship between the different quantities is recovered as part of the inversion through a Variation of Information based constraint. This constraint aims at establishing a one-to-one relationship between each parameter pair. Results from the western United States, Germany, Southern Africa and Australia show that this approach can retrieve highly detailed and strongly coupled results that can be interpreted, for example, in terms of hydration of the lithosphere. Comparison of results from different geologic domains indicates significantly different relationships depending on formation age. I will discuss how we can use data driven parameter relationships to infer the state of the lithosphere. In addition, I will outline the road towards robust quantitative inference based on these relationships.

How to cite: Moorkamp, M.: The structure and composition of the upper mantle from joint inversion derived parameter relationships, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7037, https://doi.org/10.5194/egusphere-egu23-7037, 2023.

Hot mantle plumes, the thermo-chemical instabilities rising from Earth’s deep mantle, are believed to form large, round heads, followed by narrow tails. The impact of a plume onto the continental lithosphere causes uplift, rifting, and flood basalt volcanism. The resulting large igneous provinces (LIPs) are thought to be emplaced rapidly above the plume head as it arrives and spreads, as a circle, beneath the plate. However, LIP eruptions often span up to tens of millions of years in time and are scattered unevenly over areas a few thousand kilometres across, which is inconsistent with this conventional view. Here, we use seismic waveform tomography and obtain clear images of interconnected corridors of hot, partially molten rock beneath the areas of uplift and volcanism in the East Africa-Arabia region. The spatial continuity of the hot rock corridors and the temporal continuity of the volcanism since ~45 million years ago suggest that we are witnessing an extant, integral plume head that was morphed into a three-pointed star by the topography of the lithosphere-asthenosphere boundary. Eruption ages and plate reconstructions indicate that the plume head spread south-to-north, and tomography shows it being currently fed by three upwellings beneath Kenya, Afar, and Levant. Star-shaped plume heads within thin-lithosphere valley systems can account for the enigmatic dispersed and protracted volcanism in LIPs and are, probably, an inherent feature of plume-continent interaction.

How to cite: Civiero, C., Lebedev, S., and Celli, N. L.: Dispersed East Africa-Arabia volcanism fed by a star-shaped mantle plume head, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8343, https://doi.org/10.5194/egusphere-egu23-8343, 2023.

Seismic tomography provides valuable insights into the structure, composition and evolution of the mantle. However, the origin of structures like the Large-Low-Velocity-Provinces (LLVPs) in the lowermost mantle remains debated. Their velocity anomalies have been interpreted to be due to purely thermal or also compositional variations, with implications for mantle circulation, the evolution of the core and the Earth’s heat budget.

To uniquely interpret seismic structures such as the LLVPs, it is crucial to constrain the relationships between different seismic observables, e.g. the ratio between shear-wave velocity (Vs) and compressional-wave velocity (Vp) variations. Joint inversions of seismic velocities have been performed, but their velocity amplitudes may be biased, uncertainties are typically not provided, and the resolution of Vs and Vp structures generally differs in existing models.

To overcome these issues, we make use of the recently developed SOLA method (Zaroli, 2016), which is based on a Backus-Gilbert philosophy. Instead of finding a model with a particular data fit, we aim to construct model averages of the true Earth with uncertainties, whilst having a control on the model resolution. This direct control on resolution enables us to build Vs and Vp models that sample the same parts of the mantle, and therefore to robustly constrain the Vs/Vp ratio.

Here, we test this philosophy by applying the SOLA method to normal modes. These free oscillations of the Earth are particularly useful to study the relationships between seismic velocities as they are directly sensitive to multiple physical parameters, including Vs, Vp as well as density. We illustrate our approach and discuss the trade-off between uncertainties and resolution using synthetic tests for both Vs and Vp, before showing real data inversions. Finally, we discuss the implications of our results for the Vs/Vp ratio in terms of mantle temperature and composition.

How to cite: Restelli, F., Koelemeijer, P., and Zaroli, C.: Obtaining robust estimates of the Vs/Vp ratio in the Earth’s lowermost mantle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8416, https://doi.org/10.5194/egusphere-egu23-8416, 2023.

Seismic energy that follows the theoretical arrival time of the P_diff phase is usually regarded as P_diff coda. This implies its generation by scattering of diffracted P-waves. Such waves can theoretically be observed in the core shadow from 100° up the antipode in the time window extending from the theoretical arrival of the P_diff phase until the arrival of the next direct phase which is PP or a core phase.

However, scattered energy is also observed at frequencies above 1Hz where diffraction is inefficient. We present observations of scattered energy arriving more than 100s prior to PKP at distances exceeding 150° with an emergent shape and in the complete absence of a direct P_diff arrival. These observations exclude a connection to a diffracted P-wave. Modelling of the seismic energy propagation with radiative transfer theory in an independently established model of mantle heterogeneity confirms that the scattered seismic energy in the P_diff coda time-distance window has its origin in scattering of P-waves in the whole mantle. We demonstrate that different depth layers contribute to different arrival times in the scattered wave train which explains the emergent shape of the wave train and provides means to improve the depth resolution of current heterogeneity models. 

These findings confirm earlier interpretations that connected P_diff coda with mantle scattering. They are also compatible with array observations that show an extinction of the direct P_diff phase towards 107° above 1Hz, because even the seemingly direct arrival of P_diff at distances shortern than 130° can be mimicked by mantle scattering, as our modelling shows. The observed energy is thus more directly related to P-coda or PP-precursors than to the P_diff phase.

How to cite: Sens-Schönfelder, C., Zhang, T., Bianchi, M., and Bataille, K.: Pdiff  Coda Waves as the Result of Distributed Whole-Mantle Scattering, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8438, https://doi.org/10.5194/egusphere-egu23-8438, 2023.

Terrestrial planets evolve through multiple magma-ocean stages during accretion and differentiation. Magma oceans become progressively enriched upon fractional crystallization (FC), which should be dominant at least in the upper mantle. The resulting upwards enrichment of the cumulate package drives gravitational overturn(s), and ultimately stabilizes a FeO- and SiO₂-enriched basal magma ocean (BMO) [1]. Alternatively, a ~pyrolitic BMO may be formed due to a liquid-solid density crossover at high pressures [2,3]. In any case, the slowly cooling BMO is very likely to freeze by FC. However, we find that the consequences of FC of the BMO are inconsistent with geophysical constraints for Earth (Ismail+, this meeting). For FC, the final-stage cumulates are expected to be strongly FeO-enriched (~eutectic), stabilizing a layer at the base of the mantle with density anomalies >2,000 kg/m³. Such a layer should be extremely long-lived, but is not detected by seismic imaging.

Using a thermodynamic model [4], we here investigate the chemical consequences of an alternative scenario, in which the BMO interacts with (partially) molten basaltic material in the lower mantle. We refer to such a scenario as reactive crystallization (RC). Even in the present-day, the core-mantle boundary may be hotter than the solidus of subducted basalt [5]. Accordingly, any recycled Hadean/Archean is likely to have undergone (partial) melting in the lowermost mantle, and mixed with the BMO. This scenario is attractive, because large volumes of crust may be readily delivered to the lowermost mantle, and will produce dense magmas there, which sink into the BMO to promote efficient reaction.

We find that the first BMO cumulates due to RC are Mg-rich bridgmanite (~MgSiO₃). With progressive addition of basaltic material, Al₂O₃ becomes enhanced in the BMO to promote FeO-disproportionation, leading to loss of elemental Fe to the core and crystallization of FeAlO₃. With ongoing cooling, the BMO starts effectively shrinking, and final BMO cumulates are similar in composition than, and slightly enriched compared to, basalt. The associated intrinsic density anomalies are 300~350 kg/m³, i.e., much more moderate than for FC of the BMO. These predicted densities and cumulate compositions (bridgmanitic with high FeAlO₃) are in very good agreement with the geophysical signatures of large low-velocity provinces [6]. In turn, the predicted final composition of the BMO itself may correspond to that of seismically-detected ultra-low velocity zones.

Our results imply that large rocky planets such as Earth, Venus or even Super-Earths may host only a rather short-lived BMO due to efficient crustal recycling. In turn, small stagnant-lid planets with limited crustal recycling, such as e.g. Mars, may host longer-lived BMOs (Cheng+, this meeting). These predictions have important implications for the long-term thermal and chemical evolution of terrestrial planets.

[1] Ballmer+, G-cubed, 2017; [2] Labrosse+, nature, 2007; [3] Caracas+, EPSL, 2019; [4] Boukare+, JGR Solid Earth, 2015; [5] Adrault+, science 2014; [6] Vilella+, EPSL, 2021

How to cite: Ballmer, M., Spaargaren, R., and Ismail, M.: Reactive Crystallization of the Basal Magma Ocean: Consequences for present-day mantle structure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9854, https://doi.org/10.5194/egusphere-egu23-9854, 2023.

Seismic velocity anomalies observed in the mantle can have several origins, the main contributions being anomalies of temperature and composition. The difference between P- and S-wave models has been used to separate thermal and compositional contributions in imaged seismic structures and identify large-scale compositional heterogeneity in the Earth's mantle. According to our two-step Machine Learning (ML) analysis of 28 P- and S-wave global tomographic models, P- and S-models differences are not intrinsic and can be reduced by changing the models in their respective null spaces. Because we find, P- and S-wave images of mantle structure are not necessarily distinct from each other, a purely thermal explanation for seismic structure is sufficient at present; significant mantle compositional heterogeneities do not need to be invoked. In this study, 28 commonly used tomographic models are examined, ranging from ray theory (e.g., UU-P07, MIT-P08) to Born scattering (e.g., DETOX) and full-waveform techniques (e.g., CSEM, GLAD). Combined Varimax Principal Component Analysis is used to reduce the dataset's dimensionality (by 82%) while preserving the relevant information of each tomographic model (94% of the original variance). Reduced-sized models are followed by a hierarchical clustering analysis (HC) using Ward’s method to categorize all the models into a hierarchy of groups based on their similarities. HC divided the set of tomographies into two main clusters: the first cluster, which we named "Pure P-wave", is composed of six P-wave models that only use longitudinal body wave phases (e.g., P, PP, Pdiff); the second cluster "Mixed" includes both P- and S-wave models; P-wave models in this cluster use inversion methods that include inputs from other geophysical and geological data sources, that cause them to be more similar to S-wave models than to pure P-wave models without a significant loss of fitness to P-wave data. Results suggest that the differences between some individual P-wave and S-wave models are smaller than the differences between grouping of models that are only P-wave or S-wave. These variable differences clearly convey that no consistent separation exists between the P- and S-wave models. We have also calculated the Distance Matrices along the Principal Components. Comparing clustering results with Distance Matrices shows that the differences between the "Pure P-wave" and "Mixed" clusters are mainly in the upper mantle. Accordingly, our results indicate that P-wave structures do not need to be very distinct from a thermal interpretation of S-wave structures and support a relatively “Homogenous” mantle.

How to cite: Rahimzadeh Bajgiran, M., Colli, L., and Wu, J.: Comparing 28 global P- and S- wave tomography models by Machine Learning analysis for the interpretation of the Earth’s mantle structures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10123, https://doi.org/10.5194/egusphere-egu23-10123, 2023.

The migration of mid-ocean ridges is driven by asymmetric plate motions on either ridge flank transmitted from far-field subduction forces. Within this model, the geometry and location of mid-ocean ridges are independent of lower-mantle dynamics. However, this fails to recognise the attraction between mid-ocean ridges and mantle plumes. Using numerical models of mantle convection, we show that plumes with high buoyancy flux (> 6000 kg/s) can capture mid-ocean ridges within a 1000 km radius and anchor them in place. If the plume buoyancy flux wanes below 1000 kg/s the ridge may be released, potentially resulting in rapid migration rates that trigger a major plate reorganisation. Plume-ridge interactions are commonly preserved as conjugate large igneous provinces (LIPs), which form on each flank of a mid-ocean ridge as new crust is created. The decoupling of ridges from plumes are demarcated by a switch from conjugate LIPs, formed by a plume beneath a spreading ridge, to trails of intraplate hotspot volcanoes signifying the plume and ridge have separated. We demonstrate that the waning buoyancy flux of the Kerguelen plume, inferred from the geochemistry of eruption products, resulted in its decoupling with the SE Indian Ridge spurring rapid northward migration of the Australian plate. Our modelling predicts that following plume-ridge decoupling, the waning plume can tilt 15° within the upper mantle towards the migrating ridge, providing an explanation for diffuse volcanism and low eruption volumes along the Kerguelen Archipelago. Our results have significant implications for other plume-ridge interactions globally such as the Iceland, Tristan, and Easter plumes, and the generation of intraplate hotspot volcanoes proximal to mid-ocean ridges.

How to cite: Mather, B., Seton, M., Williams, S., Whittaker, J., Carey, R., Arnould, M., Coltice, N., and Duncan, B.: The role of plume-ridge decoupling on rapid plate motion and intraplate volcanism, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10441, https://doi.org/10.5194/egusphere-egu23-10441, 2023.

Volcanic provinces within Earth's continents exhibit a wide range of characteristics that reflect the intricate nature of the dynamic interactions at their origin. To improve our understanding of the driving mechanisms at play, we address the generation of intra-plate continental volcanism by modelling the 3-D interaction between an upwelling mantle plume and a thick lithospheric block. We examine scenarios with and without plate motion and assess the spatio-temporal distribution and intensity of produced melts. Our findings demonstrate the critical role of lithospheric thickness in determining the location and volume of plume-driven magmatic provinces. Building on these results obtained using simplified lithospheric structures, we further apply our numerical methodology to simulate the inferred interaction between the Cosgrove plume and eastern Australia during the past 35 Myr. We design the Australian continent using available 3-D lithospheric architecture determined through seismic tomography and impose the inferred plate motion associated with this region. Our models incorporate updated peridotite melting parameterisations to provide quantitative estimates of generated melt volume and composition. We find that plume-driven and shallow edge-driven melting processes, modulated by the lithospheric thickness of the Australian continent, combine to explain the observed volcanic record. Our preliminary results agree well with surface observations and provide further insight into the geodynamics of eastern Australia.

How to cite: Duvernay, T. and Davies, R.: 3-D Modelling of the Dynamical Mechanisms Driving Continental Intra-Plate Volcanism, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10559, https://doi.org/10.5194/egusphere-egu23-10559, 2023.

During planetary accretion, impacts vary in mass, velocity, and angle, producing magma oceans of different sizes and temperatures. Large impactors, more common in the late accretionary stages, contain iron cores that can emulsify into extremely small drops, which then rain down into the rocky planetary core. During its descent, metal and silicate chemically react, stripping the mantle of siderophile (iron-loving) elements and leaving lithophile (rock-loving) elements behind. To estimate the fraction of volatiles remaining in the magna ocean vs. the one stored into the core is essential to model the properties of the atmosphere of newly formed rocky planets. Further, the composition of the atmosphere influences the cooling rate of the magma ocean itself. A single simulation that can quantify this entire dynamics is presently beyond existing techniques. Using a newly developed fluid-dynamic numerical approach, based on the Lattice Boltzmann Method for fluid-dynamics, and Rothman-Keller approach for multiphase flow, we model the fate of the metal-silicate fluid dynamics in response to a wide range of realistic magma ocean scenario, considering impactors falling a different angles, iron continent, speed. Our approach tracks the descent of diapirs, each representing a coherent cloud of iron drops, through an entire magma ocean, identifying the descent environment (Pressure and Temperature vs depth, collective speed, volume of the magma ocean entrained into the cloud of diapirs). 

How to cite: Morra, G., Honarbakhsh, L., and Mora, P.: Volatiles Release from Metal-Silicate Interactions in Magma Oceans During Planetary Accretion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10682, https://doi.org/10.5194/egusphere-egu23-10682, 2023.

It is well accepted that convection in the Earth’s mantle provides the torques to drive vertical and horizontal plate motions. Yet the precise nature of the interaction between flow and plates remains incomplete, because the strength of plates allows them to integrate over a presumably complex flow field in the mantle beneath – making it difficult to get a glimpse even on the recent Cenozoic mantle flow. Over the past years a pressure driven, so-called Poiseuille, flow model for upper mantle flux in the asthenosphere has gained increasing geodynamic attention – for a number of fluid dynamic arguments. This elegantly simple model makes a powerful testable prediction: Poiseuille flow induce plate motion changes should coincide with regional scale mantle convection induced elevation changes.

Here I will focus on Australia, which undergoes a profound directional change from westward to northward motion in the early Cenozoic. At the same time there is evidence for early Cenozoic high dynamic topography in the western part of the continent. Thus, suggesting a high-pressure source in the upper mantle to the west of Australia. Altogether these geological and geophysical observations indicate that the separation of Australia from Antarctica was largely driven by plume push torque from the Kerguelen plume.

How to cite: Stotz, I. L., Carena, S., Vílacis, B., Bunge, H.-P., and Hayek, J. N.: Plume driven plate tectonics: new insights from the Australia/Antarctica separation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12268, https://doi.org/10.5194/egusphere-egu23-12268, 2023.

Hydrogen reported in lunar plagioclase (one of nominally anhydrous minerals) was used to quantify the water concentration of the late stage of Lunar Magma Ocean (LMO) based on an oft-cited fixed value of partitioning coefficient between plagioclase and silicate melt. However, the partitioning coefficient of hydrogen between plagioclase and silicate melt has been poorly constrained, especially at the lunar conditions. We conducted a series of water-bearing experiments to determine plagioclase-melt partition coefficients of hydrogen under the late stage of LMO conditions. The water concentrations of plagioclase and coexisting melt were analyzed using Fourier Transform Infrared Spectroscopy. Our new results show that the partitioning behavior of hydrogen between plagioclase and melt does not obey a classical Henry’s law at the water concentration in melt lowering than ~0.7 wt.%, and that the hydrogen partition coefficients do systematically increase with decreasing the water concentrations of the coexisting silicate melt, consistent with the re-evaluating all of the previous data of hydrogen partitioning coefficients between plagioclase and silicate melt. This indicates that the water concentration of silicate melt plays a dominant role in controlling hydrogen partitioning between plagioclase and coexisting silicate melt. This finding suggests that hydrogen partitioning between nominally anhydrous minerals and silicate melt could be far more complicated than previously thoughts, and indicates that it should be in caution when using plagioclase as a watermeter.

How to cite: Xu, Y., Lin, Y., and Westrenen, W.: Non-Henrian behavior of hydrogen between plagioclase and silicate melt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13261, https://doi.org/10.5194/egusphere-egu23-13261, 2023.

Large igneous systems form either in areas of thin lithosphere at or near plate boundaries or by mantle-melting anomalies in intraplate settings with comparatively thicker lithosphere. Decompression melting or flux melt dominate at plate boundaries. Intraplate magmatism relates to thermal or compositional anomaly in the mantle. Although questions remain open, our understanding of the fundamental driving processes of these systems has dramatically improved during the last 50 years. However, some intraplate large volcanic regions display a complex distribution of magmatic activity that spans a large age range and does not appear easily explained by semi-stable mantle-melting anomalies. 

The Madeira-Tore Rise (MTR) is often associated to excess magmatism forming thick oceanic crust at Cretaceous time. However, the ~1000 km long MTR broad bathymetric swell contains numerous individual volcanic constructions of different dimensions and age, across a hundreds-of-km wide swath. The MTR and volcanic constructions origin is unclear. The MTR magmatic event is inferred to be associated to the seafloor-spreading magnetic lineation named the J-anomaly, and the MTR is often referred as J-anomaly ridge. However, when analysed in detail, the magnetic J-anomaly is located east of the rise. Many volcanoes are inferred hot-spot related.

Seismic data collected in 2018 & 2022 show that the basement ridge of the MTR swell is unrelated to thick crust but to long-wavelength lithospheric flexure. The lithospehre deformation is expressed by folding, faultiong and large-scale tilting indicated by regional angular stratigraphical uncorformities. The spatial and temporal coincident of deformation with the MTR volcanic region support that long-lived volcanism may be related to lithospheric-scale intraplate deformation unrelated to hot spot activity.

How to cite: Ranero, C. R., Gomez de la Peña, L., Prada, M., Jimenez, E., Cadenas, P., Neri, A., Merino, I., Ugalde, A., and Grevemeyer, I.: Intraplate Lithospheric Deformation Forms Large Volcanic Regions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14411, https://doi.org/10.5194/egusphere-egu23-14411, 2023.

Rifting is a large-scale planetary evolution process that forms a new oceanic crust with mid-ocean ridges in an extensional environment. In this process, mantle convection occurred and material circulates, forming a volcano in the surrounding area. It is well known that mantle flow of rifting causes volcanism, but most of the volcanic processes are concentrated in the mid-ocean ridge and rift center axis. Recently, many of theory (lithosphere delamination, edge-driven convection, slab tearing, etc.) have been discussed to explain intra-plate volcanic mechanisms at non-plume and non-extension conditions. However, has been rarely studying the correlation between intra-plate volcanism and distant rifting. To identify the origin of occurring volcanoes in the continental margin and intra-plate is necessary studying to evolution mechanism and lower mantle. The formation of rifting and continental margin is closely related, and it is assumed that mantle convection significantly affects intra-plate volcanism. Well known through previous studies that mantle convection Along the rifting axis affects various evolution such as rift propagation, ridge jump, rift fail or end tip with transform fault. In this study, we estimate the possibility mantle convection can induce intra-plate volcanism at rifting end tip and continental beyond the margin. We adopt the open-source finite element geodynamics software, ASPECT, which makes a 3-D rifting model for observing the evolution process and mantle convection below the continental margin. 

How to cite: Jang, M.-S. and So, B.-D.: Can mantle convection by distant rifting induce intraplate volcanism?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14630, https://doi.org/10.5194/egusphere-egu23-14630, 2023.

The investigation of mantle-derived products coming from Sub Continental Lithospheric Mantle (SCLM) is crucial for understanding its geochemical features and evolution, the mantle-crust interaction, and the volatiles composition. In this respect, mineral-hosted fluid inclusions (FI) in mantle xenoliths play a fundamental role, as their composition provides useful insights about the extent and timing of mobilization of volatiles during melt extraction and melt/fluid-rock reactions in the mantle, especially when their composition is combined with the information extracted from mineral chemistry and texture.

Peridotite xenoliths sampled by the intra-continental rift magmatism at West Eifel (Germany) and northern Victoria Land (Antarctica) are extremely rich in FI, and bear witness to multiple metasomatic modifications taking place in the local SCLM (Rizzo et al. 2021; Casetta et al. 2022). In this study, the concentration and isotopic signature of CO₂ in mineral-hosted FI in peridotite rocks was coupled to mineral chemistry and thermo-oxy-barometric modelling, with the aim of exploring if, and how, the provenance and mobilization of C-bearing species are related to the main melt extraction and metasomatic processes that took place in the local SCLM domains or to the recycling into the mantle of old crustal material. Our findings show that the concentration of CO₂ in FI varies from 0 up to 162 µg/g, being higher in West Eifel than in Antarctica samples, and also higher in pyroxenes- than in olivine-hosted inclusions. A correlation between the CO₂ content in FI and the Mg#, Al₂O₃   and TiO₂ concentrations in mineral phases is observed. The δ¹³C ratio of CO₂ in pyroxene-hosted FI spans a wide range, from typical mantle values of -6‰ to -4‰ in peridotites from Antarctica up to higher values (-2‰ to +2‰) in peridotites from West Eifel that overlap the range of carbonates. Interestingly, a clear correlation between the δ¹³C ratio of the FI and the Al₂O₃ concentration of their host pyroxenes is displayed by all xenoliths, indicating that the signature of fluids is related to the chemical evolution of the host mineral phases. Consistently, the δ¹³C ratio is positively correlated to the temperature recorded by both olivine-spinel and orthopyroxene-clinopyroxene pairs (T = 850-1200°C) in xenoliths from both localities.

Besides potentially widening the range of δ¹³C ratios of mantle-derived products, our results confirm that coupling the chemistry of FI to that of the host mineral phases in mantle peridotites is one of the best ways to explore the cause and effects of the melt/fluid-rock reactions taking place in the SCLM.

REFERENCES

Casetta, F., Rizzo, A. L., Faccini, B., Ntaflos, T., Abart, R., Lanzafame, G., ... & Coltorti, M. (2022). CO2 storage in the Antarctica Sub-Continental Lithospheric Mantle as revealed by intra-and inter-granular fluids. Lithos, 416, 106643.

 Rizzo, A. L., Faccini, B., Casetta, F., Faccincani, L., Ntaflos, T., Italiano, F., & Coltorti, M. (2021). Melting and metasomatism in West Eifel and Siebengebirge Sub-Continental Lithospheric Mantle: Evidence from concentrations of volatiles in fluid inclusions and petrology of ultramafic xenoliths. Chemical Geology, 581, 120400.

How to cite: Rizzo, A. L., Casetta, F., Faccini, B., Faccincani, L., Sandoval-Velasquez, A., Aiuppa, A., and Coltorti, M.: The carbon cycle in the mantle below intra-continental rift settings, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15035, https://doi.org/10.5194/egusphere-egu23-15035, 2023.

Although intra-plate volcanism is commonly attributed to the presence of thermal anomalies in the sublithospheric mantle (e.g. deep mantle plume, small-scale convection), recent geodynamic and geochemistry studies have emphasized the role of the thermochemical structure of the overlying lithosphere in dictating the type, timing and volume of surface volcanism in intra-plate environments. From the observational point of view, however, it has been difficult to formally link geophysical imaging techniques (e.g. seismic tomography) with geochemical data from erupted lavas to obtain an internally-consistent image of the thermochemical environment and melting regime responsible for intra-plate volcanism. Here we present the first geochemical-geophysical-geodynamic (‘G-cubed’) joint inversion approach capable of inverting both major and trace element lava compositions together with multiple geophysical datasets within a fully probabilistic framework. The result of this inversion is a complete thermo-chemical-dynamical model of the subsurface, including the melting regime. We illustrate the benefits and limitations of the method with a case study in eastern China. We show that our approach can successfully derive a thermochemical model that is fully consistent with all the inverted geochemical and geophysical data sets, providing fundamental constraints on the nature of the intra-plate volcanism and the underlaying mantle dynamics.  

How to cite: Afonso, J., Zhang, A., Burcet, M., Oliveira, B., Handley, H., and Klöcking, M.: 'G-cubed' joint inversions for the thermochemical environment and melting regime beneath intra-plate volcanic regions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15626, https://doi.org/10.5194/egusphere-egu23-15626, 2023.

How to cite: Kolesnikov, E., Kupenko, I., Rohrbach, A., Klemme, S., Berndt, J., Li, X., Müller, S., Liermann, H.-P., and Sanchez-Valle, C.: Strength and anisotropy of hexagonal Fe-Si-C alloy in planetary cores, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17502, https://doi.org/10.5194/egusphere-egu23-17502, 2023.

There is considerable interest in combining a range of geophysical, geochemical and geomorphic observations with a view to estimating the amplitude, wavelength and depth of mantle thermal anomalies on a global bases. Here, we wish to explore how forward and inverse modelling of major, trace and rare earth elements can be exploited to determine melt fraction as a function of depth for a mantle peridotitic source. Our focus is on an area that includes the Iberian Peninsula where previous work shows that long-wavelength topography is probably generated and maintained by sub-plate thermal anomalies which are manifest by negative shear-wave velocities. Geological and geomorphic studies suggest that this dynamic support is a Neogene phenomenon. 48 newly acquired Neogene basaltic samples from Spain were analyzed and combined with previously published datasets. Both major element thermobarometry and rare earth element inverse modelling are applied to estimate melt fraction as a function of depth. In this way, asthenospheric potential temperature and lithospheric thickness can be gauged. These estimates are compared with those obtained from calibrated shear-wave tomographic models. Our results show that potential temperatures and lithospheric thicknesses are 1250-1300 °C and 65-70 km, respectively. These values broadly agree with calibrated tomographic models which yield values of 1300-1350 °C and 45-70 km. We conclude that a region encompassing Iberia is dynamically supported by a combination of warm asthenosphere and thinned lithosphere. This conclusion broadly agrees with independently obtained residual depth anomalies which indicate that the Western Mediterranean region probably has moderately positive dynamic support.

How to cite: Tien, C.-Y., White, N., Maclennan, J., Conway-Jones, B., and Holdt, M.: Neogene Mantle Dynamics of Western Mediterranean Region Constrained by Basalt Geochemistry and Residual Depth Anomalies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-434, https://doi.org/10.5194/egusphere-egu23-434, 2023.

Transient mantle processes generate and maintain topographic variations which cannot be accounted for by crustal isostatic effects.  Accurately constraining the importance of dynamic topography across Antarctica will yield valuable insights into spatial and temporal patterns of mantle convection that inform studies of key boundary conditions for ice sheet models, such as heat flux and palaeotopography. Global studies largely neglect Antarctica because of complications associated with ice cover. In contrast, regional studies tend to oversimplify the problem by exploiting gridded datasets that ignore crustal density variations. Residual elevations, calculated by isolating and removing isostatic contributions to observed topography, enable the amplitude and wavelength of dynamic support to be gauged. Here, the results of analysing legacy (i.e. refraction) and modern (i.e. wide-angle) seismic experiments, onshore receiver functions, as well as a regional shear-wave crustal tomographic model are presented. In this way, a comprehensive suite of spot measurements (n = 195) across West Antarctica are calculated which, in conjunction with a recently augmented database of residual depths in the surrounding Southern Ocean (n = 1106), permit spatial variations of residual topography to be quantified. Positive residual anomalies (1 - 2 km) from the Transantarctic Mountains, Marie Byrd Land and the Antarctic Peninsula are consistent with regions of slow shear-wave velocity anomalies within the upper mantle, positive free-air gravity anomalies, and Cenozoic intraplate basaltic volcanism, indicating that topographic support is attributable to mantle convective processes. Lithospheric thicknesses derived from inverse modelling of basaltic rare-earth element concentrations show that elevated topography coincides with thinned lithosphere, further attesting to the relationship between positive residual elevation and mantle convective upwelling. Steepened geothermal gradients associated with regions of plate thinning have significant implications for the delivery of heat flux to the base of the West Antarctic Ice Sheet.

How to cite: Dunn, A., White, N., Larter, R., Stephenson, S., and Holdt, M.: Dynamic mantle support beneath West Antarctica's Ice Sheets: Insights from geophysical and geochemical observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-650, https://doi.org/10.5194/egusphere-egu23-650, 2023.

Remnants of the Variscan mountain belt can be found today throughout North America, North Africa, Europe, and Asia, which are typically characterized by hilly to mountainous topography. Since the topography of the Variscan orogen was already levelled in the Permian by post-orogenic erosion and thermal subsidence, processes independent of Variscan convergent tectonics must be responsible for the observed high topography. Central Europe encompasses several landscapes showing extensive post Variscan relief rejuvenation, including from west to east the Massif Central, the Vosges Mountains and Black Forest, and the Bohemian Massif. However, despite their spatial proximity, the underlying processes that led to uplift and relief rejuvenation could not be more different. For the Massif Central, mantle plume activity has been proposed, while continental rifting has been held responsible for uplift of the Black Forest and Vosges Mountains. Uplift of the Bohemian Massif has been attributed to the forebulge of the Alpine orogeny, or slab dynamics in the eastern Alps, respectively.

The aim of this study is to investigate the relationship between different uplift scenarios, relief formation and the response of the drainage system to spatial and temporal variations in uplift rates, focusing on the Massif Central, Black Forest and Vosges as well as the Bohemian Massif. The spatial and temporal succession of uplift rates as well as denudation rates in response to post orogenic uplift will be analysed based on an extensive compilation of low-temperature thermochronological data. Geomorphological analyses include the plan view and profile geometry of river networks, i.e., normalised steepness indices, across divide χ gradients and river orientation.

Although the underlying processes are different, relief rejuvenation is a striking feature in these mountain ranges. Low relief surfaces at higher elevations contrast with lower reaches, with deeply incised rivers and migrating knickpoints indicating temporal variations in uplift rates over the last millions of years. Furthermore, the organisation of river networks varies within the mountain ranges, highlighting the influence of underlying processes on the evolution of drainage networks. The Massif Central shows a radial, star-shaped drainage pattern with rivers steepening towards the centre of the plume related uplift. The Upper Rhine Graben is dominated by rift flank retreat governing drainage divide migration. This is expressed by short, steep rivers draining into the graben and long, low gradient rivers on the side facing away from the rift valley. The Bohemian Massif features a bowl-shaped topography, with tributaries of the Moldau (Vltava) draining north. However, the southern side of the Bohemian Massif drains into the Danube in short tributaries with steep lower reaches. These analyses in combination with thermochronometry pave towards constraining timing and spatial extent of the rejuvenation signal. Ultimately, this will allow for making inferences on the underlying driving mechanisms.

How to cite: Dremel, F. C., Robl, J., Friedrichs, B., and von Hagke, C.: The influence of mantle-lithosphere interaction on the evolution of relief formation and drainage networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-773, https://doi.org/10.5194/egusphere-egu23-773, 2023.

Topography and bathymetry on Earth is both isostatically and dynamically supported. The isostatic signal is dominantly controlled by variations in the thickness and density of crust and lithospheric mantle. Therefore the challenge is to identify the dynamic component of topographic support, which is caused by sub-plate density anomalies arising from convective mantle processes. Here, we exploit an observationally-led approach to determine residual (i.e., dynamic) topography across the Australian continent and its margins. Compilations of receiver function analyses, wide-angle/refraction seismic surveys and deep seismic reflection profiles are used to determine both crustal velocity structure and depth to Moho. A published compilation of laboratory measurements is used to convert crustal velocity into density. In this way, residual topography is carefully isolated and combined with existing offshore measurements. Australia’s isolation from plate boundaries combined with rapid northward translation suggest that long-wavelength dynamic topography is controlled primarily by the interaction of sub-plate convection and plate motion. Large-scale positive dynamic topography occurs along the eastern seaboard, which coincides with slow shear-wave velocity anomalies, positive long-wavelength gravity anomalies and Cenozoic basaltic magmatism. Geochemical modelling of both age-progressive and age-indepedent basalts suggests that the eastern seaboard is underlain by positive asthenospheric temperature anomalies and dramatically thinned lithosphere. These inferences are consistent with calibrated tomographic models, which show that the lithosphere is 60 km thick. In general, the pattern of continental dynamic topography is consistent with residual bathymetric anomalies from oceanic lithosphere surrounding Australia.

How to cite: Slay, P., White, N., Holdt, M., and Stephenson, S.: Observed Dynamic Topography and Cenozoic Magmatism of the Eastern Seaboard of Australia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-788, https://doi.org/10.5194/egusphere-egu23-788, 2023.

A global understanding of the evolution of oceanic lithosphere yields key insights about lithosphere-asthenosphere interaction. An important starting point is that age-depth and heatflow measurements provide the fundamental constraints for progressive cooling of oceanic lithosphere. When jointly inverting these measurements to identify an optimal plate model, the robustness of the result is predicated upon their quality, number and global distribution. Here, we exploit a revised and extensively augmented database of accurate age-depth measurements (n = 10,874) and a published database of heatflow measurements (n = 3,753). These databases are jointly modelled using both analytical and numerical methodologies to obtain a plate model, which has an average asthenospheric temperature of 1325±50oC and a lithospheric thickness of 105±10 km. These recovered values agree with independent geochemical and seismic constraints of mantle potential temperature and lithospheric thickness. This revised plate cooling model is used to improve our understanding of lithosphere-asthenosphere interaction.  First, we use plate cooling to measure residual depth anomalies, which are a reliable proxy for mantle dynamic topography. Our results demonstrate that dynamic topography varies on wavelengths as short as 1000 km with amplitudes of ±1 km. Secondly, we combine plate cooling with the depth distribution of oceanic intraplate earthquakes to identify the isothermal surface above which brittle elastic behaviour occurs. Finally, we demonstrate that age-depth and heatflow measurements exhibit a sustained flattening from ~60 Ma, suggesting that resupply of heat from the asthenosphere is an essential component of the lithosphere-asthenosphere system. Our database of accurate residual depth measurements is used to explore links between mantle dynamics, asthenospheric temperature anomalies extracted from earthquake tomographic models, and basaltic melting. 

How to cite: Holdt, M., White, N., and Richards, F.: Global Analysis of lithosphere-asthenosphere dynamics using a revised plate cooling model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-843, https://doi.org/10.5194/egusphere-egu23-843, 2023.

Vertical movements of the Earth’s surface represent mass displacements, which cause a temporal gravity signal that can be measured by dedicated satellite gravity missions such as the GRACE or GRACE-FO missions. Especially observations of vertical movements that are caused by mantle dynamic processes would enable to constrain numerical mantle convection models using geodetic data sets, thereby improving our understanding about the physical behavior of the Earth’s interior.

Using satellite gravity data to observe the above-mentioned vertical movements poses two main challenges:

First, the small amplitudes of the geoid trend signals induced by mantle dynamic signals require data accuracies and record lengths that will only be met by future satellite gravity missions. Indeed, it is known from previous simulation studies that temporal gravity signals produced by mantle convection will be detectible in future double-pair satellite gravity missions such as the planned Mass Change and Geoscience International Constellation (MAGIC).

The second challenge to make use of gravity data sets for constraining geophysical mantle models is the extraction of the signal of interest from the total gravity signal. While temporal gravity data sets include the cumulative mass displacement signal, the problem of how to separate the superimposed signals produced by phenomena in the hydrosphere, cryosphere, atmosphere, oceans and solid Earth is still unsolved.

In this contribution, using the gravity signals given by the updated ESA Earth System Model, we address the task of signal separation in temporal gravity data and present two approaches for it. To this end, the knowledge of the spatial and temporal characteristics of the individual signal components is exploited by applying principal component analysis as well as a machine learning approach.

How to cite: Heller-Kaikov, B., Pail, R., and Werner, M.: Separation of signal components in global gravity models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1257, https://doi.org/10.5194/egusphere-egu23-1257, 2023.

How the surface plates link to mantle slabs is fundamental for paleo-tectonic reconstructions and has implications on mantle dynamics. Assuming a simplified, vertical sinking slab, many tomography-based studies have vertically projected the surface features into the mantle, arguing for the tectonic explanations of mantle structures or vice versa. In contrast, geodynamic models continue to suggest that slabs can be laterally transported by a few hundred kilometers up to ~6000 km near the core-mantle boundary. The dynamics of mantle slabs remain controversial.

The Caribbean mantle has recently been suggested for vertical slab sinking. However, a vertically sinking slab at a near-stationary eastern Caribbean trench would require slab buckling in the mantle, because at least 1,200 km subduction needs to be accommodated within the upper 660 km mantle. Yet, mantle tomographies show expected (~100 km) slab thickness with limited slab thickening or buckling. With no need for a priori assumption on mantle dynamics, here, we used a slab-unfolding approach to restore and re-interpret the slab structures of the Lesser Antilles slab underneath the Caribbean. Our results show that the slab structure can be alternatively explained with limited intra-plate deformation if the slab was transported northwestward by ~900 km after subduction. Such lateral transportation in the mantle is possibly due to the physical connection with the North American plate, whose northwestward motion since the Eocene has been dragging the slab toward the same direction. We also provided our tectonic explanations on the edges and gaps of the slabs, supporting previous work that pre-existing weak zones and plate boundaries determine the fragmentation of the Lesser Antilles slab. The slab unfolding approach used in this study has the potential to be applied to other subduction zones, with no need for a priori assumption on mantle dynamics (i.e., vertical slab sinking) for future tomography-based analysis.

How to cite: Chen, Y.-W. and Wu, J.: Lesser Antilles slab reconstruction suggests significant northwestwards lateral slab transportation underneath the Caribbean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1352, https://doi.org/10.5194/egusphere-egu23-1352, 2023.

Mantle convection is a fundamental process that shapes Earth’s surface, as it provides driving and resisting forces for horizontal motions of tectonic plates, as well as for inducing non-isostatic vertical motion --- commonly termed “dynamic topography”. Growing geologic constraints of past plate motion variations and dynamic topography have led to better understanding of the history of mantle flow induced surface expression. Ultimately, the existence of a thin, mechanically weak asthenosphere allows geodynamicists to link such observables to mantle flow properties in the context of Couette/Poiseuille flow. Here we utilize publicly available geological and geophysical data sets to study Cenozoic plate kinematic changes and the spatial-temporal evolution of dynamic topography in the North Atlantic region. We employ quantitative, analytical Couette/Poiseuille flow models to link the inferred surface motion history to asthenosphere flow properties underneath. Our efforts aim at disentangling the role of asthenospheric channelized flow in influencing the Cenozoic surface expression of North Atlantic region.

How to cite: Wang, Z. R., Iaffaldano, G., and Hopper, J.: Cenozoic history of North Atlantic surface motions: Implications for asthenosphere flow processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1983, https://doi.org/10.5194/egusphere-egu23-1983, 2023.

Mantle convection is a fundamental process responsible for shaping the tectonic evolution of the Earth. It is commonly perceived that mantle convection is difficult to constrain directly. However, it affects the horizontal and vertical motion of the lithosphere. The former is observed in the spreading rates, while the latter leaves various imprints in the geological record. In particular, the positive surface deflections driven by mantle convection create erosional/non-depositional environments, which induce gaps (hiatus) in the stratigraphic record (i.e., an absence or thinning of a sedimentary layer). Modern digital geological maps allow us to map long-wavelength no-/hiatus surfaces at continental scale systematically.

Here we compare our continent-scale hiatus mapping to plate motion variations in the Atlantic and Indo-Australian realms from the Upper Jurassic onward. In general, we find the datasets correlate except when plate boundary forces may play a significant role. There is a timescale on the order of a geologic series, ten to a few tens of millions of years (Myrs), between the occurrence of continent-scale hiatus and plate motion changes. This is consistent with the presence of a weak upper mantle. Furthermore, we find significant differences in the spatial extent of hiatus patterns across and between continents, which means they cannot simply be explained by eustatic variations but should be linked to variations in the upper-mantle flow.

Our results highlight the importance of geological datasets to map the temporal evolution of geodynamic processes in the deep Earth. Also, they imply that different timescales for convection and topography in convective support must be an integral component of time-dependent geodynamic Earth models. Studies of horizontal and vertical motion of the lithosphere to track past mantle flow would provide powerful constraints for adjoint-based geodynamic inverse models of past mantle convection.

How to cite: Vilacís, B., Hayek, J. N., Stotz, I. L., Bunge, H.-P., Friedrich, A. M., Carena, S., and Clark, S. R.: Pressure-driven upper-mantle flow in the Indo-Atlantic Realm since the Upper Jurassic inferred from continent-scale hiatus surfaces and oceanic spreading rate variations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2575, https://doi.org/10.5194/egusphere-egu23-2575, 2023.

It is generally accepted that East Asian mantle dynamics has been dominated by subduction and downwelling since Mesozoic times (e.g. Müller et al. (2016)). However, seemingly in contrast to this history, a variety of observations indicate a presence of anomalously hot asthenospheric material beneath East Asia during the late Cenozoic. First of all, tomographic models consistently reveal an extensive network of seismically slow anomalies at asthenospheric depths, which align spatially with a recent (< 30 Ma) phase of intraplate volcanism. The influence of this positively buoyant material at the surface is further highlighted by induced dynamic uplift, which is recorded in the geological record through an inter-regional sedimentary hiatus during the late Eocene—Oligocene. Residual topography studies additionally find swells of dynamic uplift throughout this region in the present day. Global mantle circulation models (MCMs) show that these observations can be reproduced in a subduction-dominated region by the spillover of anomalously hot asthenospheric material from the adjacent Pacific domain during ridge subduction events. In particular, the subduction of the Izanagi-Pacific ridge at ~55 Ma provides a large window through which Pacific asthenosphere could have flowed into East Asia. We test this hypothesis by comparing these MCMs to a variety of geological observations, including the distribution of sedimentary hiatus and intraplate volcanism during the late Cenozoic. We additionally compare the present-day distribution of hot material predicted by these models with the recently published full waveform inversion tomographic model of the region, Sinoscope 1.0, which highlights the distribution of seismically slow anomalies beneath the region. We find an encouraging match between asthenospheric flow predicted by these models and the observations considered, showing this to be a viable new hypothesis in explaining these observations. The mechanism of hot asthenospheric build-up during subduction and release during slab window opening may not be limited to East Asia, and could reconcile observations of intraplate volcanism and dynamic uplift in convergent regions more generally. 

How to cite: Brown, H., Ma, J., Colli, L., and Bunge, H.-P.: The influence of slab window asthenospheric flow on intraplate volcanism, dynamic uplift, and present-day mantle heterogeneity in East Asia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3213, https://doi.org/10.5194/egusphere-egu23-3213, 2023.

Geological maps contain a large amount of information that can be used to constrain geodynamic models, but which has been often overlooked by the geodynamic community. Particularly significant are unconformable geologic contacts at continental scales: what is usually perceived as a lack of data (material eroded or not deposited) becomes instead part of the signal of dynamic topography.

We were able to use geological maps to constrain the dynamic processes in the mantle beneath Africa by understanding its Cenozoic elevation history, and by using it to distinguish between different uplift and subsidence scenarios. This was accomplished by mapping the spatio-temporal patterns of geological contacts at the series level using continental-scale geological maps, under the assumption that continental-scale unconformable contacts are proxies for vertical motions and for paleotopography. We also mapped the present-day elevation of marine sediments for each series.

We found that significant differences exist in interregional hiatus surfaces. For example, the total unconformable area at the base of the Miocene expands significantly compared to the base of the Oligocene, strongly suggesting that most of Africa underwent uplift in the Oligocene. In southern Africa there are no marine Oligocene or Pleistocene sediments, suggesting that this region reached a high in the Oligocene, subsided in the Miocene and Pliocene, and has been high again since late Pliocene to Pleistocene. More generally, to reproduce the pattern of marine sedimentation in Africa that we mapped, sea level increases between 300 and at least 500 m above present level would be required. These are well in excess of the maximum 150 m eustatic sea level rise that has been postulated by several authors for the Cenozoic. Our results therefore support a dynamic origin for the topography of Africa. Specifically, the time-scale of geologic series (at most a few tens of millions of years) is comparable to the spreading-rate variations in the south Atlantic, which have been linked to African elevation changes through pressure-driven upper mantle flow.

How to cite: Carena, S., Friedrich, A., and Bunge, H.-P.: Geological hiatus surfaces across Africa in the Cenozoic: implications for the timescales of convectively-maintained topography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3508, https://doi.org/10.5194/egusphere-egu23-3508, 2023.

It is well known that increasing pressure and temperature along upper-mantle geotherms combine to produce a zone of low seismic wave speeds. Beyond such behaviour arising from the anharmonicity of the crystal lattices of the constituent minerals, viscoelastic relaxation may result in further reduction of the wave speeds, along with appreciable attenuation of seismic waves. In order to better constrain such sub-solidus relaxation in olivine-dominated lithologies, we have recently prepared and tested in torsional forced oscillation several new specimens of synthetic polycrystalline olivine (Fo₉₀ olivine buffered by ~5 wt% En₉₀). These specimens were prepared by hot pressing sol-gel precursor powder encapsulated within metal foils (of Ni₇₀Fe₃₀ or Pt) at high temperature (1200-1350ºC) and pressure (300 MPa). Enclosure within Ni-Fe foil yields relatively reducing anhydrous conditions and average grains sizes d ≤ 5 μm. The more oxidising and hydrous conditions associated with Pt encapsulation are conducive to grain growth to at least 20 μm. Our forced-oscillation methods have been refined by replacement of the polycrystalline alumina control specimen with single-crystal sapphire, discontinuation of the use of Ni-Fe foils at the ends of the specimens in favour of direct contact with alumina torsion rods, and selective use of austenitic stainless steel as an alternative to the usual mild-steel material for the enclosing jacket. Such testing of fine-grained olivine polycrystals at periods of 1-1000 s and shear strain amplitudes < 10^-5 has consistently revealed an essentially monotonically period- and temperature-dependent high-temperature background. The onset of high-temperature anelastic relaxation involves a superimposed dissipation peak of only modest amplitude plausibly attributed to elastically accommodated grain-boundary sliding. Grain-size sensitivity is incorporated into a Burgers type creep-function model fitted to the (G,Q^-1) data for multiple specimens through power-law grain size dependencies of the key characteristic times. The Maxwell time τ_M, varying as d^-mV, defines the transition from anelastic to viscous background behaviour, and τ_P ~ d^-mA, the centre of the distribution of relaxation times for the dissipation peak. The data for the newly prepared pure synthetic specimens of 4-22 mm grain size, tested with the refined experimental methodology, require m_V ~ 3 and m_A < 1.5. These inferences are consistent with micromechanical models for grain-boundary sliding, but yield markedly stronger grain-size sensitivity than previously reported. However, mapping of the tested samples by electron back-scattered diffraction indicates that the density of geometrically necessary dislocations, responsible for lattice curvature, decreases systematically with increasing grain size, raising the possibility that any contribution from dislocation damping might enhance the apparent grain-size sensitivity. A preliminary extrapolation of the new model for grain-size sensitive viscoelastic relaxation in dry, melt-free dunite to upper-mantle conditions of grain size and pressure suggests shear modulus relaxation < 2% and dissipation Q^-1 < 0.01 – thus unable to account for seismological observations of the mantle beneath young oceanic lithosphere and in subduction zones. Uncertainties in such extrapolation will be discussed, along with other factors that might enhance sub-solidus viscoelastic relaxation including the segregation of trace-element impurities to olivine grain boundaries, and the influence of oxygen and water fugacities. 

How to cite: Jackson, I., Qu, T., and Faul, U.: Seismic wave dispersion and attenuation within the asthenosphere: the role of sub-solidus viscoelastic relaxation revisited, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4014, https://doi.org/10.5194/egusphere-egu23-4014, 2023.

The existence of a thin, weak asthenospheric layer beneath Earth’s lithospheric plates is consistent with existing geological and geophysical constraints, including Pleistocene glacio-isostatic adjustment, modeling of gravity anomalies, studies of seismic anisotropy, and post-seismic rebound. Mantle convection models suggest that a pronounced weak zone beneath the upper thermal boundary layer (lithosphere) may be essential to the plate tectonic style of convection found on Earth. The asthenosphere is likely related to partial melting and the presence of water in the sub-lithospheric mantle, further implying that the long-term evolution of the Earth, including the apparently early onset and persistence of plate tectonics, may be controlled by thermal regulation and volatile recycling that maintain a geotherm that approaches the wet mantle solidus at asthenospheric depths.

How to cite: Richards, M., Cathles, L., Fjeldskaar, W., Lenardic, A., Romanowicz, B., and Seales, J.: Influence of the Asthenosphere on Earth Dynamics and Evolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4053, https://doi.org/10.5194/egusphere-egu23-4053, 2023.

Vertical motion of the Earth’s lithosphere (uplift) occurs on different spatial and temporal scales. Commonly assumed to be primarily related to plate tectonic mechanisms and isostatic adjustment, it has become clear that mantle related forcing and in particular mantle plumes are a significant contributor to uplift events in many regions of the world, making vertical motions a powerful probe into sublithospheric processes. Significant improvements of observational methods (e.g. satellite missions) and publicly-accessible databases (e.g. digital geological maps) make it now feasible to map vertical motions from geodetic to geologic time scales. This in turn provides invaluable constraints to inform key, yet uncertain, parameters (e.g. rheology) of geodynamic models. Such models also contribute powerful insight into complex landscape evolution processes at interregional to continental scales. Here we report on a new (starting date April 2022) Research Training Group (RTG) 2698, with 10 individual dissertation projects and a Post-doc project, funded by the German Research Foundation. An interdisciplinary approach of Geodynamics, Geodesy and Geology aims to answer questions related to how the interaction of exo- and endogenic forcing shapes a diverse array of earth processes from landscape evolution to the occurrence of earthquakes. The RTG uses a combined interpretation of interdisciplinary observations with different spatial and temporal sensitivity, in conjunction with physical models, to disentangle different uplift mechanisms, including the plume, plate and isostatic mode, based on their specific spatial and temporal patterns. We will give an overview on the key philosophy and main architecture of the RTG. Core components include an integrated geophysical process model, composed of an adjoint geodynamic model that accounts for seismic tomography and mineralogy, coupled with a landscape evolution model, with the lithosphere as a filter function, and targeted observations that include geodetic (geometric and gravimetry) data to reflect contemporary uplift processes combined with high precision, geological, magnetostratigraphic and geomorphologic data to reflect uplift processes and sedimentation rates on geological time scales. The modeling will be complemented by a thorough uncertainty analysis and an enhanced visualization of the key results.

How to cite: Bunge, H.-P., Chen, Y.-W., Friedrich, A., and Pail, R. and the UPLIFT Team: Geophysical modelling of vertical motion processes constrained by geodetic and geological observations (UPLIFT), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4232, https://doi.org/10.5194/egusphere-egu23-4232, 2023.

Construction of robust mantle flow trajectories plays an important role in understanding the parameters that govern mantle convection and relating them to geologic observables. In the past, the assessment of constructed trajectories focused majorly on metrics targeted at the mantle volume whilst neglecting the surface manifestations of mantle convection in the form of dynamic topography. However, an increasing amount of interest is being built around linking convection to surface effects, including dynamic topography. As such, it is vital to study ways in which mantle flow trajectories can be assessed via their dynamic topography predictions. Commonly used assessment and comparison metrics such as root-mean-square errors, suffer from the so-called double penalty problem --- a dynamic topography prediction that does not match a reference observation one-to-one is penalized twice: first as a miss and second as a false alarm. It is therefore attractive to investigate metrics that overcome this problem. Here, we introduce an object-based approach, first applied in meteorology, and show that this approach is not only amenable to studying dynamic topography, but that it also overcomes the double penalty problem whilst providing accurate model assessment.

How to cite: Taiwo, A., Bunge, H.-P., and Craig, G.: Meteorological Tools for Assessing Mantle Flow-related Dynamic Topography Maps, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4286, https://doi.org/10.5194/egusphere-egu23-4286, 2023.

How to cite: D'Ascoli, E., Brown, H., Kohl, N., Mohr, M., and Bunge, H.-P.: TerraNeo: Ongoing development of a scalable mantle convection code for exascale computing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4326, https://doi.org/10.5194/egusphere-egu23-4326, 2023.

How can mega-dykes propagate hundreds of kilometres laterally through the crust? These blade-shaped dykes are enormous geological structures characterised by widths up to 100 metres. Ernst and Baragar (1992) showed that mega-dykes propagate away from a point at the centre of the dyke swarm. The magma for such dykes is believed to originate from a hotspot impinging on the base of the lithosphere, and this process typically precedes rifting events (Ernst, 2001; Srivastava et al., 2019). Current models do not adequately explain the mechanisms driving the propagation and termination of mega-dykes. We hypothesise that mega-dyke propagation is driven by the gradient in gravitational potential energy associated with the topography of a hotspot swell.

We present an analytical model linking the length of mega-dykes to the dimensions of a topographic swell above a hotspot. Our model accounts for various energy sources, including magma-source pressure and gravitational potential energy, and energy sinks such as viscous dissipation, elastic wall-rock deformation, and fracturing at the dyke tip. We define the ground surface deformation above a hotspot using an analytical model (Morgan, 1965) and demonstrate, in this context, that the dyke width scales with distance from the magma source. The final dyke length is computed by finding the point at which the sum of energy sources becomes less than the energy sinks. Furthermore, we explore the trade-offs between parameters controlling the swell size and the final length of a mega-dyke. We tentatively apply our findings to observed mega-dyke swarms and investigate the hot-spot sizes required to produce the observed lengths of these structures.

References

Ernst, R.E. and Baragar, W.R.A., 1992. Evidence from magnetic fabric for the flow pattern of magma in the Mackenzie giant radiating dyke swarm. Nature, 356(6369), pp.511-513. doi:10.1038/356511a0

Ernst, R.E., 2001. The use of mafic dike swarms in identifying and locating mantle plumes. Geological Society of America Special Papers, 352, p.247-265. doi:10.1130/0-8137-2352-3.247

Morgan, W.J., 1965. Gravity anomalies and convection currents: 1. A sphere and cylinder sinking beneath the surface of a viscous fluid. Journal of Geophysical Research, 70(24), pp.6175-6187. doi:10.1029/JZ070i024p06175

Srivastava, R.K., Ernst, R.E. and Peng, P. eds., 2019. Dyke swarms of the world: A modern perspective. Springer Geology. doi:10.1007/978-981-13-1666-1

How to cite: Davis, T. and Katz, R.: A theory for mega-dyke propagation as driven by hotspot topography., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5023, https://doi.org/10.5194/egusphere-egu23-5023, 2023.

The evolution of Fennoscandia following the early Devonian collapse of the Caledonian mountains is a matter of debate, due largely to the scarcity of post-Caledonian cover rocks. The preserved geological record therefore provides limited documentation of the post-Caledonian history. But a more complete understanding can be obtained by also considering evidence of rocks that were formerly present but have since been removed (‘missing section’).

We report apatite fission-track data and associated thermal history constraints in 331 samples of Precambrian basement, Phanerozoic sediments and igneous rocks from outcrops and boreholes (up to 6 km depth) from Norway, Sweden and Finland, which define multiple episodes of cooling over the last billion years.

We are therefore able to establish a post-Caledonian history of Fennoscandia involving repeated episodes of kilometer-scale burial and exhumation with key episodes of exhumation beginning during late Carboniferous, Middle Triassic, Middle Jurassic, mid-Cretaceous and early Miocene. The effects of these episodes are documented in the stratigraphic record and as prominent peneplains. Major offsets in Mesozoic paleotemperatures over short distances define kilometre-scale differential vertical displacements, emphasizing the tectonic nature of the history.

Results from Finland record events also recognized in Norway and Sweden (though less pronounced) and are thus not consistent with long-term cratonic stability. We interpret the lack of preserved Phanerozoic sedimentary cover in Finland to be due to complete removal during multiple episodes of denudation. For example, our results show that about 2 km of Cambrian to Middle Triassic sediments covered the Sub-Cambrian Peneplain in southern Finland prior to the onset of Middle Triassic exhumation. In southern Scandinavia, Miocene exhumation led to formation of a peneplain which in Pliocene times was uplifted and dissected, producing the modern landscape, also by exhuming older peneplains from below their protective cover rocks.

The Carboniferous to Cretaceous exhumation episodes affected Fennoscandia as well as East Greenland, however, post-breakup episodes affected the conjugate margins of the NE Atlantic differently. Whereas Neogene uplift began in the early Miocene in Fennoscandia, it began in the late Miocene in Greenland. Pliocene uplift affected both margins at about the same time. Far-field transmission of plate-tectonic stress and/or mantle processes may explain the vertical movements described here.

References

Bonow & Japsen, 2021, Peneplains and tectonics in North-East Greenland after opening of the North-East Atlantic. GEUS Bulletin.

Green et al., 2022a, Episodic kilometre-scale burial and exhumation and the importance of missing section. Earth-Science Reviews.

Green et al., 2022b, The post-Caledonian thermo-tectonic evolution of Fennoscandia. Gondwana Research.

Japsen & Chalmers, 2022, The Norwegian mountains: the result of multiple episodes of uplift and subsidence. Geology Today. https://doi.org/10.1111/gto.12377

Japsen et al., 2018, Mountains of southernmost Norway: uplifted Miocene peneplains and re-exposed Mesozoic surfaces. Journal of the Geological Society, London.

Japsen et al., 2021, Episodic burial and exhumation in North-East Greenland before and after opening of the North-East Atlantic. GEUS Bulletin.

Lidmar-Bergström et al., 2013, Stratigraphic landscape analysis and geomorphological paradigms: Scandinavia as an example of Phanerozoic uplift and subsidence. Global and Planetary Change.

How to cite: Japsen, P., Green, P. F., Bonow, J. M., Chalmers, J. A., Duddy, I. R., and Kukkonen, I.: How post-Caledonian burial, exhumation and peneplanation shaped the scenery of Fennoscandia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5621, https://doi.org/10.5194/egusphere-egu23-5621, 2023.

Linking geodynamic models to observations from seismology is essential for improving our understanding of the present-day thermodynamic state of the mantle. From the geodynamic perspective, 3D mantle circulation models (MCMs) yield physically relevant predictions of the global distribution of buoyancy forces, while complementing information is available from seismic data and tomography that can reveal the location and morphology of mantle heterogeneity. Investigating this powerful interplay in a fully synthetic framework has great potential. It allows us to make robust interpretations of mantle structure provided that quantitatively meaningful comparisons can be made. This especially relates to the magnitudes of heterogeneity that can not be effectively constrained by the individual modelling approaches.

Following this general concept, there are two possible links: 1) synthetic seismic data can be predicted from the MCM and statistically be compared against observed data. 2) the MCM gets modified by a tomographic operator (informing us about spatially variable seismic resolution and, if applicable, model uncertainty), and subsequently this filtered version gets compared against the corresponding tomographic image from real observations.

Here, we discuss these two strategies together based on observed data for S-wave cross-correlation traveltime residuals that have been applied to global seismic tomography. Taking the same set of source-receiver configurations, synthetic traveltime predictions are computed in a state-of-the-art MCM using ray theory (RT), paraxial finite-frequency kernels (FFK), as well as cross-correlation measurements on synthetic seismograms (SPECFEM). The latter requires computationally demanding 3D-wavefield simulations using SPECFEM3D_GLOBE for an earthquake catalog comprising over 4,200 teleseismic events.

These data sets can be used for tomographic filtering by application of the generalized inverse operator of the actual tomographic model. Filtered MCMs derived from the differently predicted data sets appear largely similar on a global scale with regards to the shape and amplitudes of imaged mantle heterogeneity. This is observed despite the lack of more accurate wave physics in RT or FFK and possible measurement errors for the SPECFEM data that, although being computed in a synthetic case, can not be completely ruled out. Stronger differences between filtered models appear in regions of higher image resolution where model uncertainty by propagated data errors can play a more prominent role.

We discuss the impact of the different filtering strategies by comparing filtered models to the original MCM and synthetic traveltime residuals to the underlying real observations. The results strongly highlight the need for incorporating both resolution and model uncertainty in combined tomographic-geodynamic studies.

How to cite: Freissler, R., Schuberth, B. S. A., and Zaroli, C.: Ray-theoretical and finite-frequency seismic traveltime predictions for tomographic filtering of 3D mantle circulation models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6676, https://doi.org/10.5194/egusphere-egu23-6676, 2023.

Earth’s upper mantle rheology controls lithosphere-asthenosphere coupling and thus its surface tectonics. Although rock deformation experiments and seismic anisotropy measurements indicate that dislocation creep can occur in the Earth's uppermost mantle, the role of composite rheology (including both diffusion and dislocation creep) on global-scale mantle dynamics and surface tectonics remains largely unexplored.

Here, we investigate the influence of composite rheology on the planform of convection and on the planetary tectonic regime as a function of the lithospheric yield strength in numerical models of mantle convection with plate-like tectonics. We show that the consideration of composite rheology in the upper mantle leads to the self-generation of a discontinuous asthenosphere evolving fast, with a low-viscosity and a maximal thickness that depend on the rheological parameters for diffusion and dislocation creep. In mobile-lid models, the spatio-temporal evolution of the asthenosphere is mainly controlled by the location of slabs and plumes that generate regions of mantle deforming dominantly through dislocation creep. Moreover, the low upper-mantle viscosities caused by composite rheology produce substantial and contrasting effects on surface dynamics. For a strong lithosphere (high yield stress), the large lithosphere-asthenosphere viscosity contrasts promote stagnant-lid convection, while the increase of upper-mantle convective vigor enhances plate mobility for low lithospheric strength (small yield stress). We further show that composite rheology does not facilitate the onset of plate-like behavior at large lithospheric strength due to decoupling between the asthenosphere and the lithosphere.

How to cite: Arnould, M., Rolf, T., and Manjón-Cabeza Córdoba, A.: The effect of asthenosphere’s rheology on mantle and surface tectonics : the role of composite rheology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7226, https://doi.org/10.5194/egusphere-egu23-7226, 2023.

During the Cenozoic, the Circum-Mediterranean has experienced extensive and widespread igneous magmatism (i.e. intraplate, subduction-related and mixed-origin) that reflects the response of the upper mantle to the geodynamic evolution of this area. The exact origin of the volcanic activities and its relation to the underlying thin lithosphere especially in the continental regions have been long-lasting debated. We investigate the structure of the lithosphere and the sub-lithospheric mantle in the Circum-Mediterranean using regional high-resolution 3-D surface wave tomography and integrated geophysical-petrological thermochemical modelling of the temperature field and explore the relation to the occurrence intraplate and mixed-origin volcanic provinces (IMVPs).

We define 9 shallow asthenospheric volumes (SAVs) across the Circum-Mediterranean upper mantle that form an almost interconnected belt of reduced shear wave velocities starting from the western Mediterranean to the Middle East and surrounding the Calabrian, Adriatic, Alpine slabs, however only interrupted by the eastern Mediterranean thick oceanic lithosphere. The SAVs are characterized by pronounced variations in shear-wave velocity not only laterally but also vertically between 70 and 300 km depths. Results from integrated geophysical-petrological thermochemical modelling show that the low velocities of the SAVs correspond to areas of thinned lithosphere (i.e., 1300 ºC at about 60-80 km depth) and anomalously warm asthenosphere (down to 300 km approximately) with respect to the average ambient mantle geotherm. A remarkable correlation between these areas and locations of IMVPs is observed with a mean lateral distance of < 100 km separating any SAV to the neighboring IMVP. The maximum separating distances are in order of ~ 350 km indicating a dense network of volcanic provinces above the shallow SAVs.

The origin of the SAVs is related either to asthenospheric upwelling caused by slab rollback and decompressional melting during the formation of the back-arc basins (i.e., Agean-Anatolia, Pannonian, Moesian, Western Mediterranean) or to lithospheric thinning and rifting (Middle East and Rhone-Rheine areas). For the origin of the remaining SAVs (Adriatic, Central European, North Africa), other processes, i.e. thermal erosion feed by input from deep mantle sources, are suggested. According to the oldest ages of the IMVPs in the Circum-Mediterranean, the development of the SAVs started at least about ~ 60 - 70 Ma ago and accelerated in the Neogene.

How to cite: El-Sharkawy, A., Hansteen, T. H., Clemente-Gomez, C., Fullea, J., Lebedev, S., and Meier, T.: Shallow Asthenospheric Volumes Beneath Cenozoic Volcanic Provinces in the Circum-Mediterranean: Evidence From Seismic Tomography And Integrated Geophysical-Petrological Thermochemical Modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8412, https://doi.org/10.5194/egusphere-egu23-8412, 2023.

Mantle convection and plate tectonics are crucial mechanisms for keeping conditions at the Earth’s surface in a suitable range for life. One important mantle process is the transport of heat out of the Earth’s outer core, which impacts the geodynamo that generates Earth’s magnetic field. This interaction makes it possible to use changes in the paleomagnetic record to infer the past dynamics of the Earth’s mantle and core.

We here couple a plate reconstruction, 3d global mantle convection models, and geodynamo simulations to quantify the largest possible influence of mantle heat transport on the magnetic field at the Earth’s surface. To constrain the core-mantle boundary heat flux, we set up compressible global mantle convection models using the geodynamic modeling software ASPECT, with material properties computed based on a mineral physics database. We prescribe the velocities at the surface using a plate reconstruction that describes plate motion history throughout the last 1 billion years, encompassing the complete cycle of supercontinent assembly and dispersal. This boundary condition imposes the location of subducted slabs in the model, which then sink down and interact with the thermal/thermochemical boundary later at the base of the mantle, affecting the amplitude and pattern of the heat flux out of the core and how it changes over time. Our models show that the distribution of hot and cold regions changes in terms of location, shape and number throughout the supercontinent cycle, depending on subduction location. Our results indicate that structures at the core-mantle boundary fluctuate and might have looked very differently throughout Earth’s history.

We then select endmember scenarios of core-mantle boundary heat flux patterns and amplitudes to apply them as boundary conditions to thermally driven numerical geodynamo simulations. To assess how well these simulations reproduce Earth’s long-term magnetic field behavior, we apply the Quality of Paleomagnetic Modeling criteria. This allows us to systematically explore the impact of the most extreme variations of CMB heat flux on the geodynamo and to determine if extreme anomalies in the paleomagnetic record, like the extreme weak field period in the Ediacaran, could be caused by mantle dynamics alone or if they require other mechanisms, such as the nucleation of the Earth’s inner core.

Our work shows how integrating multidisciplinary datasets into modeling studies improves our understanding of the mantle’s role in regulating the magnetic field throughout Earth's history, allowing us to re-evaluate the causes of variations in paleomagnetic data.

How to cite: Dannberg, J., Thallner, D., Gassmoeller, R., Sprain, C., LaCombe, F., and Ritchie, C.: Coupling Models of Plate Motion History, Mantle Convection and the Geodynamo to explain long-term Geomagnetic Field Behavior, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9490, https://doi.org/10.5194/egusphere-egu23-9490, 2023.

Mantle convection is primarily driven by gravitational forces acting on thermally buoyant structures in Earth's interior. The associated vertical stresses generate phases of uplift and subsidence of the surface, leaving observable traces in the geologic record. Utilizing new data assimilation techniques, geodynamic inverse models of mantle flow can provide theoretical estimates of these surface processes, which can be tested against geologic observations. These so-called mantle flow retrodictions are emerging as powerful tools that have the potential to allow for tighter constraints on the inherent physical parameters.

To contain meaningful information, the inverse models require an estimate of the present-day buoyancy distribution within the mantle, which can be derived from seismic observations. By using thermodynamically self-consistent models of mantle mineralogy, it is possible to convert the seismic structure of global tomographic models to temperature. However, both seismic and mineralogical models are significantly affected by different sources of uncertainty and often require subjective modelling choices, which can lead to different estimated properties. In addition, due to the complexity of the mineralogical models, the relation between temperature and seismic velocities is highly nonlinear and not strictly bijective: In the presence of phase transitions, different temperatures can result in the same seismic velocity, further complicating the conversion between the two parameters.

Using a synthetic closed-loop experiment, we investigate the theoretical ability to estimate the present-day thermal state of Earth's mantle based on tomographic models. The temperature distribution from a 3-D mantle circulation model with earth-like convective vigour serves as a representation of the "true" temperature field, which we aim to recover after a set of processing steps. These steps include the “forward and inverse” mineralogical mapping between temperatures and seismic velocities, using a thermodynamic model for pyrolite composition, as well as applying a tomographic filter to mimic the limited resolution and uneven data coverage of the underlying tomographic model. Owing to imperfect knowledge of the parameters governing mineral anelasticity, we test the effects of changes to the anelastic correction applied in forward and inverse mineralogical mapping. The mismatch between the recovered and the initial temperature field carries a strong imprint of the tomographic filter. Additionally, we observe systematic errors in the recovered temperature field in the vicinity of phase transitions. Our results highlight that, given the current limits of tomographic models and the incomplete knowledge of mantle mineralogy, amplitudes and spatial scales of a temperature field obtained through global seismic models will deviate significantly from the true state. Strategies to recover the present-day buoyancy field must be carefully selected in order to minimize additional uncertainties.

How to cite: Robl, G., Schuberth, B., Papanagnou, I., and Thomas, C.: Linking thermal and seismic mantle structure in the light of uncertain mineralogy and limited tomographic resolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9743, https://doi.org/10.5194/egusphere-egu23-9743, 2023.

Plate tectonics can explain several geological and geophysical phenomena on Earth, and a number of mantle flow models have been developed to investigate the underlying plate tectonic forces. However, these models have come to contradictory conclusions on the balance between the resisting and driving forces. Additionally, they have used the same simplified model to represent the geometry of the plates, and therefore the impact of plate boundary geometry on surface deformation remains unknown.

To address these issues, we have developed high-resolution global instantaneous mantle convection models based on recent geophysical constraints with a heterogeneous density and viscosity distribution and weak plate boundaries prescribed using different plate boundary configurations. We find a good fit to the observed GPS data for models with plate boundaries that are 3 to 4 orders of magnitude weaker than the surrounding lithosphere and low asthenospheric viscosities between 5×10¹⁷ and 5×10¹⁸ Pa s for all plate boundary configurations. We also find that the model with plate boundaries defined by the Global Earthquake Model (GEM, Pagani et al., 2018)—featuring open plate boundaries with discrete lithospheric-depth weak zones in the oceans and distributed crustal faults within continents—achieves the best fit to the observed GPS data with a directional correlation of 95.1% and a global point-wise velocity residual of 1.87 cm/year. These results show that Earth’s plate boundaries are not uniform and better described by more discrete plate boundaries within the oceans and distributed faults within continents.

Our models also quantify the contributions to the plate driving forces originating from heterogeneities in the upper mantle and the lower mantle, respectively, finding that the slab-pull in the top 300 km alone contributes ~70% of the total plate speeds. Noting the importance of slab pull as a major plate driving force, we further investigate the influence of subduction zone and slab geometry on surface plate motions and their fit to GPS data. Specifically, our models compare a simplified slab structure to a more detailed representation of slabs based on the Slab2 database (Hayes et al., 2018), and reaffirm that a realistic slab geometry is a crucial factor in the transmission of slab pull forces to the plate.

How to cite: Saxena, A., Dannberg, J., and Gassmoeller, R.: High-resolution mantle flow models reveal importance of plate boundary geometry and slab pull forces on generating tectonic plate motions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10217, https://doi.org/10.5194/egusphere-egu23-10217, 2023.

Dynamic topography is the change in topography that arises from viscous flow within the Earth’s mantle. As such, dynamic topography is sensitive to past mantle flow states. Making predictions of dynamic topography through time often relies on complex mantle convection models. To better constrain mantle convection models, we compare their implied True Polar Wander (TPW) paths for a range of model parameters. TPW is the re-orientation of a planetary solid body with respect to its rotation axis and may be produced by large scale mass redistributions on the Earth’s surface or within the mantle that perturb the Earth’s moment of inertia.

Here we compare TPW histories estimated from two global plate tectonic reconstructions that were assimilated into the TERRA mantle convection code: (1) the widely-used Earthbyte global plate model (‘corrected R’ Matthews et al., 2016); and (2) TOMOPAC-22, a newly developed global plate tectonic model of the circum-Pacific using structurally-restored slabs from mantle seismic tomography (Wu et al., 2022). The time series of geodynamically-modeled mantle states are used to calculate synthetic TPW paths from perturbations in components of Earth’s moment of inertia from mass redistribution within the mantle; multiple (>10) viscosity-depth profiles were considered. We test these modeled TPW paths by comparing them against published paleomagnetic observations (Torsvik et al., 2012; Besse and Courtillot, 2002). Predicted TPW for plate Model 1 ranges widely (~90°) in azimuth from 120°W to 59°E with no consistent pattern across viscosity profiles. TPW rates reach maximums of 1.1°/Myr with excursions of ~25°. In contrast, predicted paths for Model 2 cluster within a smaller ~30° azimuthal range centered around ~29°E irrespective of the viscosity profile.  Predicted maximum rates were up to ~2°/Myr with excursions of up to 30°. Temporally, predicted paths for Model 2 drift toward northern Russia and then veer towards Greenland. Depending on the viscosity profile used some predicted TPW paths undergo stillstands from ~80 to ~30 Ma.  Ultimately, most model scenarios show longitudinal misfits up to 60° with observed paleomagnetic data; modeled TPW rates were within observed and theoretical ‘speed limits'. We discuss similarities and differences between our preliminary TPW history results and paleomagnetic observations, with a goal of developing an effective TPW test for constraining geodynamic parameters, plate tectonic reconstructions, and dynamic topography through time.

How to cite: Calvelage, C. M., Colli, L., Wu, J., and Lin, Y.-A.: Earth’s Wandering Rotation Axis as a Diagnostic for Global Mantle Convection Models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10292, https://doi.org/10.5194/egusphere-egu23-10292, 2023.

The discovery of very rapid uplift rates under areas recently de-glaciated and the realization that such rapid uplift can stabilize ice sheets has generated interest in determining the properties of the asthenosphere.  The asthenosphere is also important to plate tectonics, and to the proper interpretation many important Earth observations.  The current approach to determining the properties of the asthenosphere is to calculate the observed rate of uplift in an area for a great many deglaciation and earth models, calculate the difference between the observed and calculated uplift rates and histories, and find the earth model (with error bars) that best matches the observations.  A faster, simpler, and in some ways better assessment method is to compute the isostatic adjustment response to a loading history consisting of linear segments.  This method determines the central response time from the dimensions of the load, the loading history, the lithosphere flexural rigidity (often not important), and the present rate of uplift.  The last can be easily measured today with GPS in INSAR.  Asthenosphere properties are indicated by the central response time so determined. The Daisy chain method will be described, evaluated against data and conventional modeling in northern Norway, and then applied to infer asthenosphere properties in a number recently-deglaciated continental localities.

How to cite: Cathles, L., Fjeldskaar, W., and Amantov, A.: Daisy chain method applied to mapping the asthenosphere, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10376, https://doi.org/10.5194/egusphere-egu23-10376, 2023.

Electrical conductivity variations provide unique constraints on chemistry, mineralogy, and physical structure of the crust and mantle. As a physical property, conductivity is highly sensitive to the presence of even small amounts of melt and water (i.e., hydrogen). Here, we present a new 3-D electrical conductivity model (MECMUS-2022) derived by inverting data from ~1300 USArray MT stations covering ∼80% of the contiguous United States on a quasi-regular 70-km grid. The use of a novel multi-scale imaging approach and locally refined meshes allows us to consistently incorporate a large range of spatial scales and image 3-D electrical conductivity distribution from the surface down to mantle transition zone. We find conductivity variations that correlate with known continental structures such as due to the active tectonic processes within the western United States (e.g., Yellowstone hotspot, Basin and Range extension, and subduction of the Juan de Fuca slab) as well as the presence of deep roots beneath cratons. We further interpret conductivity variations in terms of the upper mantle water content by coupling electrical conductivity with constrains on mantle thermo-chemical structure derived from the analysis of seismic data (in the form of P-to-s and S-to-p receiver functions). Further, we explore the links between electrical conductors and lithospheric controls on occurrence of critical mineral deposits.

How to cite: Munch, F. D. and Grayver, A.: Imaging 3-D electrical conductivity structure under US constrains lateral variations in the mantle water content, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11908, https://doi.org/10.5194/egusphere-egu23-11908, 2023.

Mantle convection has often been debated to be either a mode of ‘top-to-bottom’ whole mantle convection, or flow within separated geochemical ‘reservoirs’ such as a denser layer often proposed to be the origin of lower mantle LLSVPs. Here we propose a straightforward resolution in which plate tectonic downwelling is linked to a ~3000 km-broad N-S circumglobal ‘ring’ of higher-than-average seismic wavespeeds in the lower mantle that has been recognized since the first global models of non-radial seismic structure. In the high-viscosity lower mantle, subduction-linked downwelling occurs at speeds of <~1.3 mm/yr, which is the origin of the long-known ~1.7Ga ‘isochrons’ seen in both hotspot and mid-ocean ridge volcanism.  This ~3000 km-wide great-circle ring of slow downward flow is associated with two antipodal axial spokes of twice-as-fast but still very slow largescale upward flow in the ‘LLSVP’ regions. In addition to this background pattern of large-scale lower mantle circulation, upward counterflow to plate subduction preferentially takes material from a warmer D’’ thermal boundary layer at the core-mantle boundary through ~10-20 mantle plumes that feed a sublithospheric plume-fed asthenosphere. In the lower mantle, the relatively warmer and lower viscosity plumes preferentially rise through and are slowly attracted towards the LLSVP regions by the low-order mode of slow lower mantle flow, with plume-conduits further warming their surrounding LLSVP lower mantle.

In this contribution we review the seismological and geochemical observations that support this scenario of two interlocking modes of whole mantle convection with very slow flow in the lower mantle that is linked to and pierced by much faster flow in a D’’-plume-asthenosphere upward flow circuit. We then present 3-D thermomechanical models designed to elucidate under what conditions this mode of flow can arise from a highly variable viscosity mantle with both internal heating and significant heatflow across the core-mantle boundary. Finally we briefly touch on some further implications of this scenario for Earth’s radial mantle structure, supercontinent evolution, the geoid, and the geodynamo.

How to cite: Morgan, J. P., Shi, Y.-N., and Vannucchi, P.: Whole Mantle Convection with Two Structures and Timescales of Flow, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14852, https://doi.org/10.5194/egusphere-egu23-14852, 2023.

Over geological timescales, aside from isostatic processes arising from crustal thickness variations, flow within the mantle has long been recognised to generate a significant component of Earth's topography, i.e. "dynamic topography". Therefore, geological and geophysical evidence of Earth's surface deflection can provide spatio-temporal evidence of deep Earth processes, if tectonic/crustal processes are accounted for. Mantle convection models can be used to calculate past and present dynamic topography in a number of ways, with the aim of matching surface observations to improve our understanding of mantle properties and flow characteristics. We analyse the global spatio-temporal patterns of dynamic topography predicted by a suite of models run using the TERRA code, which solves the Stokes and energy equations for mantle flow within a spherical shell. Both compressible/incompressible models are analysed, for a range of mantle viscosity structures. We calculate dynamic topography using two widely-used methods, focussing on the present-day where the pattern of dynamic topography is constrained in greatest detail. First, we examine dynamic topography using instantaneous surface stress calculated from full-resolution 3-D TERRA output. Secondly, model output is transformed into the spherical harmonic domain, and density anomalies at depth are propagated to surface stress variations, and therefore topographic deflections, using analytic sensitivity kernels i.e. the propagator matrix method. Each method makes subtly different assumptions about boundary conditions and mantle structure and properties. We demonstrate that uplift predictions calculated using each method can be compared with observational estimates derived from palaeobiological data, oceanic residual depth measurements, and continental gravity anomalies. We highlight key similarities and differences between dynamic topographic predictions from each method across a suite of mantle convection models, and identify correlation/misfit with observational constraints.

How to cite: O'Malley, C., Roberts, G., Panton, J., Davies, H., and Milanez Fernandes, V.: Testing Dynamic Topographic Predictions of Mantle Convection Models Using Global Palaeobiological Datasets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15266, https://doi.org/10.5194/egusphere-egu23-15266, 2023.

How to cite: Ortega-Gelabert, O., Fullea, J., Arnaiz-Rodríguez, M. S., and Zlotnik, S.: Dynamic topography and satellite gravity data joint inversion using Reduced Order Models (DYGIRO), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15494, https://doi.org/10.5194/egusphere-egu23-15494, 2023.

The interaction of mantle plumes with continental or cratonic lithosphere can result in (large-scale) volcanism and continental breakup, but these consequences seem to be limited to tectonic settings with pre-existing weak zones. In contrast, most parts of continental plume tracks, or their hypothesized tracks, show no extrusive magmatism. To reconcile this, our previous work has shown that even in the absence of melt, sustained plume-lithosphere interaction leads to lithospheric thinning, followed by elevated surface heat flux about 40-140 million years after the thermal anomaly in the mantle disappears. Therefore, melt-free continental plume tracks can be initially identified by a reduced lithosphere thickness, and later by an increased surface heat flux that temporally and spatially follows the thinned lithosphere.

Yet, even if melt is not erupted, variable amounts of melt may still be generated at the base of the lithosphere above the plume, and this melt can impact local dynamics. In order to assess the role of melt in plume-lithosphere interactions, we have developed a recent suite of numerical models of mantle convection that include melting/freezing and melt migration. Our results indicate a much stronger time-dependence of models with melt compared to models without melt. In particular, small-scale convection at the base of the lithosphere becomes more vigorous, which leads to patterns that feature more localized and larger amplitude lithospheric removal and stronger asymmetry across the plume track. The generation of melt in a thinned area has a self-enhancing effect; more melt thins the lithosphere faster, resulting in more melt generation. However, the effect of thinning for a moving plate is limited, both with respect to the affected area and the time during which this local thinning can be sustained. As a result, the surface heat flux pattern, which is a long-pass filtered image of the lithosphere thinning, does not change significantly compared to a case without melt. However, melt migration brings heat closer to the surface, which increases the amplitude of the heat flux anomaly, and reduces the delay time following lithosphere thinning. The amplification of local dynamics by melt migration is especially pronounced if the plume interacts with pre-existing topography of the lithosphere-asthenosphere boundary (LAB), e.g. steps in lithospheric thickness. Depending on the LAB topography, multiple events of melt generations and magmatic intrusion can be generated by a single plume over tens of millions of years . Such a scenario may explain the pulse-like prolonged activity of the High Arctic Large Igneous Province (HALIP; which erupted between 130-85 Ma) and potentially an early phase of an Iceland plume track under Greenland (pre-62 Ma).

How to cite: Heyn, B. H., Shephard, G. E., and Conrad, C. P.: Amplification of sub-lithospheric dynamics by melt migration during plume-lithosphere interaction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15545, https://doi.org/10.5194/egusphere-egu23-15545, 2023.

Geological maps are essential products of geological work that display the results of generations of field geologists’ work. Most original geological maps are generated and utilized at local scales. At regional scales, geological maps have gained practical significance ever since William Smith’s 1815 geological map of England exemplified the robust nature of mapping and correlating strata beyond local scales. However, by comparison, geological maps compiled at continental scales appear to be of limited use outside of geological circles. They are often oversized, inhibiting their practical use, so they decorate our geoscience hallways and lecture halls with their beautiful colors and general esthetic appearance. Few outsiders can even read these maps. Their unique color-coding, the multiple non-diverging color schemes, and their complex legends further inhibit non-geologists from being able to recognize the enormous knowledge stored in these maps. I present an analysis of continent-scale geological maps by visualizing time not represented by the rock record (hiatus) and examining the dimensions of hiatal surfaces at interregional scales. The maps yield significant variability in sizes and space-time patterns of hiatal surfaces, a behavior expected in light of interregional-scale processes induced by both the plate and the plume mode of mantle convection. However, to rigorously test models of mantle convection, the temporal resolution of continent-scale maps must be increased to stages level, i.e., the temporal scale at which tectonic processes occur. In addition, synthesis of geological data on continent-scales requires the development and application of event-based stratigraphic-framework mapping.

How to cite: Friedrich, A. M.: Analyzing geological maps at the continental scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15705, https://doi.org/10.5194/egusphere-egu23-15705, 2023.

Estimates of global mean sea level (GMSL) during past warm periods provide a key constraint on ice-sheet sensitivity to future climate change and inform projections of long-term sea-level rise. Measurements from the most recent periods of enhanced warmth are especially valuable since these intervals represent the closest climatic analogues to near-future conditions. Considerable focus has therefore been placed on reconstructing sea-level during the Mid-Pliocene Warm Period (MPWP; 3.3–3.0 Ma) and the Last Interglacial (~129–116 ka), periods characterised by mean temperatures 2­–3 °C and ~1 °C above preindustrial levels, respectively. Many GMSL estimates have been obtained from palaeoshoreline deposits since these geomorphic proxies provide a more direct and potentially more precise constraint on past sea-level than stable isotope records. However, estimates from different sites differ by several metres due to spatially variable vertical crustal motions caused by geodynamic processes, including glacial isostatic adjustment and dynamic topography.

To tackle this issue, we integrate a suite of Australian sea-level markers and geodynamic simulations into a probabilistic inverse framework to quantify and remove the effect of vertical crustal motions at a continental scale. We find that dynamic topography accounts for most of the observed MPWP sea-level marker deflection and is also significant for the LIG. After correcting for this process and glacial isostatic adjustment, we obtain a revised MPWP GMSL estimate of +16.0/10.4–21.5 m (50^th/16^th–84^th percentiles). We also find that post-LIG dynamic topography may account for several metres of relative displacement across the Great Barrier Reef, potentially reconciling discrepant GMSL estimates from this region. Recalibration of sea-level projections with these revised estimates suggests a more stable Antarctic Ice Sheet under future warming scenarios and appears to rule out recent high-end forecasts.

How to cite: Richards, F., Coulson, S., Hoggard, M., Austermann, J., Dyer, B., and Mitrovica, J.: Can Correcting for Mantle Dynamics Reconcile Divergent Plio-Pleistocene Sea-Level Estimates?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16368, https://doi.org/10.5194/egusphere-egu23-16368, 2023.

Feedbacks between climatic and geological processes are highly controversial
and testing them is a key challenge in Earth sciences. The Great Escarpment of
the Arabian Red Sea margin has several features that make it a useful natural
laboratory for studying the effect of surface processes on deep Earth. These
include strong orographic rainfall, convex channel profiles versus concave
swath profiles on the west side of the divide, morphological disequilibrium in
fluvial channels, and systematic morphological changes from north to south
that relate to depth changes of the central Red Sea. Here we show that these
features are well interpreted with a cycle that initiated with the onset of
spreading in the Red Sea and involves feedbacks between orographic precipitation,
tectonic deformation, mid-ocean spreading and coastal magmatism.
It appears that the feedback is enhanced by the moist easterly trade
winds that initiated largely contemporaneously with sea floor spreading in the
Red Sea.

How to cite: Stüwe, K., Robl, J., Turab, S., Sternai, P., and Stuart, F.: Feedbacks between sea-floor spreading,trade winds and precipitation in the Southern Red Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16771, https://doi.org/10.5194/egusphere-egu23-16771, 2023.

For a thorough understanding of the impact of mantle convection on vertical motions of the lithosphere, computational modeling plays a crucial role. Mantle circulation can be modeled by solving the equations of motion of a fluid using Earth-like input parameters assimilating plate motions at the surface in discrete steps through time. Thus, a realistic Earth model relies on the robustness of the inserted information. However, apart from the general difficulty of inferring deep Earth’s properties, also the plate tectonic model introduces uncertainty. Especially the linking of relative plate motions to absolute position relies on controversial assumptions such as fixity of structures in the mantle (e.g., plumes or Large-Low-Shear-Velocity Provinces) or the association between subducted plates at depth and high velocity regions in tomographic images. The latter specifically are restricted by non-uniqueness and the need to regularize the inversions, distorting structures and damping heterogeneity amplitudes.

In order to infer secondary results from an MCM, it is thus important to validate the model against independent observations. Here, we employ Earth’s free oscillations that feature global sensitivity to 3-D structure for model assessment, complementing our earlier work using seismic body wave data. To this end, the temperature field of a published MCM is converted to seismic velocity with the help of a thermodynamic model of mantle mineralogy. An effective forward approach for the computation of normal mode data from synthetic Earth models is the calculation of splitting functions, describing the distortion of characteristic frequency peaks in the spectrum induced by even degree structural heterogeneity. A general problem is that the sensitivity of normal modes with depth often shows oscillatory behaviour preventing a straight forward relation of frequency shifts to structure in a certain depth range. This can be mitigated by combining kernels of several modes via a Backus-Gilbert approach to obtain focused sensitivity in pre-specified depth ranges of the mantle. For testing the significance of relevant model differences in splitting function data, geometrical alterations mimicking changes in the absolute reference frame and viscosity were applied to a pre-computed MCM. Current results indeed indicate that normal mode data are sensitive to such model changes within their respective uncertainty ranges.

How to cite: Schneider, A., Schuberth, B., Koelemeijer, P., Restelli, F., and Zaroli, C.: Using Earth’s free oscillations to assess mantle circulation models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17312, https://doi.org/10.5194/egusphere-egu23-17312, 2023.

Convection in the mantle provides the primary forces that shape the long wavelength structure of the Earth's surface
through dynamic topography. These forces have long been known as the cause of key events in the Cenozoic era: the
termination of large-scale marine inundation in North America in the Palaeocene, the late Tertiary rise of Africa
relative to other continents and the long-wavelength tilting of Australia since the late Cretaceous. It is an
overarching goal in geodynamics to construct reliable models that can retrodict (make predictions about the past)
these key events correctly. This year marks the 20th anniversary since the introduction of adjoint modelling as a
powerful method to retrodict mantle flow. Using the adjoint method, various datasets are assimilated to optimize
dynamic earth models by deriving the necessary gradient information. Here we explore a suite of eight high-resolution
(about 670 million finite elements), compressible, global mantle flow retrodictions going back to 50 Ma. Our
retrodictions involve the dynamic effects from an upper mantle low-viscosity zone, assimilate a past plate-motion
model for the tangential surface velocity field, probe the influence of two different present-day mantle state
estimates derived from seismic tomography, and acknowledge the rheological uncertainties of dynamic Earth models
by taking in four different realizations for the radial mantle viscosity profile, two of which were published
previously. The retrodictions show for the first time that key Cenozoic events emerge jointly as part of global
Cenozoic mantle flow histories. We show that the retrodicted mantle flow histories are sensitive to the present-day
mantle state estimate and the rheological properties of the Earth model, meaning that this input information is
testable with inferences gleaned from the geological record. Retrodictions allow one to track material back in
time from any given sampling location, making them potentially useful, for example, to geochemical studies. Our
results call for improved estimates of non-isostatic vertical motion of the Earth’s surface — provided, for
instance, by basin analysis, seismic stratigraphy, landform studies, thermochronological data or the sedimentation
record — to constrain the recent mantle flow history and suggest that mantle flow retrodictions may yield synergies
across different Earth science disciplines.

How to cite: Ghelichkhan, S., Bunge, H.-P., and Oeser, J.: Retrodicting flow of the early Cenozoic mantle: perspectives from an adjoint modelling approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17452, https://doi.org/10.5194/egusphere-egu23-17452, 2023.

Minerals from leucite lamproites of the Murunsky alkaline massif (Vladykin, 2000; 2005; Vladykin, 2009) were analyzed by electron microscopy in the sections of 700 grains of minerals (IGM SB RAS) and LA ICP MS (IIC SB RAS) - 40 grains. Pyroxenes, amphiboles, various micas including varieties of the Ba type, leucites and nephelines, Ba and K feldspars, eudialyte, barite, stroztianite, ilmenites, Cr- spinelides, Ti magnetites, apatites, tourmaline, and various carbonates and sulfides: pyrrhotite, petlandite, chalcopyrite, murunite, smithsonite, galena.

Pyroxenes are divided into 3 groups from diopsides to augites and aegirines, revealing a continuous series of compositions according to MgO (Fig. 1). Amphiboles K-richterites and arfversonites, and Ca-Fe ackermanites. Complete ranges from phlogopites to biotites have been established among micas. The proportion of Ba micas is significant. In the diagram  genetic digram (Minchell, 1995 )(Fig. 2) falls into the field of ailikites or orangeites,  and lamproites. Leucites and nephelines occurs  friquiently. Numerous apatites are characterized by Ca-Sr substitution and noticeable F contents (to 3%). K-type eudialytes and a mineral close to priderite were found.

In the TRE diagrams (Fig.3), pyroxenes are characterized by La-enriched ~200-250 weakly inclined spectra of La/Ybn (2-3) that spread out in the HREE wing. Amphiboles of the K-Na-Ca are characterized show inclined spectra with Ho-Tm depression,  LILE peaks elevated Zr, Hf, Y and Ta-Nb minima. The more alkaline amphiboles are characterized by reduced REE concentrations, more  elevated Zr-Hf. Ultra-alkaline amphiboles (richterite and arfvedsonite) have higher REE contentswith characteristic U-shaped spectra, very high LILE contents high peaks of Sr, Zr, Hf. Phlogopites have oblique U-shaped spectra with a sharp peak Eu interference Ti. Very high LILE with a peak at Va, Sr, Y, Pb are typical.

Low REE and especially LREE with a peak of Eu are characteristic of leucites. U, Sr, Pb peaks are also characteristic, and HFSE vary. The REE spectra of K-Ba feldspars are similar to those of phlogopite. High peaks of LILE, Sr, Pb, Y are expressed on spiderdiagrams

Judging by the peculiarities of mineral trends, lamproites are the result of low degrees melting  under the influence of plume melts of a mantle deeply metasomatized by subduction processes. Pyroxenes are end–to-end minerals, at an early stage their compositions were controlled by fractionation of olivine and then saturated SiO2 silicates. Further fractionation led to enrichment with rare elements P, Sr, F. In amphiboles, the growth of REE was accompanied by the accumulation of Zr, Hf, while Nb, Ta were removed during the deposition of T-magnetite. Grant RBRF 19-05-00788.

How to cite: Ashchepkov, I., Vladykin, N., Sotnikova, I., Medvedev, N., Karmanov, N., and Alymova, N.: Mineralogical and geochemical characteristics of lamproite minerals of the Murunsky massif., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3560, https://doi.org/10.5194/egusphere-egu23-3560, 2023.

Kimberlitic xenocrysts: garnets, pyroxenes, ilmenites, spinels from Anabar region were analyzed by EPMA and LAICPMS.

Reconstructed mantle sections of t Anabar region published (Ashchepkov et al., 2001; 2016; 2019; 2022 show in general, the relative rarity of sub-Ca pyropes  in lower part of the section and the frequency of wehrlite associations in the upper part. Pyroxenite -eclogite lens from 3 to 5 GPa is widely represented in most sections. Ilmenite trends are not long. In several pipes amphiboles from Cr-hornblendes to Cr-richterites were detected.

In the Anabar region (Khardakh and Staro-Rechensky fiedls) The REE patterns of  garnets are characterized by high variations in the spectra, with elevated LREE and HFSE minima, peaks of U, Pb, associated with subduction fluid flows. Pyroxenes are characterized by inclined REE spectra of La/Ybn ~15 to 20 and with varying HREE with subduction-related Ba, U, Pb peaks. But pyroxenes with plume related spectrums of with smooth spider diagrams (SD) are often found in pyroxenite lens.

Garnets from the Kuranakh field (Malokuonamskaya, Losi, Trudovaya, Universitetskaya etc) are divided into dunite-garburgite with low REE and LREE enrichment and wehrlite with convex REE maximum Gd, Eu and high concentrations of HREE often enriched in Th , U varying Ta-Nb and always low Zr-Hf.  Clinopyroxenes from the Malokuonamskaya pipe often have a local minimum of HREE and variations in the slope and enrichment of the REE spectra. On the CD, the peaks of Ba are varying, they show Ta, Nb enrichment and minima in Zr-Hf.

The garnets from the Universitetskaya pipe are mainly lherzolite-harzburgite with signs of subduction genesis (U peaks), and wide variations of HFSE sometime with Zr–Hf enrichment, due aqueous metasomatism. Clinopyroxenes are generally more diverse in REE spectra, Nb peaks with wide variations of Ba, Th-U and HFSE are common on CD

The Losi dike has a high content of perovskites, with highly enriched spectra with a slope with a decrease in highly charged and Pb and ilmenites with high and inclined REE spectra due to fractionation of proto-kimberlite (essentially carbonatite) melt. The eclogitic minerals with Eu anomalies and peaks of U, Ba and low HFSE are common.

In most mantle sections, ancient subduction sings are recorded in pyrope garnets, an partially adakite metasomatism in pyroxenes. Later they were modified by the action of plume carbonatite melts. The middle pyroxenite-eclogite lens originated as the boundary of the crust in ancient Archaic times. The upper wehrlitic part of the section arose during the melting of the pyroxene lens in the middle part and the migration of melts to the upper part. Protokimberlite metasomatism is not very pronounced. No signs of the supposed delamination of the lithosphere (Griffin et al, 2005) were found in the sections, which was also proved by Opx-Gar thermobarometry under the Duken field (Ashchepkov, 2003). The lower part of the section is depleted  so garnet and pyroxenes are rare and reflect low-temperature geotherm.

Grant RBRF 19-05-00788.

How to cite: Kostrovitsky, S., Ashchepkov, I., Medvedev, N., Karmanov, N., and Alymova, N.: Mineralogy and geochemistry of the kimberlite xenocrysts from the Anabar region, Yakutia, Russia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3860, https://doi.org/10.5194/egusphere-egu23-3860, 2023.

The fate of crust-derived melts at warm subduction zones and the transport mechanism of crustal components to the supra-subduction mantle is still matter of debate. Borgo outcrop of Monte Duria Area (Adula-Cima Lunga unit, Central Alps, Italy) is an excellent case study of melt-peridotite interaction occurred under a deformation regime at high pressure, that enabled the combination of porous and focused flow of eclogite-derived melts into garnet peridotites. Migmatised eclogites are in direct contact with retrogressed garnet peridotites and experienced a common high pressure (2.8 GPa - 750 °C) and post-peak (0.8–1.0 GPa - 850 °C) static equilibration. The contact is marked by a tremolitite layer, also occurring as boudins parallel to the garnet layering in the peridotites, derived from a garnet websterite precursor after the interaction between eclogitic melts and peridotites at high pressure. LREE concentrations of retrogressed websterites along a 120 m length profile starting from the eclogite-peridotite contact to the inner part of the peridotite, show a progressive enrichment coupled with a peculiar fractionation. Numerical modelling assuming the eclogitic leucosome as the starting percolating melt reproduces the REE enrichment and LREE-HREE fractionation observed in retrogressed websterites bulks within the first 30 m by two steps of melt-peridotite reaction: a high peridotite assimilation at eclogite-peridotite boundary, followed by reactive melt percolation within the peridotite assuming variable amounts of olivine assimilation and pyroxene + amphibole/phlogopite crystallisation. The numerical simulation aims to model the effect of interaction between crust-derived melts produced by partial melting of mafic slab component with suprasubduction mantle peridotites at sub-arc depths. The comparison between the REE composition of the retrogressed garnet websterites along the profile and the result of our model suggests that reactive melt infiltration at HP is a plausible mechanism to modify the REE budged of mantle peridotites that lie on top of the subducting crustal slab, which show peculiar LREE “spoon-like” fractionations. Moreover, the melt/peridotite interaction and the percolation of slab-derived melts into the overlying mantle may strongly modify the overall REE abundance and LREE/HREE fractionation (e.g., Ce_N/Yb_N) of the residual crustal melt within the first 30 m of slab/mantle interface.

How to cite: Malaspina, N., Borghini, G., Zanchetta, S., and Tumiati, S.: Geochemical interaction between slab-derived melts and mantle at high pressure in subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6727, https://doi.org/10.5194/egusphere-egu23-6727, 2023.

The North China Craton (NCC) has been affected by the subduction and roll-back of the Paleo-Pacific Plate in the Mesozoic. To study the thinning of the lithosphere and the melting of the NCC, a three-dimensional (3-D) resistivity model of the lithosphere is obtained from a magnetotelluric sounding (MT) deployed in the NCC (Figure 1). In addition, the cause of the low resistivity of the upper mantle of the NCC can be solved by the Nernst-Einstein Equation and the Arrhenius Equation which is used to establish the relationship between the resistivity and temperature. Moreover, the Hashin-Shtrikman (HS) boundary conditions limit the range of electrical conductivity of mixed minerals (Figure 2). Based on the 3D resistivity structure, the temperature and melt fraction model, the lithospheric resistivity of the north of 37.5°N in the Ordos Block (OB), the southern Taihang Uplift (THU) and the Luxi Uplift (LXU) are as low as 1 Ωm which the upper mantle temperature is in the range of 1400 - 1550 °C, and the melt fraction is 1-10% in the high-temperature regions. According to the resistivity model and the thermal state, the westward subduction and roll-back of the Paleo-Pacific Plate provided conditions for upper mantle melting in the LXU and the Bohai Bay Basin (BBB). It also made the Tanlu Fault Zone (TLFZ) and THU channels for the upwelling, and the front of the Paleo-Pacific Plate stagnant slab is blowing the THU. With the remote tectonic stress of the Paleo-Pacific Plate and the Indian Plate, anticlockwise rotation of the OB induced the low resistivity of grabens and rifts around the OB (Figure 3). Moreover, upper mantle volatiles (H₂O and CO₂) and slight carbonatite melts significantly lower the mantle melting temperature.

* This work was supported by National Natural Science Foundation of China (Grants 41974112 and 40434010) and project SINOPROBE on sub-project SINOPROBE-01.

Reference:

Dong, S..T. Li. (2009). SinoProbe: the exploration of the deep interior beneath the Chinese continent. Acta Geologica Sinica, 83(7), 895-909.

Hirschmann, M. M. (2010). Partial melt in the oceanic low velocity zone. Physics of the Earth and Planetary Interiors, 179(1), 60-71.

Zhao, G..M. Zhai. (2013). Lithotectonic elements of Precambrian basement in the North China Craton: Review and tectonic implications. Gondwana Research, 23(4), 1207-1240.

Figure 1 Simplified s tectonic map of the North China Craton (modified from Zhao and Zhai (2013)); Map of MT profiles and sites, in which blue dots represent MT stations in this study, supported by the “SINOPROBE” project (Dong and Li, 2009). TNCO: Trans-North China Orogen 

Figure 2 Schematic diagram of dynamic changes of water and carbon dioxide during heating and melting of upper mantle minerals. NAMs means nominally anhydrous minerals; the “Calculate” in the dashed box is the calculation category of this study; the criterion for determining the interconnection of melts was proposed by Hirschmann (2010).

Figure 3 Schematic diagram of the possible formation mechanisms of the North China Craton inferred from the crustal and upper mantle 3-D resistivity model derived from this research.

How to cite: Li, B. and Ye*, G.: Three-dimensional Lithospheric Resistivity Structure and Thermal State of the North China Craton, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6901, https://doi.org/10.5194/egusphere-egu23-6901, 2023.

In the subcratonic lithospheric mantle (SCLM) beneath Leningrad pipe (West Ukukit field), Yakutia garnet thermobarometry allows us to identify seven horizons (paleo subduction slab). Microprobe data for Cr-bearing amphiboles >500 grains from mantle xenoliths and concentrates reveal a broad range of compositions changing from Cr- pargasitic hornblendes to pargasites, edinites, kataforites, К-richterites with increasing pressure determined with new amphibole thermobarometer.  The low pressure (LP) Cr-hornblendes and pargasites compiles the high-temperature branch (90-60 mw/m2) from 3.5 GPa to Moho traced by basaltic cumulates. In the middle part of SCLM edinites mark 35 to 40 mw/m2 geotherms. In the middle part of SCLM edinites mark 35 to 40 mw/m2 geotherms. At high pressures kataforites also vary in thermal conditions. Richterites near the lithosphere base trace both low –and high temperature convective branches.

 Age samples of aillikites estimated by 40Ar/39Ar age using the method described in detail by A. Travin et al. [40]. Quartz ampoules with samples were irradiated in the Cd-coated channel of a reactor (BBP-K type) at the Tomsk Polytechnic Institute. The gradient of the neutron flux did not exceed 0.5% of the sample size. Step-heating experiments were carried out in a quartz reactor with an external heater. The blank for 40Ar (10 min at 1200°C) was not higher than 5×10–10 cm3. Ar was purified using Ti and ZrAl SAES getters. The isotopic composition of Ar was measured on a Micromass Noble Gas 5400 mass spectrometer (analyst Yudin D.S.). The results of the dating of the phlogopite grains and amphiboles occurred in the intergroup with the Phl are shown the (Figure 1). The phlogopie from the spinel lherzolite 2665 Ma corresponding to the final stge of the craton formation. Similar age was determined for the Phl from Udachnaya. The age of the intergrowth of the Amph-Phl from the sample Ol-151 is splitting. The high temperature part with the age 1368Ma may be reffered to the global activization of the plume and accretion magmatism activity found in many World regions [42] including Siberia. The more yanger plateo is close to the 380-400 Ma which is just corresponds to the Devonian plume magmatism? And the small plateau ~210 Ma refer to Triassic The . As well in the sample Ol-112 the older one 370 Ma plateo just give Devonian age. And one of the younger 160 Ma corresponds to the Jurassic stage of kimberlite volcanism.

Presence of the Phl with the 2.6 Ga referring to the major event of the crust generaion corresponding to the beginning of mertasomatic H2O bearing metasomatic processes recorded in the mantle xenoliths in the World proves the common model of the appearance of water in the mantle  at the last stages of the continental growth, The other two peaks  400 -380 Ma and 160 Ma may be referred to the plume kimberlite magmatism and even to the protokimberlite stage (latest one). 

RBRF grant 19-05-00788

How to cite: Iudin, D., Ashchepkov, I., Babushkina, S., Oleinikov, O., and Medvedev, N.: Ancient mantle metasomatism in West Ykukite field Northern Yakutia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8651, https://doi.org/10.5194/egusphere-egu23-8651, 2023.

The small plutons of anorthosite and associated gabbronorite exposed near Barabar hills form a component of Chotanagpur granite gneiss complex (CGGC) in eastern India. Plagioclase (>90 vol %) make up the majority of anorthosite rock with minor mafic minerals (amphibole, mica), while orthopyroxene (>40 vol %), plagioclase (40-50 vol %) and clinopyroxene (>20 vol %) make up the associated gabbronorite. These are cumulate rocks with anorthosite and gabbronorite showing adcumulate and mesocumulate textures, respectively. Compositionally, plagioclase ranges from anorthite to labradorite (An_60-96) in anorthosite and from oligoclase to bytownite (An₅₀-₇₀) in gabbronorite. In gabbronorite, the clinopyroxene composition ranges from diopside to augite (En_36-43 Fs_12-15 Wo_43-47), and the orthopyroxenes are hypersthene (Wo_39-40 En_46-50 Fe_10–21).

Anorthosite show enrichment of LILE (Rb, Ba, Sr, Th, Pb) with respect to the HFSE (Zr, Ti, Nb and display enrichment in LREE ((La/Yb) _N = 2.78-15.29) with positive Eu anomaly (Eu/Eu* = 1.29-3.45) and variable MREE. A flat to depleted trend for HREE ((Sm/Yb) _N = 1.02-2.95) is observed for anorthosites. Associated gabbronorites show enrichment of LREE ((La/Yb) _N=1.99-4.93), depleted HREE ((Sm/Yb) _N = 0.88-3.24) with negative to positive Eu anomaly (Eu/Eu* = 0.78-2.95). Also, the gabbronorite shows enrichment of LILE (Rb, Ba, Sr, Th, Pb) compared to HFSE (Zr, Ti, Nb). Clinopyroxenes of gabbronorite have low REE abundances (53.29-60.29 ppm). Clinopyroxenes are depleted in light rare earth elements (LREEs) (La/Yb) _N = 0.75–0.80 and depleted in LILEs such as Ba, Sr. and also exhibit negative anomalies in Zr and Ti.

REE composition of gabbronorite clinopyroxene is constrained between TMF = 15-30% calculated using the equilibrium distribution method (EDM). This is substantiated by whole rock parental melt REE composition calculated using the concentration ratio approach (Nernst equation), the result of which is consistent with those made using EDM. In chondrite normalized plot, the estimated parental melt display (1) near-horizontal trend from Lu to Gd at rock/chondrite = ~100, (2) negative anomaly at Eu, (3) gradual rise from Sm to Ce and (4) slight dip from Ce to La.

How to cite: Negi, P., Belousov, I., Danyushevsky, L. V., Saikia, A., and Ahmad, M.: Anorthosite and associated gabbronorite plutons of Barabar hills in Chotanagpur granite gneiss complex (CGGC), eastern India: Estimation of parental melt for gabbronorite using equilibrium distribution method (EDM), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10859, https://doi.org/10.5194/egusphere-egu23-10859, 2023.

The suggested olivin thermometry for mantle peridotite and zenolith (Hoog et al., 2010, Bussweller et al., 2017) allow correct estimation of the temperatures using high precision data obtained by LA ICP MA or even EPMA inn hjigh resolution. IN this version we tried to obtain the pressure eestimates using the inversion of the Ol thermometer to barometer. And also we substituted the CaO by MnO withe essential correction. In this variant  I received the pair of the Ol thermometer and Mn - in - olivine barometer which allow to work not only with the high resolution data but with the routine analyses and obtain not bad estimates for the see of data for the Udachnaya, Zarnotsa, Aykhal and other pipes (Ashchepkov et al., 2010-2021) and even fo the diamond inclusions (Ashchepkov et al., 2021-2023). RBRF grant 19-05-007888

How to cite: Ashchepkov, I.: New formulation of the olivine thermobarometer for mantle xenoliths, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12275, https://doi.org/10.5194/egusphere-egu23-12275, 2023.

The study of mantle xenoliths from kimberlite pipes allows to establish the composition, evolution processes and thermal condition of the lithospheric mantle under ancient cratons. The Mirny kimberlite field belongs to the diamond-bearing kimberlite fields in the center of the Siberian craton. The collection of mantle xenoliths from the Mir pipe (57 samples) was investigated by authors. Four main petrographic groups were identified: peridotites (Grt lherzolites), Grt websterites, Grt clinopyroxenites and eclogites. The pyroxenite xenoliths attract the special attention.   

Garnets from lherzolites and websterites are also characterized by a relatively high Mg# content (75–83) and low TiO₂ contents (up to 0.2 wt %). Eclogites are characterized by high-calcium (3.78 - 9.46 wt.%) and high-iron (7.77 - 17.20 wt.%) composition of garnet getting into the ​​wehrlite paragenesis area. Thus, the lithospheric mantle under the Mirny kimberlite field differs from the lithospheric mantle under other diamondiferous fields (for example, Udachnaya kimberlite pipe). The Mirny mantle xenoliths are characterized by the pyroxenites widespread development (up to 50%), the low-Ti composition and deformed lherzolites absence.

In addition, websterites and lherzolites show a wide range of crystallization parameters (600 - 1200°C; 2 - 6 GPa) probably due to their gradual cooling after magmatic crystallization and the exsolution structures formation. Clinopyroxenites are characterized by narrow variations in the P-T crystallization parameters (812 - 960°C; 3-4 GPa) indicated their later crystallization from asthenospheric melts. Eclogites are characterized by relatively low calculated temperature parameters (720–840°C; 2.2–3.7 GPa) confirming their origin in subduction zones at shallow depths. The sporadic calculated values for websterites and clinopyroxenites are locating within the diamond stability area. The use of the Opx - thermobarometer (in samples founding Opx) revealed 2 trends in the crystallization of orthopyroxene. Crystallization of individual Opx grains in websterites occurred earlier than Cpx with higher P-T parameters - higher by ~100С and ~0.5 Ha. The second trend (pressure reduction with a slight decrease in temperature) notes the formation of Opx decay structures in an initially homogeneous crystal of monoclinic pyroxene. Minerals from pyroxenites demonstrate a wide development of melting processes in the lithospheric mantle in the south of the Siberian craton Craton and the formation of megacrystalline pyroxene cumulates. The origin of eclogites is assumed from subducted oceanic crust marking the subduction component in the process of formation of the lithospheric mantle.

The research was supported by Russian Science Foundation grant № 22-77-10073.

How to cite: Kalashnikova, T. and Kostrovitsky, S.: The metasomatic processes and thermal condition of lithosphere mantle under the center of Siberian craton: evidences of pyroxenite xenoliths from Mir kimberlite pipe , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12888, https://doi.org/10.5194/egusphere-egu23-12888, 2023.

The Belo-Ziminsky alkaline-ultrabasic carbonatite massif contain dolomite, and calcite ankerite carbonatites essential part , syenites, melteigites and iolites cut by aillikite dikes of several generations (Ashchepkov et al., 2020; Doroshkevich et al., 2014-2021 etc). We analyzed  >4000 mineral grains by electron microscope in all types of rocks and >230 grains by  LA ICP MA  All rocks of the massif are derived from one type of mantle melt that was close to aillikite and formed at a level of >5 GPa in the mantle.

According to the nature of the PGE spectra –  and by serpentinized xenoliths in aillikites, this melt drained metasomatized enriched peorvskites and hydrogenated mantle and was initially very rich in HFSE. Above, at the level of the crust and the upper part of the mantle, the melt began to separate under liquation. In the lower and middle crust, several (3) magmatic chambers were probably formed sequentially, which separated various carbonate and silicate melts, and from dolomite to ankerite melts, judging by the slope, the number of grains in the source decreased, that is, the melts became less deep and more fractionated.

These trends are reflected both in the composition of pyroxenes from aillikites  and in the PTX diagram . All this led to significant variations in rocks and their rare-earth spectra of all rocks

How to cite: Zhmodik, S., Ashchepkov, I., Kiseleva, O., Belyanin, D., Sotnikova, I., Medvedev, N., and Karmanov, N.: Tracing of evolution of carbonatite and silicate melts of the Belo-Ziminsky alkaline-ultrabasic carbonatite massif by mineralogy and geochemistry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16857, https://doi.org/10.5194/egusphere-egu23-16857, 2023.

The chemical differentiation of mantle-derived magmas in subduction zones during the generation, transport, and emplacement has always been a concern, which is closely related to the petrogenesis of calc-alkaline granitoids. A systematic study of petrography, mineralogy, and geochemistry is conducted on typical arc granitoids and associated mafic microgranular enclaves (MME) from the Chinese Altai, Central Asian Orogenic Belt. Magma hybridization modeling using major and trace element compositions suggests that the parental magma of granitoids is a mixture of a mafic and a felsic endmember. The sharp decrease of plagioclase An values from cores to rims (e.g., from ca. 80 to 40) implies polybaric crystallization of water-saturated magmas accompanied by degassing. Petrographic evidence and plagioclase in situ Sr isotopic compositions ((⁸⁷Sr/⁸⁶Sr)i = 0.7053–0.7071) show the involvement of isotopically different magmas during the mineral crystallization. The positive zircon εHf(t) values of MME (+2.3 to +5.4) and granitoids (+0.6 to +4.6) further show that the mafic melts are mantle-derived, while felsic melts should originate from juvenile lower crust with the slightly more evolved isotopic composition. An evolution scenario of the mantle-derived mafic magma and formation of enclave-bearing calc-alkaline plutons in arc settings is demonstrated: Hydrous mantle melts rose to the deep crustal-mantle boundary, where they effectively mixed with juvenile lower crustal melts to form the hybrid parental magma of the granitoids. In the high crustal-level chambers, decompression-dominated crystallization, mingling, and limited mixing of mafic magma blobs and enclosing granitic melts ultimately determined the rock texture, mineral composition, and enclave morphology. This work was financially supported by Hong Kong RGC GRF (17302317), National Key R&D Program of China (2017YFC0601205), NSFC Projects (41730213, 42072264, 41902229, and 41972237).

How to cite: Cui, X., Sun, M., Zhao, G., Zhang, Y., Yao, J., and Wong, J.: Petrogenesis of the enclave-bearing granitoids from the Chinese Altai: implications for the differentiation of mantle-derived magmas and formation of calc-alkaline plutons in subduction zones, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-177, https://doi.org/10.5194/egusphere-egu23-177, 2023.

Dispersive grain pressure (Bagnold, 1954) is commonly used to explain the observed axial concentrations of phenocrysts in dykes and sills via flow differentiation (Komar, 1972). The idea was formulated for particle fractions exceeding 0.13 by volume. A dispersive pressure is proposed that is greatest near the intrusion walls, forcing crystals to move inward, towards the centre of the magmatic flow where shear strains are low. However, Barriere (1979) argued that this phenomenological ‘Bagnold effect’ should be confined only to narrow (<<100 m) wide intrusions. His reasoning was that in larger channels, the wall effect driving the dispersive pressure diminishes swiftly, nullifying the dispersive pressure. This is true where the relevant length scale of the problem scales with the ratio W/d, where W is the full channel width and d is particle diameter.

Here we show that for congested magma (0.5 > Φ > 0.8), with the rheology decomposed into scalar and vector components, particle fluctuations (in velocity) are dependent critically on the distance gap (h) between nearest neighbour that imparts a particle pressure. Thus, the critical ratio becomes d/h. It is fluctuations in the interparticle gap distance arising during shear in the flowing suspension that causes migration, irrespective of the channel width. We show that for a fixed particle size, d/h scales with crystal fraction (Φ) and the migration effect is enhanced as W/d increases.   We focus here on particle (crystal) migration as opposed to segregation or particle size sorting, although the latter are both amenable to analysis through modifications to our mathematical model.    

Flow differentiation via particle migration is likely to be just as effective in wider channels (W >> 100m) than in narrow ones, eliminating the need to invoke other fluid dynamical or thermal explanations (convection, multiple intrusion, gravitational settling) to explain the central concentration of phenocrysts in dykes and sills exceeding several metres in width.  As the (multiphase) migration effect exerts a strong control on both magma rheology and composition, flowage differentiation as a mechanism for compositional variation during magma emplacement in large intrusions is open for re-evaluation. 

References

Bagnold, RA, (1954). Experiments on gravity-free dispersion of large solid spheres in a Newtonian fluid under shear. Proc. Roy. Soc. London 225, 49-63.

Barriere, M, (1976). Flowage differentiation: limitation of the Bagnold effect to the narrow intrusions. Contrib. Min. Pet. 55, 139-145. 

Komar, P, (1972). Mechanical interactions of phenocrysts and flow differentiation of igneous dykes and sills. Geol. Soc. Amer. Bull. 83, 973-988.

How to cite: Koenders, C. and Petford, N.: Flow differentiation in dykes and sills NOT limited by intrusion width, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2116, https://doi.org/10.5194/egusphere-egu23-2116, 2023.

IC-FEMRES (Imperial College Finite Element Magma REservoir Simulator), is a finite-element based numerical code for simulating the 3D dynamic behaviour of a two-phase, multi-component magma reservoir with chemical reaction.  The code is built upon the open-source IC-FERST package (http://multifluids.github.io/) which includes advanced numerical features such as dynamic mesh optimization, to allow fine-scale solution features to be captured while simulating in a large domain.

The model solves for velocity using a finite-element approach, and for transport using a control-volume scheme to ensure the conservation of energy, mass, and components.  Solid, melt and volatile phases are modelled as Stokes fluids with very different Newtonian viscosities.  Individual crystals in the solid matrix are incompressible, but the solid phase is compressible to account for changes in melt fraction.  The formulation captures viscous compaction and convection of the solid matrix, and flow of melt and volatiles via a Darcy-type formulation at low melt fraction, and a hindered-settling type approach at high melt fraction.  It also captures heat transport by conduction and advection, and component transport by advection.  A chemical model is used to calculate phase fraction and composition.  The numerical package sequentially solves for: 1. Melt and solid velocity (mass and momentum conservation); 2. Enthalpy and component transport (energy and component conservation); 3. Phase fraction and composition (chemical model).  Material properties such as density and viscosity can be coupled to solution fields such as melt fraction and composition to yield a highly non-linear system of coupled equations that are solved iteratively.

We demonstrate here the validation of the formulation against well-constrained test cases, and example results for a magma reservoir in the continental crust obtained using a simple two-component chemical model created by fitting a binary phase diagram to experimental melting data.  Solutions show significant deviations from the predictions of 1- and 2D thermal models, or 1D models that include magma dynamics, and may explain some hitherto poorly understood aspects of magma reservoir formation, dynamics and chemical differentiation. 

How to cite: Hu, H., Salinas, P., and Jackson, M.: A 3D finite element magma reservoir simulator, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5441, https://doi.org/10.5194/egusphere-egu23-5441, 2023.

The structure of the magmatic system beneath subaerial volcanos, including the architecture and distribution of the bodies where magma is stored and the network of conduits that transport melt between these accumulations and the surface, plays a fundamental role in all aspects of volcano construction and evolution, from igneous differentiation to hazard assessment. However, due to inaccessibility, little is known about the geometry of the magma bodies residing beneath subaerial volcanos. 

Mid-ocean ridges host the most extensive magmatic system on Earth, with 98% of its length below the ocean surface, which makes them an ideal target to be scanned by controlled-source marine seismic techniques. Beneath some portions of this vast system, the shallowest magma bodies are present and represented by long-linear Axial Magma Lenses (AML). It is at these shallow-most AMLs where dikes nucleate and connect the magma accumulations to the surface to result in an eruption. To explore the magma plumbing systems at mid-ocean ridges, we use 3-D multichannel seismic data across a mid-ocean ridge environment and apply advanced marine seismic techniques to develop the highest resolution reflection images of the AMLs so far. The data were collected across a magmatically dynamic portion of the East Pacific Rise at 9°50’N with documented dike intrusion and eruptions in 1991/1992 and 2005/06.

The observations indicate that the magma reservoirs in the shallow crust are not represented by smooth bodies, but show strongly lineated topography that is spatially linked to the distribution of eruptive fissures and erupted lavas above. In the detailed topography, we find evidence for: 1) a dike root zone beneath where a caldera-like axial eruptive fissure zone is present, 2) deep excavation of this root zone within the primary eruption site for the last documented eruption, and 3) dikes rupturing from edges as well as the center of magma lenses. We also demonstrate that the distribution of additional, off-axis crustal magma accumulations further impact the stresses and melt budget at shallow-level magma accumulations leading to more frequent eruptions. Our results show that the mechanism behind eruptions along mid-ocean ridges is predominantly bottom-up and not fundamentally different from the eruptions’ mechanism at subaerial volcanoes. Considering the fine-scale morphology of shallow magma bodies will be critical for future generations of more realistic numerical models to aid in effective global volcanic hazard assessment and mitigation.

How to cite: Marjanovic, M., Carbotte, S., Stopin, A., Singh, S., Plessix, R.-É., Marjanović, M., Nedimović, M., Canales, J. P., Carton, H., Mutter, J., and Escartín, J.: Links Between Volcanic Eruptions and Magma Body Geometry Revealed by Seismic Reflection Imaging at the East Pacific Rise, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6783, https://doi.org/10.5194/egusphere-egu23-6783, 2023.

Xenocrysts in magmatic rocks are often found having gradients in their composition. These compositional gradients are commonly interpreted as the result of mass fractionation during crystal growth and it is quite common that these gradients are also influenced by intra-crystalline chemical diffusion. Since the interplay between element diffusion and crystal growth in the magma controls the final composition of magmatic minerals, it is not possible to uniquely constrain the high-temperature history of a zoned crystal. To address this problem, we present a numerical model that can be used in an inverse manner to constrain the rate of olivine growth in basaltic magma. The model addresses a classic moving boundary problem, whilst solving the intra-crystalline diffusion of Ca in olivine. Our model is created to account for the growth of a spherical olivine crystal in a finite (or infinite) reservoir. The diffusion equation is solved with a forward Euler scheme and we use a conservative, regridding approach to account for changes in crystal size. The model was tested against experimentally determined olivine growth rates. Our results show that the inferred growth rates agree within an order of magnitude to the results from experiments at fixed pressure, temperature and oxygen-fugacity conditions.

How to cite: Stroh, A., Moulas, E., and Botcharnikov, R.: Constraining the rates of olivine crystal growth with diffusion chronometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7287, https://doi.org/10.5194/egusphere-egu23-7287, 2023.

Mafic microgranular enclaves (MME) appear associated with most post-collisional batholiths around the world. Together with the mafic-intermediate (sanukitoid) and granitic suites, it constitutes one of the most common features of post-collisional magmatism. MME are considered to represent a mafic endmember with mantle affinity related to granite petrogenesis. Hence, they constitute an ideal tracer of the mantle involvement in crustal-scale processes. However, their exact relationship with the host granitic post-collisional suite and the role of such mantle remains unclear. In this regard, abundant MME in Los Pedroches batholith (Iberian Massif) can provide valuable constrains to this problem. Using new MME data, we provide a comparative study between MME and the mafic-intermediate (sanukitoid) suite of post-collisional batholiths, revealing an accurate overlap between the two groups. A common geochemical signature consisting of high MgO and K2O and low CaO is evidenced, pointing to a potential genetic link between MME and the sanukitoid suite in a modified mantle source. Further information provided by cotectic experimental liquids and petrographical evidence point to cotectic differentiation and orthopyroxene restite self-contamination as the main responsible mechanisms for the particular geochemistry of the series. Once the role of the mantle in MME formation and their magmatic evolution are characterized, their potential relationship with the host granites is established using isotopic criteria. Implications for post-collisional batholith petrogenesis is then discussed in a qualitative manner, suggesting a heterogeneous yet common origin for all post-collisional magmatism.

How to cite: Gómez Frutos, D. and Castro, A.: Mafic microgranular enclaves trace the origin of post-collisional magmatism, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7430, https://doi.org/10.5194/egusphere-egu23-7430, 2023.

The discovery of ¹⁸O-depleted igneous rocks at Krafla, Iceland, suggests that the system interacted with crustal rocks that experienced high-temperature hydrothermal alteration by a meteoric fluid to deviate from the expected mantle signature (δ¹⁸O = 5.5 ‰). Such assimilation is documented in low-δ¹⁸O settings worldwide, however, the mechanisms of this dynamic process remain poorly understood.  Due to intense drilling activity and exploration at Krafla, both hydrothermally altered crustal rocks and parental magma are comparably well characterized, making Krafla a great case study for the application of a numerical model that can further advance the understanding of the formation process of low-δ¹⁸O magmas. In this study, we use a new three-phase two-component thermo-chemical-mechanical model to simulate the effect of variable crustal compositions on the assimilation process and the magma chamber dynamics.  We define the simplified square-shaped magma chamber (10 x 10 m) of magma with initially basaltic composition (1250 °C) that assimilates the crustal rock (500 °C) at the top and bottom. Our results indicate that convective behaviour and the formation of cumulate layers can significantly hinder the assimilation process. While the crystal settling Stokes speed scale is the dominant driver for the formation of this boundary layer, depending on the assimilation timescales, the mushy chamber margins are able to grow to sufficient thickness to prohibit additional assimilation of low-δ¹⁸O crustal material. Density and buoyancy contrasts produce three types of convection: chamber convection, layered convection and plume driven convection. Final magma compositions in our preliminary model outputs range from mafic to intermediate but are not able to reach the felsic compositions encountered at Krafla. This suggests that evolution towards the erupted low-δ¹⁸O rhyolitic products involved multiple stages or included additional factors not yet accounted for in our model. Further refining of this and similar thermo-chemical-mechanical model setups may provide important new insights into the assimilation dynamics in the Krafla volcanic field and other low-δ¹⁸O settings worldwide.

How to cite: Aellig, P., Keller, T., Bachmann, O., and Troch, J.: Modelling three-phase magma dynamics during assimilation: Insights into the formation of low-δ18O rhyolites at Krafla, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7627, https://doi.org/10.5194/egusphere-egu23-7627, 2023.

Silicate melt inclusions (SMI) in rhyolitic volcanic rocks in the ~2699 – 2697 Ma Bousquet Formation, Subprovince, Québec were studied through integration of a variety of microanalytical methods (petrography, laser Raman microspectroscopy, LA-ICP-MS) to explore links between magmatic metal/volatile endowment and the high gold content of mineral deposits in the world-class Doyon-Bousquet-LaRonde mining district. The study is the first to present melt inclusion data from felsic volcanic rocks of Archean age.

Rhyolitic SMI of primary origin were characterized from magmatic quartz phenocrysts from tholeiitic rhyolite sills and calc-alkaline flows near gold-rich volcanogenic massive sulfide deposits. Silicate melt inclusion trace element chemistry records a continuous transition from ocean ridge to volcanic arc tectonic affinity. SMI Sr-Y-La-Yb systematics are  inconsistent with Archean tonalite-trondhjemite-granodiorite (TTG; “adakitic”) compositional domains; rather, they are consistent with post-Archean TTG (“calc-alkaline”) suggesting significant compositional modification of TTG magmas through contamination and/or plagioclase fractionation during magma storage and ascent.  Thermobarometry suggests prolonged phenocryst residence at depth prior to eruption with SMI entrapment at ~10-12 km depth. Concentrations of Au in the SMI are variable and up to two orders of magnitude higher than in the host bulk volcanic rocks. This demonstrates that whole rock data are not representative of the composition of the original magmatic liquids and, thus, cautioning the traditional use of whole rock data as a proxy for volcanic assemblage fertility in such Archean environments. Moreover, SMI show melt co-entrapment with an immiscible, high density, carbonic fluid (CO₂-dominant), indicating that rhyolitic melts were saturated in CO₂. Saturation of this fluid phase may explain, in part, the variability observed in SMI metal contents, and demands consideration of the relative importance of early separation of magmatic volatile phases versus seafloor hydrothermal leaching of volcanic products in controlling the magmatic metal endowment of Archean exhalative ore-forming systems.  

How to cite: Hanley, J., Meagher, D., Neyedley, K., Mercier-Langevin, P., and Zajacz, Z.: First insight into gold enrichment associated with Archean magmatic processes in the deep crust through melt inclusion studies: an example from the Abitibi Subprovince, Québec, Canada, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8045, https://doi.org/10.5194/egusphere-egu23-8045, 2023.

The behaviour of Group I and II elements during the petrogenesis of felsic igneous rocks is largely controlled by feldspar-liquid relationships and processes. Numerous experimental studies have addressed plagioclase/melt element partitioning, with fewer studies devoted to potassium feldspar, and very few to albite-rich ternary-composition feldspar (An ~ Or < Ab). However, the partition coefficient for Ba is known to increase at least 10-fold through the crystallization sequence sodic plagioclase – anorthoclase – potassium feldspar that is typical of sodic alkaline suites. Consequently, melt Ba concentrations may drop by orders of magnitude along such a liquid line of descent. Feldspars, glasses and whole rocks in such suites may exhibit strong enrichments and depletions in Ba that can be used to track processes of crystal fractionation, cumulate formation, and cumulate recycling.

Here, we review experimental feldspar/melt partitioning data for Ba, Sr and Rb as a function of feldspar composition. Regression of available experimental data offers the basis for expressions that appear to provide a working description for the compositional dependence of partition coefficients for albite-rich compositions. We have applied this model to feldspar and melt compositions of the products of several Holocene eruptions (Pico Viejo C, Pico Viejo H, Teide J2, Lavas Negras, Arenas Blancas, Montaña Rajada and Montaña Reventada) of the basanitic-phonolitic suite of the Teide-Pico Viejo volcanic system (Tenerife, Spain). Comparing feldspar/groundmass pairs obtained by EMPA and LA-ICP-MS analyses with predicted partition coefficients obtained with the models allows us to attribute an antecrystic or xenocrystic origin to some of the feldspars. The results confirm the existence of a distinct population of cumulate feldspars, that had undergone multiple fusion and recrystallization events, in Lavas Negras and Arenas Blancas flows. In addition, the trachytic composition of Montaña Reventada is due to melting of a feldspar-dominated cumulate. Application of these techniques to active magmatic systems will allow us a better understanding of different pre-eruptive processes, and ultimately improve volcanic hazard assessment.

This research was funded by the Intramural CSIC grant MAPCAN (Ref. 202130E083). OD was supported by an FPU grant (FPU18/02572) and a complementary mobility grant (EST19/00297) from the Ministry of Universities of Spain.

How to cite: Dorado, O., Wolff, J. A., Ramos, F., and Marti, J.: Ba, Sr and Rb feldspar/melt partitioning in the basanite-phonolite suite from Teide-Pico Viejo volcanic complex, Tenerife., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9712, https://doi.org/10.5194/egusphere-egu23-9712, 2023.

Central Asian Orogenic Belt (CAOB) with multiple blocks and suture zones is a key locality for understanding the process of plate tectonics. Extensive studies are mainly on the western CAOB, but less on the eastern side. Many questions remain unclear due to the lack of obvious structural records and ophiolite assemblages. In this study, we report the andesites sampled from Laolongtou Formation in the eastern CAOB with detailed geochronology and geochemistry analyses. The andesites are characterized by high Mg# values at their intermediate SiO₂ contents, which are defined as typical high Mg# andesites. Zircon U-Pb ages show they erupted at the Late Triassic (~236 Ma) and the Ti-in-zircon thermometer indicates a potential high primary magma temperature. Geochemically, they show relatively high contents of Al₂O₃, Na₂O, Cr, and Ni, with enrichment in light rare earth elements and depletion in high field strength elements. Besides, they are markedly depleted in Nb and Ta, enriched in Sr, Ba contents, and significantly differentiated in Th and U contents. They have homogeneous depleted Sr-Nd isotopic compositions that fall into the range of MORB and mantle-derived ranges. Together with the depleted zircon Hf isotopic compositions, showing the possible addition of a hot and depleted component. We propose that they were formed by interactions of components derived from a subducting slab and the overlying mantle wedge. The slab-derived components are most likely a low degree of partial melting of subducted oceanic crust that was able to stabilize garnet and rutile, without plagioclase in the melt residue. They subsequently interacted with the overlying mantle wedge, which resulted from an post-collisional setting related to the final closure of Paleo-Asian Ocean. The upwelling of the upper mantle triggered by the oceanic slab break-off may explain the genesis of the high Mg# andesites and the formation of the continental crust in northeast China.

How to cite: Zhang, L., Huang, F., Xu, J., and Liu, X.: Post-collision Extension in the Eastern Central Asian Orogenic Belt: Insight from the Late Triassic High-Mg Andesites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12573, https://doi.org/10.5194/egusphere-egu23-12573, 2023.

The closure of the Mongol-Okhotsk Ocean in Jurassic – Cretaceous times led to the final amalgamation of the interior of Eastern Asia, thus placing Mongolia in an intraplate tectonic setting. Small and widespread volcanic fields of Mesozoic and Cenozoic age are known through Eastern Asia, attributed to both post-collisional and intraplate mechanisms. In Mongolia, intraplate volcanic fields are scattered across the central and eastern parts of the country. Although several models have been proposed to explain the origin of this late Mesozoic – Cenozoic intraplate magmatism in Mongolia, there is still on-going debate about the process(es) that lead to it. Moreover, there are no temporal reconstructions on the extent of post-collisional magmatism in the area preceding intraplate magmatic activity, nor any hypotheses on the timing of the onset of the latter. In this study, we differentiate between post-collisional and intraplate magmatism in Mongolia using a set of geochemical, isotopic, palaeomagnetic and zircon data, and define the onset of intraplate magmatic activity at 107 Ma. Through evaluation of nearly 700 published radiometric data from the various volcanic fields across Mongolia along with newly-obtained age constraints, we reveal a complex temporal and spatial evolution of the magmatism that runs parallel in different volcanic fields through time, and we identify the extent of hiatuses in the magmatic activity. Based on the assessed data we discuss the source of bias in our understanding of the magmatic history of Mongolia and evaluate the various proposed models for the origin of the Mongolian magmatism. Finally, we suggest that asthenospheric upwellings were induced through a delamination event beneath Mongolia in the late Mesozoic. This initiated the intraplate magmatism, the temporal evolution of which is prolonged due to enhanced mantle flow related to northward progression of Tethys and the Indian plate.

How to cite: Papadopoulou, M., Barry, T. L., Dash, B., Halton, A. M., Sherlock, S. C., and Hunt, A. C.: Evidence for long-lived continental intraplate magmatism: A case study from Mongolia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12617, https://doi.org/10.5194/egusphere-egu23-12617, 2023.

One of the continuing trends in geodynamics is to develop codes that are suitable to model magmatic processes with an increasing level of self-consistency. Developing such models is particularly challenging as most magmatic processes are multiphysics problems, and require coupling between thermal, porous, mechanical and chemical processes.

Here we consider reactive flow in a deformable porous medium coupled to thermo-mechanical processes. We present a thermodynamically self-consistent set of governing equations, describing such processes. The governing equations consists of the conservation of mass, momentum, and energy in two phases. One phase represents the solid skeleton, which deforms in a poro-visco-elasto-plastic manner. The second phase represent low viscosity melts, percolating through the solid skeleton, that is described by Darcy’s law. As melt migrates through the rock skeleton we can quantify the chemical evolution of melts due to partial melting and crystallization. The system of equations is solved numerically, using the pseudo transient method, that is well suited to solve highly non-linear problems. We are going to discuss a few key end-member results, such as melt migration along dykes and fractures, along self-localized channels or by magmatic diapirism. We will discuss how the coupling between thermo-mechanical processes and melt migration might affect the chemical evolution of percolating melts.

All the codes presented here are written within a modular Julia framework, developed within the MAGMA ERC project, that permits easy future integration of the currently stand-alone software.

How to cite: Kiss, D., Moulas, E., Kaus, B., Berlie, N., and Riel, N.: Numerical modeling of magmatic transport processes, using the pseudo-transient method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12867, https://doi.org/10.5194/egusphere-egu23-12867, 2023.

Keywords: magmatic system, crustal contamination, diffusion, hybridization, partial melting

Magmatic differentiation requires a variable combination of fractional crystallization and/or crustal contamination that influences the liquid line of descent, as well as the composition and the final paragenesis of resulting magmatic rocks. However, the vectors of crustal contamination and how they influence the magmatic differentiation remain poorly constrained, notably because the depth at which they are active are usually hardly accessible. Several processes have been invoked in the literature: (1) small-scale diffusion; (2) energetically costly partial melting of crustal material coupled with magma hybridization; (3) The dissolution of crustal rocks by reactive bulk assimilation. Instead of focusing on the deepest crustal levels, we here explore crustal contamination processes active in the intermediate continental crust. We use the example of the Sondalo gabbroic complex that intruded the metasedimentary Campo unit, both exposed in the Central Alps.

The Sondalo gabbroic complex is a Permian intrusion of tholeiitic affinity (troctolite and norite, 300±12 and 280±10 Ma by Sm-Nd) that evolved towards calc-alkaline intermediate bodies (diorite and granodiorite, 289±4 - 285±6 Ma by U-Pb on Zrn). Mafic melts intruded the Campo unit composed of fertile amphibolite-facies micaschist and paragneiss (Ms-Bt-St-Grt-Pl stable), attesting of a (supposed) Carboniferous prograde P-T paths (5.5 - 6 kbar/600°C-650°C). The emplacement of this intrusion caused a HT-contact metamorphism reaching partial melting of host rocks at 289±4 – 288±5 (U-Pb on Zrn) Ma and in-situ formation of Crd-Grt-Sil-Spl granulite-facies restite composing large septa. Field and petrological observations coupled with geochemical bulk rock major and trace element analyses show the contribution of host-rock contamination, by: (1) mafic magmas of tholeiitic affinity becoming progressively calc-alkaline; (2) the increase in modal amount of garnet, biotite and cordierite in magmatic rocks around metasedimentary septa, stabilized by the influx of some major elements (e.g., SiO₂, K₂O, Al₂O₃ and H₂O) in the noritic mush; (3) liquid line of descent departs from theoretically predicted compositions (with both equilibrium and fractional crystallization) with enrichment in elements typical for crustal rocks (i.e., K₂O and Al₂O₃ at high Mg#).

Field observations and bulk rock major and trace elements composition highlight that crustal contamination is achieved through a combination of vectors having a variable spatial extent. Their respective weight is, however, still difficult to constrain. The middle crust seems to be the ideal location for crustal assimilation because host-rocks are fertile and the mafic magmas benefit from a high and durable thermal regime that appears to favor physical and chemical interactions. Further constraints will be brought by in-situ trace element analyses and Sr-Nd isotopes to estimate their respective influence on hybridization.

How to cite: Morin, M., Petri, B., and Ulrich, M.: Modes and impact of crustal contamination: Example of the Sondalo gabbroic complex (Central Alps, SE Switzerland - N Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13409, https://doi.org/10.5194/egusphere-egu23-13409, 2023.

The prevalence, durability and physical significance of crystal mushes in crustal magmatic systems is a topic of current interest in igneous petrology. Fragments of mushes brought to the surface by basaltic eruptions provide a snapshot of the temporal evolution of crustal magmatic systems.  Petrographic and geochemical analysis of such fragments give valuable insights into basaltic magma reservoirs, including information about magma storage conditions and possible eruption triggers. A detailed petrological and geochemical study was carried out on gabbroic mush nodules from the Brandur, Fontur and Saxi tuff cones to understand the processes that occur before large fissure eruptions in the Bárðarbunga system, Iceland.

Petrographic studies of the mush nodules, from QEMSCAN images, reveal a bimodal phenocryst population in a glassy vesicular groundmass. Probe analyses confirm the bimodal population consists of a primitive and evolved assemblage. The former is composed of large equant crystals of high-anorthite plagioclase (An~88), high-forsterite olivine (Fo~86) and high Mg# clinopyroxene (Mg#~86) forming an interconnected solid framework. The evolved assemblage consists of low-anorthite plagioclase (An~75), low-forsterite olivine (Fo~77) and low Mg# clinopyroxene (Mg#~79) crystallising in the pore space of the mush framework and on the rims of the primitive macrocrysts. The textures and compositions seen suggest the nodules experienced two stages of crystallisation: primitive macrocrysts crystallised first and were stored in crystal mushes. Then a later event caused a change in PTX conditions and triggered relatively rapid crystallisation in the pore-spaces of the mushes.

The quenched glass in the pore spaces of the nodules has the composition of a basaltic liquid that in chemical equilibrium with the evolved assemblage of crystals. Thermobarometry based on equilibrium between this liquid and the phases indicates that the final stage of crystallisation occurred at pressures of ~2 kbar. A putative interstitial liquid composition was reconstructed under the assumption of closed system growth of the evolved assemblage by using the QEMSCAN pixel maps to add the evolved crystals to the interstitial glass composition. This reconstructed liquid is far from chemical equilibrium with the primitive crystals in the mush framework, indicating that the assumption of simple closed system crystallisation from an initial mush liquid in equilibrium with the primitive solids is not correct. Therefore, the phase mapping and compositional relationship provide constraints on open-system processes in mushes.

The failure of the closed system models to match the observations is significant in two ways. First, the lack of equilibrium between mush liquid and cumulus plagioclase is consistent with the expected sluggish diffusion of NaSi-CaAl in plagioclase. This disequilibrium poses challenges for numerical models of magmatic systems that use the assumption of crystal-melt equilibrium to link temperature, melt fraction and phase compositions.  Second, bubble expansion during pre-eruptive ascent forces mush liquid out of solid framework in the nodules and may provide observational constraints on the physics of multiphase flow in deep magmatic systems.

How to cite: Maclennan, J., Boyes, X., and Mutch, E.: Disequilibrium during mush evolution in the Bárðarbunga volcanic system, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13522, https://doi.org/10.5194/egusphere-egu23-13522, 2023.

In NE Türkiye, an almost 30,000 km² area is covered by young volcanic rocks, ranging in age from Miocene to Quaternary and spanning the whole compositional spectrum from basanites/tephrites to high silica rhyolites. The region exhibits a plateau morphology, known as the Erzurum-Kars Plateau,  at ~2 km above sea level. That volcanic plateau continues far beyond the state border into Georgia (ie., the Samtskhe-Javakheti plateaus). Although there are a few studies, the petrological evolution of the these volcanic plateaus is still not well known. To better understand the origin, magmatic history, and geodynamic setting of the volcanism on these plateaus, we, Turkish and Georgian researchers, have been conducting a joint cross-border research project (i.e., TÜBİTAK- SRGNSF project #118Y272) across the region. The volcanic units making up those plateaus are composed of numerous volcanic cones of different shapes and sizes, lava domes, pyroclastic layers, and widespread plateau-forming lavas.

Preliminary findings of our research have revealed that the composition and structure of the lithospheric domains below the plateau might have significant effects on the geochemical character and the lithological features of the volcanics. The volcanic succession covering the Pontide Block in the north is dominated by Late Miocene-Pliocene calc-alkaline andesitic and dacitic lavas, which mostly form medium-sized volcanic edifices. These edifices are partially overlain by Upper Pliocene to Quaternary aged low-viscosity, plateau-forming basic lavas which are also calc-alkaline. Notably, pyroclastics are scarce in the north.

The portion of the plateau that overly the Northeastern Iranian Block and the ophiolitic mélange in the south consists of a much wider variety of lava and pyroclastic lithologies. It starts with a ~5.5 Mys old acid pyroclastic layer at the base, consisting of rhyolitic pyroclastics, domes, and obsidian. It is overlain by the plateau-forming basic to intermediate lavas, Pliocene in age. In turn, the plateau sequence is overlain by a previously unknown caldera-like volcanic complex, which we named “the Digor volcanic complex”, located between Kars and Digor. It has a diameter of ~60 km and consists of lavas and pyroclastics of Late Pliocene to Quaternary in age, displaying both calcalkaline and alkaline character.

All those volcanics contain a clear inherited subduction signature from previous subduction events (i.e., Pontide Arc in the north). Our petrological melting modellings revealed that the magmas were possibly derived from two contrasting metasomatized lithospheric mantle sources: (1) a spinel peridotite with or without minor amphibole and, (2) a pyroxenitic mafic source with a minor amount of phlogopite. Our data indicate that the melts derived from these two sources were mixed into each other en route to the surface. Most of the plateau lavas might have been derived from the first type (i.e., spinel-peridotite) while the younger alkaline Digor volcanics were dominantly from the second type (i.e., pyroxenite). The thinning of the lithospheric mantle by delamination and the gradual increase of heat coming from the upwelling asthenospheric mantle might be responsible for these variations. Our FC and AFC models show that plateau lavas experienced intense amphibole±garnet fractionation and moderately assimilated continental crust.

How to cite: Keskin, M., Aysal, N., Yılmaz, İ., Hanilçi, N., Okrostsvaridze, A., Koral, H., Kasapçı, C., Şişman Tükel, F., and Bochenko, G.: Deep magmatic processes beneath an active collision zone: Petrological and geochemical evidence from the volcanic plateaus in northeastern Türkiye and western Georgia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14990, https://doi.org/10.5194/egusphere-egu23-14990, 2023.

Deep low-frequency seismic events are detected in the East Eifel Volcanic Field (EEVF) since 2013. To well detect and locate such events the Deep Eifel Earthquakes Project - Tiefe Eifel Erdbeben (DEEP-TEE) started in July 2014 which now is composed of ca. 10 permanent and 15 mobile recording stations. Up to now, the DEEP-TEE seismic dataset contains eight years of continuous seismic records and the network has been reconfigured and continuously developed to achieve an optimum configuration regarding detection and location of seismic events.

In order to detect the weak deep low-frequency (DLF) events we developed a seismic event detector and found ca. 330 localizable DLF events in 2014-2021. The DLF hypocenter distribution outlines a near-vertical structure close to the Laacher See Volcano (LSV) which erupted about 13,079 years ago. The hypocenters are as deep as ca. 45 km, close to the assumed lithosphere-asthenosphere boundary, and reach to about 5-8 km depth. Most events occur close to the Moho and in the lower crust what is interpreted as magmatic underplating and deep crustal intrusion. In the same depth range but further to the west, we find seismic reflections with a negative polarity. These are also interpreted as magmatic pockets in the lower crust and the Moho region.

We try to estimate the mass flux (magma and volatiles) which is related with the seismicity. For this we apply Aki et al.'s model (JVGR, 1977) for describing the magma movement (a so-called chain of cracks connected by narrow channels) and estimate the related magma intrusion volume rate in the EEVF lithosphere. We assume an initial set of model parameters and evaluate the sensitivity and stability of the modelling results by allowing a reasonable range of each individual input parameter. Our results give an estimate of about 2,000-16,000 cubic meters of melt per year which is transported in the lithosphere.

How to cite: Ritter, J., Koushesh, M., and Eickhoff, D.: Melt Detection and Estimation of the Current Magma Intrusion Rate beneath the East Eifel Volcanic Field, Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15245, https://doi.org/10.5194/egusphere-egu23-15245, 2023.

One the world’s largest geothermal reservoirs, “The Geysers” in the California Coast Ranges, is underlain by a composite granitic pluton at shallow depth (~1–3 km, based on geothermal well penetration). Published U-Pb zircon geochronology indicates that this Geysers Plutonic Complex (GPC) intruded between c. 1.8 and 1.1 Ma in three major pulses: the oldest formed a cap of orthopyroxene-biotite microgranite porphyry, followed by orthopyroxene-biotite granite and hornblende-biotite-orthopyroxene granodiorite dominating at deeper levels. Lavas and minor pyroclastic deposits of the overlying Cobb Mountain Volcanic Center erupted between c. 1.2–1.0 Ma. The Geysers-Cobb Mountain plutonic-volcanic association shares common magmatic origins rooted in asthenospheric upwelling into a migrating slab window, where lower-crustal hybridization of mantle-derived magmas was followed by upper-crustal intrusion and differentiation. When and how shallow intrusions or eruptions were fed from this common source, however, remains unclear. This can be reconstructed from crystal-scale analysis of trace elements, oxygen and hafnium isotopes in zircon that can uniquely track magmatic processes in an evolving, long-lived magma system.

GPC microgranite zircons display strongly negative Eu anomalies, high levels of incompatible trace elements, and near-solidus Ti-in-zircon temperatures (~670 °C for aTiO₂ = 0.55 and aSiO₂ = 1). This is distinct from zircons from GPC granite and granodiorite that have moderately negative Eu anomalies, inconspicuous trace element enrichments, and variable Ti-in-zircon temperatures (~850–700 °C). Unlike trace elements, O and Hf isotopes in zircon are indistinguishable between GPC microgranite porphyry and the main population of granite-granodiorite zircons (δ¹⁸O = +4.76 to +9.18; εHf = +1.4 to +10.7). There is, however, a subgroup of zircon in GPC granite and granodiorite with elevated δ¹⁸O (~8.05) and lower εHf (~4.4) indicating that some late-stage melts experienced higher degrees of assimilation compared to the other magma types. Zircons from Cobb Mountain lavas are similar to those from the GPC granite and granodiorite, but distinct from the granophyre.

We set up a thermal model for zircon crystallization to satisfy the following observations: (1) evolved magma from which zircon crystallized was continuously present between c. 2.1 and 1.1 Ma, and (2) crystal recycling from the GPC microporphyry stage in subsequent intrusive or eruptive pulses was negligible. A magma reservoir at ~7 km depth which incrementally grew in three stages matches requirements imposed by zircon ages and compositions: (1) initial magma accumulation at low recharge fluxes starting at 2.1 Ma (0.1 km³/ka), (2) a brief flare-up at 1.6 Ma (4 km³/ka for 50 ka), (3) a return to low recharge fluxes (0.1 km³/ka) between 1.3 and 1.1 Ma. The total injected magma volume amounts to ~300 km³, three times the volume of the GPC as constrained by geothermal wells. According to this model, magma accumulation was long-lived, thus capable of sustaining protracted geothermal activity, but the main igneous growth occurred almost instantaneously. One implication is that accumulation of large volumes of magma can be rapid, and may require special circumstances that are only realized ephemerally despite overall long-lived magmatic activity.

How to cite: Schmitt, A. K., Angeles-De La Torre, C., Lovera, O. M., Gassert, H., Gerdes, A., and Harvey, J. C.: The construction of a composite magma intrusion underneath “The Geysers” geothermal reservoir (California) based on zircon ages, trace elements, and isotopic compositions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16113, https://doi.org/10.5194/egusphere-egu23-16113, 2023.

The Ivrea-Verbano Zone (IVZ) is the westernmost sector of the Southern Alps. It is constituted by granulite-to-amphibolite-facies continental crust representing the basement of the Adria plate. The IVZ contains many orogenic mantle peridotites. The largest mantle bodies are aligned along the Insubric Line at the lowest stratigraphic units, in contact with mafic-ultramafic crustal intrusives. Mantle bodies in the central and southern sectors of IVZ are spinel lherzolites with spinel dunites and variable amount of clinopyroxenite, websterite and subordinate anhydrous/hydrous gabbroic bodies (e.g. the Baldissero, Balmuccia, Premosello peridotites). Conversely, modally-metasomatised spinel harzburgites with large dunite bodies and phlogopite-and-amphibole-bearing websterites (e.g. the Finero peridotite) crop out in the northern IVZ.

The constant association of the IVZ mantle peridotites with High-T shear zones suggests that none of them was emplaced into the crust by mantle diapirism. Alternative hypotheses involve emplacement at the crustal level at the onset of the Mesozoic extensional regime or tectonic addition to accretionary wedges of Paleozoic subduction zones. Recent gravimetric and seismic data converge in indicating that high-density rocks are very close to the surface near the Insubric Line, thus supporting the possibility that the largest mantle peridotites may be a direct expression of the underlying subcontinental mantle.

This contribution focuses on new field, petrographic, geochemical and geochronological data, to address some relevant issues, such as the nature of the spinel lherzolite (refractory residue vs. refertilised mantle), the origin of pyroxenites and gabbros, the relationships with the associated crustal intrusives and the record of Mesozoic tectono-magmatic events.

The final goal is to provide new insights into the geodynamic evolution of the mantle bodies and the mantle-crust systems at the Laurasia-Gondwana margin, defining in particular how the mantle heterogeneity acquired during Paleozoic may have governed the rifting process of the Adria margin in Jurassic times.

How to cite: Ogunyele, A. C., Bonazzi, M., Sanfilippo, A., Decarlis, A., and Zanetti, A.: Reappraisal of the geodynamic evolution of the mantle massifs of the Ivrea-Verbano Zone based on new field, petrochemical and geochronological data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-243, https://doi.org/10.5194/egusphere-egu23-243, 2023.

Even though the southern Indian Dharwar craton hosts several kimberlites, lamproite, and lamprophyre fields of the Mesoproterozoic age, mantle-derived peridotitic xenoliths are very rare and are often highly altered and poorly preserved. Due to these constraints, xenolith-based direct mantle investigations have been limited beneath the Indian cratons. In this study, we report extensive geochemical analyses on peridotite xenoliths from the P3 kimberlite pipe of the Wajrakarur kimberlite field from the Eastern Dharwar craton (EDC). With the help of major and trace element compositions of the garnets and clinopyroxenes, this study aims to characterize the mantle below EDC and to comment on its evolution.

During this study, 57 peridotite xenoliths were identified. P-T estimates were carried out using garnet compositions. Based on the vertical distribution of garnets on a projected depth, it is observed that the upper part of the lithosphere is composed mostly of lherzolites(G9) with few harzburgites (G10), whereas the base of the lithosphere is dominated by Ti-Metasomatized garnets(G11).

Garnet compositions show an anomaly in the TiO₂ content, which is marked by a sudden increase in TiO₂ at ~160 km of depth. This depth coincides with an increased concentration of G11 garnets. Zr/Hf vs Ti/Eu plot for garnets shows that carbonatitic and kimberlitic fluids are involved in metasomatizing the SCLM. The Mg# and Cr# values suggest that the lithosphere gets more depleted with increasing depth. Clinopyroxene compositions show the presence of two types. Type 1 is enriched in LREE than the Type 2 clinopyroxenes showing the metasomatic enrichment.

The depth range of the studied peridotite xenoliths indicates sampling of the mantle from ~170 to 190 km of depth, indicating a 190 km thick LAB at 1.1 Ga. However, geophysical studies show a present-day estimate of a ~110 to 120 km thick lithosphere. This further indicates about 70-80 km of delamination of the lithospheric keel in post-Mesoproterozoic times. Such large-scale delamination of the lithosphere might be possible due to the increased frequency of mantle plumes, convective erosion, and the heavily metasomatized nature of the SCLM.

How to cite: Daimi, Z. and Dongre, A.: Evolution of the lithospheric mantle beneath Eastern Dharwar craton of Southern India: constraints from peridotite xenoliths from P3 kimberlite pipe of the Wajrakarur, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-293, https://doi.org/10.5194/egusphere-egu23-293, 2023.

The ability of xenoliths to preserve water lithospheric signatures remains an unsolved question for many years. We report water content in olivine and pyroxenes of peridotite xenoliths from Peylenc and Ray Pic volcanoes (French Massif central, FMC). On each site xenoliths were sampled from products of an explosive eruption (volcanic breccia and pyroclastic deposit) and an effusive eruption (frozen magma chamber and a lava flow).

In Peylenc, the xenoliths from the breccia have systematically more water than the xenoliths from the basalt quarry: ol 1-9, opx 60-95 and cpx 250-380 wt. ppm H₂O versus ol <0.2, opx 20-55 and cpx 110-240 wt. ppm H₂O.

In Ray Pic, water content in xenoliths from the lava flow is independent of its location in the lava: ol < 1, opx 190-270 and cpx 430-640 wt. ppm H₂O. Results suggest that the cooling and solidification of the lava had no impact on water content.

The xenoliths from the pyroclastic deposit have systematically more water: ol 3-12, opx 330-460 and cpx 810-890 wt. ppm H₂O. These values are either comparable with or lower than the values reported previously from the same locality¹.

The study shows that xenoliths recovered from explosive eruptions have higher water content than the ones from effusive eruptions, but also that water content can be different from one explosive event to another.

Conclusion is that water content can rapidly be reset during magma degassing prior to eruption. Degassing controls water content of xenoliths.

Among the xenoliths studied, several have spectral signatures different from others. This different spectral signature has also been reported from other volcanoes^{2, 3}. The coexisting of different spectral signatures, which have not been erased during degassing, are probably the only OH signatures fully preserved from depth.

¹ Azevedo-Vannson S.,et al. Chemical Geology 575 120257 (2021)

² Denis C.M.M. et al. Lithos 226 256-274 (2015)

³ Patkó L. et al. Chemical Geology 507 23-41 (2019)

How to cite: Ingrin, J., Thomaidis, K., and Drouka, M.: Preservation of the water concentration in mantle xenoliths. The cases of Peylenc & Ray Pic volcanoes (FMC), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2720, https://doi.org/10.5194/egusphere-egu23-2720, 2023.

The Khrami crystalline massif is located in the northern part of the Lesser Caucasus, in the Black Sea - Transcaucasian terrane. The massif outcrops Middle Paleozoic metabasites, which crosscut the Precambrian gneiss-migmatite complex and, in turn, are cut by Late Variscan granites. These metabasites have not experienced Precambrian prograde HT/LP (720-770°C, P<1.5 kbar) regional metamorphism, although retrograde LT/LP (T≈430-510⁰C, P≈0.6-1 kbar) metamorphism, associated with the Sudetian orogeny has been recorded. According to the presented geological data, the age of metabasites is within the Cambrian and Upper Paleozoic. Considering the analogy between the metabasites spread in the Dzirula crystalline massif, which is exposed in the same terrane, and the metabasites of the Khrami massif, the age of the latter is most likely Middle Paleozoic (Shengelia et al., 2022). The metabasites of the Khrami massif are represented by veins (1-60 m) and stock-shaped bodies (80-800 m) of fine-grained ophitic gabbro, gabbro-diabases and diabases of various thicknesses. They are cut by numerous granite veins and penetrated by thin quartz-feldspar injections. The paragenesis of the high-temperature magmatic stage - Cpx+Pl_78-84 has been preserved in metabasites in some places; Further, under the conditions of greenschist facies, the paragenesis Ab+Act(Tr)+Chl+Ep±Qz develops. According to the petrogenic diagrams Na₂O+K₂O – SiO₂, the metabasites of the Khrami massif belong to the formations of the subalkaline series (Irvine and Baragar, 1971), correspond to basalts and andesite-basalts (Le bas et al., 1986) and basalts and picrites (Cox et al., 1979). This is confirmed by the data of diagrams Zr/Ti-Nb/Y (Pearce, 1996) and Zr/TiO₂ – Yb/Y (Winchester, Floyd, 1977). According to the Na₂O+K₂O–FeO*-MgO (Irvine and Baragar, 1971), a great part of the metabasites is of tholeiitic composition, and only a small part is of calc-alkaline composition. On the diagram Fe*-SiO₂ (Frost et al., 2008) the dots denoting metabasites are completely disposed in the magnesian field. According to the TiO₂ - Zr/(P₂O₅*10⁴) diagram (Winchester, Floyd, 1976), the metabasites correspond to tholeiite basalts. According to the diagram V-Ti/1000 (Shervias, 1982), the metabasites belong to the MORB genetic formation, and according to the diagram Cr-Y (Pearce, 1982), they belong mainly to the VAB, and also to the MORB. According to the ratio MnO-TiO₂/10-P₂O₅ (Mullen, 1983), dots of mafic rocks are located in the island-arc tholeiitic field. Thus, the Middle Paleozoic metabasites of the Khrami crystalline massif are represented by shallow subvolcanic magmatites predominantly of andesite-basalt and tholeiite-basalt groups of the tholeiitic series. They correspond to the MORB and VAB genetic groups.

How to cite: Shengelia, D., Tsutsunava, T., Beridze, G., and Javakhishvili, I.: Geology, geochemical typification and petrogenic model of formation of Middle Paleozoic metabasites of the Khrami crystalline massif (Georgia), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2760, https://doi.org/10.5194/egusphere-egu23-2760, 2023.

The Hessian Depression in Germany represents the northern continuation of the Upper Rhine Graben and is known for Cenozoic alkaline basaltic lavas. Many of these carry peridotite xenoliths of mantle origin, which were studied mainly in the  80-ies of the XX century (Hartmann & Wedepohl 1990 and references therein). These studies documented mantle lithosphere melting followed by metasomatism. Here we describe the xenoliths from the Stöpfling quarry near Homberg upon Efze. The quarry has been recultivated and sampling is not possible now, our samples come from the archival collection of the Department of Geochemistry of the University of Göttingen. In this abstract, we give an overview of newly collected major- and trace-element mineral-chemical data from 11 xenoliths.

The xenoliths from Stöpfling are spinel-facies lherzolites and harzburgites. They consist of aggregates of few coarse (typically 4-6 mm across) grains of olivine and orthopyroxene embedded in fine-grained matrix of olivine, ortho- and clinopyroxene and spinel. Coarse-grained aggregates represent fragments of protogranular texture and are volumetrically prevailing. Spinel is commonly interstitial and has amaeboidal morphology. Locally, centimetre-thick layers of websterites cross-cut the peridotites. Hartmann & Wedepohl (1990) report traces  (<1 vol. %) of phlogopite in 2 of 12 lherzolites they studied.

The major element composition of olivine is strikingly homogeneous in all studied rocks (91±0.5 % forsterite and 0.40 wt. %. NiO), Ca content is < 500 ppm. Orthopyroxene is mildly aluminous (0.10-0.17 atoms of Al per formula unit, [pfu]) as is clinopyroxene (0.12-0.25 atoms Al pfu). Spinel Cr# [= Cr/(Cr+Al)] varies from 0.18 to 0.46. Clinopyroxene coexisting with spinel of low Cr# is Al-rich and contains 1600-2200 ppm Ti, whereas that coexisting with spinel of higher Cr# is less aluminous and contains 600-1200 ppm Ti. Clinopyroxene coexisting with spinel of Cr# 0.46 is extremely impoverished in Ti (50 ppm). The REE patterns of clinopyroxene in most samples are above the primitive-mantle (PM) level, are LREE-enriched and flat at MREE-HREE. Those extremely depleted in Ti show a decrease from HREE towards MREE, the contents of which are below PM level, and are strongly LREE-enriched.

Peridotites from Stöpfling consist of olivine which chemical homogeneity  across the xenolith suite supposedly records melt depletion. The variable content of Al in orthopyroxene from different samples probably is due to subsequent refertilization event(s) involving silicate melt, whereas the REE characteristics of clinopyroxene suggests that it was additionally cryptically  metasomatized. The unaffected olivine composition indicates low ratio of metasomatic agent to protolith.

Acknowledgements. JP is grateful to G. Wörner for enabling access to the xenoliths from Stöpfling that were originally collected by H. Wedepohl and are now archived at the Geochemistry and Isotope Geology Division of the Geoscience Center at University Göttingen (GZG).

Funding. This study originated thanks to the project of Polish National Centre of Research 2021/41/B/ST10/00900 to JP.

References:

Hartmann G., Wedepohl. K.H. (1990): Metasomatically altered peridotite xenoliths from the Hessian Depression (Nortwest Germany). Geochim. Cosmochim. Acta 54: 71-86.

How to cite: Puziewicz, J., Aulbach, S., Matusiak-Małek, M., Ntaflos, T., and Ziobro-Mikrut, M.: Peridotite xenoliths from Stöpfling in Hessian Depression (Germany) revisited, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2878, https://doi.org/10.5194/egusphere-egu23-2878, 2023.

Triassic volcanism in Greece is mainly associated with the rift phase of the Neotethys that resulted in the formation of E-MORB and OIB alkali basalts, which are widespread throughout the Hellenic mainland[1]. In most of the outcrop localities (e.g. Pindos, Koziakas, Othris, Argolis) these basalts are closely related in the field with other more differentiated volcanics that display a clear subduction signature [1,2]. In the Northern Peloponnese and specifically from the localities of Drakovouni, Palaiohouni and Perachora, three types of lavas were identified: basaltic andesites, andesites and rhyodakites, which are fine to medium grained and displaying either porphyritic or even equigranular textures in the more felsic varieties. These lavas were classified based on their Si, Na and K contents, as well as their Nb/Y vs. Zr/Ti ratios, which were subjected to rather restricted metasomatic processes (LOI:1.1-3.7, partial albitization and uratilization). Based on their potassium contents, as well as upon the AFM geochemical ternary plot and their FeO/MgO ratios, they are geochemically classified as calc-alkaline volcanics, clearly being affected by subduction-related processes. The latter is confirmed by: presence of magmatic magnesiohornblende in all types of lavas at variable amounts, enhanced Th/Yb contents (2.4-4.1), LREE enrichments [(La/Yb)_CN=6.2-10.0], lower normalized values of Th and U compared to Nb and Ta, positive K and Pb anomalies, negative Ti anomalies in the PM-normalized diagrams, noticeable LILE enrichments (e.g. Cs, Rb, Ba).

Fractional crystallization played a significant role in the differentiation processes. This is confirmed by: presence of primary clinopyroxene and amphibole in the basaltic andesites whose modal composition significantly decreases in the andesites and rhyodakites (only accessory amphibole), relatively strong correlation between Sc/Y with CaO/Al₂O₃ (R² = 0.91), positive correlation between P₂O₅/TiO₂ and (La/Yb)_N (R² = 0.87), higher Cr and Ni contents in the least differentiated lavas, increase of Nb/Yb in the highly fractionated lavas, increasing Eu negative anomalies from the compositionally basic to the felsic varieties (basaltic andesites Eu_CN/Eu*= 0.73-0.80; andesites Eu_CN/Eu* = 0.63-0.74, rhyodakites Eu_CN/Eu* = 0.51-0.61). Apart from fractional crystallization, crustal assimilation (AFC processes) likely played an additional role during differentiation, shown by the strongly positive correlation between SiO₂ and Nb/Yb (R² = 0.92). The Sr-Nd isotopic data further confirm the effect of crustal contamination and AFC processes, with lower ¹⁴³Nd/¹⁴⁴Nd and higher ⁸⁷Sr/⁸⁶Sr ratios for the rhyodakites compared to the andesites and basaltic andesites.

References: [1]Koutsovitis, P., Magganas, A., Ntaflos, T., Koukouzas, N., Rassios, A.E., Soukis, K., 2020. Petrogenetic constraints on the origin and formation of the Hellenic Triassic rift-related lavas. Lithos 368-369, 105604, [2] Pe-Piper, G., Piper, D.J.W., 2002. The Igneous Rocks of Greece. Borntraeger, Stuttgart, pp. 1–645.

How to cite: Koutsovitis, P., Soukis, K., Kokkalas, S., Magganas, A., Ntaflos, T., Jang, Y., and Kwon, S.: Evidence for the effects of subduction in Triassic lavas from the Northern Peloponnese (Greece): A mineralogical, geochemical and isotopic (Sr-Nd) approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4252, https://doi.org/10.5194/egusphere-egu23-4252, 2023.

Mount Vulture is a stratovolcano (age 0.75-0.14 Myr) located in southern Italy, which despite being at the same latitude of Vesuvius and Phlegreian Fields, has several peculiarities about its setting and erupted magma composition. Indeed, if compared to other Italian Quaternary volcanoes, it is the only one located east of the Apennine Front, about 100 km off the axis of the Campanian Magmatic Province (Peccerillo et al., 2017). Furthermore, although being a quiescent volcano (last eruption dated 0.14 Myr), previous studies (e.g., Caracausi et al., 2015, Bragagni et al., 2022) have shown extremely high CO₂ emissions (4.85 × 108 mol yr^-1), which are likely related to the carbonatitic volcanism of its final phase of activity, as well as some petrological aspects in the erupted products pointing to a mantle source metasomatism.

Recently, investigations on Vulture mantle xenoliths (Carnervale et al., 2022) revealed CO₂-rich fluid inclusions (FIs) that indicate a primary depth of bubbles entrapment in olivine and pyroxene phenocrysts coinciding with the regional crust-mantle boundary (27-30km).

This research focuses for the first-time noble gases isotopes (He, Ne, Ar) in FIs from lherzolite enclaves from Mt. Vulture tephra. The He isotopic ratios (as R/Ra; R is the ³He/⁴He ratio of the sample and Ra the same ratio in air), are between 6.2 and 5.4 ± 0.08. These values are lower than the signatures of the MORB upper mantle (8 ± 1Ra) and overlap the values of the Sub Continental Lithospheric Mantle (SCLM, 6.1 ± 0.9Ra). The Ne isotopic signatures (²⁰Ne/²²Ne and ²¹Ne/²²Ne) are in the field of the MORB values.

The He-Ne-Ar systematics is consistent with a SCLM source feeding the magmatism of the Vulture volcano. However, considering the noble gases He-Ne-Ar, in Vulture xenolites this mantle source has affinities with that feeding the volcanic activities of Mt. Etna (Nakai et al., 1997; Correale et al., 2014). This inference bears some evidence about the similitudes of the mantle below these two volcanic systems that is affected by mantle metasomatism, which is likely also responsible for the large CO₂ fluxes and the carbonatitic magmatism (Bragagni et al., 2022). New measurements of the noble gases in free gases from the two volcanoes together with a detailed comparison between the geochemistry and petrography of the Vulture and Etna most primitive products will provide new constraints on the mantle typology below the two volcanoes and its relationship with the geodynamical evolution of the central Mediterranean.

References

Bragagni et al., 2021, Geology

Carnevale et al. (2022). Geophys. Res. Lett.

Caracausi et al. (2015). Earth Planet. Sci Lett.

Correale et al., 2014. Lithos

Nakai et al., (1997). Earth Planet. Sci Lett.

Peccerillo, A. (2017). Advances in Volcanology. Springer, Cham.

How to cite: Italiano, L., Caracausi, A., Carnevale, G., Paternoster, M., and Rotolo, S. G.: First noble gases measurements in lherzolites from Mt Vulture volcano: new constraints on the mantle below Italy, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4404, https://doi.org/10.5194/egusphere-egu23-4404, 2023.

Peridotite xenoliths provide valuable insight into lithospheric mantle conditions, composition, and evolution. The origin of amphibole in the lithospheric mantle and whether amphibole melts to produce alkaline intraplate magmas is a highly debated topic. Large areas of the lithospheric mantle forming Earth’s youngest continent, Zealandia, have chemical compositions comparable to Archean mantle lithosphere but Re-Os isotope and bulk rock data indicate that lithosphere stabilisation occurred in the Mesozoic. Some areas of this refractory lithospheric mantle have been metasomatized, with one of the clearest occurrences being MARID-like veins in xenoliths in alkaline intraplate magmas in the Southern Alps of New Zealand. These xenoliths contain abundant veinlets composed of amphibole, phlogopite, clinopyroxene and apatite in rocks that have average olivine compositions exceeding Mg# 92 and spinel Cr# 70. The latter indicates that these peridotites have undergone >25% partial melting prior to metasomatism.

Using a combination of quantitative scanning electron beam methods, trace element and in-situ laser ablation inductively coupled mass spectrometry (LA-ICP-MS) analysis, and conventional ⁸⁷Sr/⁸⁶Sr isotope analysis by solution, we seek to establish the origin of hydrous phases in this mantle lithosphere. The benefit of inspecting formerly highly depleted peridotites is that the chemistry of the metasomatic agent, which is typically enriched in incompatible elements, is less diluted than in the cases where melts infiltrate fertile lithosphere. Although minor Fe-diffusion has occurred within the studied host rock, the bulk compositions of the veins are picro-basaltic. The mica separates, measured by solution chemistry, are today more radiogenic than the in-situ diopside and amphibole analyses, however, we find that the age-corrected ~25 Ma, ⁸⁷Sr/⁸⁶Sr initials fall in a tight cluster of very depleted mantle-like ratios from 0.7027 to 0.7056. Although the fluids appear to have sub-alkaline bulk compositions, the amphibole trace elements are enriched in HFSE and lack depleted Nb components.

The data suggests that these basaltic veins are not arc-related and do not derive from melting of subducted sediment, but also have no direct genetic link to the host alkaline melts. If this latter interpretation is correct, then the injection of hydrous veins was not part of a continuous process that resulted in alkaline magmatism, although they may have been subsequently melted to give rise to alkaline magmas with depleted mantle-like isotopic characters. 

How to cite: Cooper, N., Scott, J., Brenna, M., Palmer, M., Reid, M., Stirling, C., and le Roux, P.: The origin of hydrous amphibole in the subcontinental lithospheric mantle beneath the Southern Alps of New Zealand, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4569, https://doi.org/10.5194/egusphere-egu23-4569, 2023.

Earth’s mantle is highly heterogeneous, with mantle-derived rocks sampling depleted and enriched domains both in intraplate settings and along spreading ridges. The most notorious isotopic anomaly is the DUPAL anomaly, where an overall strong recycled isotopic signature occurs. Studies on Tethyan and Paleo-Tethyan ophiolites have shown the persistence of “DUPAL signature” in those oceans, which paleogeographic reconstructions place on approximately the same position as the present-day Indian Ocean and thus argue for a long-lived “DUPAL signature” in the mantle. The origin of the DUPAL anomaly is controversial, with many studies pointing to it being a primordial feature. More recently, however, it has been shown that plume products in the African Mantle Domain (AMD), of which the DUPAL anomaly region is a part of, generally bear a more enriched signal than plume-related rocks in the Pacific Mantle Domain. This observation has been hypothesized to be related to the formation of the Pangea supercontinent above the present-day AMD, and therefore offering a geodynamic scenario capable of explaining the origin of the enriched isotopic signature of the AMD. However, present-day ocean crust record is limited in time, extending to 200 Ma at maximum, younger than the formation of Pangea at ca. 320 Ma. To investigate the oceanic record of mantle enrichment further back in time and test the influence of supercontinent cycle on the composition of the AMD, it is necessary to utilise preserved oceanic terranes in orogenic belts. In this study we compiled isotopic data from preserved oceanic terranes related both to the formation of the AMD, starting from the assembly of Gondwana till the duration of Pangea, including that of the Mozambique, Adamastor, Goias-Pharusian, Iapetus, Rheic, Qilian-Shangdan, Paleo-Tethys, Meso-Tethys and Neo-Tethys paleo-oceans. Neodymium isotopic data is the most widely available for these ophiolites. The Nd isotopic data indicates a progressively more depleted signal before Gondwana formation until it reaches a maximum and stays relatively stable until shortly after Pangea break-up, where noticeable decrease in depletion occurs. Lead isotopic data is less readily available, existing data nevertheless allow to observe an increase in Th/U ratio during Gondwana formation. Taken together, these observations indicate an increase in recycled continental components in the mantle source of the AMD ophiolites. We envisage this to be evidence for mantle enrichment during the formation of Gondwana and Pangea within the AMD. New isotopic analyses are still needed to paint a clearer picture of the interplay between the supercontinent cycle and mantle geochemistry.

How to cite: Azevedo Berquo de Sampaio, P., Li, Z.-X., Doucet, L. S., and Gamaleldien, H.: Evolution of the African Mantle Domain and its enriched signal: perspective from pre-200 Ma ophiolites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4686, https://doi.org/10.5194/egusphere-egu23-4686, 2023.

Permian mafic volcanic rocks occurring in southern terrains of Scotland (United Kingdom) are rich in peridotitic xenoliths providing insight into the composition of the Subcontinental Lithospheric Mantle (SCLM) beneath this area. Peridotites from the Ruddon’s Point (Fife) xenolith suite form four textural groups: (1) protogranular and (2) porphyroclastic lherzolites, (3) equigranular wehrlites and (4) lherzolites transitional between protogranular and equigranular peridotites. The SCLM beneath southern Scotland was affected by reaction with an alkaline melt resulting in clinopyroxene crystallization (wehrlitization) and decrease of Fo in olivine from primary (protogranular and porphyroclastic) lherzolites (Fo_88.5-90.0) through transitional to equigranular (Fo_80.0-85.0) peridotites (Matusiak-Małek et al., 2022).

The sulfides occurring in the peridotites form oval, elongated or irregular grains enclosed in pyroxenes and olivine, or interstitial between these phases. The abundance of sulfides  increases from the transitional lherzolites (mean = 0.009 vol.‰), through equigranular and porphyroclastic peridotites (0.026 and 0.029 vol.‰, respectively) to protogranular lherzolites (0.050 vol.‰). Sulfide minerals present in all textural groups are pentlandite (Pn) and chalcopyrite (Ccp). There is generally an absence of pyrrhotite (Po), but protogranular and “transitional” lherzolites contain minor amounts. Porphyroclastic lherzolites occasionally contain millerite (Mlr) and covellite (Cv). The sulfides from the equigranular and protogranular peridotites are more enriched in Cu-, and depleted in Ni-phases (Po₀Pn₇₁Ccp₂₉ and Po₄Pn₆₈Ccp₂₇, respectively) in comparison to sulfides from the porphyroclastic and transitional peridotites (Po₀Pn₈₀Ccp₂₀ and Po₆Pn₈₃Ccp₁₂, respectively). The Cu/(Cu+Fe) is homogenous in sulfides of all the textural types, whereas Ni/(Ni+Fe) in pentlandite is homogenous only in transitional and equigranular peridotites (0.64–0.65 and 0.55–0.59, respectively) in contrast to porphyroclastic and protogranular ones (0.54–0.68 and 0.52–0.64, respectively). The only significant difference in trace element composition of sulfides appears in the concentrations of Co and Zn which  are  4894 ppm and 2214 ppm, respectively, in the protogranular peridotites, compared to 30090 ppm and 1391 ppm, respectively, in the transitional peridotites.

The more primitive protogranular and porphyroclastic lherzolites  are characterized by the highest sulfide abundances in comparison to the sulfides from melt-metasomatized equigranular wehrlites, with no significant differences  in sulfide mineral and chemical (major and trace elements) composition between groups. Thus, activity of the alkaline silicate melts responsible for wehrlitization of the primary lherzolites seems not to influence the sulfide enrichment in the SCLM beneath S Scotland. The presence of Cv and Mlr in lherzolites suggests alteration by hydrothermal, post-volcanic activity, affecting the xenoliths after the exhumation to the surface by basaltic lavas.

Matusiak-Małek, M., Kukuła, A., Matczuk, P., Puziewicz, J., Upton, B.J.G., Ntaflos, T., Aulbach, S., Grégoire, M., Hughes H.S.R. (2022). Evolution of upper mantle and lower crust beneath Southern Uplands and Midland Valley Terranes (S Scotland) as recorded by peridotitic and pyroxenitic xenoliths in alkaline mafic lavas. 4th EMAW TOULOUSE 2021 Book of Abstracts.

How to cite: Mazurek, H., Matusiak-Małek, M., Hughes, H. S. R., and Upton, B. J. G.: The composition and origin of sulfides in peridotitic xenoliths from Ruddon’s Point (Fife, Scotland), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4995, https://doi.org/10.5194/egusphere-egu23-4995, 2023.

The sub-continental lithospheric mantle (SCLM) of Archean cratons represents the depleted and buoyant residue left behind after crust extraction. The history of the SCLM is notably complex in all cratons, often recording multiple episodes of melting and metasomatism. Garnet is a prime target for studying this history, as it provides thermobarometric constraints and hosts incompatible trace elements that can help identify melting and refertilization. Placing the rich geological record of mantle garnet in time is crucial for resolving cratonic evolution. Robust age constraints from garnet have nevertheless been difficult to obtain. Isolating enough analyte material for Lu-Hf or Sm-Nd chronometry is challenging for small xenoliths of highly depleted mantle rock. Age estimates are typically based on external or two-point isochrons with limited statistical robustness and geological interpretability. Moreover, chronometer systematics are principally not well constrained for the conditions and processes of the mantle. The question of which assemblages and chemical features of the Archean SCLM are actually of the Archean age is often left unanswered. To address this, we used ultralow-blank Lu-Hf chronometry, in concert with trace element analysis, on a targeted analysis of texturally and compositionally different mantle xenoliths from three Archean cratons (Slave, Kaapvaal, and Siberian Cratons).

The samples analyzed in this study represent a variety of garnet-bearing lithologies: clinopyroxene-rich fertile lherzolite, harzburgite (both granular and sheared), and orthopyroxenite with pyrope in exsolution lamellae. These samples were chosen, as they capture various stages of mantle evolution, from initial melting and subsolidus equilibration to shearing and metasomatic re-equilibration. We were able to obtain multi-point internal Lu-Hf isochrons for all lithologies, including those with extremely depleted compositions. The Lu-Hf ages span the history of the SCLM, from the Mesoarchean to the ages of kimberlite eruption. The oldest ages were obtained from lithologies depleted in Ca and clinopyroxene, i.e., exsolved orthopyroxenites and harzburgites from the Kaapvaal and Siberian Cratons. Lherzolites provided younger ages corresponding to metasomatic events, some of which could be linked to synchronous magmatic episodes in the overlying crust.

The data show that compositional and geochronological signatures in garnet can be retained on billion-year time scales. Static and dynamic recrystallization, and metasomatism – rather than temperature alone – control these signatures in garnet. The exsolution of pyrope in Ca-depleted Kaapvaal and Siberian orthopyroxenites is now confirmed to have occurred in the Archean. The geochemistry and petrology of these particular samples thus can constrain the P-T evolution that led to the development of the early continents.

How to cite: Musiyachenko, K., Smit, M., Kopylova, M., and Korsakov, A.: Unlocking the secrets of the Archean cratonic mantle through garnet Lu-Hf geochronology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9276, https://doi.org/10.5194/egusphere-egu23-9276, 2023.

The Edessa ophiolite complex represents remnants of oceanic lithosphere which was thrust out of one or more ocean basins during Upper Jurassic to Lower Cretaceous time. Petrographic, geological and geochemical evidences indicate that this ophiolite complex consists of both mantle and crustal suites. It includes lherzolites, serpentinised harzburgites with high degree of serpentinisation, diorites, gabbros, diabase dolerites and basalts. We present here new data on mineral compositions and geochemistry in mafic rocks. The basalt displays N-MORB composition, having enhanced TiO₂ (1.9-2.4 wt.%) and flat REE patterns, whereas the gabbros show E-MORB affinities, having moderate to high Ti content (TiO₂ = 1.1-1.2 wt.%) with strong LREE-HREE fractionations. Such geochemical enrichment from N-MORB to E-MORB composition indicates mixing of melts derived from a depleted mantle and fertile mantle source at the spreading centre. On the other hand, diorites and partially diabase dolerites display SSZ-type composition with low Ti content (TiO₂ = 0.1-0.7 wt.%) and depleted LREE pattern with respect to HREE. They also display high Ba/Zr, Ba/Nb and Ba/Th ratios relative to primitive mantle, which strongly represents the melt composition generated by partial melting of depleted lithospheric mantle wedge influenced by hydrous fluids derived from subducting oceanic lithosphere in a forearc setting. Based on these geochemical evidence, we suggest that mid ocean ridge (MOR) type mafic rocks (basalts and gabbros) from the Edessa ophiolite represent the section of older oceanic crust which was generated during the opening of the Axios Ocean. Conversely, the diorites and diabase dolerites represent the younger oceanic crust which was formed at the forearc region by partial melting of the depleted mantle wedge modified by hydrous fluids released from the subducting oceanic slab.

How to cite: Rogkala, A., Petrounias, P., Koutsovitis, P., Giannakopoulou, P. P., Pomonis, P., and Hatzipanagiotou, K.: Geochemical characteristics of mafic rocks from the Edessa ophiolite (North Greece): Implications for their petrogenesis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10026, https://doi.org/10.5194/egusphere-egu23-10026, 2023.

Primitive mantle rocks usually contain rare earth elements (REE) in very low concentrations. Here we report an occurrence of monazite associated with REE-rich apatites in a carbonate-bearing wehrlite xenolith from Pleiku, central Vietnam. The sampled xenolith displays an equigranular matrix of rounded olivine grains. Texturally primary orthopyroxene, clinopyroxene and spinel are notably absent. Scattered within the olivine matrix two types of domains are present: domain-I contains numerous blocky clinopyroxene grains within a matrix of quenched silicate melt and is associated with a second generation of olivine, small euhedral spinel and rare grains of carbonates. Both apatite and monazite may be present. Domain-II typically contains abundant irregularly shaped patches of carbonate associated with quenched silicate melt, secondary olivine, spinel, and clinopyroxene. No phosphate phases are observed within type-II domains. Monazite occurs in different generations: monazite I is found as very small rounded to elongate grains included in primary olivine, partly crosscut by fine melt veinlets, monazite II as large grains up to 300 x 200 µm in size with embayed grain boundaries and monazite III as very small euhedral and needle-like crystals in silicate melt pools. For apatite two textural types occur: apatite I forms lath-shaped to rounded crystals up to 200 x 50 µm in size, apatite II is present within silicate melt pools of type-I domains where it forms euhedral needle-like to equant grains. Some of the apatite II crystals may have cores of monazite III. Monazites show compositional variation mainly with respect to ∑REE₂O₃ (63-69 wt%) and ThO₂ (1.1-5.3 wt%) and only minor variations in P₂O₅ (29-32 wt%) SiO₂ (<0.05-0.4 wt%) and CaO (0.2-0.4 wt%) Apatites are characterized by strongly variable and high REE₂O₃ and SiO₂ contents (4-27 wt% ∑REE₂O₃,0.6-6.8 wt% SiO₂) as well as with significant Na₂O (0.3-1.5 wt%), FeO (0.1-1.8 wt%), MgO (0.2-0.6 wt%) and SrO (0.2-0.9 wt%) contents. F and Cl contents are in the range 1.9-3.0 wt% and 0.2-0.8 wt%, respectively. Based on textural evidence and chemical composition of the metasomatized mineral phases an initial stage of metasomatism is proposed which was triggered by a P-REE-CO₂-rich agent with low a_H2O resulting in the co-precipitation of carbonates as patches and along micro-veins and of phosphates in a peridotite assemblage. A subsequent second stage is characterized by pervasive infiltration of an alkali-rich basaltic melt into the carbonate + phosphate-bearing assemblage. The presence of monazite prior to silicate melt infiltration is indicated by narrow melt veins crosscutting monazite I grains. Reactions of the silicate melt with the pre-existing phases led to the formation of domains-I and -II and changed the composition of the infiltrating melt towards phonolitic-trachytic composition. The second stage led to partial breakdown and recrystallization of monazite and apatite.

How to cite: Hauzenberger, C., Konzett, J., Joachim-Mrosko, B., and Nguyen, H.: A monazite- and REE-rich apatite-bearing mantle xenolith from Pleiku, central Vietnam, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10058, https://doi.org/10.5194/egusphere-egu23-10058, 2023.

Peridotite xenoliths from kimberlites are useful tools for exploring the architecture and composition of the thick sub-cratonic lithosphere, and thus understanding the long-term evolution of the Earth’s mantle. However, the continuous infiltration of kimberlite-related melts and fluids prior to - and during - the transport of mantle-derived fragments towards the surface makes it difficult to extract information about the original texture and chemistry of the mantle rocks and the deep-seated metasomatic processes.

In this study, fresh spinel- to garnet-bearing peridotite xenoliths from Udachnaya-East were studied to unveil the nature and composition of the lithospheric mantle beneath the Siberian craton. The studied samples have mostly harzburgitic to dunitic composition, even though lherzolites and rare wehrlites are also found. Occasionally, harzburgites are orthopyroxene-rich (up to 40 vol.%) or garnet-rich (up to 30 vol.%). The texture of the peridotites is extremely variable, ranging from protogranular to highly recrystallized and/or sheared. In spinel-bearing rocks, primary olivine is Mg- and Ni-rich (Fo_90-93; NiO = 0.34-0.46 wt%), orthopyroxene has Mg# of 92-94 and Al₂O₃ in the range of 0.3-3.0 wt%, while clinopyroxene is Mg-rich (Mg# 94-96), with Al₂O₃ comprised between 1.0 and 3.5 wt%. In garnet-bearing peridotites, olivine ranges from Mg- and Ni-rich (Fo₉₂; NiO = 0.45 wt%) to Fe-rich and Ni-poor (Fo₈₇; NiO = 0.25 wt%), while pyroxenes have Mg# from 93 to 87-88 and comparatively low Al₂O₃ contents (orthopyroxene: 0.5-1.1 wt%; clinopyroxene: 0.8-2.2 wt%). High-precision electron microprobe analyses complemented by thermo- and oxy-barometric models were used to reconstruct the thermo-chemical log of the Siberian sub-cratonic mantle, in comparison to what proposed by Liu et al. (2022). Textural-compositional studies of the reaction zones enabled to discriminate the secondary-formed minerals with composition ascribable to the liquid line of descent of kimberlite-related melts at Udachnaya (Casetta et al. 2023) from those formed during melt/fluid-rock reactions taking place in the mantle before xenoliths’ entrainment by the host kimberlites. Altogether, our results enable to trace the P-T-X evolution experienced by the Siberian mantle, opening a window onto the comprehension of the interactions between kimberlitic-related fluid/melts and the sub-cratonic lithosphere.

Casetta, F., Asenbaum, R., Ashchepkov, I., Abart, R., & Ntaflos, T. (2023). Mantle-Derived Cargo vs Liquid Line of Descent: Reconstructing the P–T–fO₂–X Path of the Udachnaya–East Kimberlite Melts during Ascent in the Siberian Sub-Cratonic Lithosphere. Journal of Petrology, 64(1), egac122.

 Liu, Z., Ionov, D. A., Nimis, P., Xu, Y., He, P., & Golovin, A. V. (2022). Thermal and compositional anomalies in a detailed xenolith-based lithospheric mantle profile of the Siberian craton and the origin of seismic midlithosphere discontinuities. Geology.

How to cite: Casetta, F., Ashchepkov, I., Faccincani, L., Abart, R., and Ntaflos, T.: Peridotite xenoliths from the Udachnaya-East kimberlite: windows onto the evolution of the Siberian sub-cratonic lithospheric mantle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12712, https://doi.org/10.5194/egusphere-egu23-12712, 2023.

The Mirdita Ophiolite (N Albania) consists of two meridional belts of different geochemical affinities: supra-subduction zone for the Eastern belt and mid-ocean ridge (MOR) for the western belt. Puke Massif described in this study is a mantle dome belonging to the MOR belt.

Structurally, the Puka Massif is interpreted as an Oceanic Core Complex formed of harzburgites cross-cut by dunitic channels grading to mylonitized plagioclase and amphibole bearing lherzolites with minor dunites and chromitites at the top of the section. The massif experienced an intense magmatic activity evidenced by gabbroic and pyroxenitic dykes. Field and petrographic evidences revealed that plagioclase, clinopyroxene and amphibole in lherzolitic mylonites crystallized from impregnating melts (Nicolas et al. 1999, 2017). Scientific question behind our study is whether this conclusion is confirmed by geochemical data.

Clinopyroxene from magmatic veins cross-cutting mylonites, has trace elements (TE) composition identical to that from the host peridotite. In general, 3 types of TE patterns can be identified in the veins and mylonites: 1. Strongly depleted (Yb=0.3-0.6x primitive mantle, PM, McDonough & Sun 1995); 2. Intermediate (Yb=1.1-4xPM); 3. Enriched (Yb=5-11xPM). The group 1 comprises only pyroxenites. Two relatively undeformed harzburgites occurring in the lowermost section of the mantle dome contain TE-poor clinopyroxene. One, which is amphibole-bearing, exhibits TE pattern resembling that in group 1, while the other one shows even more depleted signature, with Yb=0.8-1.3xPM and La <0.001xPM. Intrusive rocks from groups 2 and 3 are widespread in the whole massif while the occurrences of the depleted group are restricted to the lowermost sections. Rocks from different groups may occur within a single outcrop.

The TiO₂ content in clinopyroxene mimics the TE-based division of the rocks. Clinopyroxene in the group 1 and harzburgites has TiO₂<0.1 wt.%, whereas that from group 2 and 3 has 0.1<TiO₂<0.5 wt.% and TiO₂>0.5 wt.%, respectively. Similar relationships are observed in the composition of spinel, which has TiO₂<0.1 wt.% in group 1 rocks, 0.1 - 0.25 wt.% in group 2 and between 0.1 and 2.0 wt.% in the group 3 rocks.

As magmatic rocks and deformed peridotites share common clinopyroxene TE trends, as well as similar Ti variations in clinopyroxene and spinel, geochemical data support impregnating origin of mylonites. Impregnating melts, differing in enrichment level, were active within whole massif; only the most depleted seem to be restricted to some of its parts. Only internal or easternmost harzburgites could have escape magmatic impregnations; these samples are relatively undeformed and have depleted melting-like TE trends. These findings are in agreement with melt impregnation origin of mylonites. Presence of the depleted lithologies supports primarily harzburgitic origin of the massif, later followed by mylonitization of some of its part. 

This study was financed as a project within program “Diamond Grant” (DI 024748).

How to cite: Mikrut, J., Matusiak-Małek, M., Gregoire, M., Ceuleneer, G., Onuzi, K., and Puziewicz, J.: The impact of melt impregnation on the genesis of mantle peridotites from Puke Massif (Mirdita Ophiolite, Albania) revealed by geochemical data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13627, https://doi.org/10.5194/egusphere-egu23-13627, 2023.

The 3.5-0.5 Ma Devès volcanic field is located in the “southern” mantle domain of the French Massif Central (MC), which originated by partial melting, likely followed by refertilization by melts from the upwelling asthenosphere [1, 2]. However, the extent of melting versus degree of refertilization remains unclear. In order to obtain new insights into this fundamental question, we studied a large mantle xenolith population (n – 21) from a cinder cone in the NW of Devès, the Mt. Briançon nepheline basanite. Extensive use of EMPA and LA-ICP-MS allowed us to gather a comprehensive and representative dataset. Here, we present preliminary interpretations. Ongoing EBSD analyses will provide further data to confirm or correct our hypothesis.

The lithospheric mantle (LM) beneath the Devès is heterogeneous. It contains lherzolite with clinopyroxene (cpx) exhibiting REE patterns with relatively flat Lu-Eu and variable LREE-depletion. The coexisting spinel (spl) is highly aluminous (Cr# 0.09-0.15). By analogy with prior work [2], we suggest that cpx and spl were added to the rock by a MORB-type melt [2]. Those lherzolites probably represent refertilized LM similar to the Lherz massif [3], which obscures the original degree of depletion.

A distinct mantle region below the Devès is represented by harzburgites and cpx-poor lherzolites containing cpx with REE patterns that show moderately increasing Lu-Sm and steeply increasing towards La. The coexisting spl has medium to high Cr# (0.17-0.28). We suggest that this lithology was not refertilized by MORB-like melts, but records some other metasomatic event(s).

A single harzburgite xenolith contains LREE-enriched cpx similar to those described above, but of significantly lower element abundances. This harzburgite is the most magnesian in the entire suite, with olivine Fo ~91.2% and Mg# in pyroxenes ~0.92 (vs Fo 88.5-90.4% and Mg# 0.88-0.91 for other peridotites). Pyroxenes have the lowest Al, Fe, Ti, Na contents in the whole suite and spinel is the most chromian (Cr# ~0.43). This rock resembles harzburgites from the northern domain of the MC, interpreted as a relatively depleted residue of partial melting [4].

This study was funded by Polish National Science Centre to MZM (UMO-2018/29/N/ST10/00259).

References:

[1] Lenoir et al. (2000). EPSL 181, 359-375.

[2] Puziewicz et al. (2020). Lithos 362–363, 105467.

[3] Le Roux et al. (2007). EPSL 259, 599–612.

[4] Downes et al. (2003). Chem Geol 200, 71–87.

How to cite: Ziobro-Mikrut, M., Puziewicz, J., Aulbach, S., and Ntaflos, T.: The lithospheric mantle beneath Devès volcanic field – case study of mantle xenoliths from Mt. Briançon (Massif Central, France), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14795, https://doi.org/10.5194/egusphere-egu23-14795, 2023.

Large, single crystals (> 1cm) are a familiar component of mantle xenolith suites of many kimberlites.  Confusion between different suites exists in the literature, however, which affects petrogenetic models, and some clarification is warranted.  Megacrysts of the Cr-poor suite[1] are most common.  Cr-poor silicates (garnet, clinopyroxene, orthopyroxene, olivine) are characterized by lower Mg/(Mg+Fe) and Cr₂O₃ and higher TiO₂ values than typical mantle peridotite minerals.  Strong geochemical trends in most occurrences of Cr-poor megacryst suites (e.g., concomitant decrease in Mg/(Mg+Fe) and Cr₂O₃) are interpreted by most authors as the result of fractional crystallization of a kimberlite, or kimberlite-like, magma.   

The Cr-rich megacryst suite, comprising garnet, clinopyroxene, orthopyroxene and olivine, but not ilmenite, was described from the Sloan/Nix kimberlites in northern Colorado[1].  Constituent minerals, all four of which are essential to the definition of the suite, are characterized, in part, by high and restricted values of Mg/(Mg+Fe) and wt% Cr₂O₃ (e.g., 0.791 to 0.837 and 6.1 to 13.0, respectively, in garnet [2]).  Elsewhere, large crystals with Mg/(Mg+Fe) and Cr₂O₃ values higher than Cr-poor suite minerals do occur, but none correspond to the Sloan-Nix Cr-rich suite in paragenesis, size and/or composition[2].  For example, almost no garnet megacrysts described as “Cr-rich” or “high-Cr” from other localities (e.g., refs 3-6) contain >6 wt% Cr₂O₃ and even garnets with <2 wt% Cr₂O₃ are termed “Cr-rich” or “high-Cr”.  Most, or all, of these so-called “Cr-rich garnet megacrysts” are simply xenocrysts from coarse-grained peridotite. 

The “Granny Smith” suite, first described from Kimberley and Jagersfontein [7], is dominated by Cr-clinopyroxene associated with phlogopite (and ilmenite at Kimberley), with uncommon olivine or rutile.  Garnet and orthopyroxene do not occur in this suite, which is neither equivalent to nor a subset of the Cr-rich megacryst suite.  Other suites dominated by Cr-clinopyroxene, also not shown to coexist with garnet and orthopyroxene, have been described from Orapa and Bobbejaan [6] and Grib [8], though analogies have been drawn with the Cr-rich megacryst suite despite compositional and paragenetic differences.  A similar megacrystalline assemblage (Cr-cpx, ilmenite, phlogopite, olivine) has been described from Attawapiskat [9] and at Balmoral megacrysts of Cr-cpx occur with ilmenite, Nb-Cr rutile and zircon [10].

All of these suites of Cr-cpx +/- ilmenite, rutile, phlogopite, olivine, zircon (lacking garnet/opx), though varied, have more in common with each other than with the Cr-rich megacryst suite.  All might be best termed “Granny Smith”, and may have common origins.  The only feature they share with the Sloan-Nix Cr-rich megacryst suite is the presence of large chromian clinopyroxene.  Use of such populations as equivalents of the Sloan-Nix Cr-rich megacryst suite in mantle petrogenetic schemes can lead to faulty conclusions. 

References:  1) Eggler et al. (1979) The Mantle Sample, 2) Schulze (2022) Goldschmidt Conf. Abstr., 3) Hunter and Taylor (1984) Am. Min., 4) Kopylova et al. (2009) Lithos, 5) Bussweiller et al. (2018) Min. Pet., 6) Nkere et al. (2021) Lithos, 7) Boyd et al. (1984) GCA, 8) Kargin et al. (2017) Lithos, 9) Hetman (1996) MSc., 10) Schulze, unpub. data. 

How to cite: Schulze, D.: Megacryst suites in kimberlite, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16528, https://doi.org/10.5194/egusphere-egu23-16528, 2023.

Integrating petrography and mineral chemistry data with the determination of volatiles concentration and isotopic fingerprint in fluid inclusions (FI) in ultramafic xenoliths is a novel approach which provides crucial information on the nature and evolution of the lithospheric mantle, together with important insight into how and where volatiles are stored and/or migrate through the lithosphere.

In this work, we investigated a new suite of ultramafic peridotite xenoliths from the Massif d’Ambre by integrating petrography, mineral and glass chemistry and the concentrations of volatiles [CO₂ and noble gases (He, Ne and Ar)] in fluid inclusions (FI) hosted in olivine (Ol), orthopyroxene (Opx) and clinopyroxene (Cpx). The Massif d’Ambre is a Cenozoic stratovolcano located in northern Madagascar originated upon intense volcanic activity from ~12 to ~0.85 Ma, and the area is characterized by the widespread occurrence of mantle xenoliths, mostly, but not restricted to, spinel lherzolites and subordinately pyroxenites, which are hosted in mafic volcanic rocks. The new suite comprises 18 lherzolites, 11 harzburgites, 2 dunites, 3 wehrlites and 1 Ol-clinopyroxenite. Based on their petrographic and textural features, the suite was divided into five distinct groups: group 1A (protogranular to porphyroclastic textures), group 1B (large and porphyroclastic olivines), group 2 (infiltrated dunites and wehrlites), group 3 (cumulate-textured wehrlites) and group 4 (Ol-clinopyroxenite). Xenoliths are modally and compositionally heterogeneous and a clear separation can be observed between groups 1A-1B and groups 2-3, as testified by the large forsterite range of olivine (Fo88.4 – 93.2 vs Fo78.7 – 89.1, respectively), the Mg# of orthopyroxene (89.5 – 93.2 vs 82.7 – 87.3, respectively) and clinopyroxene (90.9 – 95.2 vs 81.4 – 89.9, respectively). This systematics corroborates the distinct origin of the groups, with xenoliths belonging to 1A-1B having the most refractory character and reflecting high extents (up to 30%) of melt extraction, while groups 3-4 xenoliths reflecting less depleted or re-fertilized mantle portions. Based on glass analyses, we propose that a carbonatitic or carbonated alkaline agent may have interacted with some portion of the source mantle, in agreement with Coltorti et al. (2000). The noble gases in FI hosted in Ol, Opx and Cpx exhibit ³He/⁴He ratio corrected for air contamination (Rc/Ra values) ranging from 5.90 Ra to 7.05 Ra, which is below the typical MORB-like upper-mantle value (8 ± 1 Ra). Furthermore, the great majority of xenoliths exhibits ⁴He/⁴⁰Ar* ratios between ca. 0.2 to 0.8.

The major element distribution in mineral phases together with the systematic variations in FI composition will be used to place constraints on the origin and evolution (in terms of melting and metasomatism) of this portion of the mantle below the Massif d’Ambre and will be exploited to obtain a possible timeline for the petrological events that have characterized this lithospheric mantle portion.

Coltorti M., Beccaluva L., Bonadiman C., Salvini L. & Siena F. 2000. Glasses in mantle xenoliths as geochemical indicators of metasomatic agents. Earth Planet Sc. Lett., 183, 303–320.

Keywords: mantle xenoliths; lithospheric mantle; metasomatism; Massif d’Ambre

How to cite: Faccini, B., Faccincani, L., Rizzo, A. L., Casetta, F., and Coltorti, M.: Combining volatiles measurements in fluid inclusions with petrology of ultramafic xenoliths from the Massif d'Ambre: unravelling the nature and evolution of the northern Madagascar Sub-Continental Lithospheric Mantle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16798, https://doi.org/10.5194/egusphere-egu23-16798, 2023.

Melts with rhyolite compositions originate from partial melting of crustal rocks or extensive differentiation of basaltic melts, at temperatures in the range of 800 °C. Accordingly, they are confined to the shallow continental crust. Nevertheless, experimental studies have demonstrated that dacite-rhyolite melts can be generated at higher temperature (> 1000°c) and pressure (>2 GPa), by partial melting of continental crustal lithotypes, but direct evidence for their occurrence has never been found. This implies that rhyolite melts may be produced at mantle conditions either by subduction of sedimentary material or exhumation of subducted continental crust.

Ephemeral rhyolite melt inclusions were found preserved in peridotite xenoliths from Tallante (Betic Cordillera, southern Spain) that are remnants of a supra-subduction mantle wedge. Here, the interaction of silica-rich melts with peridotite generated hybrid mantle domains, characterized by the occurrence of millimetre-sizes felsic veins with crust-like Sr-Nd-Pb-O- isotope compositions. The “Tallante” composite xenoliths were found among a wide population of peridotitic xenoliths, and display extreme compositional and isotopic heterogeneities both within the ambient peridotite and within the felsic veins. The latter consist of orthopyroxene, plagioclase, and quartz, and they are separated from the surrounding peridotite by an orthopyroxene-rich reaction zone. In their mineral phases, rhyolite glass inclusions and interstitial films associated to quartz crystals were observed. Petrological evidence and thermodynamic modelling indicate that rhyolite melts were originated by partial melting of near an-hydrous garnet-bearing metapelites at temperatures above 1000 °C. Partial melting was likely triggered by near-isothermal decompression during rapid exhumation of previously subducted crustal slivers. The melts reacted with the ambient lithospheric mantle at lower temperature (900 °C) and produced orthopyroxene, followed by plagioclase, quartz, and phlogopite. On the basis of chemical characteristics, it is hypothesized that potassic (HK-calc-alkalic to shoshonitic) and  ultrapotassic magmas may originate from metasomatic mantle sources generated from the interaction of crustal rhyolitic melts with mantle peridotite.

How to cite: Dallai, L., Bianchini, G., Avanzinelli, R., Gaeta, M., Deloule, E., Natali, C., Cavallo, A., and Conticelli, S.: Crustal rhyolite melts at mantle depths, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17587, https://doi.org/10.5194/egusphere-egu23-17587, 2023.

Natural processes and anthropogenic activities often generate changes in the stress state of the crust, and, consequently, measurable surface deformation. Volcanic activity produces surface displacements as a result of phenomena including magma recharge/deployment and migration, and fluid flow. The accurate measurement of surface deformation is one of the most relevant parameters to measure tectonic stress accumulation and for studying the seismic cycle. Improved monitoring capabilities also capture surface deformations related to coastal erosion and its connection to climate change, landslides and deep seated gravitational slopes, and other hydrogeological hazards. In addition, anthropogenic activity such as mining and water pumping cause measurable soil displacement.

Ground deformations are measured by space and terrestrial techniques, reaching sub-millimetric accuracy. Synthetic Aperture Radar (SAR) satellites have been quickly developing in the last decades. GNSS data allows to map nearly 3D deformation patterns, but often the network consists of few benchmarks. The joint use of SAR and GNSS data compensate the intrinsic limitations of each technique. Levelling measures the geodetic height of a benchmark. Borehole dilatometers and clinometers provide derivative measurements of the surface displacements.

Theoretical models of deformation sources are commonly employed to investigate the surface displacements observed, for example, in volcanic areas or related to a seismic event. A volcanic source can be represented by a confined part of crust with a certain shape inflating/deflating because of a change in the internal magma/gas pressure. The static seismic source is ideally represented by a tabular discontinuity in the crust undergoing relative movement of both sides. Furthermore, gas reservoir exploitation, water pumping and soil consolidation, can be represented using the same models.

Volcanic and Seismic source Modelling (VSM) is an open-source Python tool to model ground deformation detected by satellite and terrestrial geodetic techniques. It allows the user to choose one or more geometrical sources as forward model among sphere, spheroid, ellipsoid, fault, and sill. It supports geodetic from several techniques: interferometric SAR, GNSS, levelling, Electro-optical Distance Measuring, tiltmeters and strainmeters. Two sampling algorithms are available, one is a global optimization algorithm based on the Voronoi cells and the second follows a probabilistic approach to parameters estimation based on the Bayes theorem. VSM can be executed as Python script, in Jupyter Notebook environments or by its Graphical User Interface. Its broad applications range from high level research to teaching, from single studies to near real-time hazard estimates. Potential users range from early career scientists to experts. It is freely available on GitHub (https://github.com/EliTras/VSM). In this contribution I show the functionalities of VSM and test cases.

How to cite: Trasatti, E.: Volcanic and Seismic source Modelling (VSM) - An open tool for geodetic data modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2589, https://doi.org/10.5194/egusphere-egu23-2589, 2023.

Volcanic eruptions are often preceded by episodes of inflation and emplacement of magma along tensile fractures. Here we study the 2021 Cumbre Vieja eruption on La Palma, Canary Islands, and present evidence for tensile fractures dissecting the new cone during the terminal stage of the eruption. We use synthetic aperture radar (SAR) observations, together with drone images and time-lapse camera data, to determine the timing, scale and complexities associated with the fracturing event, which is diverging at a topographic ridge. By comparing the field dataset with analogue models, we further explore the details of lens-shaped fractures that are characteristic for faults diverging at topographic highs and converging at topographic lows. The observations made at Cumbre Vieja and in our models are transferrable to other volcanoes and add further evidence that topography is substantially affecting the geometry and complexity of fractures and magma pathways, and the locations of eruptions.

How to cite: Walter, T. R., Zorn, E., Gonzalez, P., Sansosti, E., Munoz, V., Shevchenko, A., Plank, S., Reale, D., and Richter, N.: Late complex tensile fracturing interacts with topography at Cumbre Vieja, La Palma, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3344, https://doi.org/10.5194/egusphere-egu23-3344, 2023.

Geophysical and geological data acquired during the 2020–2021 SISMAORE oceanographic cruise reveal a corridor of recent volcanic and tectonic features 200 km wide and 600 km long within and north of Comoros Archipelago in the North Mozambique Channel. More than 2200 submarine volcanic edifices, comparable to the Fani Maoré volcano, have been identified. Most of them are distributed according to two large submarine tectonic-volcanic fields: the N’Drounde province oriented N160°E north of Grande-Comore Island, and the Mwezi province oriented N130°E north of Anjouan and Mayotte Islands. The presence of popping basaltic rocks sampled in the Mwezi suggests post-Pleistocene volcanic activity. The geometry and distribution of recent structures observed on the seafloor are consistent with a current regional dextral transtensional context. Their orientations change progressively from west to east (∼N160°E, ∼N130°E, ∼EW). In the western part, the volcanism could be influenced by the pre-existing structural fabric of the Mesozoic crust. The wide tectono-volcanic corridor underlines the incipient Somalia–Lwandle dextral lithospheric plate boundary between the East-African Rift System and Madagascar. For details see Thinon et al. (2022;  doi 10.5802/crgeos.159).

How to cite: Thinon, I., Lemoine, A., Leroy, S., Paquet, F., Berthod, C., Zaragosi, S., Famin, V., Feuillet, N., Boymond, P., Masquelet, C., Rusquet, A., and Mercury, N. and the SISMAORE and COYOTES teams: Volcanism and tectonics unveiled in the Comoros Archipelago between Africa and Madagascar, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5046, https://doi.org/10.5194/egusphere-egu23-5046, 2023.

The Krafla Volcanic System (KVS) in the Northern Volcanic Zone (NVZ) in Iceland last erupted between 1975 and 1984, during an eruptive period called “the Krafla Fires”. The KVS is composed of a restless caldera, an array of scoria cones along a fissure swarm and is among the best-studied volcanic systems due to the exploitation of its geothermal potential. In 2009, the Icelandic Deep Drilling Project (IDDP) encountered a shallow rhyolitic magma body at 2.1 km depth beneath the caldera. To date, no geophysical method has been able to image this magma body at Krafla within the top 4 km of the crust.

  Here we present new micro-gravity data collected in June and July 2022 across a 14-station network of benchmarks in the KVS. Micro-gravimetry is a relative method that records changes in gravity between a reference and a series of benchmarks over both space and time to investigate subsurface mass or density changes via time-series analysis and modelling.

  Our 2022 survey highlights negative gravity differences of benchmarks located in the centre of the caldera with respect to a reference located to the south and outside the caldera. The most negative values are found in its eastern part. Positive gravity differences can be found south of the southern caldera wall along a set of past eruptive fissures.

  The next steps in data processing include data reduction for deformation effects to link the new data to previous joint deformation and micro-gravity surveys conducted at the KVS since 1965. This should enable us to quantify the long-term evolution of the KVS over more than 50 years providing unprecedented insights into its inner workings.

How to cite: Martinez Garcia, A., Gottsmann, J., and Rust, A.: The long-term evolution at Krafla Volcanic System, Iceland, by time-lapse microgravity., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5163, https://doi.org/10.5194/egusphere-egu23-5163, 2023.

Forecasting eruption is the ultimate challenge for volcanology. While there has been some success in forecasting eruptions hours to days beforehand¹, reliable forecasting on a longer timescale remains elusive. Here we show that magma inflow rate, derived from surface deformation, is an indicator of the probability of magma transfer towards the surface, and thus eruption, for basaltic calderas. Inflow rates ≥0.1 km³/year promote magma propagation and eruption within 1 year in all assessed case studies, whereas rates less than 0.01 km³/year do not lead to magma propagation in 89% of cases. We explain these behaviours with a viscoelastic model where the relaxation timescale controls whether the critical overpressure for dike propagation is reached or not. Therefore, while surface deformation alone is a weak precursor of eruption, estimating magma inflow rates at basaltic calderas provides improved forecasting, substantially enhancing our capacity of forecasting weeks to months ahead of a possible eruption.

How to cite: Acocella, V., Galetto, F., Hooper, A., and Bagnardi, M.: Forecasting the fate of unrest at basaltic calderas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5317, https://doi.org/10.5194/egusphere-egu23-5317, 2023.

Countries with low to lower-middle income have limited resources to deploy and maintain ground monitoring networks. In this context, satellite-based techniques such as Radar interferometry (InSAR) is a great solution for detecting volcanic ground deformation at regional-scale. With the launch in 2014 of Sentinel-1 mission, regional monitoring of volcanic unrest becomes easier as SAR data are freely available with a revisit time of 6-12 days. Here, we develop a tuned processing workflow to produce Sentinel-1 InSAR time series and to automatically detect volcanic unrest over 80 volcanic systems located along the East African Rift System (EARS). First, we show that the correction of atmospheric signals for the arid and low-elevation EARS volcanoes is less important than for other volcanic environments. For a 5-year times series (between Jan. 2015 and Dec. 2019), we show that statistically uncertainties in InSAR velocities are around 0.1 cm/yr, whereas uncertainties associated with the choice of reference pixel are typically 0.3–0.6 cm/yr. For the automatic detection, we found that volcanic unrest can be detected with high confidence in the case the cumulative displacements exceed three times the temporal noise (threshold of 3σ). Based on this criterion, our survey reveals ground unrest at 16 volcanic centres among the 38 volcanic centres showing historical evidence of eruptive or unrest activity. A large variety of processes causing deformation occurs in the EARS: (1) subsidence due to contraction of magma bodies at Alu-Dalafilla, Dallol, Paka and Silali; (2) subsidence due to lava flows compaction at Kone and Nabro; (3) subsidence due to fluid migration at Olkaria and Aluto or fault-fluids interactions at Haludebi and Gada Ale; (4) rapid inflation due to magma intrusions at Erta Ale and Fentale; (5) short-lived inflation of shallow reservoirs at Nabro and Suswa; (6) long-lived inflation of large magmatic systems at Corbetti, Tullu Moje and Dabbahu. Except Olkaria and Kone, all these volcanoes were identified as deforming by previous satellites missions (between late 90’s and early 2000), which is an indication of the persistence of activity over long-time scales (>10 years).  Finally, we fit the time series using simple functional forms and classify seven of the volcano time series as linear, six as sigmoidal and three as hybrid, enabling us to discriminate between steady deformation and short-term pulses of deformation. We found that the characteristics of the unrest signals are independent of the expected processes, which means that additional information (structural geology, seismicity, eruptive history and source modelling) will be necessary to characterize the processes causing the unrest. Our final objective will be to improve the transfer of this information to local scientists in Africa, which can be achieved by integrating our tools to an existing monitoring system and by developing web-platform where the InSAR products can be freely available.

How to cite: Albino, F., Biggs, J., Lazecký, M., Maghsoudi, Y., and McGowan, S.: Regional-scale ground monitoring of 80 East African Rift volcanoes using Sentinel-1 SAR interferometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5609, https://doi.org/10.5194/egusphere-egu23-5609, 2023.

Investigation of the dynamic magma movement beneath the volcanos could provide critical information about the mechanism of volcanic eruption and therefore enhance the accuracy of eruption forecast.  Axial Seamount is an active submarine volcano located at the intersection of the Juan de Fuca Ridge and the Cobb hotspot.  Through its submarine surveillance network of Ocean Observatories Initiative (OOI), we observed magmatic activities that occurred before and during its latest eruption on April 24, 2015, as well as the following unrest events from the temporal variations of shear-wave velocity beneath Axial Seamount.

In this study, we applied the Rayleigh-wave admittance method, which uses the frequency-domain transfer function between seismic displacement and water pressure, to invert for shear-wave velocity changes beneath the submarine seismic stations.  The results illustrated that a large magma upwelling event happened beneath the AXEC2 (southeastern caldera of Axial Seamount) several weeks prior to its 2015 eruption, implying the magma movement through a pathway near the southeastern caldera and possibly triggered the subsequent eruption.  However, another magma upwelling event beneath the AXID1 station (southern caldera) between December 2016 and June 2017 occurred without triggering any noticeable eruption event. These magmatic activities demonstrate that the eruption of Axial Seamount is controlled by a complicated magma plumbing system.  The eruption probably depends on not only the magma influx but also the status of the plumbing system and the overlying crustal layer.  With the Rayleigh-wave admittance method and the real-time data from the OOI network, we can continuously monitor the status of Axial Seamount and provide more information for the next eruption.

How to cite: Wang, L. and Ruan, Y.: Dynamic magma movements beneath the Axial Seamount revealed by Rayleigh-wave Admittance Method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5843, https://doi.org/10.5194/egusphere-egu23-5843, 2023.

One of the best-known examples worldwide of monogenetic volcanism is the Parícutin volcano. The eruption began its formation in the middle of a cornfield in February 1943 and lasted until March 1952. Parícutin is the youngest edifice of the Michoacán-Guanajuato Volcanic Field, which was witness initially by local inhabitants, and later by scientists and other observers. Observations of the eruption documented the remobilization of primary ashfall by rainfall and wind. Despite these observations, the resulting reworked deposits have not yet been described in the stratigraphic sequence. The distinction between primary pyroclastic and reworked deposits is critical for the geological understanding of eruptive processes and related hazards because of their different origins, frequencies, and environmental impacts. This categorization is not always obvious and needs a detailed study to characterize the complex interbedding of both types of deposits that coexist in the volcanic sequence. Referenced to these, we conducted new field reconnaissance, coupled with laboratory analyses of the ejecta ash fraction. The detailed composite stratigraphy obtained consists of six widely dispersed fallout deposits interbedded with seven reworked units. These reworked deposits display sedimentary structures produced by tephra remobilization due to lahars and stream flows. In addition, some layers show dunes and ripples generated by duststorms. By using GIS tools, we integrated the existing data with our new composite stratigraphic column and the distribution map of the syn-eruptive reworked deposits. This analysis reveals that more than 70% of the total thicknesses correspond to syn-eruptive reworked deposits. Therefore, previous studies had overestimated the distribution of primary tephra from the Parícutin explosive phases. The lowest and flattest areas with wide rill networks, which are located 4 to 6 km north of the volcano, are composed of up to 90% reworked deposits. In contrast, proximal locations with gentler slopes located at medium altitudes better preserve pyroclastic deposits. To that end, we constructed a new isopach map of the pyroclastic deposits based on the distribution of the reworked deposits. This study brings new light to understanding the sedimentary processes that occur during volcanic eruptions and highlights the importance of recognizing pyroclastic and reworked deposits during monogenetic eruptions.

How to cite: Bolós, X., Macias, J. L., Ocampo-Díaz, Y. Z., and Tinoco, C.: Reworking processes during monogenetic eruptions. The case of the Parícutin volcano, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5994, https://doi.org/10.5194/egusphere-egu23-5994, 2023.

The Hawaii-Emperor seamount chain stretches westward from the “Big Island” of Hawaii for over 6000 km until the oldest part of the Emperor chain is subducted at the Kuril and Aleutian trenches. Still regarded as the iconic hotspot-generated seamount chain it has been sampled, mapped, and studied to give insights into numerous oceanic phenomena, such as seamount and volcano formation and associated intraplate magma budgets, the past absolute motions of the Pacific plate and the drift of the Hawaiian plume, and the thermal and mechanical properties of oceanic lithosphere. Much early work on determining the flexural rigidity and equivalent elastic plate thickness that supports the large volcano loads that comprise the chain was focussed on the Hawaiian Ridge, with a major multichannel seismic expedition to the Hawaiian Islands in 1982 providing clear and direct evidence of plate flexure, as well as the indirect effect this deformation has on Earth’s gravity field. Numerous studies have since followed. However, the older part of the chain, beyond the ~50 Ma “bend”, has been much less well studied due to its remoteness, but recent expeditions have provided new marine seismic data to allow an estimation of elastic thickness along the Emperor chain and how they compare to the information we have along the Hawaiian Ridge. Here, we present preliminary work on determining the elastic thickness beneath the Emperor Seamounts. Unlike the Hawaiian Ridge, where the age of the lithosphere at the time of loading (i.e., the difference in age between the underlying seafloor and the formation age of a seamount or oceanic island) is remarkably constant, along the Emperor chain there are major variations in the age of loading, compounded by higher uncertainty due to limited seamount age sampling and the chain’s location within the Cretaceous Quiet Zone. Thus, models with variable elastic thickness as a function of location along the Emperor chain are required. In this presentation, we discuss several models that seek to account for the new seismic imaging of the top and base of flexed oceanic crust (i.e. Moho) at Jimmu guyot while at the same time honouring the characteristic gravimetric signature of the Emperor seamount edifices and their flanking moats. The Optimal Regional Separation (ORS) method is used to isolate the flexural loads, while seismic tomography and different velocity/density relations are explored for assigning suitable load and infill densities that vary spatially, and we search for optimal density and elastic parameters which minimize the misfit to both the residual gravity as well as the seismically observed flexure in the vicinity of Jimmu guyot. The first-order result is a clear thinning of the elastic thickness as we move from south to north: the implications of which we examine here for the tectonic evolution of the northwest Pacific Ocean and the long-term (>10⁶ a) mechanical properties of oceanic lithosphere.

How to cite: Wessel, P., Watts, T., Xu, C., Boston, B., Cilli, P., Dunn, R., and Shilington, D.: Variation in Elastic Thickness along the Emperor Seamount Chain, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6118, https://doi.org/10.5194/egusphere-egu23-6118, 2023.

Dykes (Mode I extension fractures) supply magma from deep reservoirs to the surface and subject to their propagation paths, they can sometimes reach the surface and feed volcanic eruptions. Most of the times they mechanically stall in the heterogeneous crust or deflect through pre-existing fractures forming sills. Although several studies have explored dyking in heterogeneous regimes, the conditions under which dykes propagate in glacial-volcanotectonic regimes remain unclear.

Here, we coupled field observations with FEM numerical modelling using the software COMSOL Multiphysics (v5.6) to explore the mechanical and geometrical conditions that promote (or not), dyke-sill propagation in glacial-tectonic conditions. We used as a field example the Stardalur cone sheet-laccolith system, located in the Esja peninsula proximal to the western rift zone. The laccolith is composed of several vertical dykes that bend into sills and form a unique stacked sill ‘flower structure’. We modelled a heterogeneous crustal segment composed of lavas (top) and hyaloclastites (bottom). We then studied the emplacement of a dyke with varied overpressure values (P_o = 1-10 MPa) and regional extension (Fe = 0.5-3 MPa) loading conditions at the lava/hyaloclastite contact. In the second stage, we added an ice cap as a body load to explore dyking subject to unloading due to glacier thickness variations (0-1 km).

Our results have shown that the presence of the ice cap can affect the dyke-sill propagation and the spatial accumulation of tensile and shear stresses below the cap. The observed field structure in non-glacial regimes has been formed either due to the mechanical contrast (Young’s modulus) of the studied contact, a compressional regime due to pre-existing dyking or faulting, or finally, high overpressure values (P_o  ≥ 5 MPa). Instead, in a glacial regime, the local extensional stress field below the ice cap encourages the formation of the laccolith when the ice cap becomes thinner (lower vertical loads). Our models can be applied to universal volcanoes related to glacier thickness variation and sill emplacement.

How to cite: Drymoni, K., Tibaldi, A., Pasquaré Mariotto, F., and Bonali, F. L.: Dyke-sill propagation in glacial-volcanotectonic regimes: The case study of Stardalur laccolith, SW Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6230, https://doi.org/10.5194/egusphere-egu23-6230, 2023.

Assessing the history, dynamics and magnitude of pre-historic explosive volcanic eruptions relies heavily on the completeness of the stratigraphic records, the spatial distribution, and the sedimentological features of the pyroclastic deposits. Near-vent volcanic successions provide fundamental but often patchy information, both in terms of record completeness (e.g., scarce accessibility to the older deposits) and of the spatial variability of the sedimentological features. Hence, medial to distal sections increasingly represent essential integrative records.

Campi Flegrei (CF) is among the most productive volcanoes of the Mediterranean area, with a volcanic history comprised of well-known caldera-forming eruptions (e.g., Campanian Ignimbrite, CI, ~40 ka; Neapolitan Yellow Tuff, NYT, ~14 ka). Furthermore, recent studies correlated a well-known widespread distal ash layer, the so-called Y-3, with a poorly exposed proximal CF pyroclastic unit (Masseria del Monte Tuff, 29ka), allowing a re-assessment of the magnitude of this eruption, now recognized as a third large-magnitude (VEI 6) eruption at CF. The discovery of this large eruption reduces drastically the recurrence intervals of large-magnitude events at CF and has major implications for volcanic hazard assessment.

While the most powerful Late Pleistocene (e.g., post-NYT and partially post-CI) eruptions at CF have been the subject of extensive investigations, less is known about its earliest activity. Motivated by this knowledge gap, we have reviewed the research on Middle-Late Pleistocene eruptions from the CF (~160-90 ka) in light of new compositional (EMPA + LA-ICP-MS), grain-size distribution (dry/wet sieving and laser) and morphoscopy (SEM) data of tephra layers from proximal and distal settings, including inland and offshore records. Our study provides a long-term overview and cornerstone that will help provide future eruptive scenarios, essential for the quantification of recurrence times of explosive activity and in volcanic hazard assessment in the Neapolitan area. This overview sets the basis for modelling dispersion as well as eruptive dynamics parameters of pre-CI large-magnitude eruptions, needed to better understand the behavior of the CF caldera with a long-term perspective.

How to cite: Fernandez, G., Giaccio, B., Costa, A., Monaco, L., Albert, P., Nomade, S., Pereira, A., Leicher, N., Lucchi, F., Petrosino, P., Milia, A., Insinga, D., Wulf, S., Kearney, R., Veres, D., Jordanova, D., and Sottili, G.: New constraints on Middle-Late Pleistocene large-magnitude eruptions from Campi Flegrei, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6552, https://doi.org/10.5194/egusphere-egu23-6552, 2023.

In this research, the Interferometric Synthetic Aperture Radar (InSAR) method is used to evaluate the connection between earthquakes and volcano dynamics in Azerbaijan. InSAR provides a robust technique for defining the complexity of earthquakes in spatial dimensions and provides more precise information about the effects of earthquakes than traditional methods. We assessed pre-, co-, and post-seismic scenarios to find the possible triggering relationships between moderate earthquakes and the Ayazakhtarma mud volcano. The Ayazakhtarma volcano is located 46 km from the 2021 Shamakhi and 67 km from the 2019 Basqal earthquakes, respectively. In this study, comprehensive deformation time series and velocities for the volcano using Sentinel 1A/B data between 2014 and 2022 were produced from LiCSAR products using LiCSBAS. At the same time, a radar line-of-sight (LOS) displacement map was generated based on results from the GMT5SAR for pre-, co-, and post-seismic deformation of earthquakes. Based on our observations of the following earthquakes, our results show that moderate earthquakes (Mw≤5) cannot trigger large mud volcano eruptions. In particular, the study of the Ayazakhtarma mud volcano revealed significant LOS changes that were positive and negative in the western half and eastern half of the site, respectively. Our research helps us comprehend how earthquakes impact eruptive processes. In two different situations, the interferograms enable the detection of ground displacement associated with mud volcano activity. At the Ayazakhtarma, faults also play a fairly important role in the deformation pattern. Interestingly, the observed fault system primarily exists in the region that divides sectors with various rates of subsidence. The interferometric data have been studied, providing new information on the deformation patterns of the Ayazakhtarma mud volcano.

How to cite: Gadirov (Kadirov), F. and Ahadov, B.: The Relationship Between Moderate Earthquakes and Ayazakhtarma Mud Volcano Using the InSAR Technique in Azerbaijan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6906, https://doi.org/10.5194/egusphere-egu23-6906, 2023.

Mooring networks of hydrophones is an effective way to monitor the ocean soundscape and its sources, and it is particularly efficient to better understand underwater volcanic eruptions. In October 2020, four continuous hydrophones were moored in the SOFAR channel around Mayotte Island, in the North Mozambique Channel, to monitor the Fani Maoré 2018-2022 submarine eruption. This eruption created a new underwater seamount at 3500 m below sea level, 50 km east of Mayotte. Since 2020, the MAHY hydrophones record sounds generated by the volcanic activity and the first results have evidenced earthquakes, underwater landslides, and impulsive signals that we related to steam bursts during lava flow emplacement. An automatic detection of these specific impulsive signals is being developed for a better monitoring but also a better understanding of their source. The hydroacoustic catalog obtained characterize the Mayotte lava flow activity and will help quantify the risk for Mayotte population. This detection could be used by Mayotte’s and other volcano observatories to monitor active submarine eruptions in the absence of regular seafloor imaging.

How to cite: Lavayssière, A., Bazin, S., Royer, J.-Y., and Raumer, P.-Y.: Hydroacoustic monitoring of Mayotte underwater volcanic eruption, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7141, https://doi.org/10.5194/egusphere-egu23-7141, 2023.

Phreatic and hydrothermal eruptions remain among the most difficult to forecast. The frequent absence of clear precursor signals challenges volcanologists' ability to provide timely and accurate hazard advice. They remain poorly understood and have recently caused human fatalities. It is therefore paramount to better investigate such eruptions by integrating new methodologies to fully understand the preparatory processes at play and improve our ability to forecast them.

Among the different approaches to monitor volcanoes, seismology forms the basis, and most active volcanoes are nowadays equipped with at least one seismometer. Seismology is unique amongst the Earth Science disciplines involved in volcano studies, as it provides real-time information; as such, it is the backbone of every monitoring program worldwide. With data storage capabilities expanding over the last decades, new data processing tools have emerged taking advantage of continuous seismic records. Recent advances in volcano monitoring have taken advantage of seismic noise to better understand the time evolution of the subsurface. 

The well-established seismic interferometry has allowed us to detect precursory changes (dv/v or decorrelation) to phreatic eruptions at different volcanoes, thereby providing critical insights into the triggering processes. More recent approaches have provided insights into the genesis of gas-driven eruptions using seismic attenuation (DSAR: Displacement seismic amplitude ratio) and correlation with tidal stresses (LSC). Yet, puzzling observations have been made at different volcanoes requiring the use of numerical models and machine learning-based approaches, as well as complementary dataset to reach a more comprehensive understanding. This presentation will review recent insights gained into precursory processes to phreatic eruptions using seismic noise and how we could possibly forecast them. These tools are freely available to the community and have the potential to serve monitoring and aid decision-making in volcano observatories.

How to cite: Caudron, C., Girona, T., Lecocq, T., Ardid, A., Dempsey, D., and Yates, A.: Towards monitoring phreatic eruptions using seismic noise, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7166, https://doi.org/10.5194/egusphere-egu23-7166, 2023.

Active calderas are typically characterized by shallow magmatic systems associated with marked geothermal anomalies and significant fluid releases. Ground deformation are generally associated with uplift or subsidence, induced by recharges or emptying/cooling of the magmatic storage system, by expansions or contractions of hydrothermal systems, or by combinations of these factors. The pressure variations in the hydrothermal systems can lead to an increase in the fumarolic and distributed soil degassing activity or in the sudden release of gas, leading to phreatic explosions, even to violent ones.

The Island of Vulcano (Italy), part of the Aeolian archipelago (southern Tyrrhenian Sea), contains an active caldera (La Fossa caldera) showing a widespread degassing and fumarolic activity, mainly localized in the main active volcano (La Fossa cone) and in other emissions zones within the caldera. The La Fossa caldera has shown signs of unrest since September 2021 and to date monitoring parameters have not returned to background levels.

Accordingly, the geophysical measurements obtained through the Vulcano Island monitoring infrastructures, which include geodetic and seismic data, were analysed. GNSS and DInSAR data, the former processed using the GAMIT-GLOBK software to calculate both time series and velocities of every remote station of the 7-stations network in Vulcano and Lipari islands, the latter processed through the P-SBAS technique, were used to identify the source of deformation. The seismic network data were exploited to discriminate the seismicity induced by regional tectonics from that induced by the magmatic or hydrothermal system (VT, VLP, tremor).

The inversion of the ground deformation measurements made possible to investigate the source within the hydrothermal system of the Fossa cone. Moreover. the seismic data analysis reveals the activation of regional crustal structures during the hydrothermal unrest, as well as the flow of hydrothermal fluids within the caldera structures linked to the presence of a pressurized hydrothermal system.

The presented results will provide a general overview of the main findings relevant to the Vulcano Island geodetic and seismic data inversion and analysis.

How to cite: Di Traglia, F., Bruno, V., Casu, F., Cocina, O., De Luca, C., Giudicepietro, F., Lanari, R., Macedonio, G., Mattia, M., Monterroso, F., and Privitera, E.: Dealing with hydrothermal unrest in active calderas by jointly exploiting geodetic and seismic measurements: the 2021-22 Vulcano Island (Italy) crisis case study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7174, https://doi.org/10.5194/egusphere-egu23-7174, 2023.

Understanding the factors that affect dike propagation and dike arrest in the shallow crust, and subsequently control the associated dike-induced surface deformation is fundamental for volcanic hazard assessment. In this work, we focus on two dike segments associated with the Younger Stampar eruption (1210-1240 AD) on the Reykjanes Peninsula (SW Iceland). Both segments (spaced 30 m apart horizontally) were emplaced in the same heterogeneous crustal segment composed of lavas and tuffs. Here, the first dike to be emplaced fed a lava flow, while the second dike became arrested 5 m below the free surface without producing any brittle surface deformation. Therefore, this area represents an ideal case study to analyse the conditions that promote dike arrest or, alternatively, dike propagation to the surface. The outcrop also provides further examples of the absence of brittle deformation around a dike arrested just below the surface. 

For this work, we collected structural data from the dikes and the heterogeneous layers as well as from the nearby crater rows associated with the Stampar eruptions. We integrated our field observations with a high-resolution 3D model reconstructed from UAV-collected pictures through Structure-from-Motion photogrammetric techniques. These 3D model data were then used as inputs for Finite Element Method (FEM) numerical models through the COMSOL Multiphysics® software (v5.6). We performed a range of sensitivity tests to investigate the role of dike overpressure (P_o= 2 - 4 MPa), the mechanical properties of the host rock (e.g., Young’s modulus), and the layering of the crustal segment subject to horizontal extension and compression boundary conditions.

Our multidisciplinary structural analyses show that the Stampar crater rows is consistent in strike with the orientation of the volcanic system of the Reykjanes Peninsula, as well as the other historic and prehistoric eruptive fissures in the region. Furthermore, our numerical models indicate that the layering and the dissimilar mechanical properties of the host rock contributed to the arrest of non-feeder dike and the associated absence of brittle deformation at and above its tip. In particular, the layering (stiff lava flow on top of soft tuff) magnifies (concentrates) the compressive stress induced by the earlier feeder dike which cuts through an existing lower part of the surface lava flow. The horizontal compressive stress, in turn, is one reason for the very low overpressure of the non-feeder when it approached the tuff-lava contact, hence its arrest at the contact. Our studies can be applied to other dike-fed volcanic areas in Iceland and worldwide.

How to cite: Corti, N., Bonali, F. L., Russo, E., Pasquarè Mariotto, F., Gudmundsson, A., Drymoni, K., Tibaldi, A., Esposito, R., and Cavallo, A.: Dike-arrest vs dike-propagation and associated surface stresses: an example from the Younger Stampar eruption (13th century), Reykjanes Peninsula, SW Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7218, https://doi.org/10.5194/egusphere-egu23-7218, 2023.

Correct estimation of the timing of velocity changes (break points) and associated uncertainties in ground deformation observed with Global Navigation Satellite System (GNSS) coordinate time series is crucial for understanding various Earth processes and how they may couple with each other. To simultaneously estimate break points, velocity changes and their uncertainties, we implement Bayesian modeling with Markov Chain Monte Carlo algorithm for GNSS time series. As the presence of white noise (WN) and time-correlated flicker noise (FLN) in GNSS time series was found to affect velocity estimation, synthetic data experiments are first conducted to investigate their effect on break point estimation. The results indicate that reliable estimates are obtained only when the value of velocity change is larger than FLN amplitude. With the presence of WN and FLN, whose amplitudes are one twentieth and one fourth of the velocity-change value, the estimation bias and uncertainty are <0.5 mm/yr and ~5 mm/yr for velocity change, and <30 d and ~100 d for break point, respectively. In this case the uncertainty is one magnitude larger than that with only the presence of WN. Then the proposed method is applied to model two velocity changes detected manually during 2014-2015 at the Krafla volcanic system, North Volcanic Zone (NVZ), Iceland. Similar accuracy and precision as the synthetic data experiments can be expected in east component of the real data as the velocity-change values are 6.9-16.5 times of the WN amplitudes and 2.5-4.0 times of the FLN amplitudes from preliminary analysis. Considering the uncertainty estimated with 95% confidence interval, the first break point at the three continuous GNSS stations in the Krafla area suggests a change in extension pattern across the NVZ prior to the beginning of a major rifting episode that started on 16 August 2014 at the Bárðarbunga volcanic system, which is ~130 km south of Krafla. The first break point at KRAC station in the Krafla caldera occurs on 2-4 July 2014, with 95% confidence interval being 4 May to 13 August 2014. The first velocity change is about 7.6 to 9.8 mm/yr to the west with its uncertainty ranging from 4.5 to 14.4 mm/yr. The velocities approximately resume to the original level after the second change at the end of 2014 or early 2015, whose chronological relationship with the end of Bárðarbunga-Holuhraun episode cannot be asserted because of uncertainties. The results may indicate coupling of activities between the volcanic systems in the NVZ via processes not well understood. Further work is needed to confirm these results and their significance.

How to cite: Yang, Y., Sigmundsson, F., Geirsson, H., Lanzi, C., Hreinsdóttir, S., Drouin, V., Zhou, X., and Ma, Y.: Bayesian modeling of velocity break points in GNSS time series and the effect of noise on their estimation: Did velocity anomalies in the Krafla volcanic system, north Iceland, precede the Bárðarbunga-Holuhraun 2014-2015 rifting episode?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7374, https://doi.org/10.5194/egusphere-egu23-7374, 2023.

Volcanic calderas are delimited by a ‘caldera wall’ which can be several hundred meters in height. This represents the degraded scarp of a fault that accommodates roof subsidence. Here, we assess the roles of friction and cohesion on caldera wall morphology by: (i) analysing the slope properties of several young natural calderas in the ALOS-3D global digital surface model (DSM), and (ii) comparing those observations to the results of a text-book analytical solution and of new Distinct Element Method (DEM) modelling.

Our analysis of the DSM suggest that caldera wall heights are not as closely linked to slope angle as previously suggested. Slope angles range from 20 – 65° and slope heights range from 99 m - 1085 m. We find that the smaller slope heights are not robustly tied to greater slope angle. When compared to analytical predictions, these slope-height data yield expected rock mass cohesion values of less than 0.25 MPa for all calderas, which is 2-3 orders of magnitude less than typical laboratory-scale values.

The DEM models explicitly simulated the process of progressive caldera collapse, wall formation and destabilisation, enabling exploration of the emergence of slope morphology as a function of increasing subsidence and of mechanical properties. Results confirm that low bulk cohesion values <0.5 MPa are required to reproduce the observed ranges of slope angles and slope heights, and they indicate that friction is the dominant control on slope evolution. Different failure mechanisms resulted as a function of cohesion and friction during early collapse: (1) granular flow with low friction and cohesion, and (2) block toppling at high friction and cohesion. During later collapse, shear failure dominates regardless of cohesion. At higher cohesion and/or friction values, the models resulted in non-linear concave-upward slope profiles that are seen at many natural calderas.

How to cite: Harnett, C., Watson, R., Holohan, E., and Schöpfer, M.: Mechanical controls on caldera slope morphology and failure, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7530, https://doi.org/10.5194/egusphere-egu23-7530, 2023.

Spatial-temporal ground deformation patterns of volcanoes is one of the major and more impressive observations of the volcanic dynamic. Cause of his numerous volcanic, seismic, and gravitational phenomena, Mt. Etna is one of the more studied volcanoes worldwide. We processed and analyzed GNSS and InSAR dataset from January 2015 - March 2021 period. In addition to inflation and deflation displacement pattern, we observe a spectacular velocity modulation of the superfast seaward motion of the eastern flank. Rare flank motion reversal indicates that short-term contraction of the volcano occasionally overcomes the gravity-controlled sliding of the eastern flank. On the other hand, fast dike intrusion guided the acceleration of the sliding flank, potentially evolving into sudden collapses, fault creep, and seismic release. These observations can be of relevance for addressing short term scenarios and forecasting of the quantity of magma accumulating within the plumbing system.

How to cite: Pezzo, G., Palano, M., Beccaro, L., Tolomei, C., Albano, M., Atzori, S., and Chiarabba, C.: Flank collapse and magma dynamics interactions on stratovolcanoes: InSAR and GNSS observations at Mt. Etna (Italy), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7704, https://doi.org/10.5194/egusphere-egu23-7704, 2023.

Localized ground deformation at volcanoes in extensional setting may occur because of strain localization. The magmatic system of a volcano with its liquid magma, magma mush, and hot crust will cause a rheological anomaly, where material properties may be very different from surrounding crust and mantle. Numerical models based on the Finite Element Method (FEM) are used to explore ground deformation at volcanoes in extensional environments, considering realistic volcano models with heterogeneous multi-layered structure, with both elastic and viscoelastic rheology. The effects of localized lateral and vertical variations in terms of geometry and material properties of the crust are explored, in a model domain undergoing stretching applied perpendicular to the lateral domain boundaries of one and two-layers model (at a rate of 17.4 mm/yr applied in our models). A one-layer model displays the same elastic feature throughout the whole domain except for a localized upper volume with lower elastic properties, compared to the surrounding crust, to simulate the shallow magmatic system. In a two-layer model, the top elastic layer overlies a viscoelastic layer that locally reaches shallower levels to symbolize the deep magmatic system beneath the shallow low-rigidity volume previously introduced. A localized surface subsidence signal is a characteristic feature of magmatic system with a large body of localized viscoelastic rheology at shallow depth. The subsidence signal is strongly dependent on the viscosity and volume of the up-doming viscoelastic material. A model with viscosity of 5 × 10¹⁹ Pa s in the up-doming material, and a 7 – 15 km-thick elastic layer, show a small subsidence rate, ~0.1 – 0.4 mm/yr. Our models show an increase of the localized subsidence rate, from 1.9 to 5.5 mm/yr, as the viscosity decreases from 10¹⁸ Pa s to 10¹⁶ Pa s in the up-doming material. Lower viscosities (<10¹⁶ Pa s) show no further change in subsidence rate when compared to the 10¹⁶ Pa s solution. We apply three-dimensional FEM models to improve understanding of the subsidence at the Krafla and Askja volcanic systems (1989-2018 and 1983-2018, respectively) in the Northern Volcanic Zone of Iceland. The two subsiding areas (roughly 9 × 10 km each) lie in about 50 km-wide zone which marks the North America-Eurasia divergent plate boundary. The rate of subsidence at Krafla was ~1.3 cm/yr in 1993-2000 and slowed down to 3-5 mm/yr in 2006-2015. The rate of subsidence at Askja decayed more slowly than Krafla. During the 1983-1998 the subsidence rate was ~5 cm/yr; in 2000-2009, geodetic monitoring showed that the subsidence slowed down to ~2.5 cm/yr. Comparison of FEM models to geodetic data in North Iceland suggests that plate divergence processes may account for part of the observed subsidence, dependent on how extensive rheological anomalies in relation to magma are beneath the volcanoes.

How to cite: Lanzi, C., Sigmundsson, F., Geirsson, H., Maree Parks, M., and Drouin, V.: Strain Localization at Volcanoes Undergoing Extension: Investigating Long-term Subsidence at Krafla and Askja in North Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8378, https://doi.org/10.5194/egusphere-egu23-8378, 2023.

Eruptions at long-inactive volcanoes are usually preceded by days to months of unrest as magma migrates gradually to shallower depths. This is built into plans by civil protection agencies for societal response. Here we show that at São Jorge, Azores, after 60 years of repose, magma reached almost the surface in a vertical dike intrusion within a few hours of the seismicity onset with no previous precursory signals. São Jorge lies in a rift zone where extensional stress is expected to be built over time to accommodate magma at depth. Recent eruptions at São Jorge have produced pyroclastic density currents, and the potential for an eruption to occur with little warning poses a significant risk. Deformation associated with the event reached other neighboring islands over a distance of at least 45 km away from São Jorge. Deformation was high on the first day of activity (>50 mm within March 19-20) and significantly decreased afterward. The combined analysis of GNSS and InSAR data allows using a model of segmented rectangular dislocations with multiple patches for data inversion. A maximum opening of 1.7 m at 4-6 km depth is inferred from the modeling. We interpret the cause of the initial vertical shallow injection to be due to host rock failure conditions triggered by deviatoric stresses. We investigate why lateral spreading of the dike occurred soon after the initial injection. Using a FEM simulation, we show how the tension at the tip of a vertical propagating dike is high at the start and decreases with shallower depths, reaching similar levels of tension found at the lateral parts of the dike and increasing the probability of lateral propagation.

How to cite: D'Araújo, J., Hooper, A., Lazecky, M., Sigmundsson, F., Ferreira, T., Silva, R., Gaspar, J., and Marques, R.: Sudden shallow dyke intrusion at São Jorge Island (Azores) after 60 years of repose, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9104, https://doi.org/10.5194/egusphere-egu23-9104, 2023.

Askja is an active volcano situated in the Northern Volcanic Zone of Iceland that last erupted in 1961. Since then, long-term geodetic studies of Askja’s caldera complex have tracked the deflation at a decaying rate associated with a shallow source. However, in August 2021, a rapid reversal of this trend indicated the onset of re-inflation, which, as of January 2023, has resulted in 45cm of uplift near the centre of the primary caldera. While several techniques have been used to measure the geodetic signal associated with this inflation, including gravity and InSAR data, there has yet to be a detailed examination of the seismic response. We observe a definitive increase in the rate of seismicity associated with the onset of re-inflation in August 2021. In this study we examine the sensitivity of shear wave splitting, a phenomenon arising due to seismic anisotropy in the crust, to the changing stress state of the crust within and surrounding Askja associated with this new phase of inflation. We estimate the fast orientation and delay time, which parameterise the orientation and magnitude of seismic anisotropy respectively, from split shear wave arrivals across our local network of seismometers. We leverage an extensive catalogue of microearthquakes in and around Askja spanning 2007 to 2022 in order to compare the variation in pre- and post-inflation delay times and strength of anisotropy, to better understand the sensitivity of shear wave splitting to stress changes during periods of volcanic inflation. This will give valuable information on whether shear wave splitting can be used as a proxy for stress changes when other geodetic observations cannot be performed in volcanic and other settings, as well as the role shear wave splitting has in combination with these other techniques.

How to cite: McCann, J., Winder, T., Bacon, C., and Rawlinson, N.: Testing the Sensitivity of Shear Wave Splitting to Volcanic Inflation, A Case Study from Askja, Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10409, https://doi.org/10.5194/egusphere-egu23-10409, 2023.

Measuring how the surface deforms in time and space plays a crucial role, not only for understanding volcanic mechanisms, but also for hazard assessment, risk mitigation and supporting crisis management. Mount Etna, one of the most active volcanoes in the world, with a growing population in its vicinity, has experienced an intense period of activity in recent years, mainly characterized by continuous degassing and recurring lava fountains. Due to this activity, continuous deformation can be observed at Mount Etna.

The summit craters showed brisk activity in the last months of 2020, accompanied by increasing seismicity. A period of paroxysms started in December 2020 and intensified in February 2021, with brief but violent eruptive lava-fountaining episodes, that continued throughout all the year. The focus of this study is to understand the dynamics of the near-surface feeding system by constraining the sources responsible for the observed paroxysms. To localize and describe the time-dependent ground deformation, we examine surface deformation at Mount Etna by means of an Interferometric Synthetic Aperture Radar time series analysis utilizing Sentinel-1 data between the second half of 2020 and the end of 2021. The onset of the paroxysms was preceded by an inflation period and deflation episodes were observed during the paroxysms period, which suggests a link between the volcano activity and the observed deformation. The findings may contribute to the discussion on the distribution and dynamics of magma reservoirs that form Mount Etna's conduit system and its interaction with the local tectonic regime.

How to cite: Vásquez Castillo, A., Guglielmino, F., and Puglisi, G.: On the 2021 Volcanic Paroxysmal Activity of Mount Etna: a Ground Deformation Analysis Using InSAR, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10489, https://doi.org/10.5194/egusphere-egu23-10489, 2023.

Large rhyolitic eruptions with ejecta of transcontinental scale have catastrophic effects on the environment. Despite its importance in volcanic hazard assessment and potentially influencing climate, the triggering of supervolcanoes remains enigmatic. Many valid mechanisms for mobilizing an eruptible magma reservoir exist, however, the fundamental question of how to initially form the magma reservoir responsible for a supereruption is unknown. Here we show that the deformation microstructure of partially molten rock could accelerate melt extraction and assemble a large eruptible magma reservoir. By modeling observed shape and orientation of melt pockets in deformed samples, we predict that deformation microstructure forms a melt network that enhances melt flux by up to 30 times. Our results suggest that compressing a crystal-rich magmatic mush in volcanic arcs or under glacial loading can assemble a large crystal-poor magma reservoir in a few thousand years, a timescale in consistent with petrological evidence of rapid assembly. Because external stress is common to most magmatic systems, deformation microstructure could be a ubiquitous catalyst for magmatic activities including supereruptions.

How to cite: Liu, B. and Qi, C.: Microstructure linking external forcing to supereruption, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10631, https://doi.org/10.5194/egusphere-egu23-10631, 2023.

Volcanic sector collapses generated some of the most voluminous mass transport deposits on Earth and triggered devastating tsunamis with numerous casualties. The associated sector collapse deposits occur around many volcanic islands all over the world. The shelf around the volcanic island of Montserrat (Lesser Antilles) and the adjacent Montserrat-Bouillante-Graben host more than ten surficial or buried landslide deposits with most of them classified as volcanic debris avalanche deposits by previous studies. The most intensively studied deposit (Deposit 2) is associated with a landslide that occurred at ~ 130 ka and comprises a volume of 10 km³, including remnants of the volcanic flank and secondarily mobilized seafloor sediments. Here, we present new 2D and 3D seismic data as well as MeBo drill core data from Deposit 2 that reveal multi-phase deposition including an initial blocky volcanic debris avalanche followed by secondary seafloor failure and a late- erosive event. Late-stage erosion is evidenced by a channel-like incision on the hummocky surface of Deposit 2 about 15 km from the source region. Erosional incisions into the top of sector collapse deposit have also been reported from Ritter Island, Papua New Guinea – the only other volcanic landslide deposit that was studied at similarly high resolution. This may imply that late stage erosive turbidites are a common process during volcanic sector collapse. This requires geological and oceanographic processes that can create high flow velocities close to the source of the collapse area leading to a late down-slope acceleration of sediments that were suspended in the water column.

How to cite: Kühn, M., Berndt, C., Krastel, S., Karstens, J., Watt, S., Kutterolf, S., Huhn, K., and Freudenthal, T.: Flank collapse, sediment failure and flow-transition: the multi-stage deposition of a volcanic sector collapse offshore Montserrat, Lesser Antilles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12087, https://doi.org/10.5194/egusphere-egu23-12087, 2023.

The timing of volcanic events at the Comoros archipelago (North Mozambique Channel) are currently only known by dating samples from the onshore islands. According to these data, the oldest lavas from the Comoros are 10 Ma and several distinct volcanic periods are inferred (Michon, 2016). However, the onset of the volcanism within the archipelago cannot be constrained by these data. Here we use two different datasets of wide angle, and  high resolution multichannel seismic reflexion profiles to provide insights on the birth and early evolution of the volcanism around the islands of Mohéli, Anjouan and Mayotte, in the Comoros basin (SISMAORE cruise, ANR COYOTES project, (Thinon et al., 2022)).

The seismic interpretation revealed several distinct volcanic horizons within the sedimentary cover, that could be related to the formation of the Jumelles Ridge, Geyser bank, Mohéli, Anjouan and Mayotte volcanic island. We identify the onset of the main volcanic event that led to the formation of Mayotte island. We show that the corresponding seismic volcanic horizon is located at different depths in the north and the south of Mayotte island. This indicates at least two different major volcanic phases of the Mayotte island edification. Seismic profiles also show  the presence of a magmatic feeder complex underneath. Using known regional stratigraphy, we finally propose a chronology of all the volcanic episodes in the regional volcanic context of the construction of the Comoros archipelago.

^{Michon, L., 2016. The Volcanism of the Comoros Archipelago Integrated at a Regional Scale, in: Bachelery, P., Lenat, J.-F., Di Muro, A., Michon, L. (Eds.), Active Volcanoes of the Southwest Indian Ocean, Active Volcanoes of the World. Springer Berlin Heidelberg, Berlin, Heidelberg, pp. 333–344. https://doi.org/10.1007/978-3-642-31395-0_21}

^{Thinon, I., Lemoine, A., Leroy, S., Paquet, F., Berthod, C., Zaragosi, S., Famin, V., Feuillet, N., Boymond, P., Masquelet, C., Mercury, N., Rusquet, A., Scalabrin, C., Van der Woerd, J., Bernard, J., Bignon, J., Clouard, V., Doubre, C., Jacques, E., Jorry, S.J., Rolandone, F., Chamot-Rooke, N., Delescluse, M., Franke, D., Watremez, L., Bachèlery, P., Michon, L., Sauter, D., Bujan, S., Canva, A., Dassie, E., Roche, V., Ali, S., Sitti Allaouia, A.H., Deplus, C., Rad, S., Sadeski, L., 2022. Volcanism and tectonics unveiled in the Comoros Archipelago between Africa and Madagascar. Comptes Rendus. Géoscience 354, 1–28. https://doi.org/10.5802/crgeos.159}

How to cite: Masquelet, C., Leroy, S., Sauter, D., Delescluse, M., Chamot-Rooke, N., Thinon, I., Watremez, L., and Lemoine, A.: Major volcanic events from Mohéli, Anjouan and Mayotte Island edification in the Comoros Archipelago at Northern Mozambique Channel inferred by seismic reflection data., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12116, https://doi.org/10.5194/egusphere-egu23-12116, 2023.

Unrests at calderas are usually characterized by surface uplift, which is often driven by the pressurization of a sill-like reservoir. If an unrest ends up with an eruption, the location and timing for the opening of the eruptive vent are difficult to predict. In fact, when a reservoir fails, a magmatic dyke nucleates and starts propagating towards the surface, following a direction that results from the interplay between magma pressure, local stress, and regional tectonic. Where and how a sill reservoir will fail is one of the most uncertain factors in such a pre-eruptive scenario. In order to study the transition between an inflating sill and a dyke intrusion, we developed an original analogue model set-up: We shaped the surface of a solidified gelatin block, reproducing a simplified topography of Campi Flegrei caldera (Italy). This provides our model with the local unloading stress due to the presence of the caldera. In addition, we introduced a variable horizontal extension by expanding the gelatin block in one direction, providing a regional extension. We placed a sill-type reservoir below the caldera, scaling its dimensions based on previous deformation studies at Campi Flegrei. In our experiments, the reservoir was progressively pressurized through the injection of air from the bottom of the gelatin block, simulating a process of shallow sill-reservoir activation by a deeper “feeder dyke”. Depending on the ratio between the local unloading stress and the regional extension, we observed two main behaviors for the nucleation of a shallow dyke: I) if the local stress dominates over the regional extension - when the sill overpressure reaches a critical value - we observed the lateral growth of the sill, followed by the progressive re-orientation of the intrusion towards vertical, thus forming a dike which fed a circumferential vent on the rim of the caldera; II) if the extension dominates, the sill-to-dyke nucleation still occurs at the edge of the sill, but with a vertical dyke opening in the direction of the regional extension (on the same plane as the feeder dyke). The intrusion grows towards the surface, leading to a radial fissure located at the edge of the caldera.

Previous estimates for the stress state at Campi Flegrei caldera from Rivalta et al. (2019) would suggest that the most relevant mechanism for Campi Flegrei may be the one dominated by the local stress rather than the regional extension (type I).

How to cite: Maccaferri, F., Gaete Roja, A., and Mantiloni, L.: Sill to dyke transition beneath a caldera: the competition between local stress and regional extension. Insights from analogue experiments applied to Campi Flegrei caldera, Italy., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12143, https://doi.org/10.5194/egusphere-egu23-12143, 2023.

One of the main goals of the modern volcanology is produce accurate eruption forecastings. Not only from a scientific point of view, but considering that approximately 30 million people live in the vicinity of active volcanic areas and tens of thousands of people have lost their lives as a result of the direct effects of historical eruptions. Thus, in 2017 "The US National Academies of Sciences, Engineering and Medicine" considered the forecast of eruptions as one of the great challenges of Volcanology. Generally, the focus is on forecasting the eruption onset, however, forecasting the style, size and duration becomes relevant and properly manage long-duration eruption, e.g., during the 2021 La Palma (Canary Islands) eruption, whose main hazards were air pollution, ash fall and lava flows. In particular, the 2021 eruption of La Palma lava flows caused extensive devastation to the surrounding community: more than 2800 buildings and almost 1000 hectares of banana plantations and farmland were destroyed. In this study, we use co-eruptive GNSS series of deformation data to estimate the eruption's end. The forecast was based on the relationship between displacements and pressure changes provided by a purely elastic model of the medium. We also estimated the location of a magma reservoir. A depth of 10-15 km is inferred. This reservoir is consistent with the main seismogenic volume during the eruption. We interpret that the reservoir pressure dropped due the progressive withdrawal of magma that fed the eruption. We assumed that the magmatic plumbing responsible for the eruption was a closed system and that the magma contributions in this zone do not cause detectable deformations. Thus, we used the pressure drop as an indicator of the end of an eruption. With the benefit of the hindsight, we extensively tested our model considering different deformation time series spams in order to evaluate the feasibility of making near-real time predictions of the duration of the eruption, and derive some constraints about the magma system.

How to cite: Charco, M., González, P. J., Garcia-Cañada, L., and del Fresno, C.: Pressure drop as a forecasting tool of eruption duration: 2021 La Palma eruption, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12339, https://doi.org/10.5194/egusphere-egu23-12339, 2023.

The characterization of volcano state is not a simple task due the complexity of physics processes underway. Understanding their evolution prior to and during eruptions is a critical point for identifying transitions in volcanic state. Recent developments in the field of Machine Learning (ML) have proven to be very useful and efficient for automatic discrimination, decision, prediction, clustering and information extraction in many fields, including volcanology. In Romano et al. (2022) the use of ML algorithms led to classify strain VLP families related with changes in volcano dynamics prior of paroxysmal eruptions: algorithms have been able to discriminate little differences in VLPs shape and to find a correspondence among a higher number of families and volcanic phenomenologies. For paroxysmal events occurring outside any long-lasting eruption, the initial success of our approach, although applied only to the few available examples, could permit us to anticipate the time of alert to several days, instead of few minutes, by detecting medium-term strain anomalies: this could be crucial for risk mitigation for inhabitants and tourists. 

The neural network method used in previous analysis has been extended to a wider (2007-2022) period to verify that families found in the previous narrower time interval were still present. We tried, then, to associate families with volcanic activity, confirming the conceptual model previously introduced (Mattia et al., 2021 and   Romano et al., 2022), capable of explaining the changes found. Our innovative analysis of dynamic strain, systematically conducted on several years of available data, may be used to provide an early-warning system also on other open conduit active volcanoes.

Valuable information is embedded in the data used in the current work, which could be used not only for scientific purposes but also by civil protection for monitoring reasons. Such a variety of possible usage needs the setting of principles and legal arrangements to be implemented in order to ensure that data will be properly and ethically managed and in turn can be used and accessed by the scientific community.

How to cite: Romano, P., Di Lieto, B., Sangianantoni, A., Scarpetta, S., Messuti, G., and Scarpa, R.: Dynamic strain anomalies detection at Stromboli from 2007 eruptive phase using machine learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12984, https://doi.org/10.5194/egusphere-egu23-12984, 2023.

The Campi Flegrei caldera (southern Italy) is one of the most populated volcanic areas on the Earth. It is characterized by intense uplift episodes followed by subsidence phases. Following the 1982–1984 unrest, there was about 21 years of subsidence,  followed by a new phase of inflation started in 2005 and, with increasing uplift rates over time, is still ongoing. Since 2005, the total vertical ground displacement is about 1 m near the city of Pozzuoli.

We analyze the evolution of the volcanic sources that caused the measured ground deformations since 2000 by modelling the Global Navigation Satellite System (GNSS) data from the permanent monitoring network in the caldera. Based on changes in slope in the GNSS displacement time series, we divide the recent inflation period into different phases. During time periods characterized by a near-linear trend, we can infer that a stationary pressure source is active inside the caldera. Using this inference, we describe the ground deformations of the last two decades through different sub-intervals, as “snapshots” that are the result of the time evolution of the inner volcano-dynamics.

Furthermore, over the investigated period we analyze the evolution of surface stresses from an ellipsoidal source model and the strain rate patterns from the horizontal GNSS velocities. In particular, we compute areal strain rates, shear strain rate magnitudes, associated with a strike-slip component of deformation, and rotation rates, and this helps us to infer surface manifestations of subsurface deformations.

How to cite: Bruno, V., De Martino, P., Dolce, M., Mattia, M., and Montgomery-Brown, E. K.: Modeling of volcanic sources and evolution of stress and strain rate at Campi Flegrei caldera (Italy) from GNSS data (2000-2022), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13107, https://doi.org/10.5194/egusphere-egu23-13107, 2023.

The current unrest phase at Campi Flegrei Caldera, Italy from 2000 to present is evidenced by increasing seismicity rates and magnitude, gas emissions and remarkable ground deformation. We consider multi-technique geodetic data to constrain the recent surface deformations and study the possible hazard implications. Time-series from the COSMO-SkyMed satellite mission and GNSS data in the period 2013-2020 show an increasing rate of uplift at the caldera center, reaching a total of about 1 m in the town of Pozzuoli during 2010-2020. Horizontal deformation confirms the inflationary trend. Also, new GNSS seafloor measurements, located in the Gulf of Pozzuoli and available from 2017 to 2020, show a nearly radial pattern. The use of these data in the analysis, in addition to the inland GNSS and InSAR data, helps constraining the 3D pattern of deformation also in the submerged part of the Campi Flegrei caldera.

3D finite element models are developed including the elastic heterogeneous structure of the medium based on the newest seismic tomography of the area of Campi Flegrei. We consider the potential action of a plumbing system composed of a general (without fixing the shape a-priori) “central” source, and a deep tabular layer placed at 7.5 km depth.

The results show that the central source is placed below the caldera floor, at 4.5 km depth, and has a shape of a thick spheroid with axes ratio of about 0.8 and 0.5. The use of the sill-like source, as suggested by several previous studies for the 2011-2013 time window, lead to three-four fold higher misfits. We interpret our solution as a thickened sill for which the vertical dimension is not negligible such as for the sill-like source, but has a finite dimension of about half the horizontal extension.

No significant contributions from the deep tabular layer are evidenced by the inversions,  but the hypothesis of a deep reservoir cannot be fully ruled out, since its activity may be masked by the central shallower source. Also, the implementation of seafloor measurements leads to results compatible with the inland GNSS data alone. 

In order to understand the evolution of the current inflation process, the results are compared to previous models from the beginning of the present unrest phase (2011 - 2013) and also previous unrest phases (1980-1984).

This work is part of the multidisciplinary project LOVE-CF, financed by the Istituto Nazionale di Geofisica e Vulcanologia, to study the dynamics of Campi Flegrei caldera.

How to cite: Astort, A., Trasatti, E., Polcari, M., Di Vito, M. A., and Acocella, V.: Volcanic activity of Campi Flegrei Caldera (Italy) during 2013-2020 from surface deformation mapping and modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13251, https://doi.org/10.5194/egusphere-egu23-13251, 2023.

Typically surface displacements, as a consequence of magmatic movements, are calculated by implementing either a data inversion model or an analytical model comprising of loosely constrained, generalised rock properties and simplified source geometries. In fact, these analytical models are commonly characterised by a pressurised point source embedded within a homogeneous, isotopic, flat, elastic half space (i.e. the Mogi-McTigue Models). The Mogi model, in particular, provides a quick and relatively accurate estimation of the symmetric, radial displacement patterns from a predefined pressure source. However, limitations arise from the assumptions behind the parameterisation of the model (Masterlark, 2007), namely defining the elastic moduli of the matrix and failing to account for the influence that the topography exerts on the volcanic system. 

This work seeks to address these limitations by employing GALES (GAlerkin LEast Squares), a Multiphysics finite element software (FEM) that was developed by INGV, Sezione di Pisa. GALES consists of various geophysical solvers, including, but not limited to: computational fluid dynamics, computational solid dynamics and fluid solid interaction (Garg & Papale, 2022). The GALES software is tailored towards high performance computing (HPC), on cluster machines, and has been used regularly since its inception; contributing to several significant studies pertaining to magma transport and rock deformation. Thus, GALES is seen as the ideal software platform to introduce geophysical and spatial heterogeneities to these established analytical models - this time with the topography of the volcano at the forefront of its consideration. 

As 3D simulations of this extent are computationally expensive, the open-source softwares MESHER (Marsh et. al., 2018) and GMSH were used to generate a dynamic computational mesh, of variable resolution, for the simulations by deriving a triangulated irregular network (TIN) from the Tinitaly Digital Elevation (~10 m resolution - see Tarquini et. al., 2007) and GEBCO (2022) Bathymetry datasets (~500 m resolution). Significantly, it was also possible to avail of the INGV’s extensive monitoring network by including the positions of the signal receivers stationed across a vast computational domain of 100 km x 100 km x -50 km. The integration of these receiver stations not only allows for a direct and comprehensive comparative analysis of the modelled synthetic deformation signals against the catalogues of empirical data, but also significantly, the extent of its coverage is beneficial as we can obtain deformation patterns from a variety of different source locations, both in the near-field and far-field ranges. 

Therefore, whilst recording volcanic deformation signals and distinguishing its sources at significant depths within the Earth’s crust can prove to be complex, challenging and even elusive, the combination of these numerical models, high-resolution datasets along with continuous monitoring, simulations such as these have the potential to provide new insights into the existence, behaviour and evolution of deep magmatic bodies (Dzurisin, 2003), as well as, constraining the geophysical characteristics of the medium by which they are emplaced. 

How to cite: McCluskey, O., Papale, P., Montagna, C., and Garg, D.: Integrating high-resolution topography data of Mount Etna to produce numerical simulations of surface deformation patterns associated with deep rooted magmatic pressure sources, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13482, https://doi.org/10.5194/egusphere-egu23-13482, 2023.

In 2018, four deadly (Mw 6.2 to 6.9) earthquakes struck the north coast of Lombok Island, on 28 July, 5August, and 19 August, distributed between the Flores back-arc thrust and the Rinjani-Samalas volcanic complex, causing hundreds of fatalities and extensive damage. We performed a comprehensive analysis of relocated aftershocks, static coulomb stress changes, and co-seismic and post-seismic deformation, to improve our understanding of this earthquake sequence. The fault geometries and slip distributions of the three mainshocks are modelled by inverting the co-seismic deformation imaged using an interferometric analysis of Sentinel-1 synthetic aperture radar (InSAR) measurements, based on rectangular dislocations embedded in a multi-layered elastic half-space. The earthquake sequence aftershocks were analysed using an unsupervised learning method (ST-DBSCAN) to cluster these relocated aftershocks so that we can identify the source of each aftershock. We used a time-series consisting of 658 descending and 370 ascending Sentinal-1 InSAR interferograms to investigate the time-dependent post-seismic deformation in the two years following the Lombok 2018 earthquake sequence, deriving a combined model that simulates the viscoelastic relaxation and afterslip simultaneously. The Coulomb stress change modelling based on the co-seismic and post-seismic rupture models indicates about 1 MPa of extensional stress change at 10 to 20 km of depth and 0.5 Mpa extensional stress change at 15 to 25 km of depth around the Barujari Crater region, respectively, which affects the open of the magma conduct, reflected as caldera-scale deflation and inflation. To quantify the influence of the earthquake sequence on the spatiotemporal deformation pattern of the volcano edifice, we extended our InSAR time-series range forward to the year 2014, just prior to the two eruptions that occurred on 25^th October 2015 and 1^st August 2016, and perform Principal Component Analysis to investigate the time-dependent inflation and deflation signals. We modelled the volume change and the location of the volcano pressure source for a better understanding of how changes in the magma body and magma movement may have been influenced by the 2018 Lombok earthquake sequence. A double-source compound model is used to invert the parameters of the magma chamber, including a shallow Moji point pressure source centred at 1.3 km north of the Barujari cone, and a deep source centred at 1.5 km northeast of the Rinjani cone, at ~3.9 km and ~3.5 km depth below the sea level respectively. We also used a uniform sill and dike combined model to interpret the co-eruptive signals surrounding the observed eruptive fissures. Our best-fit dike is nearly vertical, reaching a depth of 2 km below sea level with an opening of 8.5 cm, and the sill is at the depth of 3.1 km with a contraction of 40 cm.

How to cite: Zhao, S., McClusky, S., Miller, M., and Cummins, P.: The impact of the 2018 Lombok earthquake sequence, Indonesia on the unrest Rinjani-Samalas volcanic complex inferred from the time-dependent seismic and volcanic source models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13534, https://doi.org/10.5194/egusphere-egu23-13534, 2023.

In this contribution we discuss the geological structure, temporal and spatial relationships of Gegham upland between polygenetic and monogenetic volcanic activity as well as transitions from one to another as well as geochemical features of magma generation processes.

Armenia is situated in the NE part of the Anatolian-Armenian-Iranian plateau, an intensely deformed segment of the Alpine-Himalayan belt. The complex geological structure of the region is represented by a mosaic of tectonic blocks comprising fragments of volcanic arcs, continental crust and exhumed oceanic crust of the Mesozoic Tethys ocean basin (Meliksetian, 2013). The Gegham volcanic upland is located in the center part of the Neogene-Quaternary volcanic belt formed within the territory of the Armenian Highland. The duration of volcanism within the Gegham ridge spans from the Late Miocene to the Holocene (Karakhanyan et al. 2003, Karakhanyan et al. 2002). Temporal and spatial relationships between polygenetic and monogenetic volcanic activity as well as transitions from one to another are among fundamental problems in volcanology. Geological evidence such as presence of thick (abouth 500m) Vokhchaberd volcanoclastic suite at foothills of Gegham volcanic ridge suggests presence of stratovolcano (caldera-?) activity in Late Miocene-Pliocene (K-Ar dating data 3.4-6.7Ma; Bagdasaryan and Ghukasyan 1985) in Gegham, that was switched later to monogenetic activity and crater (or caldera) and slopes of former stratovolcano covered by monogenetic vents and their lava flows. After the polygenic volcanism the volcanism of Gegham upland is accompanied by fissure (plateau basalt) and monogenic volcanism.

Plateau basalts of Gegham upland distributed within town Gavar and Kotayk plateau, gorg of Hrazdan river up to village Parakar and age of these are 40Ar/39Ar 2.37±0.03 Ma (Neill et al., 2015). According to K. Karapetyan (1962, 1973) the youngest, Upper Pleistocene-Holocene volcanism of the upland is confined to the watershed part of the upland and the Eratumber plateau. According to Meliksetian (2017), there are data from extended flows from the Gegam upland - Argavand (221.1±5.0 Ka), Gutansar (314.1±16.2 Ka), Garni columnar flow of basaltic trachyandesites (127.7± 2.6 Ka) and lavas overlapping the Garni flow (49.9±9.2 Ka), which show the chronological and stratigraphic position volcanic activity of Gegham upland.

Taking into account the available and new reliable data, it is obvious that the volcanism of the Gegham upland continued from the Late Miocene-Early Pliocene time and up to the Upper Pleistocene and Holocene, and at the turn of the Pliocene-Quaternary period, due to changes in volcano-tectonic conditions, a change occurred in polygenic explosive-effusive volcanism to predominantly effusive areal.

Geochemical typification of the volcanic series of the Gegham upland indicates the predominance of "subduction" related fingerprints in them, however, some transitional to "intraplate" geochemical features are also found. The geochemical features and the petrogenetic model of the evolution of the volcanic series of the Gegham upland suggest a single magma-generating source and similar conditions for the evolution of melts within the entire Gegham upland.

How to cite: Navasardyan, G., Savov, I., Grigoryan, E., Metaxian, J.-P., Sargsyan, L., Sahakyan, E., Galstyan, A., and Meliksetian, K.: Nature of polygenetic to monogenetic transition of volcanism of Gegham volcanic ridge (Armenia), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13580, https://doi.org/10.5194/egusphere-egu23-13580, 2023.

The propagation mechanics and fluid dynamics of magma-filled fractures, such as dykes and sills, are fundamental to the generation of sub-surface signals which indicate magma is on the move. Dykes play a major role transporting magma from depth to the surface, and modelling the dynamics of dyke growth remains a primary objective to improve the interpretation of a wide range of geophysical, petrological and geochemical evidence of magma ascent. We present results from scaled analogue experiments using Liverpool’s new Medusa Laser Imaging Facility to quantify the fluid flow dynamics and solid deformation during magma ascent in dykes. Our results detail the characteristics of dyke ascent from inception to eruption, with magma flow regimes and host-rock deformation mode dependent on dyke geometry, host-rock properties, density contrasts and magma rheology. Our results pose new conceptual models upon which the signals of magma movement in nature should be interpreted.

How to cite: Kavanagh, J. and Chalk, C.: Using analogue experiments to explore fundamental processes during magma ascent, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13854, https://doi.org/10.5194/egusphere-egu23-13854, 2023.

Lanzarote is the most northeast and together with Fuerteventura is the oldest island of the Canarian Archipelago (Spain), which is located on a transitional zone, a passive margin, between oceanic and continental crust. The last volcanic eruption in Lanzarote was a 7 years voluminous eruptive cycle, occurred during the 18^th century. Historical seismicity registered in the region, is customarily attributed to diffuse tectonic activity.

This study is intended to contribute to understanding the surface thermal anomalies and the active tectonics on Lanzarote island, mainly in the Timanfaya volcanic area, which is located to the southwest of the island and covers the land extension generated by the last eruption..

First, we describe the steps taken to implement a thermo-fluid-dynamics model to study the surface thermal anomalies detected at the Timanfaya volcanic area after the volcanic activity that took place between 1730 and 1736. The origin of these anomalies is acknowledged to be due to the intrusion of a magma body and its consequent cooling, but which still might have very high temperature. This hypothesis is based on the fact that the cooling of basaltic magma, which has an initial temperature of 1200 °C, takes about 10⁴ ÷10⁵ years, as indicated by some authors. Our physical model consists of a cooling magma body, with a radius of 300 m, located at a depth of 4 km and with a temperature of 800 degrees (1073,15 K).

The model was developed in three steps: 1) accounting for the energy balance only, 2) both the energy and the momentum balance are accounted for, 3) mass balance is accounted too.

The three thermo-fluid dynamic models are based on a finite element modelling (FEM). The novelty of our model consists in including both the steady and unsteady (transient) phase, not considered in analytical solutions under purely stationary conditions developed in past modelling by other authors.

Second, we describe a detailed geodetic continuous monitoring in Timanfaya volcanic area, where, as mentioned, the most intense geothermal anomalies of Lanzarote are located.

We report on the analysis of about 6 years of CGNSS data collected on a small network consisting in 9 permanent stations, spread over Timanfaya area in Lanzarote Island. The GNSS stations are operated by several owners: the Institute of Geosciences, IGEO, DiSTAR, the Geodesy Research Group of University Complutense of Madrid, the Cartographical Service of the Government of Canary Islands and the National Geographic Institute of Spain.

Finally, we attempt to interpret the thermo-fluid dynamic model and the observed ground deformations in light of the tectonic framework derived from state-of-the-art geophysical studies.

How to cite: Tammaro, U., Romano, V., Arnoso, J., Benavent, M., Riccardi, U., Montesinos, F., Velez, E., and Meo, M.: Unsteady thermo-fluid-dynamics modelling of Timanfaya volcanic area (Lanzarote,Canary Islands) and present-day ground deformation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16329, https://doi.org/10.5194/egusphere-egu23-16329, 2023.

Under polar and subpolar climatic conditions, volcano edifice growth and stability are affected by extreme erosion rates, mass wasting, glacier loading (and unloading), and permafrost soil conditions. Relatively small changes in temperature can lead to very different snow and ice conditions in relation to all of the above. Therefore active, shallow magmatic plumbing systems and magmatic pathways might react sensitively to even minor changes of their surrounding environmental conditions. Almost constant degassing from the summit crater of Mount Curry (Zavodovski Island) and the presence of an active lava lake within the summit crater of Mount Michael (Saunders Island) suggest the existence of shallow magmatic plumbing systems at both volcanoes. They therefore represent exceptional study sites for investigating volcano processes under subpolar climatic conditions. Because of their remoteness, none of these islands are equipped with permanently installed ground-based instruments. We observe and quantify surface displacements related to volcanic activity, fumarolic activity, tectonic activity in the Scotia arc, as well as glacier flow from high-resolution combined TerraSAR-X and PAZ interferometry and amplitude offsets. Multi-temporal topographic data are available through the TanDEM-X SAR satellite mission and photogrammetric surveys conducted in April-Mai 2019 at Saunders Island and in January-February 2023 on Zavodovski Island. Here we introduce the first results of combining and exploring UAV photogrammetry with SAR satellite data. We present a geomorphological and structural analysis of Zavodovski Island and the outer subaerial and shallower submarine flanks of Saunders Island. We also estimate the glacier volume and volume change over time on Saunders as well as surface dynamics at Zavodovski. With this study we highlight the unprecedented detail and the valuable information that can be retrieved from tasked and targeted TerraSAR-X, TanDEM-X, and PAZ satellite acquisitions coupled

How to cite: Richter, N., Massimetti, F., Hart, T., Cartus, O., Leinss, S., Derrien, A., Zorn, E., Shevchenko, A., Wintersteller, P., Meschede, M., and Walter, T.: Volcano processes at the remote South Sandwich Islands of Zavodovski and Saunders observed from air and space, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17100, https://doi.org/10.5194/egusphere-egu23-17100, 2023.

The geodynamic framework of Mount Etna volcano (Italy) is characterised by two superimposed tectonic domains: a compressional one, oriented N-S, and an extensional one, oriented approximately WNW-ESE. The combination of these two domains and the volcano activity, has generated a complex system of faults prevalently on the eastern flank of the volcano. The eastern flank is the most active area of the volcano in terms of deformation and seismicity. The velocities there are at least one order of magnitude greater than in the rest of the volcano flanks due to the eastward sliding of the eastern flank.

The monitoring and analysis of the acceleration occurring on the eastern flank of Mount Etna is the keystone to understand the volcano-tectonic dynamics that, apart from the tectonic and magmatic processes, involves the instability of this flank in a densely inhabited area.

In order to monitor the deformation, Istituto Nazionale Geofisica e Vulcanologia – Osservatorio Etneo (INGV-OE) and the GeoDynamic & GeoMatic Laboratory of the University of Catania integrate GNSS and InSAR products with twofold objective: to characterize the dynamics of the area and to analyse the deformation transients, this last in view of a possible use in the framework of an alert system.

Here, we analyse the ground deformation that occurred between 2016 and 2019 across the faults of the south-eastern flank of Mount Etna. On the south-eastern flank the deformation is accommodated by several faults which have different kinematics and behaviours. We discriminate the deformation transient and the activity of the Belpasso-Ognina lineament, Tremestieri, Trecastagni, San Gregorio-Acitrezza, Linera, Nizzeti and Fiandaca faults. The latter generated the 26 December 2018 earthquake, two days after the eruption of 24 December, which induced a clear post seismic deformation, detected by GNSS and InSAR data. In particular, we discriminate the deformation occurred along the San Gregorio-Acitrezza fault, which is accommodated by the Nizzeti fault, and we analyse the post seismic deformation along the Linera fault. We analyse the Slow Slip Events (SSE) that are observed in the GNSS and InSAR time series in the vicinity of the Acitrezza fault and we quantify and discuss the tectonic origin of the Belpasso-Ognina lineament that we interpreted as a tear fault.

How to cite: Carnemolla, F., Bonforte, A., Brighenti, F., Briole, P., De Guidi, G., Guglielmino, F., and Puglisi, G.: GNSS and InSAR study of the ground deformation of the eastern flank of Mount Etna from 2016 to 2019, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17466, https://doi.org/10.5194/egusphere-egu23-17466, 2023.

In order to compare the mineral chemical effects of acid rain on surface materials under the present oxygen level and the early Proterozoic or late Archean low oxygen (before the GOE) environmental conditions, artificial chemical weathering experiments using an improved Soxhlet extraction apparatus were conducted for basalt, which had already been covered on the early earth’s surface. Some dozens of polished basalt plates put in the extraction chamber were reacted to HCI, H₂S0₄ and HN0₃ solutions at pH 4, and CO₂ saturated water, and distilled water at 50℃ for a different period of time up to 950 days in an open system. In the experiment under the low oxygen condition (5×10⁻⁴ PAL), the whole extraction apparatus was placed in the acrylic glove box, and oxygen was removed by the deoxidizer, and it was carried out in the nitrogen gas flow. The basalt was composed mainly of olivine as a phenocryst, and plagioclase, clinopyroxene, ilmenite and glass as a groundmass. The extracted sample solutions were collected, and analyzed using ICP-MS. Morphological, chemistry and altered product of each mineral surface were studied by SEM, EPMA, XRD and microscopy techniques.

Under both the low oxygen before the GOE and the present oxygen concentration conditions, SEM images showed remarkable dissolution of olivine surface by the H₂SO₄, HNO₃ and HCl solutions. The (Mg + Fe)/Si on the olivine surface and (Na + Ca + K)/ (Al + Si) on the plagioclase surface decreased significantly with increasing experimental period. In chemistry of the extracted solutions, molar ratios of many elements such as Mg, K and Zn tend to be high in the three acidic solutions at pH 4, and low by the CO₂ saturated water and distilled water. The molar ratio is calculated by dividing the cumulative total mole of each extracted element by the mole of individual element in the unaltered basaltic rock. The ratios of Fe, Mg, Ni, Zn and Co near 70 pm in ionic radius are high, and reflect the dissolution from the octahedral coordination of olivine. The ratios of Ca, Na, Sm, Ce, La and Sr near 110 pm are high, and reflect the dissolution from the cavities within the framework of plagioclase. Under the low oxygen condition, major elements such as Fe and Mn, and minor ones such as Zn tend to dissolve easily in all extraction solutions. Ce and Eu in REE, and Nb, Ti, Y and Zr in HFS elements are soluble in pH 4 HCl and H₂SO₄, CO₂ saturated water and distilled water under the low oxygen condition. The results suggest that easily extracted elements under the low-oxygen condition of the early Proterozoic or late Archean influenced the evolution of continental crust, land and ocean, and may have contributed to the formation of the early Earth's surface environment.

How to cite: Kobayashi, S., Takahashi, Y., and Naohara, J.: Artificial chemical weathering of basaltic rock under the earth surface conditions of the present and the Proterozoic era, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-76, https://doi.org/10.5194/egusphere-egu23-76, 2023.

The Proterozoic orogenic belts incorporated in and around the present-day continents preserve complex magmatic, metamorphic, and geophysical signatures of the ancient supercontinents. One such orogenic belt, the Eastern Ghats Belt (EGB) is amalgamated with the Archean cratons of India along a crustal-scale suture zone known as the Terrane Boundary Shear Zone (TBSZ). The continental margin – orogenic belt interfaces, such as the TBSZ, are the black boxes of ancient tectonic processes, since they are rheologically weakened crustal discontinuities that undergo intense deformation and metamorphism recording the complete orogenic history. There have been two schools of thought on the age of final amalgamation of the EGB with the Bastar craton, as the TBSZ records two major tectonothermal events at ~950Ma and ~550Ma, coeval with the formation of supercontinents Rodinia and Gondwana, respectively. The age and mechanism of this amalgamation have implication on the crustal architecture of the Proterozoic supercontinents.

Recent studies confirmed the presence of felsic and mafic granulites of Archean Sm-Nd model ages (3.3 – 3.1 Ga) from the TBSZ that have undergone high-pressure granulite facies metamorphism. It is speculated that these rocks are of Bastar craton in origin and the underthrusting of the Bastar craton beneath the EGB, during the final collision, led to the high-pressure metamorphic conditions. In this communication, we have carried out a comparative petrological and geochemical investigation of the Archean felsic rocks (Grt-bearing charnockites) from the TBSZ and the Hbl-Bt granites from the adjacent regions of the Bastar craton to understand origin and tectonic significance of the charnockites. The garnet-bearing charnockites from the TBSZ are characterised by coarse grained Grt + Opx + Pl + Qz + Kfs + Hbl + Bt ± Ilm. The Hbl-Bt granites of the Bastar craton, adjacent to the TBSZ, are characterized by coarse grained Hbl + Bt + Qz + Kfs + Pl, with small Opx grains forming around Hbl in few places at the interface. The Grt-bearing charnockites and the Hbl-Bt granites are both ferroan and metaluminous to slightly peraluminous in nature. The high concentrations of trace elements, high Y/Nb (>1.2) ratio and pronounced negative anomalies of Eu, Sr and Ti in both the rocks are characteristic of A₂-type within plate granitoids, similar to the other reported granitoids from the Bastar craton. The strong similarity in the geochemistry of Grt-bearing charnockites and Hbl-Bt granites along with the available Archean model ages of the charnockites indicate that the Grt-bearing charnockites of the TBSZ are granulite-facies equivalents of the Hbl-Bt granites and hence represent the remnants of cratonic margin in the TBSZ. This geochemical study along with the Tonian ages (~950 Ma) from monazite cores and inclusions in garnet within the co-exposed metapelites in the suture zone indicate that the Bastar craton underthrusted beneath the EGB during the formation of Rodinia. The ~500 Ma ages reported from the strongly recrystallized monazite rims might represent the reactivation of the intracontinental suture zone due to the far-field stress from the Kuunga orogeny (~530 – 490 Ma) during the formation of East Gondwana.

How to cite: Padmaja, J., Sarkar, T., and Dasgupta, S.: Geodynamic significance of the Archean A-type granites exposed along the western margin of a Proterozoic orogenic belt: Insights on the final docking of the Eastern Ghats Belt with the Indian subcontinent, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-363, https://doi.org/10.5194/egusphere-egu23-363, 2023.

The longevity of the cratonic lithosphere is controlled by its buoyancy, strength, and the viscosity contrast with that of the underlying sub-lithospheric mantle. A number of geodynamic models show that the style and characteristic of lithospheric removal/thinning mechanisms over cratons (i.e. whether delamination, drip, or hydration weakening) are accounted by their geological history and geodynamic evolution. For example, the question of which process(es) control lithospheric removal from beneath the Wyoming and North China cratons still enigmatic. To address this problem, we are using 2D numerical models to investigate how lithospheric mantle of the North China Block has been thinned in which geological, geophysical and petrological studies refers the areas as key example of cratonic destruction/removal that occurred (120-80 Ma). Considering the geological evolution of North China region, the main focus of the study is to investigate the effects of a set of parameters (e.g., viscosity, buoyancy and thickness) for the base of cratons which is likely weakened by fluids released from the subducting oceanic plate. Our preliminary results show that movement of the subducting plate is sensitive to the parameters affecting the stability of the lithosphere whereas overriding plate is mainly affected by viscosity. If the base of the cratonic lithospheric mantle is dense, thick and relatively less viscous, it forces oceanic slab to rollback, else the overlying plate slides through the base of the cratonic mantle. The model results with stagnated oceanic plate at the transition zone with low viscosity cratonic base is responsible for the deformation of the cratonic roots.

How to cite: Ballı Çetiner, A., Göğüş, O., and van Hunen, J.: How flat subduction and the upper plate rheology control the deformation of the North China craton, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-377, https://doi.org/10.5194/egusphere-egu23-377, 2023.

Earth is the only planet known to have continents, although how they formed and evolved is not well understood. Using the oxygen isotope compositions (SIMS) of dated magmatic zircon, we show that the Pilbara Craton in Western Australia, Earth’s best-preserved Archaean (4.0–2.5 Ga) continental remnant, was built in three stages. Stage 1 zircons (3.6–3.4 Ga) form two age clusters with one-third recording submantle δ¹⁸O, indicating crystallization from evolved magmas derived from hydrothermally-altered basaltic crust similar to that in modern-day Iceland. Shallow melting is consistent with giant meteor impacts that typified the first billion years of Earth history. Giant impacts provide a mechanism for fracturing the crust and establishing prolonged hydrothermal alteration by interaction with the globally extensive ocean. A giant impact at around 3.6 Ga, coeval with the oldest low-δ¹⁸O zircon, would have triggered massive mantle melting to produce a thick mafic–ultramafic nucleus. A second low-δ¹⁸O zircon cluster at around 3.4 Ga is contemporaneous with spherule beds that provide the oldest material evidence for giant impacts on Earth. Stage 2 (3.4–3.0 Ga) zircons mostly have mantle-like δ¹⁸O and crystallized from parental magmas formed near the base of the evolving continental nucleus. Stage 3 (<3.0 Ga) zircons have above-mantle δ¹⁸O, indicating efficient recycling of supracrustal rocks. That the oldest felsic rocks formed at 3.9–3.5 Ga, towards the end of the so-called late heavy bombardment, seems unlikely to be a coincidence.

How to cite: Johnson, T., Kirkland, C., Lu, Y., Smithies, H., Brown, M., and Hartnady, M.: Giant impacts and the origin and evolution of continents, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1941, https://doi.org/10.5194/egusphere-egu23-1941, 2023.

The Antarctic continent is a complex assemblage of geological units, ranging from Archean cratons in the east to a Cenozoic assembly of Mesozoic terranes in the west. Present are also the failed Lambert rift system, the inactive West Antarctic rift system and intraplate volcanism in Marie Byrd Land. Covered almost entirely by ice sheets, Antarctica's highly heterogeneous lithospheric structure and its upper mantle are among the least well-studied regions of the Earth’s interior.

The past two decades have seen a significant rise in the number of seasonal and temporary deployments as well as new permanent stations, supplementing and improving the still sparse station coverage in Antarctica. This provided a considerable improvement in both the quantity and quality of seismic data available for the Antarctic continent and its surrounding regions. We assemble a very large dataset of 0.8 million waveform fits, comprising all publicly accessible broadband data in the Southern Hemisphere, with sparser coverage elsewhere, for the best possible sampling of the Antarctic Plate’s crust and the upper mantle.

The new S-wave velocity tomographic model of the crust and upper mantle of Antarctica is computed using the Automated Multimode Inversion (AMI) scheme. AMI first extracts structural information from the surface, S- and multiple S-waves as sets of linearly independent equations. These equations are then combined into a single large linear system that is solved to obtain a tomographic model of the Antarctic crust and upper mantle. We observe the clear delineation of East and West Antarctica by a strong velocity gradient that bisects the continent extending from Coats Land to Victoria Land, following the Transantarctic Mountains. West Antarctica is observed to be underlain by low S-wave velocity anomalies connecting the Antarctic Peninsula, the Amundsen Sea Coast and Marie Byrd Land. The highest S-wave velocity anomalies are observed in central-eastern Antarctica, most of which is underlain by thick, cold cratonic lithosphere. Our tomography maps the boundaries of Antarctica’s cratonic lithosphere and, also, substantial intra-cratonic heterogeneity. It also reveals the patterns of the lithosphere-asthenosphere interactions beneath the cratons and the neighbouring Cenozoic terranes and offers new evidence on the origins of the Transantarctic Mountains and the intraplate volcanism in West Antarctica.

How to cite: Chua, E. L. and Lebedev, S.: Waveform Tomography of the Antarctic Plate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2083, https://doi.org/10.5194/egusphere-egu23-2083, 2023.

The Acasta Gneiss Complex (AGC) in northwestern Canada is home to the oldest known evolved (felsic) rocks on Earth, dating back to around 4.03 billion years (Ga). These rocks preserve evidence for multiple episodes of magmatism, metamorphism, and deformation, offering insights into the geological processes that shaped the Earth's crust throughout the Archean and late Hadean. However, the metamorphic pressure–temperature (P–T) conditions of this complex remain poorly constrained. In this study, we use phase equilibria modelling and in situ garnet Lu-Hf geochronology to analyse two garnet-bearing tonalitic gneisses in the AGC, providing the first quantitative P–T constraints for a late Paleoarchean tectono-metamorphic event in the AGC. Our results indicate metamorphic peak conditions of approximately 725-780°C and 4.5-6.2 kbar, with limited partial melting (<7 vol.%) of the felsic gneisses at these crustal levels. In situ Lu-Hf garnet geochronology suggests that this metamorphic event occurred between 3.3-3.2 Ga, consistent with previous findings of high-grade metamorphism at that time. Isotopic disturbance of garnet at approximately 1.9 Ga is interpreted to reflect partial resetting of the Lu-Hf systematics in response to fluid-present re-equilibration during the Paleoproterozoic Wopmay orogeny. Our study extends the limited dataset of published P–T data for Mesoarchean and older metamorphic rocks and shows that tonalitic gneisses in the AGC evolved along a high apparent thermal gradient of 125-150°C/kbar.

How to cite: Kaempf, J., Johnson, T., Clark, C., Brown, M., and Rankenburg, K.: Pressure–temperature conditions and age of metamorphism in the Archean Acasta Gneiss Complex: constraints from phase equilibrium modelling and in situ garnet Lu-Hf geochronology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2207, https://doi.org/10.5194/egusphere-egu23-2207, 2023.

Cratonic lithosphere delamination has been frequently suggested in recent studies. However, the fate of the delaminated Sub-Cratonic Lithospheric Mantle (SCLM) has not been thoroughly investigated. Here, we use 2D numerical models to study the evolution of initially delaminated SCLM whose density is initially larger than that of the ambient mantle. Our simulations reveal that after the dense lithospheric segments sink into the hot mantle, the increase of thermal buoyancy and/or removal of the dense components reverse their trajectory, and most of these segments eventually relaminate to the base of the above lithosphere. The time needed for the relamination process to complete is 100-300 Myr since initial delamination, with the exact value depending on the buoyancy of the SCLM and the mantle viscosity. Both delamination and relamination could generate a rapid hundred-meter to kilometer scale surface uplift. After the relamination, the subsequent cooling of the SCLM causes gradual subsidence by ~2 km. This model provides a novel explanation for the observed Phanerozoic vertical motion of many cratons as well as the origin of the enigmatic intracratonic basins, arches, and domes in the upper cratonic crust. According to our models, the delamination-to-relamination evolution mode could occur repeatedly during the past one billion years, as could reconcile the apparent long-term intactness of cratonic crusts and the temporal variations of cratonic topography.

How to cite: Peng, L., Liu, L., and Liu, L.: Cratonic Lithosphere Delamination and Relamination Explain the Temporal Variation of Cratons, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2391, https://doi.org/10.5194/egusphere-egu23-2391, 2023.

Earth is the only known inhabited world in our solar system. Criteria essential for planetary habitability include surface liquid water, a stable atmosphere, and a magnetic field. While the rock record suggests Earth has fulfilled these criteria for at least 4 billion years (Ga), both its environment and life have evolved over time. The Great Oxygenation Event (GOE), which occurred ~2.5 Ga ago, drastically altered the chemistry of the oceans and atmosphere. Decoding environmental and magnetic signals recorded in rocks prior to the GOE is essential for understanding the conditions under which life first emerged.

An ideal target for investigating surface conditions prior to the GOE are banded iron formations (BIFs), which precipitated directly from ancient oceans. However, BIFs have been significantly altered since their formation, and it is unclear whether a record of their depositional environment remains.  The present day mineralogy is dominated by magnetite, but it remains to be established how this relates to the precipitates deposited on the seafloor. Additionally, in spite of magnetite's ideal magnetic properties, BIFs are avoided for paleomagnetic analysis because the timing of magnetization is uncertain. It is vital to constrain the magnetic field record leading up to the GOE because it may have influenced atmospheric hydrogen loss, contributing to rapid surface oxidation.

We present paleomagnetic field tests from the Isua Supracrustal Belt that suggest a record of Earth’s 3.7-billion-year (Ga) old (Eoarchean) magnetic field is preserved in the banded iron formation in the northernmost northeast region of the belt. Our results are supported by radiometric Pb-Pb dating of magnetite from the same banded iron formation.  We show that the Pb-magnetite system has a closure temperature below 400 °C for the magnetite grain size range observed in the banded iron formation, suggesting the rocks have not been significantly heated since magnetization was acquired. This temperature range is well below the Curie temperature of magnetite (580 °C), suggesting Eoarchean magnetization has not been thermally overprinted by subsequent metamorphism.  Passed paleomagnetic field tests suggest the rocks have also avoided chemical overprints. We recover an ancient magnetic field strength, supporting previous studies that argue Earth’s magnetic field has been active throughout most of its history although variations in its strength remain poorly constrained.

How to cite: Nichols, C., Weiss, B., Eyster, A., Martin, C., Maloof, A., Kelly, N., Zawaski, M., Mojzsis, S., Watson, B., and Cherniak, D.: Using banded iron formations to understand habitable conditions on the early Earth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2404, https://doi.org/10.5194/egusphere-egu23-2404, 2023.

Whether Archean tectonics were horizontally or vertically dominated is controversially discussed because arguments bear on the kinematics and thermal state of the Archean mantle and constrain the mode of formation of the earliest continental crust. Highly deformed strata of Archean greenstone belts figure prominently in this debate because they record long periods of time and multiple deformation phases. Among the best-preserved greenstone belts counts the Barberton Greenstone Belt (BGB) of southern Africa. Geological mapping of part of the southern BGB in Eswatini (Swaziland), combined with U-Pb zircon dating, shows that the region preserves a tightly re-folded imbricate thrust stack in which metavolcanic and -volcaniclastic strata of the Onverwacht Group, deposited at 3.34–3.29 Ga, have been thrust on top of ca. 3.22 Ga siliciclastic strata of the Moodies Group. The structurally highest element, the Malolotsha Syncline, forms a tectonic klippe of substantial size and is >1,450 m thick. Forward modeling of a balanced cross section indicates that this thrust stack was part of a northwestward-verging orogen along the southern margin of the BGB and records a minimum horizontal displacement of 33 km perpendicular to its present-day faulted, ductily strained and multiply metamorphosed margin. Because conglomerate clasts indicate a significantly higher degree of prolate strain which extends further into the BGB than at its northern margin, late-stage tectonic architecture of the BGB may be highly asymmetrical. Our study documents that the BGB, and perhaps other Archean greenstone belts, preserves a complex array of both vertically- and horizontally-dominated deformation styles that have interfered with each other at small regional and short temporal scales.

How to cite: Heubeck, C., Thomsen, T. B., Heredia, B. D., Zeh, A., and Balling, P.: The Malolotsha Klippe: Large-Scale Subhorizontal Tectonics Along the Southern Margin of the Archean Barberton Greenstone Belt, Eswatini, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2429, https://doi.org/10.5194/egusphere-egu23-2429, 2023.

We present the result of an integrated petrological and geophysical 3D modelling of the lithospheric mantle over the West and Central African rift system. For modelling, the integrated geophysical and petrological forward modelling software LitMod3D has been used. The initial geometry of the model is based on the Moho depth and base lithosphere of the global model WINTERC-G, and the sediment thickness from the global model Crust1.0 and the available seismic Moho depth have been used for validation. The model is fitted to satellite gravity gradients and the Bouguer anomaly calculated from the XGM2019e-2190 model. Different classes of mantle composition data have been considered and by iteratively trying to compute the best fitting between different modelled and observed signals, the final models of density, velocity and temperature distributions have been estimated. 

The model shows lateral transitions curved shape, extending horizontally for about 50km, between the West and Central African rift system, and the surrounding Congo craton and West African craton. More in detail, the results show the lateral and vertical variation of density, temperature and velocity in respect between the different lithospheric mantle domains. We notice the absence of a clear signature of the Saharan meta-craton, making this area more similar to the West and Central African rift system than the bordering cratons. Moreover, the modelled density profile shows a continuous depth dependent gradient under the rift system, but three steps in the depth profile under the cratons, suggest a layering of the lithospheric mantle with respect to its density gradient, which can be interpreted as metasomatism of the lower lithospheric mantle.

How to cite: Fosso Teguia M, E. E. and Ebbing, J.: Integrated 3D modelling of the lithospheric mantle under the West and Central African rift system and surronding., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3477, https://doi.org/10.5194/egusphere-egu23-3477, 2023.

The emergence of continents above sea-level marks a pivotal junction in Earth’s evolution that fundamentally changed the chemistry of the atmosphere and oceans, which was critical to establishing a habitable planet. However, when and how the first subaerial continental landmasses formed remains contentious. Abrupt changes in proportion of submarine vs subaerial volcanism and in the oxygen isotopic ratios of shales and zircons at the Archean-Proterozoic transition (2.5 billion years ago, Ga) are invoked to argue for global continental emergence around that time (e.g., Kump and Barley, 2007; Bindeman et al., 2018). However, direct evidence for an earlier episode of continental emergence comes from ~3.0-2.7 Ga paleosols (like the Nsuze paleosol) and terrestrial sedimentary strata that formed atop stable cratons (cf. Eriksson et al., 2013). This attests continental emergence > 2.5 Ga, at a time when the operation of modern plate tectonics is debated.

To help resolve these issues, we focussed on the cratons like the Singhbhum and Kaapvaal cratons since they host widespread Mesoarchean terrestrial to shallow marine clastic strata and paleosols, which suggests early (> 2.5 Ga) continental emergence on Earth. We studied how crustal thickness and composition of these cratons evolved through time leading to their emergence, by linking the Paleo-to-Mesoarchean sedimentary and magmatic records of these cratons (Chowdhury et al., 2021). First, we studied the conglomerate-sandstone-shale successions that are uncomforably lying on the cratonic basement and determined their depositional ages to constrain the timing of the continental emergence. Then we analysed the chemistry of the tonalite-trondhjemite-granodiorite (TTG) suite of felsic rocks and performed petrogenetic modelling to quantify the evolution of crustal thickness and P-T conditions of crust formation, which elucidated the underlying mechanism and tectonic environment of emergence.

Our results show that the studied cratons became emergent between ca. 3.3-3.1 Ga due to progressive crustal thickening and maturation driven by granitoid magmatism. The cratonic crust  became chemically mature and extremely thick (45-50 km) by 3.2-3.1 Ga, such that isostatic compensation led to their rise about the sea level. Modelling of the TTG chemistry further elucidated that these TTGs formed at hotter thermal conditions characteristic of a thickened Archean crust atop a zone of rising mantle. Hence, we propose that emergence of stable continental crust began at least during the late Paleoarchean to early Mesoarchean and was driven by the isostatic rise of their magmatically thickened, SiO₂-rich crust without the help of plate tectonics (Chowdhury et al., 2021). We further surmise that such early episodes of emergence caused important changes in Earth’s early surficial environments including promoting transient atmospheric-oceanic oxygenation (O₂-whiffs) and CO₂ drawdown leading to glacial events.

Reference:

Bindman et al., 2018. Nature 557, 545–548.

Chowdhury et al., 2021. PNAS 118, e2105746118.

Eriksson et al., 2013. Gondwana Research 24, 468–489.

Kump and Barley, 2007. Nature 448, 1033–1036.

How to cite: Chowdhury, P., Cawood, P. A., and Mulder, J. A.: When and how did Earth’s earliest continents first emerge above the oceans?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4246, https://doi.org/10.5194/egusphere-egu23-4246, 2023.

The Earth has evolved into a habitable planet through ongoing and complex cycling. Decades of field studies, geochemical analyses and computational approaches to integrate data into feasible geodynamic models reveal that Earth’s evolution was not linear but evolved in discrete phases. The timing of changes between these phases, their loci within Earth’s crust or between discrete cratonic terranes, and most importantly the drivers or tipping point for these changes, remain elusive.

Integrating the record from the continental archive with knowledge of the ongoing cooling of the mantle and lithospheric rheology (parametrized for its evolving thermal state) allows us to determine that a number of different tectonic modes operated through the early history of the Earth. The temporal boundaries between these proposed different phases in tectonic mode are approximate, transitional, and correspond with the first recording of a key feature of that phase.

Initial accretion and the moon forming impact resulted in a proto-Earth phase (ca. 4.57-4.45 Ga) likely characterized by a magma ocean. Its solidification produced the primitive Earth lithosphere that extended from ca. 4.45-3.80 Ga, which based on the very minor fragments preserved in younger cratons provides evidence for intra-lithospheric reworking, but which also likely involved intermittent and partial recycling of the lid through mantle overturn and meteoritic impacts. Evidence for craton formation and stabilization during the primitive (ca. 3.8 Ga to 3.2 Ga), and juvenile (ca. 3.2 Ga to 2.5 Ga) phases of Earth evolution likely reflects some degree of coupling between the convecting mantle and a lithosphere initially weak enough to favour an internally deformable, squishy-lid behaviour. These regions of deformable lithosphere likely oscillated spatially and temporally with regions of more rigid, plate like, behaviour leading to a transition to global plate tectonics by the end of the Archean (ca. 2.5 Ga). Evidence for assembly of rigid cratonic blocks in the late Archean along with their subsequent rifting and breakup followed by their reassembly along major linear orogenic belts in the Paleoproterozoic marks the clear inception of the supercontinent cycle in response to a plate tectonic framework of oceans opening and closing.

Since solidification of the magma ocean early in Earth history, the available record suggests some degree of mantle-lithosphere coupling. The development and stabilization of cratons from 3.8-2.5 Ga provides evidence for the progressive development of rigid lithosphere and represents the inexorable precursor to the development of plate tectonics.

How to cite: Cawood, P., Chowdrury, P., Mulder, J., Hawkesworth, C., Capitanio, F., Gunawardana, P., and Nebel, O.: On tectonic modes of the early Earth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4566, https://doi.org/10.5194/egusphere-egu23-4566, 2023.

Isotopic proxies such as Hf, Nd and Pb are widely used to understand the evolution of Earth’s crust and mantle. Of these, Pb isotopes are particularly sensitive to crustal influences, and the extraction of mantle melts. We present a global compilation of Pb isotope data from syngenetic Volcanogenic Massive Sulphide (VMS) deposits, which allow us to track the evolution of Pb isotopes in deposits that are associated with dominantly back-arc and extensional oceanic settings through time.

Unradiogenic Pb isotope signatures, specifically low model source µ (²³⁸U/²⁰⁴Pb) values, in some Archean cratons have long been recognised, yet their origin remains elusive. For example, sulphides from the c. 2.7 Ga Abitibi Belt in the Superior Province of Canada require long-lived (> 500 my) evolution of a source component to generate the Pb isotope signatures observed. Other isotope systems, such as Lu-Hf and Sm-Nd, show relatively juvenile signatures for the Abitibi Belt, suggesting decoupling of the different systems. Low µ values are evident in ore deposits and rocks from the Archean to modern settings but are most prominent in Archean settings because of their associated low ²⁰⁷Pb/²⁰⁴Pb values, unlike for younger times.

Pb isotope data at a global and broad temporal scale show that periods with distinct low µ values have a marked cyclicity that coincides with the supercontinent cycle. We propose that during supercontinent assembly, portions of older unradiogenic, Pb-rich mantle are tapped and incorporated into VMS deposits. Pb, possibly enriched in sulphides, can explain the apparent decoupling of Pb from silicate-controlled isotope systems like Hf and Nd. We suggest that the source of this unradiogenic mantle component formed during the previous supercontinent cycle when large volumes are extracted from the mantle to form (radiogenic) crust and an unradiogenic residue, which most likely resides in the lithospheric mantle although some may also be present as discrete ‘pods’ in the circulating mantle. This process provides a mechanism to explain isolation of source regions for several hundred million years, as required to generate the low µ values, until later tapping during a subsequent supercontinent amalgamation cycle.

The low µ values in the c. 2.7 Ga Abitibi Belt represent the best-known Archean occurrence of this signature, indicating that their unradiogenic source relates to a major mantle extraction event that would have occurred at least 500 my earlier, i.e. at about 3.2 Ga.

How to cite: Armistead, S., Eglington, B., Pehrsson, S., and Huston, D.: Pb isotope heterogeneities in the mantle and links to the supercontinent cycle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4744, https://doi.org/10.5194/egusphere-egu23-4744, 2023.

Water plays a crucial role in the formation of new crust on modern Earth. Today, new continental crust is created through arc magmatism by fluid-fluxed mantle melting above subduction zones. The aqueous fluid is derived from the breakdown of hydrous phases in subducted oceanic crust as a result of a delicate interplay between phase stability and the cold thermal conditions in the slab. Hydrated and subducted ultramafic (mantle) rocks play a key role in supplying the water needed for wet mantle melting and provide an important link between the Earth’s deep water cycle and formation of crust with an average andesitic composition.

Archean felsic crust consists of the typical Tonalite-Trondhjemite-Granite (TTG) Series, which were likely produced from melting of altered basaltic precursors. Previous studies suggest that the water-present partial melting of metamorphosed basalt at temperatures of 750–950 °C is required to produce large volumes of partial melt with TTG compositions. However, the source of such water is unknown and exposed serpentinised mantle rocks likely played a negligible role in the early Earth’s water cycle.

We propose that hydrated komatiites played a vital role in TTG genesis. Using petrology, mineral chemistry and phase equilibria modelling of representative komatiite samples, combined with analysis of a global geochemical dataset of komatiites and basaltic komatiites, we show that during metamorphism hydrated komatiites can release at least 6 wt. % mineral-bound water. The great majority of this water is released by breakdown of chlorite and tremolite at temperatures between 680 and 800 °C. As the temperatures of komatiite dehydration are above the wet basalt solidus, the released water can trigger voluminous partial melting of basalt to ultimately create TTG batholiths. This considerable hydration potential of komatiites is due to their high X_Mg, which stabilises hydrous minerals during oceanic alteration on the seafloor, but also extends the stability of Mg-rich chlorite to high temperatures. During prograde metamorphism, the X_Mg, CaO and Al₂O₃ content of the reactive rock composition determines the proportion of chlorite vs amphibole, and therefore the volume of water which can be transported to temperatures of > 750 °C. Therefore, we suggest that water released from dehydrating komatiites - regardless of the prograde P–T path (i.e., tectonic scenario) they experienced - provided the free water necessary to partially melt large volumes of basalts to form the prominent and expansive TTG suits in the Archean. Even though komatiites make up moderate portions of greenstone belts, they thus likely played a key role in early crustal formation and the Earths’ early water cycle.

How to cite: Hermann, J., Tamblyn, R., Hasterok, D., Sossi, P., Pettke, T., and Chatterjee, S.: Hydrated komatiites as a source of water for TTG formation in the Archean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5476, https://doi.org/10.5194/egusphere-egu23-5476, 2023.

It is hotly debated when plate tectonics began to operate on the earth, believed to happen sometime during the Archean. We study here the relationship between metamorphism and drip and plate tectonics during the Archean. We examined metamorphic proxy, and tracked tectonic forms and processes over the Archean by synthesizing (i) zircon U-Pb age spectra and isotopes of samarium and neodymium, (ii) compiling events associated with continental crustal growth and reworking, and (iii) integrating various proxies connected to plate tectonics and special magmatism/tectonics. We propose that plate tectonics started at the latest in the Eoarchean and occurred in the form of accretion or collision without subduction around 3.7 billion years ago (Ga); suggest that 3.3-3.1 Ga and 3.0-2.9 Ga were the time of local subduction initiation and the onset of the global plate tectonics, respectively; confirm the assembly of Kenorland supercontinent at 2.8-2.5 Ga. We finally established a secular evolution model to visualize the evolution of Archean plate tectonics from stagnant to local, regional, and global scales.

How to cite: Kuang, J., Morra, G., Yuen, D., and Qi, S.: Forms and evolution of plate tectonics on the Archean Earth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5805, https://doi.org/10.5194/egusphere-egu23-5805, 2023.

Archean cratons have thick, cold lithosphere that is remarkably stable, thanks to its compositional buoyancy and mechanical strength. Despite this stability, cratonic lithosphere can, sometimes, be modified and eroded, following the impact of a mantle plume, episodes of subduction and continental collision, or stretching and rifting. Although the chemical modification and removal of the Archean lithospheric material are permanent, there is intriguing evidence for re-growth in cratonic lithosphere’s thickness in some locations. In order to understand the enigmatic lithospheric evolution of cratons and continental blocks adjacent to them, we need the knowledge of the thermo-chemical structure of the lithosphere and of the dynamics of the lithosphere-asthenosphere interaction.

Seismic surface waves yield abundant evidence on the thermal structure and thickness of the lithosphere and on the temperature of the underlying upper mantle. Tomographic maps resolve in fine regional detail the boundaries between high-velocity (cold) cratons and lower-velocity (warm) neighbouring blocks. The radial structure and thickness of the lithosphere, however, are not resolved by tomographic models quite as well, due to their non-uniqueness. As a result, seismic-velocity profiles from tomographic models are normally incompatible with plausible geotherms. How, then, can we determine the structure and thickness of the lithosphere?

Recently developed methods for computational-petrology-powered inversion (e.g., Fullea et al. 2021) relate seismic, topography, heat-flow and other data directly to temperature and composition of the lithosphere and underlying asthenosphere. The misfit valleys in the surface-wave-dominated parameter space are still broad, and it is essential to have accurate measurements and low data-synthetic misfits. Here, we achieve remarkably low misfits of ~0.1% of the surface-wave phase-velocity values by precise tuning of the petrological inversion, its parameterisation and regularisation. The data are fit closely by models with depleted harzburgite mantle compositions within the lithosphere of cratons. The inversions tightly constrain the thickness of cratonic lithosphere, which we find to vary in the ~150-300 km range over different cratons. The plume-lithosphere interactions and the associated surface uplift and volcanism are controlled, to a large extent, by the lithospheric thickness  (e.g., Civiero et al. 2022), which, in turn, evolves with time, influenced by the processes. High-resolution seismic imaging and the petrological inversion of the resulting data yield exciting new discoveries on the evolution of continental lithosphere and its interactions with the underlying mantle.

References

Civiero, C., Lebedev, S., Celli, N. L., 2022. A complex mantle plume head below East Africa-Arabia shaped by the lithosphere-asthenosphere boundary topography. Geochemistry, Geophysics, Geosystems, 23, e2022GC010610.

Fullea, J., Lebedev, S., Martinec, Z., Celli, N.L., 2021. WINTERC-G: mapping the upper mantle thermochemical heterogeneity from coupled geophysical–petrological inversion of seismic waveforms, heat flow, surface elevation and gravity satellite data. Geophysical Journal International, 226(1), 146-191.

How to cite: Lebedev, S., Xu, Y., Davison, F., and Fullea, J.: Continental lithosphere and its interactions with the asthenosphere: New insights from seismic imaging and petrological inversion, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7113, https://doi.org/10.5194/egusphere-egu23-7113, 2023.

The impact that ancient Earth surface processes had on long-term thermal regimes remain uncertain despite their potentially important role in fostering craton stabilization and preservation. The distribution and redistribution of heat producing elements (HPEs) during craton development plays a major role in lithospheric cooling and strengthening. Whereas the redistribution of HPEs via erosion has theoretically been suggested to alter the long-term geotherm and contribute to Moho cooling, direct temporal constraints from the field are lacking to adequately assess the role that ancient Earth surface processes may have had on long-term thermal regimes. Here, we used apatite U-Pb thermochronology to assess the thermal evolution of the Archean Bundelkhand craton of central India immediately following its amalgamation and final phase of silicic magmatism at ~2.5 Ga. Apatite from both ~3.4 Ga granitic gneisses and ~2.5 Ga granitoids collected across the ~250 km-wide craton yielded near-uniform apatite U-Pb dates between ~2.4–2.3 Ga, indicating that the craton was broadly exhumed through mid-crustal depths shortly following shallow granitoid emplacement. Unroofing of the craton at this time is further corroborated by the presence of a distinct ~2.5 Ga detrital zircon U-Pb age peak obtained from ~2.2–2.3 Ga sandstones in direct non-conformable contact with Bundelkhand granitoids. We speculate that a two-step redistribution of HPEs largely contributed to the stabilization of the Bundelkhand craton. First, the concentration of HPEs within shallowly emplaced granitoids at ~2.5 Ga reduced the heat production of the lower-most crust. Second, post-emplacement exhumation of HPE-enriched Bundelkhand granitoids further modified the heat source distribution to a thermal regime that promoted cooling of the lower-crust. Although the mechanism driving exhumation through mid-crustal depths remains uncertain, temporal relationships from the Bundelkhand craton suggest that erosional processes may have had a significant role in promoting the craton’s stability and longevity.

How to cite: Colleps, C., McKenzie, N. R., Chen, W., and Sharma, M.: Did Earth surface processes promote stabilization of the central Indian Bundelkhand craton?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7623, https://doi.org/10.5194/egusphere-egu23-7623, 2023.

Characterizing the internal lithospheric architecture of Archean cratons is key to establishing the large-scale tectonic controls that contributed to their nucleation and formation and may play an important role in identifying the occurrence and distribution of mineral deposits. As many Archean cratons have experienced a polygenetic history, including multiple magmatic, metamorphic, and/or hydrothermal events, the primary architecture of cratonic crust may be reworked and obscured. The Rae craton in northern Canada, is no exception in that it grew through the accretion of Neoarchean (dominantly 2.58-2.75 Ga) crustal blocks followed by its amalgamation with the Slave, Hearne, and Superior cratons during <2.0 Ga Palaeoproterozoic orogenic events.

Hafnium (Hf) and oxygen (O) isotopic analysis of zircon in crustal rocks has proven to be a powerful tool to elucidate crustal architecture by identifying spatial and/or temporal changes in isotopic composition that directly relate to distinct crustal age and compositional domains within a craton. Specifically, Hf isotopic data addresses the age (and compositions) of the source to igneous rocks, including degree of contamination of juvenile magmatism, while O isotope compositions monitor the extent of recycling of hydrothermally altered or weathered crust. However, systematic Hf and O isotopic data for different bedrock source terranes within Archean terranes of northern Canada is not widely available limiting the ability to refine lithospheric structures that may be preserved in the crustal column.

In this study, we present preliminary in-situ U-Pb-Hf-O-trace element data from 115 Archean samples from across the Rae craton that were selected from the geochronology archive at the Geological Survey of Canada. All samples have been previously dated and were selected to cover the full spatial and temporal breadth of the craton with priority given to those preserving the highest quality zircon with the most unimodal age distributions. A small number of grains per sample were first dated by secondary ion mass spectrometry (SIMS) to confirm prior age determinations and to identify key grains for subsequent O and Hf isotope/trace element analysis by SIMS and laser ablation – inductively coupled plasma mass spectrometry, respectively. Collectively, these data will help refine petrological models of Rae crust formation, differentiate crustal domains that may or may not have experienced contrasting processes of formation, and contribute to identifying potential boundaries between isotopically different crustal blocks representing cryptic tectonic transitions within the cratons.

How to cite: Cutts, J. and Davis, W.: Delineating the lithospheric architecture of the Rae cratons using Hf and O isotopes and trace elements in zircon, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9348, https://doi.org/10.5194/egusphere-egu23-9348, 2023.

We performed reinterpretation of the DEKORP-BASIN’96 offshore deep reflection seismic profiles PQ-002 and PQ-004-005 running ENE-WSW in the South Baltic area through the transition zone between the East European Craton (EEC) in the NE and the Palaeozoic Platform in the SW. These profiles intersect the Teisseyre-Tornquist Zone (TTZ) and the Sorgenfrei-Tornquist Zone (STZ) to the south and north of the Bornholm Island, respectively. While the STZ is considered to be an intra-cratonic structure within the EEC, the TTZ is often believed to represent the actual edge of the Precambrian craton. Regardless of their origin and tectonic position, both zones are characterized by intense compressional deformations associated with the Alpine inversion of the Permian-Mesozoic basins at the transition from the Cretaceous to Paleogene.

Our research aimed to explain the structure of the transition zone between the EEC and the Palaeozoic Platform and check whether its structure differs north and south of Bornholm. We also aimed at documenting the nature of the Late Cretaceous deformations and their relationship to the STZ and TTZ, as well as the marginal zone of the EEC.

Both PQ profiles show a continuation of the EEC crust toward the WSW beyond the STZ and TTZ. The cratonic crust has a considerable thickness and is characterized by a deep Moho position along the entire length of the profiles. The depth of Moho is in our interpretation much greater than that postulated in previous interpretations. Consequently, numerous reflections once interpreted as upper mantle reflections occur within the lower crust in our opinion.

The most spectacular feature of both PQ profiles is related to the zones of thick-skinned compressional deformation associated with the Alpine inversion along the STZ and TTZ. Crustal-scale, ENE-vergent thrusts have been traced from the top of the Cretaceous down to the Moho in terms of the detachment faults through the entire crust. They are accompanied by back thrusts with vergence toward the WSW, which also reach the Moho. The Late Cretaceous deformation resulted in the uplift of a block of cratonic crust as a pop-up structure, bounded by thrusts and back thrusts, and displacement of the Moho within the STZ and TTZ. It also led to the formation of the Late Cretaceous syn-inversion troughs on both sides of the uplifted wedge providing evidence for the age of deformation.

The STZ and TTZ, imaged by the PQ profiles, appear as zones of the localised Late Cretaceous thick-skinned deformation that is superimposed on the EEC crust and its sedimentary cover. Within these zones, the Moho is faulted in several places and a large block of the basement is uplifted as a crustal-scale pop-up structure. A similar crustal architecture characterises the Dnieper-Dontes Paleorift, which was also inverted in the Late Cretaceous. A special position is occupied by the island of Bornholm, located in the middle of the pop-up structure, which owes its formation to the Late Cretaceous inversion of the sedimentary basin in this place.

This study was funded by the Polish National Science Centre grant no UMO-2017/27/B/ST10/02316.

How to cite: Ponikowska, M., Stovba, S., Mazur, S., Malinowski, M., Krzywiec, P., Maystrenko, Y., Nguyen, Q., and Hübscher, C.: Deeply rooted inversion tectonics in the southern Baltic Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9440, https://doi.org/10.5194/egusphere-egu23-9440, 2023.

Interpreting Archean geology is often challenging due to the rocks having obscure field relationships and polymetamorphic histories (Kusiak et al. 2019; Dunkley et al. 2020). In such circumstances, U-Pb isotopic analysis of zircon is crucial for revealing the geological history. This study investigates Archean gneisses from the Saglek Block in Canada, which record magmatic and metamorphic history between ca 3.9 Ga and 2.5 Ga. The predominant lithology is the Uivak gneiss which is primarily composed of tonalite-trondhjemite-granodiorite (TTG) with subordinate intermediate to mafic components. Uivak gneiss is traditionally divided into Uivak I and Uivak II, where Uivak I is grey gneiss and Uivak II is characterized by augen texture and Fe-rich geochemistry (Collerson and Bridgwater, 1979). Ages for the magmatic protoliths of Uivak I are >3.6 Ga, whereas Uivak II ages vary between ca 3.6-3.3 Ga (Sałacińska et al. 2019; Wasilewski et al. 2021 and references therein). 

This study presents geochemical and U-Pb zircon geochronology from Mentzel and Maidmonts Islands. Augen gneiss on Mentzel Island fits the definition of Uivak II augen gneiss and yield a U-Pb zircon age of ca 3.3 Ga. A similar age was reported for Maidmonts gneiss (Sałacińska et al. 2019) and Illuilik gneiss (Wasilewski et al. 2021). On Mentzel Island, granitic bodies intruded the augen gneiss at ca 2.7 Ga and 2.5 Ga during high-T metamorphism. New dating confirms that augen gneiss on Mentzel Island and elsewhere in the Saglek Block belongs to Uivak II gneisses of ca 3.3 Ga. Variations in rare earth element concentration between different ca 3.3 Ga rocks can be attributed to the involvement of different crustal components in the magmatic protolith. On Maidmonts Island, the augen gneiss intrudes grey gneiss with a protolith age of ca 3.7 Ga, which confirms deformation and metamorphism of Uivak I gneiss before ca 3.3 Ga. 

This research was funded by NCN grants UMO2019/34/H/ST10/00619 to MAK.                  

References:
Collerson, K.D. & Bridgwater, D. 1979. Metamorphic development of early Archaean tonalitic and trondhjemitic gneisses: Saglek area, Labrador. In: Barker, F. (Ed.), Trondhjemites, Dacites, and Related Rock. Elsevier, Amsterdam, 205–271.

Dunkley et al. 2020. Journal of the Geological Society, 177 (1), 31–49.

Kusiak et al. 2018. Chemical Geology, 484, 210–223.

Sałacińska et al. 2019. International Journal of Earth Sciences, 108, 753-778.

Wasilewski et al. 2021. Precambrian Research, 359, 106092.

How to cite: Keluskar, T., Kusiak, M. A., Dunkley, D. J., Whitehouse, M. J., Wilde, S. A., Yi, K., and Lee, S.: Uivak II augen gneiss from the Saglek Block, Labrador: the current state of play, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9487, https://doi.org/10.5194/egusphere-egu23-9487, 2023.

Because Earth is the only known planet to host both plate tectonics and life it is sometimes concluded that the two phenomena are related. While life is thought to have originated by the Eoarchean (or earlier), the onset of plate tectonics remains unknown, with proposed initiation ages ranging as old as the Hadean. Paleomagnetism can be used to distinguish between mobile and fixed lithospheres, but studies have been impeded by the high-grade metamorphism and deformation that makes most rocks older than Paleoarchean in age unsuitable for analysis. However, select detrital zircons can preserve primary magnetizations, providing an opportunity to conduct direct tests. Here we examine the zircon paleomagnetic history recovered from Western Australia which provides evidence for near constant paleolatitudes between ca 3.9 and ca. 3.4 Ga. We further assess this record with select zircons bearing primary magnetic inclusions from South Africa, which yield magnetizations consistent with this history. The simultaneous recordings of the magnetic field by zircons from two continents with vastly different Phanerozoic geologic histories provide further support for the primary record of the zircon magnetizations, and for a pre-Paleoarchean stagnant lid regime of Earth. These data also indicate that life on Earth originated and was sustained without plate tectonic-driven geochemical cycling.

How to cite: Tarduno, J., Cottrell, R., Bono, R., Nimmo, F., and Watkeys, M.: Hadean to Eoarchean stagnant lid tectonics recorded by the paleomagnetism of zircons, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10278, https://doi.org/10.5194/egusphere-egu23-10278, 2023.

The Northwest Indian shield (NWIS) comprises of Archean Bundelkhand, Marwar and Dharwar cratons, Proterozoic mobile belts of Aravalli Delhi fold belts (ADFB) and Central Indian tectonic zone (CITZ), and the basins such as Vindhyan (VB), Cambay (CR) and the Kutch (KR). The major area of the NWIS is covered by the Cretaceous Deccan Volcanic Province (DVP) that makes it difficult to assess the lithosphere structure in this region. Here we present the seismically constrained multi-scale geopotential field interpretation of  gravity, magnetic and geoid across the major Precambrian terrains of NWIS to delineate the lithosphere structure and further to understand the evolution of these terrains. The Bouguer gravity anomaly map shows overall high gravity values except the Bundelkhand and Dharwar cratonic parts over the NWIS region. The subsurface extension of the Precambrian  terrains of the NWIS are indicated by the distinct anomaly signatures in regional gravity anomaly map. The residual gravity anomaly map is able to delineate the shallow source bodies and boundaries between various terranes that correlat well with the surface geological expressions. The constrained geopotential modelling carried out along SW-NE trending profile across the region reveals that the Moho and  Lithosphre Asthenosphere Boundary (LAB) below the DVP and CR is relatively shallow as compared to the ADFB. It has also been noticed that a high density layer at the base of the lower crust, represents the presence of  underplated crust. The shallower lithosphere structure observed below the CR region might indicate the Cretaceous reworking. The imprints of the Deccan magmatism through intrusive bodies and the modelled structure below NWIS have implications on the lithosphere evolution in the region. 

How to cite: Sathapathy, S. K. and Radhakrishna, M.: Delineation of lithosphere structure below Northwest Indian Shield (India) through constrained geopotential field modelling : geodynamic evolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11348, https://doi.org/10.5194/egusphere-egu23-11348, 2023.

The Earth is a dynamic planet that has been evolving ever since it was formed. The formation of protocontinents and their amalgamation to supercontinents and later dispersals are one of the fascinating geologic events during the course of the evolution of Earth. Studies on the assembly and dispersals, therefore, provide insights into the mechanisms of extraction of mantle materials at different time periods, the formation of mountain belts, the recycling of crustal materials, magmatism, metamorphism, etc. The recent supercontinent assembly, namely "Gondwanaland," took place during one of the most dynamic periods of the earth's history, and almost all of the existing continental fragments have records of this great geological event. The Southern Granulite Terrane (SGT) of South India is made up of a variety of crustal blocks and collisional sutures/shears that developed during the period of multiple orogenic cycles from the Mesoarchean to the late Neoproterozoic-Cambrian, including that of Gondwana period. Among this, the Palghat Cauvery Shear Zone (PCSZ) marks a major Neoproterozoic structure of crustal accretion, and it is considered the extension of major terrain boundaries identified in Madagascar and Sri Lanka in the final stages of the Gondwana assembly. Even though there have been plenty of studies carried out to understand the nature of the lower crust, terrain assembly, and shear sense indicators along the PCSZ, most of them are concentrated on the eastern side of the shear zone, and only a few have been carried out in the high-grade western terrain; therefore, unequivocal evidence showing collisional orogenesis is lacking from this terrain. The present study attempts to infer the geochemical characteristics of charnockites from the western parts of the PCSZ in terms of accretionary and/or collision tectonics. The geochemistry suggests that the charnockites are tonalitic to granodioritic in composition and have calc-alkaline affinity, indicating an origin related to collision tectonics. These are the products of granulite-facies metamorphism, most probably of an I-type granitic magma, with a low Rb/Sr ratio and a high Ba/Rb ratio suggesting resemblance with Archaean tonalites, and as a product of the remelting of protoliths of tonalite–trondhjemite–granodiorite (TTG) composition. The whole-rock major and trace element compositions indicate that charnockites are formed as the product of partial melting of garnet amphibolite or eclogite-facies basaltic crust during granulite-grade metamorphism at a lower crustal level during a collisional event.

How to cite: Nandan T, N. and Chettootty, S.: A geochemical perspective on the petrogenesis of charnockites from the western parts of the Palghat-Cauvery Shear Zone, southern India: implications for collisional geodynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11847, https://doi.org/10.5194/egusphere-egu23-11847, 2023.

Greenland’s tectonic history is complex, and the resulting lithospheric structure is, although extensively studied, not well constrained. Most models agree regarding the location of the North Atlantic Craton in South Greenland, and the most recent surface heat flow model also predicts a cold lithosphere for that area. However, the velocity anomaly from the regional tomography NAT2021 shows two additional cratonic blocks in North Greenland that are not included in geological maps and previous lithospheric models.  

To resolve these differences, we built a lithospheric model for Greenland that is compatible with multiple observables and focuses on data integration. In the first step, a background model is set up that uses petrological information of the mantle to model coherent seismic velocities, densities, and temperatures down to a depth of 400 km. The lithospheric model is then adjusted to reproduce the seismic velocities from NAT2021, the gravity field from satellite data and the isostatic elevation. In a second step, we jointly inverted the residual gravity field data from the lithospheric background model together with airborne magnetic data to estimate the crustal density and susceptibility structure. Both rock properties are coupled with a variation of information coupling constraint that establishes a distinct parameter relationship. To assess the compatibility of the thermal structure of our model with the most recent geothermal heat flow model for Greenland, we perform a grid search for the crustal radiogenic heat production, which would be necessary to reproduce this recent geothermal heat flow map. Finally, the results from the different steps are combined by cluster analysis and compared with petrophysical data from a newly established database of Greenland.

The iterative workflow provides novel insights into the sub-ice geology of Greenland. We can model three cratonic blocks with LAB depths greater than 200 km and simultaneously fit the gravity, magnetic and elevation data in Greenland and the most recent geothermal heat flow model. 

How to cite: Wansing, A., Ebbing, J., Moorkamp, M., and Heincke, B.: Greenland’s lithospheric structure from integrated modelling of potential field data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12192, https://doi.org/10.5194/egusphere-egu23-12192, 2023.

The North China Craton is located on the Eurasian continental margin. Since the Mesozoic, the Izanagi and Pacific plates are subducting westward with the trench retreating eastward over time. This process is accompanied by extensive magmatism, development of rift basins, and the formation of the Japan sea. The lithosphere of the North China Craton, which is about 220 km thick, gradually becomes thinner from west to east down to around 60-80 km.

Due to extensive magmatism between 140-120Ma, we believe that the North China Craton was positioned at the back-arc area of the Eurasian continental margin where the Izanagi plate currently subducts, and the trench gradually migrated eastward. We assume that the subduction event formed a large-scale high-temperature weak zone, similar to the high-temperature back-arc region mentioned in (Currie & Hyndman, 2006). By using thermo-mechanical modeling, we simulated the Craton break-up process. Following a continuous eastward extension model characterized by normal faulting and lithospheric thinning, we approximated the observed lithospheric variations. If the extension of the Japan sea is not considered, lithospheric thickness was simulated to decrease from 220 km to 60 km eastward. Within 600 km of tension, continuous lithospheric thinning will eventually lead to the formation of oceanic crust (Japan sea).

        We tested the mechanism affecting lithosphere thinning and found that a large-scale initial high-temperature weak zone and a low-viscosity mantle (with a large amount of fluid participation) are the key factors for the break-up of the North China craton.

How to cite: Zheng, M.-J., Lee, Y.-H., and Tan, E.: Numerical modeling of north china craton Thinning and destruction., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12838, https://doi.org/10.5194/egusphere-egu23-12838, 2023.

The 3.33 Ga Josefsdal Chert in the Barberton Greenstone Belt, South Africa, records a sequence of sediments deposited under shifting energy conditions in a nearshore paleoenvironment (1, 2). At the base, volcanoclastic sediments were deposited under somewhat dynamic conditions on top of pillow basalt and hydrothermal chert. They grade gradually upwards into alternating deposits of chemical silica and very fine scale microbialites tabular phototrophic mats) formed under very quiet conditions frequently interrupted by storm currents, which then transitioned sharply into thinly bedded tuffs with much hydrothermal activity at the base. Growth faults permitted thick sequences of very shallow sediments to accumulate. While the REE data show the global, background Eu signature of hydrothermal influence throughout, local Sm/Yb:Eu/Sm ratios document local hydrothermal hot spots. Fluvial inflow is documented by flat REE patterns in the middle to upper sequences (2).

Within this environmental background, microbialites abound, their nature (phototrophic/chemotrophic), distribution and preservation being influenced by environmental factors, such as water depth (phototrophy), sedimentation flux, and hydrothermal vents and activity. Phototrophic activity was abundant during the middle, volcanically quiet period and was present also during the lower and upper volcanoclastic depositional periods, with biofilms and mats forming on the tops of individual fining upwards layers (3,4). Chemotrophic colonies were abundant in the vicinity of hydrothermal vents (5). Amost instantaneous silicification of both sediments and the microbialites resulted in excellent preservation, although the organo-geochemical signatures are heavily diluted (SiO₂ contents ranging from ~ 90-99.9%). Biogenicity of the different microbialites was evaluated on the basis of their morphology, interactions with the immediately surrounding sediment and environmental conditions (e.g.current flow), organic carbon and δ¹³C compositions, as well as their transition element compositions and the presence of minerals precipitated as by-products of microbial metabolism (e.g. aragonite, sulphate). Periodic exposure of some of the phototrophic biofilms, as indicated by desiccation and entrapped layers of pseudomorphed evaporite minerals (aragonite, calcite, gypsum, and halite)(3,4), as well as desiccation texture on certain bedding planes, indicates a littoral, on shore environment of formation.

(1) Westall, F. et al., 2015, Geology, 43, 615; (2) Westall, F., Bréhéret, J. et al. in prep.; (3) Westall, F. et al., 2006, Phil. Trans. Roy. Soc. Lond. B., 361, 1857; (4) Westall, F. et al., 2011, Earth Planet. Sci. Lett., 310, 468; (5) Hickman-Lewis, K., et al. 2020, Sci Rep 10, 4965.

How to cite: Westall, F., Bréhéret, J., Hickman-Lewis, K., Campbell, K., Giudo, D., Foucher, F., and Cavalazzi, B.: Environmental controls on the distribution of life in shallow seas on the early Earth in the 3.33 Ga Josefsdal Chert, Barberton Greenstone Belt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12866, https://doi.org/10.5194/egusphere-egu23-12866, 2023.

A major contribution to the crustal growth and construction of the Congo Craton was the addition and preservation of the ≤ 45 000 km² Kunene AMCG Complex (KC), which straddles the international border between Angola and Namibia. KC magmatism encompasses dominantly juvenile anorthositic rocks (anorthosite, leuco-gabbro, -norite, -troctolite) and A-type granitoids (Red Granite Suite) of mixed crustal and juvenile signature. High-precision U-Pb dates of zircon and baddeleyite from the exposed western parts of the KC (~15 000 km²) in between 1500 and 1360 Ma indicate that both the anorthosites and Red Granites were pulsed and exceptionally long-lived. The remaining eastern portion of the KC can only be imaged using potential field geophysical methods as it is covered by a thin (≤ 300 m) cover of Cenozoic Kalahari sediments. Field mapping and recent remote sensing in the exposed part of the complex, together with airborne geophysics of the entire KC, indicate that the anorthosites were emplaced in up to 12 layered or massive batholiths, which are elliptical in a NNE-SSW or E-W direction. They are commonly separated by relatively thin and elongated KC granitoid bodies and are in tectonic or intrusive contact with Paleoproterozoic basement rocks.

Regional horizontal contraction in the Angolan portion of the KC is dated by U-Pb in zircon and Ar-Ar in micas at 1400-1370 Ma. Contraction formed N-S to NE-SW-striking, cm- to km-wide, discrete, syn- to post-magmatic thrust zones mainly localised in KC granitoids. The shear zones are parallel to magmatic foliation in the granitoids and magmatically layered anorthosites. A compilation of crystallisation ages (n = 60) suggests that the regional shortening triggered the magmatism that formed ~ 60% of the exposed KC by mobilising magmas from deep crustal mush zones. In contrast, the southern part of the KC in Namibia exhibits E-W- to ENE-WSW-striking magmatic layering, gneissic foliations and shear zones formed at amphibolite to greenschist facies conditions. These are compatible with north-directed ductile to brittle thrusting over the Angolan KC. Northward thrusting post-dates KC emplacement and is broadly constrained in between 1360 and 1330 Ma by Ar-Ar dating of micas. Airborne aeromagnetic and satellite gravimetric data indicate that the southern KC is parallel to and overlies a crustal and continental-scale geophysical lineament, which is interpreted as the relic of a linear Mesoproterozoic orogenic belt extending to the Kibaran Belt of Central Africa. The orogenic activity was terminated by 1127 Ma, which is the oldest age of a suite of mafic dykes crosscutting post-KC and undeformed capping siliciclastic units. U-Pb dates of detrital zircon and Hf-in-zircon data for these siliciclastic rocks overlap with those of the KC granitoids, indicating local recycling of KC rocks between 1360 and 1127 Ma.

Our results highlight that the 1500-1360 Ma period of the Congo Craton was a time of significant crustal growth in the form of voluminous Kunene Complex magmatism. The assembly of the entire KC magmatic edifice was facilitated by syn- to post-magmatic contractional deformation that juxtaposed distinct crustal domains during two newly defined Mesoproterozoic orogenic events.

How to cite: Lehmann, J., Bybee, G. M., Milani, L., Owen-Smith, T. M., Hayes, B., Ferreira, E., and Jelsma, H.: Modes of crustal growth and construction for the southwestern Congo Craton in the Mesoproterozoic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13221, https://doi.org/10.5194/egusphere-egu23-13221, 2023.

Our understanding of the geological history of early Archean crust is limited by poor preservation of igneous features in rocks that have experienced multiple metamorphic and deformation events. Thus, regions with the best preserved Eoarchean rocks, as for example, the northern part of the Itsaq Gneiss Complex (IGC) of Greenland, have been the most intensively studied. The IGC underwent metamorphism at ca 3.6 and 2.7 Ga (Nutman & Bennett 2018). The grade of 2.7 Ga metamorphism varies from granulite facies in the southern part of the IGC (Fӕringehavn terrane) to lower amphibolite facies in the north (Isukasia terrane). This study compares the preservation of zircon in rocks from both terranes of the IGC.

Zircon grains from granitic gneisses in the Fӕringehavn terrane have rounded igneous cores with weak oscillatory zoning, surrounded by well-developed light-CL metamorphic rims. The ²⁰⁷Pb/²⁰⁶Pb zircon age obtained by in situ Secondary Ion Mass Spectrometry (SIMS) of these grains is ca 3.64 Ga for the cores, with metamorphic rims recording an age of ca 2.7 Ga. The Isukasia terrane extends either side of the Isua Supracrustal Belt (ISB), rock samples were collected from both the outer (SSE of the ISB) and inner (NNW of the ISB) Isukasia sub-terranes (Nutman & Bennett 2018). Zircon grains from the outer sub-terrane have well preserved igneous morphologies with evidence of metamictisation and fluid alteration but little to no metamorphic rims. The ²⁰⁷Pb/²⁰⁶Pb zircon ages are scattered towards 2.7 Ga, interpreted as the time of metamorphism, with a subgroup at ca 3.79 Ga that is interpreted as a minimum age for magmatic zircon. However, as the samples collected in the vicinity yielded an age of 3.82 Ga (Nutman et al. 1999, Kielman et al. 2018), the age of ca 3.79 Ga may have been disturbed by subsequent events. Zircon grains from the inner sub-terrane of Isukasia have well-preserved igneous cores with oscillatory zoning. Rounding of pyramidal terminations and thin rims are due to metamorphism. The age of crystalization of the protolith as recorded by igneous zircon is ca 3.71 Ga. 

The difference in the degree of the metamorphism at 2.7 Ga is visible in the structures and preservation of zircon grains. In this example, rounded cores and well-developed metamorphic rims characterize granulite facies, whereas well-preserved cores with oscillatory zoning and thin metamorphic rims represent lower amphibolite facies.

This research was funded by NCN grant UMO2019/34/H/ST10/00619 to MAK

References
Kielman, R., Whitehouse, M.,Nemchin, A., & Kemp, A., (2018). A tonalitic analogue to ancient detrical zircon. Chemical Geology, 499, 43-57.
Nutman, A.P. & Bennett, V.C., (2018). The 3.9-3.6 Ga Itsaq Gneiss Complex of Greenland. In: Van Kranendonk, M.J., Bennett, V.C. & Hoffmann, J.E., (Eds.). Earth’s Oldest Rocks (2^nd ed.), Elsevier, 375-399.
Nutman, A.P., Bennett, V.C., Friend, C.R. & Norman, M.D., (1999). Meta-igneous (nongneissic) tonalites and quartz-diorites from an extensive ca. 3800 Ma terrain south of the Isua supracrustal belt, southern West Greenland: constraints on early crust formation. Contrib. Mineral. Petrol. 137, 364–388.

How to cite: Mieszczak, M. J., Kusiak, M. A., Dunkley, D. J., Wilde, S. A., Whitehouse, M. J., Yi, K., and Lee, S.: Polymetamorphism and zircon preservation in the Itsaq Gneiss Complex, SW Greenland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13831, https://doi.org/10.5194/egusphere-egu23-13831, 2023.

Sulfate minerals are rare in the geological record prior to the oxygenation of the Earth’s atmosphere circa 2.4 billion years ago (Ga). An exception to this are a few isolated occurrences of early Archean (3.6-3.2 Ga) barite (BaSO₄), hosted in volcano-sedimentary rocks in South Africa, India and Western Australia. The origin of these barite deposits is controversial, despite having been studied over decades. Here, we combine field observations and geochemical data from a multi-year investigation into barite occurrences on the Kaapvaal and Pilbara cratons to derive a holistic model for the formation of early Archean barite. Studied deposits include the 3.52 Ga Londozi deposit in Eswatini and the 3.49 Ga North Pole deposit in Western Australia that are hosted in volcanic rocks, and the 3.26-3.23 Ga Barite Valley deposit in South Africa and possibly time-equivalent but little-known Cooke Bluff deposit in Western Australia that are found in sedimentary successions. Our field observations indicate that barite is closely associated with chert on both the Kaapvaal and the Pilbara cratons, although the scale of barite mineralization is much larger in the Pilbara and cross-cutting barite veins are only observed at North Pole and Cooke Bluff. These findings suggest that the fluids from which the chert precipitated are the same as the fluids from which the barite formed, and geochemical data support an origin for these barium-rich fluids that is related to low-temperature hydrothermal circulation of seawater. Barite precipitation could have been triggered by silica removal from these fluids. The ubiquity of chert in the early rock record suggests that these settings may have been common in the early Archean and that barite formation was therefore limited by sulfate abundance, and could only occur in settings where hydrothermal circulation and local sulfate enrichment occurred together.

How to cite: Roerdink, D., Mason, P., van Zuilen, M., and Wilmeth, D.: The origin of early Archean barite deposits on the Kaapvaal and Pilbara cratons, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13945, https://doi.org/10.5194/egusphere-egu23-13945, 2023.

The present-day thermochemical structure of the subcontinental mantle holds key information on its origin and evolution and informs exploration strategies, natural hazard management and evolutionary model of the Earth system. As such, unravelling the nature of the continental lithosphere, its modification through time and its interactions with the sublithospheric mantle and the atmosphere/hydrosphere constitute some of the main goals of modern geoscience. Despite its fundamental importance, imaging the fine-scale thermochemical structure of the lithosphere using indirect (remote) data is plagued with difficulties, which has traditionally left the analysis of xenoliths and xenocrysts as the only reliable approach.

In recent years, however, ‘simulation-based’ inverse methods that integrate multiple geophysical and geochemical datasets within an internally- and thermodynamically-consistent platform have opened new and promising ways to address this ‘grand challenge’. In this presentation, I will discuss i) some recent progress, case studies and future directions on the mapping of the thermochemical structure of the continental lithosphere, and ii) their predictive power for the energy and critical minerals sectors and possible implications for planetary exploration in general.

How to cite: Afonso, J. C.: Unravelling the thermochemical structure and evolution of cratonic lithosphere with multi-observable probabilistic inversions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14694, https://doi.org/10.5194/egusphere-egu23-14694, 2023.

We interpret the crustal and upper mantle structure along ~2500 km long seismic profiles in the northeastern

part of the Sino-Korean Craton (SKC). The seismic data with high signal-to-noise ratio were acquired with a nuclear

explosion in North Korea as source. Seismic sections show several phases including Moho reflections (PmP)

and their surface multiple (PmPPmP), upper mantle refractions (P), primary reflections (PxP, PL, P410), exceptionally

strong multiple reflections from the Moho (PmPPxP), and upper mantle scattering phases, which we

model by ray-tracing and synthetic seismograms for a 1-D fine-scale velocity model. The observations require a

thin crust (30 km) with a very low average crustal velocity (ca. 6.15 km/s) and exceptionally strong velocity contrast

at the Moho discontinuity, which can be explained by a thin Moho transition zone (< 5 km thick) with

strong horizontal anisotropy. We speculate that this anisotropy was induced by lower crustal flow during delamination

dripping. An intra-lithospheric discontinuity (ILD) at ~75 km depth with positive velocity contrast is

probably caused by the phase transformation from spinel to garnet. Delayed first arrivals followed by a long

wave train of scattered phases of up to 4 s duration are observed in the 800–1300 km offset range, which are

modelled by continuous stochastic velocity fluctuations in a low-velocity zone (LVZ) below the Mid-Lithospheric

Discontinuity (MLD) between 120 and 190 km depth. The average velocity of this LVZ is about 8.05 km/s, which

is much lower than the IASP91 standard model. This LVZ is most likely caused by rocks which are either partially

molten or close to the solidus, which explains both low velocity and the heterogeneous structure.

How to cite: Zhang, X., Thybo, H., Artemieva, I. M., Xu, T., and Bai, Z.: Upper Mantle Structure in the NE Sino-Korean Craton Based on Nuclear Explosion Seismic Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16587, https://doi.org/10.5194/egusphere-egu23-16587, 2023.

Ureilites are ultramafic achondrite meteorites that likely represent a large parent body. Large olivine and pyroxene grains display a high degree of textural equilibrium, forming “triple-junction” contacts at their grain boundaries. However, ureilites also have primitive characteristics, for example high siderophile and carbon content, high noble gas content, and unequilibrated olivine and pyroxene compositions. So far, the origin of ureilites and their parent body are still debated as it is difficult to explain the observation of textural equilibrium juxtaposed with such primitive properties. Conventionally, ureilites are considered to be mantle residues from within an unknown, large rocky body. Because feldspar is completely depleted from most ureilite samples, it has been thought that the parent body accreted early and experienced extensive igneous differentiation processes, with primary heating attributed to short-lived ²⁶Al decay in the early solar system. Here we report on polymict ureilite breccia Elephant Moraine 87720. We found that the sample has several unusually magnesian-rich olivine clasts with mg# (Mg/(Mg+Fe)) up to 98.7 and calcium-poor pyroxene with Wo as low as to 1.0. Moreover, we discovered two coarse-grained aluminous spinel grains with over 56.4-58.7 wt% Al₂O₃ and 11.3-11.8wt% Cr₂O₃, in contact with olivine and pyroxene grains_. These aluminous spinel clasts are unique among ureilite samples. To determine the provenance of the spinel grains and other clasts (e.g., high magnesian olivine and low calcium pyroxene) in this sample, we conducted in situ oxygen 3-isotope analyses by Secondary Ion Mass Spectrometry SIMS (IMS 1280), University of Wisconsin-Madison. SIMS mineral data plot along the slope ~1 line in the oxygen 3-isotope diagram, similar to those of bulk ureilites (Greenwood et al., 2017, Chemie der Erde 77, 1-43) including ureilitic samples found in Almahata Sitta, with the same range of ∆¹⁷O (from –2.3‰ to –0.2‰). These grains follow the Fe-loss/addition trend defined by a molar plot of Fe/Mn versus molar Fe/Mg, showing a near constant and chondritic Mn/Mg ratio, falling in among common ureilitic compositions. We conclude that the origin of these clasts, including the aluminous spinel, is primarily ureilitic, but they extend the δ¹⁸O measurement for ureilites up to 9.7 ‰. We hypothesize a magmatic origin for these clasts that they were formed under low-oxygen fugacity, in a high Al/Si ratio hot melt, favouring the crystallization of Al-spinel instead of a Cr-rich endmember. The clasts in this EET 87720 specimen may possibly represent a new type of high Al, low Ca, low Cr lithic material within the ureilite parent body. Finally, we calculated a possible crystallization temperature of 1379 K using spinel-olivine equilibrium crystallization (Roeder et al 1979, Contrib. Min. Petrol. 6, 325-334). Our estimate corresponds well with the theoretical model proposed by Goodrich et al. (2004, Chemie der Erde 64, 283-327) that the UPB was hot, with a temperature above 1100 °C (1373 K). Our results are consistent with other petrological evidence and olivine-pigeonite-melt thermometry (Singletary and Grove, 2003, Met. Planet. Sci. 38, 95-108) which constrain smelting temperatures within the ureilite parent body.

How to cite: Li, Y., McCausland, P. J. A., Flemming, R. L., and Kita, N. T.: Thermal constraints on the ureilite parent body (UPB): Evidence from the refractory spinel in polymict ureilite EET 87720 using in situ SIMS, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-326, https://doi.org/10.5194/egusphere-egu23-326, 2023.

     Constraining thermo-chemical evolution for the interior of terrestrial planets is substantial to understanding their evolutionary path. Thermo-chemical processes is controlled by stages of large-scale melting, or magma oceans (MO), due to the energy released during accretion, differentiation, radioactive decay of heat-producing elements and crystallization of the melt. Previous work shows that one of the product of considering fractional crystallization (FC) for  MO is a FeO-enriched molten layer or basal magma ocean (BMO) which is stabilized at the core-mantle boundary for a few billion years. The BMO is expected to freeze by FC because it cools very slowly. FC always yield a highly iron-enriched BMO and last stage cumulates. Other crystallization mode could be dominated and has not yet been systemically explored – at least for the Earth-like planets.

To explore the fate of the BMO cumulates in the convecting mantle, we explore 2D geodynamic models with a moving-boundary approach. Flow in the mantle is explicitly solved, but the thermal evolution and related crystallization of the BMO are parameterized. The composition of the crystallizing cumulates is self-consistently calculated  in the FeO-MgO-SiO₂ ternary system according to Boukaré et al. (2015). In some cases, we also consider the effects of Al₂O₃ on the cumulate density profile. We then investigate the  entrainment and mixing of BMO cumulates by solid-state mantle convection over billions of years as a function of BMO initial composition and volume, BMO crystallization timescales, distribution of internal heat sources, and mantle rheological parameters (Ra# and activation energy), . We varied the initial composition of BMO by manipulating the molar fraction of FeO, MgO, and SiO₂  -based on published experiments- to model different BMO-compositions: Pyrolitic composition, After 50% crystallization of Pyrolitic composition Boukaré et al. (2015), After 50% crystallization of Pyrolitic composition Caracas et al. (2019), and Archean Basalt.

For all our model cases, we find that most of the cumulates (first ~90% by mass) are efficiently entrained and mixed through the mantle. However, the final ~9% of the cumulates are too dense to be entrained by solid-state mantle convection, and rather remain at the base of the mantle as a strongly FeO-enriched solid layer. We conclude that this inevitable outcome of BMO FC – at least for Earth - leads to inconsistent evolutionary path comparing to recent geophysical constraints. FC substantially change the compositional, thermal, and geometrical properties for the lower mantle structures.  An alternative mode of crystallization may be driven by an efficient reaction between a highly-enriched last-stage BMO with the overlying mantle due to chemical disequilibrium. 

How to cite: Ismail, M. and Ballmer, M.: The Consequences of Fractional Crystallization for Basal Magma Ocean on the Long-term Planetary Evolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-723, https://doi.org/10.5194/egusphere-egu23-723, 2023.

The Martian crust is made up of sedimentary and volcanic rocks that are mainly mafic in composition. Nevertheless, orbital and in-situ observations have revealed the presence of felsic rocks (Payré et al, 2022), all located in the southern hemisphere, where the crust is thicker. These rocks likely formed by differentiation of a basic protolith. On Earth, this process occurs at plate boundaries and is linked to active plate tectonics. But on Mars, we have no evidence of active or ancient plate tectonics.

On one-plate planets, there exists a positive feedback mechanism on crustal growth: the crust being enriched in heat-producing elements, the lithosphere is hotter and thinner where the crust is thicker, which implies a larger melt fraction at depth and therefore a larger extraction rate and a larger crustal thickening where the crust is thicker. We proposed that this mechanism could have been at the origin of the Martian dichotomy (Bonnet Gibet et al, 2022). This mechanism further implies that regions of thicker crusts, characterized by a larger amount of heat sources, a thinner lithosphere and an increased magmatism, are also marked by higher temperatures. Here we investigate whether crustal temperatures in regions of thick crust may be maintained above the basalt solidus temperature during crust construction, which would allow for the formation of partially molten zones in the crust and hence differentiated rocks by extraction of the melt enriched in water and silica. In this scenario, felsic rock formation would be concomitant to crustal construction and dichotomy formation on Mars.

We use a bi-hemispheric parameterized thermal evolution model with a well-mixed mantle topped by two different lithospheres (North and South) and we account for crustal extraction and magmatism in these two hemispheres. We formulate a Bayesian inverse problem in order to estimate the possible scenarios of thermal evolution that are compatible with constraints on crustal thickness and dichotomy amplitude derived from the InSight NASA mission. The solution is represented by a probability distribution representing the distribution on the model parameters and evolution scenarios. This distribution is sampled with a Markov chain Monte Carlo algorithm, and shows that a non-negligible range of scenarios allows for partial melting at the base of the Southern crust below the Highlands during the first Gyr of Mars' evolution. On the contrary, partial melting of the base of the northern crust is insignificant. Models that fit InSight constraints and allow for differentiation of a fraction of the Southern crust point to a relatively low reference viscosity (~10²⁰ Pa.s) that can be explained by a wet mantle at the time of crust extraction.

How to cite: Bonnet Gibet, V., Michaut, C., Bodin, T., Wieczorek, M., and Dubuffet, F.: Differentiation of the Martian Highlands during its formation., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2786, https://doi.org/10.5194/egusphere-egu23-2786, 2023.

Zircon is an important silicate mineral to help understand the evolution of geochemistry and genesis of magma in early planets. The composition of evolved magma can be deduced from the concentrations of elements in zircon and their partition coefficients between zircon and silicate melt. Although the phosphorus (P) contents range from ~100 to ~100000 ppm in extraterrestrial zircon, the effects of P on REE partition coefficients between zircon and silicate melt are still debated. Here we have studied the effect of P contents on the partition coefficients of elements between zircon and silicate melt using high-temperature experiment. With the increase of phosphorus content, the partition coefficients of alkaline elements and Al between zircon and silicate melt show a negative and positive trend, respectively, and there is no effect on itself and Ti. It is worth mentioning that phosphorus content has a negligible effect on REE partitioning, indicating that the REE partition coefficients in this study can be applied to extraterrestrial zircon even with varying P concentrations. After filtering out altered zircon and combining the experimentally updated partition coefficients of REE, the characteristic of evolved melt equilibrated with early protogenetic zircon can thus be yielded and then help to understand early magmatism on the planets. 

How to cite: Shang, S. and Lin, Y.: Experimentally revisiting the REE partition coefficients between zircon and silicate melt, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3076, https://doi.org/10.5194/egusphere-egu23-3076, 2023.

Analysis of the lunar Bouguer gravity field under major basins reveals how gravity varies with spherical harmonic degree L and, potentially, with depth (to relate the two we use a relationship based on point masses).  We have studied 19 lunar basins based upon a GRAIL 1200 degree and order gravity model (GRGM1200B).  The vertical component of Bouguer gravity shows how the gravity is distributed in spherical harmonic degree between the lowest degree, 2, and the highest degree, 1200. Under each basin, this gravity spectrum of accelerations per individual spherical harmonic degree shows a benign region for L from 800 to 100, a range of approximately 20 km immediately below the surface, consistent with the observation that the upper crust is largely homogenous (Zuber et al., 2013). A region of more varied gravity signal occurs down to L~20, approximately 60 km deeper. The basin gravity signal merges with the deep interior at L~10, approximately 150 km below the surface. A set of profiles over latitude or longitude through an individual basin anomaly shows how the magnitude of the gravity signal changes with depth as it passes from the annular moat to the central high of the anomaly; all of which takes place between L~100-20, a depth range estimated to be ~20-80 km.  However, all basins are different to some extent. Outside of the basin anomaly the gravity spectra are relatively benign from just below the surface to L~40, a depth of approximately 45 km and consistent with the approximate average thickness of the lunar crust.  An exception to the general characteristics of the spectra of basins is South Pole-Aitken (SPA) which indicates a structure with few variations that is very similar to the regions that have near zero Bouguer gravity at the surface with no large anomalies in the top 100 km. We interpret this result for SP-A as a result of its largely compensated state.

How to cite: Smith, D. E., Goossens, S., and Zuber, M. T.: Implications of Bouguer Gravity Structure Under Major Lunar Basins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3530, https://doi.org/10.5194/egusphere-egu23-3530, 2023.

A tectonic regime is the surface expression of interior dynamics in a planet. With the help of numerical models, different tectonic regimes have been proposed. Some of these are: (1) plate tectonics or mobile lid, (2) stagnant lid, (3) episodic lid, (4) plutonic-squishy lid, (5) and heat pipe (e.g., Lourenço et al., G3 2020). Over time, a tectonic regime shapes the surface of a planet, including its surface topography. Using the numerical models, we can compute the topographies associated with different tectonic regimes including spatial and temporal measures of variations. In this study, we compute statistics for the topography formed by different tectonic regimes in numerical models and compare with the statistics of observed topography of different terrestrial planets, with the aim of linking a planet to a tectonic regime at the present-day. Venus’ topography is better matched by topography distributions obtained for plutonic-squishy lid models than those for stagnant- or episodic-lid models, while Earth’s oceanic topography is best matched by mobile-lid models.

How to cite: Louro Lourenço, D., Manga, M., and Tackley, P.: Topographic signatures and statistics of different tectonic regimes and application to terrestrial planets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3622, https://doi.org/10.5194/egusphere-egu23-3622, 2023.

In this work, we test the hypothesis of surface-erosion controlled plate tectonics preceded by plume-induced retreating subduction tectonic regime on Earth proposed by Sobolev and Brown (2019) using 2D global compressible convection models. To simulate the effect of increased sediment supply as a result of surface erosion after the emergence of continents in the late Archean and after the Neoproterozoic "snowball Earth" glaciation, we decrease the effective frictional strength of the oceanic lithosphere in models spanning the age of the Earth. These StagYY models self-consistently generate oceanic and continental crust while considering both plutonic and volcanic magmatism (Jain et al., 2019). Pressure-, temperature-, and composition-dependent water solubility maps calculated with Perplex (Connolly, 2009) are also utilised, which control the ingassing and outgassing of water between the mantle and surface (Jain et al., 2022). The core cools with time and different initial mantle potential temperature values are tested within the range of 1750-1900 K (Herzberg et al., 2010; Aulbach and Arndt, 2019).

Models that consider a more realistic upper mantle rheology (diffusion creep and dislocation creep proxy) show higher recycling of denser basaltic-eclogitic (oceanic) crust, efficient cooling of the planet, and higher mobilities (ratio of surface to mantle rms velocities) (Tackley (2000); Lourenço et al. (2020)). These models exhibit intermittent episodes of long-lasting mobile-lid regime and short-lived plutonic-squishy-lid regime in the Hadean and the early Archean accompanied by extensive subduction leading to rapid production and recycling of the continental crust. Models that consider adaptive frictional strength (to mimic sedimentation post glaciation and continental emergence) predict the transition to continuous plate tectonics in the late Archean, reproduce features of supercontinent cycles, and appear to be consistent with cooling history of the Earth inferred from petrological observations (Herzberg et al., 2010). 

The thermo-compositional evolution can vary between models due to the inherent randomness arising from the initial thermal perturbations and the initial positions of the tracers/particles. Accordingly, we intend to run multiple instances of every model considered in our parameter space to present statistically robust results. We also aim to test more realistic models where the lithospheric frictional strength adapts with the surface topography.

How to cite: Jain, C. and Sobolev, S.: Exploring the interplay between continent formation, surface erosion, and the evolution of plate tectonics on Earth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4755, https://doi.org/10.5194/egusphere-egu23-4755, 2023.

The compositional diversity of volcanic rocks revealed by NASA’s MESSENGER at the surface of Mercury has been interpreted to result from partial melting of a heterogenous sulfur-rich Mercurian mantle. However, melting relations and the composition of partial melts for iron-free and sodium-rich mantle, together with the effect of sulfur as a key volatile, have not yet been studied in detail. In this study we present results from high-pressure and high-temperature experiments on the mineralogical and geochemical evolution of the mantle residue and melting products of primitive deep Mercury’s mantle with two starting compositions differing by their Mg/Si ratios. Both compositions have sulfur added as FeS. Experiments were conducted using a multi-anvil press under reduced conditions (by controlling the Si/SiO₂ ratio of the starting composition) at pressures of 3 and 5 GPa.

The residual mantle of Mercury with the lower Mg/Si ratio of 1.02 contains olivine + orthopyroxene above ~15 wt% melting at 3 and 5 GPa, and olivine disappears at melting over ~30 wt.% at 5 GPa. The Mercurian mantle with the Mg/Si of 1.35 contains olivine + orthopyroxene in the residue above ~15 wt% melting at 3 and 5 GPa, and olivine only when the melting degree is over ~50 wt.%. Our experiments also show that the majority of chemical composition of the High-Magnesium region (HMR) can result from ~25±15 wt.% melting of a deep primitive mantle. Further work will enable us to evaluate the compositional diversity of the mantle that is needed to explain the broad range of surface lavas. We also aim at understanding the role of the highly refractory residual mantle as a controlling factor for the end of major volcanic activity on Mercury at 3.5 Ga.

How to cite: Wu, P., Xu, Y., Lin, Y., and Charlier, B.: Melting relations for putative mantles of Mercury and the compositional diversity of the crust, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6480, https://doi.org/10.5194/egusphere-egu23-6480, 2023.

The absence of seismic anisotropy in most regions of the lower mantle suggests that diffusion creep may be the dominant mechanism in the lower mantle. Because the diffusion-creep rate is inversely proportional to the 2~3 power of grain size, knowledge of the grain-growth kinetics is crucial for studying lower-mantle dynamics. For these reasons, this study determined the grain-growth kinetics of bridgmanite at a pressure of 27 GPa using advanced multi-anvil techniques.

We first measured the grain sizes of bridgmanite in an olivine bulk composition with various annealing durations at 2200 K. The results were fitted to an equation dⁿ – d₀ⁿ = kt, where d and d₀ are the final and initial grain sizes, respectively, n is the grain-size exponent, t is the annealing duration, and k is the growth-rate constant. This fitting yielded n = 5.2 ± 0.3, which is much smaller than given by a previous study [Yamazaki et al., 1996], n = 10.6 ± 1.1. This discrepancy may be because Yamazaki et al.’s [1996] olivine starting material may have contained adhesive water, which enhanced grain growth at the beginning of annealing. We then conducted runs at various temperatures, yielding the activation energy of 260 ± 20 kJ/mol. These results suggest that the bridgmanite grain sizes over 0.1 – 1 Gyr should have grain sizes of 150-230 μm, which is one order of magnitude larger than Yamazaki et al.’s [2006] estimation. Consequently, the lower mantle should be much harder than previously considered.

Furthermore, we measured the grain-growth kinetics as a function of the fraction of coexisting ferropericlase. Although the grain-growth kinetics is almost independent of the ferropericlase fraction down to 20 vol.%, it rapidly increases with decreasing ferropericlase fraction at lower fractions. Over 0.1~4.5 Gyr, the bridgmanite grain sizes in pure-bridgmanite rock should be 2 ~ 3 orders of magnitude larger than those coexisting with 20 vol.% of ferropericlase. These results suggest that pure-bridgmanite rock has 4 ~ 9 orders of magnitude lower flow rates than pyrolite if the diffusion creep is dominant. Since the diffusion creep rate in pure-bridgmanite rock is so low, the dislocation creep should dominate in pure-bridgmanite rock. We estimated that the pure-bridgmanite rock should have 1 ~ 2.5 orders of magnitude more viscous than pyrolite if the stress condition is 0.1~0.5 MPa in the lower mantle. This variation may interpret the viscosity variation in the lower mantle inferred from the geoid analysis [Rudolph et al., 2015], subduction speed [van der Meer et al., 2018], and plume morphology [French & Romaniwicz, 2016].

How to cite: Fei, H., Faul, U., Ballmer, M., Walte, N., and Katsura, T.: Grain growth kinetics of bridgmanite under topmost lower-mantle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7732, https://doi.org/10.5194/egusphere-egu23-7732, 2023.

New terrestrial exoplanets are being discovered at an ever faster pace, and each discovery leads to a widening of our understanding of planetary diversity. A key aspect in the quest to better quantify terrestrial planet diversity is to gain information on plausible bulk compositions, as this physical-chemical quantity determines the planet's structure, which in turn controls physical properties of the its layers (core, mantle, crust, atmosphere). Recent insights in the expected range of bulk planet compositions allow us to investigate how this fundamental parameter affects the evolution of the planetary interior and surface, and consequently to guide next-generation ground- and space-based telescopic observations of exoplanet properties, such as atmospheric composition.

Here, we first simulate mantle mineralogies for exoplanets with various bulk compositions, using a Gibbs energy minimization algorithm, Perple_X. Using mineralogy and resulting physical properties, we employ a 2D global-scale model of thermochemical mantle convection to investigate the variations between Earth-sized exoplanets of different compositions in terms of interior evolution. We include the effects of composition on planet structure, mantle physical properties, and mantle melting. We investigate how composition affects thermal evolution, and whether it has an effect on the propensity of a planet towards plate tectonics-like behaviour.

In general, Earth tends to have an average composition for most elements, except for iron, which it is relatively rich in, and therefore it has an above average core size. Our preliminary results show that core size (and thus iron abundance) affects convective vigor, and thus thermal evolution of the interior. We further find major differences for planets with different ratios of Mg-silicates, as these minerals control mantle viscosity, and thereby thermal evolution. Planets with lower Mg/Si than Earth will have a significantly stronger mantle, impeding cooling on planetary lifetimes, while planets with much higher Mg/Si have weaker upper mantles, impacting surface mobility. Stellar Mg/Si is a good indicator of the relative abundances of these minerals, and can be an important source of information. Therefore, the host stellar abundances seem to be an indicator of rocky planet properties, and can be used in the target selection for future missions.

How to cite: Spaargaren, R., Ballmer, M., Mojzsis, S., and Tackley, P.: Exploring the effects of terrestrial exoplanet bulk composition on long-term planetary evolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7777, https://doi.org/10.5194/egusphere-egu23-7777, 2023.

The short-lived isotope systems, including ¹⁴⁶Sm-¹⁴²Nd (half-life = 103 Ma) and ¹⁸²Hf-¹⁸²W (half-life = 8.9 Ma), provide evidence for mantle differentiation events in early Earth, as both the daughter nuclides are more incompatible than the parent nuclides. For the ¹⁴⁶Sm-¹⁴²Nd system, both positive and negative μ¹⁴²Nd measurements are observed in Hadean-Archean mantle-derived rocks, which possibly indicates a major differentiation event of the silicate Earth before the extinction of ¹⁴⁶Sm (e.g., Boyet and Carlson, 2005, Science). The diminishing trend of μ¹⁴²Nd between Hadean and Archean, on the other hand, suggests continuous mantle mixing during this period. However, for the ¹⁸²Hf-¹⁸²W system, Hadean-Archean mantle-derived rocks often show positive μ¹⁸²W anomalies followed by a decline in at 2.5~3.0 Ga ago without a mixing trend (e.g., Carlson et al., 2019, Chem. Geol.). Also, μ¹⁴²Nd and μ¹⁸²W often show no or negative correlation in Hadean-Archean mantle derived rocks (e.g., Rizo et al. 2016, Geochim. Cosmochim. Acta), which requires a mechanism to decouple these two isotopic systems.

In this study, we implement both ¹⁸²Hf-¹⁸²W and ¹⁴⁶Sm-¹⁴²Nd system in a global thermochemical geodynamic model, StagYY (Tackley, 2008, PEPI), to track the evolution of these isotope systems through Earth’s mantle evolution. Based on the particle-in-cell method, the geodynamic model incorporates melting and magmatic crust production that allow us to track both fractionation (by melting and crustal production) and mixing (through mantle convection) of trace elements through time. We discuss in detail how (1) the ‘basalt barrier’ at the base of the mantle transition zone (Davies, 2008 EPSL), (2) crustal delamination from intrusive magmatism, or plutonic-squishy-lid tectonics (Lourenco et al., Nat. Geo. 2018; GCubed 2020), and (3) late accretion could affect the tectonics of early Earth, and the preservation of geochemical heterogeneities and decoupling of two isotopic systems in the mantle through time.

How to cite: Tian, J. and Tackley, P.: Long-term preservation of geochemical heterogeneities in early Earth: tracking short-lived isotopes in geodynamic models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8965, https://doi.org/10.5194/egusphere-egu23-8965, 2023.

Grain-size evolution is a crucial controlling factor for the lower mantle rheology. Notably, one order of grain size change can produce a viscosity change of the order of 100-1000 times. As diffusion creep dominates in the lower mantle, grain growth of lower mantle mineral assemblages, e.g., bridgmanite and ferropericlase, increase viscosity considerably. It has been quite challenging to constrain the grain-size evolution parameters for lower mantle mineral assemblages until recently; a new high-pressure experimental study (27 GPa, cf. Fei et al, 2021, EPSL) parameterised them. The experimental data found a slower grain growth of bridgmanite-ferropericlase phases than of the upper mantle mineral phases, e.g., olivine and spinel. Using the most updated knowledge of grain-size evolution, we develop 2-D spherical annulus numerical models of self-consistent mantle convection using the finite volume code StagYY and explore how grain-size evolution affects the lower mantle dynamics. We test our models with different heterogeneous grain size evolution and composite rheology that evolve self-consistently for 4.5 billion years. Our preliminary models show the self-consistent formation of thermochemical piles at the base of the core-mantle boundary where the grain size is maximum (~3 times than the surroundings). Even though the bridgmanite-ferropericlase grain growth is slower, a slight increase in the grain size of thermochemical piles can make them ~100-1000 times viscous, subsequently helping them to achieve morphological stability over billion years. In some of our models, we find sweeping stability of the piles for ~500 million years. 

How to cite: Paul, J., Golabek, G., Rozel, A., Tackley, P., Katsura, T., and Fei, H.: Effect of grain-size evolution on the lower mantle dynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9100, https://doi.org/10.5194/egusphere-egu23-9100, 2023.

Our understanding of the compositional structure of Earth's mantle is still incomplete. Heterogeneity in the lower mantle, documented by both geochemical and geophysical observations, has not yet been explained within a definitive geodynamic framework. Moreover, the origin, geometry and interaction of such heterogeneities remain controversial. In the “marble cake” mantle hypothesis, slabs of basaltic Recycled Oceanic Crust (ROC) are subducted and deformed but never fully homogenized in the convecting mantle. Conversely, MgSiO₃-rich primordial material may resist convective entrainment due to its intrinsic strength, leading to a “plum pudding” mantle. While previous geodynamic studies have successfully reproduced these regimes of mantle convection in numerical models, the effects of the physical properties of ROC on mantle dynamics have not yet been fully explored. Furthermore, predictions from numerical models need to be tested against geophysical observations. However, current imaging techniques may be unable to discriminate between these two end members, due to limited resolution in the lower mantle.

Here, we model mantle convection in a 2D spherical-annulus geometry with the finite-volume code StagYY. We investigate the style of heterogeneity preservation as a function of the intrinsic density and strength (viscosity) of basalt at lower-mantle conditions. Additionally, we use the thermodynamic code Perple_X and the spectral-element code AxiSEM to compute, respectively, seismic velocities and synthetic seismograms from the predictions of our models.

Our results fall between two end-member regimes of mantle convection: low-density basalt leads to a well-mixed, "marble cake"-like mantle, while dense basalt aids the preservation of primordial blobs at mid-mantle depths as in a "plum pudding". Intrinsically viscous basalt also promotes the preservation of primordial material. These trends are well explained by lower convective vigour of the mantle as intrinsically dense (and viscous) piles of basalt shield the core. In order to test these results, we translate the predicted compositional, temperature and pressure fields to seismic velocities for two opposite end-member cases. These two synthetic velocity maps are first analysed and compared in terms of their respective radial correlation matrices and spherical harmonic spectra. Then, we use AxiSEM to simulate wave propagation through the two velocity models. Finally, we discriminate between the two end-members by comparing statistical properties of the corresponding ensembles of synthetic seismograms. Our results highlight how the interplay between primordial and recycled heterogeneities shape the evolution of the thermal and compositional structure of the lower mantle. Furthermore, they provide a framework for relating the style of heterogeneity preservation in the Earth's lower mantle with specific features of the seismic waveforms.

How to cite: Desiderio, M., Gülcher, A. J. P., and Ballmer, M. D.: The Heterogeneous Earth Mantle: Numerical Models of Mantle Convection and their Synthetic Seismic Signature, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10101, https://doi.org/10.5194/egusphere-egu23-10101, 2023.