GD1.1 | Inter-disciplinary constraints on the structure, dynamics and evolution of Earth's mantle, with a focus on melts and intra-plate volcanism.
EDI
Inter-disciplinary constraints on the structure, dynamics and evolution of Earth's mantle, with a focus on melts and intra-plate volcanism.
Convener: D. Rhodri Davies | Co-conveners: Wolfgang Szwillus, Juliane Dannberg, Emma Chambers, Marthe Klöcking, Juan Carlos Afonso, Nestor Cerpa
Orals
| Mon, 24 Apr, 14:00–17:55 (CEST)
 
Room D3
Posters on site
| Attendance Mon, 24 Apr, 10:45–12:30 (CEST)
 
Hall X2
Posters virtual
| Attendance Mon, 24 Apr, 10:45–12:30 (CEST)
 
vHall GMPV/G/GD/SM
Orals |
Mon, 14:00
Mon, 10:45
Mon, 10:45
Improving our understanding of the mantle requires an interdisciplinary approach, combining investigations into fluid dynamic processes, the role of melts and volatiles, and the mantle's present-day structure and its evolution through the geological past. In particular, the present-day structure of Earth's mantle — in terms of seismic velocity, density, conductivity, rheology, and other physical properties — is a crucial constraint for understanding Earth's dynamics and evolution. Recent breakthroughs in joint modelling/inversion of geophysical fields, petrology, transport phenomena and mineral physics allow for a more accurate description of Earth's upper mantle, providing tighter bounds on the physical and chemical processes that it hosts, and linking the evolution of our planet’s surface to its deep interior.

One such link comes via volcanism, our understanding of which remains incomplete. Intra-plate volcanism manifests irrespective of plate boundaries and includes volcanic fields with diverse characteristics and uncertain dynamical origin. Historically, studies have focused on voluminous lava fields and ocean-island tracks, with many now believed to mark the surface expression of mantle plumes. More recently, alternative driving mechanisms, such as edge-driven convection and shear-driven upwelling, have been explored to explain the generation of smaller intra-plate volcanic fields. To further improve our comprehension of intra-plate volcanism, it is critical to determine the applicability of these dynamical mechanisms across different geological settings and to understand how they interact and evolve in space and time.

For this session, we invite contributions integrating multiple methodologies/datasets to address the current state, evolution and interaction with the lithosphere of Earth's upper mantle. We particularly welcome contributions targeting the nature of mantle melts and the generation of intra-plate volcanism. Topics covered by this session include (1) combined dataset inversions through Bayesian and machine learning approaches, (2) dynamic modelling of deep-rooted mantle plumes and their magmatic expression, (3) investigations of possible shallower melt-generation mechanisms, and (4) the role of melts and volatiles in the evolution of Earth and other planetary interiors.

Orals: Mon, 24 Apr | Room D3

Chairpersons: D. Rhodri Davies, Emma Chambers
14:00–14:05
14:05–14:15
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EGU23-10441
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ECS
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solicited
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Highlight
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On-site presentation
Ben Mather, Maria Seton, Simon Williams, Joanne Whittaker, Rebecca Carey, Maëlis Arnould, Nicolas Coltice, and Bob Duncan

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.

14:15–14:25
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EGU23-12268
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ECS
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Highlight
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On-site presentation
Ingo L. Stotz, Sara Carena, Berta Vílacis, Hans-Peter Bunge, and Jorge N. Hayek

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.

14:25–14:35
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EGU23-10559
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ECS
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Highlight
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On-site presentation
Thomas Duvernay and Rhodri Davies

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.

14:35–14:45
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EGU23-8343
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solicited
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Highlight
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On-site presentation
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Chiara Civiero, Sergei Lebedev, and Nicolas L. Celli

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.

14:45–14:55
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EGU23-4570
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ECS
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On-site presentation
Cunrui Han, James Hammond, and Maxim Ballmer

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.

14:55–15:05
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EGU23-3846
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ECS
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On-site presentation
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Jordan J.J. Phethean, Martha Papadopoulou, Alex L. Peace, and Jeroen van Hunen

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.

15:05–15:15
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EGU23-2386
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On-site presentation
Sierd Cloetingh, Alexander Koptev, Alessio Lavecchia, István Kovács, and Fred Beekman

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.

15:15–15:25
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EGU23-2410
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Highlight
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On-site presentation
Bernhard Steinberger

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.

15:25–15:35
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EGU23-3400
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ECS
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Highlight
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On-site presentation
James Hazzard, Fred Richards, and Gareth Roberts

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.

15:35–15:45
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EGU23-15035
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On-site presentation
Andrea Luca Rizzo, Federico Casetta, Barbara Faccini, Luca Faccincani, Andres Sandoval-Velasquez, Alessandro Aiuppa, and Massimo Coltorti

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.

Coffee break
Chairpersons: Wolfgang Szwillus, Juliane Dannberg
16:15–16:25
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EGU23-1366
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ECS
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solicited
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Highlight
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On-site presentation
Vojtěch Patočka, Nicola Tosi, and Enrico Calzavarini

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.

16:25–16:35
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EGU23-9936
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ECS
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On-site presentation
Vaporization of He and C from a Pyrolite Melt: Implications for the Early Earth’s Atmosphere and Interior
(withdrawn)
Anne Davis and Razvan Caracas
16:35–16:45
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EGU23-9854
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Highlight
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On-site presentation
Maxim Ballmer, Rob Spaargaren, and Mohamed Ismail

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.

16:45–16:55
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EGU23-2770
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On-site presentation
Tomoo Katsura, Takayuki Ishii, Giacomo Criniti, Eiji Ohtani, Narangoo Purevjav, Hongzhan Fei, and Ho-kwang Mao

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.

16:55–17:05
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EGU23-6574
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On-site presentation
Judith Bott, Magdalena Scheck-Wenderoth, Ajay Kumar, Mauro Cacace, Sebastian Noe, and Jan Inge Faleide

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.

17:05–17:15
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EGU23-7037
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On-site presentation
Max Moorkamp

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.

17:15–17:25
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EGU23-5459
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On-site presentation
Yihe Xu, Sergei Lebedev, Chiara Civiero, and Javier Fullea

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.

17:25–17:35
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EGU23-6820
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ECS
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On-site presentation
Isabel Papanagnou, Bernhard S. A. Schuberth, and Christine Thomas

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.

17:35–17:45
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EGU23-8416
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ECS
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On-site presentation
Federica Restelli, Paula Koelemeijer, and Christophe Zaroli

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.

17:45–17:55
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EGU23-10123
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ECS
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Virtual presentation
Moloud Rahimzadeh Bajgiran, Lorenzo Colli, and Jonny Wu

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.

Posters on site: Mon, 24 Apr, 10:45–12:30 | Hall X2

Chairpersons: Marthe Klöcking, Juan Carlos Afonso
X2.153
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EGU23-5041
Jianfeng Yang, Manuele Faccenda, and Liang Zhao

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.

X2.154
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EGU23-467
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ECS
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Ziqi Ma and Maxim Ballmer

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.

X2.155
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EGU23-14630
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Min-Seok Jang and Byung-Dal So

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.

X2.156
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EGU23-14411
César R. Ranero, Laura Gomez de la Peña, Manel Prada, Estela Jimenez, Patricia Cadenas, Alejandra Neri, Irene Merino, Arantza Ugalde, and Ingo Grevemeyer

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.

X2.157
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EGU23-15626
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Highlight
Juan Afonso, Anqi Zhang, Marti Burcet, Beñat Oliveira, Heather Handley, and Marthe Klöcking

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.

X2.158
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EGU23-8438
Christoph Sens-Schönfelder, Tuo Zhang, Marcelo Bianchi, and Klaus Bataille

Seismic energy that follows the theoretical arrival time of the Pdiff phase is usually regarded as Pdiff 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 Pdiff 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 Pdiff 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 Pdiff 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 Pdiff 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 Pdiff 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 Pdiff 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.

X2.159
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EGU23-17502
Efim Kolesnikov, Ilya Kupenko, Arno Rohrbach, Stephan Klemme, Jasper Berndt, Xiang Li, Susanne Müller, Hanns-Peter Liermann, and Carmen Sanchez-Valle

The observed density of planetary cores is lower than in pure iron-nickel alloy at corresponding conditions. Therefore, the cores of terrestrial planets should be composed of iron-nickel alloyed with some lighter elements. These elements should be abundant in the solar system, siderophile, and compatible with iron at high-pressure high-temperature conditions. Si and C comply with these requirements and could be planetary core constituents. Seismic observations of the Earth's inner core revealed anisotropy of seismic wave propagation. For instance, compressional waves travel 1-3% faster along the polar axis compared to waves travelling in the equatorial plane. One of the hypotheses of the origin of the anisotropy is the plastic deformation and development of textures in inner-core materials under pressure. We employed Fe-Si-C alloy to study its yield strength and anisotropy at high-pressure high-temperature conditions to compare its properties with those observed in the Earth's core. The experiments were conducted by radial X-ray diffraction coupled with resistively heated diamond anvil cells that acted as a deformation apparatus. We performed experiments up to 120 GPa pressure with temperatures exceeding 1100 K. The strength values of Fe-Si-C alloy are higher than the strength of pure Fe and Fe-Si alloys. Our results show lower anisotropy of sound-wave velocities in hexagonal Fe-Si-C alloy compared to the seismic observations. We detected the change in main texture orientation upon compression from [0001] to  in Fe-Si-C alloy. In our presentation, we will discuss the dominant mechanisms of plastic deformation, responsible for these observations, and the overall effects of carbon and silicon on the strength and anisotropy of hexagonal iron alloys in planetary cores. 

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.

X2.160
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EGU23-13261
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ECS
Yongjiang Xu, Yanhao Lin, and Wim Westrenen

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.

X2.161
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EGU23-10682
Gabriele Morra, Leila Honarbakhsh, and Peter Mora

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.

Posters virtual: Mon, 24 Apr, 10:45–12:30 | vHall GMPV/G/GD/SM

Chairpersons: Marthe Klöcking, Juan Carlos Afonso
vGGGS.30
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EGU23-711
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ECS
Bruno Araújo, Ricardo Pereira, João Duarte, and João Mata

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.