GD1.3 | The Earth surface as a powerful window into the dynamics of the asthenosphere and deeper mantle
EDI
The Earth surface as a powerful window into the dynamics of the asthenosphere and deeper mantle
Co-organized by GMPV2/SM5
Convener: Ingo L. Stotz | Co-conveners: Simon Stephenson, Yi-Wei Chen, Megan Holdt, Audrey Margirier, Roland Pail, Sergei Lebedev
Orals
| Mon, 24 Apr, 08:30–12:30 (CEST)
 
Room D3
Posters on site
| Attendance Mon, 24 Apr, 14:00–15:45 (CEST)
 
Hall X2
Orals |
Mon, 08:30
Mon, 14:00
Vertical motions of the Earth’s lithosphere act as a powerful lens into the dynamic behavior of the asthenosphere and deeper mantle. Surface observations, therefore, provide important constraints on mantle convection patterns through space/time and constitute important constraints for theoretical models and numerical simulations. The asthenosphere is a crucial layer in Earth system.  Its structure and dynamics control processes such as postglacial rebound and dynamic topography, and it plays a crucial role in facilitating plate-like surface motions by reducing horizontal shear dissipation of mantle flow. Vertical motions can now be monitored geodetically with unprecedented precision. At the same time, geological records provide invaluable spatial-temporal information about the deeper history of vertical motion of the lithosphere.  For instance: thermochronological methods, studies of river profiles, sediment provenance, landform analysis, or hiatus mapping at interregional and continental scale. The challenges of using Earth's surface records to better understand asthenospheric and deep Earth processes involve (1) signal separation from other uplift and subsidence mechanisms, such as isostasy and plate tectonics; (2) different spatial resolutions and scales between models and observables; and (3) The challenges of recognizing on what (intercontinental) scales to compile geologic and stratigraphic data.

This session will provide a holistic view of the surface expression of the asthenosphere and deep Earth processes from geodetic to geological time scales using multi-disciplinary methods, including (but not limited to) geodetic, geophysical, geochemical, geomorphological, stratigraphic, and other observations, as well as numerical modeling. Thus, it will provide opportunities for presenters and attendees from a range of disciplines, demographics, and stages of their scientific career to engage in this exciting and emerging problem in Earth science.

Orals: Mon, 24 Apr | Room D3

Chairpersons: Ingo L. Stotz, Megan Holdt, Roland Pail
08:30–08:50
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EGU23-4053
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solicited
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Highlight
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On-site presentation
Mark Richards, Lawrence Cathles, Willy Fjeldskaar, Adrian Lenardic, Barbara Romanowicz, and Johnny Seales

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.

08:50–09:00
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EGU23-14852
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Highlight
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On-site presentation
Jason P. Morgan, Ya-Nan Shi, and Paola Vannucchi

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.

09:00–09:10
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EGU23-8412
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On-site presentation
Amr El-Sharkawy, Thor H. Hansteen, Carlos Clemente-Gomez, Javier Fullea, Sergei Lebedev, and Thomas Meier

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.

09:10–09:20
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EGU23-3213
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ECS
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On-site presentation
Hamish Brown, Jincheng Ma, Lorenzo Colli, and Hans-Peter Bunge

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.

09:20–09:30
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EGU23-4014
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Highlight
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On-site presentation
Ian Jackson, Tongzhang Qu, and Ulrich Faul

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 τM, varying as d-mV, defines the transition from anelastic to viscous background behaviour, and τP ~ 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 mV ~ 3 and mA < 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.

09:30–09:40
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EGU23-6676
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ECS
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On-site presentation
Roman Freissler, Bernhard S.A. Schuberth, and Christophe Zaroli

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.

09:40–09:50
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EGU23-4232
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On-site presentation
Hans-Peter Bunge, Yi-Wei Chen, Anke Friedrich, and Roland Pail and the UPLIFT Team

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.

09:50–10:00
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EGU23-15705
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On-site presentation
Anke M Friedrich

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.

10:00–10:10
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EGU23-9490
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solicited
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On-site presentation
Juliane Dannberg, Daniele Thallner, Rene Gassmoeller, Courtney Sprain, Frederick LaCombe, and Chloe Ritchie

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.

10:10–10:15
Coffee break
Chairpersons: Simon Stephenson, Audrey Margirier, Sergei Lebedev
10:45–11:05
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EGU23-16771
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solicited
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On-site presentation
Kurt Stüwe, Jörg Robl, Syed Turab, Pietro Sternai, and Fin Stuart

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.

11:05–11:15
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EGU23-1257
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ECS
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On-site presentation
Betty Heller-Kaikov, Roland Pail, and Martin Werner

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.

11:15–11:25
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EGU23-2575
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ECS
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On-site presentation
Berta Vilacís, Jorge N. Hayek, Ingo L. Stotz, Hans-Peter Bunge, Anke M. Friedrich, Sara Carena, and Stuart R. Clark

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.

11:25–11:35
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EGU23-4286
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ECS
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Highlight
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On-site presentation
Ayodeji Taiwo, Hans-Peter Bunge, and George Craig

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.

11:35–11:45
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EGU23-5621
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On-site presentation
Peter Japsen, Paul F. Green, Johan M. Bonow, James A. Chalmers, Ian R. Duddy, and Ilmo Kukkonen

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.

11:45–11:55
|
EGU23-773
|
ECS
|
On-site presentation
Fabian Christopher Dremel, Jörg Robl, Bjarne Friedrichs, and Christoph von Hagke

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.

11:55–12:05
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EGU23-16368
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ECS
|
On-site presentation
Fred Richards, Sophie Coulson, Mark Hoggard, Jacqueline Austermann, Blake Dyer, and Jerry Mitrovica

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 (50th/16th–84th 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.

12:05–12:15
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EGU23-15545
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ECS
|
On-site presentation
|
Björn H. Heyn, Grace E. Shephard, and Clinton P. Conrad

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.

12:15–12:25
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EGU23-17452
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ECS
|
solicited
|
On-site presentation
Siavash Ghelichkhan, Hans-Peter Bunge, and Jens Oeser

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.

12:25–12:30

Posters on site: Mon, 24 Apr, 14:00–15:45 | Hall X2

Chairpersons: Yi-Wei Chen, Megan Holdt, Ingo L. Stotz
X2.163
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EGU23-434
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Chia-Yu Tien, Nicky White, John Maclennan, Benedict Conway-Jones, and Megan Holdt

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.

X2.164
|
EGU23-650
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ECS
Aisling Dunn, Nicky White, Robert Larter, Simon Stephenson, and Megan Holdt

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.

X2.165
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EGU23-788
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ECS
Philippa Slay, Nicky White, Megan Holdt, and Simon Stephenson

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.

X2.166
|
EGU23-843
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ECS
Megan Holdt, Nicky White, and Fred Richards

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.

X2.167
|
EGU23-1352
|
ECS
Yi-Wei Chen and Jonny Wu

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.

X2.168
|
EGU23-1983
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ECS
Zhirui Ray Wang, Giampiero Iaffaldano, and John Hopper

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.

X2.169
|
EGU23-2726
|
ECS
Uncertainty quantification for mantle convection models
(withdrawn)
Andreas Burkhart
X2.170
|
EGU23-3508
Sara Carena, Anke Friedrich, and Hans-Peter Bunge

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.

X2.171
|
EGU23-4326
|
ECS
Eugenio D'Ascoli, Hamish Brown, Nils Kohl, Marcus Mohr, and Hans-Peter Bunge

Simulating the Earth’s mantle convection at full convective vigor on planetary scales is a fundamental challenge in Geodynamics even for state of the art high- performance computing (HPC) systems. Realistic Earth mantle convection simulations can contribute a decisive link between uncertain input parameters, such as rheology, and testable preconditions, such as dynamic topography. The vertical deflections predicted by such models may then be tested against the geological record. Considering realistic Earth-like Rayleigh numbers (∼ 108) a resolution of the thermal boundary layer on the order of ∼ 10 km is necessary considering the volume of the Earth’s mantle. Simulating Earth’s mantle convection at this level of accuracy requires solving sparse indefinite systems with more than a trillion degrees of freedom, computational feasible on exascale HPC systems. This can only be achieved by mantle convection codes providing high degrees of parallelism and scalability. Earlier approaches from applying a prototype framework using hierarchical hybrid grids (HHG) as solvers for such systems demonstrated the scalability of the underlying concept for future generations of exascale computing systems. In consideration of the TerraNeo project, here we report on the progress of utilizing the improved framework HyTeG (Hybrid Tetrahedral Grids) based on matrix-free multigrid solvers in combination with highly efficient parallelization and scalability. This will allow to solve systems with more than a trillion degrees of freedom on present and future generations of exascale computing systems. We also report on the advances in developing the scalable mantle convection code TerraNeo using the HyTeG framework to realise extreme-scale mantle convection simulations with a resolution on the order of ∼ 1 km.

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.

X2.172
|
EGU23-7226
|
ECS
Maelis Arnould, Tobias Rolf, and Antonio Manjón-Cabeza Córdoba

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.

X2.173
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EGU23-10292
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ECS
Christopher M. Calvelage, Lorenzo Colli, Jonny Wu, and Yi-An Lin

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.

X2.174
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EGU23-10775
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ECS
4-D data assimilation for the last billion years – insight into the long-term influence of mantle global circulation on the evolution of the plate-mantle system
(withdrawn)
Roberta Carluccio, Sabin Zahirovic, Nicole Januszczak, Michele Anthony, Jonathon Leonard, and Daniel James Bower
X2.175
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EGU23-15266
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ECS
Conor O'Malley, Gareth Roberts, James Panton, Huw Davies, and Victoria Milanez Fernandes

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.

X2.176
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EGU23-15494
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ECS
Olga Ortega-Gelabert, Javier Fullea, Mariano S. Arnaiz-Rodríguez, and Sergio Zlotnik

Geophysical observables, such as surface elevation, gravity field anomalies, seismic data, surface heat flow, etc, are essential pieces of information used to make inferences about the structure and dynamics of the Earth’s interior. Simultaneously fitting different observable datasets is crucial in order to obtain consistent models. Among geophysical data, gravity data from ESA’s GOCE satellite mission provides key information in properly constraining the Earth’s density distribution. WINTERC-G is a new global thermochemical model of the lithosphere and upper mantle (currently being extended into the transition zone and lower mantle) based on terrestrial and satellite gravity data (Fullea et al., 2021). The inversion procedure behind WINTERC-G has two main steps. In step 1, a 1D column-wise inversion of surface wave tomographic, surface elevation (isostasy) and heat flow data is performed. Then, in step 2, the output model from step 1 is used as prior information for the inversion of the gravity field data (filtered geoid anomalies and gravity gradients from GOCE at satellite height) to refine the 3D crustal density and upper mantle composition. The model predicts a residual, non-isostatic topography that can be considered as a proxy for dynamic topography.

However, within a rigorous framework, dynamic topography cannot be simply taken as a non- isostatic residual, but it should be explicitly computed (i.e. solving the Stokes equation for a given rheological and density distribution) and consistently integrated into the joint inversion of the gravity field and the terrestrial observation with feedback from both the static and dynamic parts. The goal of DYGIRO project is to add a third step into the global WINTERC-G inversion scheme that consistently integrates dynamic topography as an additional model constrain.

We present here the first steps of such integration at global scale. To do that, the dynamic topography is computed by solving the Stokes flow problem associated with the current WINTERC-G model down to the transition zone. The dynamic topography thus obtained is coupled with the static thermochemical model constrained by gravity and seismic data within an iterative scheme where the observed surface elevation coincides with the model’s isostatic plus dynamic elevation contributions. The high computational cost associated with the large- scale 3D flow computations will be alleviated by means of Reduced Order Models. Such models are based on the idea of creating surrogate models that approximate the solution at a much lower computational cost.

 

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: 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.

X2.177
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EGU23-17312
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ECS
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Anna Schneider, Bernhard Schuberth, Paula Koelemeijer, Federica Restelli, and Christophe Zaroli

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.

X2.178
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EGU23-10217
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ECS
Arushi Saxena, Juliane Dannberg, and Rene Gassmoeller

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.

X2.179
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EGU23-11908
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ECS
Federico Daniel Munch and Alexander Grayver

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.

X2.180
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EGU23-5023
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ECS
Timothy Davis and Richard Katz

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.

X2.181
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EGU23-9743
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ECS
Gabriel Robl, Bernhard Schuberth, Isabel Papanagnou, and Christine Thomas

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.

X2.182
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EGU23-10376
Lawrence Cathles, Willy Fjeldskaar, and Aleksey Amantov

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.