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.

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.

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.

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.

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

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

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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

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

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.