EGU General Assembly 2024  

The growing global demand for metal resources requires new high-grade ore deposit discoveries. Known large sediment-hosted clastic-dominated base metal deposits predominantly occur in failed continental rifts and the passive margins of successful rifts. Understanding the large-scale geodynamic controls on rift-related mineralizing processes occurring on much smaller spatial and temporal scales can thus help identify new areas for exploration.

We numerically model 2D rift systems from inception to break-up with the geodynamic code ASPECT (Kronbichler et al., 2012; Heister et al., 2017) coupled to the landscape evolution model FastScape (Braun and Willett, 2013; Neuharth et al., 2022). With ~300-m resolution simulations, we investigate how rift type and the efficiency of sedimentary processes affect the formation of potential metal source and host rock domains, identified by their lithology and temperature. We subsequently analyse the optimal alignment of these domains where metals are respectively leached and deposited  with faulting events providing potential fluid pathways between them (e.g., Rodríguez et al., 2021). For favourable co-occurrences of source, pathway and host, we identify the tectonic conditions that predict the largest clastic-dominated lead-zinc deposits.

We show that the largest potential for metal endowment is expected in narrow asymmetric rifts at a distance of several tens of kilometres to the shore (Glerum et al., 2023). Characterized by rift migration, these rifts generate a wide and a narrow conjugate margin. On the narrow margin, the long-lived border fault accommodates a thick submarine package of sediments, including deep permeable continental sediments and shallower layers of organic-rich sediments. Elevated temperatures from continued thinning could lead to fluids leaching metals from the permeable sediments. Both the border fault and later synthetic faults can provide fluid pathways from the source to the shallow host rock in potential short-lived mineralisation events. In wide rifts with rift migration, these favourable configurations occur less frequently and less potential source rock is produced, limiting potential metal endowment. In simulations of narrow symmetric rifts, the potential for ore formation is low. Based on these insights, exploration programs should prioritize identifying exhumed ancient narrow margins formed in asymmetric rift systems.

Braun and Willett 2013. Geomorphology 180–181. 10.1016/j.geomorph.2012.10.008.

Glerum et al. preprint. EGUsphere 1-40. 10.5194/egusphere-2023-2518.

Heister et al. 2017. Geophys. J. Int. 210 (2): 833–51. 10.1093/gji/ggx195.

Kronbichler et al. 2012. Geophys. J. Int. 191: 12–29. 10.1111/j.1365-246X.2012.05609.x.

Neuharth et al. 2022. Tectonics 41 (3): e2021TC007166. 10.1029/2021TC007166.

Rodríguez et al. 2021. Gcubed 22: 10.1029/2020GC009453.

How to cite: Glerum, A. C., Brune, S., Magnall, J. M., Weis, P., and Gleeson, S. A.: Geodynamic controls on sediment-hosted lead-zinc deposits in continental rifts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5404, https://doi.org/10.5194/egusphere-egu24-5404, 2024.

Geodynamics is an actively expanding young quantitative science, which defined its mission very generally as introducing of physical-mathematical methods into traditionally observations-focused Earth and planetary sciences in order to understand and quantify origin and evolution of Earth and other planets. As such, this young science is not limited by any specific object or subject and widens its scope through time. This is a very natural process (‘instinctive evolution’) since human scales of direct observation are extremely limited in both time and space and since rapid progress of quantitative physical-mathematical and computational methods offers every day new and exceptional possibilities to explore sophisticated physical-mathematical models for understanding intrinsically complex natural processes. As the result of this ‘instinctive evolution’, new frontiers in geodynamics are (and always were) defined by its expansion toward other fields. Initially, Geodynamics mainly expanded towards Structural Geology and Tectonics. Currently, new Geodynamics expansion tendencies are clearly visible toward: Seismology, Geomorphology, Geochemistry, Petrology, Climatology, Planetology/Astronomy and Biology/Astrobiology. In this lecture, I will give some recent examples of this impressive expansion and outline future expectations and challenges.

How to cite: Gerya, T.: New Frontiers in Geodynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8300, https://doi.org/10.5194/egusphere-egu24-8300, 2024.

Accurately constraining past and future ice sheet evolution requires a quantitative understanding of key boundary conditions in ice sheet models, including topography and heat flux. Both of these conditions are in part moderated by spatially and temporally variable mantle dynamics. This study exploits an interdisciplinary approach to probe the mantle beneath Antarctica to better understand sub-crustal processes. First, observed bathymetry and topography are corrected for isostatic effects to isolate the residual topographic signal, a proxy for dynamic mantle support. In this way, a comprehensive suite of oceanic residual depth (n = 1120) and continental residual elevation (n = 237) spot measurements are calculated. Secondly, basaltic rare earth element concentrations acquired from an augmented database of Neogene volcanic samples (n = 264) are inversely modelled to determine melt fraction as a function of depth. Thus, we constrain mantle potential temperature and depth to the top of the melting column (i.e. lithospheric thickness). Finally, results from these approaches are interpreted alongside other geological and geophysical data, including free air gravity anomalies and mantle tomographic models to understand present day mantle-lithosphere interactions. Sequence stratigraphic analysis along continental margins (e.g. offshore from Dronning Maud Land and the Wilkes and Aurora Subglacial Basins) is also used to constrain temporal changes in mantle-induced vertical plate motion. Robust observations in the oceanic realm evidence dynamic support beneath the central Scotia Sea, the Marie Byrd Seamounts, in the vicinity of the Astrid Ridge, and beneath the Emerald Fracture Zone. Residual topography measurements define the extent to which these dynamic swells continue onto the continent, with 1-2 km of mantle support throughout West Antarctica, the Transantarctic Mountains, and the Gamburtsev Subglacial Mountains. Collectively, these results highlight considerable spatial and temporal variation in dynamic mantle support throughout Antarctica, making it imperative to account for such mantle-lithosphere interactions when modelling the onset and evolution of glaciation.

How to cite: Dunn, A., White, N., Larter, R., Holdt, M., Stephenson, S., and Tien, C.-Y.: Spatial and temporal variation in dynamic mantle support of the Antarctic plate: Implications for ice sheet evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-440, https://doi.org/10.5194/egusphere-egu24-440, 2024.

The ubiquity of detrital zircon in clastic sediments and their typical high U and low common Pb contents, resulting in relatively high precision U-Pb age determination, made zircon one of the primary minerals for provenance studies. Yet, its high closure temperature (>900^oC), limited growth of new zircon under upper amphibolite-eclogite facies, inherited bias towards zircon-rich sources (e.g., felsic plutonic rocks), and the refractory behavior in sedimentary deposits rarely representing first-cycle sedimentation, can hamper the ability to detect some key tectonomagmatic events. In this sense, other mineral assemblages, like detrital rutile, that is formed in medium- to high-grade metapelite and metabasite mainly during high-pressure and low-temperature subduction metamorphism, can be used to provide a more complete record of orogenesis with polyphase evolution. Herein, we present U-Pb detrital rutile ages from the Cambrian-Ordovician Tacaratu Formation (lowermost unit of the late Jurassic to Cretaceous Tucano-Jatobá Basin, that directly overlies the Borborema Province in its southern region) to track the complete polyphase evolution of southern Borborema Province in the northeastern Brazil. The geodynamic evolution of this structural province is still a matter of debate, with interpretations varying from reworking of Paleoproterozoic continental crust with sedimentation and metamorphism in intracontinental setting, to oceanic closure during a complete Wilson Cycle with or without terrane accretion. Considering the southern Borborema Province Sergipano Belt, subduction started ca. 740 Ma ending with collisional processes (ca. 590-570 Ma) associated with the closure of the Sergipano-Oubanguides oceanic basin. The Neoproterozoic Pernambuco-Alagoas Domain and Sergipano Belt, both formed due to the collision between São Francisco-Congo Craton and the Pernambuco-Alagoas superterrane, are the main source of detritus of the Tacaratu Formation. Coupled U-Pb detrital zircon and rutile analysis revealed that detrital zircon ages lags (i.e., are younger) detrital rutile ages by around 100 Ma. Detrital rutile and zircon present main young peaks at ca. 650 Ma and 545 Ma, respectively. Recently, Neoproterozoic arc-back-arc amphibolite (ca. 743 ± 3 Ma), a rare setting for the early phases of Brasiliano Orogeny, and Cordilleran-type medium- to high-K granites (ca. 645-610 Ma), were recognized in southern Borborema Province, in agreement with our detrital rutile U-Pb ages. Thus, our detrital rutile ages record earlier phases of Brasiliano Orogeny in the southern Borborema Province (subduction-related metamorphism; closure of Sergipano-Oubanguides ocean), since the Brasiliano Orogeny culminated in the collision of blocks that were followed by high-temperature metamorphism (hampering the formation of younger rutile?). Notwithstanding, detrital rutile ages interesting marks around late Tonian to Cryogenian subduction-related metamorphism, perhaps in a magma-poor orogenic phase.

How to cite: Cerri, R. I., Caxito, F. A., Spencer, C., Luvizotto, G. L., Junior, G. W. C., Santos, N. M., and Warren, L. V.: Detecting subduction-related metamorphic events during the early Brasiliano Orogeny in southern Borborema Province using detrital rutile , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1686, https://doi.org/10.5194/egusphere-egu24-1686, 2024.

Calderas are steep morphological and collapse basins that continue to reshape long after initial structural collapse. While large landslides are associated with caldera collapse and widen the basin, little is known about the morphological and structural changes that occur long after caldera formation. Here, we investigate the shape and slope of the Tambora caldera in Indonesia, which formed in 1815 during one of the most devastating eruptions of the past  centuries. The release of over 150 cubic kilometers of volcanic ash created a caldera 6 kilometers wide and 1250 meters deep, causing climatic effects worldwide. Here we explore an ultra-high-resolution dataset we generated from Pleiades, a tri-stereo satellite, that now allows us to apply computer vision approaches to study the morphology and geometry of the Tambora caldera. We generated a 12 million pixel point cloud resampled to a 1 m resolution Digital Elevation Model and a 0.5 m orthomosaic. We explore the dimension, slope, and outline of the caldera and find localized open fissures, tension cracks, and morphological scars. We also apply an unsupervised image classification approach to the stereo multispectral data and find locations of fumarole activity and hydrothermal alteration in close proximity to these structural features. Hydrothermal alteration sites are commonly located in the caldera wall below the scars and open fissures. We explore this proximity of alteration, scarring, and faulting using newDistinct Element Method models, emphasizing that caldera morphology and structure is strongly influenced by hydrothermal weakening that causes flank instability, localized shedding of material, and large-scale morphological changes.

How to cite: Walter, T. R., Harnett, C. E., Troll, V. R., and Heap, M. J.: Morphology, structure and gravitational instability of the steep caldera walls of Tambora (Indonesia) influenced by hydrothermal alteration., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2023, https://doi.org/10.5194/egusphere-egu24-2023, 2024.

Mantle convection is an essential component of the Earth system. Yet its history is not well known , in part, as the strength of tectonic plates conceals the underlying flow. To date, global mantle convection models have reached an impressive level of sophistication due to significant advancement of computational infrastructures and numerical techniques. This ultimately allows geodynamicists to reconstruct past mantle states through using, for instance, inverse geodynamic models based on adjoint equations. However, key input parameters of these models --- such as thermo-chemical flow properties and rheology --- are complex and poorly known. This in turn limits their ability to effectively interpret the reconstructed mantle flow, thus motivating one to pursue an approach that aims to conceptualize paleo-mantle-flow at a simple analytical level.

To this end, the existence of thin, mechanically weak asthenosphere permits one to develop an analytical Couette/Poiseuille model of asthenospheric flow, where flow is associated with moving tectonic plates, and with lateral pressure gradients due to rising plumes and sinking slabs. Here we present estimates of the Cenozoic asthenospheric flow history from such models in the Atlantic realm. We, moreover, link them to azimuthal seismic anisotropy as well as mantle flow retrodiction simulated by inverse geodynamic models. Our analytically derived asthenospheric flow indicates that it is in broad agreement with the orientation of seismic azimuthal anisotropy, and with the large-scale flow patterns from mantle flow retrodictions. In light of these results, our study suggests exploiting a hierarchy of geodynamic models together with growing observational constraints on mantle flow induced surface expressions to gain a better understanding of paleo-mantle-flow.

How to cite: Wang, Z. R., Stotz, I. L., Bunge, H.-P., Vilacís, B., Hayek, J. N., Ghelichkhan, S., and Lebedev, S.: Cenozoic asthenospheric flow history in the Atlantic realm: Insights from Couette/Poiseuille flow models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2321, https://doi.org/10.5194/egusphere-egu24-2321, 2024.

The influence of climate on landscape evolution in natural settings remains debated. Here, we focus on tropical hotspot volcanic islands because they exhibit relatively uniform lithology and experience significant precipitation and climate gradients. Furthermore, intermittent volcanic flows effectively “reset” the landscape that begins to evolve post-eruption. Thus, we can constrain initial conditions by reconstructing the initial geometry of radiometrically dated volcanic flows. We constrain landscape evolution through time in several volcanic islands with strong climate gradients to assess the role of climate on incision. We perform topographic reconstructions to calculate long-term basin-averaged erosion rates in two islands of the Réunion hotspot (Réunion, Mauritius) and compile published erosion rates on Réunion and Kaua’i (Hawaii hotspot). We define the time since incision started as the age of the surface incised lava flow. To calibrate incision parameters on all three islands, we use the stream power model and apply a data-driven Bayesian approach to obtain the erodibility, K, the drainage area exponent, m, and the slope exponent, n. We also calculate a normalized erodibility index, K_n, using n = 1 to directly compare results among the different study sites. Erosion rates of Réunion Island range from 9.9 ± 0.5 mm/yr to 5.2 x 10^-3 ± 2 x 10^-4 mm/yr and erosion rates in Mauritius Island range from 6.5 x 10^-2 ± 8 x 10^-3 mm/yr to 5.1 x 10^-3 ± 4 x 10^-4 mm/yr. Incision efficiency seems to decrease with time since incision started from 63 ka to ~300 ka and then does not vary significantly with time since incision started from ~300 ka to 4300 ka. This is likely due to the covariation between the age of volcanism repaving and precipitation rates on Réunion, which is related to the configuration of the island’s two volcanoes – the active Piton de la Fournaise located on the windward side and the dormant Piton des Neiges on the center and leeward side. Our empirical calibration of the stream power law shows high dispersion in n and K_n on each individual island. m ranges from 0.2 to 2.9, and K_n ranges from 2.3 x 10^-7 to 9.8 x 10^-4 m^1-2m/yr. For Réunion, we identify a positive trend between mean annual precipitation and erosion rates, and between mean annual precipitation and K_n, for low to moderate erosion rates (<1 mm/yr). For all basins of Réunion, there is also a positive trend between mean annual cyclonic precipitation rates and erosion rates, and between mean annual cyclonic precipitation rates and n. In Kaua’i, there is a positive trend between erosion rates and mean annual precipitation, consistent with previous studies. In Réunion, the proportionality coefficient between erosion and mean annual precipitation is three times greater than in Kaua’i. In addition, considering all three islands, a nonlinear relationship exists between channel slope and incision rate: best-fit n values range from 0.5 to 6, with n generally lower than one on Kaua’i. Our results highlight different sensitivities of fluvial relief to incision, and of incision to climate, between Kaua’i and Réunion islands.

How to cite: Gourbet, L., Gallen, S. F., Famin, V., Michon, L., Ramanitra, M. O., and Gayer, E.: River incision on hotspot volcanoes: insights from paleotopographic reconstructions and numerical modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2631, https://doi.org/10.5194/egusphere-egu24-2631, 2024.

The basal Cambrian sandstone unit in the North China craton (NCC) is an example of globally widespread siliciclastic succession that resides on the Great Unconformity and deposited on a hypothesized low-lying peneplain during the Cambrian global eustatic sea-level rise. Detrital zircon age signatures from this distinct sequence enable recognition of the ancient drainage system of the NCC in deep time and track its potential linkage with the Gondwana landmass. LA-ICP-MS U–Pb dating of the fossil-calibrated basal Cambrian (Series 2) detrital zircon samples from seven measured sections reveal marked spatial changes in their age signatures that can be divided into three distinct types. The first is generally characterized by the bimodal age populations with broad peaks at ~1.85 Ga and ~2.5 Ga that correlate with the Archean to Paleoproterozoic basement inboard of the NCC. The second is featured by multi-modal distribution with diagnostic Neoproterozoic peaks that correspond to subregional magmatic record. The third also shows multiple-zircon age populations, but yields significant crystallization ages close to the early Cambrian age. Comparing our new data with existing age spectra for the Cambrian strata across the NCC and the northern Gondwana demonstrates that separate drainage systems did exist in the peneplained basement during global Cambrian transgression and the basal Cambrian unit in the NCC was not a part of the far-travelled sand sheet across the northern margin of Gondwana. The most suitable source for Cambrian-aged grains constrained by paleogeographic restoration is the arc terrane developed along the northern margin of the NCC as a result of subduction of the Paleo-Asian oceanic plate. Our new continental-scale detrital zircon provenance signatures in the basal Cambrian unit suggest that the NCC should be considered a discrete continental block separated by the Proto-Tethys Ocean in the Cambrian, rather than an integral part of the northern Gondwana.

How to cite: Wei, R. and Duan, L.: Detrital zircon age signatures of the basal Cambrian sandstone unit in North China: implications for drainage divides during global Sauk transgression and separation from Gondwanaland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2721, https://doi.org/10.5194/egusphere-egu24-2721, 2024.

Mantle convection is driven by buoyancy forces in Earth’s interior. The resulting radial stresses generate vertical deflections of the surface, leaving traces in the geological 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 geological observations. These inverse models are emerging as powerful tools, providing the potential for tighter constraints on the relevant physical parameters governing mantle flow.

The geodynamic inversions mentioned above require an estimate of the present-day thermal state of the mantle, which can be derived from seismic observations. Using thermodynamically self-consistent models of mantle mineralogy, it is possible to convert the seismic structure imaged by global tomographic models to temperature. However, both seismic and mineralogical models are significantly affected by inherent limitations and different sources of uncertainty. In addition, owing to the complexity of the mineralogical models, the relation between temperature and seismic velocities is highly non-linear and not strictly bijective: In the presence of phase transitions, different temperatures can result in the same seismic velocity, making the conversion from seismic heterogeneity to thermal structure non-unique.

We investigate the theoretical ability to estimate the present-day thermal state of the mantle based on tomographic models in the case of isochemical convection. The temperature distribution from a 3-D mantle circulation model with earth-like convective vigour serves as the “true” temperature field. Using a closed-loop experiment, we aim to recover this initial model after: 1) mineralogical mapping from the “true” temperatures to seismic velocities, 2) application of a tomographic filter to mimic the effect of limited tomographic resolution, and 3) mapping of the “imaged” seismic velocities back to temperatures. We test and quantify the interplay of smoothed seismic structure due to tomographic filtering with different approximations for the conversion from seismic to thermal structure. Additionally, owing to imperfect knowledge of the parameters governing mineral anelasticity, we test the effects of changes to the anelastic correction applied in the mineralogical mapping. The observed mismatch between the recovered and initial temperature field is dominated by the effect of tomographic filtering, with a depth-dependent average error of up to 200 K. Additionally, we observe systematic large errors in the vicinity of phase transitions. Our results highlight that, given the current limitations of tomographic models and the incomplete knowledge of mantle mineralogy, magnitudes and spatial scales of a temperature field obtained from global seismic models will deviate significantly from the true state, even under the assumption of purely thermally driven mantle flow. Strategies to estimate the present-day thermodynamic state of the mantle must be carefully selected to minimize additional uncertainties.

How to cite: Robl, G., Schuberth, B., Papanagnou, I., and Thomas, C.: Deriving mantle temperatures from global seismic models: A quantitative analysis in the light of uncertain mineralogy and limited tomographic resolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2858, https://doi.org/10.5194/egusphere-egu24-2858, 2024.

Global plate reconstructions that constrain the surface plate motions provide crucial boundary conditions for mantle circulation models. Earth-like plate kinematics could reduce the impact of the uncertain mantle initial conditions and generate slab structures in the mantle that are comparable with seismic tomographies. However, due to the subduction of the oceanic plates, uncertainty increases in global plate reconstruction over time. Here, we utilize a novel slab unfolding technique to retrodeform mantle slabs imaged in the MITP08 seismic topography back to the pre-subduction states at Earth’s surface. Such a technique provides additional constraints on plate reconstructions, especially in regions dominated by intra-oceanic subductions, such as Southeast Asia.

Our reconstruction shows a significant trench retreat along Southeast Asia and Northern Australia between 90 and 65 Ma that opened a gigantic, >3,000 km wide backarc basin. This basin, named the East Asian Sea plate, was later consumed by the west-moving Philippine Sea plate and North-moving Australian plate in the Cenozoic. We then embed our reconstruction in a mantle circulation model, TERRA, testing the fidelity of the reconstruction in a closed-loop experiment.

We found that fragmented, sub-horizontal East Asian Sea slabs can be reproduced in the mantle circulation model. These slabs lying underneath the current Philippine Sea plate and northern Australia are similar to the MITP08 tomography on which the reconstruction is built. Moreover, these slabs at 800-1000 km depths result in a more negative dynamic topography on the present Philippine Sea plates comparable with the observed residual topography. On the contrary, the traditional, Andean-style reconstruction can only produce positive dynamic topography. Other Mesozoic, intra-oceanic subductions in NE Asia and western North America embedded in our reconstruction also produce negative, yet smaller magnitude, dynamic topography, possibly due to the older subduction history and deeper slabs. We conclude the negative dynamic topography within the present Pacific plate is the result of ancient intra-oceanic subductions. 

How to cite: Chen, Y.-W., Bunge, H.-P., Stotz, I., and Wu, J.: Testing tomography-based plate reconstructions from a paired, inverse-forward closed-loop experiment in a mantle circulation model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3083, https://doi.org/10.5194/egusphere-egu24-3083, 2024.

The Island of Vulcano is the emerged portion of a composite volcanic edifice within the Aeolian volcanic archipelago, situated in the southern Tyrrhenian Sea. The remobilization, triggered by heavy rainfall, of loose volcaniclastic material from La Fossa cone and the generation of small debris flows are recurrent hazards on Vulcano. Although these debris flows generally transport small volumes of material, in the case of severe events, they can  be channeled along the roads, flood several buildings, inundate the main harbor, and eventually be discharged into the sea. Gravitational and erosive processes, mainly due to rainfall, have formed several gully systems around the La Fossa cone. The presence of gully systems along slopes enhances both runoff and downslope mass wasting, and, above all, the gullies themselves act as a source of mass wasting due to the collapse of their walls and the processes of aggradation and degradation of their beds. Therefore, understanding the behaviour of gullies and their response to rainfall is crucial for predicting the effects of environmental changes, whether climatic or volcanic, on gully dynamics. 

In the frame of "VOlcaniclastic debris flows at La Fossa cone (Volcano  Island): evolution and hazard implication (VOLF)" project funded by the Istituto Nazionale di Geofisica e Vulcanologia, we here analyze aerial photos of the NW sector of La Fossa cone to describe the evolution of its gully system from the 1954 to 2022. First, we create a georeferenced dataset of photos by orthorectifying existing photos and generating new ones through the Structure from Motion (SfM) method applied to Unmanned Aerial System (UAS) photos. Second, we describe the geomorphological features of the gullies in the NW sector of La Fossa cone, identifying features to be parameterized. Finally, we qualitatively and quantitatively describe their evolution over almost 70 years.  

This work aims to investigate the morphological evolution of the NW flanks of La Fossa cone, a crucial aspect for assessing hazards associated with volcaniclastic sediment-charged flows and floods on Vulcano Island. This is especially relevant in a scenario where ongoing climate changes may potentially disturb the current equilibrium, heightening the likelihood of short-term extreme rainfall events.

How to cite: Fornaciai, A., Favalli, M., Nannipieri, L., Turchi, A., Bonasia, R., and Di Traglia, F.: The gully system on the NW sector of La Fossa cone (Vulcano Island): 2D evolution and hazard implication, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3473, https://doi.org/10.5194/egusphere-egu24-3473, 2024.

The Cheakamus basalts are a set of ~31 km long, 1.65 km³ valley-filling olivine basalts which erupted into the glaciated Callaghan-Cheakamus Valley system of the Garibaldi Volcanic Belt (GVB), British Columbia. Combined paleomagnetic and radiometric (⁴⁰Ar/³⁹Ar) analysis dates the lavas as a short-lived (< 2 ka duration) eruption at 15.95 ± 7.9 ka (2σ); additional field evidence, including well-glaciated lava flow surfaces overlain by till, indicate the eruption coincided with the early stages of the Fraser Glaciation (LGM) at ~20-18 ka. The lavas preserve features indicative of a landscape hosting diverse and dynamic paleoenvironments. Subaerial eruption of basalt lava filled an ice-free Callaghan Creek drainage system before inundating and damming of the paleo-Cheakamus River, creating an upstream rising body of water. Periodic overtopping of the lava dam resulted in syn-eruptive intermittent flooding and overtopping of lavas expressed by discontinuous lenses of interflow sediment and well-developed entablatures in the upper portions of lava flows. Rare instances of enigmatic cooling columns indicate localized ice contact with glaciers that partially filled the Cheakamus Valley. Emplacement features and morphologies in the Cheakamus Valley have been heavily altered by the erosional overprinting of a glacial lake outburst flood (GLOF) that preliminary ¹⁰Be analysis dates at the close of the LGM (11-10 ka). Lavas in the Callaghan valley remain untouched by the GLOF. Their aerial extent and distribution, especially at high elevations in tributary valley mouths suggest bottlenecking and backing-up of lavas due to narrowing in valley topography. Current work combines field mapping and analogue modelling and aims to provide insight into the emplacement dynamics of effusive lavas in the steep, confined terrain of the BC Coast Mountains. Despite, and in part because of, their heavily modified morphology, the Cheakamus basalts act as an excellent recorder of both effusive volcanic processes and the paleoenvironments into which they erupted. Their thorough and accurate analysis is especially pertinent temporally, as they erupted during a time of glacial flux and can provide additional evidence for the timing and location of the advancing Cordilleran ice sheet. Spatially, the Cheakamus basalts are proximal to population centers and transport infrastructure and thus have implications for potential volcanic hazards and attendant risks, as any future effusive, valley-filling basaltic eruption from the GVB will likely share similar emplacement characteristics and processes.

How to cite: Borch, A., Russell, J. K., Barendregt, R., and Friele, P.: Emplacement and erosion of valley-filling basalt lavas in shifting Quaternary environments of the Garibaldi Volcanic Belt, British Columbia, Canada, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4176, https://doi.org/10.5194/egusphere-egu24-4176, 2024.

How to cite: Brown, H., Vilacís, B., Stotz, I., Chen, Y.-W., and Bunge, H.-P.: Synthetic Hiatus Maps as a Tool for Constraining Global Mantle Circulation Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4552, https://doi.org/10.5194/egusphere-egu24-4552, 2024.

Peninsula India and Scandinavia are elevated passive continental margins (EPCMs) characterized by asymmetric relief with high mountains in the west and a gentle slope towards lowlands in the east.

New AFTA data from southern India reveal major Phanerozoic episodes of cooling, reflecting exhumation. Here we focus on the early Miocene episode possibly related to the hard India-Asia collision (van Hinsbergen et al. 2012). The Miocene exhumation resulted in a low-relief landscape; e.g. the Karnataka and Mysore plateaus (Gunnel and Fleitout, 1998) with residual regions of higher ground (e.g. Palani Hills). Today, these plateaus reach an elevation of 1 km along the coast of SW India, sloping towards the east. The Miocene peneplains were graded towards the base level of the adjacent ocean (Green et al. 2013), and therefore reached their present elevation after their formation. Thick piles of Pliocene sediments off SW India (Campanile et al. 2008) suggests that this happened during the Pliocene.

Richards et al. (2016) studied river profiles in Peninsula India and concluded that the regional tilt grew since 25 Ma, maintained by sub-lithospheric processes. However, we find that the relief is the result of two episodes: 1) Miocene peneplanation related to far-field stress. 2) Late Neogene, asymmetric uplift driven by sub-lithospheric processes.

We identified a similar development in SW Scandinavia, where two Neogene episodes of uplift and erosion define main features of the relief (Japsen et al. 2018): 1) Early Miocene uplift leading to formation of the Hardangervidda peneplain (possibly related to the hard India-Asia collision). 2) Uplift beginning in the Pliocene, raising Hardangervidda to its present elevation at 1.2 km. Pliocene uplift raised margins around the NE Atlantic with maximum elevations reached close to Iceland. This suggests support from the Iceland Plume due to outward-flowing asthenosphere extending beneath the conjugate margins (Rickers et al. 2013; Japsen et al. 2024). 
Lithospheric as well as sub-lithospheric processes appear to shape main features of EPCMs.

Campanile et al. 2008. Basin Research. Green et al. 2013. GEUS Bull. Gunnell, Fleitout 1998. ESPL. Japsen et al. 2018. JGSL. Japsen et al. 2024. ESR. Richards et al. 2016. G cubed. Rickers et al. 2013. EPSL.

How to cite: Japsen, P., Green, P. F., Bonow, J. M., and Chalmers, J. A.: The large-scale landscapes in SW Scandinavia and in SW India are the result of two episodes of Neogene uplift, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6544, https://doi.org/10.5194/egusphere-egu24-6544, 2024.

Deflection of the Earth’s surface supported by mantle flow, known as dynamic topography, is associated with a free-air gravity anomaly because such topography is not isostatically compensated. Consequently, the ratio of the gravity anomaly to the dynamic topography, known as the admittance, has been used to estimate the amplitude of dynamic topography, which can be difficult to measure directly. However, at long wavelengths (e.g., spherical harmonic degrees 2 to 6) both dynamic topography and gravity anomalies, and thus the admittance, are sensitive to the mantle’s viscosity structure. Previous studies [e.g., Colli et al., 2016] demonstrate a reversal in sign of the free-air gravity anomaly resulting from lower mantle structures as the viscosity of the lower mantle is increased. This indicates potential complexity for inferring long-wavelength dynamic topography from observations of gravity anomalies, because the upper-lower mantle viscosity contrast is poorly constrained. We further investigated the relationship between dynamic topography and gravity anomalies by introducing lateral viscosity variations into a finite element model of global mantle flow. We find that the gravity anomaly above lower mantle density heterogeneity can change dramatically as we begin to introduce different models for lateral viscosity variations into the upper and lower mantle viscosity fields. In such models we find that the sign of the admittance varies laterally, with the horizontal gradients in mantle viscosity perturbing mantle flow patterns in ways that produce large changes gravity anomalies and smaller changes in dynamic topography. A spatially-varying admittance will greatly complicate estimation of dynamic topography from observed gravity, and may help to explain mismatches between observations of dynamic topography and predictions made using global mantle flow models. On the other hand, the reconciliation of such mismatches may help to constrain viscosity heterogeneity in the lower mantle.

Colli, L., S. Ghelichkhan, and H. P. Bunge (2016), On the ratio of dynamic topography and gravity anomalies in a dynamic Earth, Geophysical Research Letters, 43(6), 2510-2516, doi:10.1002/2016GL067929.

How to cite: Conrad, C. P. and Ramirez, F.: Sensitivity of Long-Wavelength Dynamic Topography and Free-Air Gravity to Lateral Variations in Lower Mantle Viscosity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6721, https://doi.org/10.5194/egusphere-egu24-6721, 2024.

A consequence of alluvial processes acting on scoria cones is the development of a drainage network composed of radially distributed rills and gullies parallel to the volcanic edifice's downslope direction. This work focuses on the quantification of the degree of development of the drainage network by applying the Average Erosion Index method to scoria cones from the arid to semi-arid Lunar Crater volcanic field and comparing with previously obtained results from two tropical volcanic fields (Sierra Chichinautzin volcanic field and Paricutin-Tancitaro region, both in central Mexico). The results show that the method helps to determine geomorphic age relations when calibrated separately for each field. Furthermore, the differences in the resultant rates at which AEI varies as a function of time obtained for the three studied fields indicate that the method provides a tool to quantify the effects of different alluvial rates at volcanic fields across various environments.

How to cite: Zarazúa-Carbajal, M. C., Valentine, G. A., and De la Cruz-Reyna, S.: Gully incision development on scoria cones: different behaviors in three volcanic fields reflect environmental conditions., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6783, https://doi.org/10.5194/egusphere-egu24-6783, 2024.

A region located in the SW sector of the Michoacán-Guanajuato monogenetic field, in central Mexico displays a high spatial density of scoria cones, mostly around Tancítaro, a large central volcano active in the middle Pleistocene. This region became well known when in 1943 a new volcano, Paricutin, was formed in a cornfield at 11 km to the NW of the extinct stratovolcano. The birth of Paricutin was preceded by significant swarm-type seismicity. Afterward, new seismic swarms were reported in the area in 1997, 1999, 2000, 2006, 2020, 2021, 2022, and 2023, with a mean recurrence interval of only 4 yr, most of them (not all) showing the characteristics of a magmatic origin.  Aiming to shed some light on the relation between the high density of monogenetic cones and the recurrent seismicity, we have made a morpho-chronometric estimate of the relative ages of 170 scoria cones located in the Paricutin-Tancítaro region (PTR) within latitudes 19°N and 20°N and longitudes -102.0° E and -102.7° using the Average Erosion Index (AEI) which quantifies the degree of alluvial erosion of scoria cones from a Fourier analysis of their level contours. Monogenetic activity began in the PTR at about 1 Ma, and the AEI analysis shows that such activity increased after the end of the Tancítaro activity, around 232 ka, and further increased in the Holocene when about one-third of the scoria cones in the region were formed, with a mean interval between eruptions between 120 and 240 yr. On the other hand, a detailed study of two of the most energetic seismic swarms, recorded in 2020 and 2021 shows that the magma intrusion volume required to produce the measured cumulative seismic moment of both swarms amounts to about 140 million cubic meters, which is seemingly insufficient to produce a Paricutin-size eruption, which ejected about 1.3 cubic km of magma. We thus propose a possible conceptual explanation of the recurrent emplacement of monogenetic volcanoes and the frequent seismic swarm activity in terms of a persistent magma source under the crustal extension of the PTR producing numerous dike and sill forming intrusions. In some cases, such intrusions may have a cumulative effect forming temporary magma reservoirs capable of producing new monogenetic eruptions. Assuming that about 0.5 to 1 cubic kilometer of magma needs to accumulate to begin an eruption, about 7 to 14 sizable (similar to the 2020-2021) swarms may then represent a significant precursor.    

How to cite: De la Cruz-Reyna, S., Zarazúa-Carbajal, M. C., Caballero-Jiménez, G. V., and Mendoza-Rosas, A. T.: Cumulative storage of magma in the Paricutin-Tancítaro region, Mexico, revealed by recurrent swarm seismicity and a high spatial density of morpho-chronometrically dated Holocene monogenetic cones., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6885, https://doi.org/10.5194/egusphere-egu24-6885, 2024.

Various subduction zone characteristics, including the slab dip, plate velocity, seismicity, and back-arc stress regime, show the global asymmetry with respect to the subduction direction. In particular, the east-directed subducting slabs show shallow dips and slow convergences, contrast to the steep dips and fast convergences of the west-directed subducting slabs. To explain the global asymmetry, the westward lithospheric motion or the eastward mantle wind with respect to the underlying mantle and the overlying plate, respectively, have been proposed. However, the causative force for the lithospheric motion, the tidal force between the Earth and Moon, is only acceptable when the asthenospheric viscosity is dramatically low such as 10¹⁵ ~ 10¹⁶ Pa·s, which could not globally exist in the mantle. The causative force for the mantle wind has left unknown even though the impact of the mantle wind has been verified. Past studies have shown that slabs sinking into the lower mantle can cause global mantle flow. That is, the slabs sinking at the eastern and western trenches around the Pacific ocean can cause the global mantle flow above the low-viscosity liquid outer core, expressed as the mantle wind. Therefore, to verify whether the subducting slabs around the Pacific ocean cause the mantle wind, we conducted a series of 2-D numerical models using an annulus-shape model domain, which simplifies the subduction history in the paleo- and present-Pacific ocean. Along with an allowance of dynamic subduction, both the realistic mantle viscosity and the major phase transition in the mantle were considered. Results show that the global-scale mantle wind is spontaneously formed by the imbalance in lateral mantle stresses owing to the subducting slabs around the Pacific ocean when the slippery core-mantle boundary operates as a lubricant layer, and the direction and magnitude of the mantle wind are periodically changed every tens of million years. When he eastward mantle wind occurs, it induces the relative westward drift of the plate, and as a result, the westward plate velocity becomes greater than the eastward plate velocity with respect to the hotspot reference frame. Simultaneously, the mantle wind pushes the west-directed subducting slab toward the ocean, forming steep slab dips but does the east-directed subducting slab toward the arc, forming shallow slab dips, consistent with the present subduction asymmetry in the Pacific ocean. After that, the negative buoyancy of the shallow slab steepens the slab itself, changing the direction of mantle wind westward; the opponent slab dips and plate velocities occur in the subduction zones. This study reveals that the present subducting asymmetry is a snapshot expression of the evolving global mantle flow, formed by the subducting slabs.

How to cite: Lee, Y. and Lee, C.: Spontaneous Formation of Mantle Wind by Subduction and Its Impacts on Global Subduction Asymmetry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7187, https://doi.org/10.5194/egusphere-egu24-7187, 2024.

Understanding the relationships between the onset of volcanic eruptions and external forcings, such as solid Earth and ocean tides, can help us to understand the underlying dynamics of volcanic processes and have implications for volcanic monitoring and prediction efforts.

Many studies that explored the relationship between tidal forces and volcanic activity have shown that certain phases of tidal cycles are associated with an increased likelihood of eruptions. At longer-time scales of hundreds of thousands of years, pronounced sea level variations related to ice melting or climatic and astronomical periodic variations have also been associated with pulses of volcanic activity.

Oceans participate in significant redistributions of mass that can affect the stress field within the Earth’s crust over different time scales. Considering that most volcanoes lie near, within or beneath the oceans we hypothesize that stresses induced by ocean loading participate in destabilizing volcanic dynamical systems and ultimately contribute to eruption triggering.

In a previous study we analyzed the worldwide number of monthly volcanic eruptions from the Global Volcanism Program and the global mean sea level between 1880 and 2009 using the Singular Spectrum Analysis time-series analysis technique. We found common periodicities and particularly multi-decadal components of similar periodicities of 20, 30 and 50 years present in both time-series.

In this work we further explore the connection between volcanic activity and sea level by mapping the spatial patterns of volcanic eruptions at the previously identified temporal scales of correlation, ranging from the fortnightly tide to cycles of approximately 100 years. Geographical Information System tools are used to create spatial data layers, perform spatial analysis, and provide geographical visualization. The analysis might reveal global conditions and space-time patterns favorable to eruption triggering.

This work was funded by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES through national funds (PIDDAC) –

UIDB/50019/2020 (https://doi.org/10.54499/UIDB/50019/2020),

UIDP/50019/2020 (https://doi.org/10.54499/UIDP/50019/2020) and

LA/P/0068/2020(https://doi.org/10.54499/LA/P/0068/2020).

How to cite: Scala, M., Neves, M. C., and Dumont, S.: Patterns of volcanic eruptions in connection to sea-level change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8475, https://doi.org/10.5194/egusphere-egu24-8475, 2024.

Earth’s topography is both isostatically and dynamically supported. Sub-crustal density anomalies, caused by convective mantle processes, generate transient vertical motion at Earth's surface, producing the dynamic component of topographic support. Residual depth measurements are a well-established proxy for quantifying dynamic topography on oceanic crust and provide an observation-led approach to probing mantle dynamics. A global database of residual depth anomalies compiled from seismic reflection profiles and wide-angle seismic experiments is augmented with results obtained from interpreting further seismic experiments in the oceans surrounding the African continent. Residual depth anomalies are calculated by isolating and removing isostatic signals arising from sediment loading and crustal heterogeneity. Following these corrections, observed water-loaded depth-to-basement is compared to that predicted by the plate cooling model, with deviation equal to the residual depth anomaly. Coverage surrounding the African continent is improved, particularly in the Gulf of Guinea and Mozambique Channel. Results are consistent with previous observations, showing dynamic support of ± 1 km out to and including spherical harmonic degree l = 40 (i.e. ~ 1000 km). Results are corroborated by independent geologic and geophysical markers of subsidence and uplift. For example, volcanism and slow shear-wave upper mantle velocity anomalies associated with the Cameroon Volcanic Line indicate dynamic support. Improving the spatial sampling of residual depth anomalies provides insight into the influence of convective circulation on Earth’s surface, culminating in a more robust database against which geodynamic models of mantle convection can be benchmarked.

How to cite: Slay, P., Holdt, M., and White, N.: Implications of dynamic topographic measurements along Africa’s passive margins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8609, https://doi.org/10.5194/egusphere-egu24-8609, 2024.

It is widely recognized that mantle dynamics and plate flexure both contribute to Earth’s topography and gravity fields at different wavelengths, yet the actual transition wavelength between them is not well quantified, ranging from ~100 km to ~1000 km. Here we use the observed relationship between topography and the free-air gravity anomaly fields (admittance) to infer the relative contribution of plate flexure and mantle dynamics based on mantle flow models which incorporate an essentially elastic plate. Global and regional Pacific Ocean data studies show that plate flexure and mantle convection potentially contribute to the topography and gravity for wavelengths larger than ~600 km. Plate flexure mainly contributes at wavelengths shorter than ~600 km and is consistent with the support of uncompensated topography for wavelengths shorter than ~200 km. To investigate the admittance associated with mantle dynamics at long wavelengths we have constructed mantle flow models based on a number of different seismic tomography models. The finite element software CitcomS was used to calculate mantle flow and related surface dynamic topography and associated free-air gravity anomaly. Admittance analysis in the Pacific Ocean from different mantle flow models show that the dynamic admittance is generally larger than the observed admittance, while the admittance from plate flexure is smaller than the observed admittance, suggesting that both mantle dynamics and plate flexure contribute to Earth’s topography and gravity at long-wavelengths. The difference between the dynamic admittance and the observed admittance is smallest for cases with temperature-dependent viscosity and weak asthenosphere, and the combined admittance in the presence of both flexure and mantle convection for these cases is generally consistent with the observed admittance. We use a new method to separate the effects of plate flexure and mantle convection to the topography and gravity fields at long wavelengths which has been developed from the plate flexure and dynamic admittances. We assume that the topography and gravity at long wavelength are the combination of plate flexure and mantle dynamics and further assume that the topography and gravity are linearly related through the admittance. The final separated dynamic topography in the Pacific Ocean is generally consistent with previously published residual topography studies at long-wavelengths.

How to cite: Yang, A., Watts, A., and Zhong, S.: Long-wavelength gravity and topography of the Pacific Ocean: Relative contribution of mantle dynamics and plate flexure , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9346, https://doi.org/10.5194/egusphere-egu24-9346, 2024.

Fluid dynamics simulations are a powerful tool for understanding processes in the Earth's deep interior. Mantle circulation models (MCMs), for example, provide important insight into the present-day structure of the mantle and its thermodynamic state when coupled with mineralogical models, which is essential information for other fields in the geosciences. The evolution of the heat flux through the core-mantle boundary, for instance, is a prerequisite for geodynamo simulations that aim to model the reversal frequency pattern of the Earth's magnetic field on geologic time scales. However, geodynamical modelling requires extensive knowledge of deep Earth properties and plate motions over time. Uncertainties in these model inputs propagate into the MCMs, which subsequently have to be evaluated with independent data, such as the seismological or geological record. Although state-of-the-art MCMs typically explain statistical properties of seismological data, they do not consistently reproduce the location of features in the mantle.

In this contribution, we explore the effect of varying the absolute position of mantle structure on seismic data by applying first-order modifications to an initial MCM. Normal mode data are particularly well suited for assessing the resulting changes in the location of mantle structure, as they capture its long-wavelength component throughout the entire mantle. In addition, the global sensitivity of normal modes reduces the drawbacks of uneven data coverage. Specifically, we use two different seismic forward modelling approaches, an iterative direct solution method for computing full-coupling spectra and a splitting function calculation that is based on the self-coupling approximation. Our goal is to quantify the effects of a limited number of large-magnitude earthquakes, the adequacy of the self-coupling approximation, and the resolvability of relevant model differences through a comprehensive data analysis. Our synthetic forward modelling framework is moreover well suited for testing the depth sensitivity associated with specific frequency intervals in the spectrum that generally is inferred from seismic 1-D profiles within the splitting function approximation.

How to cite: Schneider, A., Schuberth, B., Koelemeijer, P., Shephard, G., and Al-Attar, D.: Exploring the potential of normal mode seismology for the assessment of geodynamic hypotheses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10128, https://doi.org/10.5194/egusphere-egu24-10128, 2024.

Interpretations of seismic tomography and applications of the resulting tomographic images, e.g. for estimating present-day mantle temperatures, require information on their resolution and uncertainty. Assessing these model properties is often difficult due to the large size of tomographic systems on global scales. In consequence, there have been only few attempts to consistently analyse the spatially variable quality of tomographic images of deep mantle structure. For linear problems, both resolution and uncertainty can be quantified with the tools provided by classic Backus–Gilbert (B–G) inversion. In this theory, averaging kernels define the local resolving power at each model parameter, while uncertainties represent the propagation of data errors into the model values. By using a more efficient variant of B–G inversion, the method of 'Subtractive Optimally Localized Averages' (SOLA), global tomography can be performed with complete information for model appraisal.

Based on the SOLA framework, we present a concept for the assessment of the 3-D resolution information contained in a global set of averaging kernels. It is based on the rigorous estimation of resolution lengths from a 3-D Gaussian parametrization of the averaging kernels, together with a test for the robustness of this approximation. This is a necessary step because a perfectly bell-shaped or delta-like behaviour of resolution can not always be guaranteed in global tomography due to the inhomogeneous data coverage. Therefore, we also develop a classification scheme, which enables a basic identification of those averaging kernels that are too complex to be sufficiently described by the chosen definition of resolution length. We note that this approach is more generally applicable, i.e. it can be used with any explicitly available set of averaging kernels or point-spread functions, but also with alternative parametrizations.

In the context of the SOLA method, our resolution analysis can be further used to locally calibrate the inversion parameters. This involves on the one hand the specification of a target (resolution) kernel. On the other hand, a trade-off parameter needs to be selected that regulates the fit of the averaging to the target kernel, and the conversely affected propagation of data errors.

To this end, we apply our concept for robust resolution estimation to different sets of averaging kernels from SOLA inversions with varying parameter combinations. Most notably, we systematically increase the spatial extent of the target kernels (taken as 3-D Gaussian functions here as well). The final maps of global (and classified) resolution and uncertainty can be viewed together for a complete picture of the model quality. They reveal where, and for which target size and amount of error propagation, resolution lengths are meaningful and model values can be interpreted appropriately.

How to cite: Freissler, R., Schuberth, B. S. A., and Zaroli, C.: Global assessment of tomographic resolution and uncertainty with the SOLA method, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10566, https://doi.org/10.5194/egusphere-egu24-10566, 2024.

We present a new book aimed at graduate students, and academics, as well as all volcano enthusiasts. We chose to publish on the topic of volcano geomorphology for two main reasons. Firstly, although several geomorphology textbooks have been published, ones focussed on volcano geomorphology are scarce or outdated and out of print (Cotton, 1944, McDonald, 1972; Ollier, 1969 and 1988). Secondly, many volcanology books have been published over the past few decades, but they do not describe landforms and geomorphic processes in sufficient detail (as stated by the late P. Francis in 1993). To our knowledge, only five modern books on volcanology include a chapter on volcanoes as landforms and landscapes (Francis, 1993 and Francis & Oppenheimer, 2004; Chester, 1993; Scarth, 1993; Lockwood and Hazlett, 2010). They are less process-oriented than modern books on geomorphology.

Our book on Volcano Geomorphology is organised into five main themes, and contains 10 chapters. The first theme is an overview of the geodynamic environments in which the Earth's volcanoes are created.  The second is a detailed account of elementary “constructional” landforms, from lava forms to monogenetic volcanoes, both terrestrial and subaqueous, reflecting a variable degree of magma-water interaction. The third deals with polygenetic volcanic edifices including shield volcanoes, composite cones and volcanic clusters. This is followed by landforms and processes that form calderas, caldera complexes, and volcano-tectonic depressions. The fourth is oriented towards the degradation of volcanoes by short- and long-term erosion processes. The fifth and final theme is twofold: first, we deal with geomorphic hazards on active and dormant volcanoes, along with five specific case studies of recent events; and lastly, we conclude with a chapter presenting a wide array of methods (morphometry, simulations of processes, structural geology, age determination, etc.) that are used to unravel processes on active and dormant volcanoes.
            In summary, our textbook aims to: (1) review the most recent research in geomorphology and physical volcanology, e.g. an improved classification and understanding of volcanic landforms, with respect to geodynamic settings, lithology, and climate; (2) update our knowledge of processes and rates of growth and destruction of volcanic landforms and landscapes by integrating recent results from the expanding sector of volcanology both in the field and in the laboratory; (3) consider how volcanic landforms, landscapes, and processes can be studied by reviewing classical and modern methods.  

In this way, we hope that our compilation, which provides a richly referenced and illustrated piece of work on volcano geomorphology, will be of interest to a broad audience. It is expected to be published later this year (2024).  

How to cite: Karátson, D. and Thouret, J.-C.: ‘Volcano Geomorphology: landforms, processes and hazards’  ̶̶ A new book in ‘Advances in Volcanology’ Collection, Springer Verlag , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11744, https://doi.org/10.5194/egusphere-egu24-11744, 2024.

 Active volcanic catchments within low-latitude tropical humid climates constitute some of the most dynamic and sediment-rich fluvial systems globally. The combination of factors such as active explosive vulcanism, frequent high-magnitude earthquakes, dense biodiverse vegetation, and intense rainfall leads to very high sediment supply and very active channel morphodynamics within such fluvial systems.

Our research focused on channel dynamics in three remote and challenging-to-access reaches of the Sucio River, situated within the Irazú stratovolcanic structure in Costa Rica's central volcanic chain. This unique setting experiences extreme conditions, including rainfall exceeding 8000 mm annually, infrequent but significant volcanic eruptions (occurring over three times per century), high-magnitude earthquakes (>Mw5), and dense pristine vegetation. The mapped river reaches within this active volcano exhibit a distinctive confined multi-thread channel morphology predominantly comprised of coarse sediments, notably boulders, displaying exceptional dynamism. These reaches showcase rapid shifts between braided, island-braided, and anabranching morphologies in relatively short periods (<20 yrs.). Additionally, the primary sediment sources located in crateric areas have undergone rapid and substantial changes, resulting in the emergence of large landslides and drastic alterations in vegetation.

Employing remote sensing techniques, geostatistical analysis, and fieldwork, we investigated the impacts of eruptions, earthquakes, and rainfall on the Sucio River's channel morphology and its primary sediment sources (craters) from 1961 to 2023. Over 65 images were processed to generate various derived raster products, including supervised classification datasets, change detection outputs, and morphometric parameters (such as channel width, braided index, anabranching index, and area of bars and islands). Moreover, we constructed a precipitation database spanning the study period to assess the frequency, magnitude, and duration of extreme rainfall events. Historical seismic data was utilized to compile a database of relevant earthquakes that might have affected the catchment, given the river's proximity to several active faults. Subsequently, exploratory statistical analysis employing linear regression models helped discern the influential factors behind channel dynamics and changes.

Our findings provide a novel understanding of how this specific fluvial volcanic environment responds to external perturbations and adapts its channel morphology over time. Key outcomes include the rarity of the multithread boulder morphologies observed in these reaches, rapid morphological transformations occurring within this multithread system in short intervals, the significant role of dense pristine vegetation in stabilizing banks and islands, and the cyclic stability-instability phases (erosion-deposition) triggered by pivotal events like eruptions, hurricanes, and high-magnitude earthquakes.

This study presents novel insights into channel morphology dynamics in one of Central America's most extensively studied active volcanoes, likely having the river transporting the most sediments in Costa Rica's volcanic regions.

How to cite: Granados, S., Surian, N., and Alvarado, G. E.: River dynamics in an active volcano with tropical humid conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11817, https://doi.org/10.5194/egusphere-egu24-11817, 2024.

Late Paleozoic Ice Age (LPIA), which peaked during the mid Permian, resulting in widespread ice centers across Gondwana during its coldest periods. Assessing the climate change across this glaciation and the following deglaciation interval contribute important data not only in terms of understanding the end-Permian extinction event but also present-day global change. Tasmania, located in a high-latitude setting, forming a bridge between the continents Antarctica and Australia provides a valuable record of the environmental and climatic shifts that occurred in areas proximal to glaciation during the acme and waning stages of the LPIA.

At the time of glaciation, Tasmania was a distinct landmass located within the Paleo-Antarctic Circle at a paleo-latitude of ~78°S. Here we present new high-resolution bulk organic carbon isotope analyses (δ¹³C_TOC), mercury, bulk and trace elemental and sedimentological data combined with palynology and conodont biostratigraphy from the late stage (P3 and P4) of the LPIA Glacial-Deglacial Episode III. We base the data on samples from the Bicheno-5 core, from Eastern Tasmania, which contains approximately 83 meters of middle Permian glaciomarine sediments.

Three negative carbon isotope excursions (CIEs) have been identified in the middle Permian (mPN1, mPN2, and mPN3). The latter two are correlated with the deglaciation episodes in Eastern Australia's glacial intervals P3 and P4 phases. Diamictites and dropstones are typically present in the sediments that record the most positive carbon isotope values, which likely correspond to the peak of the glaciation period. Elemental proxies indicate two cycles of increased weathering and terrestrial sediment influx to the marine system. These cycles coincide with the most negative carbon isotope values and are associated with deglacial cycles in Tasmania and within the paleo-Antarctic circle. The first deglacial cycle (mPN1) coincides with elevated mercury (Hg/TOC) which may hint at a link between deglaciation and volcanism, possibly from the Tarim III LIP.

Comparisons with similar records from the marine Pingdingshan (PDS) section in South China confirms that our data from Tasmania reflect global carbon cycle perturbations providing new insights into the significant global climatic shifts that occurred during the middle Permian. The end stage of the LPIA offers a unique comparison to modern environmental and climatic change in Antarctica associated with anthropogenic global warming.

How to cite: Lestari, W., Al Suwaidi, A., Fox, C., Vajda, V., Ceriani, A., Sun, Y., Frieling, J., and Mather, T.: Unraveling Tasmania's Late Paleozoic Ice Age: Carbon Isotopic and Stratigraphic Signatures in Response to Glacial-Deglacial Cycles and Large Igneous Province (LIP) Events, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12015, https://doi.org/10.5194/egusphere-egu24-12015, 2024.

Mantle convection is a fundamental process governing the evolution of our planet. Buoyancies in the mantle induce horizontal and vertical motion of the Earth’s lithosphere, which can be mapped using independent geological datasets. Positive surface deflections induced by mantle convection create erosional/non-depositional environments which lead to gaps (hiatuses) in the stratigraphic record, while negative deflections provide accommodation space for sedimentation to occur. We use continental- and country-scale digital geological maps and regional and local stratigraphic studies at the temporal resolution of geological series (ten to tens of millions of years) to map the distribution of hiatus through geological time.

Here we present global continental hiatus surfaces since the Upper Jurassic. We find that they vary inter-regionally at timescales of geological series and that they correlate with known mantle dynamic events. For example, we tend to observe the appearance of a hiatus surface before the arrival of a mantle plume. In Europe, we mapped a large-scale sedimentary hiatus during the Paleocene, prior to the arrival of the Iceland plume. In Africa and South America, we found a widespread absence of the Upper Jurassic prior to the arrival of the Tristan plume. This pattern can be seen as characteristic of plume-induced dynamic uplift. We observe a sea level signal during some geological series, such as in the Oligocene, when there is a global increase of hiatus areas, coinciding with the onset of Antarctic glaciation and associated sea level drop. At other times, we find that the hiatus areas evolve differently for different continents, precluding their interpretation as an eustatic signal. Spectral analysis shows that hiatus surfaces have shorter wavelengths than no hiatus surfaces, requiring higher spherical harmonic degrees to describe the geological series with larger amounts of hiatus. These include the Upper Jurassic, the Paleocene, the Oligocene and the Pleistocene.

Our results imply that a key property of time-dependent geodynamic Earth models must be a difference in timescale between mantle convection itself and resulting dynamic topography. Moreover, they highlight the importance of continental-scale compilations of geological data to map the temporal evolution of mantle flow beneath the lithosphere, which can provide powerful constraints for global geodynamic models.

How to cite: Vilacís, B., Brown, H., Carena, S., Bunge, H.-P., Hayek, J. N., Stotz, I. L., and Friedrich, A. M.: Global continental hiatus surfaces as a proxy for tracking dynamic topography since the Upper Jurassic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12118, https://doi.org/10.5194/egusphere-egu24-12118, 2024.

While the isostatic compensation of crustal thickness and density heterogeneity provides the dominant contribution to Earth’s observed topography, there nonetheless remains a substantial difference (the ‘residual topography’) between these two fields. This difference is a consequence of dynamic processes occurring within the mantle, most notably due to time-dependent vertical surface stresses driven by mantle convection. Mantle convection dynamics also produce differences between the observed geoid and the isostatic geoid generated by crustal heterogeneity: the ‘residual geoid’. The joint consideration of both residual geoid and topography anomalies provides unique and fundamental global constraints on the amplitude and spatial distribution of density anomalies in the convecting mantle.
Despite the crucial role of isostasy in determining residual geoid and residual topography, accurate constraints depend heavily on the quality of the isostasy calculations. The classical theory of isostasy relies on a 1^st-order treatment of hydrostatic equilibrium, which is not sufficiently accurate for the calculation of isostatic geoid anomalies on a compressible, self-gravitating mantle. Consequently, we present a geodynamically consistent approach that is based on the surface loading response (via dynamic kernels) calculated with a viscous flow model that incorporates a fully compressible mantle and core (given by the PREM reference model) with self-gravitation.
Another critical issue that remains outstanding is the accuracy inherent in global crustal heterogeneity models. Here we show that the differences between the residual geoid and topography fields predicted using CRUST1.0 (Laske et al. 2012) and the most recent ECM1 (Mooney et al. 2023) crustal heterogeneity models are substantial. We discuss the importance and implications of these differences in the context of determining the most accurate constraints on density anomalies in the convecting mantle.

How to cite: Kamali Lima, S., Forte, A. M., and Greff, M.: A Geodynamically Consistent Approach to Residual Topography and Geoid Anomalies on the Convecting Mantle: Importance of Global Crustal Models , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12457, https://doi.org/10.5194/egusphere-egu24-12457, 2024.

Analogue experiments can enhance our understanding of complex natural volcanic landscapes formed by eruptions, intrusions, remobilisation of volcanic material and erosional processes. Experimental setup in a laboratory offers a controlled setting to investigate the development of rainfall-induced radial drainage basins on scaled volcano cones. It allows to simulate surface runoff, a prominent sediment transport process in volcanic landscapes, primarily influenced by climate, lithology, and topography. By controlling the flowrate within the setup, maintaining a uniform lithology, and using initial axisymmetric cones with the same size, this study aims to record the variations in erosion patterns caused by systematic cone slope and shape changes.

Analogue volcanic cones made up of water-saturated 70 μm silica powder were built upon a drainage layer of coarse sand at the VUB volcanology analogue laboratory. The cones were scaled based on the height/basal width ratios of natural pristine composite volcanoes with a scaling factor of 4.5*10^-6 for the basal width. Initial cones had basal widths of 33 cm with two sets of cones with heights ranging from 4.2 to 6.9 cm. For the highest cones, the lower flank was 21 degrees and the upper slope 30 degrees, with a break-in-slope at 45% of the cone height. Experiments included cones with and without summit craters, the craters were 5 cm wide and 0.5 cm deep. Rainfall-induced erosion was simulated with two atomizer sprinklers, creating a mist of droplets of circa 30 μm. Experiments were run for 3 to 5 hours, simulating erosion taking place over several millions of years at natural volcanoes. We generated a minimum of ten Digital Elevation Models (DEMs) by photogrammetry with sub-millimetre spatial resolution, enabling the estimation of volume loss and erosion rates. The automated algorithms MorVolc and DrainageVolc were used to extract morphometric and drainage parameters (e.g., height/basal width ratio, drainage density, irregularity index) from the DEM of each timestep.

The analogue models' drainage networks and morphological characteristics replicate those found on natural volcanoes. Having a steeper slope for the upper flank of the cone delayed the forming of erosional features on the lower flank, while the top part of the volcano incised deeper than the cones with one slope gradient. The cones without a summit crater develop a radial drainage network from an initial set of narrow gullies to a more stable pattern with fewer valleys that gradually widen. The introduction of a summit crater substantially modifies the resulting erosional patterns: the incision of the crater rim forms two to four dominant watersheds that widen faster than the basins of cones lacking a crater. Migration of drainage divides ceases when equilibrium in the landscape is attained, with cones featuring a summit crater reaching this equilibrium later than those without. Analogue experiments are a valuable tool for studying erosional processes in a controlled manner and give insight into complex volcanic landscapes, thereby improving our understanding of long-term volcanic landscape evolution.

How to cite: van Wees, R. M. J., Paguican, E., O'Hara, D., Kereszturi, G., Grosse, P., Lahitte, P., and Kervyn, M.: Modelling volcano degradation through analogue experiments: the impact of volcano slopes and summit craters on erosion patterns, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13012, https://doi.org/10.5194/egusphere-egu24-13012, 2024.

Understanding the interaction between oceanic plates and the underlying asthenosphere and its impact on plate thickness is essential for explaining plate motions and mantle convection patterns. While sub-lithospheric small-scale convection provides an explanation for why oceanic plates do not continue to thicken after a certain age, many open questions still surround this process. Here, we link dynamic models of mantle flow, grain-scale processes, seismic imaging, and surface observations to gain new insights into the mechanisms of asthenospheric small-scale convection and its surface expressions.

We have performed a series of high-resolution 3D numerical models of the evolution of oceanic plates and the development of thermal instabilities at their base using the open-source geomodeling software ASPECT. These simulations use an Earth-like rheology that includes coupled diffusion and dislocation creep as well as their interplay with an evolving olivine grain size. Our models quantify how the effective asthenospheric viscosity and the balance between diffusion and dislocation creep affect the morphology and temporal stability of small-scale sub-lithospheric convection, including the age of its onset, the average depth and wavelength of the small-scale convection rolls, and the amplitude of the temperature and grain size anomalies within the rolls.

All of these quantities predicted by the dynamic models can be directly related to both geophysical observables and to surface manifestations such as dynamic topography and heat flux. To accurately compare our model outputs to geophysical data, we convert them to seismic velocity and attenuation using laboratory-derived constitutive relations and taking into account variations in temperature, pressure, grain size, water content and calculated stable melt fraction. We then create synthetic seismic tomography models of different dynamic scenarios and analyze their fit to observations from the Pacific OBS Research into Convecting Asthenosphere (ORCA) experiment. Comparison with both seismic imaging and surface expressions allows us to determine the parameter range in which geodynamic models fit these observations, providing new constraints on the convection patterns and the rheology of the oceanic asthenosphere beneath the Pacific Plate.

How to cite: Dannberg, J., Eilon, Z., Russell, J. B., and Gassmoeller, R.: Sub-Lithospheric Small-Scale Convection as a Window into the Asthenosphere: Insights from Integrating Models Of Mantle Convection, Grain Size Evolution and Seismic Tomography, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13895, https://doi.org/10.5194/egusphere-egu24-13895, 2024.

Volcanic edifices are dynamic landforms whose morphology encodes the long-term (thousands to millions of years) interplay between construction and erosion. Short-term, stochastic episodes of volcanic activity cumulatively build topography, competing with stochastic erosive processes associated with climate and mass wasting to degrade edifices over longer timescales, thus generating a variety of morphologies from simple, cone-like edifices to complex, non-axisymmetric volcanoes. Understanding how these processes interact to shape volcano morphologies over the landform’s lifespan is still in its infancy, especially as construction and erosion are often spatially-heterogeneous and temporally-varying. Despite this, disentangling edifice morphologic histories provide new avenues to better discern an edifice’s volcanic record, assess potential hazards, and quantify the role of climate in landscape evolution.

Numerical modeling has been shown to be a useful approach to exploring long-term landscape evolution. Although the majority of studies have applied landscape evolution models to tectonic settings, modeling has also been applied to simulate erosion and drainage development for specific volcanic features (e.g., channel incision on shield volcanoes, soil diffusion on cinder cones). However, thus far no modeling frameworks have been developed to explore evolution over the full spectrum of edifice types

Here, we investigate volcanic edifice erosion and drainage basin formation using a simplified landscape evolution model. Assuming that the various erosive processes that shape a volcano can be simplified to the competition between advection and diffusion, we use common transport laws (stream power law and linear soil diffusion) to conduct a nondimensional parameter analysis. We then test various parameter combinations to demonstrate the range of morphologic evolutions that can occur over different edifice classifications and environments. Afterwards, we compare our results to previously-derived relationships of natural volcano evolutions to test the ability for simplified models to recreate nature. Finally, we explore the effects of edifice size on the competition between incision- and diffusion-based erosion within the framework of our nondimensional parameters by quantifying drainage development of 156 cinder cones from the Springerville Volcanic Field (AZ, U.S.) and comparing these to both edifice age and planform area.

Our results demonstrate that simplified numerical models are able to recreate the trends observed in nature. Furthermore, we show that the combination of model parameters predicts threshold sizes that volcanic edifices must overcome to begin generating fluvial drainage networks and becoming incised by gullies, broadly inferring parametric thresholds that describe the ratios of erosion processes on these landforms. Our results thus establish a new foundation to study edifice morphologies over several volcano types (cinder cones, shield volcanoes, composite volcanoes) and construction styles (intrusion-driven surface uplift, mantling by lava flows and ash deposits), and provides a basis to test how volcanic environments respond to past and future changes in climate and tectonics.

How to cite: O'Hara, D., Goren, L., Campforts, B., van Wees, R., Zarazúa-Carbajal, M. C., and Kervyn, M.: Understanding volcanic edifice erosion and morphologic evolution using numerical models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15103, https://doi.org/10.5194/egusphere-egu24-15103, 2024.

Lower Jurassic sedimentary successions from the Neuquén Basin, Argentina are unique in the abundance of radiometrically datable material (ash-beds) present, which can be tied to bio- and chemostratigraphic (carbon-isotope) zonations. Here, we present new U-Pb radio isotopic dates, integrated with carbon-isotope and Hg/TOC data, from three localities in Argentina (Arroyo Lapa, Arroyo Serrucho/Las Overas and Chacay Melehue) to generate a biostratigraphically calibrated composite carbon-isotope curve and geochronological framework for the Pliensbachian–Toarcian transition in South America. Using a Bayesian framework we present an age-depth model for this composite record and estimate the age and duration of key intervals extending from the Latest Pliensbachian carbon isotope excursion (CIE) through the Early Toarcian negative CIE. Using a  statistical analysis of all available Karoo and Ferrar Large Igneous Province (LIP ) U-Pb and Ar-Ar radioisotopic ages we create a timeline of the key events and examine the timing of the carbon cycle perturbations specifically looking at potential links to peaks of extrusive emplacement of the Karoo and Ferrar LIP. The geochronological framework is further compared with other available radioisotopic dates from correlative sections, allowing for a more precise constraint and validation of the timing and duration of these Early Jurassic events.

How to cite: Al-Suwaidi, A., Ruhl, M., Kemp, D., Storm, M., Hesselbo, S., Jenkyns, H., Mather, T., Percival, L., and Condon, D.: A Southern Hemisphere Chronostratigraphic Framework for the Pliensbachian–Toarcian Carbon Cycle Perturbations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15374, https://doi.org/10.5194/egusphere-egu24-15374, 2024.

The Transantarctic Basin is a continental basin system developed for ca 200 Myr, from the Devonian to the Early Jurassic, along the Panthalassa margin of Gondwana and above the peneplained Ross Orogeny rocks. The Beacon Supergroup strata form the clastic sedimentary infill of the Transantarctic Basin.

Geodynamic interpretation of the Transantarctic Basin is not univocal and likely geodynamic conditions accounting for basin subsidence have been changed in space and time. Involvement of the basin into the Gondwanian orogenic deformation is a key question for defining the geodynamic setting and the tectonic environment during the Beacon Supergroup deposition. Nonetheless, involvement of  Beacon Supergroup  in orogenic shortening is  poorly assessed for the limited exposed rocks and because formation of the Cenozoic  Transantarctic rift shoulder modified the Paleozoic geometry of the Beacon strata.

Here we explored the exhumation pattern and thermal evolution of the basement rocks and the immediately overlain Beacon sandstones through low-temperature apatite fission track and (U-Th)/He zircon thermochronology along the Prince Albert Mts, where Beacon deposits are particularly thin to suppose a relevant erosional event during the Paleozoic. Thermochronological data and thermal modelling pointed out that basement rocks and Beacon sandstones of the Prince Albert Mts have preserved evidence of a Late Paleozoic erosional event that allows to infer an actively eroding topographic high that lasted from Early to Late Paleozoic times, as a consequence of the far-field stress transmitted from the active Gondwanian convergent margin.

How to cite: Olivetti, V., Cattò, S., Balsamo, F., Zurli, L., Perotti, M., Cornamusini, G., Fioraso, M., Rossetti, F., and Zattin, M.: Uplift and erosion of an intraforeland topographic high: implication for the evolution of the Gondwanian Transantarctic foreland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15516, https://doi.org/10.5194/egusphere-egu24-15516, 2024.

Volcanoes display a wide range of morphologies, resulting from the cumulative imprints of deposition from multiple eruptive events and processes, deformation by intrusive and gravitational processes, as well as erosion throughout the active volcanic phase and beyond. Quantitative documentation of the morphometry of volcanoes offers opportunities to compare volcanic edifices across tectonic regions, define evolutionary trends for volcanoes of different ages and/or stage, or compare natural volcanoes with results from analogue or numerical modelling. Although such morphometric studies exist, the comparability of their results faces challenges related to the contrasted approaches used for delineating volcanic edifices, defining morphometric metrics to characterize volcano sizes, shapes, and erosion patterns, and deriving the pre-erosional volcano volume.

Building upon the MORVOLC (Grosse et al. 2012) and ShapeVolc (Lahitte et al. 2012) algorithms, the EVoLvE project has produced a suite of scripts in MatLab to semi-automatically document the morphometry of stratovolcanoes systematically. First, the manual delineation of a volcano’s base is aided by implementing a slope threshold (suggested to be at 3°) after applying a 300m low-pass filter on the volcano’s topography to identify the prominent volcano landform. Morphometric parameters documenting volcano-scale size, plan-shape, profile shape and slope, as well as metrics derived at regular elevation intervals, following the MORVOLC approach of Grosse et al. (2012), are complemented with a new set of parameters (DrainageVolc) that document the erosion pattern of volcanoes, specifically the drainage density and the geometry of drainage basins. Finally, assuming basins’ divides or local quasi planar surfaces represent the least eroded sections of an edifice, a surface fitting algorithm (ShapeVolc, Lahitte et al. 2012) is used to find the best approximate pre-erosional shape of the volcano,  making it possible to compute its erupted and eroded volumes, and dismantling and degradation rates.

In this contribution, we illustrate how the EVoLvE toolkit can be used to systematically document the morphometry of stratovolcanoes across volcanic arcs, and with contrasted ages to highlight morphological evolution through time. The toolkit can as well be used to compare the morphometry of natural volcanoes with those of synthetic volcanic cones whose erosion is simulated through analogue experiments and numerical landscape evolution models. The Matlab codes of the EVoLvE toolkit are open-source: they aim to contribute to homogenizing the morphometric datasets for volcanoes around the world as a first step towards a more comprehensive understanding of the morphological evolution of volcanoes.

References:

Grosse, P., van Wyk de Vries, B., Euillades, P. A., Kervyn, M. & Petrinovic, I. A. 2012: Systematic morphometric characterization of volcanic edifices using digital elevation models. Geomorphology 136, 114-131.

Lahitte, P., Samper, A. & Quidelleur, X. 2012: DEM-based reconstruction of southern Basse-Terre volcanoes (Guadeloupe archipelago, FWI): Contribution to the Lesser Antilles Arc construction rates and magma production. Geomorphology, 136, 148-164.

How to cite: Kervyn, M., van Wees, R. M. J., Grosse, P., Lahitte, P., and O'hara, D.: The EVoLvE toolkit: a set of methods for systematic quantification of volcano morphometry and their temporal evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15687, https://doi.org/10.5194/egusphere-egu24-15687, 2024.

Understanding the temporal variations in erosion dynamics is crucial when exploring the intricate relationship between climates and the evolution of landforms. Volcanic surfaces constitute an undeniable asset for documenting temporal variations in erosion dynamics, as they readily reveal the onset of erosion. Indeed, the dating of volcanic materials constrains the age of eruptive activity, volcanic surface formation, and the time since erosion occurred. This study quantifies the Neogene and Quaternary erosional processes that shaped the current Lesser Antilles's volcanic reliefs. We apply morphometric approaches on high-resolution digital topographies of very densely dated volcanoes to discern the influence of factors driving erosion, focusing on climatic context and erosion duration.

The detailed analysis of the erosion signature's evolution was carried out on the French volcanic oceanic arc islands of Basse-Terre (Guadeloupe) and Martinique, thanks to the large number of geochronological constraints (around 100 K-Ar datings on each of them) and the high-resolution topography (LIDAR DEM at horizontal 1m resolution). The meticulous examination of erosion signatures is facilitated because magmatic activity, which produced the same kind of volcanic edifices in both islands, has undergone a spatial migration (westward in Martinique, southward in Basse-Terre). It results in outcrops of terrains spanning vastly different ages (0-3 and 0-25 Ma, respectively), providing a unique opportunity to investigate the distinct influences of geological processes on erosion signature. The study focuses on quantitative analysis of river-long profiles by scaling river profile concavity, hypsometric indexes and knickpoints, which are noticeable slope breaks or abrupt changes in the gradient of the river channel. Thanks to the dense geochronological database, metrics computed for each geomorphological feature can be associated with the age of formation of the local volcanic surface. Then, as these ages are relevant to the cumulated erosion process occurring since the end of the volcanic activity, such metrics can be correlated to the time and evolution trends in morphometric parameters can be investigated.

The 25 Ma-long erosion history of Martinique Island reveals two distinct patterns. During the initial 5 million years of erosion, there is a rapid increase in river concavities and a decrease in the intensity and number of heterogeneities along river profiles, resulting in smoother stream patterns. In contrast, over the 5-25 Ma erosion period, every river's morphometric parameters evolve slowly, suggesting a preservation of river concavity. This transition phase in concavity evolution could mark the moment when the rivers’ incision, driven by regressive erosion and carving into the volcano from every side, having finally affected the summit area, also reached a maximum concavity. Erosive processes then reduced the volcano's elevation but maintained a relatively uniform profile shape and, consequently, concavity over time. Despite Basse-Terre Island's shorter erosion history of 3 million years, morphometric parameters testify that this island experienced strictly similar evolution as Martinique Island during the same erosion lifespan, suggesting a comparable evolution of the Basse-Terre reliefs in the future.

How to cite: Lahitte, P., Bergerot, L., Grosse, P., van Wees, R. M. J., O’Hara, D., and Kervyn, M.: Dynamism of the Neogene and Quaternary erosional processes in the Lesser Antilles volcanoes, constrained by morphometric approaches, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15825, https://doi.org/10.5194/egusphere-egu24-15825, 2024.

The Cascadia Subduction Zone is characterized by young subducting lithosphere, its isolation from other subducting systems, and its ability to produce megathrust earthquakes (M>9.0) and devastating tsunamis. Due to its high potential hazard and risk, it is also a well-studied subduction zone where modern, diverse and detailed observational datasets are available through the USGS and initiatives like GeoPrisms and EarthScope. These datasets include high quality GPS, onshore and offshore geophysical imaging, geochemical and seismic anisotropy data. Integrating these data sets with geodynamic modeling presents an opportunity to gain insight into outstanding questions regarding slab structure, tectonic evolution, seismic hazards, and the physical processes that can self-consistently explain all these observations. For example, geologic and geophysical data suggest that there may be one or two prominent slab gaps or tears, while tomographic data does not fully constrain the depth extent of the slab. Furthermore, the overriding plate is composed of different terranes and contains numerous active and slowly moving faults, complicating efforts to accurately constrain variations in present-day stress and deformation rates.

In this study we test whether comparison of observations to geodynamic model predictions can distinguish between different slab geometries for the Cascadia Subduction Zone. To this end, we have created regional 3D geodynamic models of Cascadia including the slab based on the Slab 2.0 dataset. The model setup is built with the Geodynamic World Builder, and the models are run with the geodynamics code ASPECT. We present results which compare the Juan de Fuca plate velocities against the present day Euler poles. We have found that matching the plate velocity magnitude and direction is sensitive to the rheological model overall, while at the same time being insensitive to certain aspects of the plate boundary rheologies. During the evolution of these models we track the development of the CPO (Crystal Preferred Orientation) with an implementation of the DREX algorithm, so we can compare it against observations of seismic anisotropy in the region. Our presentation will focus on the importance of the geometry of the slab and the strength of different sections of the interface. Furthermore, these models and demonstrate workflows for linking the model results to surface tectonics.

How to cite: Fraters, M., Billen, M., Naliboff, J., Staisch, L., and Watt, J.: Exploring the structure of the Cascadia Subduction Zone by coupling 3D thermomechanical modeling and CPO evolution with observations., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16531, https://doi.org/10.5194/egusphere-egu24-16531, 2024.

Tectonic processes shape the Earth's lithosphere and surface. Deformation, as a result of tectonic forcings, arises mainly in the regions of plate boundaries. A recurring process is the subduction of oceanic lithosphere, which is widely regarded as the main driver of plate tectonics and the recycling of surface material into the mantle. In geodynamic models, the breaking of the strong crust is facilitated by processes that mimic plastic deformation. Most efforts to include plate tectonics self-consistently into mantle convection models, combine Newtonian diffusion creep with a stress-dependent pseudo-plastic rheology, given in the form of a yield criterion. Studies from seismology and geodynamic modelling indicate that cold lithospheric crust can reach the lowermost mantle regions, even the core-mantle-boundary. Additionally, the agglomeration of continental lithosphere (the most extreme variants of which are called supercontinents) inhibits the escape of heat over large surface areas, resulting in an abnormally heated mantle beneath. Therefore, it can be argued, that surface processes exert control on mantle dynamics as a whole, by introducing thermal and compositional heterogeneities.

An example of the influence of surface tectonics on the interior can be found in the study of the Earth's geodynamo. Theoretical considerations and numerical models indicate, that the heat flux at the core-mantle boundary partly governs the variability of the geodynamo, and therefore the frequency of geomagnetic reversals and excursions. 

We run several numerical mantle convection simulations in a 2D-spherical annulus geometry, with a visco-plastic rheology to facilitate surface mobilisation. The models are evaluated with respect to well-known diagnostic values, used to recognise plate-like surface deformation, as well as the thermal structure of the lower mantle. In this, we aim to connect tectonic regimes or continental configurations that arise dynamically at the surface, to evolutionary trends in the mantles thermal structure.

How to cite: Henke-Seemann, O. and Noack, L.: Surface regimes can provide an inherent perspective into interior dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17475, https://doi.org/10.5194/egusphere-egu24-17475, 2024.

The topography of the Iberian Meseta located between the Pyrenees-Cantabrian Mountains and the Betics Chain is moderately high (660 m on average) compared to the high plateaus on Earth (> 1 km) albeit higher than the topography of the surrounding western European plate. The Iberian Meseta encompasses Cenozoic sedimentary basins, active or inactive Alpine mountain ranges, and low-relief erosional surfaces represented by plateaus with elevations between 600 and 1400 m asl. It is commonly accepted that ~600-700 m surface uplift occurred during the Cenozoic, but the underlaying processes and the precise timing of the onset of the plateau growth are strongly debated. The main objective of the present study is to find out to what extent the topography of the Iberian Meseta has a crustal, lithospheric or a sublithospheric origin. We used the results of a recent modelling based on the joint inversion of both the crustal and lithospheric mantle structure. It encompasses an integrated geophysical-lithological multi-data modelling. The inversion is framed within an integrated geophysical-petrological setting where mantle seismic velocities and densities are computed as a function of temperature and composition whereas crustal density, shear and compressional wave velocities are lithologically linked based on empirical relationships from global petrophysical databases.

We computed the relative contribution to topography of crustal and lithospheric mantle thickness variations and density structure. The topography of the Alpine mountain belts in Iberia is largely associated with thickened crust. We find that the elevated topography in the NW Iberian Meseta (elevation > 700 m) is mostly related to the lithospheric mantle thinning. This is in agreement with Inversion of topographic data, landform dates, and erosion rates suggesting a late Cenozoic mantle-related surface uplift of several hundreds of meters in NW Iberia (EGU24-11613) and in the central Iberia (EGU24-16382). Similarly, a thin and warm lithospheric mantle is responsible for the positive elevation of the onshore Mediterranean margins. A negatively buoyant lithospheric mantle causes >1 km subsidence in the Gibraltar Arc and western Pyrenees.  We solved the Stokes flow to evaluate the contribution of temperature-related buoyancy forces at asthenospheric depths. These forces cause a long wavelength topographic response located in the centre of the Iberian Peninsula reaching a maximum value of only 100-150 m, which is much lower than the values reported in previous works assuming an isostatic balance.

How to cite: Negredo, A. M., Fullea, J., Ortega-Gelabert, O., Clemente, C., and Babault, J.: On the different contributions to the peculiar topography of the Iberian Peninsula, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18172, https://doi.org/10.5194/egusphere-egu24-18172, 2024.

Lava tubes are an important transport mechanism in active lava flows. Their presence in a lava flow can influence its distance of emplacement due to the insulation of the hot molten lava by a cooled overlying crust. Understanding mechanisms of formation and development of lava tubes is fundamental to comprehend lava flow propagation and improve knowledge to better manage the hazard during a volcanic crisis. Vesuvius is known for its major explosive eruptions; however, in its history it underwent extensive periods of open conduit, with prolonged explosive activity and lava flows. After the 1631 eruption, Vesuvius entered an effusive period that ended with the 1944 eruption. During these 313 years, over one hundred lava flows emplaced on Vesuvius flanks, particularly the 1858 eruption which produced a compound pahoehoe lava flow that emplaced on the western flank of Vesuvius. 

In this study, we conducted: (1) a temporal and spatial reconstruction of the 1858 lava flow using historical documents (geological maps, paintings, descriptions of eruptions), (2) a morphological and surficial analysis of the 1858 lava flow as well as the definition of new contours based on geological maps and digital elevation models and (3) a complete morphological analysis of the lava tube using high-end technologies (time-of-flight terrestrial laser scanner, Lidar equipped drone and optical cameras).  

On the 1858 lava flow field surface we found numerous tumuli and ephemeral vents. We discovered a small lava tube present in a flat area of the lava flow field (<3°) with ropy to slabby pahoehoe surface lavas. The lava tube is oriented north-south, perpendicular to the main flow direction. It is triangularly shaped with a length of 30.05 meters and a width that varies from 1.20 to 17.61 meters from the northern to the southern part. The average height is around 2 meters. The slope along the flow direction is on average 4.48°. We measured a mean roof thickness of 2.4 meters. The roof is fractured and has collapsed in different areas of the lava tube. Inside, we observed features that relate to the temporal evolution of the lava tube. Stalactites are present on the ceiling of the tube suggesting a prolonged flow of lava within the tube. Multiple layers of lava are covering the wall of the lava tube, the last wall lining is five to seven centimeters thick and, in some areas of the lava tube, has detached from the wall and rolled down on itself, testifying to a sudden drainage of the lava tube when the lining was still plastic.  

The results of the study of the 1858 lava flow field and of its lava tube are essential for expanding our knowledge about the processes at the basis of lava flow field emplacement and development on Vesuvius and the first attempt focused on understanding effusive dynamics governed by lava tube formation (i.e., lava emplacement) at Vesuvius.

How to cite: Lemaire, T., Morgavi, D., Petrosino, P., Calvari, S., Repola, L., Esposito, L., Di Martire, D., and Morra, V.: Lava tubes formation and extensive flow field development during the 1858 eruption of Mount Vesuvius. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18291, https://doi.org/10.5194/egusphere-egu24-18291, 2024.

Gondwana Basins of eastern India preserves sediment record from Carboniferous to Triassic, which were possibly sourced partially from Antarctica through a radial drainage system. This study attempts to test the hypothesis regarding source of sediments based on petrographical and mineral chemical analysis of siliciclastic Paleo-Mesozoic sediments of eastern India. We present an integrated provenance and paleodrainage analysis on the sediments of Bokaro and Raniganj basins, outcrops of which occur along E-W trend along eastern part of India. The sedimentation in these Gondwana basins initiates with basal Talchir Formation, consisting of alternation between conglomerate and fine- to medium-grained sandstones, and is succeeded by Barakar-Barren Measures-Raniganj and Panchet Formation with sandstone-mudstone alternation, with or without coal.  Petrographic study of sandstones reveals moderate sorting, with angular to sub-rounded quartz and feldspar and rounded to well-rounded lithic fragments; however, the abundance of lithic fragments drastically reduces from Talchir to Panchet formation. Feldspar grains shows the dominance of K-feldspar over plagioclase.  Most of the sandstones are classified as feldspatho-quartzose arenite. The Qm-F-Lt plot indicates that these sandstones were derived primarily from transitional continental sources. Heavy minerals in sandstones include garnets, tourmaline, epidote, rutile, zircon, monazite in order of decreasing abundance. Mineral chemistry of garnet in sandstones points their source to metasedimentary amphibolite facies rocks and granitoid. The tourmaline mineral chemistry suggests the derivation of sediments from various sources, including Li-poor granitoids associated with pegmatites, aplites and Ca-poor metapelites. Rutile chemistry in sandstones indicates the predominance of metapelitic source over metamafic source. Insights from heavy mineral analysis indicates that the Gondwana sediments were derived from multiple sources, and such variation in sources bears information about paleogeographic and paleotectonic evolution of the depositional basin.  The mineral composition of source rocks and paleocurrent data tracks the source of sediments to Eastern Granulite-Schist belt and the Eastern Ghat mobile belt, situated to the east and southwest parts of the Gondwana succession.  This study when integrated with geochronological data would reveal the extent to which a particular source provided sediments to these basins, evolution of sediment sources from bottom to top and ultimately will lead to a refined understanding of timing and evolution of East Gondwana assembly.

How to cite: Dutta, A. and Banerjee, S.: Facies Analysis, Petrography, heavy mineral analysis of paleo-Mesozoic sediments of Eastern India: Implications on provenance and basin evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18433, https://doi.org/10.5194/egusphere-egu24-18433, 2024.

The East Africa - Arabia topographic swell is an anomalously high-elevation region of ~4000 km long (from southern Ethiopia to Jordan) and ~1500 km wide (from Egypt to Saudi Arabia) extent. The swell is dissected by the Main Ethiopian, Red Sea, and Gulf of Aden rifts, and characterized by widespread basaltic volcanic deposits emplaced from the Eocene to the present. Although most agree that mantle plumes play a role in generating the swell, several issues including the number and locations of plumes and the uplift signatures remain debated. We seek to address these questions and provide a general evolutionary model of the region. To this end, we conduct a quantitative analysis of topography to infer isostatic and dynamic contributions. When interpreted jointly with geological data including volcanic deposits, the constraints imply causation by a single process which shaped the past and present topography of the study area: the upwelling of the Afar superplume. Once hot mantle material reached the base of the lithosphere below the Horn of Africa during the Late Eocene, the plume flowed laterally toward the Levant area guided by pre-existing discontinuities in the Early Miocene. Plume material reached the Anatolian Plateau in the Late Miocene after slab break-off and the consequent formation of a slab window. During plume material advance, buoyancy forces led to the formation of the topographic swell and tilting of the Arabia Peninsula. The persistence of mantle support beneath the study area for tens of million years also affected the formation and evolution of the Nile and Euphrates-Tigris fluvial networks. Subsequently, surface processes, tectonics, and volcanism partly modified the initial topography and shaped the present-day landscape.

How to cite: Sembroni, A., Faccenna, C., Becker, T. W., and Molin, P.: The uplift of East Africa-Arabia swell: the signature of the mantle upwelling and spreading, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18733, https://doi.org/10.5194/egusphere-egu24-18733, 2024.

Silicic ignimbrite volcanism played a major role in the Miocene evolution of the Central Paratethys. The most voluminuous ignimbrites identified to date (18.1–14.4 Ma) were emplaced in various paleoenvironments in the North Pannonian Basin, thus they are extremely helpful in regional stratigraphy. Here, we present the discovery of a previously unknown but widespread, youngest member of the “Upper Rhyolite Tuff“, referred to as Dobi Ignimbrite, which shows a distinctive glass geochemistry. High-precision sanidine and plagioclase Ar-Ar dating yielded 13.066±0.019 Ma (earliest Sarmatian stage in Paratethys chronology), significantly shifting the previously claimed termination (i.e. Badenian) of the North Pannonian ignimbrite flare-up. In addition, we demonstrate that, although the Dobi Ignimbrite is underlain by a marine sedimentary succession, it was emplaced on land, as it bears leaves and tree trunk fragments and is rich in charcoal. Despite the highly faulted terrain as well as intense dissection and erosion controlled by the neotectonic evolution of the Pannonian Basin, the observed areal extent (c. 1000 km²) and calculated minimum volume (c. 50 km³) of the ignimbrite may represent a VEI= 6 or 7 eruption, which needs to be further delineated. At the same time, the ignimbrite has a strongly phreatomagmatic character, suggesting an abundant, possibly shallow sea- or residual lake water source that was likely limited to the vent area (e.g. caldera graben). The detected sharp environmental change from submarine to terrestrial, as defined by the timing of ignimbrite emplacement at c. 13 Ma, marks the latest Badenian regressive period, followed by a Sarmatian erosion during the Central Paratethethys evolution.

How to cite: Biró, T., Lahitte, P., Portnyagin, M., Márton, E., Mohr, E., Palotai, M., Józsa, S., Iván, L., Krasznai, M., Hencz, M., Paquette, J.-L., Hír, J., Vörös, F., and Karátson, D.: A newly discovered youngermost (13.07 Ma) “Upper Tuff”, a large-volume phreatomagmatic ignimbrite in the Pannonian Basin, drapes the present, faulted/dissected topography , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20357, https://doi.org/10.5194/egusphere-egu24-20357, 2024.

Four monogenetic volcanoes were formed during the last 100 ka (Late Pleistocene), west of the city of Morelia (Mexico), in the central-eastern part of the Michoacán-Guanajuato Volcanic Field, located in the central region of the Trans-Mexican Volcanic Belt. These include four scoria cones (Melón, Mina, Tzinzimacato Grande, and Tzinzimacato Chico) and some lava flow deposits associated with the material emitted during the effusive phase of the volcanoes. From the study of stratigraphic relationships in the field and geological mapping, the eruptive chronology of the monogenetic volcanoes was determined. Subsequently, based on the analysis of the morphological (flow dimensions) and petrographic characteristics, the eruptive parameters (effusion rate and emplacement time) and the rheology of the lavas were estimated. The flow units of the effusive phase of the volcanoes present different morphological and mineralogical characteristics. The flows with greater slopes have average viscosities of 2.7x10⁸ P and a higher volume content of phenocrysts; the value of this property decreases in the flows with lower slopes, 1.7x10⁸ P as respectively. The results indicate that the most voluminous eruption corresponds to that emitted by the Mina volcano, with an effusion rate of 2.3 m³/s and a total duration of 239 days. The Tzinzimacato Chico volcano emitted a smaller volume of lava during its eruption, with an effusion rate of 0.9 m³/s and a total duration of 117 days, which is considered the most recent.

How to cite: Delgado Granados, H. and Hernández Villamizar, D.: Eruptive parameters of volcanoes Melón, Mina, Tzinzimacato Grande, Tzinzimacato Chico (Mexico) from morphology and petrographic studies , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20487, https://doi.org/10.5194/egusphere-egu24-20487, 2024.

During the 2021 eruption on La Palma Island, the predominant volcanic hazard was lava flows, while tephra fall and gas emission were significant concerns. Consequently, monitoring the expansion of the lava flow perimeter considering the variations in volcanic activity became fundamental. The interaction of lava with the sea water was also a major concern for emergency managers due to its associated hazards like gas emission and explosive activity due to interaction lava-water, leading to a specific focus on the formation and development of lava deltas.

Almost 10 days after the beginning of the eruption, the lava reached the sea, forming a main structure (south delta) that grew in different phases until nearly the end of the eruption, covering an area of approximately 83 ha. The south delta encroached upon the sea and additionally buried the northern part of a pre-existing lava delta from the 1949 San Juan eruption. About 1300 m from the northernmost tip of the south delta, a new lava flow entry to the sea occurred 64 days into the eruption, feeding a second lava delta (north delta) of about 5 ha over a 4-day period.

This study has made significant technical and scientific contributions, not only during the emergency but also in preparation for future recovery efforts on La Palma. Remotely Pilot Aircrafts (RPAs) provided valuable information about the lava-flow development and enhanced a deeper understanding of the formation and evolution of lava deltas and their potential hazards. Moreover, the study highlights the potential impact on new inhabited or economically exploited areas and is imperative its preservation for the geological heritage, including marine zones. Furthermore, it will play a crucial role in forecasting the behaviour of lava deltas and in the development of mitigation measures for potential future eruptions.

How to cite: Sáez-Gabarrón, L., Sanz-Mangas, D., Galindo-Jiménez, I., Vegas, J., García-Davalillo, J. C., Hernández, M., Pérez-López, R., Camuñas, C., Lozano, G., Lorenzo Carnicero, C., Rodríguez-Pascua, M. Á., Perucha, M. Á., López Gutiérrez, J., and Sánchez, N.: Evolution and Growth of Lava Deltas: Insights from the 2021 La Palma Eruption (Canary Islands), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21095, https://doi.org/10.5194/egusphere-egu24-21095, 2024.

Recent advances in computational capabilities make it possible to compute global geodynamic earth models at near earthlike convective vigor. This paves the way to systematically obtain a range of synthetic data from such models in an approach that is known as closed loop experiments. Here we present results from closed loop experiments in geodynamic earth models targeted at three classes of data that are sensitive to the mantle convection process, namely seismic data, global stress patterns as reflected by the world stress map, and continent scale stratigraphy processed for the distribution of conformable and unconformable successions in recently developed so called hiatus maps. Our results reveal effects from spatially variable data collection and quality (as expected), mantle flow geometries (less expected) and (still poorly known) histories of paleo mantle flow. We conclude that the derivation of process based synthetic data from geodynamic earth models provides crucial information for data interpretion, that closed loop experiments are
a powerful tool to link geodynamic earth models to data, and that closed loop experiments could be helpful to guide future data collection efforts.

How to cite: Bunge, H.-P., Stotz, I. L., Hayek, N., vilacis, B., brown, H., freissler, R., schuberth, B., carena, S., and friedrich, A.: Closed loop experiments in global geodynamic earth models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21895, https://doi.org/10.5194/egusphere-egu24-21895, 2024.

Continental intraplate volcanic systems, with their location far from plate tectonic boundaries, are not well understood: the crustal and lithospheric mantle structure of these systems remain enigmatic and there is no consensus on the mechanisms that cause melt generation and ascent. The Cenozoic saw the development of numerous volcanic provinces on the African plate. This includes the Hoggar volcanic province, located in Northwest Africa, part of the Tuareg shield. It is composed of several massifs with contrasting ages and eruptive styles. The magmatic activity began at around 34 Ma and continued throughout the Neogene-Quaternary. Phonolite and trachyte domes as well as scoria cones and necks are found in the Manzaz and Atakor volcanic districts. In order to image the crustal and lithospheric mantle structure of this region, and to understand the origins and potential mechanisms of the continental intraplate volcanic activity in the Central Hoggar and specifically the Atakor/Manzaz area, we acquired magnetotelluric (MT) measurements from 40 locations and generated a 3-D electrical resistivity model. The model covers an area of about 100 km by 200 km. Images of the subsurface architecture, in terms of electrical resistivity, from the near-surface to the lithospheric mantle, allow us image the deep plumbing system of the volcanic system. Low resistivity features (i.e., conductors) in the crust that are narrow, linear structures trending approximately north-south, are revealed along the two boundaries of the Azrou N’Fad terrane, in the Manzaz area. They likely reflect the Pan-African mega-shear zones, which were reactivated throughout the tectonic evolution of the region. The model reveals that these faults are lithospheric-scale. In addition, the low-resistivity features likely represent the signatures of past fluid flow. The location of the recent Cenozoic volcanic activity was likely influenced by the pre-existing structure. A deep feature of moderate conductivity is located in the upper lithospheric mantle directly beneath the Manzaz and Atakor Volcanic Districts. It may represent the origin of the overlying anomalies and may suggest metasomatism of the sub-continental lithospheric mantle.

Keywords:  intraplate, Hoggar, alkaline volcanism, magnetotelluric, electrical resistivity.

How to cite: Boukhalfa, Z., J. Comeau, M., Benhallou, A., Bouzid, A., and Bendaoud, A.: Deep plumbing model of the Cenozoic Manzaz / Atakor intraplate volcanic system, Central Hoggar, Northwest Africa, based on electrical resistivity models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-473, https://doi.org/10.5194/egusphere-egu24-473, 2024.

Large Igneous Provinces are defined as magmatic provinces with large magma volumes (> 100,000 km³) emplaced and/or erupted in an intraplate tectonic setting over a vast area within a few Myr, thus having the potential for significant impact on the global climate. The High Arctic Large Igneous Province (HALIP) was emplaced during the Cretaceous. The available ages, ranging between ~140 and 80 Ma, suggests that the magmatism was apparently long-lived and multi-phase. Extrusive and intrusive remnants of the HALIP can be found across the circum-Arctic, specifically in Arctic Canada, Russia, Svalbard, Northern Greenland, and the Arctic Ocean. On Svalbard, the HALIP magmatism is regionally called the Diabasodden Suite. Here, the dolerites have mainly been emplaced as sills at shallow depths and occur all over the archipelago. Despite the relative accessibility of outcrops, the HALIP on Svalbard has been mostly unexplored. As such, available U-Pb geochronology of the Diabasodden Suite is limited, but indicates a shorter time span of 125 – 122 Ma.

Yearly field campaigns since 2020 have resulted in over 150 collected samples from Spitsbergen and Nordaustlandet. This has been accomplished through a collaborative effort, and by strategically targeting outcrops to build a good representative dataset of the Diabasodden Suite. Additionally, a large number of samples have also been taken for a detailed case-study in central Spitsbergen. The dolerite samples are used for whole-rock major and trace element geochemical analysis, U-Pb baddeleyite geochronology and petrological studies. Furthermore, during all field campaigns, high-resolution drone images have also been acquired. These data form the basis for digital outcrop models (DOMs), which are used for thickness measurements of the sills and to put the geochemical data into a 3D perspective. The resulting DOMs are made openly available through the geoscientific database of Svalbard, SvalBox.

Here we present a review of the available geochronology of the HALIP in the circum-Arctic, as well as new data from Svalbard. Specifically, new U-Pb baddeleyite ages of one mafic sill in northern Isfjorden, and an extensive dataset of whole-rock geochemical data from the HALIP on Svalbard to better understand the magmatic history of the HALIP as a whole.

How to cite: Sartell, A. M. R., Beier, C., Söderlund, U., Senger, K., Shephard, G. E., Jørgen-Kjøll, H., and Galland, O.: Geochemistry and geochronology of the High Arctic Large Igneous Province on Svalbard, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1021, https://doi.org/10.5194/egusphere-egu24-1021, 2024.

The origin of intraplate magmatism is debated, with two main hypotheses having been proposed. These are deep-seated high-temperature sources (plumes), and  intraplate extension driven ultimately by plate tectonics. A test region in this debate is the 'Jurassic Corridor,' a geological feature proposed to span North America, which contains igneous rocks including kimberlites that are attributed to the Great Meteor Hotspot (GMH). Despite longstanding assumption of this model, close inspection using modern, much-expanded geological information sets shows that the existence of a Jurassic Corridor and GMH lacks support. In this paper we reassess the distribution of kimberlites in North America and on neighboring landmasses. We demonstrate the lack of a clear Jurassic Corridor and show instead that the kimberlites and related rocks are more likely linked to the breakup of the Pangaean Supercontinent and controlled by lithospheric structures. Furthermore, by comparing these findings with global plate models for the last 300 Myr we identify three prominent age peaks in North American kimberlite occurrence that broadly align with periods of heightened plate velocity with respect to Africa. Additionally, the analysis reveals in Africa two peaks in kimberlite abundance and two velocity peaks with respect to North America. Here, however, the velocity peaks occurred approximately 20-30 Myr before the kimberlite abundance peaks. These observations underscore the significance of plate kinematics in controlling kimberlite magmatism and add to a growing body of work linking periods of tectonic upheaval to kimberlite production. The implications of this extend to our broader understanding of intraplate magmatism and warrant a global revaluation of similar phenomena.

How to cite: Peace, A. and Foulger, G.: Beyond the Jurassic Corridor: Exploring North American Kimberlites and their relationship to plate tectonics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1799, https://doi.org/10.5194/egusphere-egu24-1799, 2024.

The Parana Basin is one of the larger continental Paleozoic basin in Central South America. Although several studies investigated the flooring mantle of the Parana Basin, mantle-scale oceanic relicts have not been interpreted by previous regional geophysical studies. For this work, we used the global-scale tomographic model of P-wave velocity perturbation UU-P07 for mapping slab-like anomalies, and qualitative gravity and magnetic anomalies for indicating orogenic trends. Positive P-wave anomalies were mapped along fifty-two profiles, and revealed slab-like anomalies (long and segmented tabular mantle bodies), and four top slab surfaces (S1, S2, S3 and S4). The biggest anomalous mantle body (top surface S1) is transversal to the central-southern Brasilia Belt trending, and therefore it can be directly linked to the Southern São Francisco craton. However, the other three slab-like tabular bodies cannot be linked to outcropping orogenic trends, due to the extensive and thick sedimentary cover of the Parana Basin. Southwestern São Francisco Craton, elongated bodies coincide with Brazilian/Pan-African island arc collisions (top surface S2), but other possible slabs (top surfaces S3 and S4) are underneath Paraná Basin. Positive anomalies in the residual geoid anomalies (XGM2019e_2159 model) and transformed total magnetic field (vertical integration) follow the possible accretionary trend formed by S2, S3 and S4. Although the assumptions about the origin of these slab-like anomalies need to be investigated further, all these observations have shown the high complexity of the upper mantle beneath Parana floods. Facing the geophysical anomalies, we realize that the mapped slab-like bodies are mostly located under the Central-Northern Parana Basin, where several studies interpreted the existence of remnants of Proterozoic subductions in the mantle. Previous geochemical analysis had linked the high-Ti domain in the Central-Northern Parana floods with the partial melting of oceanic subduction relics. Nonetheless, the abundance of other incompatible elements (e.g., P, F and B) in the early phase of Central-Northern basaltic floods can be inherited from subduction remnants in the mantle. The remarkable early enrichment contrasts with the primitive mantle affinity in tholeiitic magmas of the relative late northern floods of the Parana Basin, the southern floods of the Parana Basin, the Etendeka counterpart, and the continental margins. In agreement with the previous understanding of the chemical evolution, we consider that the early magmatic phase was highly influenced by subcontinental subduction relicts. On the other hand, the advancing lithospheric embrittlement, due to the Atlantic opening process, intensified the rise of primitive fluids. Therefore, geophysical observations support the hypothesis of the existence of oceanic remnants from oceanic closure southern São Francisco Craton, due to the Western Gondwana’s assembly. The location of highly preserved oceanic-like mantle bodies supports the occurrence of enriched magmas in the early magmatic phase of the Northern Parana-Etendeka LIP.

How to cite: Szameitat, L., Heilbron, M., Bongiolo, A., Licht, O., Aragão, M. A., and Ferreira, F.: Oceanic remnants in the mantle of the Parana Basin, Central South Atlantic: supporting the large-scale geochemical anomaly in the Northern Parana-Etendeka LIP, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3168, https://doi.org/10.5194/egusphere-egu24-3168, 2024.

Seamounts are theorized to originate from deep mantle plumes or shallow, plate-related activities. The mantle plume hypothesis suggests that abnormally hot materials rise from the lowermost mantle and produce large volumes of volcanism on the surface. However, the accuracy of morphological analysis and volume estimation is highly influenced by the representation accuracy of irregularly shaped seamounts and the extent to which thick sediment coverage obscures their bases. As a result, the precise contribution of magma from mantle plumes to surface volcanism remains unclear.

Our study introduces a novel approach using Gaussian Process Regression to reconstruct the complex topography of seamounts, both above and beneath sedimentary covers. This approach advances previous analyses by (1) taking account of irregular seamount topography and (2) correcting for the varying sediment thicknesses that obscure seamount bases. Our investigation yields two principal findings.

1. Refined Volcanism Distribution Mapping

Analysis in the Pacific Ocean indicates that only 18% of total intraplate volcanic activity is attributable to plume-related volcanism. In addition, the volume statistics of plume-related seamounts and those along the Large Low-Shear-Velocity Province margins show no significant distinction from those of other intraplate seamounts. These results suggest that proposed plumes account for only a minority of the volume of intraplate volcanism in the Pacific plate, and that shallow rather than deep processes are dominant.

Along the volcanic Kyushu-Palau Ridge, high seamount volumes are observed near lithospheric weak zones, implying that tectonic inheritance significantly influences magma distribution during volcanic arc formation.

2. Comprehensive Morphological Analysis

Employing machine learning clustering analysis on high-resolution multibeam bathymetry data, we categorize seamounts in the South China Sea basin into three distinct morphological types: Type I, large seamounts with steep slopes and rounded bases, predominantly located along extinct ridges; Type II, linear seamounts characterized by gentler slopes, situated along ridges; and Type III, smaller, elliptically-based seamounts found along transform faults or off-ridge areas. This morphological classification provides a novel quantitative framework correlating seamount shapes with their tectonic environments during volcanic activity.

Overall, this research advances our understanding of seamount genesis, highlighting the importance of shallow tectonic processes in shaping submarine volcanic landscapes.

How to cite: Zhao, Y., Riel, B., Ding, H., and Deng, D.: Understanding Seamount Genesis: Utilizing Gaussian Process Regression and Clustering for Morphological Analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4616, https://doi.org/10.5194/egusphere-egu24-4616, 2024.

Volcanic seamount chains are widespread throughout ocean basins, but their formation and structure are not well understood. Active-source refraction seismology can provide images of the interiors of these volcanoes via P wave travel time tomography, but that requires proper identification of seismic phases that are generated by and propagate across complex volcanic structures. Unfortunately, the current limitation on the number of seismic phases that can be included in tomographic analyses leads to less detailed images and a limited geological understanding of the structures being imaged. The primary objective of this study is to compare recorded seismic wavefields from recent surveys across the Hawaiian-Emperor Seamount Chain with synthetic wavefields generated through waveform modeling. We use simplified yet realistic models of volcanic edifices, the underlying oceanic crust, and the mantle to better understand observed seismic phases and their origins. In previous studies (Dunn et al., 2019; Watts et al., 2021; Xu et al., 2022; MacGregor et al., 2023), several seismic phases were identified in recorded sections along the Hawaiian-Emperor Chain. However, interpreting the origins of some of these phases remains challenging. In this study, we developed an idealized seamount model based on the seismic structure of Jimmu Guyot in the Emperor Ridge (Xu et al., 2022). We calculated the seismic P-SV wavefield for various source and receiver positions using a finite difference wavefield modeling code (Levander, 1988; Lata and Dunn, 2020). Our goal is to model the observed seismograms and identify additional phases, including P-to-S converted waves. Additionally, we aim to verify recent tomographic images of the Hawaiian-Emperor Seamount Chain created by P wave travel time inversion via wavefield comparison. By resolving ambiguities and pinpointing new seismic phases, our aim is to improve seismic images of the Hawaiian-Emperor Chain. This contribution will enhance our understanding of specific structures, such as volcanic cores (a high-density and high-wave-speed interior core of the seamount), the hypothesized magmatic underplating of the oceanic crust by mantle melts rising beneath the volcanic chain, and the nature of the Moho and upper oceanic crust beneath these volcanic edifices.

How to cite: Fujimoto, M., Dunn, R., and Xu, C.: Modeling seismic wave propagation across complex volcanic structures of the Hawaii-Emperor Ridge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6451, https://doi.org/10.5194/egusphere-egu24-6451, 2024.

Unique intraplate volcano eruptions and westward volcano migration since the Oligocene are observed in NE China, an overriding continental zone tectonically controlled by the subduction of the northwestern Pacific plate and the opening of Japan Sea. Interestingly, these intraplate magmatic events occur around a subsiding basin (the Songliao Basin), but no volcanic activities have been observed within the Songliao Basin. The geodynamic mechanism responsible for these volcanoes remains unclear. To address the geodynamic process beneath NE China, numerical experiments are conducted constrained by datasets from regional reconstruction, seismic and volcanic studies. Vertical velocity field of mantle convection and lithospheric partial melting structures yielded from our numerical model show mantle upwelling and melting center migrates from the east to the west of NE China with the westward propagation of the stagnant slab, leading to the volcano migration. Also, with the subduction retreat of NW Pacific plate and the opening of the Japan Sea, significant lithospheric thickness differences between Changbaishan-Mudanjiang Region and the Songliao Basin develop, leading to lithospheric unstable dripping. This dripping structure prevents the partial melting of the lithosphere but facilitates the subsidence of the Songliao Basin in central NE China. Moreover,  the lithospheric dripping model successfully predicts upper mantle structures consistent with the proposed tomography model, the observed Moho depth, and surface topography variations. Thus, the lithospheric dripping induced by lithospheric thickness difference and the subduction of the Pacific slab provides a robust mechanism for the unique geodynamic process in NE China.

How to cite: Lin, F., Qi, L., Zhang, N., and Guo, Z.: An ongoing lithospheric dripping process beneath Northeast China and its impact on intraplate volcanism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7314, https://doi.org/10.5194/egusphere-egu24-7314, 2024.

The Great Meteor Seamount is a guyot and the largest seamount in the North Atlantic Ocean with an estimated volume of some 24,000 km³. Located ~1280 km west of Africa and ~720 km south of the Azores, the seamount forms part of a group of seamounts which include Hyeres, Irving, Cruiser, Plato, Atlantis, and Tyro. Previous dredged rock, magnetic anomaly lineation, and predicted hotspot track studies suggest the seamount is ~17 Myr in age, was emplaced on oceanic crust and lithosphere with a thermal age of ~68 Ma and is linked to the New England Seamount Chain. However, bathymetric, free-air gravity anomaly and geochemical data are inconsistent with these ages and such a tectonic setting: bathymetric data suggest a guyot depth of ~400 m which is deeper than expected (~187 m), gravity data suggest an effective elastic thickness, T_e, of ~20 km which is lower than expected (~26 km) and geochemical data suggest a link, not to the New England Seamount Chain, but to the Azores Islands instead. To address these inconsistencies, we used legacy Ocean Bottom Hydrophone, free-air gravity anomaly and bathymetry data to reassess the seismic structure, T_e, and tectonic evolution of Great Meteor Seamount and its neighbouring seamounts. We show the uppermost crustal structure of Great Meteor Seamount is characterised by a relatively low velocity volcano-clastic sediments (2.0-4.5 km/s) and extrusive lava (5.0-6.0 km/s) drape which overlies a relatively high P-wave velocity intrusive ‘core’ of 6.0-6.5 km/s. The lowermost crust, in contrast, is characterized by a 4-km-thick body of P-wave velocity 7.00-7.75 km/s intermediate in velocity between the crust and mantle, the base of which is at depths at ~16 km. This seismic structure has been verified by gravity modelling assuming a Gardner and Nafe-Drake relationship between P-wave velocity and density, but 3-D flexure modelling reveals that a Moho depth at ~16 km requires a low elastic thickness (T_e ~10 km) which is inconsistent with the amplitude and wavelength of the free-air gravity anomaly and the relatively flat depth to the top of the oceanic crust beneath the flexural moats flanking the guyot ‘core’. We found that gravity and seismic data are consistent if the T_e of flexed oceanic crust at Great Meteor Seamount is ~20 km and is underlain by a ~4-km-thick magmatic underplated body. In contrast, we found that the Irving, Cruiser, Plato, Atlantis, and Tyro seamounts are characterised by a best fit T_e of ~10 km and no evidence of underplating. We discuss these findings here with respect to the guyot depth at Great Meteor, terrace depths at Plato, and the tectonic setting of Great Meteor and its neighbouring seamounts.

How to cite: Watts, A. and Grevemeyer, I.: Legacy seismic refraction and gravity anomaly data in the vicinity of Great Meteor Seamount and its implications for plate flexure , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11610, https://doi.org/10.5194/egusphere-egu24-11610, 2024.

Transcaucasus - the westernmost part of the southern Caucasus, represents an area where the Tethys Ocean was closed in the Late Cenozoic because of Eurasian and Africa-Arabian plate convergence. The lithosphere of the region represents a collage of Tethyan, Eurasian, and Gondwanan terranes. During the Late Proterozoic–Early Cenozoic a system of island arc and back-arc basins existed within the convergence zone. Geological and palaeogeographical data supported by paleomagnetic studies indicate the presence of several tectonic units in the regions that have distinctive geological histories.

The region comprises a 30-55 km thick continental crust with significant lateral variations in thickness of the overlying sediments (0-25 km). The travel times velocity anomalies of the P- and S-waves are interpreted as high-velocity bodies down to about 100 km depth, where the mantle lithosphere is thin or even missing.

The Mesozoic-Cenozoic magmatic assemblages reflect a diversity of paleogeographic -paleotectonic environments. They are indicative of a west Pacific-type oceanic basin setting under which the mature continental North Transcaucasian arc developed with zones of rifting and alkaline basaltic volcanism on the active margins of the oceanic domain.

Within-plate magmatic activity in the North Transcaucasus is represented by volcanic and plutonic complexes, including Late Triassic to Early Jurassic subaerial alkali basalts and alkali gabbro; the Late Bathonian-Late Jurassic high titanium alkali basalts and minor trachytes with coal-bearing shales and evaporites intercalations; Albian alkali basalts alternating with redeposited volcaniclastics and shallow marine carbonates.

The Late Cretaceous volcanics are associated with intraplate-type titanium rich alkali basalts and basanites with minor trachytes and phonolites, while the Eocene volcanics are associated with highly potassic to ultrapotassic basalts and basanites. The Late Miocene-Pleistocene volcanism is represented by alkaline basalt-trachytes as well.

The Great Caucasus, a NW–SE-directed mountain range, extends westwards along the pre-Caucasian strip of the Eastern Black Sea and is bounded to the south by the Transcaucasian Massif. The shoreline of the Eastern Black Sea Basin cuts off the Colchis intermontane trough formed over the rigid Georgian Block, the Achara–Trialeti trough and the Artvin–Bolnisi rigid block.

Onshore and offshore data confirm that the subaerial structures have immediate submarine prolongations. Deep drilling conducted within the onshore zone of the Transcaucasus, in the immediate vicinity of the shoreline, revealed that the volcanic formations below the modern sea level extend further into the Eastern Black Sea basin.

Recent data on structure and evolution of the Transcaucasus and adjacent area provide new constraints on the geological history of the lithosphere of the region, particularly on the Eastern Black Sea basin located in the collision zone between Eurasian and Africa-Arabian lithosphere plates, proximal to ancient sutures.

How to cite: Sadradze, N., Adamia, S., Cloetingh, S., Koptev, A., and Sadradze, G.: TRANSCAUCASUS: Record of 200 My plume activity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11775, https://doi.org/10.5194/egusphere-egu24-11775, 2024.

Eastern Australia and the neighbouring Tasman and Coral Seas are home to extensive age-progressive volcanism spanning from ~55 Ma in the north to ~6 Ma in the south. This volcanism forms two offshore seamount trails, the Lord Howe and the Tasmantid Chains, as well as the onshore central volcanoes and leucitites of the East Australian Chain. The three volcanic chains are an average of just 500 km apart, erupted contemporaneously from 35-6 Ma, and share a common age-distance relationship, strongly suggesting a common source, most likely a deep-origin plume. However, they have erupted through lithosphere ranging from oceanic with well-developed seafloor spreading to drowned continental fragments to mainland Australia. How do these diverse settings influence the chemical and physical properties of the resulting mafic volcanism? The East Australian Chain has more fractionated mafic samples, reflecting more complex magmatic plumbing and longer magma residence times in the thick continental lithosphere. However, the most striking result is that the trace element and isotopic ratios remain remarkably similar across the three suites, showing little evidence of crustal or lithospheric assimilation affecting the mafic magmas. 

How to cite: Kalnins, L. M., Douglas, A. K., Cohen, B. E., Fitton, J. G., and Mark, D. F.: The influence of the lithosphere on deep-origin volcanism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12578, https://doi.org/10.5194/egusphere-egu24-12578, 2024.

The western Eger Rift (Czech Republic) is a non-volcanic rift setting of intraplate seismicity that is characterized by abundant degassing of mantle-derived fluids. Since 2019, gases obtained from the free gas phase and volcanic rock samples of Quaternary age have been collected in order to determine the origin and evolution of volatiles in the system and define the magma chamber p-T conditions. Results of the CO₂-dominated gas discharges of the Bublák and Hartoušov mofette fields yield an ~93 % mantle input (considering a subcontinental lithospheric mantle) for He. Ne isotopic ratios range from 9.8 to 11.0 for ²⁰Ne/²²Ne and from 0.0282 to 0.0480 for ²¹Ne/²²Ne. Notwithstanding the samples enriched in ²⁰Ne likely due to mass fractionation, many samples show a mixed atmospheric-mantle type source for Ne. However, an additional crustal input cannot be excluded. ⁴⁰Ar/³⁶Ar ratios also cover a wide spectrum of values (between 300 and 4680). Overall, gas samples typically present a higher-than-atmospheric value with ⁴⁰Ar likely deriving from the mixing of an atmospheric and deep source. The ⁴He/⁴⁰Ar* ratio is moderately constant and falls within the MORB range, suggesting an unfractionated magma that originates from mantle sources.. Results obtained from mineral quantitative analyses and by using thermobarometry of orthopyroxene and clinopyroxene rim pairs of matrix grains yield predominantly temperature and pressure conditions of 700 ±100 °C and 1.1 ±0.5 GPa, respectively, indicating a lithospheric depth that ranges between 40 - 45 km for 1.5 GPa and 20-25km for 0.5 GPa. In addition, pairing cores of mm-sized pyroxenes point to a temperature of 1100 ±100 °C and a pressure of 2.5 ±0.5 GPa that correspond to a lithospheric depth of ~75 km. Those minerals that indicate greater depths are likely the oldest ones as they were able to grow for longer times during their ascent. On the other hand, secondary overgrowths or smaller matrix grains represent younger grains that have grown during magma evolution. Therefore, their diverse chemistry and the wide range of p-T conditions reveal rising (and cooling) of magma.

This research is a part of the “MoRe-Mofette Research” and MoCa - “Monitoring Carbon” projects, which were funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – 419880416, 461419881.

How to cite: Daskalopoulou, K., Niedermann, S., Wilke, F. D. H., Martin, M., and Woith, H.: First insights into the geochemical and petrological features of the Eger Rift’s plumbing system (Czech Republic), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12916, https://doi.org/10.5194/egusphere-egu24-12916, 2024.

The Eurasia Basin, one of two major oceanic basins of the Arctic Ocean, is composed of the Amundsen and Nansen basins, which were created due to the slow and ultra-slow seafloor spreading at the mid-oceanic Gakkel Ridge initiated during the Paleocene-Eocene transition (53-56 Ma). Since the beginning of the current millennia the Gakkel Ridge and the Eurasia Basin have been subject of marine geological and geophysical studies leading to the collection of diverse datasets including rock samples, seismic, and potential-field datasets. New marine seismic data has become available in the western Eurasia Basin in the very last years, including data acquired by the Norwegian Petroleum Directorate in the context of the UN Law of the Sea, together with seismic lines gathered by Norwegian research institutions and partners. During October-November 2022 the first High Arctic GoNorth marine expedition collected new seismic reflection and refraction, as well as gravity and magnetic datasets. It is considered that this polar region may hold important clues for the understanding of global processes such as passive margin formation, and the complex links between plate tectonics and climate. Volcanic additions have been suggested within the flanks of the Eurasia Basin during different stages in the Cenozoic. Existing hypotheses further postulate corridors of exhumed mantle formed across the western Eurasia Basin because of the magmatic segmentation imposed by the Gakkel Ridge. Consequently, the oceanic basement of this area should be prone to deformation, hydrothermal alteration and serpentinization. However, little is known about the relationships between such processes with the sedimentary units above, or whether such processes occur away from the ridge and to what extent.

The new compilation of multi-channel seismic reflection profiles provides an image of the sedimentary structure and the upper crust, within the oceanic crust and the continent-ocean transition (COT) between northern Svalbard margin and Eurasia Basin. The preliminary analysis of these datasets indicates that the sediments and basement structures within the southwestern corner of the Eurasia Basin have been modified in a unique manner due to an underlying geothermal anomaly beneath the lithosphere. This is expressed as focused late Miocene (< 20 Ma) to recent sill intrusion events resulting in basement and sediment deformation, and intense hydrothermal and sediment evacuation features. We present unique examples of hydrothermal venting on seismic reflection data and discuss implications of the post-rift NE Atlantic and Arctic setting, including the role of breakup magmatism, post-breakup intraplate volcanism, and sheared/passive margin development during the Cenozoic.

How to cite: Meza, J. C., Faleide, J. I., Minakov, A., and Gaina, C.: Intraplate magmatism, serpentinization and hydrothermal venting in the ultra-slow spreading setting of the Eurasia Basin, Arctic Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13068, https://doi.org/10.5194/egusphere-egu24-13068, 2024.

Some prior active-source seismic studies beneath oceanic seamount chains indicate a sub-crustal layer of what is considered to be underplated magmatic material. The classic example is the Hawaiian Ridge, where a seismic study in the early 1980s first proposed the existence of such a layer. Since then, Hawaii has been considered one end-member in a range of possible scenarios, extending from underplating to no underplating, but with possible magmatic intrusion into the lower oceanic crust. Magmatic underplating affects mass flux and lithospheric loading calculations. All else being equal, underplating would be expected to lower the amplitude of the gravity anomaly over the crest of the edifice and provide a positive buoyancy force that makes the plate appear more rigid than it actually is. One hypothesis put forward to explain variations in the style of magmatic emplacement at intraplate volcanoes hinges on the age of the lithosphere at the time of volcano formation. In this model, shallow intrusion into the oceanic crust and overlying edifice is favored for seamounts growing on younger lithosphere, while magmatic underplating is favored for seamounts growing on older lithosphere such as Hawaii. However, recent seismic, gravity, and plate flexure studies conducted along the Hawaiian-Emperor Seamount Chain collectively provide clear evidence for shallow magmatic emplacement and contradict the notion of significant magmatic underplating for ages at the time of loading of ~57 Ma (Emperor Seamounts) and ~90 Ma (Hawaiian Ridge). Additionally, reprocessed legacy seismic data has not revealed evidence for underplating beneath the Hawaiian Ridge. In this presentation, results from these recent studies will be shown, compared, and the evidence for a simple mantle structure without underplating will be presented along with seismic synthetic tests that explore the degree of underplating that may be 'hidden' in the data.

How to cite: Dunn, R., Fujimoto, M., Xu, C., Watts, A., Boston, B., and Shillington, D.: Seismic Silence Speaks Loud: No extensive magmatic underplating found in recent seismic studies of the Hawaiian Ridge, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13901, https://doi.org/10.5194/egusphere-egu24-13901, 2024.

Establishing the mechanisms for craton modification is critical for understanding cratonic stability and architecture. Cratons are intrinsically strong with long-term stability, but plate tectonics or mantle plumes cause craton weakening, mechanical decoupling, and lithospheric removal. By comparison, craton modification—craton destruction accompanied or followed by rejuvenation—has received less attention. Oceanic plate subduction dominantly destroys the craton, with a lesser degree of rebuilding. Mantle plumes can facilitate decratonization, by weakening and peeling off the lithospheric mantle, or recratonization, by healing the craton with refractory mantle residues. Compared with the effects of oceanic plate subduction and mantle plumes, the role of continental subduction in craton modification remains an open question. The North China Craton (NCC), a previously stable continent with a lithospheric thickness of >200 km since the Paleoproterozoic, was reworked and partially destroyed due to lithospheric delamination triggered by Early Cretaceous Paleo-Pacific oceanic subduction. In eastern NCC, lithospheric thickness decreased from 200 km to 35 km in the Early Cretaceous in only 10 m.y. The NCC experienced an early Mesozoic continent–continent collision (as the overriding plate) with the South China Block (SCB). The collision provides an opportunity to understand the potential for craton modification due to deep continental subduction induced by continental collision.

In the NCC, combined structural geology, magnetic fabrics, zircon U-Pb dating, and Hf-O isotopes, we report the presence of martial derived from a partially melted SCB’s crust. We proposed a three-stage model to interpret the material sourced from the subducted plate into the overriding carton: (1) SCB bulldozed and rebuilt NCC during 250–220 Ma; (2) during 220-200 Ma, the subducted SCB exhumed along the exhumation channel to underplate beneath the NCC, associated with partial melting; (3) finally, Late Jurassic granite derived partial melting of the SCB entrained Latest Triassic reworked SCB’s crust to emplace.

Combining our new results with previous geophysical observations, we estimate the extent of the bulldozing and rebuilding. We argue that a 200-km-long tract of the NCC lithosphere was bulldozed and rebuilt by the subducted SCB, resulting in a lithospheric suture far from the suture zone at the surface. This lithospheric removal occurred at middle-lower crustal levels (16–20 km depth)—much shallower than previously thought possible. The bulldozed NCC lithosphere was replenished by the subducted SCB continental lithosphere rather than the asthenosphere, thus terminating the lithosphere modification. With essentially no net loss of lithosphere during deep continental subduction, the NCC maintained its stability until Early Cretaceous paleo-Pacific oceanic subduction. This “bulldoze and rebuild” model can thus account for how a craton maintains its stability during a collision with another continental plate.

How to cite: Meng, L., Yang, C., Lin, W., Mitchell, R. N., and Zhao, L.: Bulldoze and rebuild: Modifying cratonic lithosphere via removal and replacement induced by continental subduction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13934, https://doi.org/10.5194/egusphere-egu24-13934, 2024.

Mesozoic intraplate igneous activity is abundant on the Canadian shield and includes multiple kimberlite fields, a province of alkaline magmatism, and individual bodies of kimberlites and ultramafic lamprophyres. Models have variously attributed the emplacement of these intrusions to the influence of Farallon plate subduction, opening of the Atlantic Ocean, or one or several Atlantic hotspots which North American plate is postulated to have drifted over during the Mesozoic. The latter hypothesis relies of the attribution of spatially, temporally and compositionally distributed and diverse magmatic rocks into a poorly defined, age-progressive, ‘corridor’ which may be derived from a common geochemical reservoir. In this study, we aim to test the spatiotemporal association between intraplate igneous activity along this postulated Triassic-Jurassic corridor and several elements of fixed mantle reference frame, such as the Atlantic hotspots and the hypothesised plume-generating zone (PGZ) of the African Large Low Shear Velocity province (LLSVP).

We use published geochronological databases containing locations and isotopic ages of the Mesozoic intrusions of North America and published global plate reconstructions to dynamically calculate distances between the loci of intraplate magmatism and features of the upper and lower mantle assuming the latter remained fixed in the mantle reference frame throughout their history. We use GPlates 2.3.0 software package and pygplates 0.36.0 Python library to build the reconstructions and implement our calculations.

Results demonstrate that none of the examined mantle features show a consistent association with all instances of intraplate magmatism across the Canadian shield during the Triassic-Jurassic. The coeval kimberlitic magmatism in the western Slave province (Jericho kimberlite field) and Baffin Island (Chidliak kimberlite field) appears to be completely spatially unrelated to any of the examined mantle features. The kimberlite fields of the Superior province (Attawapiskat, Kirkland Lake, Timiskaming) experience emplacements long before and after their passage over the PGZ, but their frequency increases in the PGZ’s vicinity, i.e. 76% of emplacement events in these provinces occur within 200 km of the PGZ’s surface projection.

Our results show that intraplate magmatism across many Triassic-Jurassic fields of North America could be initiated independently of the influence of deep mantle structures. Thereby, a geodynamic mechanism nested in the asthenosphere or lithospheric mantle suffices for melt generation in an intraplate setting. However, it cannot be ruled out whether proximity to deep mantle structures is capable of facilitating “shallow” melt generation and emplacement and that deep-seated mantle structures could provide an influx of fluids or thermal energy, increasing melting intensity and volume.

How to cite: Koptev, E. and Peace, A.: The Triassic-Jurassic corridor of North America: are deep mantle structures a sufficient explanation for intracontinental magmatism?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14228, https://doi.org/10.5194/egusphere-egu24-14228, 2024.

Intraplate volcanism signifies persistent magmatic activity within plate interiors far from active plate boundaries. However, due to limited assessment of the detailed physical conditions of the intraplate upper mantle, the fundamental mechanism behind the genesis of mantle magma remains poorly understood. We analyzed the temperature conditions of the upper mantle beneath global intraplate volcanic regions estimated from seismic velocity and geochemical data. We revealed that excluding volcanoes near major plumes, large proportions (> 70%) of the volcanoes are situated above the upper mantle with moderate temperatures comparable to or colder than those found at mid-oceanic ridges (potential temperature (Tp) ~1250–1350°C). These volcanoes also overlie regions of low vertical and horizontal asthenospheric shear estimated by global mantle convection simulations. Without peculiarities in thermal and large-scale mantle dynamics, we inferred that these volcanic activities are likely driven by a small-scale local convective process confined to the shallow upper mantle. To constrain a more detailed process of intraplate volcanism, we focus on analyzing the upper mantle rheology and melt distribution beneath intraplate volcanoes in NE Asia. Thermodynamic properties, conservatively constrained by high-frequency seismic attenuation and velocities, revealed the common presence of low-viscosity zones concentrated beneath the volcanoes at shallow asthenospheric depths (< 200 km). These regions contain a small fraction of melt (~0.05–0.8%) at cold-to-moderate temperatures (Tp ~1300–1350°C) compared to the average mantle aligning with global analyses. A series of evidence potentially suggests the existence of localized mantle upflux focused beneath intraplate volcanoes. Considering the amount and extent of the estimated mantle melts and numerical mantle convection simulations with lithospheric structures, we propose that undulations in the lithosphere and asthenosphere boundary could play a primary role in controlling the small-scale mantle convection and the location of intraplate mantle melting. Our estimation supports the possibility of the ubiquitous occurrence of intraplate volcanoes independent of dynamic forces for deriving active mantle upwellings (e.g., thermal or chemical buoyancy).

How to cite: Song, J.-H., Kim, S., Rhie, J., and Kang, T.-S.: Intraplate Volcanism by Spontaneous Shallow Upper Mantle Melt Focusing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14365, https://doi.org/10.5194/egusphere-egu24-14365, 2024.

A volcanic edifice much larger than the current one must have existed in Santiago Island, Cape Verde, because the granular rocks and dyke-in-dyke complex representing magma chambers and deep feeders currently outcrop up to 700 m altitude. Therefore, we must find an explanation for the massive destruction of the original edifice. We developed a new tool for the quantitative reconstruction of ancient topographies in a volcanic ocean island to address this problem, because it allows us to estimate the shape and volume of volcanic rock removed at a certain time. The reconstruction of the topography of the basement complex at ca. 6 Ma ago, before the unconformable deposition of the submarine complex, shows a concave depression coincident with the asymmetric distribution of volcanic complexes east and west of the main divide of the island. This concave depression is here interpreted as the remnant of an island-scale, summit collapse. Instituto do Mar de Cabo Verde bathymetry and RRS Charles Darwin (8/85) seismic reflection profile data suggest that the west side of Santiago is characterised by a narrow insular shelf, a major debris avalanche deposit with scattered blocks and at least one lateral sector collapse structure. Data, however, east of Santiago are limited and so the full extent of mass wasting on the east side of the island is not known. Maio Island, which is similar in age to Santiago, would have acted as a buttress in the east, and it is possible that any eastward collapse might have rotated and travelled to the northeast. Irrespective, one or more mass wasting events west or east of Santiago are consistent with a major destruction of the original volcano edifice which removed the summit, exposed the basement complex of the island, and redistributed volcano-clastic material over a large area of the adjacent seafloor. 

How to cite: Ornelas Marques, F., Catita, C., Watts, A., Hildenbrand, A., and Victória, S.: Santiago Island, Cape Verde: Evidence for island-scale collapse from paleotopography onshore and bathymetry offshore, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14871, https://doi.org/10.5194/egusphere-egu24-14871, 2024.

The Eifel volcanic area in western Germany has been active for tens of million years. Geodetic observations, geochemical analysis and seismological studies all indicate that the source of these long-term volcanic activities is a mantle plume. However, it still remains controversial whether the Eifel plume has a deep origin. This is because the tomography images do not consistently show a continuous plume conduit between the surface and the core-mantle boundary. The Eifel plume is also not associated with any flood basalt province or a clearly age-progressive hotspot track, which is regarded as a key surface feature indicating a deep plume origin. In addition, it has been proposed that the Alpine subduction zone, south-east of the volcanic area, has created a stagnant slab in the mantle transition zone, which might be interacting with the Eifel plume.

Based on the previous studies and observations, our two contrasting hypotheses are as follows: (1) The Eifel plume is not rooted in the lower mantle. In this case, subduction beneath the Alps might trigger a return asthenospheric flow and the ascent of an upper-mantle plume, leading to the formation of intraplate volcanism beneath the European plate. (2) The Eifel plume is assisted from an upwelling in the lower mantle. In this case, the subducting plate might tilt the plume conduit and influence the position where volcanism takes place.

In this study, we apply the Finite-Element-Method geodynamic modeling code ASPECT to model the ascent of the Eifel plume and its interaction with the subducting slab. We design both slab advancing and slab retreating model set-ups, with and without a plume from the lower mantle beneath the subducting plate. We check whether and under what conditions the Eifel plume will be triggered behind the slab due to slab overturn. Preliminary results show that the return flow induced by subduction can help generate an upper-mantle plume and lead to the formation of volcanism. A series of models are also performed to investigate the effects of mantle viscosity and plume temperature on the plume-slab interaction.

How to cite: Li, Y., Steinberger, B., Brune, S., and Le Breton, E.: Intra-plate volcanism generated by slab-plume interaction: Insights from geodynamic modeling of the Eifel plume and its interaction with the European subducting lithosphere beneath the Alpine subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15020, https://doi.org/10.5194/egusphere-egu24-15020, 2024.

Compared to oceanic hotspot tracks, volcanic provinces within Earth's continents generally exhibit more intricate surface characteristics, such as spatio-temporal distribution and geochemical signatures of erupted lavas. These complex surface patterns relate to dynamic interactions in the uppermost convective layer of the mantle, where decompression melting occurs. The Cosgrove Track of Eastern Australia constitutes a compelling example of such continental volcanic activity. Recent studies support a mantle plume having sustained the volcanism and discuss several notable features, such as lithosphere-modulated volcanic activity, plume waning, separate volcanic tracks, and plate-motion change.

Here, we simulate the proposed interaction between the Cosgrove plume and eastern Australia during the past 35 Myr. We design a 3-D analogue of the Australian continent using available lithospheric architecture determined through seismic tomography and impose the inferred plate motion associated with this region. Our models incorporate updated peridotite melting and melt chemistry parameterisations that provide quantitative estimates of generated melt volume and composition. We find that plume-driven and shallow edge-driven melting processes, modulated by the lithospheric thickness of the Australian continent, combine to explain the observed volcanic record. Our preliminary results agree well with surface observations and provide further insight into the geodynamics of eastern Australia.

How to cite: Duvernay, T. and Davies, D. R.: 3-D Modelling of Plume-Lithosphere Interaction: The Cosgrove Track, Eastern Australia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15229, https://doi.org/10.5194/egusphere-egu24-15229, 2024.

Sal is the oldest island of the Cape Verde archipelago, with magmatic activity starting around 25 Ma (Torres et al., 2010). Located to the northeast of the archipelago, it forms part of a north-south islands alignment and features intrusive bodies potentially representing the subvolcanic roots of exposed volcanic rocks. These intrusions, dated from ≈ 14 to 17 Ma (Torres et al., 2010) are intrusive into the Old Eruptive Complex, located in the central-western part of the island and mostly comprised by gabbro bodies, dyke swarms and several circular gabbro to monzonite complexes.

There are no previous detailed studies concerning mineral chemistry and crystallization conditions of these intrusions, which are a first step, together with precise geochronology, to correlate them with any of the different volcanic series occurring in Sal. In this work we present preliminary mineral chemistry, whole-rock geochemistry and radiogenic (Sr, Nd, Pb) isotope data of the circular complexes aiming to characterize their main features, magmatic evolution and mantle source composition.

The studied rocks range from gabbros to monzonites, sometimes displaying cumulate textures. The main mafic minerals present variable compositions: olivine chemistry ranges from Fo_61-81 in gabbros to Fo_39-49 in monzogabbros; clinopyroxene is classified as augite-diopside in all samples; amphibole is mainly kaersutite-pargasite-Mg-hastingsite and biotite-phlogopite Mg# is in the range 0.4-0.7. Plagioclase is bytownite-andesine (An_30-86) in gabbros, whereas it is more sodic in monzogabbros and monzonites (An_16-66), while nepheline (Ne_70-86) turns more potassic from gabbros to monzonites. Alkali feldspar (Or_20-98) only appears in monzogabros and monzonites. The main accessory phases are ilmenite/Ti-magnetite, chromite, ulvospinel, titanite and apatite.

Major and trace element chemistry points to a progressive evolution from mafic to intermediate types characterized by a linear decrease of MgO, TiO₂, FeO_T, CaO, Ni and Cr, and a gradual increase of SiO₂, Al₂O₃, K₂O, Na₂O, Rb, Ba, Zr and Nb. These patterns suggest initial crystallization of mafic phases (olivine, clinopyroxene, ilmenite-magnetite) and calcic plagioclase. The intra-complexes positive correlation between strongly incompatible element pairs: U-Th, La-Ce and Nb-Ta, suggests the predominance of fractional crystallization within each circular complex.

The studied rocks display ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd initial ratios typical of some OIB having more Sr-radiogenic and Nd-unradiogenic compositions than the N-MORB. These signatures and the Pb isotope ratios are close to the FOZO composition, in an intermediate position between the HIMU and N-MORB mantle components. Small εNd and ²⁰⁶Pb/²⁰⁴Pb differences between the several circular complexes define two compositional groups, which implies slight heterogeneities in the mantle sources. These isotopic results support the association of Sal intrusive with the Cape Verde northern islands as no low Nd isotopic ratios have been found that could imply EM-1 enriched components, as those described by Torres et al. (2010) for some lavas.

Torres, P., Silva, L.C., Munhá, J., Caldeira, R., Mata, J., Tassinari, C. (2010): Petrology and geochemistry of lavas from Sal Island: Implications for the variability of the Cape Verde magmatism. Comunicaçoes Geológicas, 97: 35-62.

How to cite: García-Rodríguez, M., de Ignacio, C., Orejana, D., Villaseca, C., Mata, J., and Caldeira, R.: Petrology and geochemistry of alkaline Circular Complexes from Sal Island, Cape Verde archipelago., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17719, https://doi.org/10.5194/egusphere-egu24-17719, 2024.

Central East Asia has experienced intraplate volcanism over the past ~110 Myrs. The mechanism for this volcanism is enigmatic, with several potential causes put forward for the origin, including a mantle plume, edge convection, and lithospheric delamination. One of the big questions for the region is the role played by the long-term subducting systems of the Pacific/Izanagi and the Tethys Ocean(s). And secondarily, how much the volcanism is influenced by the lithospheric conditions and its changing thicknesses across the region.  

To recreate the conditions of mantle circulation and flow beneath Central East Asia, a mantle circulation model has been created using the fluid dynamics code ASPECT; the mantle circulation model is coupled with the plate reconstruction of Muller et al. (2019) for the surface conditions of the past 200 Myrs. To better understand the patterns of mantle flow, particles are emplaced into the model to track flow beneath the region, particularly around the subducted slabs. The mantle flow is compared to localities of intraplate volcanism across Central East Asia to assess whether any upwelling regions correlate with the spatial and temporal origins of the volcanism. Initial results show colder downwelling mantle from the surface boundary beneath Central East Asia at ~120-110 Ma, with warmer mantle upwelling into the region to replace it. The timing of this upwelling mantle coincides with the initiation of intraplate volcanism in the region; however, whether this results in the onset of intraplate volcanism in the region and the following 110 Myrs of intraplate volcanism is still being investigated. The mantle flow from the global models will then be used to inform the boundary conditions of a localised box model for Central East Asia. This model will be used to examine any potential effect of delamination beneath Central East Asia, and whether this model can explain any of the timings of intraplate volcanism formation. 

How to cite: Rutson, A., Barry, T., Fishwick, S., and Lane, V.: A geodynamic perspective on the formation of intraplate volcanism in Central East Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18227, https://doi.org/10.5194/egusphere-egu24-18227, 2024.

The Hawaii-Emperor seamount chain stretches westward from the “Big Island” of Hawaii for over 6000 km until the oldest part of the chain are subducted at the Kuril and Aleutian trenches. Still regarded as the iconic hotspot-generated seamount chain it has been sampled, mapped, and studied to give insights into numerous oceanic phenomena, including seamount and volcano formation and associated intraplate magma budgets, the past absolute motions of the Pacific plate, the drift of the Hawaiian plume, and the thermal and mechanical properties of oceanic lithosphere. Previous work (Wessel et al., EGU 2023 abstract) used a high-resolution free-air gravity anomaly and high-resolution bathymetry data set, together with fully 3-dimensional flexural models with variable volcano load and infill densities, to estimate the optimal effective elastic thickness, T_e, and load and infill densities along the Emperor Seamount chain. Here, we use these parameters to calculate the tectonic tilt of a pre-existing volcano that occurs as each new volcano in a seamount chain is progressively added by flexure to the Pacific oceanic plate. We found tilts in the range 0.1-2.1 degrees which are modest compared to other cases of progressive flexure, for example, at seaward dipping reflector sequences in volcanic rifted margins (~5-15 degrees) but may be significant enough to modify the morphology of volcano summits and the stratigraphy of the sequences that accumulate in their flanking moats. They may also modify the physical properties of the edifice such as their magnetisation vectors.

Wessel, P., A. B. Watts, B. Boston, C. Xu, R. Dunn, and D. J. Shillington “Variation in Elastic Thickness along the Emperor Seamount Chain”, EGU 2023 Abstract

How to cite: Xu, C., Wessel, P., Watts, A., Boston, B., Dunn, R., and Shillington, D.: Plate flexure and tectonic tilt along the Emperor Seamount Chain , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18822, https://doi.org/10.5194/egusphere-egu24-18822, 2024.

Seamounts and carbonate mounds are ubiquitous features of the global deep seascape. They often provide habitat for unique benthic species communities and support increased production and aggregation of phytoplankton, zooplankton, micronekton, and fish. Seamounts and carbonate mounds interact with the surrounding currents generating flow phenomena over a wide range of spatial and temporal scales including stable Taylor caps, energetic internal waves and turbulent mixing, all with the potential to enhance productivity, biomass, and biodiversity in an often food-limited deep-sea environment. We present hydrodynamic and ecological framework conditions at two contrasting topographic features in the North Atlantic, Great Meteor Seamount and Haas Mound. Great Meteor Seamount is of volcanic origin and one of the largest seamounts in the subtropical North Atlantic rising from 4200 m depth at the seafloor to a summit depth of 270 m. Great Meteor Seamount shows remarkable endemism in meiofaunal groups of copepods and nematodes. Haas Mound is one of the largest biogenic carbonate mounds of the Logachev mound province along the Southeast Rockall Bank in the Northeast Atlantic with a species rich benthic fauna dominated by the cold-water coral Desmophyllum pertusum (Lophelia pertusa). We used results from hydrodynamic models to identify the physical processes, which potentially support seamount and carbonate mound biodiversity. The models employ high-resolution local bathymetry, basin-scale lateral forcing and tidal forcing. Our model simulations provide a detailed three-dimensional picture of the fine-scale motions and physical processes, which potentially drive bio-physical connections such as particle retention and continuous or episodic food supply to benthic communities. 

How to cite: Mohn, C., Schourup-Kristensen, V., Larsen, J., Schwarzkopf, F., Biastoch, A., Tojera, I., Souto, M., Kaufmann, M., van der Kaaden, A.-S., Soetaert, K., and van Oevelen, D.: Seamounts and giant carbonate mounds drive bio-physical connections in the deep-sea: Two case studies from the North Atlantic., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19827, https://doi.org/10.5194/egusphere-egu24-19827, 2024.

Extensive igneous activity, currently identified from NE Brazil and western Africa to the Falkland Islands and South Africa, preceded the fragmentation of the Western Gondwana supercontinent in the Early Cretaceous. The Paraná-Etendeka Magmatic Province (PEMP) is characterized by continental basaltic flows and igneous plumbing systems in SE South America and its African counterpart. In NE Brazil, dyke swarms and sill complexes compose the Equatorial Atlantic Magmatic Province (EQUAMP). A prominent feature of EQUAMP is the Rio Ceará-Mirim dyke swarm, an arcuate igneous plumbing system approximately 1,100 km in length. Aeromagnetic data suggests that the Rio Ceará-Mirim dykes stretch from the corner of South America to the northwest border of the São Francisco Craton. At this point, the dykes shift orientation to the NNW, extending towards the south, where they appear to connect with the Transminas dyke swarm (northern PEMP). The apparent continuity of dykes as a single entity would constitute a massive transcontinental swarm of about 2,300 km. A similar relationship is observed for the Riacho do Cordeiro (southern EQUAMP) and Vitória-Colatina (northern PEMP) dykes, indicating continuity across the São Francisco Craton of about 1,600 km. This study, supported by new petrological, geochemical, isotopic, and geochronological data, combined with geophysical and geodynamical analyses, demonstrates that the Transminas and Vitória-Colatina dyke swarms share the same composition and age as the Rio Ceará-Mirim and Riacho do Cordeiro dyke swarms, respectively. The set of new evidence supports a genetic connection between the PEMP and EQUAMP. Therefore, they can be collectively referred to as a single large igneous province related to the early stage of the South Atlantic rifting process in the West Gondwana realm: The South Atlantic Magmatic Province.

How to cite: Avelino de Macedo Filho, A., Oliveira, A., Janasi, V., and Hollanda, M. H.: The South Atlantic Magmatic Province: An Integration of Early Cretaceous LIPs in the West Gondwana, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-415, https://doi.org/10.5194/egusphere-egu24-415, 2024.

            The type of lithosphere subducted between India and Tibet since the Paleocene remains controversial; it has been suggested to be either entirely continental, oceanic, or a mixture of the two. As the subduction history of this lost lithosphere strongly shaped Tibetan intraplate tectonism, we attempt to further constrain its nature and density structure with numerical models that aim to reproduce the observed history of magmatism and crustal thickening in addition to present-day plateau properties between 83˚E and 88˚E. By matching time-evolving geological patterns, here we show that Tibetan tectonism away from the Himalayan syntaxis is consistent with the initial indentation of a craton-like terrane at 55±5 Ma, followed by a buoyant tectonic plate with a thin crust, e.g., a broad continental margin (Himalandia). This new geodynamic scenario can explain the seemingly contradictory observations that had led to competing hypotheses like the subduction of Greater India versus largely oceanic subduction prior to Indian indentation.

How to cite: Liu, L., Liu, L., Morgan, J., Xu, Y.-G., and Chen, L.: The hypothesis of a lost Cenozoic “Himalandia” between India and Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1934, https://doi.org/10.5194/egusphere-egu24-1934, 2024.

The OHANA experiment comprises a 15-month deployment of 25 broadband ocean bottom seismometers (OBSs) in the northeast Pacific Ocean, about halfway between Hawaii and the North American west coast. The primary objective of this project is to explore the crust, lithosphere and asthenosphere in a 600~km wide region west of the Moonless Mountains, covering mainly 40-to-50 Myr old Pacific lithosphere. A fundamental question to be addressed is whether this particular area has the signature of a typical oceanic lithosphere that has a normal plate cooling history. Alternatively, we seek evidence for a previously proposed reheating process, e.g. resulting from small-scale shallow-mantle convection. 

The new data enhance seismic imaging in a regional as well as in a global context. Regionally, short-period ambient noise and long-period earthquake-derived Rayleigh wave dispersion provide the centerpiece for imaging the crust and upper mantle. In  a top-down approach,
we start with the assembly and analysis of ambient-noise cross-correlation functions between 5 and 25 s. We present an initial assessment of high signal-to-noise quality cross-correlation functions. We derive path-averaged dispersion curves for the fundamental mode and present tomographic images from initial inversions. 

Furthermore, our cross-correlation functions contain prominent waveforms from overtones that can help improve resolution as a function of depth.

How to cite: Laske, G., Atkisson, G., Talavera Soza, S., Collins, J., and Blackman, D.: Rayleigh-wave Ambient Noise Investigation for the OHANA Experiment in the NE Pacific, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2317, https://doi.org/10.5194/egusphere-egu24-2317, 2024.

We investigated the impacts of the Kerguelen and Amsterdam-St. Paul (ASP) hotspots on mantle evolution and crustal accretion of nearby spreading ridges in the Southeastern Indian Ocean. Gravity analysis revealed enhanced magmatism and thickened crust along the ridge caused by the Kerguelen and ASP hotspots. By employing plate motions derived from the GPlates global plate reconstruction model, along with the ASPECT 3-D mantle convection code, we presented a comprehensive depiction of the ridge-dual hotspot system, which has been relatively underexplored in previous research. Model results indicated that the Kerguelen hotspot had a significantly greater influence on mantle temperature and ridge crustal thickness compared to the ASP hotspot. Furthermore, there is evidence suggesting a potential interaction between the dual hotspots, leading to the migration of ASP plume materials towards the Kerguelen plume.

How to cite: Luo, Y., Lin, J., Zhou, Z., Zhang, F., Zhang, X., and Zhang, J.: Ridge-dual hotspots interaction and potential hotspot-hotspot interaction in the Southeastern Indian Ocean , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2624, https://doi.org/10.5194/egusphere-egu24-2624, 2024.

As part of mantle convection, mantle plumes rise from the deep Earth, leading to volcanic eruptions during which large volumes of mafic magma are emplaced at Earth’s surface over a few million years. In 1971, Jason Morgan showed that seamount chains could be used to calculate the absolute motion of tectonic plates above fixed mantle plumes. This ground-breaking work notably led to the study of the relationship between Earth’s deep interior and its surface. Mantle plumes have been critical to constrain absolute plate motions in Earth’s recent geological past, with the development of both fixed-hotspot and moving-hotspot plate-motion models. Recent studies also revealed a statistical link between large volcanic eruptions and basal mantle structures in space and time, suggesting that large volcanic eruptions, mantle plumes, and hot basal structures are intrinsically connected. In these studies, mantle plumes were considered as the implicit process connecting volcanic eruptions at the surface to hot basal mantle structures. Geodynamic models suggest that mantle plumes are generated by two large antipodal hot basal mantle structures, up to ~1,200 km thick, and shaped by subducted oceanic crust through time. Here, we systematically compare three volcanic-eruption databases, four global tomographic models, and six reconstructions of past global mantle flow, to investigate the spatio-temporal links between volcanic eruptions, hot basal mantle structures, and modelled mantle plumes from 300 million years ago to the present day. We find that large volcanic eruptions are spatially closer to fixed and moving hot basal mantle structures than to modelled mantle plumes, because mantle plumes cover an area that is five orders of magnitude smaller than the area covered by hot basal mantle structures. The strength of the spatial-statistical relationships is largest between volcanic eruptions and modelled mantle plumes and, overall, it is larger between volcanic eruptions and moving basal mantle structures than between volcanic eruptions and fixed basal mantle structures.  This suggests that large volcanic eruptions are preferentially associated with mantle plumes generated from the interior of mobile basal mantle structures, which is in sharp contrast to previous studies that suggested mantle plumes are generated from the edges of fixed basal mantle structures.

How to cite: Cucchiaro, A., Flament, N., Arnould, M., and Cressie, N.: Links between large volcanic eruptions, basal mantle structures and mantle plumes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2711, https://doi.org/10.5194/egusphere-egu24-2711, 2024.

Between about 130 and 75 Ma, the Arctic was impacted by widespread and long-lived volcanism known as the High Arctic Large Igneous Province (HALIP). HALIP is a very unusual large igneous province because it exhibits prolonged melting over more than 50 Myr with pulses of activity, an observation that is difficult to reconcile with the classic view of large igneous provinces and associated melting in plume heads. Hence, the suggested plume-related origin and classification of HALIP as a large igneous province has been questioned, and alternative mechanisms have been invoked to explain at least part of the volcanism. However, the Arctic also exhibits a very complex and time-dependent tectonic history that includes cratons, continental margins and rifting, all of which are expected to interact with the rising plume and affect its melting behaviour.

Here, we use 2-D numerical models that include melting and melt migration to investigate a rising plume interacting with a lithosphere of variable thickness, i.e. an extended-basin-to-craton setting. Models reveal significant spatial and temporal variations in melt volumes and pulses of melt production, including protracted melting for at least about 30-40 Myr, but only if feedback between melt and mantle convection is accounted for. In particular, we find that melt migration transports heat upwards and enhances local lithospheric thinning, resulting in a more heterogeneous distribution of melting zones within the plume head underneath the Sverdrup Basin. Once the thicker continental and cratonic lithosphere move over the plume, plume material is deflected from underneath the Greenland craton and can then re-activate melting zones below the previously plume-influenced Sverdrup Basin, even though the plume is already ∼500 km away. Hence, melting zones may not represent the location of the deeper plume stem at a given time. Plume flux pulses associated with mantle processes, rifting of tectonic plates or magmatic processes within the crust may alter the timing and volume of secondary pulses and their surface expression, but are not required to generate pulses in magmatic activity. Hence, we propose that the prolonged period of rejuvenated magmatism of HALIP is consistent with plume impingement on a cratonic edge and subsequent plume-lithosphere interaction. Based on melt fractions, our models suggest that HALIP magmatism should exhibit plume-related trace element signatures through time, but potentially shifting from mostly tholeiitic magmas in the first pulse towards more alkalic compositions for secondary pulses, with regional variations in timing of magma types.

How to cite: Heyn, B., Shephard, G., and Conrad, C.: Prolonged multi-phase volcanism in the Arctic induced by plume-lithosphere interaction, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4020, https://doi.org/10.5194/egusphere-egu24-4020, 2024.

The India-Asia convergence has persisted since the onset of collision at ~55 Ma, indicating the driving forces of Indian indentation do not disappear on continental collision in the convergence process. What drives ongoing India-Asia convergence? This puzzle cannot be well resolved by the traditional theory of plate tectonics and the concept of Wilson Cycle. Consequently, questions concerning the primary driving force of the ongoing India-Asia convergence and the magnitude of this force still await an answer. Previous works have proposed multiple candidates for the primary driver of India-Asia convergence, including the continental subduction of the Indian lithosphere under Tibet, oceanic subduction at the Sumatra-Java trench, as well as the basal drag exerted by the mantle flow on the base of Indo-Australia plate. Here we present global geodynamic models to investigate the driving forces behind the India-Asia convergence, which produce good fits to the observed motions, stresses and strains within the Indo-Australia plate. On this basis, we quantitatively calculate the magnitude of effective forces of boundary forces (slab pull and ridge push) and basal drag. We conclude that the Sumatra-Java subduction is the primary driver of the ongoing India-Asia convergence. Indo-Australia plate motion is driven at the Sumatra-Java trench, impeded along the Himalaya, which could increase the shear stress within the plate. Different from the recent emphasis on the basal drag as a dominant driving force for the India-Asia convergence, this study shows that basal drag acts as the resisting force for the northeastward motion of the giant Indo-Australia plate, though it serves as a driver in some local regions.

How to cite: Zheng, Q. and Hu, J.: Driving forces for the ongoing India-Asia convergence: insight from global high-resolution numerical modeling of mantle convection, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4314, https://doi.org/10.5194/egusphere-egu24-4314, 2024.

With recent progress in resolution in global seismic mantle imaging provided by numerical wavefield computations using the Spectral Element Method and full waveform inversion, Jason Morgan’s suggestion from over 50 years ago that mantle plumes may be rooted at the core-mantle boundary (CMB) has been confirmed. Yet the imaged plumes present intriguing features that contrast with the classical thermal plume model and should inform our understanding of mantle dynamics. Among other features, they are broader than purely thermal plumes, and do not extend straight from the CMB to the corresponding hotspot volcanoes, but they are frequently deflected horizontally in the extended transition zone (400-1000 km depth), so that their lower mantle location can be significantly offset (as much as a 1000 km) from their surface expression. They appear to be thinner in the upper mantle. This, together with similar horizontal flattening observed in subduction zones suggests a change in the radial viscosity structure of the mantle that may occur deeper than usually assumed to be related to the 660 km phase change. The fattest plumes have been shown to be anchored within the perimeter of the large low shear velocity provinces (LLSVPs) and an increasing number of them appear to house mega-ultra low velocity zones within their roots.  Moreover, in the upper mantle, they appear to be associated with regularly spaced low velocity channels aligned with absolute plate motion.

We discuss these features in the light of recent regional imaging updates in the south Atlantic and beneath Yellowstone, contrasting the corresponding mantle plumes, and in particular showing mounting evidence that the LLSVPs are not compact “piles” extending high above the CMB, but rather a bundle of thermo-chemical plumes feeding secondary scale convection in the top 1000 km of the mantle.

How to cite: Romanowicz, B., Munch, F., and Kumar, U.: Mantle plumes imaged by seismic full waveform inversion: from the core-mantle-boundary to surface hotspots, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4754, https://doi.org/10.5194/egusphere-egu24-4754, 2024.

Subduction is one of the most fundamental processes on Earth, linking the lithosphere and mantle and is a key driving force in mantle circulation. Despite this, and the advancement of geophysical methods which allow us to better understand mantle dynamics, our understanding of slab behaviour is still limited. The Earth is a very complex system, and so conclusions regarding slab dynamics are also sensitive to the interplay between countless processes acting within the mantle. 

There is much to learn about slab sinking in the mantle from considering a single 'perfect' plate, such that the dynamics can be isolated from any pre-established or distal processes. We present a range of 3D spherical mantle circulation models which evolve from the initial condition, driven by a 'perfect' plate at the surface. Each of these plates comprises a rectangular geometry, bound by a subduction zone on one side, a spreading ridge on the opposite side, and two tranform faults on the adjacent edges. We vary the geometry of the plate, both in terms of the length of the subducting trench, and the distance from the trench to the ridge, and vary the plate velocity.

We will report the slab behaviour in terms of plate geometry, mantle properties, and plate velocity, focussing on the evolution of downwellings, upwellings and other mantle structures in response to mantle circulation models driven solely by a single plate at the surface.

How to cite: Plimmer, A., Davies, H., and Panton, J.: Slab dynamics in the mantle: a back-to-basics approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6247, https://doi.org/10.5194/egusphere-egu24-6247, 2024.

We implement an innovative method of plate identification for the purpose of evaluating plate motion in numerical mantle convection models. Our method utilizes an existing tool,  Automatic Detection Of Plate Tectonics (ADOPT), which applies a tolerance (threshold) algorithm to elevation maps, to detect candidate plate boundaries at the surface of 3-D spherical mantle convection models. The logarithm of the strain-rate field yields a well-defined elevation map where local maxima lineations indicate spreading centres, zones of convergence, transform faults or diffuse deformation zones. For the plates found by ADOPT’s analysis, we determined rotation (Euler) poles implied by the velocities  within  the plate interiors. Subsequently, we examined the velocity field of each model plate for its agreement with rigid motion about the Euler poles.  We apply our method to snapshots taken from three previously published mantle convection calculations that appear to generate plate-like surface behaviour. Self-consistently generated model plates were obtained by combining a highly temperature-dependent viscosity with a yield stress that adds a strain-rate dependence to the viscosity, thus allowing for both intra-plate low strain-rate and weakening along tightly focussed plate boundaries. We generally identify more (and smaller) rigid plates for low yield stress or low threshold. Strong agreement of the surface velocities with rigid-body rotation around Euler poles is found for many of the plates identified; however, some plates also exhibit internal deformation. Regions that show a departure from rigidity can be decomposed into subsets of rigidly moving plates. Thus, the identification of a mantle convection model's maximally rigid plate surface may require plate boundary detection at both low and high thresholds. We suggest that as global mantle convection models superficially converge on the generation of plate boundary network similar to those observed with plate tectonics (including transform fault generation), testing for plate rigidity through the determination of Euler poles can serve as a quantitative measure of plate-like surface motion.

How to cite: Ojo, T., Guerrero, J., Fairservice, C., Javaheri, P., and Lowman, J.: Utilizing Euler poles for the evaluation of plate rigidity in numerical mantle convection models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6549, https://doi.org/10.5194/egusphere-egu24-6549, 2024.

Delamination of continental lithospheric mantle is now well-recorded beneath several continents. However, the fate of delaminated continental lithosphere has been rarely noted, unlike subducted slabs that are reasonably well imaged in the upper and mid mantle. Beneath former Gondwana, recent seismic tomographic models indicate the presence of at least 5  horizontal fast-wavespeed anomalies at ~600 km depths that do not appear to be related to slab subduction, including fast structures in locations consistent with delamination associated with the Paraná Flood Basalt event at ~134 Ma and the Deccan Traps event at ~66 Ma. These fast-wavespeed anomalies often lie above broad slow seismic wavespeed trunks at 500-700 km depths beneath former Gondwana, with the slow wavespeed anomalies branching around them. Numerical experiments indicate that delaminated lithosphere tends to stagnate in the transition zone above a mantle plume where it shapes subsequent plume upwelling. For hot plumes, the melt volume generated during plume-influenced delamination can easily reach ~2-4×10⁶ km³, consistent with the basalt eruption volume at the Deccan Traps. This seismic and numerical evidence suggests that observed high wavespeed mid-mantle anomalies beneath the locations of former flood basalts are delaminated fragments of former continental lithosphere, and that lithospheric delamination events in the presence of subcontinental plumes induced several of the continental flood basalts associated with the multiple breakup stages of Gondwanaland. Continued upwelling in these plumes can also have entrained subcontinental lithosphere in the mid-mantle to bring its distinctive geochemical signal to the modern mid-ocean spreading centers that surround southern and western Africa.

How to cite: Shi, Y.-N. and Morgan, J.: Gondwanan Flood Basalts Linked Seismically to Plume-Induced Lithosphere Instability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6630, https://doi.org/10.5194/egusphere-egu24-6630, 2024.

There are rare occurrences on Earth where mantle plumes intersect with continents, resulting in surface volcanism.Unlike their more common counterparts in oceanic lithosphere, where the ascent of melts is facilitated by a thinner lithosphere, identifying continental plumes is challenging. Surface volcanism, traditionally a key indicator of mantle plumes, may play a diminished role in regions characterized by complex tectonics and variations in lithospheric thickness.

Eastern Oman provides an excellent example where a continental mantle plume has remained undetected due to the absence of current surface volcanism. The region exhibits evidence of intraplate basanites, although with an age of ~35-40 Ma. Given their geochemical signature, these alkaline rocks likely originated from a mixture of melts from a plume-derived source and those from a lithosphere-derived component. Using P- and S-wave arrival-time residuals from distant earthquakes, we image a new mantle plume in eastern Oman, which we name the Salma plume. This continental plume is revealed in our 3-D P- and S-wave tomographic models as a 200 km low-velocity conduit extending to at least the base of the upper mantle, and located below the area of Tertiary intraplate volcanism. Despite experiencing minimal shortening since the Paleogene, the shallow-marine sediments of the Salma Plateau in eastern Oman reach elevations exceeding 2000 meters. Ongoing uplift, indicated by elevated Quaternary marine terraces, suggests that the plateau is still rising. The present uplift rate is modest but maps of residual topography show a positive trend in eastern Oman that can be associated to the presence of a plume.

Incorporating a geodynamic perspective, our analysis of noise-mitigated Indian plate motion relative to Somalia reveals that India underwent a constant-velocity reorientation of approximately 15˚  from 48 to 30 Ma, concurrent with the arrival of the plume head beneath eastern Oman. We quantitatively demonstrate that increased asthenospheric flow induced by the plume flux in eastern Oman, adjacent to the Indian plate in the Eocene, may be responsible for deflecting the Indian plate path, as indicated in kinematic reconstructions.

The consequence of ignoring a plume in Oman is that we were unable to understand many of the enigmatic observations from plume impingement at ~40 Ma. Our study underscores the potential of combining seismology, geology, geochemistry, and geodynamics to be a more effective approach for detecting continental plumes than relying solely on surface volcanism, and has transformed our understanding of the tectonic evolution of the area and beyond.

How to cite: Pilia, S., Iaffaldano, G., Davies, R., Sossi, P., Whattam, S., and Hu, H.: Absence of surface volcanism and the indeterminate evidence for continental mantle plumes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7075, https://doi.org/10.5194/egusphere-egu24-7075, 2024.

Many hotspots worldwide display evidence of fluctuating magmatic emplacement rates in their history, at periods of 1-20 Myr, indicative of changing melt production within underlying mantle plumes. Here we report unprecedentedly short fluctuations of magmatic activity in the Réunion hotspot, emblematic because it started with the Deccan traps suspected to have caused the Cretaceous-Paleogene mass extinction. Using K-Ar geochronology, field observations, and geomorphology, we reconstructed the volcanic history of La Réunion and Mauritius islands, the two latest manifestations of the Réunion hotspot. Our reconstruction reveals coeval magmatic activity pulses and rest intervals for the two islands over the past 4 Ma. The period of these pulses, of ~400 kyr, is an order of magnitude shorter than any fluctuation found on other hotspots. Given the distance between La Réunion and Mauritius (~230 km), this synchronous short-period pulsation of the Réunion hotspot cannot stem from the lithosphere (≤70 km thick), and must be attributed to deeper plume processes. Moreover, this ~400 kyr periodicity coincides with the recurrence time of magmatic phases in the Deccan traps, suggesting that the pulsation began with the initiation of the hotspot. We propose that the Réunion plume is regularly pulsing with a periodicity of ~400 kyr, possibly since the Cretaceous-Paleogene transition, thus delivering extremely short-period waves of magma to the surface, synchronous over hundreds of kilometers. Understanding the geodynamic causes of this superfast beat of the Réunion plume is the objective of the four-year project “Plum-BeatR”, funded by the Agence Nationale de la Recherche (ANR- 23-CE49-0009), starting in 2024.

How to cite: Famin, V., Quidelleur, X., and Michon, L.: Short-period (400 kyr) pulsation of the Réunion plume, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7255, https://doi.org/10.5194/egusphere-egu24-7255, 2024.

Plate tectonics plays a pivotal role in shaping the Earth's surface and is intricately linked to internal processes, including the subduction of cold slabs and the ascent of hot mantle plumes. Statistical analyses have unveiled a strong correlation between the distribution of large igneous provinces (LIPs) over the past 320 Ma and two large low-velocity provinces (LLVPs) beneath Africa and the Pacific Ocean. Consequently, hypotheses have emerged suggesting the long-term stability of these LLVPs. However, numerical modeling challenges this notion, suggesting that these basal mantle structures are mobile. To resolve these debates, we attempt to study these basal mantle structures from the evolution of intermediate-scale thermochemical anomalies. We report such an intermediate-scale thermochemical anomaly beneath the NW Pacific Ocean based on existing tomographic models and use paleogeographically constrained numerical models to study its evolution. Considering different plate configurations in North Pacific, our models consistently show that this anomaly was separated from the Perm anomaly by the subduction of the Izanagi slab in the Cretaceous. After the separation, it generated a mantle plume, inducing an oceanic plateau that got subducted beneath Kamchatka in Eocene. This scenario is consistent with multiple lines of evidence, including the seismic anomaly in the lower mantle, a seismically detected megameter-scale reflector that coincides with the subducted oceanic plateau and changes in Pacific Plate motion that correlated with the Eocene trench-plateau collision. We propose that intermediate-scale low velocity structures constantly undergo segregation and coalescing, and are sources of plumes that lie outside the two major LLVPs. Merging of the reported anomaly with the Pacific LLVP suggests the latter is still under assembly.

How to cite: Zhang, J. and Hu, J.: Segregation of thermochemical anomaly and associated deep mantle plume outside the large low-velocity provinces, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8432, https://doi.org/10.5194/egusphere-egu24-8432, 2024.

We present initial tomographic findings from the ERC-funded UPFLOW (Upward mantle flow from novel seismic observations) project, showcasing results from a large-scale passive seismology experiment conducted in the Azores-Madeira-Canaries region between July 2021 and September 2022. Recovering 49 out of 50 ocean bottom seismometers (OBSs) in a ~1,000×2,000 km2 area with an average station spacing of ~150-200 km, we analyze approximately ~8000 multi-frequency (T ~2.7-30 s) body-wave travel time cross-correlation measurements derived from UPFLOW OBS data and over 120 teleseismic events. A preliminary P-wave tomographic model is presented, offering insight into the region's mantle dynamics.

Furthermore, by integrating UPFLOW's OBS data with global seismic data from both temporary and permanent stations, we expand the dataset to around 600,000 multifrequency measurements. This comprehensive dataset is employed to construct a global P-wave model, providing enhanced resolution throughout the entire mantle column beneath the Azores-Madeira-Canaries region. A comparative analysis with existing global tomography models is performed, and we discuss the geodynamical implications of our new, high-resolution model.

How to cite: Tsekhmistrenko, M., Ferreira, A., and Miranda, M.: UPFLOW body wave tomography of the whole mantle column beneath the Azores-Madeira-Canaries region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8563, https://doi.org/10.5194/egusphere-egu24-8563, 2024.

The North Atlantic region is a prime example of the interaction between plate tectonic movements and thermal instabilities in the Earth’s mantle. The opening of the Labrador Sea/Baffin Bay and the North Atlantic, the widespread volcanism and the localized uplift of the topography in Greenland and the North Atlantic are traditionally attributed to the thermal effect of the Iceland mantle plume. However, several prominent features of the region – the temporal synchrony of magmatism and break-up events, the symmetrical configuration of the Greenland-Iceland-Faroe Ridge, and the diachronous domal uplift of the North Atlantic rifted margins – have inspired alternative, “non-plume” views. According to these, the North Atlantic Igneous Province (NAIP) and Iceland magmatism originate from plate tectonic processes sourced in the shallow upper mantle, at odds with the unequivocal presence of deep-seated low-velocity seismic anomalies beneath Iceland and the isotopic signatures of plume-derived melts in Cenozoic magmatic units.

We resolve apparent contradictions in the observations and reconstructions and reconcile end-member concepts of the Late Mesozoic-Cenozoic evolution of the North Atlantic realm. We show that simultaneous Paleocene (~62-58 Ma) magmatism in Western Greenland/Baffin Island and the British Isles, which together form the NAIP, is driven by two processes accidently coinciding in time: 1) the propagation of the Labrador Sea/Baffin Bay spreading axis has overlapped with the ~100-80 Ma dated segment of the Iceland hotspot track near the West Greenland margin, while 2) the actual tail of the Iceland plume has reached the eastern continental margin of Greenland, allowing a horizontal flow of hot plume material along corridors of relatively thinned lithosphere towards Southern Scandinavia and Scotland/Ireland. In this framework, the subsequent formation of the symmetrical Greenland-Iceland-Faroe Ridge can be coherently explained by the continuous supply of hot plume material through an established channel between Eastern Greenland and the British Isles. In contrast to the Scotland/Ireland region, the South Norway continental lithosphere remains too thick to enable localized uplift of the topography and melting immediately after plume lobe emplacement at ~60 Ma. Therefore, the development of topographic domes in Southern Scandinavia only started ~30 Myr later in the Oligocene as a consequence of increasing ridge-push compression that built up during the opening of the Norwegian-Greenland Sea.

The evolution of the North Atlantic region shows that a thermal anomaly that has been hidden below a thick lithosphere for tens of Myr without signs of excessive magmatism can be re-initialized (or “re-awakened”) by the lateral propagation of spreading ridges or by the tapping of its source beneath thinner segments of the overlying lithosphere due to horizontal plate movements. We dub this type of Large Igneous Province (LIP) as LIP-Dornröschen (LIP-Sleeping Beauty). We hypothesise that the term LIP-Dornröschen may be applicable to a broad family of LIPs, including Precambrian and oceanic LIPs. This means that the interpretation of the timing of LIP formation from the perspective of mantle dynamics should be treated with caution, as there may be delays between the timing of upwelling in the mantle and detectable magmatic manifestations at or near the Earth’s surface.

How to cite: Koptev, A. and Cloetingh, S.: Iceland plume and its magmatic manifestations: LIP-Dornröschen in the North Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8567, https://doi.org/10.5194/egusphere-egu24-8567, 2024.

Hotspot-related anomalies observed in mid-ocean ridge systems are widely interpreted as the result of upwelling mantle plumes interacting with spreading ridges. A key indicator of this interaction is 'waist width', which measures the distance of plume flow along the ridge. Current scaling laws for waist width, premised on a gradual decrease in plume temperature along the ridge, often overlook sub-ridge longitudinal thermal variations, potentially biasing width measurements at various depths. In this study, we refined waist width measurements by tracking the material flow and its thermal diffusion from the plume source in plume-ridge interaction models. These non-Newtonian viscoplastic models integrate ridge spreading, lithospheric cooling with hydrothermal circulation, and mantle dehydration. Model results show that the hot plume initially boosts upwelling from the deep mantle to near the dehydration zone, followed by a slowdown and lateral spread across and along the ridge. In addition to strongly correlating with plume flux and spreading rate, the pattern and distance of plume flow vary with depth. At deeper depths, the plume expands radially in a pancake-like thermal pattern with shorter along-ridge distances, while shallower, it shows an axial pipe-like dispersion over longer distances, forming a concave structure. This is shaped by the cooling of the plume material during the phase of decelerated upwelling and along-ridge dispersion within the dehydration zone and cooling of the oceanic lithosphere associated with plate spreading. Estimates of plume buoyancy flux, derived from both material- and isotherm-tracking waist widths, show significant variations at different depths, suggesting that understanding depth-dependent plume dynamics beneath mid-ocean ridges is crucial for reconciling the observed discrepancies in buoyancy flux estimates.

How to cite: Liu, S., Zhang, F., Zhao, L., Zhang, X., and Lin, J.: Depth dependence of mantle plume flow beneath mid-ocean ridges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9504, https://doi.org/10.5194/egusphere-egu24-9504, 2024.

Mantle plumes play major role in modifying the continental lithosphere producing rifts and massive amounts of basaltic volcanism as the anomalously hot mantle undergoes decompressive melting. If conditions are favourable the rift may widen and a new ocean is formed. During the break up of Eastern Gondwana at ~ 130 Ma, the Kerguelen mantle plume influenced the separation of India from Antarctic and Australian plates and generation of the Eastern Indian Ocean. Eastern India-Bangladesh region (83-94ºE, 21-26ºN) carries imprints of the plume activity in the form of the Rajmahal and Sylhet traps and their subsurface expression in Bengal basin and extensive lamproytes. Existing geophysical studies of the region are mainly crustal scale and do not explicitly refer to the Kerguelen plume activity providing geophysical evidence for the same. We present here lithospheric shear velocity structure of the region up to a depth of ~ 175 km by trans-dimensional Baysian inversion of Rayleigh group velocity dispersion data (7-100s at 1º X 1º resolution). Using the same, we investigate the influence of the Kerguelen plume on the lithosphere of the Eastern India-Bangladesh region that comprises the Eastern India craton, the Bengal basin, the Bhrahmaputra basin, Bangladesh and the Shillong- Mikir plateau.

How to cite: Mullick, N., Kumar, V., Saha, G., Rai, S. S., and Bodin, T.: Influence of the Kerguelen hotspot on eastern Indian lithosphere by trans-dimensional Bayesian inversion of Rayleigh wave dispersion data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9647, https://doi.org/10.5194/egusphere-egu24-9647, 2024.

Melt inclusions hosted in highly magnesian olivine crystals have proven invaluable for probing the composition of the mantle through time since their geochemical signature is reflecting that of parental melt. Additionally, the geochemical study of melt inclusions has shown to be more suited to identify the heterogeneity in the magma from which they crystallized, particularly the chemically depleted domains [1, 2]. Here, we will present new major, minor & trace elements, H₂O contents and Sr-isotope signature of more than 300 olivine-hosted naturally quenched melt inclusions from Pu’u Wahi (910 yr-old) and Puʻu Mahana (ca. 50 kyr-old), two ash cones associated with Mauna Loa, the largest shield volcano of the Hawai’ian seamount chain. In order to have a high degree of confidence in the geochemical proxies, Sr-isotope and trace elements analyses were conducted through laser ablation split stream (LASS) protocol on top of EPMA and Raman (for H₂O contents) analytical spots. Preliminary results in our new set of inclusions show the presence of high (Sr/Ce)_N inclusions, previously interpreted as indicating either gabbro influence in the source of the plume [3] or interactions between plagioclase-rich cumulates and percolating mantle-derived melts [4]. Further, “ultra-depleted melts”, UDM, indicated by K₂O contents < 0.1 wt.% identified in [1], have also been re-identified in this new set of inclusions (not analyzed for Sr-isotope yet). ⁸⁷Sr/⁸⁶Sr of non-UDM inclusions ranges from 0.70361±0.00025 to 0.70427±0.00025, i.e. analogous to the most recent TIMS values [4, 5]. Additional LASS analyses will be conducted before the meeting. The full set of analyses will be confronted to published results on the same volcano [1, 3-6] and integrated in a larger framework of interactions between mantle plume and consequences for plate tectonic.

References:

• Sobolev, A.V., et al., Nature, 2011. 476(7361).
• Stracke, A., et al., Nature Geoscience, 2019. 12(10).
• Sobolev, A.V., et al., Nature, 2000. 404(6781).
• Anderson, O.E., et al., Geochemistry, Geophysics, Geosystems, 2021. 22(4).
• Reinhard, A., et al., Chemical Geology, 2018. 495.
• Sobolev, A.V., et al., Nature, 2005. 434(7033).

How to cite: Vezinet, A., Barbera, B., Sobolev, A. V., Batanova, V. G., Kazzy, C., and Chugunov, A. V.: Heterogeneous mantle source of Mauna Loa volcano (Hawai’ian plume) revealed by Sr-isotope and trace elements signatures of olivine-hosted melt inclusions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10288, https://doi.org/10.5194/egusphere-egu24-10288, 2024.

Pyroxenites are generated by the subduction of sediments and oceanic basalts into the deep mantle. These rocks, together with the larger volume fraction of their surrounding mantle peridotites make up a lithologically heterogeneous two-component mantle, sometimes called a ‘marble-cake’ or ‘plum-pudding’ mantle. Geochemical and petrological observations have shown that pyroxenites play a significant role in the genesis of oceanic island basalts (OIB). However, the consequences of preferential pyroxenite melting on bulk mantle properties have yet to be systematically explored. For example, how does the plume melting process modify a plum-pudding mantle’s bulk density and viscosity? This question could be very important, in particular if the asthenosphere is formed by material from upwelling, melting plumes.

To explore the above questions, we use the thermodynamic software Perple_X to determine densities for different degrees of depleted (i.e. partially melted) peridotites and pyroxenites. We then include these relations into a one-dimensional numerical simulation code for the upwelling and pressure-release melting of a potentially wet multi-component mantle. We investigate the density changes associated with the melting of this idealized mantle’s pyroxenites and peridodites, and also the viscosity change by assuming that the reference viscosity of pyroxenite is 10-100 times that of dry peridotite at similar P-T conditions, since the peridotite’s olivines are the weakest large volume-fraction minerals in the upper mantle. We have explored the effects of mantle temperature, initial water contents, initial fractions of pyroxenites and peridotite, peridotite solidi, and the thickness of the overlying lithosphere which will affect the depth-interval of upwelling and melting. Preliminary results show that significant density and viscosity changes should take place during plume upwelling and melting. ~30% partial melting of pyroxenite would lead to a net bulk density reduction of 0.3%, comparable to the thermal buoyancy associated with a ~100° temperature increase. As long as the surrounding peridotites do not melt, the mixture’s aggregate viscosity will remain that of wet peridotitic mantle; after the peridotites have melted a percent or so, the aggregate viscosity will increase 10-100-fold to that of dry peridotite. This could lead to the formation of a 10-100x asthenospheric viscosity restitic hotspot swell root. Eventual peridotitic melting will reduce the density of the more depleted peridotites relative to fertile peridotite as originally noted by Oxburgh and Parmentier (1977), but to a lesser degree than the density reduction associated with the preferential removal of pyroxenites by their partial melting. A dynamical consequence is that the asthenosphere is likely to be strongly stratified by density, with its most pyroxenite-depleted materials likely to rise to form a layer along the base of the overlying oceanic lithosphere. 

How to cite: Shao, J. and Morgan, J.: The density and viscosity of a bilithologic plume-fed asthenosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10507, https://doi.org/10.5194/egusphere-egu24-10507, 2024.

The evolution of modern plate tectonics is described by the Wilson cycle, which portrays the dynamics of the supercontinental cycle through the interaction of the oceanic plate with the continental plate over periods of hundreds of millions of years. This cycle is characterized by a phase of supercontinent assembly and enhanced orogenic collision, followed by a phase of supercontinent fragmentation and dispersal, as shown by the geological record. The dynamics of the Wilson cycle is intrinsically linked to mantle convection and subduction dynamics. While the assembly phase appears to follow a degree-2 mantle convection style, the mechanism responsible for supercontinent fragmentation is still debated. We hypothesize that the dispersal phase is mostly governed by trench roll-back from subductions and mantle plumes. To test this hypothesis, we have built a series of 2D and 3D geodynamic models of the Earth on a global scale using the ASPECT code. We have tested different scenarios in which we prescribe the distribution of the supercontinent Rodinia at 1Ga or Pangea at 250 Ma and let the models evolve self-consistently.  In some model variants, the strength of the supercontinent and that of the surrounding oceanic area is changed. We will present our preliminary results and discuss the dynamics of continental dispersal and its link to subduction and mantle dynamics. In particular, 3D models will demonstrate how regional plume-induced retreating subduction zones evolve into a global network of subduction zones and tectonics plate boundaries which ultimately leads to the break-up of the supercontinent.

How to cite: Pons, M., V. Sobolev, S., Jain, C., and Kendall, E.: From plumes to subduction network formation and supercontinent break-up, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10967, https://doi.org/10.5194/egusphere-egu24-10967, 2024.

While the temperature drop across the thermal boundary layer (TBL) at the base of the mantle is likely > 1000 K, the temperature anomaly of plumes, which are believed to rise from that TBL is only up to a few hundred K. Reasons for that discrepancy are still poorly understood. It could be due to a combination of (1) the adiabat inside the plume being steeper than in the ambient mantle, (2) the plume cooling due to heat diffusing into the surrounding mantle as it rises, (3) the hottest plume temperature representing a mix of temperatures in the TBL, and not the temperature at the core-mantle boundary (CMB), (4) plumes not directly rising from the CMB due to chemically distinct material at the base of the mantle, (5) a plume-fed asthenosphere which is on average warmer than the mantle adiabat, reducing the temperature difference between plumes and asthenospheric average. Here we use the ASPECT software to model plumes from the lowermost mantle and study their excess temperatures. We use a mantle viscosity that depends on temperature and depth with a strong viscosity increase from below the lithosphere towards the lower mantle, reaching about 10²³ Pas above the basal TBL, consistent with geoid modelling and slow motion of mantle plumes. With a mineral physics-derived pyrolite material model, the difference between a plume adiabat and an ambient mantle adiabat just below the lithosphere is about two thirds of that at the base of the mantle, e.g. 1280 K temperature difference at the CMB reduces to about 835 K at 200 km depth. In 2-D cartesian models, plume temperature drops more strongly and is rather time variable due to pulses rising along plume conduits. In contrast, 3-D models of isolated plumes are more steady and, after about 10-20 Myr after the plume head has reached the surface, their temperatures remain rather constant, with excess temperature drop compared to an adiabat for material directly from the CMB usually less than 100 K. This extra temperature drop is small because plume buoyancy flux is high. Hence the above points (2) and (3) do not contribute much to reduce temperature of isolated 3-D plumes. In our models, the asthenosphere is on average about 200-400 K hotter than the mantle beneath, due to plume material feeding into it. While this appears to reduce the plume temperature anomaly, a resulting cooler mantle adiabat also corresponds to an even stronger temperature drop in the basal TBL, offsetting that effect. In the Earth, plumes are likely triggered by slabs and probably rise preferrably above the margins of chemically distinct piles. This could lead to reduced excess temperatures, if plumes are more sheet-like, as the 2-D models, or temperature at their source depth is less than at the CMB.

How to cite: Steinberger, B. and Roy, P.: Why are plume excess temperatures much less than the temperature drop across the core-mantle boundary?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11566, https://doi.org/10.5194/egusphere-egu24-11566, 2024.

Much has been learned about the deep Earth through a combination of geophysical constraints, theories of Earth’s formation, and seismic measurements. However, such methods alone cannot directly resolve the full structure of the inner Earth, e.g. in terms of matter density, composition and temperature distributions.

Complementary information about Earth’s interior can be provided by small, nearly massless elementary particles called neutrinos that propagate through the Earth. Neutrinos exist in different flavours and are known to experience a quantum phenomenon of flavour oscillation as they propagate. With an extremely small chance of interacting with matter, neutrinos can travel long distances through very dense materials (e.g., the Earth’s core). For atmospheric neutrinos of energy ~GeV crossing the Earth, the flavour oscillation patterns are distorted due to coherent forward scattering on electrons along their path. Measuring the flavour, energy and angular distributions of such neutrinos therefore provides sensitivity to a new observable of geophysical interest: the electron number density in the layers of matter traversed.

After a short introduction to the concepts of neutrino oscillation tomography, we will discuss the potential of this method to address open questions concerning inner Earth's structure and composition (such as the amount of light elements in the core and the nature of LLSVPs), the status of sensitivity studies, and the perspectives opened by the next generation of atmospheric neutrino detectors.

How to cite: Van Elewyck, V., Coelho, J., Deniz Hernandez, Y. A., Durand, S., Fuji, N., Kaminski, E., Maderer, L., Mittelstaedt, E., and Pestes, R.: Prospects of Neutrino Oscillation Tomography of the Earth , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11719, https://doi.org/10.5194/egusphere-egu24-11719, 2024.

The Rajmahal Traps is one of the two major Large Igneous Provinces (LIPs) that erupted in the Indian subcontinent in the Mesozoic. The trap was the product of activity at the Kerguelen hotspot, located in the Indian Ocean, that initiated around 117 Ma. Earlier studies on the eruption location of the Rajmahal trap show that its location does not coincide with the present-day location of the Kerguelen Hotspot. This difference in the paleo-locations could be the result of mantle dynamics beneath the Indian Ocean during the Cretaceous and has been explained with concepts such as the multiple diapir-single plume model, the migration pathway of the hotspot beneath the mantle, and the complex plume-ridge interaction.

In this study, we use paleogeographic reconstruction software GPlates to reconstruct the paleogeography of the Rajmahal Traps on the Indian subcontinent plate in an Antarctica fixed reference frame since 117 Ma to pin-point the paleo-location of the Kerguelen hotspot and eruption location of the Rajmahal trap along with the tectonic changes that the Indian Ocean was encountering. The mantle structure below the Indian Ocean was further studied using publicly available P-wave tomography data. The paleogeographic reconstruction linked to the mantle structure hints towards the presence of a tree-like hotspot-plume structure beneath the Kerguelen hotspot where a deep-seated single plume feeds into various fissures at the surface which are active at different points in time.

Our kinematic analysis for the Indian Plate reveals significant changes in the velocity of the plate since the Cretaceous at specific points in time in response to tectonic activities initiated by the plumes present in the Indian Ocean. These activities that link to changes in the velocity include interactions with the Morondova plume (velocity increase at 90 Ma) and Reunion hotspot (velocity increase between 78 – 62 Ma), and other processes like continental collision (velocity decrease at 56 Ma and between 50-43 Ma) and slab pull (velocity increase at 56 Ma). Using this new velocity profile, we have developed a revised velocity model for the drift of the Indian subcontinent since the Cretaceous.

How to cite: Guleriya, S., Beniest, A., and Tiwari, S. K.: Change in eruption location in Kerguelen hotspot and Kinematic Reconstruction of Rajmahal Trap:  Implications for Cretaceous to present day Geodynamics of Indian plate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11883, https://doi.org/10.5194/egusphere-egu24-11883, 2024.

W. Jason Morgan’s seminal development of plate tectonic theory set the foundation for current investigations of mantle convection and the nature of deep mantle plumes. More recently, hotspots have been proposed to occur at the edges of stationary African and Pacific large low shear velocity provinces (LLSVPs) and that this has a special significance in terms of plume/hotspot generation. The basis for this proposed global correlation has in turn been challenged, and whether LLSVPs edges are the sites of initial mantle plume formation debated. A different approach is to consider hotspots with the greatest buoyancy flux because to be successful, any global model should be able to explain their origin. In all analyses of buoyancy flux, the Pacific’s Hawaiian hotspot, which figured prominently in Jason’s early papers, stands out above all others. However, paleomagnetic and age-distance relationships indicate that the Hawaiian hotspot originated >1500 km N of the Pacific LLSVP and subsequently drifted to its edge where it may have become anchored. The hotspot with the highest buoyancy flux in the Atlantic is Iceland, which is far from the African LLSVP. Iceland represents the youngest of three past episodes of extraordinary volcanism affecting the North Atlantic-Arctic region, namely the North Atlantic Tertiary Volcanic Province, the High Arctic Large Igneous Province, and the Siberian Traps. This recurrent volcanism spanning more than 250 million years requires either drift of a single pulsing plume, or separate plumes, generated far from the edge of the proposed stationary African LLSVP. Thus, the nature and histories of these robust hotspots in the Pacific and Atlantic imply an origin distinct from stationary LLSVPs.  

How to cite: Tarduno, J.: Robust hotspot origin far from LLSVP margins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12584, https://doi.org/10.5194/egusphere-egu24-12584, 2024.

The rate of ocean-crust production exerts control over mantle heat loss, sea level, seawater chemistry, and climate. Reconstructing ocean-crust production rates back in time relies heavily on the distribution of present-day seafloor age. Different strategies to account for the incomplete preservation of older seafloor have led to differing conclusions about how much production rates have changed since the Cretaceous, if at all. We have constructed a new global synthesis of ocean-crust production rates along 18 mid-ocean ridges for the past 19 Myr at high temporal resolution.  We find that the global ocean-crust production rate decreased by ~37% from its maximum during 19-15 Ma to its minimum during 6-4 Ma. Our ability to resolve these changes at a statistically significant level is due to the availability of many new plate reconstructions at high temporal resolution and our use of an astronomically calibrated magnetic time scale with small uncertainties in reversal ages. We show that the reduction in crust production occurred because spreading rates slowed down along almost all ridge systems. While the total ridge length has varied little since 19 Ma, some fast-spreading ridges have grown shorter and slow-spreading ridges grown longer, amplifying the spreading-rate changes. The change in crust production rate skews the seafloor area-age distribution toward older crust, and we estimate that sea level may have fallen by as much as 32-37 m and oceanic heat flow may have been reduced by 6%. We also show, using a simple model of the carbon cycle, that the inferred changes in tectonic degassing resulting from the crust-production changes can account for the majority of long-term surface-temperature evolution since 19 Ma.

How to cite: Dalton, C., Herbert, T., Wilson, D., and Si, W.: Changes in the Rate of Ocean Crust Production Over the Past 19 Myr: Implications for Sea Level, Mantle Heat Loss, and Climate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13570, https://doi.org/10.5194/egusphere-egu24-13570, 2024.

Laboratory and numerical experiments and boundary layer analysis of the entrainment of buoyant asthenosphere by subducting oceanic lithosphere (cf. Morgan et al., Terra Nova, 2007) implies that slab entrainment is likely to be relatively inefficient at removing a buoyant and lower viscosity asthenosphere layer. Such asthenosphere would instead be mostly removed by accretion into overlying oceanic lithosphere, both at mid-ocean ridges where a ~60-km compositional lithosphere forms due to the melt-induced dehydration of upwelling peridotitic mantle, and later with the thermal growth of  overlying oceanic lithosphere. When an oceanic plate subducts, the lower (hot) side of a subducting slab entrains a 10– 30 km-thick downdragged layer, whose thickness depends upon the subduction rate and the density contrast and viscosity of the asthenosphere, while the upper (cold) side of the slab may entrain as much by thermal ‘freezing’ onto the slab as by mechanical downdragging.  

Here we use 2-D numerical experiments to investigate the dynamics of entrainment and counterflow at subduction zones. We explore situations with both stable subduction geometries and slab rollback. Due to its low viscosity, a plume-fed asthenosphere is particularly likely to be stratified in its internal density, with variable amounts of plume melt-extraction leading to variable pyroxenite fractions and associated vertical density stratification within a bilithologic ~80-90% peridotite, ~10-20% pyroxenite asthenosphere. While this type of vertical density stratification appears to lead to similar predicted entrainment by subducting slabs, it will generate more complex patterns of asthenospheric counterflow that involve shallower and time-dependent counterflow behind the subducting slab.

How to cite: Li, X., Shao, J., Wang, G., Shi, Y., and Morgan, J.: Counterflow and entrainment within a buoyant plume-fed asthenosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13786, https://doi.org/10.5194/egusphere-egu24-13786, 2024.

Nickel-Copper (Ni-Cu) sulphide deposits are a diverse class of deposits, formed during the cooling and crystallisation of metal-rich mafic to ultramafic magmas. Despite sharing several key ore-forming processes, many of these deposits form in contrasting geologic environments and periods. The objective of this research project is to investigate the spatial and temporal distribution of Ni-Cu sulphide deposits in a mantle convection and plate tectonic context, and to explore the influence of different mantle and tectonic parameters on their origins and occurrence. We first determine the location of these deposits in relation to relevant geologic and tectonic features through time, including subduction zones, large igneous provinces (LIPs), and mantle plumes. Using a 1 billion year plate model we extract key parameters relating to subduction, as well as the spatio-temporal distribution of LIPs through time. Employing an associated geodynamic model, we identify model mantle plumes and quantify their key properties. Preliminary findings indicate that certain mantle plumes associated with deposits exhibit increased plume flux in the upper mantle preceding deposit formation, and that many deposits are spatially associated with LIPs throughout their formation history. For several deposits located in convergent margin settings, we have identified a notable spike in subduction volume and convergence rate during a 50-100 million year period prior to the onset of mineralisation. While the angle of the subducting slab is highly variable throughout the evolution of these deposits, several deposits are associated with a distinct steepening of the subducting plate in the lead-up to deposit formation. The findings of this study aim to contribute new insights into the dynamic processes governing the genesis of magmatic Ni-Cu sulphide deposits. These insights aid in our understanding of the interplay between mantle dynamics, plate tectonics, and deposit formation, and hold implications for future critical mineral exploration.

How to cite: Page, I., Mather, B. R., Januszczak, N., Anthony, M., and Muller, R. D.: Understanding Ni-Cu Sulphide Deposits in a Plate Tectonic and Mantle Convection Context, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13826, https://doi.org/10.5194/egusphere-egu24-13826, 2024.

The plate ‘interface’ at subduction zones has often been idealized as a single fault with ‘asperities’, however there is increasing evidence that plate boundary motions typically occur across a ~100-1000m channel or shear zone. Here we investigate the dynamics of slip in a mechanically heterogeneous plate boundary shear zone, and will typically use periodic boundary conditions to model the channel at a ~m-scale.  In contrast to most previous numerical studies, we imagine that this shear zone is embedded within finite strength wall-rock associated with the downgoing and overriding plates that themselves are capable of subduction-related deformation, for example during bend-faulting of the lower-plate or a forearc deformation event. We first look at how stress-concentrations can form by the clogging of strong blocks in a channel with a weaker matrix. We find that the strength of the surrounding wall-rock will play a key role in the channel’s response to a clogging event. In general, a clogging event can be mitigated by failure of surrounding relatively weak wallrock along the edges of a subduction channel in the conceptual process put forward by von Huene et al. (2004) to drive basal erosion of the forearc. We also consider cases where metamorphic transitions have led to the existence of weaker blocks within a stronger matrix. In this case, frequent tremor-like failure of the weak blocks can coexist with rarer earthquake failure of the stronger surrounding matrix.  Finally we explore the mechanical effects of channel widening and narrowing events that will invariably lead to a component of local pressure-driven flow within a subduction shear channel. Numerical snapshots and videos are used to visualize these potential modes of subduction shear zone deformation.

How to cite: Wang, G., P. Morgan, J., and Vannucchi, P.: Numerical exploration of the dynamics of the subduction plate boundary channel , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13939, https://doi.org/10.5194/egusphere-egu24-13939, 2024.

Both dynamic topography and seismic tomography have played crucial roles in providing invaluable insights into the Earth's interior structure and geological processes. Here we explore to what degree dynamic topography within ocean and back-arc basins can be correlated with the upper mantle seismic structure that has been imaged in recent high-resolution global models.

To explore the global ocean dynamic topography associated with subsurface mantle convection, we need to remove the influences of known contributing factors to seafloor relief such as the cooling of the ocean floor and the thickness of the ocean crust and sediments. We developed a series of scripts in PyGMT and MATLAB to do this, based on seafloor ages in GPLATES and sediment/crust information in CRUST1.0. With these corrections for near-surface structure, we obtained global average residual-depth values that serve as a basis for analyzing global subsurface structures linked to the asthenosphere and upper mantle, which we then compare to the vertically averaged shear-wave seismic structure above the transition zone. Our preliminary study highlights that the significant ~km-difference in dynamic topography between the Philippine back-arc basin and the Lau-Tonga backarc appear to be linked to a major difference in asthenosphere thickness and density beneath these two regions.

How to cite: Qiu, J., Padavini, N., Vannucchi, P., and Morgan, J.: Using Dynamic Topography and Seismic Tomography to explore the compensation of seafloor in oceanic and back-arc basins, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14528, https://doi.org/10.5194/egusphere-egu24-14528, 2024.

Chemical diffusion in the mantle has typically been viewed to play a negligible role in geodynamic processes.  However, diffusion rates for water (H) and helium (He) are large enough that they lead to observable differences between pyroxenite-rich melting associated with ocean island volcanism (OIB) and more peridotite-rich melting associated with mid-ocean ridge basalts (MORB). Laboratory measurements of diffusion rates of H and He at ambient mantle temperatures in olivine are of order ~10 km/1.7Gyr for He and ~250 km/1.7 Gyr for H. If the mantle is an interlayered mixture of recycled oceanic basalts and sediments surrounded by a much larger volume of residual peridotites, then chemical diffusion can shape the mantle in two important ways.  Hydrogen will tend to migrate from peridotites into adjacent pyroxenites, because clinopyroxene has a much stronger affinity for water than the olivine and orthopyroxene that form the bulk of mantle peridotites. Therefore pyroxenite lithologies will typically have twice or more the water content of their surrounding damp peridotites. This will strongly favor the enhanced melting of pyroxenites that is now mostly agreed to be a common feature of the OIB source. Radiogenic ⁴He will have the opposite behaviour — it will tend to migrate from where it is produced in recycled incompatible-element-rich (e.g. U and Th-rich) pyroxenites into nearby, larger volume fraction, but U+Th-poorer peridotites, while the radioisotopes of Ar and Ne that are also produced by the decay of the incompatible elements K, U, and Th will diffuse much less, and thus remain within their original pyroxenite source.  This effect leads to lower ⁴He/²¹Ne and ⁴He/⁴⁰Ar ratios in OIB in comparison to the predicted values based on the mantle’s bulk geochemistry, and complementary higher ⁴He/²¹Ne and ⁴He/⁴⁰Ar ratios in the MORB source that is formed by the plume-fed asthenospheric residues to OIB melt extraction at plumes.

 The recent observation of a 150-km-deep positive shear velocity gradient (PVG) beneath non-cratonic lithosphere (Hua et al., 2023) is further evidence for the initiation of pyroxenitic melting at this depth within the asthenosphere. It also implies that lateral temperature variations at this depth are quite small, of order +/- 75°C. This near uniformity of temperatures near both mantle plumes and mid-ocean ridges is, in turn, strong evidence in favor of the hypothesis that the asthenosphere is fed by mantle plumes. We propose that two filtering effects occur as plumes feed the asthenosphere, removing both the hottest and coldest parts of upwelling plume material. First, the peridotite fraction in the hottest part of upwelling plume material melts enough for it to dehydrate, thereby transforming this fraction into a more viscous and buoyant hotspot swell root that moves with the overlying plate, not as asthenosphere. Second, since plume material is warmer than average mantle, it is more buoyant, creating a natural density filter that prevents any cooler underlying mantle from upwelling through it. These rheological and density filters make the asthenosphere sampled by melting at mid-ocean ridges have a more uniform temperature than its typical underlying mantle.

How to cite: Morgan, J. P. and Morgan, W. J.: H, He, and seismic evidence for a bilithologic plume-fed asthenosphere , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16479, https://doi.org/10.5194/egusphere-egu24-16479, 2024.

Meimechite (i.e., rare high MgO and TiO₂ ultramafic rocks) concluded the Permo-Triassic Trap magmatism ca. 250 Ma-ago, known as a Siberian Large Igneous Province (SLIP) in the Meimecha-Kotui region, northern Siberia (e.g. [1]). In addition to their elevated MgO contents, meimechite’s melts display almost no crustal contamination, making them ideally suited to investigate the mantle source of the SLIP. Formerly, two opposing models were evoked for the origination of the meimechite: i) the hottest phanerozoic mantle plume [1] or ii) water fluxing of the asthenospheric mantle in a long-lived subduction zone [2]. Based on an extended analytical workflow we will shed new light on the source of these unusual rocks.

Here we present new results for more than 300 olivine-hosted homogenized melt inclusions from Siberian meimechite including major, minor and trace elements, water and Sr-isotopes contents (EPMA, LA-ICP-MS and Raman spectrometry) along with the chemical composition of their host olivine (EPMA, LA-ICP-MS). When encountered, spinel inclusions were analysed by EPMA for major element abundances.

We show that the Siberian meimechite crystallised from a highly magnesian (MgO > 22 wt%) parental melt deficient in H₂O compared to Ce and K concentrations, which was degassed of most of its CO₂ and likely part of its H₂O while rising to shallower depths. Three independent geothermometers (Mg-Fe and Sc-Y olivine melt and Al olivine-spinel) confirm the high crystallisation temperature of the Siberian meimechite, ca. 1400^oC. Furthermore, the calculated potential temperatures (over 1500^oC) imply a mantle plume origin of the Siberian meimechite and, consequently, of the SLIP.

Initial ⁸⁷Sr/⁸⁶Sr values of melt inclusions reveal heterogeneous populations ranging from 0.7022±0.0002 to 0.7039±0.0004 suggesting mixing between at least two depleted mantle components. The less depleted group has an average Bulk Silicate Earth (BSE) model age of 876±88 Ma, whereas the more depleted group is significantly older with an average model age of 1716±76 Ma. All source components display significantly fractionated proxies of continental crust extraction (Nb/U, Th/U and Ce/Pb [3]), indicating major events of continental crustal formation and deep recycling of residual lithosphere before the Proterozoic Eon.

References:

[1] – Sobolev, A.V., et al., Russ. Geol. Geophys., 2009 and references therein. [2] – Ivanov, A.V., et al., Chem. Geol., 2018. [3]- Hofmann, A.W. et al. EPSL, 1986.

How to cite: Esteban, M., Sobolev, A., Batanova, V., Vezinet, A., Asafov, E., and Krasheninnikov, S.: Insight into the formation of the Siberian Large Igneous Province: A study of olivine-hosted melt inclusion in meimechite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17078, https://doi.org/10.5194/egusphere-egu24-17078, 2024.

Our understanding of plate tectonics and mantle convection has made significant progress in recent decades, yet the specific impact of mantle plumes on plate tectonics remains a topic of controversy. The motions of the Earth’s lithosphere serves as a powerful lens into the dynamic behavior of the asthenosphere and deeper mantle, helping to untangle such controversies. Surface observations, therefore, provide important constraints on mantle convection patterns through space/time. Among these observations, the record of plate motion changes stands out, as it enables the geographical identification of torque sources. Consequently, surface observations provide essential constraints for theoretical models and numerical simulations.

The analytical Poiseuille flow model applied to upper mantle flux in the asthenosphere offers a robust and testable prediction: Poiseuille flow induced plate motion changes should coincide with regional scale mantle convection induced elevation changes. Mantle plumes can generate such pressure driven flows, along with intraplate magmatism and induce buoyancy-driven uplift that leaves an imprint in the sedimentary record.

Here, I will present a synthesis of geological and geophysical observations, supported by analytical calculations, to illustrate that a significant number of plate motion changes can be attributed primarily to torques originating from mantle plumes.

How to cite: Stotz, I. L., Vilacís, B., Hayek, J. N., Carena, S., Friedrich, A., and Bunge, H.-P.: The Influence of Mantle Plumes on Plate Tectonics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17341, https://doi.org/10.5194/egusphere-egu24-17341, 2024.

Models depicting the plate kinematic development of the Indian Ocean have a range of applications including in paleogeographic studies and in formulating and testing ideas about plume/plate interactions. Until now, these applications have been forced to tolerate egregious model/observation inconsistencies concerning the relative motion history of India and Madagascar. Whilst the Phanerozoic record of these motions begins with ∼90 Ma basalts that erupted along a narrow rift basin, all modern plate kinematic models for the Indian Ocean predict hundreds of kilometres of relative motions, in diverse and conflicting senses, over several tens of millions of years prior to the eruptions. The diversity of these predicted motions suggests they are artefacts that arise from differing approaches taken to modelling the development of the eastern and western parts of the ocean, rather than a reflection of insufficient or absent geological observations. In this contribution, I present a new model for the early plate kinematic development of the Indian Ocean that is constrained by observational evidence for relative plate motion azimuths in the Enderby and western Bay of Bengal basins and by explicitly maintaining a rigid mid- and early Cretaceous Indo-Malagasy body. This approach requires the model to feature two small tectonic plates between the continental margins of eastern India and East Antarctica. The older of the two, Mandara, is an intraoceanic plate in the Enderby Basin that may have formed in relation to delivery of excess melt from the Kerguelen plume to the basin's mid-ocean ridge. The younger plate, Vasuki, in the western Bay of Bengal Basin, also accommodated plume-related melt at its boundaries, in its case from the Marion and possibly also the Crozet plume. The model shows this plate transporting Sri Lanka ∼800 km southwards along the eastern Indian continental margin to its present location. The model also requires the presence of around half a million square kilometres of continental crust beneath the Kerguelen Plateau, which lies within the range of published observation-led estimates of its extent. Neither the absence of evidence for relative motions between India and Madagascar prior to ∼90 Ma, nor the modelled Euler rotation pole's location afterwards, are consistent with suggestions that traction forces related to the ascent of the Marion plume drove the mid-Cretaceous onset of subduction in the western Neotethys.

How to cite: Eagles, G.: A new model of plate kinematics describing the early development of the Indian Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17862, https://doi.org/10.5194/egusphere-egu24-17862, 2024.

Most volcanic activity on Earth is linked to well-known processes like plate tectonics and mantle plumes, typically through mechanisms such as flux-melting in subduction zones and decompression-melting at ridges and mantle plumes. However, recent discoveries point to a different origin for some intraplate volcanism, a key example being 'Petit-Spots'—small volcanic mounds that erupt on incoming plates near subduction zones. Here we propose that flexural pumping, occurring as the subducting slab unbends, transports fluids released by intra-slab dehydration to the slab's base where these fluids induce flux-melting in the warm slab base and asthenosphere beneath the slab. Counterflow in the buoyant asthenosphere beneath the subducting plate further expands the region of petit-spot volcanism. This mechanism not only explains the origin of petit-spot volcanism but also suggests a broader conceptual model for generating low-degree melts in the oceanic asthenosphere.

How to cite: Vannucchi, P., Shi, Y., Yang, T., Fujie, G., and Morgan, J. P.: Flexural Pumping and the Origins of Petit-Spot Volcanism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18017, https://doi.org/10.5194/egusphere-egu24-18017, 2024.

The extensive Paleocene magmatism of the British and Irish Tertiary Igneous Province (BITIP)—a part of the North Atlantic Igneous Province (NAIP)—was accompanied by significant uplift and exhumation, as evidenced by geothermochronological and other data. The enigmatic origins of the volcanism and uplift are debated. The Iceland Hotspot reached the North Atlantic at that time and could probably supply anomalously hot asthenospheric material to the volcanic areas of NAIP, but they were scattered over a broad area thousands of kilometres across. This motivates alternative, non-plume explanations.

Here, we obtain a map of the lithosphere-asthenosphere boundary (LAB) depth in the region using thermodynamic inversion of seismic surface-wave data. Love and Rayleigh phase velocity maps in broad period ranges were computed using optimal resolution tomography with direct model error estimation and supplied the data for the inversion.

Our results reveal a consistently thinner-than-average lithosphere beneath the Irish Sea and surroundings, encompassing northern Ireland and western Scotland and Wales. The Paleocene uplift, BITIP volcanism and crustal underplating are all located in the same regions, which are underlain, consistently, by anomalously thin lithosphere.

The previously unknown lithospheric anomalies we discover yield a new insight into how the Iceland Plume could cause volcanism scattered over the vast NAIP. Plume material is likely to have flowed into pre-existing areas of thin continental lithosphere, whose thickness was then reduced further by the erosion by the hot asthenosphere. The thinning of the lithosphere and the presence of hot asthenosphere beneath it can account for the uplift, volcanism and crustal underplating. The localisation of the plume material in scattered thin-lithosphere areas, such as the circum-Irish-Sea region, can explain the wide scatter of the volcanic fields of NAIP.

How to cite: Bonadio, R., Lebedev, S., Chew, D., Xu, Y., and Fullea, J.: How could a single Iceland Plume produce the widely scattered North Atlantic Igneous Province volcanism? New clues from Britain and Ireland., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18296, https://doi.org/10.5194/egusphere-egu24-18296, 2024.

The X-discontinuity at 300 km beneath the Hawaiian hotspot has been hypothesized to require at least 40% basalt, a figure that would far exceed the plume's buoyancy and thus be irreconcilable with initial entrainments.
We had previously explored the potential for large basalt accumulations to form over time by simulating a section of the plume conduit, with known quantities of basaltic material flowing in as discrete heterogeneities. For entrainments of 10-20%, we had estimated average accumulations of 20-25% at ~300 km depth.
While this simplified setting recreated segregation of the denser material, it did not feature a realistic plume. On the other hand, employing mechanical mixture compositions hamper quantitative analyses of the recycled basalt.

I have overcome this issue by developing a novel implementation to the ASPECT code.
My advancement features a mechanical mixture composition (82% harzburgite — 18% basalt) for both the background mantle and the plume. The recycled material is then added to the self-consistent rising plume in the form of compositionally distinct basaltic heterogeneities. By combining these two approaches, I was able to successfully reproduce and quantify material segregation while keeping an accurate plume composition.

Preliminary results, conducted in a 2000 km * 1000 km 2D domain, with entrainments of 10-20%, and a maximum resolution of 0.98 km in the heterogeneities, show average basalt accumulations of 20-22% around 300 km depth. Occasional, transient peaks at 31% and 35% can be observed for plumes incorporating 15% basalt. Over the model time (20 Ma), the denser material tends to sink between 360-660 km depth, generating large average accumulations of 35-40%. 

This new strategy not only opens promising scenarios by overcoming long-standing model limitations, but also reinforces the potential for mantle plumes to accumulate more denser material than classically thought, shedding further light on the controversial link between the X-discontinuity and the Hawaiian plume activity.

How to cite: Monaco, M.: A Novel Implementation to Simulate Basalt Segregation in the Hawaiian Mantle Plume Overcomes Model Limitations and Elucidates the Origin of the X-discontinuity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18845, https://doi.org/10.5194/egusphere-egu24-18845, 2024.

Classic models of continental rifting predict that after continental break-up, the extended lithosphere returns to its original thermal state (McKenzie, 1978). At this time, the heat-flow should decrease from the proximal margin sectors, where the radiogenic crust is still relatively thick, towards its distal sectors, where the crust has extensively thin and the thermal lithosphere thickness approximates that of the adjacent untinned continental lithosphere. This should occur after approximately ~50 Myr for 120 km thick continental lithosphere (McKenzie, 1978). Although, good quality heat flow data is very scarce along margins, some of them, such as the Voring basin, show instead increasing heat flow towards the distal margin sectors ~60 Myr after break-up (Cunha et al., 2021). Recent numerical models have suggested, instead, that the lithosphere under the hyper-extended continental margins, does actually not return towards its original thermal thickness, instead it acquires a thickness which is similar to that of the adjacent plate, resulting in higher heat-flow towards the distal margins at ~80-100 Myr after break-up (Perez-Gussinye et al., 2023). In those models, the delay in thermal relaxation under the hyper-extended margins is caused by small-scale convections cells, a process which also prevents the oceanic lithosphere to infinitely cool and is responsible for the flattening of the oceanic bathymetry at old ages. Interestingly, the models show that the delay in thermal relaxation under both the hyper-extended rifted margins and the old oceanic crust increases with decreasing rifting and spreading velocity, such that is most obvious in ultra-slow margins and adjacent oceanic basins (Perez-Gussinye et al., 2023). Here we use updated 2D numerical models which include the thermal consequences of serpentinisation, melting and melt emplacement to understand the thermal evolution of oceanic plates and compare the resulting plate structure, heat-flow and bathymetry with the observations from seismic LAB structure, and global heat-flow and bathymetry databases.

References

Cunha, T.A., Rasmussen, H., Villinger, H. and Akinwumiju, A.A., 2021. Burial and Heat Flux Modelling along a Southern Vøring Basin Transect: Implications for the Petroleum Systems and Thermal Regimes in the Deep Mid-Norwegian Sea. Geosciences, 11(5), p.190.

McKenzie, D., 1978. Some remarks on the development of sedimentary basins. Earth and Planetary science letters, 40(1), pp.25-32.

Pérez-Gussinyé, M., Xin, Y., Cunha, T., Ram, R., Andrés-Martínez, M., Dong, D. and García-Pintado, J., 2024. Synrift and postrift thermal evolution of rifted margins: a re-evaluation of classic models of extension. Geological Society, London, Special Publications, 547(1), pp.SP547-2023.

How to cite: Gudipati, R. R., Pérez-Gussinyé, M., and García-Pintado, J.: Influence of small-scale convection on the cooling of oceanic lithosphere at slow and fast spreading ridges, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19459, https://doi.org/10.5194/egusphere-egu24-19459, 2024.

The western North American margin records multiple phases of rifting and convergence, resulting from the interaction between western Laurentia, rifted continental fragments, and intra-oceanic terranes originating in the Panthalassa and Pacific oceanic plates. Quantitative plate reconstructions of this margin have prioritised diverging interpretations regarding the subduction polarities of eastern Panthalassa terranes during Jurassic to Cretaceous times. These discrepancies arise from the reliance on either seismic tomography or surface geology as the first-order constraint for determining subduction polarity. We present an updated tectonic reconstruction for western North America from the Devonian to present day. In this new model, we reconcile geological histories based on surface geology, geochronology, paleomagnetism and isotopic data, with interpretations of seismic tomography. The new reconstructions account for the tectonic evolution of the Alaska orocline, western Canada and western United States (US) and south-western (SW) North America, which have not been implemented in detail in previous tectonic models. Our model suggests that most of the terranes of western North America were rifted off Laurentia and Baltica during Devonian to Triassic extension and trench-retreat. Following back-arc rifting and opening, many of the terranes (e.g. Insular, Intermontane, Angayucham) experienced an intra-oceanic phase before accreting to the continental margin of North America at different times, between Early Triassic to Late Cretaceous times. The model illustrates the collision of the Angayucham Terrane, counterclockwise rotation and orocline formation in Alaska during the middle Jurassic. In western US and SW North America, the model showcases Jurassic to Cretaceous extension and rifting. Extension starts first in western US (170-145 Ma) and is then propagated south, causing the opening of the Bisbee Basin (161-105 Ma). The model also captures the Late Cretaceous collision of the Insular Terrane, which triggered transpression, terrane translation for thousands of kilometers and clockwise rotation in western US during Late Cretaceous to Paleogene times. Our updated model highlights the importance of surface geology in constraining the polarity of ancient subduction zones interpreted from seismic tomography.

How to cite: Rodriguez Corcho, A. F., Zahirovic, S., Anthony, M., Tarkyth, D., Alfonso, C., Seton, M., Muller, D., Eglington, B., and Tikoff, B.: The tectonic evolution of the western North American margin since the Devonian, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19570, https://doi.org/10.5194/egusphere-egu24-19570, 2024.

Geodynamicists have long proposed that mantle convection creates dynamic topography — a long-wavelength, low-amplitude signal extending beyond plate tectonics. This predicts transient vertical Earth surface movement of 1–2 km across thousands of horizontal kilometers at any location, including continental interiors. Despite these claims, experts working on local observations, using the multitude of high-resolution geological, sedimentological, and geomorphological data, face challenges in finding clear evidence to unequivocally support dynamic models of whole mantle convection, including the plume mode. Moreover, regional-scale stratigraphic techniques, such as sequence stratigraphy, which enabled hydrocarbon exploration, invoke unconformities on multiple scales but, from their far-field perspective, render correlation to distinct geodynamic events difficult.

To circumvent this scaling and correlation problem, I propose to reverse the stratigraphic perspective to an outwards-directed view. This approach requires a theoretical geodynamic framework and the identification of tectonic events (center, near field), such as magmatic arcs, flood basalts, or uplifted domes, followed by outward-directed geological mapping of regional-scale stratigraphic unconformities —predicted by theory— to distal regions. This approach is analogous to the way in which paleoseismologists examine so-called event horizons, i.e., unconformities in the stratigraphic record adjacent to fault scarps that preserve a record of the Earth's surface at the time of earthquake rupture.

This event-based stratigraphic mapping method (EVENT-STRAT) enables analysis of geological events on geological maps compiled at regional to continental scales. The technique connects local work into a continent-scale framework, allowing identification of transient patterns related to dynamic mantle-derived events. The EVENT-STRAT mapping method is designed to visualize geological effects resulting from both the plate and the plume mode of mantle convection. The toolbox consists of the hiatus mapping method (Friedrich 2019, Geological Magazine) and the event-based stratigraphic framework mapping (e.g., Friedrich et al. 2018, Gondwana Research). The upcoming EVENT-STRAT mapping method involves multiple polygonal stacking to analyze various stratigraphic event horizons, such as hiatus surfaces and unconformities. The most significant current challenge is to add the high-precision stratigraphic data compiled on local chronostratigraphic charts to continent-scale geological maps. This effort requires the attention of geological surveys on international scales seeking to compile theory-based geodynamic-stratigraphic parameters on the next generation of global and continent-scale geological maps.

How to cite: Friedrich, A. M.: Geodynamic Stratigraphy — Defining the Need for Mapping Strategies to link Models of Mantle Dynamics to Surface Processes on Geological Scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19837, https://doi.org/10.5194/egusphere-egu24-19837, 2024.

Redox state of parental magma would have undergone significant changes from partial melting in the mantle to emplacement in the shallow crust, which might play a critical role in the genesis of magmatic Ni-Cu sulfide deposits in convergent tectonic settings. In this study, we present mineralogy, petrology, and fO₂ calculations of the Xiarihamu Ni-Cu deposit and the Shitoukengde non-mineralized intrusion in the East Kunlun orogenic belt. Olivine-spinel pairs in different magmatic stages were chosen to estimate the magma fO₂ (olivine-spinel oxybarometer), track the changes in oxygen fugacity during magmatic evolution, and reveal its influence on the metallogenic mechanism of the Ni-Cu sulfide deposit. Spinel Fe³⁺/ΣFe ratios determined by a secondary standard calibration method using electron microprobe. Those ratios of the Xiarihamu Ni-Cu deposit vary from 0.32±0.09 to 0.12±0.01, corresponding to magma fO₂ values ranging from ΔQFM+2.2±1.0 to ΔQFM-0.6±0.2. By contrast, those of the Shitoukengde mafic-ultramafic intrusion increase from 0.07±0.02 to 0.23±0.04, corresponding to magma fO₂ varying from ΔQFM-1.3±0.3 to ΔQFM+1.0±0.5. A positive correlation between fO₂ and Cr-spinel Fe³⁺/ΣFe ratios suggests that the Cr-spinel Fe³⁺/ΣFe ratios can be used as an indicator for magma fO₂. The high fO₂ (QFM+2.2) of the harzburgite in the Xiarihamu Ni-Cu deposit suggests that the most primitive magma was characterized by relatively oxidized conditions, and then became reduced during magmatic evolution, causing S saturation and sulfide segregation to form the Xiarihamu Ni-Cu deposit. The evolution trend of the magma fO₂ can be reasonably explained by metasomatism in mantle source by subduction-related fluid and addition of external reduced sulfur from country gneisses (1.08–1.14 wt.% S) during crustal processes. Conversely, the primitive magma of the Shitoukengde intrusion was reduced and gradually became oxidized (from QFM-1.3 to QFM+1.0) during crystallization. Fractional crystallization of large amounts of Cr-spinel can reasonably explain the increasing magma fO₂ during magmatic evolution, which would hamper sulfide precipitation in the Shitoukengde intrusion. We propose that the temporal evolution of oxygen fugacity of the mantle-derived magma can be used as one of the indicators for evaluating metallogenic potential of Ni-Cu sulfide deposits, and reduction processes from mantle source to shallow crust play an important role in the genesis of magmatic Ni-Cu sulfide deposits.

How to cite: Jia, L., Chen, Y., Su, B., Mao, Q., and Zhang, D.:  Oxygen-fugacity evolution of magmatic Ni-Cu sulfide deposits in East Kunlun: Insights from Cr-spinel composition , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-103, https://doi.org/10.5194/egusphere-egu24-103, 2024.

Petrological investigations of large alkaline provinces with carbonatites are very important to understanding the generation and evolution of alkaline melts, as well as processes provided generation of related ore deposits. Most often, generation of large alkaline massifs with carbonatites accompanied by intrusion of related ultramafic alkaline and related alkaline-ultramafic melts as dykes swarms and explosive pipes. These melts could be generated on the initial stages of magmatic activities of alkaline province magmatism, or fix the final stages of alkaline magmatism, after the formation of large alkaline massifs with carbonatites. Studying of these melts could provide insights into the composition of primary melts for large alkaline province, as well as understanding their evolution during magmatic activities. Moreover, the latest melts forming dykes and explosive pipes could provide information about the evolution of the mantle source of these rocks including of processes of lithospheric mantle transformations (enrichment, depleting, mantle metasomatism etc.).

The Kola alkaline province (KAP) with carbonatites is a good natural laboratory for investigation petrology of alkaline melts and their evolutions. KAP includes large alkaline massifs with carbonatites, the early dyke swarms of ultramafic and alkaline lamprophyres and late explosive pipes of the alkaline rocks (Arzamastsev et al., 2005). To investigate the composition of alkaline melts at the late stages of the province's magmatic activity, we have studied the petrography and mineralogy (olivine composition) of the Namuaiv pipe rocks.

The Namuaiv pipe (363 ± 3 Ma; Arzamastsev et al., 2005) erupted the alkaline rocks of the north part Khibiny massif (377± 3 Ma). The detailed petrographical studied suggested, that the pipe breccia was formed during mixing of two portions of alkaline melts close in composition to alkaline picrite and melanephelinite.

The Namuaiv rocks contain several types of olivine grains: (1) picritic melt phenocrysts; (2) antecrysts of ultramafic lamprophyres of the Kandalaksha Bay (Vozniak et al., 2023) that traced the first stages of the province magmatism; and (3) disintegrated fragments of the lithospheric mantle peridotites (mantle xenocrysts). The composition of olivine phenocrysts suggests that in the final stage of KAP activity, the alkaline melts have not fractionated in deep magmatic chambers and their composition is close to primary melts. That is in contrast to the first stages of KAP magmatism, where lamprophyre dikes were formed as fractionated melts (Vozniak et al., 2023). The present of the olivine antecrysts assumes that the Namuaiv melts ascent trough magmatic channels modified by previous portions of alkaline melts, that consistent with the presence metasomatic clinopyroxene-phlogopite xenoliths within the pipe.

The study was supported by the Russian Science Foundation under Grant No 23-77-01052.

Arzamastsev A.A., Belyatsky B.V., Travin A.V. et al. 2005. Dyke rocks in the Khibiny massif: relation to plutonic series, age, and characterization of mantle sources // Petrology. V.42. N3. P.1-23.

Vozniak A.A., Kopylova M.G., Peresetskaya E.V. et al. 2023. Olivine in lamprophyres of the Kola Alkaline Province and the magmatic evolution of olivine in carbonate melts // Lithos 448–449, 107149. doi:10.1016/j.lithos.2023.107149

How to cite: Shaikhutdinova, D., Kargin, A., Sazonova, L., Lebedeva, N., Nosova, A., and Vasiliy, Y.: The Namuaiv picrite-melanephelinite pipe, Kola alkaline province, Russia: petrography and evolution of late alkaline melts during forming large alkaline province with carbonatites., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-616, https://doi.org/10.5194/egusphere-egu24-616, 2024.

The lower crust and Moho pyroxenites and xenocrysts from Cenozoic volcanoes studied with the EPMA, SEM and LA ICP MS for trace elements evidence about the structure and composition of the transitional zone from the crust to mantle in Cenozoic volcanic regions In Vitim (picrite basalts), Dzhida, (Bartoy volcanoes) and Tunka valley (Karierny volcano). For the comparisons the lower crust xenocrysts from the Angara Vitim batholite were studied. The calculated PT conditions show the PT estimates are localizing within the Moho –and just beneath giving the vast range of temperatures. Lower they trace 90 mw/m2 geotherm. Within the crust the variation of temperature regime are varying from the conductive to advective. Xenocrysts and pyroxenite xenoliths mainly trace 90 mw/m2  SEA plume geotherm the area of the intrusions is over heated to 1350oC.

Fig.1 PT diagram for the xenoliths from Vitim Miocene  Picrite basalts

Fig.2 PT diagram for the xenoliths from Bartoy Pleistocene basalts

Fig.3 PT diagram for the xenoliths from Tunka Pliocene basalts

Fig.4 PT diagram for the xenocrysts from  Magmas of Angara-Vitim batholite

The granulites are typically represent the more colder conditions than SEA geotherm.  Xenocrysts from Angara Vitim batholith magmas reveal more depleted material of lower crust than those found in Cenozoic lavas and possibly are skialites. The xenocrysts and granulate xenoliths in Cenozoic lavas are mainly basic cumulates. The lower crust became more acid to the upper part. The lateral variations in the lower crust sampled material show enrichment in K2O at the boundary with the Siberian craton in Tunka, more metasomatic and hydrous nature in Dzhida zone and more basic and CaO rich characteristic in Vitim area.  These data give the evidence for the conditions of the creation of magmas of Angara-Vitim Batholiths.  It was created by the hot spot created kimberlites and basalts in north and Center of Yakutia in Silurian- Devonian time and Ingashi lamproites,  than it turned in Transbaikalia and after returned to central and Northern Siberia.   

 Supported by Ministry of Science and Higher Education of the Russian Federation. Supported by Russian Science Foundation (23-17-00030). Work is done on state assignment of IGM SB RAS, Geological institute SB RAS Ulan Ude and Institute of Earth crust SB RAS, Irkutsk

How to cite: Ashchepkov, I., Tsygankov, A., Burmakina, G., Rasskazov, S., Ailow, Y., and Karmanov, N.: Thermal state and nature of the low crust in the Baikal Rift zone according to the lower crust xenoliths of Cenozoic volcanics and Paleozoic magmas. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1231, https://doi.org/10.5194/egusphere-egu24-1231, 2024.

Finding of the giant diamond in Ebelyakh of CLIPPIR type of IIa type (Moor, 2014) suggest that similar diamonds should be found in the source kimberlites in Anabar basing and nearest Northern fields located within collision Khapchan terrain. To predict the finding authors are using the method of 5E diagrams based on the principle of analogy of the compositions Fe/(Fe+Mg) – Cr/(Cr+Al) – (Mn,Na) (Mitchell, 1986) for satellite minerals (Gar, Cpx, Chr and Ilmenites) of diamond (DSM) comparing with the etalon diagram for Karowe pipe (reference) and any other pipe. The forecast is quantified by the probability of convergence of these compositions using the division to the cluster groups. It was shown that the convergence of the DSM compositions of the Karowe and Grib pipes is 74%, which can be regarded as an indicator of the possible presence of diamonds in the predicted CLIPPIR pipe (Zinchenko et al., 2021).

 The application of this technique to two weakly diamondiferous kimberlite pipes of the Anabar region is demonstrated that the Leningrad pipe (Lower Devonian) have probability (75%) and Malokuonamskaya (Lower Triassic) (20%). Methods of constructing 5E diagrams and complementary PTXfO₂ diagrams by I.V. Ashchepkov (2010-2023) of reconstructed lithospheric mantle sections (SCLM) to predict the crystallization of CLIPPIR diamonds. The petrological meaning of such characteristic suggest diamond formation in pipe in permeable mantle within protokimberlite magmatic chamber located near the lithosphere boundary and  connected with the asthenospheric source supplying by low oxidized magma, sulfides and extra pressure. The pipe should be surrounded by the low oxidized mantle eclogites rich C and dunites with the high pressure-temperature and Mg-rich ilmenite-chromite metasomatites.

A.

B.

Fig.1.  Mitchels’s diagram for minerals from Leningrad  and Malokuhamskay (B) pipes in comporisond with the Karowe pipe (contur lines) Cr- pyropes, Cr-diopsides, Ilmenites, Cr -spinels together. B. Triangle Na-Mn-Ti and C. Triangle Na-Al-Cr for Cr-diopsides and pyropes. D. distributions of the cluster groups for different minerals. E. Correltions of diamond grade with TiO₂ in garnest, Cr-diopsides and Cr-spinels and Fe₂O₃ in ilmenites

The application of this technique to two weakly diamondiferous kimberlite pipes of the Anabar region is demonstrated that the Leningrad pipe (Lower Devonian) have probability (75%) and Malokuonamskaya (Lower Triassic) (20%). Methods of constructing 5E diagrams and complementary PTXfO₂ diagrams by I.V. Ashchepkov (2010-2023) of reconstructed lithospheric mantle sections (SCLM) to predict the crystallization of CLIPPIR diamonds. The petrological meaning of such characteristic suggest diamond formation in pipe in permeable mantle within protokimberlite magmatic chamber located near the lithosphere boundary and  connected with the asthenospheric source supplying by low oxidized magma, sulfides and extra pressure. The pipe should be surrounded by the low oxidized mantle eclogites rich C and dunites with the high pressure-temperature and Mg-rich ilmenite-chromite metasomatites.

A.

B.

C.

Fig.2. PTXFO₂ diagram for all xenocrysts from Leningrad (A), Malokuonamskaya (B) and Karowe AK-6 pipes. Symboles see legend

Russian Science Foundation grant 23-17-00030

How to cite: Ivanov, A., Zinchenko, V., Ashchepkov, I., Babushkina, S., Oleinikov, O., and Shelkov, P.: The perspectives of finding of giant CLIPPIR-type diamonds in weakly diamondiferous kimberlites of the north of Yakutia (Western Anabar region) using method of 5E Mitchells’s diagrams and cluster analyses, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3574, https://doi.org/10.5194/egusphere-egu24-3574, 2024.

The influence of the hot spot for the AVB was assumed by (Kuzmin and Yarmolyuk, 2011). It may be the same hot spot that cause the creation of the kimberlites at 420 Ma at the north of Siberian craton (Sun et al,, 2014; 2018) than in the central part of Yakutian kimberlite province 350- 370 Ma. and transferred to the Prisayanie forming kimberlite fields covered by Carboni ferrous Permian sedimentary sequences in the basins of Tumanshet, Biryusa and Chuna rivers. Than it produced the Ingashi kimberlites - lamproites 310 -300 Ma (Kostrovitsly et al., 2022).

Granites of Angara-Vitim batholith were caused and influenced by this huge thermal event. The A-type granitoid magmatism and acid and mafic magmatism accompanied by mingling between these magmas suggest influence of the mantle plume (Litvinovsky et al., 2002; Tsygankov et al., 2019). This explains the K-nature of the granitoid magmatism, corresponding to the selective melting of the K-feldspars (Litvinovsky et al., 2000). This is the reason of the alkaline magmatism widely distributed among the  AVB magmas (Tsygankov et al., 2010-2021).

The huge amount of the volatiles that accompany plumes are responsible for melting in the mantle and crust (White and McKenzie, 1995). But essential parts of plume volatiles are CO₂ and CH gases (Marty and Tolstikhin, 1998).. The H₂O fluxes correspond to the starting and final stages of plume impulses (Ivanov et al., 2013). The periods of such pulses are nearly close to 30- Ma what is regulated by the Cosmic forces (Abbott, and Isley, 2002). Boundaries of the geological periods correspond to plume events In Transbaikalia, the H₂O-rich flux was designated by transition to more acid magmas at 270 Ma. The CO₂-rich flux at the maximum was manifested by the generation of the Burpala alkali-carbonatite massif (Vladykin et al., 2017).

Further, numerous already granitic and associated magmas and massifs were found in Eastern Sayan and Southern Pribaikalie. In Svyatoi Nos in Baikal 310 Ma (Kruk et al., 2023). 

The simultaneously and later the hot spot  created the main massifs of the AVB at the time span 275 -320 Ma (Khubanov et al., 2016; 2021).  The further continuation could be found in Khangai  batholith (270-240 Ma) (Yarmolyuk et al., 2013).

Than at the eastern margin, the plume turned to the NNW again and created the Siberian large igneous province- Permo-Triassic traps (Kuzmin and Yarmolyuk, 2011) 260-240 Ma.  the development of the plume magmatism in Early Triassic and later  in Jurassic time probably was transformed to the Island hot spot (Kuzmin and Yarmolyuk, 2010).

RNF grant 23-17-00030

Kostrovitsky  S.I. ea  2021.  Special Publications 513, 45 - 70.

Khubanov V.B ea 2021.   Russian Geology  Geophysics. 62, 1331-1349.

Kuzmin, M.I. , Yarmolyuk,   2014.   Russian Geology and Geophysics, 55, 120-143.

Kuzmin M.I. ea 2010.   Earth-Science Reviews, 102, 29-59.

Yarmolyuk V.V ea 2013,   Petrologiya , 21/2, 115–142.

How to cite: Tsygankov, A., Ashchepkov, I., and Galina, B.: The influence of the Siberian plume to the formation of Angaro-Vitim batholiths, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3630, https://doi.org/10.5194/egusphere-egu24-3630, 2024.

Based on the analysis of the tectonophysical characteristics of the actual seismofocal zone (SFZ) in the lithosphere of the Kuril-Kamchatka region and adjacent Oceanic areas,  we estimated the boundary conditions necessary for constructing the quantitative models of heat and mass transfer dynamics in compacted heterophase media under active volcanoes located over the mantle and crustal magmatic   sources of the ocean–continent transition regions of the northwestern sector of the Pacific Ocean.

The methodology of obtaining the information  used for developing of the mathematical models of magmatogenic processes includes: 1) the study of individual porphyry deposits associated with active fluid volcanogenic systems; 2) the study of morphological structures using cosmic satellite images (Sharapov et al., 1980); 3) the study of mantle and crust xenoliths of volcanics (Kutyev, Sharapov, 1979; Sharapov et al., 2009, 2017, 2020); 4) parametric tectono-physical analysis of the modern SFZ of the studied region (Sharapov et al., 1984, 1992); 5) experimental modeling of the  processes of deformation   Earth's crust and lithospheric mantle rocks of modern SFZ (Sharapov et al., 1984, 1992); 6) construction of mathematical models of the petrogenesis under volcanoes (Sharapov et al., 2007, 2020)

According to data on the structure of the Earth's crust under the Avacha volcano; (Koulakov et al., 2014), permeable zones are linear fractures 2-4 km wide, which are conductors of melts and magmatogenic fluids coming from magmatic systems (Koloskov et al., 2014).

An analysis of the time characteristics of formation porphyric deposits in the active margins of the Pacific Ocean (Sharapov et al., 2013) showed that more than 70% of the described deposits are formed during the evolution of fluid mantle-crustal ore-magmatic systems. This study analyzes the data on the structure of the modern SFZ of Kamchatka and the Kuril Island arc, used in constructing a model of heat and mass transfer under volcanoes.

Based on the analysis of the tectonophysical characteristics of the actual seismofocal zone (SFZ) in the lithosphere of the Kuril-Kamchatka region and adjacent Oceanic areas,  we estimated the boundary conditions necessary for constructing the quantitative models of heat and mass transfer dynamics in compacted heterophase media under active volcanoes located over the mantle and crustal magmatic   sources of the ocean–continent transition regions of the northwestern sector of the Pacific Ocean.

T

An analysis of the time characteristics of formation porphyric deposits in the active margins of the Pacific Ocean (Sharapov et al., 2013) showed that more than 70% of the described deposits are formed during the evolution of fluid mantle-crustal ore-magmatic systems. This study analyzes the data on the structure of the modern SFZ of Kamchatka and the Kuril Island arc, used in constructing a model of heat and mass transfer under volcanoes.

RNF grant  24-27-00411

How to cite: Sharapov, V., Perepechko, Y., Mikheeva, A., Vasilevsky, A., Sorokin, K., Ashchepkov, I., and Kuznetsov, G.: Analyze of the structural conditions of heat and mass transfer under volcanoes of the northwestern sector of the Pacific ocean- Eurasian continent transition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4048, https://doi.org/10.5194/egusphere-egu24-4048, 2024.

Small-volume alkaline magmatism has now garnered due attention in geosciences, wherein these rocks provide essential information about deep mantle processes, geochemical composition, and the prevailing geodynamics. The continental alkaline magmatism of deep-seated ultramafic lamprophyres (UML) is spatially and temporally linked with continental breakup and rifting. Additionally, they have gained significant attention in terms of mineralization.

Deccan hosts one of the most extensive and peculiar suites of lamprophyre complexes in India, and this magmatism holds valuable geological information to unveil the geodynamic processes and provide significant implications on the enrichment/depletion processes of SCLM during Deccan times. The present research delves into the mineral and whole-rock geochemical compositions and paleomag dating of lamprophyres from the West Coast Alkaline Complex (WCAC) of the Deccan Large Igneous Province. The study has implications for the relation of lamprophyre magmatism with the Réunion mantle plume, the associated main phase of Deccan tholeiite magmatism, the initiation of rifting in the western Indian subcontinental margin, the separation of Seychelles from the Indian subcontinent, as well as the role of lithosphere thinning in triggering lamprophyre magmatism. WCAC lamprophyres are principally composed of olivine and phlogopite phenocrysts/ macrocryst embedded in a mesostasis of carbonate, clinopyroxene, olivine, nepheline, spinel, and melilite groundmass. The presence of titanian aluminous phlogopite, clinopyroxene, and Al-enriched spinels with high Fe²⁺/(Fe+Mg) ratios are the characteristic features of WCAC lamprophyres. They are primitive, undersaturated in silica (SiO₂: 38.43 – 38.99), and rich in MgO (up to 10 wt. %), TiO₂ (up to 4.2 wt. %), and light rare earth elements. Mineral genetic classification schemes and geochemical compositions demonstrate a resemblance with ultramafic lamprophyres. 

High LREE/HREE (La/Yb= 75-82) ratios, similar to UMLs reported globally, and low Ba/Rb and Rb/Sr ratios exhibit the predominance of phlogopite and amphibole in the mantle source. Geochemical investigations inarguably trace their genesis back to the enriched garnet lherzolite mantle, metasomatised by silicate and carbonate veins. They show compositional similarity with global damtjernites and derivation from moderate pressure depth (3-4 GPa) corresponding to 90-100 km thick lithospheric mantle. Paleomagnetic studies support the intrusion of lamprophyres, predominantly during the chron C29n, thereby substantiating their radiometric eruption age at ~65 Ma. Seismic tomography models reveal a current lithospheric thickness of approximately 50 km beneath the WCAC, suggesting delamination of the lithosphere after the intrusion of lamprophyres at 65 Ma. UML magmatism in WCAC resulted from the initiation of a rift, which ultimately led to the separation of the Indian subcontinent and the Seychelles. The impetus behind the emplacement of UML dykes is intricately tied to passive rifting and external plate boundary forces, surpassing the influence of the Reunion mantle plume. The lithospheric thinning presumably occurred after the emplacement of lamprophyres and other alkaline rocks and continued with continental rifting in response to greater plate-tectonic stresses in the region of persistent lithospheric weakness.

How to cite: Singh, A. and Dongre, A.: Post-tholeiite rifting and genesis of ultramafic lamprophyres at ~65 Ma in the Deccan Large Igneous Province, India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4288, https://doi.org/10.5194/egusphere-egu24-4288, 2024.

While heavy molybdenum (Mo) isotope compositions in arc-related rocks have been linked to slab-derived fluids, the origins of arc lavas with light isotopic Mo compositions remain enigmatic. The two potential sources for the origin of light Mo isotopes in arc rocks are (1) dehydrated oceanic crust ^{1, 2} and (2) subducting sediments ^{3, 4}. Although the former has been extensively recognized, the latter still poses an enigma. We present the Mo-Sr-Nd-Hf isotope compositions and elemental data of a suite of Jiang Tso andesites to elucidate the chemical compositions of sediment-derived melts in the central Tibetan Plateau. The andesites from the Jiang Tso area show elevated Mg# values, along with trace element characteristics reminiscent of melts derived from sediments. Their Sr-Nd-Hf isotope compositions (⁸⁷Sr/⁸⁶Sri = 0.710260–0.710671, ε_Nd(t) = –10.63 to –8.97, and ε_Hf(t) = –9.38 to –8.02) closely resemble those of contemporaneous sediments in the central Tibetan Plateau. In addition, these andesites exhibit higher Ce/Mo ratios (396–587) and extremely lighter δ^98/95Mo values (−1.62‰ to −0.69‰) compared to the depleted mantle (δ^98/95Mo = –0.21‰ ± 0.02‰) ^{5, 6} and the majority of arc lavas (δ^98/95Mo = –0.07‰ ± 0.04‰) ³, suggesting a more plausible explanation lies in the involvement of subducting sediments rather than dehydrated oceanic crust in the source. Our latest findings, integrated with previous studies, indicate that the arc-related rocks exhibiting light Mo isotopes may not solely originate from the rutile-breakdown oceanic crust source but could also result from sediment melting at various sub-arc depths. Consequently, sediment-derived melts play a crucial role in Mo isotope cycling and the formation of arc magmas in subduction zones.

¹ Chen, S., et al., Nat. Comm. 10, 4773 (2019). ² Freymuth, H., et al., EPSL 432, 176-186 (2015). ³ Huang, F., et al., GCA 341, 75-89 (2023). ⁴ König, S., et al., EPSL 447, 95-102 (2016). ⁵ McCoy-West, A.J., et al., Nat. Geos.12, 946-951 (2019). ⁶ Willbold, M. & Elliott T., CG 449, 253-268 (2017).

How to cite: Huang, F., Li, J., Xu, J., and Zeng, Y.: Role of sediment-derived melts in Mo cycling of subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4498, https://doi.org/10.5194/egusphere-egu24-4498, 2024.

Massif-type anorthosite intrusions are enigmatic and significant crustal components widespread worldwide. They occur either as individual massifs or accompanied by mangerite, charnockite, and granite (AMCG suite). This Proterozoic phenomenon has been studied in numerous complexes, generating long-lasting discussions regarding the magmatic source and the tectonic setting where these rocks form. This controversy is still a matter of debate after decades of scientific research. In this sense, Mexico represents a unique and new opportunity to explore such petrological issues because its exposures of massive anorthosite and associated lithologies are mainly unstudied. These rocks are better exposed in the Oaxacan Complex, the most extensive Mexican inlier of Grenvillian rocks. This work is focused on its northern portion. This area is characterized by 1.4-1.1 Ga metamorphic rocks from the El Catrín and El Marquez units that were later intruded by anorthosite, gabbro, leucogabbro, oxide-apatite gabbronorites (OAGN), and granite bodies from the Huitzo suite. New LA-ICP-MS U-Pb zircon data revealed similar crystallization age ranges in the gabbro-anorthositic (1013-960 Ma) and granitic (1012-964 Ma) rocks. Their zircon Hf-O isotopic composition was compared with previous and new data from the older units of the area to assess the possible interaction between mantle- and crustal-derived melts during their generation. The intrusions of massive anorthosite and gabbro exhibit ε_Hf(t) values of -2.54-4.79 and δ¹⁸O = 6.84-8.03‰. The granitic rocks have ε_Hf(t) values of -0.79-2.87 and δ¹⁸O = 7.80-8.42‰. The lack of mantle-like ε_Hf(t) and δ¹⁸O values suggests the participation of high-δ¹⁸O supracrustal material with more radiogenic Hf signatures during their generation. Simple binary mixing modeling indicates that the gabbro-anorthositic intrusions incorporated ~20-30% of metasedimentary country rocks, supporting a mantle-dominated origin. A slightly higher crustal component is recognized in the studied granitic intrusion. We also propose that these rocks permit an alternative model where Oaxaquia is paleogeographical relocated close to the eastern margin of Laurentia during the final stages of Rodinia amalgamation due to the resemblance in age to the late- to post-Grenvillian AMCG rocks (1016-956 Ma) outcropping there (e.g., Roseland, Mattawa, Labrieville, and Vieux Fort). This new tectonic view challenges the classical Amazonia-Oaxaquia-Baltica connection.

How to cite: Elizondo Pacheco, L. A., Solari, L., He, H., Ramírez Fernández, J. A., and Maldonado, R.: Geochronological, petrological and tectonic implications of the Proterozoic massif-type anorthosite intrusions and related rocks from the northern Oaxacan Complex, southern Mexico, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4770, https://doi.org/10.5194/egusphere-egu24-4770, 2024.

The geodynamic regime driving formation of Archean felsic continent crust is still an ongoing debated and unsolved fundamental issue. The episodic Archean TTGs and associated granitoids, with emplacement ages of ca. 2.9, 2.7 and 2.5 Ga, occurred in the Jiaobei Terrane, North China Craton (NCC), provide prolonged continuous records of formation processes of Meso-Neoarchean felsic continental crust. To track patterns of crust-mantle differentiation, crustal reworking and recycling, and accordingly, constrain underlying geodynamic regimes associated with formation of the Meso-Neoarchean felsic continental crust, we present comprehensive zircon U-Pb dating, Hf-O isotopes and whole-rock major- and trace-element geochemical data for the episodic Archean TTGs and associated granitoids. The comprehensive dataset decodes the generation of the episodic Archean TTGs over wide-range pressure conditions from amphibolite to eclogite facies and Meso-Neoarchean coupled crust-mantle differentiation, which was likely driven by episodic hot mantle (plume) upwelling. In addition, the ca. 2.9 and 2.7 Ga TTGs shared identical Mesoarchean juvenile crust source and exhibit consistent mantle-like zircon δ¹⁸O values, whereas the ca. 2.5 Ga TTGs mainly derived from distinctly younger Neoarchean juvenile crust, implying removal and replacement of the Mesoarchean juvenile lower crust. Importantly, some ca. 2.5 Ga TTGs, granitic gneisses and sanukitoids exhibit significantly higher zircon δ¹⁸O values than mantle δ¹⁸O values, demonstrating occurrence of Neoarchean supracrustal recycling. Consequently, the combined geochemical dataset with geological evidence allow us to track the geodynamic processes for the formation of the Meso-Neoarchean felsic continent crust in the Jiaobei Terrane, NCC: Episodic hot upwelling mantle (plume)-lithosphere interactions at ca. 2.9, 2.7 and 2.5 Ga resulted in the coupled crust-mantle differentiation over different depths to produce the spatial-temporally coexisted various-pressure-type TTGs, juvenile crust and voluminous dense lower crustal restite, respectively. Subsequently, dense lithospheric delamination triggered by gravitational instability occurred, followed by continental uplifting, subduction of altered oceanic crust, and asthenosphere and mantle-derived mafic melts upwelling, resulting in extensive occurrences of anatexis and metamorphism with anticlockwise P-T paths in the medium-lower crust at ca. 2.5 Ga. Along with large-scale melting and cooling of mantle, thick stable craton lithosphere with strong rigidity and viscosity had likely developed by the end of Neoarchean. The geodynamic processes in Meso-Neoarchean were likely diverse, especially episodic hot upwelling mantle (plume) -lithosphere interaction could be a favored geodynamic regime responsible for formation of Archean felsic continental crust in the Jiaobei Terrane, NCC.

How to cite: Liu, J.: Meso-Neoarchean coupled crust-mantle differentiation followed by gravity-driven lithospheric delamination and subduction initiation in the North China Craton, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4864, https://doi.org/10.5194/egusphere-egu24-4864, 2024.

Venus and Mars have operated as one-plate planets for some or all of their history and intraplate magmatic activity on Earth has been suggested as an analogue for the observed volcanic activity on these bodies. Flipping the question around, what can we learn about intraplate magmatism on Earth from other planets?

Volcanic features, including extensive lava flows and vast lava plains, cover large portions of the Martian surface. Mars has two large volcanic provinces: Tharsis and Elysium. While the continent-sized region of elevated terrain called the Tharsis rise receives most of the attention, Elysium—the second largest volcanic province on Mars—is larger than the Ontong-Java plateau—the largest LIP on Earth. Activity detected by the InSight seismometer near Cerberus Fossae (located in Elysium Planitia, southeast of the Elysium volcanic province) is consistent with fluid flow at depth. Cerberus Fossae is among the youngest tectonic structures on Mars and large discharges of water and lava have been proposed to explain the geomorphic structures observed at Cerberus Fossae. The regional gravity and topography, volcanic history, and seismic activity at Cerberus Fossae are consistent with a present-day 2,000-km-radius plume head beneath Elysium Planitia. The characteristics of the Elysium Planitia plume are comparable to terrestrial plumes proposed to explain the formation of terrestrial LIPs. Plumes on Mars appear to be spatially stable for long periods of time, reflecting the stabilizing influence of a thick stagnant lid and sluggish mantle convection.

While Venus is nearly the same size as Earth, there is no evidence supporting Earth-like plate tectonics for the past 250-750 Myrs. The similarity in size invites comparison of present-day volcanic activity between the two planets. This is complicated by the presence of plate tectonics where volcanic activity at ridges and subduction zones has no clear analogue on Venus. Expanding intraplate volcanism on Earth suggests as many as 100 active volcanic events per year on Venus. While detecting surface changes is one goal of the upcoming NASA and ESA Venus missions, surface change associated with volcanic activity has already been found in the Magellan image archive. Herrick and Hemsley identified a 2 km² volcanic vent that changed shape in the eight months between two Magellan radar images. While sulfuric acid clouds obscure our view of the surface, those same clouds provide the best evidence for ongoing volcanic activity. Assuming the primary mechanism removing atmospheric SO₂ is a reaction between calcium minerals on the surface and SO₂, an SO₂ residence time of ~2 Myrs is required. This requires an outgassing rate of ~6x10¹⁰ kg SO₂/year—about the same yearly SO₂ outgassing rate measured on Earth over the past decade. Converting this outgassing rate to erupted lava, an eruption rate on Venus of ~1 km³/yr is obtained.

How to cite: King, S., Duncan, M., Euen, G., Murphy, J., Parrish, S., and Weller, M.: Can Venus and Mars Inform Us About Intraplate Magmatism on Earth?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5761, https://doi.org/10.5194/egusphere-egu24-5761, 2024.

This study presents the first comprehensive investigation into the petrography, major and trace element mineral chemistry of a mantle-derived eclogite xenolith suite from the Balmoral kimberlite. Most of the eclogite xenoliths from the Balmoral kimberlite pipe are bimineralic (garnet and clinopyroxene) rocks with a substantial number of corundum-bearing xenoliths also recognised. The bimineralic eclogites are classified into low MgO (<15 wt% MgO) and high MgO (<15 wt% MgO) varieties. Mica with average modal abundances ≤10 vol% is observed as an accessory phase in bimineralic xenoliths. Modal abundances of corundum in corundum-bearing samples range between 1 and 6 vol%. Textures are ambiguous in Balmoral eclogites, while the chemical criteria of McCandless and Gurney (1989) place all of them into Group II. The temperature range of Balmoral eclogites (at an assumed pressure of 50 kbar; Ellis and Green, 1979) is between 1046 and 1311 °C. The low-MgO bimineralic eclogites are characterised by relatively higher temperatures than the high-MgO variety. Corundum-bearing eclogites have the highest equilibration temperatures. Based on calculated temperatures, corundum-bearing eclogites have the highest inferred pressures of equilibration with the high-MgO eclogite variety having the lowest. The reconstructed Balmoral major element bulk compositions are characterised by variations in MgO, CaO and Al₂O₃ contents, with less variation in FeO contents. Reconstructed major element bulk compositions from bimineralic eclogites coincide with those of tholeiitic basalts, and to a lesser extent, basalts from mid-ocean ridges and oceanic gabbros. Corundum-bearing eclogites are similar to oceanic gabbros in general. The REE pattern of bulk eclogite commonly show humped-shaped REE_N patterns. High MgO eclogites have a slight enrichment in the LREE_N pattern while low MgO eclogites have enrichment in HREE_N patterns. These REE_N patterns are broadly comparable to those of oceanic gabbro and MORB. The protolith for these Balmoral eclogite xenoliths is thought to be a once composite oceanic crustal section which underwent partial melting during subduction and/or dehydration and, subsequent metasomatic re-enrichment in incompatible trace elements.

How to cite: Pattnaik, J. and Viljoen, F.: Petrology and geochemistry of a Cratonic mantle-derived Eclogite Xenolith Suite from the Balmoral Kimberlite, Kimberley Region, South Africa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6583, https://doi.org/10.5194/egusphere-egu24-6583, 2024.

The Tibetan lateral mantle flow bears considerable significance in deciphering the material movement mechanisms within global plate convergence zones. However, the front edge of this mantle flow is unclear. Here we conduct petrological, geochronological, mineralogical, geochemical and Sr-Nd-Pb isotopic investigations on Quaternary intracontinental alkali basalts from the southwestern Yunnan (the south of 27°N), to determine the source characteristics and geodynamic mechanisms of the Quaternary alkali basalts in southeastern Tibetan Plateau and to trace the recent Tibetan mantle flow. Alkali basalts in the region are mainly basanite and trachybasalt with eruptions during the Pleistocene epoch. They possess a highly incompatible elemental and radiogenic Sr-Nd-Pb isotopic composition similar to those of the Ocean Island Basalts, consistent with melts derived from asthenospheric mantle with low-degree partial melting. Calculated magma-water contents of regional alkali basalts range from 1.32 ± 0.48 wt.% to 2.23 ± 0.18 wt.%, corresponding to 269 ppm to 3591 ppm water contents of their mantle source, which are significantly higher than that of the normal upper mantle (i.e., 50–250 ppm). Quantitative trace-element modelling and dramatic variations in oceanic crust-sensitive indicators such as Eu/Eu*, Sr/Sr*, Ce/Pb, (Nb/Th)_N-PM and (Ta/U)_N-PM indicate variable contributions of upper and lower oceanic crust to magma sources. Systematic examinations of petrological, geochemical, and geophysical evidence reveal that the temporary small-volume Quaternary volcanism in southeastern Tibetan Plateau is not related to Tibetan southeastward mantle flow but is primarily attributed to stagnant Neo-Tethyan slab in the mantle transition zone.

How to cite: Kang, H., Zhao, Y., Zhang, X., Zhang, L., Zhang, H., and Zou, H.: Quaternary volcanism in southeastern Tibetan Plateau: A record of stagnant oceanic slab in the mantle transitional zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7403, https://doi.org/10.5194/egusphere-egu24-7403, 2024.

A low-velocity layer atop the mantle transition zone has been extensively observed worldwide, which may play an important role in mantle dynamics and Earth habitability. In subduction zones, this layer is widely explained as partial melting triggered by slab subduction on a regional or global scale. However, direct observational evidence is still absent, and the response of the layer to slab subduction is not well known. Here, we image the seismic velocity around the mantle transition zone by matching synthetic and observed triplicated seismic P and sP waveforms in the Indian–Eurasian continental subduction zone. Our observations reveal a laterally varied low-velocity layer atop the mantle transition zone beneath the Hindu Kush, where a subducted slab extends to the mantle transition zone. It is characterized by thickness of 56-94 km and P-wave velocity drop of -2.8~-4.7%. The geometric morphology of the low-velocity layer indicates that it is a partially molten layer induced by the subducted slab on a regional scale. Interestingly, our observations also support that the layer has a low viscosity. The decreased viscosity possibly facilitates slab motion in the deep domain; however, the buoyant continental crust in the shallow domain likely resists downwards movement of the slab. This differential movement is more likely to cause slab stretching, tearing and break-off in the middle region, which may contribute to explaining rare recurring large intermediate-depth earthquakes in an intracontinental setting.

How to cite: Li, G.: Seismic evidence of upper mantle melt caused by a subducted slab in the Indian-Eurasian continental subduction zone, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7577, https://doi.org/10.5194/egusphere-egu24-7577, 2024.

An alkaline magma undergoes significant modification during its ascent to the surface due to assimilation of mantle and crustal material, exsolution of volatiles, trapping of crystals from earlier crystallized melt batches, fractional differentiation and explosive processes, making a thorough understanding of the petrogenesis of the magma and the nature of its mantle source in large igneous provinces difficult. The dikes and pipes of ultramafic lamprophyres, picrites and nephelinites are characterised by rapid rise of melt batches that could provide a high chance of preserving unworked mantle and crustal material. A study of olivine from these rocks may help to resolve some issues of their mantle sources and melt evolution.

The Namuaive pipe located in the northern part of the nepheline syenite Khibina Massif, Kola alkaline province. The pipe is filled by pyroclastic alkaline picrite (melanephelenite). The rock is texturally heterogeneous, consisting of 30-40 vol % magmaclasts and lapilli, phenocrysts and macrocrysts (up to 40 vol %) of phlogopite, olivine and clinopyroxene, xenoliths of Khibina Massif rocks, and fine grained matrix composed of phlogopite, apatite, perovskite, spinel, Ti-magnetite, nepheline, sodalite, high-Ti garnet.

Olivine is one of the most abundant macrocrysts in alkaline picrite, ranging up to 30 vol %; it is fresh or slightly replaced by serpentine or clinopyroxene-phlogopite intergrowth. Three groups of olivine based on core-to-rim zonation were observed:

• Euhedral-to-subhedral olivine grains up to 5 mm are phenocrysts. Some grains have spinel inclusions. Phenocrysts show normal Mg#-zonation. They consist of a more magnesian core (Mg# = 0.90-0.89) with Ni content from 1595 to 3058 ppm and a thin marginal ferruginous zone (Mg# = 0.89-0.83) with Ni content from 363 to 2663 ppm.
• Antecrysts have rounded and often corroded edges. Their size ranges from the first few hundred µm to 1 mm. They are characterised by Fe-rich cores (Mg# = 0.84-0.87) with a wide range of Ni contents from 1200 to 3200 ppm, surrounded by a transitional zone with a gradual increase in magnesium (Mg# = 0.86-0.89) and Fe-rich rind (Mg# = 0.89-0.86) with Ni contents from 1500 to 605 ppm. They have a small clinopyroxene-phlogopite rim and spinel along cracks.
• The xenocrysts have been divided into two subgroups according to their Mg# and Ni contents. The cores of the first subgroup have Mg# 0.90-0.91 and Ni contents from 2800 to 3200 ppm, the cores of the second subgroup have Mg# 0.91-0.93 and Ni content about 2000 ppm. The rims of both subgroups have Mg# 0.83-0.85 and Ni contents from 1236 to 433 ppm. Some olivine grains are intergrown with high-Cr clinopyroxene and high Mg phlogopite.

The antecrysts reflect mixing of the evolved lamprophyric melts during previous pulses with the partial melt batch that formed the Namuaive pipe. Phenocrysts and other olivine rims formed during fractional crystallization. Antecrysts and phenocrysts equilibrated to melts from wehrlite sources.

The study was supported by the Russian Science Foundation under Grant No 23-77-01052

How to cite: Lebedeva, N., Nosova, A., Sazonova, L., Kargin, A., Shaikhutdinova, D., Yapaskurt, V., and Shcherbakov, V.: The alkaline rocks olivine variety: a case study of Namuaive Pipe, Kola alkaline province, Russia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8338, https://doi.org/10.5194/egusphere-egu24-8338, 2024.

The modal metasomatic alteration for lithosphere mantle may be investigated using mantle xenoliths from kimberlite pipes. The pyroxenite xenoliths from diamondiferous upper-Devonian Udachnaya kimberlite pipe (Daldyn field, Yakutia) were studied, mineral chemical composition was researched. The several stages of metasomatic processes were observed in the lithospheric mantle under the Udachnaya kimberlite pipe.

The most garnets from studied xenoliths demonstrated so-called “normal” trace element distribution that closed to the element coefficients the basalt - silicate melt. All garnets are characterized by a maximum in Ta, a minimum in La-Ce, and a minimum in Ti. Eclogites (especially with a mosaic texture) are characterized by a small minimum in Eu, which may indicate the presence of Pl in the initial rock. The presence of eclogitic xenoliths (with Eu-minimum in garnet) indicates the influence of the subduction component. The pyroxenite xenoliths with narrow variations in the composition of minerals indicates their crystallization from melts, accompanied later by metamorphic recrystallization. The 10% studied xenoliths are observed the secondary metasomatic amphibole (pargasite - taramite) - the evidence of modal Amph metasomatism. The Ti/Eu – La/Yb distribution for clinopyroxene and amphibole demonstrate the influence of silicate (not carbonatite) melts.The increasing concentrations of HFSE and REE group elements can also be traced by the Cpx and Grt chemical composition, it may be indicating the asthenospheric melts. Several garnet samples from high-Zr (80–100 ppm) eclogites demonstrated the features of fluid metasomatism (fluid-produced, accompanied by phlogopite crystallization). Another sign of the alkaline melts influence is secondary Na silicates crystallization (according reaction Grt + Omphacite + K - Fluid = Amph + Сpx2 ± Cal ± Sodalite).

Thus, several stages of metasomatic processes were observed in the lithospheric mantle under the Udachnaya kimberlite pipe. The presence of eclogite xenoliths (with a Eu minimum) indicates the influence of a subduction component. The presence of pyroxenite xenoliths with narrow variations in mineral composition indicates their crystallization from melts - the second stage of metasomatic processes, subsequently be accompanied by metamorphic recrystallization. The content of trace elements in garnets indicates the asthenospheric nature of the melts. Such melts brought elements of the HFSE and REE groups, as well as Pt, Pd and Re. The last stage is most clearly traced using modal Amph metasomatism. The presence of secondary amphibole indicates widespread occurrence of silicate pre-kimberlite metasomatism in the lithospheric mantle beneath the center of the Siberian craton.

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

How to cite: Kalashnikova, T. and Kostrovitsky, S.: The silicate and carbonatite metasomatic alterations in lithospheric mantle under Siberian craton (the evidence of mantle xenoliths from Udachnaya pipe), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11448, https://doi.org/10.5194/egusphere-egu24-11448, 2024.

The problem of the introduction of heterophase magmatic melts into the conducting channels of the lithospheric mantle under the cratons of the Siberian platform has been studied numerically. The analysis of the features of the introduction of melts was carried out on the basis of a hydrodynamic model of the evolution of magmatic and fluid-magmatic systems. The mathematical model describes the two-speed dynamics of the redistribution of hot heterophase melts and magmatogenic fluids in the flow during their movement from the generation zones to the platform cover, as well as the processes of heat and mass transfer between melts and rocks in permeable zones of the lithosphere. The nature of the flow of mixtures of liquid fractions of aluminosilicate, sulfide, native and oxide liquids, in which a sub-liquid solid phase appears during movement and decompression boiling occurs, the features of heat and mass transfer processes determine the type of magmatic and magmatogenic deposits of the trap formation of the Siberian platform. The flow of magmatic melts in a wide temperature range of 300-1200 °C, the viscosity of the melt phases of 101-106 N, as well as the rate of penetration and the degree of stratification of the heterophase magmatic flow were studied.

The figure shows an example of the randomization of an intrusive flow. (a) (b) An example of the development of heterogeneity in the distribution of the concentration of particles of the dispersed phase (a, m-3) and temperature (b, °C) in an initially stratified magmatic flow embedded in the host rocks. The temperature of the introduced flow is 500 °C, in the channel at the initial moment standard thermodynamic conditions; the dynamic viscosity of the melt is 102 P. The work was carried out with the financial support of the Russian Science Foundation, grant No. 24-27-00411.

How to cite: Perepechko, Y., Sorokin, K., and Imomnazarov, S.: Features of the introduction of magmatic melts in permeable zones of the platform cover, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14538, https://doi.org/10.5194/egusphere-egu24-14538, 2024.

Comparative study of the mantle xenocrysts from Anabar region (Ary-Mastakh, Dyuken, Orto-Yargyn fields) and Boomerang kimberlites and pipe show essential differences with the mantle in surrounding area from Olenek (Chomurdakh field)

The PTX diagram show presence of the rare lherzolitic pyrope and abundant eclogitic almandines to 6 GPa. In suture zone of Daldyn and Magan terranes (Boomerang pipe) eclogitic omphacites and Cr less pyroxenites and Cr diopsides occurs mainly in the middle mantle part the pyroxenite layer possibly formed after eclogites due to plume melt interaction. Long ilmenite fractionation trend extends from the lithosphere base to the GPa 2.5, which is typical. Geochemistry of minerals vary from most depleted pyropes with V-U shaped REE patterns typical of arc mantle and Ba, U peaks and HFSE minima of subduction type. The fertilization produced the increase of the incompatible elements and sometimes LILE and The marginal parts of the SCLM of Anabar shield are extremely enriched in eclogitic deep-seated material located in lower SCLM part and demonstrating similar thermobarometric trends and features to the diamond inclusions from the Ebelyakh (Mayat) placers. Mantle column beneath several pipes (Losi, Universitetskaya, Kuranakh) contain Cr amphiboles distributes from lithosphere base to Moho. Comparison of reconstructed SCLM beneath Anabar and Chomurdakh field reveal more fertile compositions of the mantle rocks and simpler structure for later field. Abundance of eclogites in Kuranakh and Orto-Yargyn kimberlite in the lower mantle lithosphere part and their PTX trends are similar to the eclogitic diamond inclusions from the Ebelyakh placers. This increase the possibility of finding of diamonds deposits in Anabar shield kimberlites.

RNF grant No. 24-27-00411

How to cite: Kostrovitsky, S., Ashchepkov, I., Babushkina, S., and Mdevedev, N.: Reconstructions of mantle structure beneath kimberlites of Anabar shield and surroundings – similarities and differences., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14806, https://doi.org/10.5194/egusphere-egu24-14806, 2024.

Melilitites are ultramafic magmas characterized by normative Ca₂SiO₄, larnite, high FeO* and TiO₂. Liquids compositionally close to melilitites were experimentally reproduced from carbonated lherzolites in alkali, Fe and Ti-free model systems at 3.2-3.3 GPa, approx.  1500 °C (Gudfinnsson & Presnall, 2005), at relatively high melt proportions. In complex compositions, MORB-eclogite derived, carbonated, partial melts reacted with a fertile peridotite were proposed at the origin of melilitites (Mallik & Dasgupta, 2013, 2014). The experimental reconstruction of phase relationships along a join olivine melilitite - carbonate revealed that at 3 GPa, clinopyroxene and olivine or garnet are stable on the liquidus (Brey & Ryabchikov, 1994), suggesting that carbonated wehrlites are potential sources for the genesis of melilitites.

Here, we explore phase relationships on the high pressure melting of a model wehrlite, initially composed of a mechanical mixture of San Carlos olivine, diopside, aegirine, dolomite, rutile and kyanite. Starting materials were loaded in graphite capsules, inserted in sealed platinum capsules. Vitreous carbon spheres and synthetic diamond grains were adopted for liquid traps. 

Preliminary experimental results show that at 3 GPa the solidus is located at temperatures lower than 1200 °C. A thick, orthopyroxene-rich layer, with polygonal microstructure, forms at contact with aggregates resulting from quenched liquids, both at 1200 °C and 1400 °C. Estimates of liquid composition are melilititic, with TiO₂ approx. 2.5 wt.% on a volatile free basis.

Currently available experiments suggest that the solidus is controlled by the reaction dolomite + olivine + clinopyroxene = orthopyroxene + liquid, as suggested in Eggler (1976). This is feasible only if the liquid composition is located on the CaO-rich side of the plane diopside-forsterite-dolomite in the model system CaO-MgO-SiO₂-CO₂, i.e. on the normative larnite (akermanite) portion of the tetrahedron.

Brey G.P. & Ryabchikov I.D. (1994). Carbon-dioxide in strongly silica undersaturated melts and origin of kimberlite magmas. Neues Jahrbuch Fur Mineralogie-Monatshefte, (10), 449-463.

Eggler D.H. (1976). Does CO₂ cause partial melting in the low-velocity layer of the mantle?. Geology, 4(2), 69-72

Gudfinnsson G.H. & Presnall D.C. (2005). Continuous gradations among primary carbonatitic, kimberlitic, melilititic, basaltic, picritic, and komatiitic melts in equilibrium with garnet lherzolite at 3–8 GPa. Journal of Petrology, 46(8), 1645-1659.

Mallik A. & Dasgupta R. (2013). Reactive infiltration of MORB-eclogite-derived carbonated silicate melt into fertile peridotite at 3 GPa and genesis of alkalic magmas. Journal of Petrology, 54(11), 2267-2300

How to cite: Poli, S. and Melluso, L.: The origin of melilitites: preliminary results on melting of a carbonated wehrlite, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16571, https://doi.org/10.5194/egusphere-egu24-16571, 2024.

Joint analysis of tectonics, magmatism, metallogeny, and hydrocarbons (HC – oil-gas) for the South Caspian - west Baluchestan, Middle East (Alpine time mainly) was made. Different anomalies and degassing here are of interest too.  Specific anomalous deep regime and degassing of CH4, H2 etc. due to a giant African superPlume activity are noted too. Such points discussed as follows:

1.      Alpine North-Eastern (NE) tectonic zoning exists in this region up to Present (Q4). Anomalous long-lived African superPlume activity influences on regional tectonics, related magmatism and fluid regime (Fig.). There are different anomalies in this region on gravity, hydrocarbons (HC), degassing etc.

2. Miocene – Recent (N1-Q) intraplate magmatism with: different subalkaline- alkaline rocks directly relates to superPlume mentioned. There are data about Sr, Ca etc. input in upper younger Caspian Sea sediments from the lower older magmatites. Such magmatic trend exists as: Quaternary carbonatites, Hanneshin, Helmand block (Afghanistan) - Ca-rich volcanites with CaO up to 34.8% -  trachyandesites with CaO = 7.2%.  

• Oligocene-Recent (Pg3-Q) calk-alkaline subduction-related rocks are as antipodes to mentioned intraplate rocks (intrusive, extrusive and volcaniclastic ones). Relation with African superplume is not formally necessary, but there are our data about warmer calk-alkaline rocks here, ex., warm melt inclusions in them with T crystallization as 1180oC.
• Decreasing of earthquakes activity from South to the Middle Caspian Sea, at

least (Khain, Bogdanov, 2003 etc.). HC resources decreasing from Persian Gulf to North Caspian Sea

• Lesser order HC zoning (west to east: oil - gas) in the S-M Caspian Sea exists. Is Great Caucasus a barrier for HC in lesser order?
• A regional tectonic - HC correlation in Iraq - South Caspian- Turkmenistan exists: more compression and oil in west of region versus less compression and gas in the east of region up to the east Turkmenistan with, however, non-deep sea conditions (transitional facies) in the latter. Moreover, unusual several times repeating of oil - gas - gas-condensate in a stratigraphic section is revealed in west Turkmenistan. Is it a result of deep fluids input too? HC behavior and zoning is not quite clear in this unique economic and geological region.
• Other HC north-south (N-S) zoning is as follows: HC in the old rocks - since Devonian up to Paleogene (D-Pg) – North Caspian Sea vs. HC in Triassic-Jurassic, Paleogene rocks in the Middle Caspian Sea, and in Low Pliocene (N2) rocks - South Caspian Sea. It could be in agreement with northeastern (NE) superplume activity decreasing. Giant HC resources in Saudi Arabia – Caspian region could be related with this hot regime. HC localizations are in agreement with a regional general geology. Surely, the oil genesis is traditional – organic one.

There is a good correlation as detailed HC structural map - HC maximum. It is in agreement with a young concrete HC localization despite the different age of host rocks.  Mud volcanoes (Kholodov, 2012 etc.) – HC – Salt – magmatism - tectonics in this region studied is the one system.    

This work was made due to the State program of the Geological Institute RAS.

How to cite: Romanko, A., Imamvderdiyev, N., Vikentiev, I., Rashidi, B., Heidari, M., and Poleshchuk, A.: On a tectonics, magmatism and hydrocarbons (HC, oil-gas) of the South Caspian - West Baluchestan, Middle East: some problems and constraints, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20570, https://doi.org/10.5194/egusphere-egu24-20570, 2024.

The depleted mantle and the continental crust are largely geochemically and isotopically complementary. However, the question of when the depleted mantle reservoirs developed on Earth remains a topic of considerable debate. In this study, we report the existence of a ca. 3.8 Ga detrital zircon from the quartzite of the Paleoproterozoic Songshan Group in the southern North China Craton. In situ zircon hafnium isotopic characteristics of the 3.8–3.2 Ga detrital zircons indicate the presence of source rocks as old as ca. 4.5 Ga in the southern North China Craton. Together with the global zircon U-Pb-Hf isotope dataset from the North China Craton, Jack Hills, Acasta as well as available μ¹⁴²Nd values of ancient rocks from Archean craton worldwide, the new results indicate that the silicate Earth has differentiated at 4.5–4.4 Ga almost immediately after accretion, developing continental crust and a complementary depleted mantle reservoir at that same time.

How to cite: Si, B., Diwu, C., and Si, R.: Eoarchean-Paleoarchean crustal material in the southern North China Craton and possible mantle reservoir of early Earth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-406, https://doi.org/10.5194/egusphere-egu24-406, 2024.

Silicate+metal worlds like Earth form hot owing to gravitational heating from accretion and differentiation, and intrinsic radioactive decay. Concurrent cooling sets off a chemical and mechanical cascade wherein siderophile elements (Fe+Ni) form a metallic core, and lithophile elements (Mg, Si, Al, Ca, Na, etc.) partition into mantle and siliceous crust. The outcome is a rocky surface beneath an outgassed fluid envelope composed of atmophile elements and compounds (CO₂, H₂O, H₂, etc.). In its first 500 Myr (q.v. Hadean eon), Earth’s crust co-existed with liquid water; it was molded by volcanism, affected by late accretion bombardments and harbored diverse hydrothermal systems. Volcanism and differential buoyancy of the crust mandates the presence of scattered emergent landmasses. Such Hadean surfaces could host diverse (sub-)aqueous where organic chemical ingredients became concentrated to reactivity beneath a dense atmosphere bathed by the active young Sun. Soon after planet formation, it seems proto-biochemical reactions led to full-fledged living biochemistry. We do not know whether the earliest environments for life were ideally suited for its origin, or merely just good enough to accomplish the task. The inferred complexity for even the minimum biological entity means that operative and persistent biochemistry are the most difficult developmental stages to reach.

How to cite: Mojzsis, S. J. and Medvegy, A.: Recipes for a Hadean Earth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1479, https://doi.org/10.5194/egusphere-egu24-1479, 2024.

The Isua and Tussaap supracrustal belts of the Itsaq gneiss complex, southwestern Greenland, form the largest and best-preserved exposure of Eoarchean supracrustal materials on Earth. Previous studies have almost exclusively focused on the ∼35-km-long, arc-shaped Isua supracrustal belt and adjacent ca. 3.8–3.7 Ga meta-tonalite bodies, which are the basis for competing Archean tectonic regime interpretations (i.e., plate versus heat-pipe tectonics). In this study, we performed geologic field mapping of the seldom-explored Tussaap supracrustal belt, located ~11 km south of the Isua supracrustal belt, to better constrain its litho-structural framework and test the predictions of existing Eoarchean tectonic models. Observations from this study and previous works show that the Tussaap supracrustal belt consists of a east-northeast-striking, ~12-km-long and <1-km-wide, mostly continuous belt of greenstone rocks flanked to the north and south by ca. 3.8 Ga meta-tonalite. Lithologies of the Tussaap supracrustal belt consist of interlayered garnet ± staurolite ± sillimanite paragneiss, felsic schist, garnet mafic schist, amphibole-rich garbenschiefer, and minor pegmatite bodies and meta-ultramafic rocks. The northern and southern contacts between the Tussaap supracrustal belt and meta-tonalite are ~100-m-wide transitional zones featuring interlayered and folded meta-tonalite and greenstone rocks that increase in abundance towards each lithologic unit. Both the Tussaap supracrustal belt and adjacent meta-tonalite feature well-developed, southeast-dipping foliation and southeast-plunging stretching lineation (average 162° trend, 40° plunge). Macroscopic sheath and often rootless, disharmonic folds with hinges parallel to stretching lineation occur throughout the study area. In contrast with previous interpretations, no discrete tectonic discontinuities (i.e., brittle faults and ductile shear zones) were observed within the Tussaap supracrustal belt and meta-tonalite. Similarly, no apparent metamorphic field gradient was observed in the study area. This litho-structural framework is consistent with that of the Isua supracrustal belt and meta-tonalite bodies to the north, indicative of spatially-uniform strain and metamorphism. Based on our preliminary observations, the Archean development of the region can be explained by uniform subvertical shearing and folding of an interlayered volcanic-intrusive sequence (i.e., heat-pipe tectonics). Additional structural, geochronologic, and geochemical analyses of the Tussaap supracrustal belt and meta-tonalite are required to further elucidate their emplacement and metamorphic histories and differentiate end-member models of Archean tectonics.

How to cite: Haproff, P., Webb, A., Leung, C. Y. E., Hauzenberger, C., Zuo, J., and Ramírez-Salazar, A.: Litho-structural framework of the Eoarchean Tussaap supracrustal belt, Itsaq gneiss complex, southwestern Greenland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1792, https://doi.org/10.5194/egusphere-egu24-1792, 2024.

An Archean ancestral landmass of Columbia supercontinent is a matter of concern to geologists. A single supercontinent called “Kenorland” or several supercratons have been mainly proposed, but more evidence from geological records and palaeomagnetism argue for the latter supercraton solution, in which two long-lived supercratons Sclavia and Superior were recently reconstructed. Studies has shown that the Northern China blocks, including the North China and Tarim cratons, the Alxa, Quanji blocks, were involved in the reconstruction of Columbia. However, their affinity in Archean supercratons remained little constrained. Owe to the lack of reliable palaeomagnetic data old than 1.8 Ga, the geological piercing points in these blocks could allow us to figure out the question. Then, compilation and comparison of Neoarchean–early Paleoproterozoic magmatism, metamorphism, and sedimentary records, have been conducted among these blocks. As a result, 2.4-2.2 Ga magmatism and khondalite-like sedimentary sequence may be used as indicators of the affinity of these blocks in northern China. Consequently, the Kuruktag Block, Quanji Block, Alxa Block, TNCO, Khondalite Belt have similar evolutionary history during the Neoarchean-Paleoproterozoic, suggesting their close affinity at that period. Besides, the North China craton and Dharwar craton of India shield were proved to be connected during the Archean-Proterozoic. And latest study indicate the Dharwar craton was one of the Sclavia supercraton. Therefore, we speculate that during the Neoarchean–early Paleoproterozoic, the Kuruktag-Quanji-Alxa-TNCO-Khondalite Belt link was close to the Dharwar craton in Sclavia supercraton. The absence of Siderian glacial event (ca. 2.4 Ga) in the Alxa, Quanji, Kuruktag blocks and TNCO, Khondalite Belt of the North China craton rule out the link with Superia, which is common in Superia supercraton. Further geological and paleomagnetic studies are required to constrain the above hypothesis, the relation between these blocks clusters and other cratons, which is crucial to understand the origins of blocks in northern China.

How to cite: Zhang, Q. and Yao, J.: Paleogeographic affinity of Northern China block clusters in Archean-Paleoproterozoic supercraton solution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2507, https://doi.org/10.5194/egusphere-egu24-2507, 2024.

¹ Deep Space Exploration Laboratory / School of Earth and Space Sciences, University of Science and Technology of China, Hefei, Anhui, China.

²Department of Earth Sciences, The University of Hong Kong, Hong Kong, Hong Kong.

³Department of Geology, State Key Laboratory of Continental Dynamics, Northwest University, Xi'an, China.

* Corresponding author: wuzq10@ustc.edu.cn.

The origins of the Archean cratons were most important events in the early Earth and crucial for understanding how the early Earth worked. The mechanisms for the origins of the Archean cratons remain unclear. It is widely accepted that Archean tonalite-trondhjemite-granodiorite (TTG) plutons were derived from hydrous mafic magmas in the garnet/ amphibole stability field. Although the subduction can bring water to the mantle to produce granitic magma, the island Arc Model for the origin of continents meets fundamental challenges. The growing evidences support the plume-driven oceanic plateau models for the origin of continents. However, the lower parts of the oceanic plateau have been thought to be dry. How to generate the hydrous meta-basalt at the base of the oceanic plateau remain an open question.

Here we show that the Archean cratons resulted from the evolution of the hydrous magma ocean (Wu et al., 2023). The whole-mantle magma ocean created by the moon-forming giant impact likely evolved into an outer magma ocean and a basal magma ocean because the magma ocean would initially crystallize in the mid mantle and the basal magma ocean is denser than the overlying solid mantle. The basal MO at the beginning should contain a certain amount of water since extensive studies suggest substantial accretion of water-rich bodies during core formation. The major lower-mantle minerals have limited water storage capacity. Therefore, with progressive crystallization, the basal magma ocean becomes increasingly enriched in water. The basal magma ocean eventually becomes gravitationally unstable because of the enrichment of water. The triggered massive mantle overturns transported a large amount of water upward to the shallow part of the Earth and resulted in the major pulses of the crust and thick SCLM generations. The model can account for many observations including the source of water needed for generation of the continental crust, the major pulse of crustal growth around the end of the Archean, why the TTG and thick SCLM basically occurred in the Archean, and why only the Earth among inner planets was covered with the continental crust.

Wu, Z., Song, J., Zhao, G., & Pan, Z. (2023). Water-induced mantle overturns leading to the origins of Archean continents and subcontinental lithospheric mantle. Geophysical Research Letters, 50, e2023GL105178. https://doi.org/10.1029/2023GL105178

How to cite: Wu1, Z.: Water-induced mantle overturns and the origins of Archean cratons, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2870, https://doi.org/10.5194/egusphere-egu24-2870, 2024.

The BIFs in Bundelkhand Craton occurred as a discontinuous unit within the east-west trending Bundelkhand Tectonic Zone (BTZ). The BIFs were associated with amphibolite, calcsilicate rocks, and quartzite. The BIFs were massif in appearance in the Mauranipur (east of Bundelkhand Tectonic Zone, BTZ) that graded to layered variety in the Babina area (west of the BTZ).

The Bundelkhand BIFs were characterized by 45 to 55 wt.% SiO₂ and 44 to 55 wt.% Fe₂O₃ content. The Al₂O₃ content was usually low and varied between > 1 to 3 wt%. Barring a few samples, the MnO and CaO contents are < 1 wt.%. The higher MnO (~ 3.70 wt.%) and CaO (~ 1 wt.%) implied a different redox condition and involvement of CaCO₃ in the early stages of BIF formations. The ΣREE content of Bundelkhand BIFs varied between 10 – 38 ppm, with Eu/Eu*_SN values between 1.1 to 1.5. Geochemically, the BIFs were classified as Algoma-type BIFs deposited by low-temperature hydrothermal fluids. Monoclinic amphiboles, quartz and garnet were the dominant silicate phase for Mauranipur BIFs. Hornblende was present with monoclinic amphibole in the garnet-absent BIFs. Isolated grains of magnetite were dispersed throughout the Mauranipur BIFs. In contrast, alternate hematite and SiO₂-rich layers with locally developed low-T amphiboles characterized Babina BIFs. The Fe-rich oxides were mostly hematite. Mineral microstructure and P-T pseudo-section modeling implied Minnesotaite and Fe-Ca carbonate phases were the primary minerals in BIFs, deposited at temperature ~ 200°C at 0.05 to 0.1 GPa. The primary minerals experienced dehydration and decarbonization reactions, leading to the stabilization of amphibole and garnet at a temperature of ~450°C and pressure of 0.1—0.2 GPa. When plotted in a P-T diagram, the increase in temperature corresponds to tectonic activity and plutonism, leading to micro-bock accretion and growth of Bundelkhand Craton.

How to cite: Raza, M. B. and Nasipuri, P.: Mineralogy and P-T condition of Algoma type Banded Iron Formation from Bundelkhand Craton, North-Central India and their implications, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2992, https://doi.org/10.5194/egusphere-egu24-2992, 2024.

Iron Formations (IF) are economically significant sedimentary rocks primarily formed in the Precambrian evolutionary history of the Earth. In the Precambrian period, Iron Formations were deposited within marine sediments on stable continental margins (superior-type) and in association with volcanic rocks and many volcanic Massive Sulphide (VMS) deposits (Algoma-type). Most scientists agree that for BIF to form, photosynthesis and changing ferrous iron from seawater into mixed-valence iron (oxy-hydroxide) oxides and carbonate phases during oxidation are needed.
The present study is based on the Superior-type BIFs from the Girar Supracrustal Belt of Southern Bundelkhand terrane, which mainly consists of Neoarchean K-rich granitoids with a minor volume of a schist complex, TTG, sanukitoids, and mafic-ultramafic layered intrusion. The Girar schist (metasedimentary) belt is mostly made up of two types of rocks: (i) quartzite and (ii) BIFs. There are also some dolomitic marble and chlorite schist lenses close to the quartzite/BIF boundary. The BIFs consist of thick-bedded quartz and hematite with magnetite. The quartzites display low-grade metamorphism of fuchsite- and hematite-bearing quartz arenite with thick meta-argillite (schist) laminae and lesser quartz pebble conglomerates.
P-T pseudosection modelling indicates that Fe-carbonates and iron-oxyhydroxides (minnesotaite) are the primary phases that stabilize at 200 – 250 ^O C, 0.1–0.15 GPa. Subsequently, the low-temperature phases experienced dehydration and decarbonisation reactions with an increase in temperature, leading to the stabilisation of hematite and magnetite. The absence of orthopyroxene in the BIFs suggests these rocks suffer amphibolite facies
metamorphism, which is uncommon in generally undeformed superior-type BIFs.

How to cite: Bisht, B. P. S.: Mineralogy and P-T conditions of Superior- type Iron Formation fromBundelkhand Craton, North Central India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3109, https://doi.org/10.5194/egusphere-egu24-3109, 2024.

The position of the Tarim craton within the Rodinia supercontinent has long been the focus of scientific debate, with competing models varying from internal to external positions. The Altyn belt in the southeast Tarim margin records an extensive Neoproterozoic magmatic-sedimentary successions which likely recorded the convergence of Tarim to Rodinia. Thus, we here investigated the granitoids exposed in the Kuoshi-Kalaqiaoka and Tula areas in the eastern and western segment of the South Altyn belt. We present new field geology, zircon U–Pb–Hf–O isotopes and H₂O, and whole rock geochemistry data from these granitoids. Zircon U–Pb data yielded ages of 914 ± 3.9 Ma for the Tula granite, 919 ± 5.2 Ma and 932 ± 6.5 Ma for the Kuoshi granite. The Tula and Kalaqiaoka granite samples mostly display high ACNK values that are typical of S-type granitoids, consistent with the presence of Al-rich minerals, such as garnet and muscovite. In addition, the Tula granite have higher zircon δ¹⁸O (7.62 to 10.85‰, peaked at 8.9‰) and lower εHf(t) (-4.0 to +0.3) values, along with lower H₂O content (medium values at 102 and 251 ppmw), indicating that the primary magmas were generated from recycled ancient crust in a water-deficient syn-collisional setting, with minor juvenile contribution. On the other hand, the Kuoshi granite have high Sr (169–259 ppm), Sr/Y (17.85–19.33) and (La/Yb)_N (30–49) ratios that are indicating of adakitic affinity. The Kuoshi granite are also characterized by lower δ¹⁸O (4.15 to 9.81‰, peaked at 8.2‰) and εHf(t) values(−2.4 to 0.6), along with higher H₂O content (medium values at 255 and 795 ppmw) and MgO. These signatures suggest that the Kuoshi pluton was formed by recycling ancient crust and subducted continental crust. Overall, the granitoids across the South Altyn belt reflect a transformation of tectonic regime from water-enriched subduction setting to water-deficient syn-collisional setting. Moreover, the Hf isotopes evolution tend of the early Neoproterozoic granitoids and Suoerkuli Group across the South Altyn belt also suggest a transformation from slab retreat to syn-collision in the early Neoproterozoic. Therefore, overall data and field relations across the Altyn belt indicate an early Neoproterozoic magmatic-sedimentary successions that are similar to that of the Eastern Ghats Belt in India. Given the available paleomagnetic data and detrital zircon age patterns, we conclude a position of the Tarim craton between Australian and North India block in the periphery of Rodinia, close to East Antarctica as well. This research was supported by NSFC Projects (42322208 and 41972238), National Key Research and Development Programs of China (2022YFF0802700 and 2023YFF0803604) and Hong Kong RGC GRF (17308023).

How to cite: Li, W., Yao, J., Zhao, G., and Han, Y.: Reconstruction of the Tarim craton within Rodinia: constraints from magmatic- orogenic records in the Altyn belt, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3114, https://doi.org/10.5194/egusphere-egu24-3114, 2024.

The interplay of geological, chemical and biological processes that drive the oxygenation of the oceans-atmosphere of the early earth are spatially linked to the emergence of biosphere. Banded Iron Formations (BIFs) from the Archean greenstone belts form important archives for understanding the redox conditions of Archean surface environments. The Archean Dharwar craton preserves BIFs in the volcano-sedimentary greenstone belts of two distinct stratigraphic units (older Sargur Group and younger Dharwar Supergroup) corresponding to a time span of 3300-2600 Ma.  These BIFs are confined to the highest stratigraphic levels forming summits of greenstone belts.  They show alternate layers of chert and iron oxides, and petrographic data reveal diverse mineralogy including oxides, carbonate, sulphide and silicate facies. The occurrence of riebeckite and stilpnomelane in BIFs of younger Dharwar Supergroup indicates recrystallization under low-grade metamorphism. Slightly higher abundances of CaO and Al₂O₃ reveal significant influence of crustal source and precipitation of CaCO₃ during BIFs formation. Mesoscopic layers of chert and iron oxide with variable thickness suggest fluctuating redox state of surface environments. The higher enrichment of Ni (6-26 ppm) than the Cr content (3-19 ppm) with variable Sr concentrations may be attributed to feldspar breakdown during hydrothermal fluid acceleration. Trace element ratios (Y/Ho, Sm/Yb, Eu/Sm) coupled with positive Eu anomalies of the BIFs from both older Sargur Group and younger Dharwar Supergroup BIFs reveal dominant hydrothermal input in BIFs origin. The PAAS normalized REE data preclude major continental input in the origin of BIFs. The variable negative Ce anomalies imply periodic fluctuating surface environments (oxic to anoxic) at the dawn of the Great Oxidation Event close to 2340 Ma. This is consistent with the published Fe, N, and S isotope data on the BIFs of the Western Dharwar craton.

How to cite: Mukherjee, A., Mudlappa, J., Nasipuri, P., and Krishnasamy Raveendran, A.: Redox state of Archean surface environments: Insights from the Banded Iron Formations (BIFs) of the Western Dharwar Craton, Southern India , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3303, https://doi.org/10.5194/egusphere-egu24-3303, 2024.

In this study, the c. 3.334 Ga Kromberg Formation of the Onverwacht Group, in the south-eastern limb of the Onverwacht Anticline in the Barberton greenstone belt (South Africa) is investigated. Various geodynamic models have been proposed for the evolution of the Kromberg Formation, but detailed geochemical constraints on the mafic-ultramafic sequence are sparse. The objectives are to constrain the Paleoarchean mantle source characteristics and geodynamic setting for the Kromberg mafic-ultramafic rocks, placed in the context of recent high-resolution field mapping data. To study the protolith volcanic rocks, sampling has been conducted to avoid areas affected by deformation-related alteration. In addition, screening for alteration due to Archean seawater silicification has also been conducted. In conjunction with major, trace and rare earth element data, this study presents the first whole-rock Lu-Hf isotope analyses of mafic-ultramafic rocks of the Paleoarchean Kromberg Formation type-section in the Barberton greenstone belt (Grosch et al., 2022). Three compositionally distinct volcanic rock types are identified namely Group 1 metabasalts, Group 2 metabasalts and komatiitic metabasalts. The geochemistry of these rock types will be presented, and a possible geodynamic setting on the early Earth will be explored.  

Grosch, E.G., Ndlela S., Murphy D., McLoughlin N., Trubac J., Slama J., (2022) Geochemistry of mafic-ultramafic rocks of the 3.33 Ga Kromberg type-section, Barberton greenstone belt, South Africa: Implications for early Earth geodynamic processes. Chemical Geology 605, 120947

How to cite: Grosch, E., Ndlela, S., Murphy, D., McLoughlin, N., Trubac, J., and Slama, J.: Paleoarchean volcanic stratigraphy and geochemistry of the mafic-ultramafic Kromberg Formation type-section, Barberton greenstone belt, South Africa., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3394, https://doi.org/10.5194/egusphere-egu24-3394, 2024.

The oxidation of iron from rocks during subaqueous alteration is a key source of the molecular hydrogen (H₂) used as an energy source by chemosynthetic organisms, which may represent some of the earliest forms of life on Earth. In the Archean, a potential source of ultramafic material available for serpentinisation reactions that release H₂ are komatiites. Komatiites are highly magnesian lavas, which contain evidence of extensive serpentinisation and magnetite (Fe²⁺Fe³⁺₂O₄) production close to the Archean seafloor. H₂ production in komatiitic compositions has been modelled and experimentally investigated; however, the natural rock record has remained unexplored. Here, we examine the geological evidence of H₂ production from the basaltic to komatiitic rock record held in Archean cratons. From the petrological investigation of thirty-eight samples of komatiitic basalt to komatiite, we identify the unique serpentinisation reaction responsible for H₂ production from these lithologies. With support from over 1100 bulk rock geochemical analyses, we directly quantify Fe³⁺ and therefore H₂ production of komatiites in the Archean. The chemical (high Mg) and physical (low viscosity flow) characteristics of komatiite flows allowed for extensive hydration and serpentinisation in oceanic plateaus, and therefore high H₂ production available to chemosynthetic early life.

How to cite: Tamblyn, R. and Hermann, J.: The geological record of H2 production in the Archean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3563, https://doi.org/10.5194/egusphere-egu24-3563, 2024.

Magmas from mantle plumes are potentially the best monitors of Earth's compositional and thermal evolution over time. However, their erupted products are commonly modified by syn- and post-magmatic processes and thus do not fully retain original information about their mantle sources. Such data can be recovered from melt inclusions in olivine phenocrysts in the most primitive magmas from mantle plumes. Such inclusions, shielded by host olivine, retain original isotopic and critical trace element signatures of deep mantle sources even for Archean and Hadean Eons.

We will present the results of a study of chemical and Rb-Sr isotope composition (EPMA, LA-ICP-MS and RAMAN) of melt inclusions and chemical (EPMA, LA-ICP-MS) compositions of host olivines for komatiites and plume-related picrites with eruption age from 3.3 Ga to 1 Ka.

Recent advances in in-situ split stream LA-ICP-MS measurements of ⁸⁷Sr/⁸⁶Sr ratios and trace element contents of olivine-hosted melt inclusions revealed significant mantle source heterogeneities of magmas from individual plumes. The results are confirmed by geodynamic modelling (Jain et al., this meeting).

We show that the melt inclusions of most studied mantle plumes display heterogeneous populations in age-corrected ⁸⁷Sr/⁸⁶Sr ratios and include groups with model ages more than 1 Ga older than the emplacement age. The oldest inclusion groups found in Archean komatiites correspond to Hadean (4.3±0.2Ga, Vezinet et al., in review) and Eo-Paleoarchean (3.6±0.2 Ga) model ages. These and most inclusions from studied komatiites and picrites display Nb/U, Nb/Th and Ce/Pb significantly higher than in BSE.

Evolution over time of canonical proxies of continental crust generation (Nb/U, Th/U and Ce/Pb, Hofmann et al., 1986) in mantle plumes, combined with geodynamic modelling, suggests:

• Most of the continental crust was generated in several Hadean and Archean pulses by plume-induced subduction and melting of the hydrated mafic/ultramafic crust or mantle. Hadean continental crust was subducted or/and reworked.
• Restites left after extraction of continental crust were continuously subducted to the core-mantle boundary from the mid-Hadean and later recycled in Archean mantle plumes.
• Active formation of both continental and oceanic crust in Hadean was governed by plume-induced subduction, which ceased after cold subducted material hindered the propagation of large plumes at the core-mantle boundary. After heating the recycled lithosphere at the core-mantle boundary, the process repeats, producing oscillating subduction and crustal formation in Hadean-Archean.

How to cite: Sobolev, A., Vezinet, A., Chugunov, A., Esteban, M., Batanova, V., Arndt, N., Jain, C., Sobolev, S., Asafov, E., and Valley, J.: Earth's evolution over time revealed by the Nb/U, Ce/Pb and Nb/Th ratios in the sources of mantle plumes., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4334, https://doi.org/10.5194/egusphere-egu24-4334, 2024.

The results of the U-Pb-Hf-O isotope study of zircon from (meta)igneous rocks sampled in all domains of the Ukrainian Shield allow recognition of the four main stages of continental crust formation:

1. The Eoarchean stage (ca. 4000-3600 Ma). Rocks of this stage occur in the Dniester-Bouh and Azov domains. In the former, they are represented by heavily metamorphosed enderbites and mafic schists reaching an age of 3.8 Ga. In contrast, tonalites with an age of 3.67 Ga were identified in the Azov Domain. The oldest zircon reaching an age of 3970 Ma was found in the Mesoarchean metadacite in the Azov Domain. The Eoarchean rocks are rare, but their presence indicates that crust-forming processes have started already in the Eoarchean, or even in Hadean, time.

2. The second major event took place between c. 3.2 and 2.7 Ma. Rocks, formed during this age interval, compose around half of the Ukrainian Shield. Considering the long duration of this event, it may have consisted of several separate episodes. The whole set of rock associations typical for the Archean continental crust, including TTG series, greenstone belts and sedimentary basins, has been formed. Hafnium isotope composition in zircon reveals the juvenile nature of this event. Some remobilization of the older crust is also recorded from several samples.

3. Nearly half of the rock assemblages were dated at ca. 2.15-1.90 Ga. In contrast to the Archean events that resulted in the formation of apparently more or less equant terranes, the Paleoproterozoic events led to the formation of orogenic belts. These belts comprise metamorphosed in amphibolite or epidote-amphibolite facies supercrustal sequences, and abundant granitic intrusions. According to the existing models, the formation of the orogenic belts was related to the assembly of Baltica as a part of the Columbia/Nuna supercontinent. Hafnium-in-zircon and whole-rock Nd isotopes indicate the predominantly juvenile nature of these rocks, with some contamination by the Archean crust.

4. The last major stage of the Ukrainian Shield evolution was linked to the formation of the Prutivka-Novohol large igneous province, which between 1.8 and 1.72 Ga affected the whole Shield. It resulted in the emplacement of numerous mafic dykes and layered massifs, alkaline intrusions, and huge anorthosite-mangerite-charnockite-granite complexes. All igneous rocks formed during this stage reveal signs of crustal contamination, although input of moderately depleted mantle material is also evident.

Obtained isotope and geochronological data demonstrate that the growth of the continental crust in the Ukrainian Shield was episodic. The mechanisms of the crustal growth were different at different times. During both Archean events, the main mechanism was mafic underplating with further remelting and generation of TTG series, whereas greenstone belts represent the results of mantle plume activity. In the Paleoproterozoic, the main mechanism of crustal growth was the subduction of the oceanic lithosphere that led to the formation of volcanic arcs. Mantle plumes remained an important mechanism of the input of mantle-derived material into the continental crust.

How to cite: Shumlyanskyy, L.: The main stages of the Ukrainian Shield evolution and plate tectonics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4724, https://doi.org/10.5194/egusphere-egu24-4724, 2024.

The origin of Earth’s felsic continental crust is still a mystery. The continental crust requires two-steps partial melting of mantle rocks. There are two proposed hypotheses for the continental crust growth in the Early Earth. One is the subduction-related magmatism, e.g. island arc, that produces intermediate to felsic magma which constitutes the early buoyant continental crust. The other is that the magmatism induced by mantle plume creates the thick basaltic crust, and which partially melts into continental crust. However, both two models have their deficiencies. It is still a controversial topic that when plate tectonics begins, which is an obstacle for applying the subduction-induced model in the Early Earth. On the other hand, the plume-induced model seems to be inefficient to support the continental crust growth. The previous numerical studies haves generally focused on the mechanisms of the continental crust formation, while efficiency of the model remains unknown. Thus, we simulated the melt transport process and integrated petrological model in our numerical model to evaluate the efficiency and the plausibility of continental crust production by mantle plume in the Earth’s history. The comparison between our model results and the reconstruction model of continental crust growth provides a new insight for the problem. The results indicates that the mantle plume is an efficient and possible way to support rapid continental crust growth in the Archean. Other mechanisms, e.g. subduction, may take dominant role since the Proterozoic because of low efficiency of plume-induced continental crust production.

How to cite: Zhong, X., Li, Z.-H., and Wang, Y.: Plume-induced continental crust growth rate in Early Earth：Insight from numerical modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4875, https://doi.org/10.5194/egusphere-egu24-4875, 2024.

Banded Iron Formations (BIFs) are authigenic, marine sediments directly reflecting the chemical composition of ancient seawater. BIFs serve as prime geochemical archives for the reconstruction of Precambrian marine environments. However, due to the scarcity of well preserved Archean rocks, atmospheric and hydrospheric environmental conditions within this time frame are still incompletely understood. In particular, elemental fluxes derived from continental weathering and submarine hydrothermal fluxes that affected ancient seawater chemistry are cornerstones for our understanding of the evolution of marine habitats through time. Here we present major- and trace element concentrations in combination with Nd isotopic compositions of 13 samples of Mesoarchean Algoma-type greenschist-facies BIFs from the ca 3.0 Ga old Murchison Greenstone Belt, South Africa. Individual Fe- and Si-rich layers are monitored for sample purity based on their chemical composition. Neodymium isotope compositions, in combination with trace element contents of BIF samples with varying amounts of clastic detritus, are further used to reconstruct the Murchison depositional environment and identify the origin of dissolved and detrital components entering the ancient ocean around 3.0 Ga ago.

Eight samples with low immobile element concentrations display typical shale-normalized Archean seawater-like rare earth and yttrium (REY_SN) patterns with positive La_SN, Eu_CN, and Gd_SN anomalies, super-chondritic Y/Ho ratios, and an enrichment of heavy REY_SN over light REY_SN, implying an open marine-dominated depositional setting with contributions from submarine high-temperature, hydrothermal systems. A Sm-Nd regression line yields an age of 2.98 ± 0.19 Ga that overlaps with the proposed depositional age, suggesting negligible post-depositional alteration on the REY composition of the pure BIF layers. In contrast, higher concentrations of immobile elements (e.g., Zr) and/or non-seawater-like REY_SN patterns are characteristic for the remaining five BIF samples, indicating elevated detrital input or post-depositional alteration. A regression line of the impure BIF layers yields an age of 2.49 ± 0.15 Ga, reflecting a potential post-depositional overprinting event such as the 2.6 Ga old Limpopo orogeny. The Nd isotopic compositions of pure and impure BIF samples cover a wide range of ca. two epsilon units suggesting a mixture of weathered mafic and felsic sources for the dissolved and suspended fluxes into the Murchison ocean.

How to cite: Krayer, J., Viehmann, S., Mayer, A., Schulz, T., Koeberl, C., Hofmann, A., Jodder, J., Willbold, M., and Weyer, S.: Elemental fluxes into 3.0-billion-year-old marine environments: evidence from trace elements and Nd isotopes in banded iron formations from the Murchison Greenstone Belt, South Africa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5245, https://doi.org/10.5194/egusphere-egu24-5245, 2024.

The Neoarchean greenstone-granite rock association preserved in the Eastern Block of the North China Craton exhibits distinctive dome-and-keel structures. Although the metamorphic data from these rock assemblages provide valuable insights into the tectonic evolution of this region, the interpretation of the clockwise paths with nearly isothermal decompression (ITD) and the anticlockwise P–T paths involving near-isobaric cooling (IBC) remain inconsistent and controversial. By conducting 2D numerical models with the initial and boundary conditions similar to those of the Neoarchean Eastern Block, we investigated the coexistence of diverse P-T paths and determined their possible geodynamic regime. The model results demonstrate that the combination of crustal density inversion and heat from the high-temperature lower boundary initiates a crustal-scale sagduction process, leading to the formation of dome-and-keel structures. Additionally, we identified four primary types of P-T-t paths. Firstly, an anticlockwise IBC-type P-T-t path reveals the supracrustal rocks gradually subside to a deep crustal level, where they experience a prolonged residence period characterized by ambient mantle cooling without significant exhumation. Secondly, a clockwise ITD-type P-T-t path suggests the supracrustal rocks descend to the deep crust and are partly entrained by upwelling TTG magmas, leading to their rapid ascent to a middle crustal level. Thirdly, a newly identified crescent-type P-T-t path indicates an integrated burial-exhumation cycle, consisting of an initial burial stage with high dT/dP, followed by a rapid exhumation stage and a subsequent cooling stage exhibiting low dT/dP. Lastly, a hairpin-type P-T-t path highlights the slow exhumation rate experienced by deeply buried supracrustal rocks. The dome-and-keel structure and P-T-t paths observed in the numerical model are consistent with the geochronological, metamorphic and structural data of the Eastern Block. Based on these observations, we propose that the crustal-scale sagduction involving a mantle plume could responsible for the geological complexity of eastern China.

This work was financially supported by the National Natural Science Foundation of China (42025204) and National Key Research and Development Program of China (No. 2023YFF0803804).

How to cite: Yu, C., Yang, T., Zhang*, J., Zhao, G., Cawood, P. A., Yin, C., Qian, J., Gao, P., and Zhao, C.: Diverse P-T-t paths within the Neoarchean sagduction regime of North China Craton: insights from field data and numerical modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5391, https://doi.org/10.5194/egusphere-egu24-5391, 2024.

Oxygen is the most abundant element in the terrestrial mantle and crust. We have recently reported on a 0.2‰ δ¹⁸O decrease of continental mantle peridotites from the original primary Bulk Silicate Earth-Moon value of 5.57‰ [1] in the mid-Archean to the Phanerozoic explained by the initiation of surface recycling (linked to intensity and style of plate tectonics) sometime in the Archean. Even small variations in the volatile mass balance are critical in explaining phenomena such as the Great Oxidation Event at ~2.4 Ga that may have mantle origin. As low-δ¹⁸O subduction fluids are derived by the dehydration (and potentially oxidation) of low-δ¹⁸O interiors of subducted slabs, this work further explores this process to observe temporal changes related to the progressive input of volatile elements and potential lithospheric mantle oxidation. This study presents a record of trace elements measured in same olivines (Li, Na, Al, P, Ca, Sc, Ti, V, Cr, Mn, Co, Ni, Cu, Ga, Y, Zr) including oxidation-sensitive elemental ratios V/Sc and Zn/Fe for this collection. Prior melt-depletion of mantle peridotites, estimated using bulk Al₂O₃ content of the xenoliths, increases with age from ~25 to 35%, leading to depletion of Yb, Y, Co, Mn, Ca, P, with smaller effects on the elemental ratios.  We observe significant ranges of V/Sc (0.2-14), Li/Y and other ratios, not related to prior melt depletion that may be linked to subduction-related re-distribution of incompatible elements by subduction [2], and scattered correlation with age and δ¹⁸O values. Further trends will be analyzed during the talk after considering craton-specific domains and global trends. This work can potentially contribute to constraining a global mass balance of crustal growth and recycling based on co-variations of isotopes of a major element oxygen and trace elements in the predominant lithospheric reservoir of subcontinental mantle.

^[1]Bindeman ea, (2022) Nat Comm 13, 3779; ^[2] Doucet ea, (2020) NatGeosci 13, 511.

How to cite: Bindeman, I., Batanova, V., Sobolev, A., Ionov, D., and Danyushevsky, L.: Evolving Chemistry of Lithospheric Mantle Based on Oxygen Isotope and Trace Element Analyses of Olivines from Mantle Xenoliths across Earth’s History, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6614, https://doi.org/10.5194/egusphere-egu24-6614, 2024.

The operation of a hydrological cycle (i.e., exchange of water between the land, oceans, and atmosphere) has significant implications for the emergence of life. The oldest confirmed single-celled organisms at ~3.48 billion years ago (Ga) (Pilbara Craton, Western Australia) are thought to have formed in the presence of meteoric (fresh) water on emerged (subaerial) land in a hot spring environment. However, when widespread interaction between fresh water and emerged continental crust first began is poorly constrained. In this study, we use >1000 oxygen isotope analyses of Jack Hills detrital zircon to track fluid-rock interactions from the Hadean to the Paleoarchean (~4.4–3.1 Ga). We identify extreme isotopically light O (i.e., δ¹⁸O < 4.0 ‰) values older than 3.5 Ga. The data define two periods of magmatism with extreme isotopically-light O as low as 2.0 ‰ and –0.1 ‰ at around 4.0 and 3.4 Ga, respectively. Using Monte Carlo simulations, we demonstrate that such values can only be generated by the interaction of crustal magmatic systems with meteoric water. Our data constrains the earliest emergence of continental crust on Earth, the presence of fresh water, and the start of the hydrological cycle that likely provided the environmental niches required for a life less than 600 million years after Earth’s accretion.

How to cite: Gamaleldien, H., Wu, L.-G., Olierook, H. K. H., Kirkland, C. L., Kirsche, U., Li, Z.-X., Johnson, T., Makin, S., Li, Q.-L., Jiang, Q., Wilde, S. A., and Li, X.-H.: Fresh water on Earth four billion years ago, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7106, https://doi.org/10.5194/egusphere-egu24-7106, 2024.

Several studies have already concluded the presence of 7-8 ocean equivalent water (OCE) in the mantle of earth, structurally occurring as H⁺/OH^–. This can affect the seismic anomaly, mechanical strength, ionic diffusion, etc. of the mantle. The upper mantle is primarily composed of olivine, which first transforms to wadsleyite and then to ringwoodite at ~13 and ~18 GPa, respectively. Petrological and mineralogical experiments have demonstrated that H, occurring as point defects can act as a source of water in the upper mantle. Being the abundant mineral in upper mantle, it is very important to investigate the ability of olivine to act as a potential mineral phase to house water. Incorporation of water in mantle minerals has been a burning topic for many theoretical and experimental works. Even a trace amount of water in mineral structure can significantly alter their physical (e.g., elastic behaviour, seismic velocities, etc.) and chemical properties (e.g., ionic diffusion, electrical conductivity, etc.). FT-IR studies suggested that a rapid diffusion of H⁺ in olivine makes it a better candidate for point defects compared to larger and heavier OH^– ions. Karato & Jung (2003)  showed that increment of H concentration in olivine decreases its strength. Later, Mao et al. (2008) and Panero et al. (2010) observed qualitatively similar trend in high pressure olivine polymorphs. They observed drastic reduction in selective elastic constants of C₁₁compared to C₁₂ and C₄₄ as H content increases in ringwoodite. Huang et al. (2005) found that temperature and water increases electrical conductivity in both the polymorphs. Yoshino et al. (2009) reported that a hike in temperature switches H-diffusion mechanism in olivine from proton conduction to small polaron conduction. The H diffusion in Fe-bearing olivine is experimentally shown to be dictated by (i) Proton-polaron (PP) mechanism and (ii) Proton-vacancy (PV) mechanism in <1 GPa. The PV is found to be valid for incorporating more water in olivine compared to PP. However, the second method, despite being strongly anisotropic, allows a faster diffusion. Much of the existing studies deals with temperature and water content as the key physical factors in controlling proton diffusivity. The fact that most of these studies have not carried out in the exact pressure (p) and temperature (T) conditions of mantle of Earth demand further studies on the same. Present study involves the study of H diffusion in lattice structure of olivine and wadsleyite; their mechanical stability, physical and chemical properties under mantle p–T conditions. Our results suggest a drop in seismic velocities in both olivine and wadsleyite phases. This can explain few outstanding geological events such as, weakening of upper mantle etc. This study will also provide a water budget in these mantle minerals. Therefore, the proposed research embarks on advancing theoretical understanding of hydrous mineral phases, which have a stability under extreme thermo-mechanical conditions.

How to cite: Das, P. K. and Karangara, A.: First principle investigations on the water budget in olivine phases: Implications towards the behavior of hydrous mantle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7388, https://doi.org/10.5194/egusphere-egu24-7388, 2024.

The potential impact of the increased rates of tidal energy dissipation on the climate on early Earth is usually assessed in terms of the global contribution to the energy balance which is small compared to the incoming solar radiation. However, tidal energy dissipation depends strongly on the distribution of landmasses, and regional energy input could, in principle, impact the local and global climate state via changes in circulation patterns and feedbacks in the Earth system. Here we investigate these effects by calculating tidal energy dissipation for a randomly generated continental distribution representative of early Earth, and three different rotation rates, and feeding it into a coupled climate model. Despite marginal global impacts, tidal energy dissipation can have significant regional effects caused by changes in ocean circulation and amplified by the ice-albedo feedback. These effects are strongest in climate states and regions where meridional heat transport close to the sea-ice margin is altered. This suggests that tidal heating could have contributed to sustaining regions with no significant ice cover.

How to cite: Feulner, G., Biewald, B., Green, J. A. M., Hofmann, M., and Petri, S.: Spatially explicit simulations of the effect of tidal energy dissipation on the climate on early Earth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9476, https://doi.org/10.5194/egusphere-egu24-9476, 2024.

Ancient rocks documenting early silicate Earth processes are only sparsely preserved on its modern surface. Some of the oldest known crustal lithologies (≤3.7 Ga) can be found within the Indian Shield. However, a substantial area of the western and central Indian basement has been covered by the ~66 Ma old Deccan flood basalts. Some Deccan-related mafic dykes in the Nandurbar-Dhule region of the Narmada-Tapi rift zone host xenolithic crustal material, which can be used to study the otherwise inaccessible basement. Textural and mineralogical heterogeneity amongst these xenoliths implies that they derive from different depths of a single column of crust and represent randomly sampled crustal rock types with possibly distinct heritages. Well studied examples of these dykes are the adjacent Rajmane and Talwade dykes south of Duhle, which host Neoarchean-aged [1] crustal xenoliths with highly variable ⁸⁷Sr/⁸⁶Sr ratios between 0.70935 and 0.78479 [2]. This led previous researchers to infer a genetic relationship of these xenoliths with rocks from the Dharwar Craton [1, 2].

In this study, xenolith samples are used to investigate the evolution of sub-Deccan continental crust and evaluate whether randomly sampled crustal lithologies share a common Hadean heritage that is similar to published data for Dharwar granitic rocks. Our samples (n = 17) originate from two mafic dykes near Talwade and Ranala in the Nandurbar-Dhule region. We report major and trace element abundances and ¹⁴²Nd isotopic compositions. The CIPW norms of xenoliths define a nearly continuous petrological evolution trend from tonalites to reworked, orthoclase-rich granites, with subordinate trondhjemitic compositions. The vertical cross-section of crust underlying the dykes therefore provides an opportunity to study the geochemistry of evolving primitive continental crust. Trace element abundance data also conform to a tonalite-trondhjemite-granodiorite-like (TTG) composition for a subset of the xenoliths, whereas others resemble younger granitoids, which might represent reworked TTG equivalents, or younger intrusions.

The short-lived (t_1/2 = 103 Ma) ¹⁴⁶Sm-¹⁴²Nd decay system is particularly sensitive to magmatic fractionation processes that occurred within the first ca. 500 Ma of Earth’s history. Heterogeneous ¹⁴²Nd/¹⁴⁴Nd compositions (expressed as μ¹⁴²Nd = [(¹⁴²Nd/¹⁴⁴Nd)_sample/(¹⁴²Nd/¹⁴⁴Nd)_JNdi – 1] * 10⁶) are typically restricted to Archean-aged rocks and reveal information about the preservation of mantle heterogeneity over geological timescales. The μ¹⁴²Nd of dyke host lavas (n = 3) are heterogeneous (μ¹⁴²Nd = -2.0 ±5.1 to +6.1 ±5.1) but unresolved from the terrestrial standard. Such heterogeneity suggests that the parental magmas to the dykes experienced complex lithospheric and crustal assimilation during their ascent. Felsic xenoliths have homogeneous μ¹⁴²Nd compositions (μ¹⁴²Nd = -0.9 ±2.3, 95% c.i., n = 7). Combined with the major and trace element data, this implies an extensively reworked crust underneath the Deccan Traps. The lack of recognizable μ¹⁴²Nd anomalies is consistent with data of younger Dharwar granitoids [3] and may reflect regional overprinting of mantle μ¹⁴²Nd heterogeneity at or before the Neoarchean emplacement age of the xenoliths.

[1] Upadhyay et al. (2015) J. Geol. 123(3), 295–307.

[2] Ray et al. (2008) Gondwana Res. 13, 375–385.

[3] Ravindran et al. (2022) Goldschmidt Abst. 10986.

How to cite: Halfar, M. C., Peters, B. J., Day, J. M. D., and Schönbächler, M.: Geochemical and Nd isotopic constraints on the evolution of Neoarchean continental crust underlying the central Deccan Traps, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10677, https://doi.org/10.5194/egusphere-egu24-10677, 2024.

In recent times, the Archaean geological record of the Singhbhum Craton has been scrutinized regarding early Earth crustal processes, tectonics, magmatic-detrital zircon geochronology, early life research, and Fe-Mn mineralization associated with volcano-sedimentary successions. However, many of these studies are hampered by a lack of a basic stratigraphic framework of the various litho-stratigraphic units, complicating our understanding of the overall Archaean geology of the Singhbhum Craton. Here, we share first-hand information on the Palaeoarchaean greenstone belts and Meso-Neoarchaean intracontinental volcano-sedimentary sequence of the Singhbhum Craton.

New magmatic zircon U-Pb ages determined from felsic volcanic rocks of the Badampahar Group are represented by their crystallization age at c. 3.51 Ga. Intrusive granitoids exposed in the Daitari and Gorumahisani greenstone belts yield crystallization ages ranging from 3.38 to 3.29 Ga and having inherited zircons being 3.58, 3.55, and 3.51 Ga old. A granitoid intrusive into iron formation of the Gorumahisani greenstone belt has an age of c. 3.29 Ga.  Detrital zircons recovered from Koira Group sandstone intercalated with iron formation yield a maximum depositional age of 2.63 Ga. 

We demonstrate that Palaeoarchaean greenstones exposed in the northern and southern parts of the Singhbhum Craton consists largely of sub-marine mafic-ultramafic volcanic rocks interlayered with minor felsic volcanic and chemical sedimentary rocks. Importantly, the ca. 3.51 Ga felsic volcanic rocks from the Badampahar Group permit comparison with co-eval felsic volcanic units reported from the lower part of the Onverwacht, Nondweni, Warrawoona groups of the Kaapvaal and Pilbara cratons. Otherwise, new age constraints of the Koira Group allow for better correlations with Meso-Neoarchaean cratonic cover successions elsewhere. 

How to cite: Jodder, J., Hofmann, A., Elburg, M., and Ngobeli, R.: Archaean record of the Singhbhum Craton, India: new insights from greenstone belts and cratonic cover sequences. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10889, https://doi.org/10.5194/egusphere-egu24-10889, 2024.

Granitoids of the Tonalite-Trondhjemite-Granodiorite (TTG) group are a prime constituent of Archean cratons. Differences in the composition of these rocks relative to modern-day, more potassic granitoids have been proposed to reflect changes in the conditions and mechanisms of crust generation. By extension, these differences may indicate changes in the tectonic regime through geological time. Despite a continuously growing body of TTG research, consensus on TTG generation and Archean tectonic settings has not yet been reached. A remaining open question regarding TTGs is whether a reworked crustal component is present. Silicon and O isotopes have been previously employed to address this question and both isotope systems suggest that at least some TTGs indeed contain reworked material. Boron provides an alternative isotope system that can trace surface-altered material in magmatic rocks because B isotopes fractionate significantly at Earth’s surface but remain relatively unaltered at high temperatures. On modern-day Earth, the deep recycling of isotopically heavy seawater-derived B through subduction results in a diverse, but on average heavy, B isotope composition in arc granitoids. Conversely, juvenile granitoids formed in settings unrelated to subduction typically have mantle B-isotope values. These systematics are likely uniform and would apply to the Archean as well, given that Archean seawater also appears to exhibit isotopically heavy B. The B isotope system may thus be used to investigate the presence of subducted or otherwise surface-derived material in Archean granitoids. To this end, B isotopes were analyzed for a geographically and temporally spread sample set of pristine TTGs and related granitoids (n=45, from 9 different Archean terranes covering an age range of 3.78 to 2.68 Ga). This is a considerably larger and more geographically spread sample set than a B-isotope pilot study on TTGs (Smit et al., 2019), and may as such provide more globally representative results. The B isotope signature of TTGs seem to diversify over time, diverging more from mantle-derived values starting between 3.3 and 2.9 Ga. TTGs younger than 2.9 Ga exhibit up to δ¹¹B = +10.5 ± 0.2‰, and 48% of the samples have δ¹¹B values heavier than depleted mantle, whereas this is 18% for TTGs older than 3.3 Ga. The B isotope signature additionally diversifies with decreasing K₂O/Na₂O and La/Sm. Boron isotope compositions do not correlate with geochemical or petrological proxies for (post-)magmatic processes, such as weathering, metamorphism, hydrothermal alteration, or the loss of magmatic fluids, and therefore seem to be at least not significantly altered by these processes. Instead, isotopically heavy B in TTGs may be explained by the addition of a sodic and ¹¹B-rich contaminant into the TTG source. These contaminant characteristics point to seawater-altered oceanic crust, possibly introduced to the TTG source through subduction. If this is correct, the temporal trend observed in the δ¹¹B values in TTGs may reflect a shift from local and episodic to global and systematic subduction of oceanic crust in the Mesoarchean.

Smit, M.A. et al., 2019, Formation of Archean continental crust constrained by boron isotopes: Geochemical Perspectives Letters, doi:10.7185/geochemlet.1930.

How to cite: Goumans, J., Smit, M., and Musiyachenko, K.: Boron isotopes in global TTGs trace the increase in deep crustal recycling in the Mesoarchean  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12762, https://doi.org/10.5194/egusphere-egu24-12762, 2024.

Tectonic mode manifests how a planet’s interior is cooling, and it encompasses all the geological activities (e.g., magmatism, deformation, metamorphism, sedimentation) that characterize the planetary body. Tectonic processes exert first-order control on factors key to planetary habitability (e.g., Southam et al., 2015). For example, tectonic mode controls the long-term prevalence of surface oceans, the sustenance of physicochemical conditions (e.g., temperature) favourable for metabolic activity, fluxing of elements in and out of the planet’s interior and thereby, the availability of bio-essential nutrients (e.g., C, O, H, N, P, S) (Cockell et al., 2016). However, all tectonic modes do not regulate these processes efficiently. For example, stagnant-lid mode restricts heat and material exchange between a planet’s interior and surficial reservoirs compared to plate tectonics. Further, certain factors determining a planet’s tectonic mode – like internal heat budget, mechanical behaviour of rocks, and volatile content – can vary with time, leading to the prevalence of different tectonic modes during planetary evolution. Thus, a planet’s habitability is critically intertwined with its tectonic evolution.

Modern Earth is the only known planet with plate tectonics, felsic crust, and life. Plate tectonics has resulted in a Goldilocks environment for long-term habitability via chemical cycling across the Earth system, regulating temperature through the carbonate-silicate cycle, sustaining oceans at the surface, and developing bimodal hypsometry with emergent felsic crust releasing bio-essential minerals through weathering and erosion. This has resulted in diverse habitats facilitating life’s complex phylogenetic tree. However, life initiated on Earth in the Hadean or early Archean when non-plate-tectonic modes like the stagnant- or squishy-lid modes are inferred to be prevalent (e.g., Cawood et al., 2022). Their potential to promote habitability is unknown, with few studies suggesting that they may lead to habitable conditions (e.g., Tosi et al., 2017). Nevertheless, our terrestrial planetary neighbours’ records suggest that such modes are unlikely to provide the environmental stability necessary to develop a long-term phylogenetic landscape. The geochemical cycling of elements through these modes may occur (e.g., via magmatism and episodic recycling of lithosphere) but is likely to be spatially and temporally discontinuous and limited, thereby limiting the supply of bio-essential nutrients and longevity of oceans on a planetary surface. As such, these modes inhibit a surficial environment in long-term dynamic equilibrium, leading to inhospitable habitats either through the development of a run-away greenhouse (e.g., Venus) or the loss of early atmosphere and oceans to space (e.g., Mars).

Thus, the tectonic evolution of Earth and its resultant habitability are a predictable consequence of its position, composition, size, and heat energy within the solar system. These conditions may serve as a template to search for exoplanet habitability; however, a degree of unpredictability will remain in knowing whether a similar set of planetary criteria would produce the same outcome.

References:

Cawood et al., 2022. Reviews of Geophysics, 60, e2022RG000789

Cockell et al., 2016. Astrobiology, 16(1), pp.89-117.

Southam et al., 2015. Planets and Moons, 10, pp.473-486.

Tosi et al., 2017. Astronomy & Astrophysics, 605, p.A71.

How to cite: Cawood, P. and Chowdhury, P.: Earth’s early tectonic modes and implications for habitability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12921, https://doi.org/10.5194/egusphere-egu24-12921, 2024.

The Limpopo Belt of southern Africa is a classical Paleoproterozoic orogenic belt that is believed to have resulted from the collision between the Kaapvaal and Zimbabwe Cratons. Previous studies have primarily focused on geochronology, petrology, and geochemistry of different rock assemblages, resulting in a general tectonic framework indicating at least two significant tectonothermal events from Mesoarchean to Paleoproterozoic. However, the spatial and temporal relationships between these events, as well as their overall structural patterns in the field, are poorly understood. The Central Limpopo Belt contains the best lithological exposures of different ages, making it the most promising area for detailed structural mapping and analysis, and for gaining a better understanding of these issues.
Based on the detailed field-based structural analyses, four generations of deformation were identified. The earliest D1 deformation is characterized by the penetrative S1 foliations only preserved within the 3.6-3.4 Ga anorthosites that now occur sporadically as xenoliths or boudins in the highly deformed 2.9-3.3 Ga Sand River gneiss. S2 are penetrative gneissic foliations that were extensively developed in the Sand River gneiss and were intensively superimposed by subsequent deformations into tight to isoclinal folds. After restoration of their attitude, S2 foliations strike NW-SE and dip steeply to SW at high angles, indicating that the D2 deformation experienced a roughly NE-SW-oriented compression between 2.9-2.6 Ga. D3 deformation resulted from significant NW-SE-oriented compression that intensively superimposed the earlier S2 fabrics into vertically inclined isoclinal folds and tectonites S3-L3. Strain measurements on these tectonites indicate that all pre-existing rock assemblages were stretched or sheared along the vertical orientation, resulting in the development of numerous sheath folds in the Sand River gneiss and 2.6-2.7 Grey gneiss. Associated with the zircon ages from anatexis melts, the D3 deformation most likely occurred at 2.1-2.0 Ga. SHRIMP U-Pb zircon age dating recorded these two metamorphic ages of ~2.6 Ga and 2.0 Ga on a single zircon of the foliated Sand River gneiss. A regional large scale inclined open fold F4 gently refolded the D1-D3 fabrics and marked the final deformation of the Central Limpopo Belt, occurring sometime after ~2.0 Ga. 
Detailed structural data of this study, in combination of available geochronological and metamorphic data lead us to propose that the ~2.65 Ga and ~2.0 Ga tectonothermal events occurred under different tectonic environments. The ~2.65 Ga tectonothermal event developed coevally with D2 deformation and high-grade metamorphism during the NE-SW collisional event. In contrast, the ~2.0 Ga tectonothermal event occurred during a NW-SE-oriented collisional event between the Kaapvaal and Zimbabwe Cratons, resulting in the formation of the major Limpopo tectonic linear belt seen today.

Acknowledgement
This work was financially supported by the National Natural Science Foundation of China (42025204) and National Key Research and Development Program of China (No. 2023YFF0803804).

How to cite: Zhang, J., Brandl, G., Zhao, G., Liu, J., and Zhao, C.: Deciphering a complex Neoarchean-Paleoproterozoic collisional history between the Kaapvaal and Zimbabwe Cratons: new constraints from polyphase deformation of the Central Limpopo Belt, southern Africa , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14565, https://doi.org/10.5194/egusphere-egu24-14565, 2024.

Plate tectonics exerts a first-order control on the interaction between Earth’s reservoirs. Atmospherically-altered surface materials are recycled to the mantle via subduction, while volatiles from the mantle are liberated to the atmosphere via volcanism. This cycle regulates much of Earth’s climate, ocean levels and metallogenetic processes within the continental crust. However, the interplay between Earth’s atmospheric changes and the geochemical evolution of mantle-derived magmas has remained obscure for the ancient geological history. This has led to multiple conflicting models for the crustal evolution in the early Earth.

A time-integrated evolution of the mantle-crust-atmosphere-hydrosphere interaction is yet to be fully established. For instance, secular change of the ocean and atmosphere system is evident from several proxies but the feedback of these changes to magmatic and geochemical processes in the lithosphere remain unclear. Moreover, no clear consensus has been reached on the timing of modern-style plate tectonic initiation and the evolution of net growth of the continental crust.

To explain overt and cryptic global trends in the geochemistry of magmatic rocks, a better understanding of mineral reactions and how these control trace element evolution in magmas at the lithosphere-scale is paramount. For example, the elemental and isotopic composition of apatite inclusions hosted by zircon offers a way to better understand the evolution of magmas and, to some extent, the nature of magma sources. These proxies rely on the robust data acquisition of other isotope systems with different geochemical behaviour, such as U-Pb and Lu-Hf analyses in the host zircon crystal.

A combination of methods and proxies including the elemental composition of apatite via EPMA and the oxygen fugacity based on sulphur speciation via μ-XANES of apatite inclusions was applied to ancient sub-arc magmas formed in regions akin to modern subduction zones. These magmas share a common mantle source but crystallised more than 200 million years apart (at 2.35 and 2.13 billion years ago). Importantly, they bracket the Great Oxidation Event, when atmospheric oxygen levels increased by five orders of magnitude, causing a permanent and dramatic change in Earth’s surface chemistry. As such, these sub-arc magmas were investigated as potential tracers of the interaction between Earth’s atmosphere and the mantle.

The information from several inclusions from co-magmatic rocks can then be interpreted in the light of U-Pb, Lu-Hf, trace elements and oxygen isotope analyses of the host zircon grains. Altogether, the results show a shift in oxygen fugacity of sub-arc magmas across the Great Oxidation Event. The change in oxygen fugacity is thought to be caused by recycling into the mantle of sediments that had been geochemically altered at the surface by the increase in atmospheric oxygen levels. This study opens a wide window of opportunities for the time-integrated investigation of the interaction between atmosphere and oceans with the evolving terrestrial mantle.

How to cite: Moreira, H., Storey, C., Bruand, E., Darling, J., Fowler, M., Cotte, M., Villalobos-Portillo, E. E., Parat, F., Seixas, L., Philippot, P., and Dhuime, B.: Linking early Earth’s internal and external reservoirs: a change in oxygen fugacity of sub-arc magmas across the Great Oxidation Event, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16380, https://doi.org/10.5194/egusphere-egu24-16380, 2024.

Large swaths of juvenile crust with tonalite-trondhjemite-granodiorite (TTG) composition were added to the continental crust from about 3.5 billion years ago. Although TTG magmatism marked a pivotal step in early crustal growth and cratonisation, the petrogenetic processes, tectonic setting and sources of TTGs are not well known. Part of this issue is the general difficulty in disentangling the chemical effects of fractional crystallization and partial melting, which impedes constraining primitive melt compositions and, by extension, investigating source-rock lithology and composition. To investigate these aspects, we assessed the composition and petrogenesis of Archaean TTGs using high field-strength elements that are fluid immobile, uniformly incompatible, but differently compatible between various residual minerals. The Nb concentrations and Ti anomalies of TTGs show the overwhelming effects of amphibole and plagioclase fractionation and permit constraints on the composition of primary TTGs. The latter are relatively incompatible element-poor and characterised by variably high La/Sm, Sm/Yb and Sr/Y, and positive Eu anomalies. Differences in these parameters do not represent differences in melting depth, but instead indicate differences in the degree of melting and fractional crystallisation. Primary TTGs formed by the melting of rutile- and garnet-bearing plagioclase-cumulate rocks that resided in the roots of mafic proto-continents. The partial melting of these rocks likely was part of a causal chain that linked TTG magmatism to the formation of sanukitoids and K-rich granites. These processes explain the growth and differentiation of the Archean continental crust, without requiring external forcing such as meteorite impact or the start of global plate tectonics.

How to cite: Smit, M., Musiyachenko, K., and Goumans, J.: Archean continental crust formed by melting mafic cumulates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18408, https://doi.org/10.5194/egusphere-egu24-18408, 2024.

The Sittampundi Anorthosite complex (SAC), in the Southern Granulite terrain of Peninsular India, is a layered Archean anorthosite comprising gabbroic rocks at the base overlain by leucogabbros and anorthosites interlayered with well-developed massive chromitites. The complex has been subjected to high-pressure granulite facies (800-900°C and 11-14 Kbar) metamorphism and later retrogressed to amphibolite-facies metamorphism (550-480°C and 5.5-4.5Kbar) during exhumation (Chatterjee et al., 2022). Detailed petrography, mineral chemistry as well as major and trace element geochemistry have been used to constrain its petrogenesis and geodynamic setting.

The presence of highly calcic plagioclase and igneous amphibole indicates that magma was quite hydrous in nature. Chromites are Fe-Al rich in nature, and on the differentiation diagram, they plot near to podiform chromites and supra-subduction zone setting. Geochemical trends in major and trace elements indicate that the gabbro, leucogabbro and anorthosites were derived from the fractionated magma. However, the mineral assemblage and chromite chemistry in chromitite indicate they formed due to magma mixing.  Based on experimental studies, the composition of plagioclase limits the pressure to 2-3kb and depth of crystallization to approximately 7-11 kilometres. The findings of this study indicate the hydrous magma parental to SAC originated in a subduction zone setting in the Neoarchean.

How to cite: Kaur, A., Krishnamurthi, R., and Rai, N.: Petrogenetic and Geochemical studies of Sittampundi Anorthosite Complex, Southern Granulite Terrain, India., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19222, https://doi.org/10.5194/egusphere-egu24-19222, 2024.

The difficulty in direct differentiation of the felsic crustal components from Earth’s mantle peridotite leads to a requirement for the presence of a large amount of hydrated mafic precursor of TTG in Earth’s proto-crust, the origin of which, however, remains elusive. The mafic proto-crust may have formed as early as  4.4 Ga ago as reflected by the Hf and Nd isotopic signals from Earth’s oldest geological records, i.e., zircons. The Archean continents, primarily composed of the felsic tonalite–trondhjemite–granodiorite (TTG) suite, were formed or conserved since  3.8 Ga, with significant growth of the continental crust since  2.7 Ga. Such a significant time lag between the formation of the mafic proto-crust and the occurrence of felsic continental crust is not easily reconciled with a single-stage scenario of Earth’s early differentiation. 
Here, inspired by the volcanism-dominated heat-pipe tectonics witnessed on Jupiter’s moon Io and the resemblances of the intensive internal heating and active magmatism between the early Earth and the present-day Io, we present a conceptual model of Earth’s early crust-mantle differentiation and the formation of habitability, which involves the tremendous heat obtained by the Moon-forming giant impact. It  forces Earth to choose an Io-like tectonics, which can efficiently dissipate heat and extract a mafic proto-crust from the early mantle, then followed by an intrusion-dominating regime that could account for the subsequent formation of the felsic continents as Earth cools. The episodic heat-pipe tectonics destroy most of rocks formed during Hadean era. The cool and hard rock layer formed due to the heat-pipe tectonics is essential for the formation of habitability of the earth. By this way, the required conditions by a habitable Earth, e.g., adequate surface temperature, aqueous sphere, and towering mountains, etc., would be appeared within a surprisingly short time. Therefore, the Moon-forming giant impact is the most important reason to make a habitable Earth. It not only brought tremendous heat into Earth and forced Earth to choose the volcanism-dominated heat-pipe tectonics but also completely destroyed the proto-atmosphere to avoid over-heated situations occurred like that of Venus at present. 

How to cite: Liu, Y.: The conceptual model of the formation of Earth’s habitability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19385, https://doi.org/10.5194/egusphere-egu24-19385, 2024.

The scarce geological record of Earth’s infancy, particularly before 3 billion years ago (Ga), is restricted to cratons, many of which likely originated as volcano-plutonic plateaus in a non-mobile lid geodynamic regime. However, this scarcity is at odds with the significant volumes of continental crust at 3 Ga that multi-proxy models of mantle depletion and crustal growth predict. This challenges the notion that plateau-type cratonic nuclei represent the predominant tectonomagmatic settings operating on the early Earth. Reconciling this paradox necessitates a “silent majority” of missing off-craton Archean crust of an uncharacterized affinity.

To investigate a potential rare remnant example of an Archean crust constructed away from cratonic nuclei, we report major and trace-element chemostratigraphic data from the 3.1 Ga Whundo Group of the Pilbara Craton, investigating the petrogenetic processes related to its formation. These data reveal three magmatic cycles of intercalated supracrustal successions comprising six groups: tholeiites, boninites, calc-alkaline BADR (basalt-andesite-dacite-rhyolite), high-magnesium ADR (including a subset of transitionally adakitic affinity), Nb-enriched basalts (NEB), and boninite-calc-alkaline hybrids. Th/Yb-Nb/Yb, Gd/Yb_N-Al/Ti_N, and Nd isotope systematics are inconsistent with contamination by felsic basement characteristic of cratonic cores, suggesting eruption onto thin, juvenile lithosphere that was only later incorporated into the Pilbara Craton.

How to cite: Vandenburg, E., Nebel, O., Cawood, P., Capitanio, F., Miller, L., Millet, M.-A., and Smithies, H.: A widespread, short-lived, off-craton subduction source for hidden crustal growth in Earth’s infancy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21184, https://doi.org/10.5194/egusphere-egu24-21184, 2024.

Dome-shaped uplifted and fractured terrain observed at the surface of the Moon and Mars includes floor-fractured impact craters. Such deformation features are inferred to form by the emplacement and inflation of sill- and laccolith-shaped magma bodies in the shallowest 1-2 km of a planetary body’s rocky crust. Only the final surface deformation features can be observed from space, modelling helps to understand the emplacement dynamics and the deformation of the overlying rock. A mismatch exists, however, between the complex mechanical response of host rocks to magma-induced stresses observed on Earth in exposed volcanic plumbing systems and the linearly elastic deformation assumed by most of the often-used numerical models.

We have implemented simulations of the inflation of a laccolith intrusion in a particle-based host medium in the two-dimensional (2D) Discrete Element Method (DEM). Our approach allows us to investigate magma-induced, highly discontinuous, deformation and dynamic fracturing and visualizes the localization of subsurface strain. We systematically varied a range of numerical model parameters that govern host rock strength (bond cohesion, bond tensile strength, bond elastic modulus), and specific gravity known for the Moon, Mars and Earth. For equal rock stiffness and amounts of intruded magma, our model results show that we can expect more vertical surface displacement on the Moon due to the lower gravity there compared to Mars, and Earth. Rock toughness and rock stiffness control the amount of fracturing more than gravity does.

We also tested how host rock strengths in our 2D DEM model could be upscaled from intact strengths of rock samples collected at Earth analogue sites, or by implementing a digital crack network that simulates the highly fractured conditions of the intensively impacted Lunar and Martian crusts. Our results show that laccolith inflation in pre-cracked host rocks results in higher surface displacements and a higher amount of magma-induced cracking in broader fractured zones. We expect that our model results will induce a better understanding of the emplacement and architecture of shallow magmatic intrusions below magma-induced uplifted terrain and floor-fractured craters on the Moon and Mars.

How to cite: Poppe, S., Morand, A., Harnett, C. E., Cornillon, A., Awdankiewicz, M., Heap, M., and Mège, D.: Modelling magma-induced surface uplift and dynamic fracturing around laccoliths on the Moon, Mars, and Earth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2138, https://doi.org/10.5194/egusphere-egu24-2138, 2024.

The rock and rock-ice mixtures of the core-enveloping spherical shells comprising terrestrial body interiors have thermally determined viscosities well described by an Arrhenius dependence. Accordingly, the implied viscosity contrasts determined from the activation energies (E) characterizing such bodies can reach values exceeding 10⁴⁰, for a temperature range that spans the conditions found from the lower mantle to the surface. In this study, we first explore the impact of implementing a cut-off to limit viscosity magnitude in cold regions. Using a spherical annulus geometry, we investigate the influence of core radius, surface temperature, and convective vigour on stagnant lid formation resulting from the extreme thermally induced viscosity contrasts. We demonstrate that the cut-off viscosity must be increased with decreasing curvature factor, ƒ (=r_in/r_out, where r_in and r_out are the inner and outer radii of the annulus, respectively), in order to obtain physically valid solutions. We find that for statistically-steady systems, the mean temperature decreases with core size, and that a viscosity contrast of at least 10⁷ is required for stagnant lid formation as ƒ decreases below 0.5. Inverting the results from over 80 calculations featuring stagnant lids (from a total of approximately 180 calculations), we apply an energy balance model for heat flow across the thermal boundary layers and find that the non-dimensionalized temperature in the Approximately Isothermal Layer (AIL) in the convecting layer under a stagnant lid is well predicted by T'_AIL=½{ -(2T'_out+γ) + √[γ² + 4γ(1+T'_out)] } where γ is a function of E and ƒ, and T'_out is the non-dimensionalized surface temperature. Moreover, the normalized (i.e., non-dimensional) thickness of the stagnant lid, L', can be obtained from a measurement of the non-dimensional surface heat flux once T'_AIL is determined. Stagnant-lid thicknesses increase from 10 to 30 percent of the shell thickness as ƒ is decreased, and thick lids can overlie vigorously convecting underlying layers in small core bodies, potentially delaying secular cooling and suggesting that small objects with small cores may have developed thick elastic outer shells early in the solar system's history while maintaining vigorously convecting interiors. However, we also find that for the small number of 3-D calculations that we examined, parametrizations based on 2-D calculations overestimate the temperature of the convecting layer and the thickness of the conductive lid when ƒ is small (less than 0.4).

How to cite: Javaheri, P., Lowman, J., and Tackley, P.: Spherical geometry convection in a fluid with an Arrhenius thermal viscosity dependence: the impact of core size and surface temperature on the scaling of stagnant-lid thickness and internal temperature, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3226, https://doi.org/10.5194/egusphere-egu24-3226, 2024.

Nearly three decades of investigation has made steady progress towards self-consistently generating multiple features of plate tectonics from global mantle convection models.  Accordingly, the modelling of dynamic plates with migrating boundaries and evolving areas has become commonplace in both 2-D and 3-D geometries. Investigating the properties required for obtaining durable deep mantle formations similar to the Large Low Shear-wave Velocity Provinces (LLSVPs) has received similar attention. In this study, we model LLSVPs by assuming their composition is persistent  (i.e, we assume steady-state chemistry). To this end, we incorporate a Compositionally Anomalous Intrinsically Dense (CAID) mantle component comprising 2–3.5 per cent of the total mantle volume. We explore the impact of both an intrinsic contrast in density and viscosity for the CAID component, in an effort to stimulate the formation of a pair of LLSVP-like structures and a surface that exhibits the principle features of terrestrial plate tectonics; including recognizable and narrowly focused divergent, convergent and (in 3-D) transform plate boundaries that separate 8–16 distinct plate interiors. Although we find that a pair of CAID material provinces can be readily obtained in 2-D calculations while maintaining a surface exhibiting plate-like behaviour, specifying the same system parameters in 3-D calculations does not yield a pair of enduring provinces for any values of the parameters investigated.  In addition, CAID component inclusion in the calculations can affect global geotherms, so that in comparison to the surface behaviour obtained for the initial condition isochemical model, the cases incorporating the dense component do not yield surfaces that simulate plate tectonics. In general, CAID material components that are 3.75–5 percent denser than the surrounding mantle (at surface temperatures), and up to a factor of 100 times greater in intrinsic viscosity, form layers populated by voids, or nodes connected by ridges that reach across the core–mantle boundary (CMB), rather than distinct piles resembling the morphology of the LLSVPs. However, due to their temperature, we find the CAID material forms masses on the CMB that are relatively less dense (0.625–1.5 per cent) and viscous than the adjacent mantle material, in comparison to the percentage differences obtained at common temperatures. By adjusting our yield stress model to account for the influence of the CAID material on the geotherm, we find a highly satisfactory plate-like surface can be re-attained. Nevertheless, the formation of a pair of LLSVP-shaped masses remains elusive in 3-D calculations with plate-like surface behaviour and we suggest that caution is required if inferring the physical properties of the LLSVPs from 2-D models.

How to cite: Lowman, J., Langemeyer, S., and Tackley, P.: Model geometry determined contrast in the feedback between compositionally originating LLSVPs and dynamically generated plates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4709, https://doi.org/10.5194/egusphere-egu24-4709, 2024.

The Earth/Moon system likely results from a giant impact between a Mars-size object and the proto-Earth 70 to 110 Myrs after the formation of the first solids of the Solar System. This high-energy context leads to extreme conditions under which volatile elements would not normally be preserved in the protolunar disk. However, recent measurements of lunar samples highlight the presence of a significant amount of water in the Moon's interior (1.2 to 74 ppm). The aim of the present work is to quantify the water contribution of the late accretion on the early Moon. Here, we use a 2D axisymmetric model with the hydrocode iSALE-Dellen to study the fate of a large impactor on a target body similar to the early Moon with a crust, a magma ocean, and a mantle. For this purpose, we compute different models to monitor the depth to which the impacted material is buried at the end of the impact event and the degree of devolatilisation of the impactor. Three parameters are explored: the crustal thickness (ranging from 10 to 80 km), the impactor radius (ranging from 25 to 200 km) and the impactor velocity (ranging from 1 to 4 times the target escape velocity). Our models show that impactors with a radius greater than 50 km impacting a partially molten lunar body with a crust thinner than 40 km could significantly contribute to the water content of the lunar mantle even for impact velocities of less than 5 km s^-1. For larger impact velocities (≥ 10 km s^-1) the impactor material is significantly molten and its water content is devolatilised within the lunar atmosphere. Depending on the water content of the impactor material and the ability of the lunar magma ocean to maintain chemical heterogeneities, the late lunar accretion following the Moon-forming giant impact could explain the differences in water content between the lunar samples.

How to cite: Engels, T., Monteux, J., Boyet, M., and Bouhifd, A.: Large impacts and their contribution to the water budget of the Early Moon., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6343, https://doi.org/10.5194/egusphere-egu24-6343, 2024.

High-resolution images taken by the Lunar Reconnaissance Orbiter show the existence of many boulder tracks within the Finsen crater. Current research suggests that shallow moonquakes and meteorite impacts are likely to be the cause of boulder falls. Based on a simplified model, we simulate the rolling process of the boulder along the slope when the lunar surface shakes and provide the critical PGA (peak ground acceleration) required for the boulder to start rolling under different conditions. The results show that boulders may roll down slopes within one or more cycles under strong ground shaking. The critical PGA of seismic waves required for a boulder to conduct slope rolling is related to the size of the boulder, the slope at the initial location, the dominant period of the seismic wave, and the ratio of horizontal and vertical peak ground accelerations. Except for rolling against the slope, in some cases, boulders may jump and roll downhill. Using the high-resolution images taken by the LRO to determine how the boulders rolled downhill, we can then estimate the lower limit of the magnitude of moonquakes in the region under different conditions. Finally, we provide a preliminary estimation of the lower limit of the paleo-moonquakes magnitude in the Finsen Crater.

How to cite: Tao, S., Shi, Y., and Zhu, B.: Magnitude estimation of Paleo-moonquakes from boulder tracks in Finsen crater, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6814, https://doi.org/10.5194/egusphere-egu24-6814, 2024.

The Large Low-Velocity Provinces (LLVPs) beneath West Africa and the Southern Pacific are characterized by low seismic wave velocities and are associated with plate-unrelated magmatism such as hotspots, large igneous provinces, and kimberlite. Despite their significance, the structure, origin, and feeding processes of LLVPs remain elusive.

Previous studies have suggested that the LLVPs have remained stationary for over 300 million years, but their morphology appears to have changed. While geodynamic simulations favor denser LLVPs, a recent free-oscillation analysis has suggested lighter ones. The High-Velocity Region (HVR), which surrounds the LLVPs, is located beneath present and past subduction zones. Plumes of varying morphology are imaged between hotspots and LLVP margins, with intensive plumes revealing ultra-low velocity zones (ULVZs) at their roots. Ocean island basalts (OIBs) from hotspots are geochemically enriched and originate from multiple reservoirs. Interestingly, OIB chemistry does not correlate with seismic plume imaging and differs between the two LLVPs. OIB near the African LLVP is influenced by fluid-related subducted materials.

In the light of these results, I propose the following new model for the LLVPs. The LLVPs are at higher temperatures than the HVR and the surrounding mantle. They are composed of Fe-enriched mono-mineral bridgmanite rock, called bridgmanitite. The large grain size of bridgmanitite results in high viscosity despite the high temperatures, thereby stabilizing the LLVPs. The LLVPs are block-structured and the relative movement of the blocks changes the LLVP morphology. Bridgmanitite was formed by the solidification of a primordial magma ocean. Its deposition at the core-mantle boundary forms LLVP precursors in the early mantle. These LLVP precursor blocks can be moved by the thrust and sweep of subducted slabs to form the present-day LLVPs. Erosion and plume formation have reduced the volume of the LLVPs and resulted in different LLVP heights. The HVR consists of harzburgite brought from the surface by subduction. It contains only a limited amount of basaltic rock because the basaltic rock was detached from slabs in the mid-mantle due to suppressed grain growth. As a result, the HVR material is high-density due to the low temperature but is intrinsically low-density due to its chemistry. The HVR material has been heated using the LLVP heat to form plumes. Plumes are geochemically depleted when they have formed in the deep mantle. However, they are enriched in incompatible elements and volatiles in the shallow mantle. This enrichment results from melt migration due to the temperature gradient around the plume. Thus, although LLVP heat drives plume formation, the plate-unrelated magmas such as OIB are not directly derived from the LLVPs.

How to cite: Katsura, T.: Large Low-Velocity Provinces (LLVPs): a new model for their structure, origin, and evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8054, https://doi.org/10.5194/egusphere-egu24-8054, 2024.

Recent years have seen the discovery of a huge number of exoplanets, including several planets with very high densities suggesting that they also have rocky interiors which may be 9 – 10 times more massive than Earth. Mineralogy of these so called ‘super-Earth’ planets have been an interesting topic, as it gives implications on the planetary processes (Plate tectonics, geodynamo, etc.) and their habitability. Many studies concluded that such planets may contain ultra-high-pressure analogues of Earth’s lower mantle minerals. (Mg,Fe)O, a binary solid solution of MgO-FeO system is the second most abundant mineral of Earth’s lower mantle. If these super-Earth’s interior can have high pressure analogue of perovskite which is another most abundant phase of lower mantle of Earth as shown by some recent studies then there is a possibility of finding high pressure phase of (Mg,Fe)O also in the lower mantle of those super-Earths. MgO is stable in a NaCl structure (B1) in lower mantle condition of earth. It transforms to CsCl₂ (B2) at high pressure (p) and Temperature (T) conditions. However, FeO is stable in B1 structure which transforms to a rhombohedral phase first and then to NiAs-type structure (B8) with increasing p. Finally, above 240 GPa and 4000 K, FeO transforms directly from B1 to B2. Along with structural phase transitions, FeO also undergoes a spin transition from high spin (HS) to low spin (LS) state with increasing pressure. In this study, we performed first principles DFT calculations on the structural phase transitions of Mg_xFe_1-xO (x % = 0, 25, 50, 75 & 100) from B1 to B2 coupled with spin transition. Their mechanical and thermal properties under pressures ranging from 0 – 500 GPa relevant to super-earth planets have also been estimated. Our investigations have confirmed the presence of B1 phase of (Mg,Fe)O in lower mantle of earth with a spin transition from HS -LS which is thought to be responsible for the seismic anomalies of lower mantle of Earth. Spin transition of magnesiowustite and its effect on mechanical and thermal properties have been the topic for several experimental studies for many years. Most of them tried to explain the shear anisotropy of lower mantle with the help of (Mg,Fe)O with various Fe concentrations. Present study attempts to explore the stable phases of Mg_xFe_1-xO relevant to super-Earth conditions. Both mechanical and dynamical behaviour have been investigated in the entire pressure range. Results show a new tetragonal phase of Mg_0.25Fe_0.75O above 125 GPa, which is found to be both mechanically and dynamically stable. These findings will also attempt to predict the mineralogy and seismicity of those giant planets.

How to cite: Karangara, A. and Das, P. K.: High pressure phase of Magnesiowustite: Implications to the mineralogy of super-Earths, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8194, https://doi.org/10.5194/egusphere-egu24-8194, 2024.

Isotopic systems and trace elements are ideal proxies to constrain the production and recycling of crust (both mafic and felsic) over time. Within the Rubidium-Strontium (Rb-Sr) system, Rb-87 decays to Sr-87 and due to the preferential partitioning of Rb into the crust (relative to Sr) during partial melting, ⁸⁷Sr/⁸⁶Sr ratio of the crust is higher than that of the mantle over time. Trace elements such as Niobium (Nb) and Uranium (U) do not fractionate when mantle melts to form mafic magma (oceanic crust) but they do fractionate when oceanic crust is recycled and undergoes fluid-present melting, i.e., during the production of felsic magmas (continental crust) [Hofmann et al., 1986], thereby resulting in a lower Nb/U of the felsic crust compared to the mantle. In this work, we couple the evolution of the above-mentioned geochemical proxies with the melting processes in global convection models using the code StagYY [Tackley, 2008]. Results from these geodynamic models are then compared with geochemical data obtained from olivine-hosted melt inclusions extracted from komatiites of 3.27 Ga Weltevreden formation (Barberton Greenstone Belt, South Africa).

These models self-consistently generate oceanic and continental crust while considering both plutonic and volcanic magmatism [Jain et al., 2019] and incorporate a composite rheology for the upper mantle. Pressure-, temperature-, and composition-dependent water solubility maps calculated with Perple_X [Connolly, 2009] control the ingassing and outgassing of water between the mantle and surface [Jain et al., 2022]. These models show intense production and recycling of continental crust during the Hadean and the early Archean, which is in agreement with new geochemical data [Vezinet et al., in review] and previous geochemical box models [Rosas & Korenaga, 2018; Guo & Korenaga, 2020]. The thermal evolution is also consistent with cooling history of the Earth inferred from petrological observations [Herzberg et al., 2010].

As the estimates of total amount of water (at the surface and in the deep interior) vary from 5-15 ocean masses (OMs) based on magma ocean solidification models to 1.2-3.3 OMs based on petrological models [Nakagawa et al., 2018], different initial values of water are also tested, which show a strong influence on the amount of felsic melts produced. Ongoing work includes incorporating the effect of water on the density and viscosity of mantle minerals and adapting the lithospheric strength with surface topography.

How to cite: Jain, C., Sobolev, S., Sobolev, A., and Vezinet, A.: Thermochemical models of early Earth evolution constrained by geochemical data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9734, https://doi.org/10.5194/egusphere-egu24-9734, 2024.

The radial density of planets increases with depth due to compressibility, leading to impacts on their convective dynamics. To account for these effects, including the presence of a quasi-adiabatic temperature profile and entropy sources due to dissipation, the compressibility is expressed through a dissipation number proportional to the planet's radius and gravity. In Earth's mantle, compressibility effects are moderate, but in large rocky or liquid exoplanets (super-earths), the dissipation number can become very large. We explore the properties of compressible convection when the dissipation number is significant. We start by selecting a simple Murnaghan equation of state that embodies the fundamental properties of condensed matter at planetary conditions. Next, we analyze the characteristics of adiabatic profiles and demonstrate that the ratio between the bottom and top adiabatic temperatures is relatively small and probably less than 2. We examine the marginal stability of compressible mantles and reveal that they can undergo convection with either positive or negative superadiabatic Rayleigh numbers. Lastly, we delve into simulations of convection in 2D Cartesian geometry performed using the exact equations of mechanics, neglecting inertia (infinite Prandtl number case), and examine their consequences for super-earth dynamics.

How to cite: Ricard, Y., Alboussière, T., and Labrosse, S.: Compressible convection in large rocky planets, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9939, https://doi.org/10.5194/egusphere-egu24-9939, 2024.

Plate tectonics is a fundamental framework for understanding the geodynamic processes shaping our planet, including seismicity, volcanism, mountain building, and even the long-term climate system and habitability of our planet. However, how plate tectonics evolved over 4.5 billion years remains a major unanswered question. In this study, we employ dynamically self-consistent three-dimensional thermochemical geodynamic models to simulate plate tectonics evolution with physically realistic parameters. Our results demonstrate that plate tectonics undergoes three main stages due to differing dominant mantle cooling modes. Initially, magmatism dominates surface heat transport, with extrusive volcanism leading to a mobile heat-pipe mode, characterised by a high level of volcanism, large surface heat flux, and highly mobile plates in the first 1.5 billion years. This differs from the "heat-pipe" mode occurring on Jupiter's satellite Io by additionally having plate-like behaviour as well as crustal delamination and lithospheric dripping. As the mantle cools, it transitions to a stable mode where mantle convection patterns and their surface expressions become stable for around 1-2 billion years, followed by a smooth evolution to present-day plate tectonics. Our model matches key observations of the surface heat flux, strain rate, plate velocity, and plate distribution patterns, indicating that the early mobile heat pipe mode plays a crucial role in efficiently extracting heat from the mantle. Magmatic intrusion is also expected to have important effects, which we will examine. This study may provide insights into the Earth's dynamic processes and mantle-atmosphere feedback related to plate tectonics and the dynamic evolution of other terrestrial planets, which ultimately affect the long-term climate system and habitability of our planet.

How to cite: Yan, J. and Tackley, P.: How did plate tectonics evolve? Insights from 3-D spherical thermochemical convection simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11554, https://doi.org/10.5194/egusphere-egu24-11554, 2024.

The Earth is the only planet in our Solar System with active plate tectonics. Answering questions such as why plate tectonics started on Earth and which tectonic regime came before are fundamentally important for understanding the evolution of the early Earth. Currently, the most popular answers are (i) before plate tectonics on Earth, there was stagnant lid or plutonic-squishy-lid tectonic regime with no or minor contribution of subduction; (ii) plate tectonics took over when the initially high mantle temperature on Earth dropped by 100-200K due to secular cooling. In this work, we challenge both these statements based on published and new data and models.

Plenty of observations suggest that plate tectonics started on Earth during mid-Archean. At the same time, the numerical models and petrological data on the thermal evolution of the Earth show that mid-Archean was likely the time of the highest temperature of the Earth’s mantle and that significant secular cooling took place later in the Proterozoic. Moreover, previously published and our new thermochemical models also suggest that among all proposed tectonic regimes, only mobile-lid regime (i.e. plate tectonics) can lead to significant cooling of the Earth. Therefore, we conclude that plate tectonics in mid- or early Archean was unlikely to be initiated due to the significant secular cooling of the Earth’s mantle. The existence of no-subduction regimes, such as stagnant-lid or plutonic-squishy-lid, prior to plate tectonics are challenged by the new geochemical data which suggest extensive subduction and continental crust production already in the Hadean and early Archean.

Here we present global geodynamic models of Earth’s evolution computed using StagYY and ASPECT codes in 2D spherical annulus and 3D geometries respectively. StagYY models suggest that during the Hadean and the early Archean, the tectonic regime was oscillating between plume-induced subduction and plutonic-squishy-lid. The mantle temperature remains high during this time, but significant amount of continental crust is produced in these models, which is in agreement with the new geochemical data (melt inclusions from Weltevreden komatiites). After the emergence of continents in the mid- to late Archean, we decrease the effective friction of the oceanic lithosphere in the models to mimic the lubricating effect of continental sediments in subduction channels. This leads to a transition of the tectonic regime from oscillatory to continuous mobile-lid and to an efficient secular cooling of Earth, which is consistent with petrological observations. Being 2D, all plume-induced subduction zones in StagYY models are global. With the preliminary 3D ASPECT models, we show how a number of plume-induced regional subduction zones in early Earth evolve into a global network of plate boundaries and result in plate tectonics.

How to cite: Sobolev, S., Jain, C., and Pons, M.: Why does Earth have plate tectonics and what was before?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12766, https://doi.org/10.5194/egusphere-egu24-12766, 2024.

How to cite: Tian, J. and Tackley, P.: The influence of deep mantle thermal conductivity on the long-term thermal evolution of Earth's mantle and core, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12993, https://doi.org/10.5194/egusphere-egu24-12993, 2024.

Outgassing from the interior is a key process influencing the evolution of the atmospheres of rocky planets. For planets with a stagnant lid tectonic mode, previous models have indicated that increasing planet size very strongly reduces the amount of outgassing, even to zero above a certain planet mass (Dorn et al., A&A 2018). This is because melt is buoyant only above a certain depth, which becomes shallower with increasing planet size (hence "g"); for large enough planets this depth may even lie within the lithosphere, preventing eruption and outgassing.

            However, uncertainties in rheology strongly influence the temperature structure of planets, hence (i) the depth at which melt is generated and (ii) the thickness of the lithosphere. One major uncertainty is the rheology of post-perovskite, which constitutes a large fraction of the mantle in large super-Earths. Ammann et al. (Nature 2010) find that diffusion is anisotropic; it is not clear whether the "upper bound" or "lower bound" is relevant to large-scale deformation, but both result in high viscosity at very high pressures, strongly influencing the radial temperature profile (Tackley et al., Icarus 2013). In contrast, Karato (2011, Icarus) argues that a different mechanism - interstitial diffusion - acts to make viscosity almost independent of pressure and relatively low in the post-perovskite regime.

            Another uncertainty is the reference viscosity (the viscosity at a reference temperature, pressure and stress), as this depends on bulk composition, water content, grain size and other properties. Lower reference viscosity results in thinner lithosphere and crust (e.g., Armann & Tackley, JGR 2012).

            Thus, numerical simulations are performed of the long-term (10 Gyr) thermo-chemical evolution of stagnant-lid planets (coupled mantle and core) with masses between 1 to 10 Earth masses, varying the reference viscosity and the rheology of post-perovskite. The simulations are based on the setup of Tackley et al. (2013 Icarus) with the addition of partial melting and basaltic crustal production, and outgassing of a passive tracer that partitions into the melt and outgasses 100% upon eruption.

            Results indicate that:

• the previously-found trend of lower percentage outgassing with larger planet size is reproduced, but
• outgassing does not fall to zero even in a 10 Earth mass planet. Outgassing of between 15% and 70% is found for 10 Earth mass planets (up to ~100% for Earth mass planets).
• Post-perovskite rheology (interstitial, lower-bound or upper-bound) makes only a minor difference to long-term outgassing, but does influence the timing of outgassing.
• Reference viscosity makes a large difference to outgassing, with lower viscosities leading to substantially larger outgassing percentages.
• Internal heating plays a major role: stagnant-lid planets initially heat up due to low heat transfer efficiency, thinning the lithosphere and producing widespread melting.

How to cite: Tackley, P.: Outgassing on Stagnant-Lid Planets: Influence of Rheology, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13059, https://doi.org/10.5194/egusphere-egu24-13059, 2024.

How to cite: Récalde, N., Davies, J. H., Panton, J., Porcelli, D., and Andersen, M.: Investigating the stability and composition of LLSVP-like material in mantle convection models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13510, https://doi.org/10.5194/egusphere-egu24-13510, 2024.

Plate tectonics is the most prominent surface manifestation of mantle convection in Earth. Current observational results suggest that Earth is the only planet displaying plate tectonics. However, whether plate tectonics has accompanied the entire evolutionary history of Earth is a key question. If not, questions such as when plate tectonics began and what kind of tectonic mode prevailed before plate tectonics, have always been at the forefront and hot topics in the field of Earth science.

In this study, we employed three-dimensional spherical mantle convection numerical simulations to explore various mantle convection modes. Results indicate that, under different parameter frameworks, mantle convection modes can be categorized into five types: I) non-plate active lid convection mode, where the surface exhibits multiple concentrated weak zones, resulting in relatively fragmented plates; II) plate-like mobile lid convection mode, characterized by a higher number of subduction zones and mid-ocean ridges on the surface, which spontaneously form, develop and disappear over time, dividing the surface into about 10 plates; III) episodic plate-like mobile lid convection mode, where the surface experiences plate-like mobile lid mode for most of the time, interspersed with transient surface stagnation; IV) episodic stagnant lid convection mode, characterized by long periods of surface stagnation interspersed with short periods of surface movement with the surface mostly featuring only one subduction zone. V) stagnant lid convection mode, where the surface appears as a single rigid layer.

We mainly analyze the influence of lithospheric strength, i.e., yielding stress, Rayleigh number and internal heat rate on these five mantle convection modes. We can better explain the plate tectonics of the present Earth using mode Ⅱ. Because of the higher internal heat rate, higher mantle temperature and lower mantle viscosity, resulting in a larger Rayleigh number, our research suggests that the early Earth was in mode III or IV. Our results suggest that even if there was some type of plate tectonics in the early Earth, it is different from present plate tectonics. Before the onset of plate tectonics, the Earth might have experienced episodic lid convection. The results hold important scientific significance for understanding the evolution of the Earth's plate tectonics.

How to cite: Xiang, S. and Huang, J.: Mantle convection modes in 3D mantle convection simulations and its implications for the evolution of Earth’s plate tectonics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13588, https://doi.org/10.5194/egusphere-egu24-13588, 2024.

One of the most informative ways of studying the interior structure and geodynamics of terrestrial planets is the joint investigation of gravity and topography data. In the case of Venus, this is in fact one of the only sources of information about the planet's interior, along with estimations of the tidal Love number [1], moment of inertia factor [2], and the absence of an internally generated magnetic field [3].

Early gravity and topography studies that made use of Pioneer Venus and later Magellan data revealed unique properties of Venus's interior. They showed that Venus has a notably higher gravity-topography correlation for long wavelengths compared to Earth and a globally large apparent depth of compensation [4]. Considering these characteristics and analyzing the wavelength-dependent ratio between gravity and topography, the so-called spectral admittance, [5] concluded that the long-wavelength topography of the planet was supported dynamically, i.e., through convection in the mantle.

Since then, several studies have investigated the gravity and topography signature of Venus with the goal of understanding the planet’s interior by constraining geophysical properties of the mantle, such as the mantle viscosity. Some estimated the dynamic geoid contribution from three-dimensional geodynamic simulations [6,7]. Others adopted the analytical viscous flow model by [11] to study the viscosity structure of Venus's mantle [8,9,10]. The main advantage of the latter method is that it is computationally inexpensive, allowing for the performance of inversions. However, it is a simplified model which neglects lateral viscosity variations.

In this study, we estimate the dynamic topography and geoid signatures from the geodynamical models by [12], which include a strongly temperature-dependent viscosity, hence lateral viscosity variations, to evaluate the influence of different parameters such as the increase of viscosity with depth, the presence of viscosity jumps, and the ratio between intrusive and extrusive magmatism. In a second step, we plan to systematically evaluate the influence of lateral viscosity variations on the geoid and topography and thus to quantify the importance of the simplifications adopted in the analytical model.

Our first results show that the increase of viscosity with depth should be no more than 2 orders of magnitude, since larger values strongly decrease the spectral correlation and admittance at long wavelengths which is inconsistent with the observations. In addition, scenarios where extrusive magmatism dominates tend to overestimate the admittance due to the generation of thick thermal lithospheres in excess of 300 km thickness. These results underscore the importance of gravity and topography analyses for deciphering the geodynamical evolution and tectonic style of Venus.

[1] Konopliv and Yoder (1996) GRL, 23; [2] Margot et al. (2021) Nat Astron; [3] Phillips and Russel (1987) JGR, 92; [4] Sjogren et al. (1980) JGR, 85;  [5] Kiefer et al. (1986) GRL, 13; [6] Huang et al. (2013) EPSL, 362; [7] Rolf et al. (2018) Icarus, 313; [8] Pauer et al. (2006) JGR, 111; [9] Steinberger et al. (2010) Icarus, 207; [10] Maia et al. (2023) GRL, 50; [11] Hager & Clayton (1989) Mantle Convection; [12] Plesa et al. (2023) EGU.

How to cite: Maia, J., Plesa, A.-C., Tosi, N., and Wieczorek, M.: Constraining Venus's interior with gravity and topography predictions from geodynamic models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15952, https://doi.org/10.5194/egusphere-egu24-15952, 2024.

So far, most numerical models focused on understanding different aspects of the Earth’s system, such as mantle convection, tectonics, or atmospheric dynamics, have typically adopted a limited perspective constrained to the specific region of interest. Recently, efforts have been made to couple these simulations, enabling them to interact seamlessly with one another. Abstaining from doing so may lead to results that don't accurately represent how the various systems interact.

Achieving the successful integration of the deep carbon cycle and water transport into our mantle dynamics code (StagYY) represents a crucial step towards this goal - a comprehensive, large-scale model of our planet, encompassing phenomena from the Earth's core to the uppermost layers of the atmosphere resulting from a collaborative effort between different research groups. We adopt a thermodynamic approach to quantify the H₂O solubility of important water-carrying minerals within the mantle, with the goal of faithfully coupling geodynamic models and realistic transport/incorporation of water across the silicate part of our planet. The details of the numerical implementation are yet the subject of ongoing discussion; however, several crucial considerations must be thoroughly evaluated. These include the assessment of density variations resulting from water integration into nominally anhydrous minerals, the complex multi-stage degassing process of subducting slabs, and the inclusion of exotic phases that are currently absent from the thermodynamic databases being utilized.

The anticipated effects of a water-bearing mantle on the overarching dynamics are still under investigation. Nevertheless in-gassing, degassing, and the internal transport of water within the mantle exert a direct influence on various aspects. These include the governing viscosity field, the extent of H₂O-induced melting, and atmospheric CO₂ concentrations, among others. If water can, in fact, permeate deep into the mantle, it has the potential to introduce significant deviations in the dynamics of lower mantle convection compared to what current models predict. Furthermore, recent considerations of the stability regime of hydrous phases also point towards interesting implications in the study of water-rich exoplanets as stronger gravity profiles should result in colder geotherms, significantly expanding the thermodynamical stability of water-transporting phases across the P-T parameter space.

Quantifying this process will provide valuable insights for the geodynamic modeling community and help advance our understanding of the deep-Earth system. Furthermore, the distinct chemical exchange dynamics arising from our applications can be investigated further and prove advantageous for the study of exoplanetary atmospheres, especially those around bodies characterized by abundant water, such as water worlds and hycean planets.

How to cite: Moccetti Bardi, N., Tackley, P. J., and Metternich, M. A.: Mantle hydration and implications for Earth and exoplanetary research, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16140, https://doi.org/10.5194/egusphere-egu24-16140, 2024.

Crystallization processes, a partial or complete overturn of the early mantle and other processes can lead to a compositionally stably stratified mantle which may hinder of even prevent convective currents. In the classical view, the layer will be stable if the restoring force, generated by the compositional stratification will exceed the driving force as provided by heating the layer from the core. The situation resembles the diffusive scenario of double diffusive convection, characterized by the fast diffusing component (heat) being the driving force, while the slowly diffusing component (composition) acts as the restoring force. If perturbed, subcritical convection can eventually take plain ce.  While in  pure thermal convection , subcritical flow only develops as localized patterns, in the double diffusive case, a perturbation can lead to a global destabilization (blue sky bifurcation) of the system, due to a sufficient finite  amplitude perturbation. . In this study we have investigated the influence of a finite amplitude perturbation of varying magnitudes , namely realze by an impact on a stably stratified mantle. Numerical experiments in 2- and 3D, cartesian and spherical simulations, based on a Finite Volume scheme  have been conducted to study the evolution of such a system. Key parameters  which characterize the evolution are the (1) initial stratification and the structure f the perturbation. The viscosity structure is a further influencing factor.

The experiments show that an impact into a stably stratified mantle can lead to a global destabilization, giving rise to complex flow patterns, including local and transient layering of the mantle flow. An evolutionary path of a planet from a stably stratified state to a complex layered period and/or to a full convection mode seems sensitive.

How to cite: Hansen, U. and Dude, S.: Spontaneous destabilization of a compositionally stably stratified mantle in the Early Earth, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16401, https://doi.org/10.5194/egusphere-egu24-16401, 2024.

We present a numerical model of a cooling magma ocean (MO) and the atmosphere degassing from it. The solidification of the MO leads to the enrichment of the silicate melt in volatiles, thus favoring degassing. Both reservoirs interact via heat and volatile exchange, where the volatiles are H2O and CO2. The aim of this model is to explore the influence of the atmosphere on the surface conditions after the MO stage, and especially the conditions required for the condensation of a water ocean to occur. For example, for an early Earth at 1 AU initially containing 1 Earth's water ocean mass, a water ocean could form for initial CO2 content as large as 1,000 bars. Moreover, a tenth of the actual Earth's water ocean mass would be sufficient to generate a water ocean on early Venus. Liquid water could also be present on the surface of the two exoplanets Trappist-1e and 1f. Comparing our results with other recent models, we discuss the relative influence of the model hypotheses, such as mantle composition, the treatment of the heat transfer in the atmosphere, and the treatment of the last stages of the MO solidification.

How to cite: Massol, H., Davaille, A., Sarda, P., and Delpech, G.: Early formation of a water ocean as a function of initial CO2 and H2O contents in a solidifying rocky planet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16653, https://doi.org/10.5194/egusphere-egu24-16653, 2024.

 New high-pressure, high-temperature layered partial melting experiments have been performed to simulate the interaction between the last stage, dense Fe-Ti-rich cumulate layer that remained after about 99.5% crystallization of the lunar magma ocean (LMO), and the underlying solidified Mg-rich mantle. For this, a synthetic assemblage of an upper Fe-Ti-rich cumulate layer (6.1 wt.% TiO₂ and 39.7 wt.% FeO) and a lower forsteritic olivine layer (Mg# = 92.8) has been taken in 1:4 weight ratio, respectively, and subjected to experiments at pressures ranging between 1 to 3 GPa and temperatures varying between 1100 ⁰C and 1525 ⁰C using a piston cylinder apparatus. In the top cumulate layer, phases such as Fe-rich clinopyroxene, Fe-poor clinopyroxene, pigeonite, orthopyroxene, rutile, ilmenite, quartz and melt were formed, depending upon different P-T conditions. The Fe-Ti-rich basaltic melts (5-18.5 wt.% TiO₂, 13-28.6 wt.% FeO, and 35-59 wt.% SiO₂) produced in this cumulate layer at different degrees of partial melting approach the lunar mare basalts in their compositions and can be used to explain the huge variation in TiO₂ enrichment that is observed in lunar basalts (between 0 to ~17 wt. %). Following LMO crystallization, the last stage dense mineral-melt cumulate layer is expected to undergo a gravitational overturn due to density instability. This work aims to simulate the partial melting of the cumulates in this layer as a result of the overturn. The consequent compositional heterogeneity of the lunar mantle is used to justify the observed variation in Ti-rich basalt compositions on the lunar surface. The basaltic melts produced in these experiments are mostly Al, Mg-poor compared to available lunar basalt samples. However, this deficiency may be addressed by assimilation of these melts into low-Ti, Mg-rich basalt magmas that would have subsequently erupted from the underlying mantle. Simulations of such assimilation using thermodynamic modelling have also been done and the results support this theory. The possible fate of the last stage melt of the LMO has thus been studied and used to understand the variable compositions of lunar basalts.

How to cite: Moitra, H., Ghosh, S., Mukherjee, T., and Gupta, S.: Understanding the variability in the titanium contents of lunar basalts using high-pressure, high-temperature layered partial melting experiments and thermodynamic modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17525, https://doi.org/10.5194/egusphere-egu24-17525, 2024.

The InSight mission's SEIS instrument has provided a unique opportunity to probe the deep interior of Mars. This seismic exploration of the Martian interior has emerged as a promising avenue for revealing the enigmatic geophysical properties and dynamic processes within the planet's mantle.

In this study, we present an analysis of the seismic signature of marsquakes which transit deep into the mantle, providing crucial information on the seismic velocity profile and potential heterogeneities. The quakes show a characteristic late emergence of the first energy at higher frequencies which can be analysed as due to the scattering of seismic energy as it transits the mantle. From this we are able to quantify the size distribution of the mantle's small-scale heterogeneity as well as to constrain the rheological properties and convective vigor of the Martian mantle.

As unlike Earth, Mars has sealed its mantle contents under a stagnant lid, we use our observations to provide evidence about the early stages of planetary formation and differentiation on Mars. Our findings contribute to the better understanding of the Martian mantle's geodynamics and allow a comparative assessment of the evolution of planetary interiors that likely apply to other planets that lack plate tectonics.

How to cite: Charalambous, C., Pike, T., Fernando, B., Samuel, H., Bill, C., Lognonné, P., and Banerdt, B.: Small-scale Structure of the Martian Mantle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17640, https://doi.org/10.5194/egusphere-egu24-17640, 2024.

Geodynamic modelling is increasingly dependent on the initial conditions. Non-steady-state planetary evolution models are complex enough that several solutions can be achieved with small variations in the initial temperature, composition, etc. Models of magma ocean evolution predict an overturn of a layer enriched in iron and incompatible elements. The absence of this layer in any tomographic inversion of the Earth suggests that our models of magma ocean evolution are missing key phenomena. Since these models are the basis for the initial conditions of Earth-applied geodynamic planetary models, there is an urgency to find the origin of the discrepancies between our idea of magma ocean crystallization and the current state of the Earth.

To advance our understanding of the consequences of magma ocean crystallization, we carry out high resolution models of mantle flow coupled with (1D) magma ocean evolution (including melting and crystallization processes). We allow two different forms of topography to arise with a sticky air (sticky magma ocean) approximation: dynamic topography and thermodynamic topography. We explore how different equilibration times affect melt segregation and magma ocean composition, as well as how crystal settling influences solid state convection and differentiation. We calculate, as well, chemical exchange between the solid and liquid parts of our model by expanding on previous work, studying different equilibrium constants and allowing the system to self-regulate.

Preliminary results suggest a competition effect between the two forms of topography mentioned above. This competition implies that the equilibrium constant of chemical exchange, as well as melting segregation speed and crystal growth and settling, will have an essential role in the equilibration between the solid mantle and the liquid magma ocean. This and other results have implications for Earth, but also for other discovered magma oceans such as those on the Moon, Mars or even exoplanets.

How to cite: Manjon Cabeza Cordoba, A., Ballmer, M. D., and Shorttle, O.: Melting and Remelting in a Crystallizing Magma Ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19267, https://doi.org/10.5194/egusphere-egu24-19267, 2024.

The origin of the martian crustal dichotomy is a long-standing mystery since its discovery in the Mariner 9 era. Among various proposed hypotheses, a single giant impact origin (i.e. the Borealis impact) is the most well known, and the most studied. However, studies that include realistic impact models often adapt a simplified geological and geophysical model for predicting the final crustal distribution, while long-term mantle convection studies have mostly employed an over-simplified parametrization of the impact. Here we use a coupled SPH-thermochemical approach to first simulate an impact event, and then use the result of this realistic model as the initial condition for the long-term mantle convection model. We demonstrate that a giant impact collision results in a mantle-deep magma pond, which upon crystallisation leads to a thicker crust production on the impacted hemisphere. In other words, an impact-origin of Mars's southern highlands requires the giant impact to occur in the southern hemisphere. We find that both the impact scenario and the mantle properties affect the geometry of the impact-induced crust ("highlands'') and the subsequent state of the interior, and that the formation of "highlands'' extends beyond the initial magma pond.  We show that a near head-on (15^o from the normal) impact event with impactor radius of 750 km, together with a mantle viscosity of 10²⁰ Pa s, can best reproduce the southern highlands of Mars with a geometry similar to that of present-day observations.

How to cite: Cheng, K. W., Ballantyne, H., Golabek, G., Jutzi, M., Rozel, A., and Tackley, P.: Combined impact and interior evolution models in three dimensions indicate a southern impact origin of the Martian Dichotomy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22090, https://doi.org/10.5194/egusphere-egu24-22090, 2024.

Venus' rotation is the slowest of all planetary objects in the solar system and the only one in the retrograde direction. It is commonly admitted that such a rotation state is the result of the balance between the torques created by the gravitational and atmospheric thermal tides¹. The internal viscous friction associated with gravitational tides drive the planet into synchronization (deceleration) while the bulge due to atmospheric thermal tides tend to accelerate the planet out of this synchronization^1,6. Other torque components (related to the two first one) also affect the rotation². This work first provide an estimate of the viscosity of Venus' mantle explaining the current balance with thermal atmospheric forcing. Second, this study quantify the impact of the internal structure and its past evolution on the gravitational tides and thus on the rotation history of Venus. Using atmospheric pressure simulations from the Venus climate database^4,5,7, we first estimated the atmospheric thermal torque and showed that topography and interior response to atmospheric loading, usually ignored in previous studies, have a strong influence on the amplitude of thermal atmospheric torque. Computing the viscoelastic response of the interior to gravitational tides and atmospheric loading³, we showed that the current viscosity of Venus' mantle must range between 2.3x10²⁰ Pa.s and 2.4x10²¹ Pa.s to explain the current rotation rate as an equilibrium between torques. We then evaluated the possible past evolution of the viscosity profile of the mantle considering different simple thermal evolution scenarios.  We showed that in absence of additional dissipation processes, viscous friction in the mantle cannot slowdown the rotation to its current state for an initial period shorter than 2-3 days, even for an initially very hot mantle. Beyond Venus, these results has implications for Earth-size exoplanets indicating that their current rotation state could provide key insights on their atmosphere-interior coupling.

¹Correia, A. C. M. and J. Laskar (2001), Nature.
²Correia, A. C. M. (2003), Journal of Geophysical Research.
³Dumoulin, C., G. Tobie, O. Verhoeven, P. Rosenblatt and N. Rambaux (2017), Journal of Geophysical Research.
⁴Lebonnois, S., F. Hourdin, V. Eymet, A. Crespin, R. Fournier and F. Forget (2010),  Journal of Geophysical Research.
⁵Lebonnois, S., N. Sugimoto and G. Gilli (2016), Icarus.
⁶Leconte, J., H. Wu, K. Menou and N. Murray (2015), Science.
⁷Martinez, A., S. Lebonnois, E. Millour, T. Pierron, E. Moisan, G. Gilli and F. Lefèvre (2023), Icarus.

How to cite: Musseau, Y., Dumoulin, C., Tobie, G., Gillmann, C., Revol, A., and Bolmont, E.:  Viscosity of Venus' mantle as inferred from its rotational state, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3129, https://doi.org/10.5194/egusphere-egu24-3129, 2024.

As part of a long-term monitoring program, full disk thermal maps of HDO (near 7 microns) and SO₂ (near 7 and 19 microns) have been obtained at the cloud top of Venus in 2023, using the TEXES(Texas Echelon Cross-Echelle Spectrograph)  imaging spectrometer at the Infrared Telescope Facility (IRTF) at Mauna Kea Observatory. Assuming a constant D/H isotopic ratio, the water abundance has been more or less constant since 2018, at about half its value in 2012-2016. In contrast, the SO₂ abundance, which was very high in 2018-2019 and very low between July 2021 and March 2023, has increased by a factor of about 5 between February and July 2023 (close to its maximum level of 2018-2019), and has remained at its high level in September 2023. The origin of these long-term variations is still unclear. In addition, stringent upper limits of NH₃ (at 927-931 cm^-1), PH₃ (at 1161-1164 cm^-1) and HCN at 744-748 cm^-1) at the cloud top have been obtained in July 2023. These results will be presented and discussed.

How to cite: Encrenaz, T., Greathouse, T., Giles, R., Widemann, T., Bezard, B., Lefevre, F., Lefevre, M., Shao, W., Sagawa, H., Marcq, E., and Arredondo, A.: Ground-based thermal mapping of Venus:  HDO and SO2 monitoring and upper limits of NH3, PH3 and HCN at the cloud top, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4022, https://doi.org/10.5194/egusphere-egu24-4022, 2024.

Coronae are crown-like, tectono-volcanic features found on Venus that typically range in diameter from 100-700 km. Diapirs of warm upwelling material impinging on the lithosphere are often invoked to explain coronae formation. With more than 500 coronae identified on the surface of Venus, if these diapirs are individually linked to a mantle plume, Venus must have a very different mantle structure than Earth. I consider three cases designed to assess the potential relationship between large-scale, long-wavelength lower mantle structure and smaller-scale upper mantle structure that could potentially form diapirs consistent with those that are envisioned to interact with the lithosphere and form coronae. I use the geoid and topography to identify the large-scale pattern of convection because the geoid contains and integral of the temperature anomalies over the depth of the mantle. Plume tails—narrow vertical conduits—integrate to give a positive geoid anomaly while small-scale, time-dependent drips or upwellings are minimized in the depth integration. The first case—the reference case—has a small, stepwise decreases in viscosity between the lower mantle (10²² Pa s), transition zone (10²¹ Pa s), and upper mantle (5x10²⁰ Pa s) with no phase transformations. This led to 20 ~1000-km diameter mantle plumes that remained stationary for more than 1.5 Gyr. This calculation is consistent with a number of geophysical observations it does not support the formation of coronae by plume-lithosphere interaction. To decouple the lower and upper mantle, I further decrease both the upper mantle and transition zone viscosities to 10²⁰ Pa s while leaving all other parameters unchanged. In this calculation the same 20 ~1000-km diameter mantle plumes formed and remained stationary for more than 1.5 Gyr. The geoid and topography are anti-correlated, inconsistent with the observed values on Venus and, the spatial scale, number, and topographic evolution of the plumes are not consistent with coronae. This calculation does not support the formation of coronae by plume-lithosphere interaction. In an attempt to further decouple the upper and lower mantle I add an endothermic phase transformation at the ringwoodite-bridgmanite boundary in addition to the decreased upper mantle and transition zone viscosities while leaving all other parameters unchanged. Unique to this calculation, a very large number of ~100-km diameter small topographic upwellings form some associated with the large-scale geoid high but never associated with the large-scale geoid low. The inclusion of a phase transformation decoupling the upper and lower mantle has the potential to create diapir-like structures in the upper mantle consistent with coronae formation.

How to cite: King, S.: Linking global-scale mantle flow with diapir-like coronae formation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5857, https://doi.org/10.5194/egusphere-egu24-5857, 2024.

The recent analysis of radar data from NASA’s Magellan mission suggests that volcanic activity is ongoing on Venus [1], providing unprecedented evidence that Venus’s evolution and present day state has been dominated by volcanic processes. Venus’s geodynamics and tectonics seem to be well characterized by the so-called “plutonic squishy lid” regime, where part of the melt that is formed in the interior rises to the surface but a significant part remains trapped in the crust and lithosphere forming intrusions [2]. These intrusions strongly influence the mantle’s thermal evolution, heat flow, and the present-day thermal state of the subsurface.

This study focuses on the effects of intrusive magmatism on the lithosphere thickness and thermal gradient. The latter is used to evaluate our models by comparing our results to estimates based on studies of the elastic lithosphere thickness [3,4,5]. We use the geodynamic code Gaia in a 2D spherical annulus geometry [6]. Our models vary the intrusive to extrusive ratio from a fully intrusive case to a fully extrusive one and the intrusive melt depth from 10 km to 90 km.

Our models show that depending on the percentage of extrusive melt and the depth of magmatic intrusions, the maximum thermal gradient varies from a few K/km up to almost 40 K/km at present day, with higher values obtained for higher percentages of intrusive melt and shallower the magmatic intrusions. Moreover, our results show that the thermal gradients have remained similar during the last 750 Myr. Models in which the extrusive magmatism is higher than 60% and the depth of magmatic intrusions lies deeper than 50 km cannot explain high local thermal gradients as suggested by studies of elastic lithosphere thickness [3,4,5].

In a recent study [7], the presence of a low viscosity layer (LVL) in the shallow Venusian mantle has been suggested to be related to the presence of partial melt. The LVL starts beneath the lithosphere at depths shallower than 200 km. This places constraints on the depth of melting that we can use to select successful models. Models that are compatible with partial melting starting at depth of 200 km or less beneath the surface require less than 40% extrusive magmatism and an intrusive melt depth strictly higher than 10 km.

We use our models to estimate ranges for melting conditions in the interior at present day. The range of melt temperatures lies between 2000 and 2250 K and the depth of melting between ~200 and 360 km. These estimations serve as a starting point for and will be compared with high-pressure-high-temperature laboratory experiments that will be performed at the University of Münster to select the most likely mantle compositions of Venus that can explain the Venera and Vega data.

References:

[1] Herrick & Hensley, Science, 2023. [2] Rolf et al., SSR, 2023. [3] Smrekar et al., Nature Geoscience, 2023. [4] Borelli et al., JGR, 2021. [5] Maia et al., JGR, 2022. [6] Hüttig et al., PEPI, 2013. [7] Maia et al., GRL, 2023.

How to cite: Herrera, C., Plesa, A.-C., Maia, J., Klemme, S., and Jennings, L.: Thermal evolution and magmatic history of Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5946, https://doi.org/10.5194/egusphere-egu24-5946, 2024.

The Venusian atmosphere has rich and diverse chemistry and much of it remains to be explored. Here I present our recent work in identifying new reactions and quantifying their rate constants, along with UV-Vis spectral simulation using quantum chemistry calculations. The research focuses on elemental sulfur allotropes and sulfur oxides. Our UV-Vis spectral simulations are used to narrow the search of the unknown UV absorber by excluding molecules/isomers/conformers without the appropriate absorption and similarly include those with absorption profiles that fit the unknown absorber. Furthermore, we present a mechanism for how substituted sulfuric acid molecules can be formed in the Venusian atmosphere which can impact aerosol formation.

How to cite: Frandsen, B. and Skog, R.: Breaking New Ground in Venusian Atmospheric Sulfur Chemistry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7533, https://doi.org/10.5194/egusphere-egu24-7533, 2024.

Previous studies have inferred volcanic activity on Venus from indirect evidence, including variations in atmospheric composition and thermal emissivity data [1, 2, 3]. More recently, a study hypothesized ongoing volcanic activity on Venus, evidenced by a volcanic vent that collapsed between two different Magellan observing cycles [4]. Expanding upon this premise, we are investigating the surface geology of Venus using the extensive radar and altimetric data acquired by the Magellan spacecraft.

In particular, by properly processing the SAR images, we are conducting a detailed geomorphological analysis of Venus' surface, in order to identify and characterize various surface morphologies. Additionally, the altimetric data provided valuable insights into the topographical variations across Venus, further contributing to the geomorphological assessment.

Our research not only enhances the understanding of the geology of Venus but also underscores the significance of radar imaging in the study of planetary surfaces, where no other imaging techniques are available. The findings highlight the crucial role of continued exploration of Venus, which could be greatly advanced by upcoming missions such as VERITAS and EnVision [5, 6]. Equipped with superior radar technology, these missions are expected to provide images of Venus's surface at an unprecedented resolution and signal-to-noise ratio, far surpassing that of the Magellan SAR, thus enabling a more detailed characterization of Venus's surface morphology.

References

1. Truong, N. & Lunine, J. Volcanically extruded phosphides as an abiotic source of Venusian phosphine. Proceedings of the National Academy of Sciences 118, e2021689118 (2021).

2. Esposito, L. W. Sulfur dioxide: Episodic injection shows evidence for active Venus volcanism. Science 223, 1072-1074 (1984).

3. Smrekar, S. E. et al. Recent hotspot volcanism on Venus from VIRTIS emissivity data. Science 328, 605-608 (2010).

4. Herrick, R. R. & Hensley, S. Surface changes observed on a Venusian volcano during the Magellan mission. Science, eabm7735 (2023).

5. Hensley, S. et al. VISAR: Bringing Radar Interferometry to Venus. In Proceedings of International EnVision Venus science workshop, Berlin, Germany (2023).

6. Ghail, R. C. et al. VenSAR on EnVision: Taking earth observation radar to Venus. International journal of applied earth observation and geoinformation 64, 365-376 (2018).

Acknowledgments

G.M., D.S., and M.M. acknowledge support from the Italian Space Agency (2022-15-HH.0).

How to cite: Sulcanese, D., Mitri, G., and Mastrogiuseppe, M.: Investigating the volcanic activity on Venus with Magellan data, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8135, https://doi.org/10.5194/egusphere-egu24-8135, 2024.

The Venusian atmosphere has everything to be an exciting natural sulfur laboratory. In addition to relatively high concentrations of sulfur dioxide, suitable conditions in the atmosphere make both thermo- and photochemical reactions possible, allowing for complex chemical reactions and the formation of new sulfur containing compounds. These compounds could explain or contribute to the enigmatic 320-400 nm absorption feature in the atmosphere. One of the proposed absorbers is polysulfur compounds. While some experimentally obtained UV-VIS spectra have been published, studying the different polysulfur species individually is extremely difficult due to the reactive nature of sulfur. In this work UV-VIS spectra for polysulfur species S₂ to S₈ were simulated using the nuclear ensemble approach to determine if they fit the absorption profile of the unknown absorber.

Geometries were optimized at the ωB97X-D/aug-cc-pV(T+d)Z level of theory, with the S₂, S₃, and S₄ structures also being optimized at the CCSD(T)/aug-cc-pV(T+d)Z level of theory. For the lowest energy isomers UV-VIS spectra were simulated using a nuclear ensemble of 2000 geometries, with vertical excitations calculated at the EOM-CCSD/def2-TZVPD or the ωB97X-D/def2-TZVPD levels of theory.

The simulated UV-VIS spectra for the smaller species were in quite good agreement with experimental results. Two different molecules were identified with substantial absorption cross sections in the range of the unknown absorber: The open chain isomer of S₃, and the trigonal isomer of S₄ However, the mixing ratios of these species in the Venusian atmosphere are also needed to make a more conclusive statement. Other polysulfur compounds have insignificant absorption cross sections in the 320-400 nm range and can therefore be excluded.

The calculated absorption cross sections can be used to calculate photolysis rates, which can be straight away added to atmospheric models of Venus. In addition, this work will help future space missions to Venus, for example by focusing their search for the unknown absorber.

How to cite: Skog, R., Frandsen, B., and Kurtén, T.: Simulating UV-VIS Spectra for Polysulfur Species in the Venusian Atmosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8798, https://doi.org/10.5194/egusphere-egu24-8798, 2024.

Venus’ mass and radius are similar to those of Earth. However, Venus’ interior structure and chemical composition are poorly constrained. Seemingly small deviations from the Earth might have important impacts in the long-term evolution and dynamics of Venus when compared to our planet and could help to explain the different present-day surface and atmospheric conditions and geophysical activity between these two planets. Shah et al. (ApJ 2022) presented a range of possible bulk compositions and internal structures for Venus. Their models, designed to fit Venus’ moment of inertia and total mass, predict core radii ranging from 2930-4350 km and include substantial variations in mantle and core composition. In this study, we pick ten different Venus models from Shah et al. (ApJ 2022) that range from a small to a big, and from a S-free to a S-rich core. We run mantle convection evolution models for the different scenarios using the code StagYY (Tackley, PEPI 2008; Armann and Tackley, JGR 2012) and explore how different interior structures and chemical compositions affect the long-term evolution and dynamics of Venus. In our models, the bulk composition of the mantle affects the basalt fraction and the solidus and liquidus temperature profiles. We investigate how the composition and size of the core affects magmatism hence outgassing of water and other volatiles to the atmosphere, the basalt distribution, heat flow, temperature of the mantle and lithosphere, and observables such as the moment of inertia and Love numbers. Since the tectonic regime active on Venus is still unknown, we test different evolution scenarios for a planet covered by a stagnant lid, an episodic lid, and a plutonic-squishy lid. The models produce a range of predictions that can be compared to observations by planned missions to Venus, including EnVision measurements by the VenSpec spectrometers, comprising outgassing of water and other volatiles and surface composition. These can be used to constrain Venus’ interior composition and structure, and reveal key information on the differences between Earth and Venus.

How to cite: Louro Lourenço, D., Tackley, P., Rolf, T., Grünenfelder, M., Shah, O., and Helled, R.: Influence of Possible Bulk Compositions on the Long-Term Evolution and Outgassing of Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9470, https://doi.org/10.5194/egusphere-egu24-9470, 2024.

Venus has regained great interest from planetary scientists in recent years because of the multiple upcoming Venus missions (e.g., EnVision, DAVINCI+ and VERITAS). Studying Venus is crucial for understanding the evolution of terrestrial planets as well as projecting the Earth’s future. One important component of the Venus climate system, the sulfuric acid clouds, has exhibited spatial and temporal variabilities. These variabilities are closely connected with the interactions between dynamics, photochemistry, radiative transfer and cloud physics. Current modeling studies of the Venus atmosphere have shed light on the underlying physics of the cloud variabilities. However, none of them has resolved the cloud radiative feedback. As an essential step to fully understanding the complex interactions, we develop a state-of-the-art General-Circulation Model (GCM), with cloud condensation/evaporation and radiative feedback processes included. In this talk, I will quantify the radiative forcing caused by the acidic clouds and provide indications of how the radiative forcing can influence the Venus climate evolution.

How to cite: Shao, W., Mendonca, J., and Dai, L.: Cloud radiative feedback on the Venus climate simulated by a General-Circulation Model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10478, https://doi.org/10.5194/egusphere-egu24-10478, 2024.

The investigation into Venus's atmosphere has highlighted deficiencies in photochemical models when it comes to explaining the distribution of trace gas species, particularly crucial elements like CO and OCS, which play a vital role in Venus's sulfur cycle and cloud formation.

To gain a comprehensive understanding of the abundance and variability of these trace gases ahead of the DaVinci probe's descent, we initiated an observational study using NASA's IRTF telescope equipped with the high-resolution ISHELL spectrometer. Conducted from June 11 to June 30, 2023, our study involved capturing K, H, and J-band spectra of Venus's night side. We employed the SMART software to calculate synthetic spectra, considering various gas abundances and emission angles.

With our high-resolution spectral data (R=λ/Δλ~25,000), we successfully mapped the abundances of CO, H2O, and OCS in the equatorial region, revealing both daily and latitudinal variations. Our focus was on examining the delicate balance between chemistry and transport, evident in the observed anti-correlation between OCS and CO abundance with cloud opacity.

Through near-infrared observations, this study aims to unravel the intricate interplay between atmospheric dynamics and chemical reactions in Venus's cloud formation. By providing insights into observed cloud patterns and elucidating the relationship between atmospheric chemistry, dynamics, and cloud creation on Venus, we contribute crucial parameters to refine existing photochemical models.

How to cite: Liao, T.-J., Young, E., Bullock, M., crisp, D., and Yung, Y.: Unraveling Venus's Atmospheric Composition: Insights into CO, H2O, and OCS Abundances through Observations and Modeling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10655, https://doi.org/10.5194/egusphere-egu24-10655, 2024.

The spin period of Venus is anomalously large. With one Venusian day being 243 Earth days, the rotational bulge of
Venus has the amplitude of only tens of centimetres, making the Earth’s hotter twin the least rotationally stable planet in
the Solar System. Being a slow-rotator creates a unique link between internal and rotational dynamics. This is because,
on a slow-rotator, convection driven redistribution of mass may produce perturbations of the body’s inertia tensor that
are comparable in amplitude with the inertia of the rotational bulge. Venus thus may respond to mantle convection by
wobbling (Spada et al., 1996), and wobbling is detectable when both the rotational and the figure axes are measured
accurately. The present-day estimate of the angle between the two axes is 0.5°, but it is based on gravity models with a
limited resolution (Konopliv et al., 1999). Future missions to Venus, namely VERITAS and EnVision, are likely to provide
a more robust measurement.

The geodynamic regime of Venus’ mantle remains enigmatic. Observational data does not support the existence of
continuous plate tectonics on its surface, but some recent evidence of ongoing tectonic and volcanic activity (e.g. Herrick
and Hensley, 2023) and crater statistics analyses (e.g. O'Rourke et al., 2014) indicate that the planet is unlikely to be in a
stagnant lid regime (see also Rolf et al., 2022). Here we perform 3D spherical mantle convection simulations of the different
possible tectonic scenarios and compute the resulting reorientation of Venus. The reorientation is accompanied by a wobble
whose average amplitude we evaluate and compare to the present day estimate of 0.5° (Konopliv et al., 1999). Since the
different convective regimes predict vastly different rotational dynamics, the comparison provides a useful constraint on
the interior dynamics of Venus. This work was supported by the Czech Science Foundation through project No. 22-20388S.

References
Herrick, R., Hensley, S., 2023. Surface changes observed on a venusian volcano during the magellan mission. Science
doi:10.1126/science.abm7735.

Konopliv, A., Banerdt, W., Sjogren, W., 1999. Venus gravity: 180th degree and order model. Icarus 139, 3–18.
doi:10.1006/icar.1999.6086.

O'Rourke, J.G., Wolf, A.S., Ehlmann, B.L., 2014. Venus: Interpreting the spatial distribution of volcanically modified
craters. Geophys. Res. Lett. 41, 8252–8260. doi:10.1002/2014gl062121.

Rolf, T., Weller, M., Gulcher, A., Byrne, P., O’Rourke, J.G., Herrick, R., Bjonnes, E., Davaille, A., Ghail, R., Gillmann,
C., Plesa, A.C., Smrekar, S., 2022. Dynamics and evolution of venus’ mantle through time. Space Science Reviews 218,
70. doi:10.1007/s11214-022-00937-9.

Spada, G., Sabadini, R., Boschi, E., 1996. Long-term rotation and mantle dynamics of the Earth, Mars, and Venus.
J. Geophys. Res. Planets 101, 2253–2266. doi:10.1029/95JE03222.

How to cite: Patočka, V., Maia, J., and Plesa, A.-C.: The link between internal and rotational dynamics of Venus: The amplitude of mantle convection-driven wobble, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12316, https://doi.org/10.5194/egusphere-egu24-12316, 2024.

With the selection of multiple missions to Venus by NASA and ESA that are planned to launch in the coming decade, we will greatly improve our understanding of Venus. However, none of these missions have determining the seismicity of the planet as one of their primary objectives. Nevertheless, constraints on the seismicity remain crucial to understand the tectonic activity and geodynamic regime of the planet and its interior structure. 

Funded by the International Space Science Institute (ISSI) in Bern, Switzerland, we have gathered an interdisciplinary team of experts in seismology, geology, and geodynamics to assess the potential seismicity of Venus, specific regions that could be seismically active at present, and the methods to detect them.

Here, we present the findings from our second ISSI team meeting (January 29 - February 2, 2024), aiming to review knowledge on Venus's seismicity and interior and identify the best approaches for future missions. We present the feasibility, advantages, and disadvantages of different seismic observation techniques on the surface (e.g., broadband seismometers, distributed acoustic sensing methods), from a balloon (acoustic sensors), and from orbit (airglow imagers). We make a recommendation for the instrumentation of a future seismology-focused mission to Venus. 

We also suggest target regions with a high likelihood of significant surface deformation and/or seismicity. These targets are useful for the upcoming VERITAS (Venus Emissivity, Radio Science, InSAR, Topography and Spectroscopy) and EnVision missions and would specifically benefit from the repeat pass interferometry of VERITAS, which detects surface deformation and can therefore in principle constrain the maximum displacement of surface faulting at locations that are visited twice during the mission. 

How to cite: van Zelst, I., De Toffoli, B., Garcia, R. F., Ghail, R., Gülcher, A. J. P., Horleston, A., Kawamura, T., Klaasen, S., Lefevre, M., Lognonné, P., Maia, J., Näsholm, S. P., Panning, M., Plesa, A.-C., Sabbeth, L., Smolinski, K., Solberg, C., and Stähler, S.: Seismicity on Venus: optimal detection methods and target regions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12790, https://doi.org/10.5194/egusphere-egu24-12790, 2024.

EnVision radio science investigation will deepen our understanding of Venus’ gravity, interior structure and atmospheric properties. To address these scientific questions, a two-way link communication (configuration X/X/Ka-band) is established with the ESA ESTRACK ground stations enabling precise orbit determination (POD) during the science phase. An accurate modeling of the spacecraft’s dynamics, including the atmospheric drag acceleration, is key for retrieving EnVision’s trajectory and constraining Venus’ gravity field, tides and orientation parameters.

Dedicated radio occultation campaigns are designed to characterize electron density profiles in the ionosphere and atmospheric density, pressure and temperature in the mesosphere and upper troposphere of Venus. Furthermore, an accurate POD of the spacecraft also provides complementary information on the atmospheric density at the altitudes crossed by the probe, extending the science return of the EnVision mission.

The atmospheric drag perturbation strongly affects spacecraft trajectories that are characterized by a pericenter altitude above Venus’ surface of less than 220 km. By accounting for different Venus’ atmospheric models, e.g., the Venus Climate Database (VCD) and the Venus Global Reference Atmospheric Model (Venus-GRAM), we investigate the impact of potential errors and uncertainties in the predicted atmospheric properties on the orbit evolution of the spacecraft. We note significant inconsistencies between Venus’ atmospheric models at the spacecraft altitudes including atmospheric density differences of more than 200%. These discrepancies may be representative of the current knowledge of Venus’ upper atmosphere and thermosphere. Thus, we carried out a perturbative analysis of the dynamical forces by introducing a mismodeling in the atmospheric density profiles. We assumed the VCD for the simulation of the radio tracking measurements and we included as a priori model in the estimation process the Venus-GRAM. By developing a batch sequential filter that adjusts a set of atmospheric density scale factors, we compensated for the mismodeling and improved the quality of the dynamical model and of the orbit determination. The proposed approach enables an estimation of the atmospheric density at the spacecraft altitudes with an accuracy of 25% and accuracies in the orbit reconstruction of 1-2 m, 30-40 m and 20-30 m in the radial, transverse and normal directions.

How to cite: Gargiulo, A. M., Genova, A., Petricca, F., Del Vecchio, E., Andolfo, S., Torrini, T., Rosenblatt, P., Lebonnois, S., Marty, J.-C., and Dumoulin, C.: Estimation of Venus' atmospheric density through EnVision precise orbit determination, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13314, https://doi.org/10.5194/egusphere-egu24-13314, 2024.

The electrical environment of Venus has been investigated through extensive considerations of whether lightning has been detected in the atmosphere [1]. Although an important process, the presence or absence of lightning does not completely describe Venus’ electrical environment. Little consideration has been made of other related aspects, such as the possible presence of a global atmospheric electric circuit, as is present on Earth. In this context, lightning would be regarded as the source in a possible global circuit, which distributes charge across a planet. New arguments for and against a global electric circuit in Venus’ atmosphere are presented here which arise from re-analysis of data from the Venera 13 & 14 landers.

On Earth, the global atmospheric electric circuit connects regions of disturbed weather to distant regions of fair weather, by current flow between the conducting ionosphere and surface. Disturbed weather regions produce the potential difference between these conducting layers, which drives the current flow. The presence of a similar global circuit on other planets has been proposed, but their existence remains an open question, which motivates further work [2].

The Venera 13 & 14 landers descended through Venus’ atmosphere carrying a wealth of instrumentation. Each lander carried a point discharge sensor, which recorded electrical discharges between the spacecraft and the atmosphere [3]. The discharges recorded were difficult to explain using existing models of Venus’ environment, so it was previously proposed that low atmosphere haze layers could have caused them [4]. Further evidence for these haze layers has been provided by spectroscopic data from the Venera landers, which showed significant atmospheric extinction in the same region [5]. We have attempted to investigate whether it would be plausible for haze layers to cause both the electrical and extinction effects, and whether this favours a global electric circuit in Venus’ atmosphere.

To investigate this, a model describing electrical interactions in Venus’ atmosphere has been produced. The effects of different haze layers on Venus’ electrical environment were able to be studied, via different inputs to the model. The haze layer properties have been constrained by the spectroscopic observations. Results from the electrical modeling were compared with the electrical discharges recorded by the landers, allowing us to determine the conditions which best recreate these observations. Our investigations show that similar results to the observed Venera data can be produced by the electrical model when the effects of a global atmospheric electric circuit are included, but not when they are neglected. These findings are not definitive, but they do provide supporting evidence for the presence of a global electric circuit in Venus’ atmosphere.

References:
[1] R.D. Lorenz (2018). Progress in Earth and Planetary Science, 5. [2] K.L. Aplin (2006). Surveys in Geophysics 27. 63-108. [3] L. Ksanfomality et al. (1982). Soviet Astronomy Letters, 8. 230–232. [4] R.D. Lorenz (2018). Icarus, 307. 146-149. [5] B. Grieger (2003). Proceedings of the International Workshop Planetary Probe Atmospheric Entry and Descent Trajectory Analysis and Science. 63–70.

How to cite: McGinness, B., Harrison, G., Aplin, K., Airey, M., and Nicoll, K.: New Evidence for a Global Atmospheric Electric Circuit on Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13391, https://doi.org/10.5194/egusphere-egu24-13391, 2024.

Studies of exoplanet habitability involving GCMs typically consider the potential for long-lived surface liquid water—or, in other words, climates that Earth-life may find survivable. However, the presence of life and remotely detectable biosignatures on an exoplanet additionally requires an independent origin of life and that life subsequently thrives rather than simply survives. The origin and proliferation of life are both strongly influenced by climate, and both can therefore be informed by GCM studies in parallel with traditional habitability metrics. 

Wet-dry cycles are thought to be an essential ingredient for the origin of life. Cyclic wetting and drying may arise from either diurnal or seasonal cycles, and thus the likelihood of an origin of life may differ between worlds with very different rotation rates, obliquities, or eccentricities. At the same time, seasonal mixing in aqueous environments can trigger highly productive blooms and amplify biosignatures relative to scenarios lacking temporal variability.  

We used ExoPlaSim (an atmospheric GCM) and cGENIE-PlaSim (a 3D model for ocean dynamics and marine biogeochemistry coupled to a 3D atmospheric GCM) to explore diurnal and seasonal cycles on other worlds—with an eye towards origin of life chemistry and biosignatures. This presentation will ultimately identify the planetary scenarios most conducive to exoplanet life detection. 

How to cite: Olson, S., Jernigan, J., Lafleche, E., and Brown, H.: Exploring origin of life chemistry and exoplanet biosignatures with GCMs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14161, https://doi.org/10.5194/egusphere-egu24-14161, 2024.

The NASA Magellan Mission (1990 to 1994) produced a valuable resource that planetary geologists continue to use three decades later to unravel the geological characteristics of Venusian Large Igneous Provinces. The ability to be the first to map the surface of Venus is a powerful engagement tool to inspire the next generation of planetary geologists, as illustrated by the size of the Mount Royal University (MRU) Venus geological mapping team (now 25, nearly ¼ of the MRU Geology Major program). MRU is a public undergraduate university. Students are recruited out of 1^st and 2^nd year courses. In year one (Y1) of the research program students learn how to use the ArcGIS software while being introduced to the geological features of Venus as they map their quadrant, in Y2 or Y3 the students present a poster at an internal research day. The goal by Y4 is for these students to publish a peer-reviewed journal article. Currently one student who ran into pandemic roadblocks through high school could be published while she upgrades her marks, before she is in the MRU Geology Major Program. Such opportunities could prove to be incentives to guide other students past similar roadblocks (we will start working with local junior and high school students in the near future). Collectively we are working towards completing the geological map of the Henie Quadrangle (V-58, south Venus). Detailed mapping (at 1:500,000) revealed that lava canali extend across the entire quadrangle, with evidence for at least three generations of canali. Three canali originate from corona features (e.g. the circumferential dykes around Fotla Corona) suggesting that some canali may be linked to corona formation. The orientation of compressional wrinkle ridges (WR) in northern Henie suggest that these WRs were formed due to strain associated with the formation of the Artemis tectonomagmatic feature which is directly north of Henie. Artemis is possibly the largest such feature in the Solar System. The extent of the Artemis influence is being constrained across the Henie Quadrangle. The source of strain that formed a differently oriented WR swarm to the south of Henie is unknown. There is no evidence for the strain localization into master faults that we see on Earth. More work is needed to develop a model for the formation of the paired Latmikaik-Xacau Coronae and the associated Tellervo Chasma, Sunna-Laverna Dorsae and the Sonmunde-Mdeb-Arubani Flucti. A fissure eruption out of the Sunna Dorsa is proposed as the origin for the surrounding Arubani Fluctus.      

How to cite: Boggs, K., Shackman, J., Demorcy, J., Pendleton, C., Hall, J., Chowdhury, M., Bley, H., Varga, E., Shustova, J., Dear, B., Fontaine, P., Dhami, L., Herrington, S., Ernst, R., El Balil, H., Bethell, E., and Hamner, S.: Henie Quadrangle (V-58, Southern Venus); Large Igneous Province Features, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14443, https://doi.org/10.5194/egusphere-egu24-14443, 2024.

Often termed the twin sister of the Earth, Venus represents an alternative outcome of the evolutionary path taken by large terrestrial planets. Given its extreme surface conditions, lack of surface water, and the absence of plate tectonics, the present-day thermal state of its mantle is likely very different from the Earth. Venus also remains the most enigmatic of terrestrial worlds in terms of interior structure. Both its tidal Love number k₂ and the moment of inertia factor, the main sources of information on the core size and interior structure, are known with a large uncertainty of about 10% [1, 2], and the magnitude of tidal dissipation, sensitive to the planet’s thermal state, has only been determined indirectly [e.g., 3]. Yet, the set of observables acquired by the Magellan and Pioneer Venus Orbiter missions can still be used to put constraints on the interior structure.

In this study, we perform a Bayesian inversion of several observational and theoretical constraints (such as the tidal Love number, maximum elastic thickness, or absence of intrinsic magnetic field) to gain insight into the present-day interior structure and thermal state of Venus. This is done by combining the calculation of a global tidal deformation with a 1d parameterised model of mantle convection in the stagnant-lid regime [4,5]. The convection model is based on the thermal boundary layer theory and incorporates partial melting, crustal growth, and inner core crystallization. The elastic structure of the mantle for three selected mineralogical models is obtained from the software Perple_X, based on the minimisation of Gibbs free energy [6]. Finally, to find the tidal parameters, we calculate the deformation of a layered compressible viscoelastic sphere [7]. The mantle is described by the Andrade rheological model, which has proven essential for distinguishing between a fully solid and a fully or partially liquid Venusian core [8]. We vary a large set of rheological, structural, and thermodynamic parameters and predict a range of mantle temperatures consistent with previous stagnant-lid models, average mantle viscosities between 10²⁰-10²² Pa.s, and a tidal quality factor of Q=50⁺⁷⁴_-24, corresponding to a phase lag of 1.12^+1.06_-0.67 degrees. Additionally, we discuss how the future measurements of the tidal deformation and the moment of inertia of Venus from EnVision [9] and VERITAS (Venus Emissivity, Radio Science, InSAR, Topography, and Spectroscopy) [10] can improve our understanding of the planet's interior.

[1] Konopliv & Yoder (1995), doi:10.1029/96GL01589.

[2] Margot et al. (2021), doi:10.1038/s41550-021-01339-7.

[3] Correia & Laskar (2003), doi:10.1016/S0019-1035(03)00043-5.

[4] Morschhauser et al. (2011), doi:10.1016/j.icarus.2010.12.028.

[5] Baumeister et al. (2023), doi:10.1051/0004-6361/202245791.

[6] Connolly (2009), doi:10.1029/2009GC002540.

[7] Takeuchi & Saito (1972), doi:10.1016/B978-0-12-460811-5.50010-6.

[8] Dumoulin et al. (2017), doi:10.1002/2016JE005249.

[9] Rosenblatt et al. (2021), doi:10.3390/rs13091624.

[10] Cascioli et al. (2023), doi:10.3847/PSJ/acc73c.

How to cite: Walterová, M., Plesa, A.-C., Baumeister, P., Rückriemen-Bez, T., Wagner, F. W., and Breuer, D.: Constraining the interior structure and thermal state of Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14638, https://doi.org/10.5194/egusphere-egu24-14638, 2024.

Dynamics of the Venus atmosphere is still an unsolved fundamental problem in the planetary physics. ESA’s Venus Express collected long imaging time series in several wavelengths from UV to near-IR. It was later complemented by JAXA’s Akatsuki observations, thus providing the longest almost uninterrupted monitoring of the Venus atmosphere dynamics for about 26 Venus years. Tracking of cloud features allowed determination of wind speed at different levels within the cloud deck thus enabling significant progress in characterization of the mean atmospheric circulation. The analysis revealed wind variability including changes with altitude, latitude, local solar time as well as influence of the surface topography and long term 12.5 years periodicity.

The images also provided morphological evidences of dynamical processes at the cloud level. UV dark low latitudes were found to be dominated by convective mixing that brings UV absorbers from depth, while bright uniform clouds at middle-to-high latitudes are typical for the regions with suppresses vertical mixing. The latter feature correlates with drastic increase of the total cloud opacity poleward from ~60° latitude that likely indicates presence of a dynamical mixing barrier here. Similarity of the global UV cloud morphology at the cloud top (~70 km) and that in the deep cloud (50-55 km) observed in the near-IR on the night side suggested similar morphology shaping processes throughout the cloud deck. Venus Express observed gravity waves poleward of 65°N concentrated at the edges of Ishtar Terra likely indicating their generation by wind interaction with the surface. 

Venus Express performed about 800 radio occultations providing precise measurements of the atmospheric temperature structure and static stability parameter in the altitude range 40-90 km. The Richardson number latitude-altitude field derived from the wind and temperature measurements suggests presence of convection in the cloud deck and stable mesosphere above it with the convective layer extending to greater depth at high latitudes. The talk will present recent results on the atmospheric circulation, supplemented by a summary of the Venus Express observations related to the atmospheric dynamics and an outlook for further analysis of these data.  

How to cite: Titov, D., Khatuntsev, I., and Patsaeva, M.: Venus atmosphere dynamics: digging into the Venus Express observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14689, https://doi.org/10.5194/egusphere-egu24-14689, 2024.

The dynamic regime prevailing in the mantle of present-day Venus is still unknown. The surface of Venus seems uniformly quite young; it has  been proposed that it was due to a catastrophic resurfacing 150-700 Ma, and that the planet was in a stagnant lid regime since. Indeed, Magellan observations have failed to reveal a continuous set of accretion ridges and subduction zones, signatures of plate tectonics. But subduction features (trench, elastic bulge) are present in a number of localized spots, for exemple around two of the largest coronae, Artemis and Quetzelpetlal. There, subduction would be mainly by roll-back and could have been induced by the impingement of a mantle plume under the lithosphere, as predicted by our recent fluid dynamics laboratory experiments. Further analysis of our experiments suggest that subduction would be facilitated by the presence of a few % of a liquid phase in the asthenosphere. Melt would be most likely for the Venusian case, as anyway hinted by the amount of volcanic features on the surface of the planet. The experimental scaling laws further suggest that roll-back and subduction could be quite fast (10 cm/yr) because of the old age of the subducting lithosphere and the transformation to eclogite of the basaltic crust. This is turn would generate the rapid opening of a back-arc basin. Laboratory experiments show that for Venus temperature conditions, the produced crust and lithosphere could be quite disorganized with a contorted spreading center, large transforms and microplates. Moreover, the buoyancy of the newly created plate would cause it to remain quite elevated compared to the surrounding plains. Hence, inspection of the topography of Venus suggests several new plates created by subduction: beside the interior of Artemis coronae, Enyo Fossae and Asthik Planum could be plausible candidates. 

How to cite: Davaille, A.: Signatures of a regime of episodic localized subduction: from laboratory experiments to Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16255, https://doi.org/10.5194/egusphere-egu24-16255, 2024.

The next ESA mission to Venus, EnVision, aims to study the planet as a whole, including its various constituting parts as well as their interactions and coupling processes. Several instruments will therefore compose the payload: a synthetic aperture radar (VenSAR, NASA), a subsurface radar sounder and a suite of three spectrometers (VenSpec) will be embedded, and a radioscience experiment will be implemented. Among them, the UV channel of the spectrometer suite, VenSpec-U, will observe the atmosphere above the clouds and will focus on the characterisation of the sulphured gases SO₂ and SO, the monitoring of the unknown UV absorber and dynamical processes. These four topics have been identified as the main science objectives of the instrument and have driven the elaboration of a preliminary design based on the requirements (e.g. spectral range, spectral and spatial resolution) that were formulated with respect to these goals.

The compliance of the current design with respect to these requirements, regarding in particular the precision of the retrieved science data, can then be assessed. Sensitivity studies are therefore performed using the Radiative Transfer Model (RTM), updated from the one used for SPICAV-UV/Venus Express retrievals (Marcq et al., 2020), that allows to link atmospheric features and UV reflectance spectra. Two types of perturbations are considered : errors of random nature arising from the presence of noise on the signal, or systematic errors caused by various effects that induce biases on the measurements. The first ones can be characterised through the influence of the Signal-to-Noise Ratio (SNR) on the uncertainties associated to each retrieved parameter through the fitting algorithm. Limits in terms of SNR can then be defined in order to ensure the compliance with the specifications. The second ones are referring to the impact of biases on the retrievals’ accuracy, and evaluate more specifically the effects of the similarities between the spectral characteristics of these biases and those of the atmospheric components aiming to be detected. The implemented method is based on the Effective Spectral Radiometric Accuracy (ESRA) requirement, previously defined within the framework of the ESA Sentinel missions. It allows to study biases independently as well as potential compensations, so that allowable envelopes of residual errors can then be estimated for each of the considered biases.

How to cite: Conan, L., Marcq, E., Lustrement, B., Rouanet, N., Vandaele, A. C., and Helbert, J.: Sensitivity studies for the VeSUV/VenSpec-U instrument onboard ESA’s EnVision mission, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16442, https://doi.org/10.5194/egusphere-egu24-16442, 2024.

Until now, the Venus PCM (Planetary Climate Model) was using precomputed tables for the distribution of the solar heating rates in the atmosphere of Venus. A new scheme is now implemented to compute online the radiative transfer of the solar flux, which allows more flexibility to study sensitivity to opacity sources. We have investigated the sensitivity of the temperature and circulation of the Venusian cloud region to the distribution of the UV absorber. Different vertical distributions of the UV absorber, as well as variations of this along latitudes, have been tested, and comparison is discussed of the vertical profile of computed solar heating rates, temperature distribution in the cold collar region, as well as the resulting mean zonal wind field.

How to cite: Han, P. and Lebonnois, S.: Influence of the UV absorber distribution on the temperature and circulation ofthe Venusian cloud region, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16505, https://doi.org/10.5194/egusphere-egu24-16505, 2024.

The cause of the inhomogeneous near-ultraviolet absorption observed in the upper clouds of Venus remains a key question in Venusian research. One possible candidate in the literature is ferric chloride. The absorption spectrum of ferric chloride currently in use by models uses ethyl acetate as a solvent and does not reproduce the absorption features observed on Venus. The study of the optical properties and chemistry of ferric chloride in the sulphuric acid cloud droplets is required to draw valid conclusions regarding its suitability as a candidate for the near-UV absorption.

In this study, we measure the absorption spectrum of ferric chloride in sulphuric acid from 200 – 600 nm at a range of temperatures and measure the rate of conversion of the ferric chloride ions into ferric sulphate ions. We then use the resulting ferric chloride absorption coefficients in a 1D radiative transfer model and estimate the required concentration of ferric chloride in the clouds to be 0.6 – 0.9 wt% in the mode 1 (~0.3 µm radius) cloud droplets to match observations. We also predict the atmospheric concentrations of ferric chloride formed from the reaction of iron ablating from cosmic dust entering Venus’ atmosphere around 120 km with hydrogen chloride emitted by volcanic activity, and estimate the accumulation timescale of ferric chloride to produce the required concentrations in the clouds.

How to cite: Egan, J., Feng, W., James, A., Manners, J., Marsh, D. R., and Plane, J. M. C.: Laboratory studies and modelling of ferric chloride as the cause of the anomalous UV absorption in the Venusian atmosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16898, https://doi.org/10.5194/egusphere-egu24-16898, 2024.

High-resolution runs of the Venus PCM (1.25° in longitude and latitude) successfully simulated Venus atmospheric superrotation. The results show a clear spectrum and structure of atmospheric waves, primarily with periods of 5.65 days and 8.5 days. The simulation successfully reproduces long-term quasi-periodic oscillation of the zonal wind and primary planetary-scale wave seen in observations. These oscillations are obtained with a period of about 163-222 days close to the observations. The Rossby waves show robustness in wave characteristics and angular momentum transport due to Rossby-Kelvin instability by comparing the 5.65-day wave with the 5.8-day wave simulated by another Venus GCM, AFES-Venus. Similarities are also evident between the 8.5-day wave in our simulation and the 7-day wave obtained in AFES-Venus. Furthermore, the long-term variations in angular momentum transport indicate that the 5.65-day wave is the dominant factor of the oscillation on the superrotation, and the 8.5-day wave is the secondary. When the 5.65-day wave grows, its angular momentum transport is enhanced and accelerates (decelerates) the lower-cloud equatorial jet (cloud-top mid-latitude jets). Meanwhile, the 8.5-day wave weakens, reducing its deceleration effect on the lower-cloud equator region. Consequently, this flattens the background wind and weakens instability, leading to the decay of the 5.65-day wave. And vice versa when the 5.65-day wave is weak.

How to cite: Lai, D., Lebonnois, S., and Li, T.: Planetary-scale wave study in Venus cloud layer, simulated by the Venus PCM, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17524, https://doi.org/10.5194/egusphere-egu24-17524, 2024.

EnVision is ESA’s next mission to Venus, in partnership with NASA, where NASA provides the Synthetic Aperture Radar payload and mission support. The ESA mission adoption is scheduled for January 2024, and the launch for 2031. The start of the science operations at Venus is early 2035 following the mission cruise, and aerobraking phase around Venus to achieve a low Venus polar orbit. The scientific objective of EnVision is to provide a holistic view of the planet from its inner core to its upper atmosphere, studying the planets history, activity and climate. EnVision aims to establish the nature and current state of Venus’ geological evolution and its relationship with the atmosphere. EnVision’s overall science objectives are to: (i) characterize the sequence of events that formed the regional and global surface features of Venus, as well as the geodynamic framework that has controlled the release of internal heat over Venus history; (ii) determine how geologically active the planet is today; (iii) establish the interactions between the planet and its atmosphere at present and through time. Furthermore, EnVision will look for evidence of past liquid water on its surface.

The nominal science phase of the mission will last six Venus cycles (~four Earth years), and ~210 Tbits of science data will be downlinked using a Ka-/X-band communication system. The science objectives will be addressed by five instruments and one experiment, provided by ESA memberstates and NASA. The VenSAR S-band radar will perform targeted surface imaging as well as polarimetric and stereo imaging, radiometry, and altimetry. The high-frequency Subsurface Radar Sounder (SRS) will sound the upper crust in search of material boundaries. Three spectrometers, VenSpec-U, VenSpec-H and VenSpec-M, operating in the UV and Near- and Short Wave-IR, respectively, will map trace gases, search for volcanic gas plumes above and below the clouds, and map surface emissivity and composition. A Radio Science Experiment (RSE) investigation will exploit the spacecraft Telemetry Tracking and Command (TT&C in Ka-/X bands) system to determine the planet’s gravity field and to sound the structure and composition of the middle atmosphere and the cloud layer in radio occultation. All instruments have substantial heritage and robust margins relative to the requirements, with designs suitable for operation in the Venus environment, and were chosen to meet the broad range of measurement requirements needed to support the EnVision scientific objectives. The EnVision science teams will adopt an open data policy, with public release of the scientific data after verification and validation. Public calibrated data availability is <6 months after data downlink.

The mission phase B1 was concluded in December 2023 following the successful Mission Adoption Review and positive science review and recommendations by the ESA Solar System and Exploration Working Group (SSEWG) and Space Science Advisory Committee (SSAC). The mission adoption is scheduled for 25 January 2024. The scientific objectives and status of the EnVision mission preparations will be presented, including an overview of the scientific topics being studied and the next steps in the mission preparation.

How to cite: Straume-Lindner, A. G., Schulte, M., Pacros, A., Voirin, T., Bruzzone, L., Byrne, P., Carter, L., Dumoulin, C., Gilli, G., Helbert, J., Hensley, S., Jessup, K. L., Kiefer, W., Marcq, E., Mason, P., Moreira, A., Vandaele, A. C., and Widemann, T.: Science objective and status of the EnVision Mission to Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18247, https://doi.org/10.5194/egusphere-egu24-18247, 2024.

Venus is a natural laboratory to study the atmospheric circulation on a slowly rotating planet. The dynamics of its upper atmosphere (60-120 km) is a combination of retrograde zonal wind found in the lower mesosphere and solar-to-antisolar winds that characterize the thermosphere, and it is subject to a strong turbulence and a dramatic variability both on day-to-day as well as longer timescales. Moreover, several wavelike motions with different length scales have been detected at these altitudes within and above the clouds and they are supposed to play an important role in the maintenance of the atmospheric circulation. The basic processes maintaining the super-rotation (an atmospheric circulation located at the clouds level and being 80 times faster than the rotation of the planet itself) and other dynamical features of Venus circulation are still poorly understood [1].

Different techniques have been used to obtain direct observations of wind at various altitudes: tracking of clouds in ultraviolet (UV) and near infrared (NIR) images give information on wind speed at cloud top (~70 km altitude) [2] and within the clouds (~61 km, ~66 km) [3], while ground-based measurements of doppler-shift in CO₂ band at 10 μm [4] and in several CO (sub-)millimeter lines [5,6] sound thermospheric and upper mesospheric winds, showing a strong variability.

In the mesosphere, at altitudes where direct observations of wind are not possible, zonal wind fields can be derived from the vertical temperature structure using the thermal wind equation. Previous studies [7,8,9] showed that on slowly rotating planets, like Venus and Titan, the strong zonal winds at cloud top can be successfully described by an approximation of the Navier–Stokes equation, the cyclostrophic balance in which equatorward component of centrifugal force is balanced by meridional pressure gradient.

We will present zonal thermal winds derived by applying the cyclostrophic approximation from the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) temperature retrievals. VIRTIS was one of the experiments on board the European mission Venus Express [10]. For this study, we will analyze the complete VIRTIS dataset acquired between December 2006 and January 2010 [11,12].

References

[1] Sanchez-Lavega, A. et al. (2017) Space Science Reviews, Volume 212, Issue 3-4, pp. 1541-1616.

[2] Goncalves R. et al. Atmosphere, 12:2., 2021. doi: 10.3390/atmos12010002.

[3] Hueso, R. et al. (2012) Icarus, Volume 217, Issue 2, p. 585-598.

[4] Sornig, M. et al. (2013) Icarus 225, 828–839.

[5] Rengel, M. et al. (2008) PSS, 56, 10, 1368-1384.

[6] Piccialli, A. et al. A&A, 606, A53 (2017) DOI: 10.1051/0004-6361/201730923

[7] Newman, M. et al. (1984) J. Atmos. Sci., 41, 1901-1913.

[8] Piccialli A. et al. (2008) JGR, 113,2, E00B11.

[9] Piccialli A. et al. (2012) Icarus, 217, 669–681

[10] Drossart, P. et al. (2007) PSS, 55:1653–1672

[11] Grassi D. et al. (2008) JGR., 113, 2, E00B09.

[12] Migliorini, A. et al. (2012) Icarus 217, 640–647.

How to cite: Piccialli, A., Grassi, D., Migliorini, A., Politi, R., Piccioni, G., and Drossart, P.: Zonal winds in Venus mesosphere from VIRTIS/VEx temperature retrievals, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18366, https://doi.org/10.5194/egusphere-egu24-18366, 2024.

Observations of Venus imply ongoing tectonic and volcanic activity, suggesting the planet is dynamically active^[1,2]. Tectonically altered regions, such as ridges or tesserae, indicate surface mobility. However, unlike Earth, no evidence of active plate tectonics has been identified. The tectonics and volcanism of terrestrial planets are closely tied to active mantle convection modes. Rheology, a crucial element in tectonics, is influenced by the presence of water^[3]. Despite this, the impact of water has largely been overlooked in Venus studies, as its interior is typically assumed to be dry. This assumption is being challenged by indications of significant hydrodynamic escape into space, requiring volcanic replenishment. Consequently, water is likely still present in Venus' interior, even if the concentrations are unknown. Importantly, the potential effects of water on Venus' dynamics and evolution remain poorly understood. The interplay between water, mantle dynamics, and volcanic activity would likely contribute to a more comprehensive understanding of Venus' evolution.  This underlines the need to consider complex dynamic thermo-magmatic models that account for water, including composition-dependent finite water solubilities.

In this study, we use the numerical code StagYY to perform state-of-the-art 2D models in a spherical annulus geometry to assess the effects of water on the tectono-magmatic evolution of Venus^[4,5]. Particular attention will be given to the way water influences mantle convection and tectonics. Indeed, results show that the presence of water can dramatically change the geodynamic regime through the rheology, melting and outgassing. With the introduction of composition-dependent water solubility maps, dehydration processes will redistribute water throughout the mantle^[6]. Since water content is directly related to the viscosity structure, the convective regime is expected to change as well. The main question we want to address is how dehydration processes and water distribution influence the convective and tectonic regimes of Venus. Studying the impact of water on Venus's interior may not only unveil insights into its tectonic evolution but also sets the stage for crucial future research, advancing our broader understanding of planetary processes and habitability.

^[1] Smrekar, S. E., Stofan, E. R., Mueller, N., Treiman, A., Elkins-Tanton, L., Helbert, J., ... & Drossart, P. (2010). Recent hotspot volcanism on Venus from VIRTIS emissivity data. Science, 328(5978), 605-608.

^[2]Gülcher, A. J., Gerya, T. V., Montési, L. G., & Munch, J. (2020). Corona structures driven by plume–lithosphere interactions and evidence for ongoing plume activity on Venus. Nature Geoscience, 13(8), 547-554.

^[3]Karato, S. I. (2015). Water in the evolution of the Earth and other terrestrial planets. Treatise on Geophysics, 9, 105-144.

^[4] Tackley, P. J. (2008). Modelling compressible mantle convection with large viscosity contrasts in a three-dimensional spherical shell using the yin-yang grid. Physics of the Earth and Planetary Interiors, 171(1-4), 7-18.

^[5]Tian, J., Tackley, P. J., & Lourenço, D. L. (2023). The tectonics and volcanism of Venus: New modes facilitated by realistic crustal rheology and intrusive magmatism. Icarus, 399, 115539.

^[6]Nakagawa, T. (2017). On the numerical modeling of the deep mantle water cycle in global-scale mantle dynamics: The effects of the water solubility limit of lower mantle minerals. Journal of Earth Science, 28(4), Article 4. https://doi.org/10.1007/s12583-017-0755-3

How to cite: Metternich, M., Tackley, P. J., Moccetti Bardi, N., and Lourenço, D. L.: Water and the tectonic regime of Venus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19372, https://doi.org/10.5194/egusphere-egu24-19372, 2024.

A planet with a significant water content can give rise to a steam atmosphere (dominated by water vapor) when the incoming stellar flux exceeds the so-called runaway limit or after large impacts or accretion. All steam-atmosphere current models predict that the greenhouse effect of an ocean worth of water vapor is sufficient to generate a surface magma ocean. This has far reaching consequences for the early evolution of warm rocky planets and the coupling of their interior with the atmosphere. In this paradigm, the solidification of the mantle of Venus is believed to have happened only after the escape of its steam atmosphere to space, leaving the mantle desiccated.

However, these conclusions rely on the assumption that atmospheres are fully convective below their photosphere. This hypothesis was introduced in the 80s and is used in a large part of the literature on the subject. Its validity had however not been assessed thoroughly. We will present the results of a climate model that has been specifically designed to model the radiative-convective equilibrium of steam atmospheres without any a priori hypothesis on their convective nature. These results show that steam atmospheres are generally not fully convective, which yields much cooler surfaces than previous models. A runaway greenhouse does not systematically melt the surface. This changes completely our view of the early evolution of Venus', with even more drastic changes for planets around stars redder than the Sun.

The equilibrium thermal structure of a steam atmosphere, which affects observable signatures and mass-radius relationships of warm Earth-like to water-rich planets, becomes strongly dependent on the stellar spectrum and internal heat flow. Our current constraints on the water content of the internal Trappist-1 planets should for example be revisited. For ultracool dwarfs, these results even question the nature of the inner edge of the sometimes called habitable zone.

How to cite: Selsis, F., Leconte, J., Turbet, M., Chaverot, G., and Bolmont, E.: Steam atmospheres and the implications for Venus and Venus-like planets , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22187, https://doi.org/10.5194/egusphere-egu24-22187, 2024.

The Ediacara Member of the Rawnsley Quartzite hosts one of the best preserved and most diverse assemblages of the Ediacara Biota. In it, soft-bodied organisms are preserved across various depositional environments, with a proposed connection between sedimentary facies and fossil assemblages. Recent studies have questioned previously-established facies models, undermining links between paleoenvironment, paleoecology, and taphonomy. Here, we revisit these models using field observations from across the central Flinders Ranges, supplemented by two new cores drilled through the Ediacara Member at the Nilpena fossil site. The two drill sites are 2 km apart and span strata from the top of the underlying Chace Member through the overlying fossiliferous facies of the Ediacara Member. These two cores are easily correlated to surface outcrops and provide the most complete record of the deposition of the Ediacara Member thus far. The core drilled at “One Tree Hill” (OTH-1) reaches a depth of 65 m and records characteristic “petee laminations” below the erosional contact with the Ediacara Member, which is marked by a breccia horizon. The basal breccia of the Ediacara Member gradationally passes into thinly laminated planar to slightly wavy siltstone that then transitions into alternating thin beds of siltstone and thick beds of massive sandstone often affected by soft-sediment deformation. These beds grade into wavy-laminated siltstone interbedded with thin beds of arenite. Forming the top of the core are thick beds of massive arenite. The second drill core (MR-1) spanning 75.8 m records analogous facies with changing thickness and siltstone/sandstone ratio but lacks a breccia horizon at the base of the Ediacara Member. Both cores highlight repeated cycles of alternating deposition of sandstone and siltstone often obscured in the surface exposure. We investigate an array of sedimentary structures observed in the cores and surface exposures in thin sections, exploring the role of microbial matgrounds and silica cementation in sediment binding and transport. Both are critical for any depositional model developed for the Ediacara Member across the Nilpena site and central Flinders Ranges, its accumulation rate, sediment sources and potential triggers for repeated channelized flows observed throughout the unit. A unified depositional model built across this basin will be critical to further untangle the complex interplay between time, changing taxonomic diversity, water depth, and paleoenvironment at the dawn of animal life.

How to cite: Faehnrich, K., García-Bellido, D. C., Droser, M. L., and Gaines, R. R.: Revisiting depositional models for the Ediacara Member of the Rawnsley Quartzite in South Australia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-547, https://doi.org/10.5194/egusphere-egu24-547, 2024.

Identifying the geological drivers of long-term climate change is key to improve our understanding of the interactions between the deep Earth and the Earth’s surface. Long-term Cenozoic climate cooling has been largely attributed to an increase in atmospheric carbon consumption by enhanced silicate weathering linked to the uplift of the Tethyan orogenic belt. Alternatively, this cooling trend has been explained by decreasing magmatic CO₂ outgassing during the progressive closure of Neo-Tethys Ocean. However, the outgassing rates associated with Neo-Tethyan magmatism remain poorly constrained, making it difficult to assess its contribution to Cenozoic climate change. Here, we present the first results of numerical geodynamic experiments aimed at obtaining improved quantitative estimates of the magmatic CO₂ outflux along the Neo-Tethyan margins. To this end, we use 2D numerical petrological-thermomechanical models of oceanic subduction and continental collision that account for partial melting and slab decarbonation. Calibrating these numerical experiments on available geological constraints from the Neo-Tethyan margin, we estimate the Neo-Tethyan magma production volumes through the Early Cenozoic. We discuss how these results are sensitive to changes in model setup and input parameters such as convergence rates, rheology, and crustal composition. To quantify the time-dependent magmatic CO₂ emissions, we combine the magma production histories with both modelling- and observation-based quantifications of the volatile contents of pre- and post-eruptive igneous rocks. Finally, we discuss the potential Neo-Tethyan magmatic forcing of Early Cenozoic climate change in light of our new results and its implications for the global carbon cycle and surface-deep Earth feedbacks.

How to cite: Vaes, B., Sternai, P., Ostorero, L., Castrogiovanni, L., Gonzalez, C., and Donnadieu, Y.: Numerical modelling of magmatic CO2 emissions from the Neo-Tethyan margin during the Early Cenozoic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-620, https://doi.org/10.5194/egusphere-egu24-620, 2024.