Kimberlites, carbonatites and alkaline silicate rocks occur in intraplate settings across all continents, with emplacement ages ranging from Mesoproterozoic to Quaternary. Their geodynamic nature remains a subject of vigorous debate, with various models linking them to development of subduction zones, rifts, plumes, and edge-driven convection. In this work, we demonstrate that emplacements of the Jurassic – Cretaceous kimberlites and alkaline intrusions of the Superior craton were controlled by a Mesozoic reactivation of the Neoproterozoic St. Lawrence paleorift system (SLPRS) in response to the development of the Atlantic Ocean. We draw parallels with kimberlite provinces of Baltica and Siberia, showing that kimberlitic magmatism there was similarly associated with Proterozoic paleorift systems subjected to Phanerozoic reactivations.

We use regional aeromagnetic data to demonstrate that the Mesozoic kimberlites of the Kirkland Lake and Timiskaming fields and alkaline intruisons of the Monteregian Hills alkaline province are confined to the limbs of the SLPRS – Timiskaming and Ottawa-Bonnechere grabens, respectively. We reconstruct the Mesozoic evolution of the stress field in the Superior province via stress inversions of tensile fracture sets’ orientations measured at 22 sites in the Ordovician – Silurian carbonates present in south-eastern Superior. We apply fault slip and dilation tendency analyses to assess reactivation potentials of SLPRS normal faults under the calculated stress tensors. We analyze available geochronological data and depth-to-basement maps of Baltica and Eastern Siberia to constrain the structural settings of Arkhangelsk and Yakutia kimberlite provinces.

We demonstrate that the intraplate intrusions of the Superior province were emplaced into sequentially reactivated SLPRS segments in response to the Mesozoic counter-clockwise rotation of the main extension axis (σ3) of the stress field from W-E to NW-SE. This sequential re-activation explains apparent age progression of magmatism in SLPRS along the NW- SE trend. In Arkhangelsk province, the kimberlites are associated with parallel N-S trending Proterozoic Kandalaksha and Leshukov paleorifts and are coeval with the Late Devonian development of the Timan – Pechora rift system along the eastern boundary of Baltica. In Siberia, the late Devonian kimberlites are emplaced in the then-active Viluy (in the south) and limbs of the West Verkhoyan (in the north) rift systems. The Mesozoic kimberlitic magmatism in Siberia seems to be mostly confined to the Sukhanov continental rift system and occurred in several pulses from Middle Triassic to Early Cretaceous, corresponding to the development of West Verkhoyan passive margin. The timing of kimberlitic magmatism cessation coincides with the docking of the Oloy volcanic arc, when Siberian stress field transitioned into a compressional state.

We conclude that kimberlitic magmatism across the Laurasian platforms was primarily controlled by reactivations of the Proterozoic continental paleorift systems throughout the Phanerozoic in response to extensional stress orthogonal to the paleorifts’ axes. The results of numerical modelling of fault stress response validate this model for the Superior province of the Canadian shield. A similar quantitative approach is required to further validate this conclusion for other provinces of intraplate magmatism around the world.

How to cite: Koptev, E. and Peace, A.: Continental palaeorift reactivations drive kimberlitic and alkaline magmatism: a case study from the Superior province of the Canadian shield., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-901, https://doi.org/10.5194/egusphere-egu26-901, 2026.

The origin of geochemically enriched mantle in the asthenosphere is important to understanding the physical, thermal and chemical evolution of Earth’s interior. While subduction of oceanic sediments and deep mantle plumes have been implicated in this enrichment, they cannot fully explain the observed geochemical trends found in some oceanic volcanoes. We present geodynamic models to show that enriched mantle can be liberated from the roots of the subcontinental lithospheric mantle by highly organised convective erosion ultimately linked to continental rifting and break-up. We demonstrate that a chain of convective instabilities sweeps enriched lithospheric material into the suboceanic asthenosphere, in a predictable and quantifiable manner, over tens of millions of years—potentially faster for denser, removed keels. We test this model using geochemical data from the Indian Ocean Seamount Province, a near-continent site of enriched volcanism with minimal deep mantle plume influence. This region shows a peak in enriched mantle volcanism within 50 million years of break-up followed by a steady decline in enrichment, consistent with model predictions. We propose that persistent and long-distance lateral transport of locally metasomatised, removed keel can explain the billion-year-old enrichments in seamounts and ocean island volcanoes located off fragmented continents. Continental break-up causes a reorganisation of shallow mantle dynamics that persists long after rifting, disturbing the geosphere and deep carbon cycle.

How to cite: Gernon, T., Brune, S., Hincks, T., Palmer, M., Spencer, C., Watts, E., and Glerum, A.: Enriched-mantle oceanic volcanism driven by prolonged convective erosion of continental roots, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5121, https://doi.org/10.5194/egusphere-egu26-5121, 2026.

It has long been supposed that Earth’s asthenosphere contains small amounts of seismically visible melt; how and why this melt persists has remained a similarly long-supposed mystery. Here we show how this observation is a simple consequence of the preferential diffusion of hydrogen (‘water’) from a harder-to-melt peridotite lithology forming ~80% of the mantle into an easier-to-melt pyroxenite lithology that exists as ~m-10km blobs within a peridotitic ‘matrix’.  

Pyroxenites, due to their higher Al content, will have higher trace water contents when in diffusive equilibrium with neighboring peridotite.  Their higher water contents, in turn, will tend to lower their solidi, and favor their partial melting over nearby peridotite sharing similar p-T conditions. In addition, the latent heat consumed during early pyroxenite melting can locally cool this mantle, favoring the inward diffusion of both heat  (~1e-6 m^2/s) and hydrogen from surrounding peridotites.

Here we use 2-D numerical models of flow and melting in upwelling mantle that include the possibility of both heat and hydrogen diffusion between nearby peridotite and pyroxenite lithologies, assuming experimentally measured hydrogen diffusivities of ~1e-7 – 1e-8 m^2/s. Several interesting effects are found. ‘Thin’ (~1-100m) pyroxenite layers will rapidly suck both heat and water from nearby peridotite, so locally cooling and drying this peridotite before it starts to pressure-release melt –– while at the same time increasing its viscosity with respect to warmer and damper peridotite. At ~10-100mm/yr ascent rates, larger (~1-10km-scale)  blobs of recycled pyroxenitic basalts will instead tend to melt as chemically isolated regions that more slowly suck heat and water from their surrounding peridotites.

Finally, laterally moving regions of asthenosphere containing partially melting pyroxenitic blebs and blobs will continue to partially melt for ~10s of Ma due to inward water diffusion even as small-degree melts form and escape from this partially molten bilithologic asthenosphere. This provides a simple geodynamic mechanism for why Earth’s suboceanic asthenosphere appears to persistently contain small amounts of partial melt at depths shallower than ~150km, while also leading to the formation of small degree melts far from plumes, ridges, or subduction zones.  We present and discuss numerical experiments that illustrate each of these effects.

How to cite: Morgan, J. P. and Hasenclever, J.: How Water Diffusion can Shape the Melting and Viscosity of a Bilithologic Mantle, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9363, https://doi.org/10.5194/egusphere-egu26-9363, 2026.

Phosphorus is a fundamental element essential for all life on Earth, and its cycling plays an indispensable role in the emergency and evolution of life. Intraplate magmas sourced from the deep mantle, extending to the mantle transition zone or even lower mantle, commonly exhibit anomalously high P₂O₅ contents (0.6-1.8 wt%) compared to mid-ocean ridge basalts (MORBs, 0.06-0.25 wt%) and arc basalts (0.1-0.35 wt%), highlighting its critical role in deep Earth-surface phosphorus cycling. Previous studies have proposed that these anomalies are linked to recycled high-pressure phosphate phases—tuite (γ-Ca₃(PO₄)₂)—yet how tuite is transported into the deep mantle, and its role in deep mantle processes remains poorly constrained. Sediment is the dominant phosphorus (0.2-1 wt% P₂O₅) reservoir in the subducted slab, largely due to the biogenetic deposition process. To investigate the behaviour of phosphorus during subduction, we performed high-temperature and high-pressure experiments (6-33 GPa, 800-1600 ℃) on subducted sediment. Our results show that apatite in the sediment transforms into tuite at 6-8 GPa, and tuite remains stable to lower mantle depths (> 33 GPa) along the subducted slab geotherms. The breakdown of tuite from these high-P sediments in deep mantle further provides an efficient mechanism for supplying phosphorus to the source region of intraplate magmas. In addition, this process releases tuite-favored elements U and Th into the mantle, whose radiogenic decay may promote sustained mantle heating and magmatic activity. In contrast, within the mafic oceanic crust, phosphorus is progressively incorporated into the majoritic garnet structure with increasing pressure, and discrete phosphate phases becomes unstable pressures higher than 2 GPa. Given the refractory affinity of majorite, phosphorus stored in subducted mafic oceanic crust is unlikely to be released into mantle melts. This contrast further highlights the critical role of sediment in intraplate magmas genesis and phosphorus cycling.

How to cite: Guan, S., Gao, M., Wang, Y., Wang, L., and Xu, Y.: Deep phosphorus cycling carried by subducted sediments and its role on intraplate magma genesis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5254, https://doi.org/10.5194/egusphere-egu26-5254, 2026.

Volcanic hotspots are commonly attributed to hot mantle plumes rooted at the core-mantle boundary. Yet the absence of expected surface signatures at some hotspots challenges this classical view. Seismic tomography reveals a prominent low-velocity mantle anomaly (named the Hainan plume) beneath the Leiqiong volcanic field; however, this region lacks a linear volcanic chain and shows low ³He/⁴He ratio, making its genesis highly controversial. Here we integrate receiver-function imaging with mineral physics modeling to reveal the interaction between the Hainan mantle plume and remnant slabs within the mantle transition zone (MTZ). We find that the plume ascends along a low-velocity corridor at the slab edge, while the slab acts as a thermochemical filter, resulting in notable radial stratification within the MTZ. Although a thermal anomaly of 150 K near the 660-km discontinuity indicates plume ponding, this heat dissipates markedly by 410 km depth. Instead, the ascending plume becomes enriched in basaltic components (up to ~60%). We demonstrate that slab-induced cooling and density crossovers drain the plume of its thermal buoyancy, trapping basaltic oceanic crust within the upper MTZ. This results in a low-buoyancy upwelling that limits the plume’s contribution to Leiqiong volcanism. These findings suggest that the ascent of deep mantle plumes can be effectively arrested by ambient mantle heterogeneities, providing a unique explanation for the lack of surface plume signatures at some hotspots.

How to cite: Zhu, S. and Deng, Y.: Slab-Plume Interaction Arrests the Ascent of the Hainan Plume, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9180, https://doi.org/10.5194/egusphere-egu26-9180, 2026.

Mantle plumes, the hot upwellings from the Earth’s core-mantle boundary, are thought to trigger surface uplift and the emplacement of large igneous provinces (LIPs). Magmatic centres of many LIPs are scattered over thousands of kilometres. This can be attributed to lateral flow of plume material into thin lithosphere areas, but evidence for such flow is scarce. Here, we examine evidence for this process in different LIPs and at different scales. First, we use the now abundant seismic data and recently developed methods of seismic thermography to map previously unknown plate-thickness variations in the Britain-Ireland part of the North Atlantic Igneous Province, linked to the Iceland Plume. The locations of the ~60 Myr old uplift and magmatism are systematically where the lithosphere is anomalously thin at present. The strong correlation indicates that the hot Iceland Plume material reached this region and eroded its lithosphere, with the thin lithosphere, hot asthenosphere and its decompression melting causing the uplift and magmatism. We demonstrate, further, that the unevenly distributed current intraplate seismicity in Britain and Ireland is also localised in the thin-lithosphere areas and along lithosphere-thickness contrasts. The deep-mantle plume thus appears to have created not only a pattern of thin-lithosphere areas and scattered magmatic centres but, also, lasting mechanical heterogeneity of the lithosphere that controls long-term distributions of deformation, earthquakes and seismic hazard.

At larger scales, recent waveform tomography of different continents shows that lateral variations of the lithospheric thickness exert primary controls on the distributions of LIP magmatism. Joint evidence from tomography and kimberlites reveals the temporal evolution of the lithospheric thickness and indicates where the relevant lithospheric thickness variations pre-dated the LIP and where they are likely to have been changed by the processes that gave rise to the LIP emplacement.

References

Bonadio, R., Lebedev, S., Chew, D., Xu, Y., Fullea, J. and Meier, T., 2025. Volcanism and long-term seismicity controlled by plume-induced plate thinning. Nature Communications, 16(1), 7837.

Civiero, C., Lebedev, S. and Celli, N.L., 2022. A complex mantle plume head below East Africa‐Arabia shaped by the lithosphere‐asthenosphere boundary topography. Geochemistry, Geophysics, Geosystems, 23(11), e2022GC010610.

de Melo, B.C., Lebedev, S., Celli, N.L., Gibson, S., De Laat, J.I. and Assumpção, M., 2025. The lithosphere of South America from seismic tomography: Structure, evolution, and control on tectonics and magmatism. Gondwana Research, 138, 139-167.

Dou, H., Xu, Y., Lebedev, S., de Melo, B.C., van der Hilst, R.D., Wang, B. and Wang, W., 2024. The upper mantle beneath Asia from seismic tomography, with inferences for the mechanisms of tectonics, seismicity, and magmatism. Earth-Science Reviews, 255, 104841.

How to cite: Bonadio, R. and Lebedev, S.: Dispersed intraplate magmatism controlled by pre-existing and plume-induced plate thickness variations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7779, https://doi.org/10.5194/egusphere-egu26-7779, 2026.

Hotspots are generally interpreted as the surface expression of lithospheric plates moving over mantle plumes, progressively forming volcanic chains aligned with plate motion. However, it is increasingly recognized that hotspots—such as Hawaii, Samoa, and Tristan–Gough— can exhibit two volcanic lineaments that are not necessarily parallel and display distinct geochemical characteristics.

Here we report the discovery of a previously unrecognized volcanic chain related to the Réunion hotspot in the Mascarene Basin (western Indian Ocean), which we term the Mascarene Chain (MASC). This chain extends from the Seychelles across the seafloor through a series of seamounts and records a southward progression of volcanism from ca. 67 to 6 Ma. This age progression is constrained by multi-technique geochronology (⁴⁰Ar/³⁹Ar on biotite; U–Pb on zircon; (U–Th)/He on zircon and apatite) performed on dredged volcanic samples. Petrology, whole-rock major and trace elements and Sr–Nd–Pb isotopes, as well as zircon trace elements and δ¹⁸O–Hf isotopes, indicate that these volcanoes formed from extremely low (<1%) degrees of partial melting of a fertile, metasomatized mantle source with a clear enriched-mantle affinity, distinct from the Réunion plume signature.

The MASC is synchronous with the main Réunion hotspot track, from the Deccan Traps (67–65 Ma) to Réunion Island (5–0 Ma), and converges toward the current apex of the Réunion plume. The chain also lies along the boundary of an uplifted region in the Mascarene Basin, interpreted as resulting from plume-related buoyancy forces. We therefore propose that the MASC represents a secondary track of the Réunion hotspot, generated by the indirect action of the plume uplifting the Mascarene lithosphere. The progressive convergence of volcanism is consistent with a decreasing radius of influence as the plume waned. Our results further suggest that secondary hotspot tracks are generated by plume-induced upper-mantle melting, rather than by compositional heterogeneities within the plume source.

How to cite: Famin, V., Révillon, S., Danišík, M., Sauter, D., Zaragosi, S., Beaufort, L., Ricci, J., Quidelleur, X., Robert, B., de Bernardy de Sigoyer, A., Schmitt, A. K., Olierook, H., Seghi, J., Eude, A., Vinet, N., Leroy, S., Nauret, F., Michon, L., and Bachèlery, P. and the MASC Team:  A second track of the Réunion hotspot in the Mascarene Basin , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4542, https://doi.org/10.5194/egusphere-egu26-4542, 2026.

Petit-spots are volcanoes with relatively small volumes of magma production found on the seafloor of subducting plates (Hirano et al., 2006, Harmon et al., 2025). Geochemical observations suggest petit-spots are derived from low-degree asthenospheric melts with a crustal and/or carbonatitic component (Mikuni et al., 2024), while others suggest additional interaction with metasomatic zones during migration (Buchs et al., 2013). Their occurrence near the outer-rise region, where plate bending generates extension at the base of the lithosphere and compression at the top, suggests creation of fast melt pathways through otherwise cold, thick lithosphere (Hirano et al., 2006). However, the extent to which flexure-induced stresses influence melt migration, especially in a lithosphere with strong rheological contrasts, remains poorly quantified. 

Here, we use numerical models of melt transport across the brittle–ductile transition (Li et al., 2023, 2025, Pusok et al., 2025) to investigate how plate flexure influences melt transport that facilitates petit-spot volcanism. Flexure is introduced in our models through prescribed boundary loading, producing depth-dependent compression and extension separated by a neutral surface. We systematically test how the magnitude of bending, the position of the neutral surface, hydraulic and rheological parameters influence the style of melt transport, melt focusing and melt ascent efficiency. We demonstrate that extensional stresses at the base of the lithosphere can localise melt into efficient ascent pathways that traverse the overlying compressional domain. Conversely, strong rheological contrasts near the brittle–ductile transition can divert melt laterally and accumulate melt at interfaces, limiting flux to the surface despite extension at the base of the lithosphere. This work provides a quantitative basis for understanding when flexure promotes upward melt transport versus trapping melt at rheological interfaces within the oceanic lithosphere.

References 

Buchs et al. (2013). Low-volume intraplate volcanism in the Early/Middle Jurassic Pacific basin documented by accreted sequences in Costa Rica. G-cubed 14, doi:10.1002/ggge.20084.

Harmon et al. (2025). Evidence for petit-spot volcanism in the Puerto Rico Trench. GRL 52, doi:10.1029/2024GL114362.

Hirano et al. (2006) Volcanism in response to plate flexure. Science 313, doi:10.1126/science.1128235.

Li et al. (2023), Continuum approximation of dyking with a theory for poro-viscoelastic–viscoplastic deformation, GJI, doi:10.1093/gji/ggad173.

Li et al. (2025), Models of buoyancy-driven dykes using continuum plasticity and fracture mechanics: a comparison, GMD 18, doi:10.5194/gmd-18-6219-2025.

Mikuni et al. (2024) Contribution of carbonatite and recycled oceanic crust to petit-spot lavas on the western Pacific Plate, Solid Earth 15, doi:10.5194/se-15-167-2024.

Pusok et al. (2025). Inefficient melt transport across a weakened lithosphere led to anomalous rift architecture in the Turkana Depression. GRL 52, doi:10.1029/2025GL115228.

How to cite: Repac, M. and Pusok, A.: Plate Flexure Control on Melt Transport in the Oceanic Lithosphere: Implications for Petit-Spot Volcanism, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14759, https://doi.org/10.5194/egusphere-egu26-14759, 2026.

The Reykjanes Peninsula (RP), or rather its volcanism, could be seen as a transition from the ocean ridge volcanism of the Mid-Atlantic Ridge to the hot spot volcanism of the Iceland Plume. Historic volcanic activity in the RP suggest a roughly 1200 year volcanic cycle during which all main volcanic systems there are active periodically during a longer time span of approximately 400 years. These volcanic periods are followed by volcanic quiescence lasting about 800 years. A prospect for the RP is thus intermittent volcanism there for the coming decades, or even centuries. Key to understanding the ongoing eruptions in the RP is to understand where the magma comes from and how it is transported through the crust. This is also important for predicting which systems are likely to erupt in the near future. We show by analyzing the seismicity and with seismic tomography that the magma first erupted on the 19 March 2021 came from a reservoir below 9 km depth in the Fagradalsfjall Volcanic Lineament (FVL). Two eruptions in the same region during 2022 and 2023 followed. In late 2023 volcanism shifted about 4 km to the west to the Sundhnúkur Volcanic Lineament (SVL). Geodetic data has shown that magma accumulated in a shallow reservoir (at about 4-5 km depth) below the Svartsengi geothermal power plant prior to the eruption. Continuous geodetic monitoring shows the inflation of this reservoir between the nine eruptions that has occurred in the SVL since then. An outstanding question is if there is a common source for this magma, and where it is located. Again, with studying the seismicity and refining the tomographic model we show that magma feeding the reservoir beneath Svartsengi is coming from the same source located beneath the FVL where the first three eruptions occurred. This suggest that the two volcanic lineaments (FVL and SVL) are connected, and the system is in fact a two-chamber system. For furthering our understanding of magma transport through the crust to eruption it is important to have good knowledge of geometry of the magma plumbing system, level of major storage zones and the recurrence history of magma injection pulses.

How to cite: Tryggvason, A., Thordarson, T., Höskuldsson, Á., Troll, V., and Burjanek, J.: Recent volcanism on the Reykjanes Peninsula, Iceland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18154, https://doi.org/10.5194/egusphere-egu26-18154, 2026.

The Higher Himalayas in Sikkim consist of two-mica leucogranites (2mg), tourmaline leucogranites (Tg), and pegmatites. The leucogranites in North Sikkim intrude the Higher Himalayan Sequences (HHS). In this study, we present the first systematic dataset of whole-rock oxygen isotopic compositions for Higher Himalayan leucogranites from Sikkim, providing insights into their magmatic sources and evolution. Oxygen isotope measurement was accomplished using bulk fluorination and isotope ratio mass-spectrometry, and the oxygen isotope ratios (δ¹⁸O) were measured relative to Vienna Standard Mean Ocean Water (VSMOW). The analyses were calibrated against international standards NBS-28 (quartz). The two-mica leucogranites (7 samples) are characterized by biotite and muscovite, exhibit a mean δ¹⁸O_W.R value of 9.6 ± 1.7‰, whilst tourmaline leucogranites (3 samples), characterized by the presence of tourmaline, yield a mean δ¹⁸O_W.R value of 11.6 ± 3.9‰. The variations in δ¹⁸O values possibly reflect the originally distinct δ¹⁸O signatures of the source sediments, which were moderated by diffusive exchange during diagenesis and metamorphism (France-Lanord et al., 1988). The higher δ¹⁸O values observed in leucogranite samples may be attributed to the pelite-rich sediments, and the lower δ¹⁸O values can result from metagreywacke source or due to the presence of epidotized calc-silicates.

How to cite: Srivastava, T., Harris, N., Spencer, C., Mottram, C., and Wanjari, N.: Oxygen Isotopic composition of Higher Himalayan Leucogranites from the Sikkim Himalaya, India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3120, https://doi.org/10.5194/egusphere-egu26-3120, 2026.