Orals: Thu, 7 May, 14:00–15:45 | Room K1
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 δ¹⁸OW.R value of 9.6 ± 1.7‰, whilst tourmaline leucogranites (3 samples), characterized by the presence of tourmaline, yield a mean δ¹⁸OW.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.
Posters on site: Thu, 7 May, 16:15–18:00 | Hall X2
Intraplate volcanism occurring far from active plate boundaries is commonly attributed to mantle plumes or lithospheric stress reorganization. However, several oceanic rises exhibit magmatic histories that challenge these conventional models. The Conrad Rise in the southern Indian Ocean represents a particularly enigmatic case of oceanic plateau formation. The Conrad Rise was previously interpreted as a Late Cretaceous oceanic plateau, but its origin and magmatic evolution remained poorly constrained.
Recent geochronological and isotopic analyses of volcanic rocks from the Conrad Rise (Sato et al., 2024) have significantly revised this perspective. 40Ar/39Ar dating demonstrates that the primary volcanic edifices formed during distinct intraplate episodes in the middle–late Eocene (~40 Ma) and late Miocene (~8.5 Ma), significantly younger than the surrounding oceanic lithosphere (ca. 84 Ma). Furthermore, the Sr–Nd–Pb–Hf isotopic signatures cannot be explained by a single depleted mantle or plume-derived source and instead indicate contributions from enriched reservoirs, including components consistent with lower continental crust compositions.
In addition to these volcanic constraints, dredging at the Conrad Rise has recovered granitoid and high-grade metamorphic rocks with clear continental affinities. These rocks record Proterozoic to early Paleozoic crustal histories comparable to those of the Gondwana terranes in East Antarctica and eastern India. The occurrence of continental-derived rocks in such a remote offshore setting recalls similar observations from the Rio Grande Rise in the South Atlantic. While alternative explanations, such as iceberg-rafted debris, must be considered, the size, abundance, and lithological diversity of the recovered rocks, together with the geochemical signatures of the associated volcanism, collectively suggest the involvement of continental material within or beneath the rise.
We propose that the unusual episodic intraplate magmatism of the Conrad Rise may result from interactions between mantle upwelling and inherited lithospheric heterogeneity associated with continental components. This “hotspot-less” model, distinct from classical plume-head- or ridge-related mechanisms, drives episodic melt generation and compositional diversity, underscoring the critical influence of inherited lithospheric structures on offshore intraplate volcanism.
How to cite: Sato, H., Machida, S., Ishizuka, H., Fujii, M., Sato, T., and Nogi, Y.: Unusual intraplate volcanism at the Conrad Rise, Indian Ocean: the role of inherited continental lithosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6224, https://doi.org/10.5194/egusphere-egu26-6224, 2026.
Relatively low degrees of partial melting of the non-convecting subcontinental lithospheric mantle (SCLM) typically produces a low-silica melt enriched in magnesium, iron, and calcium. When in route towards the shallow crust, they may interact with rocks of the whole lithospheric column including the uppermost sections of the mantle and continental crust, inducing substantial modifications to its chemical composition. This interaction, characterized by chemical disequilibrium, usually results in assimilation through partial (or complete) melting and/or mineral reactions between the melt and the country rock. Numerous experimental studies have been conducted to characterize these processes; however, natural examples are also essential for elucidating them. A clear example of this crustal rock assimilation by mantle-derived basalts leading significant variations of chemistry is observed in the Morrón de Villamayor volcano, belonging to the Campos de Calatrava Volcanic Field (Ciudad Real, Spain). This volcanic edifice originated ca. 7.4 million years ago is mainly composed by ultrapotassic alkali basalt (SiO2 39.87-40.89 wt% and K2O 3.52–4.41 wt%) and consist of dark gray, hipocrystalline, inequigranular and medium-fine-grained volcanic rocks made up of large olivine phenocrysts (Fo=72.08–80.49) with and small clinopyroxene (diopside) microphenocrysts light green (Wo=50.18–53.29; En=44.91–46.38; Fs=1.78–3.42), surrounded of K-Na-rich feldspathoid microliths (leucite and nepheline), clinopyroxenes microliths and small inclusions of ilmenite and titanite. The presence of foids and the enrichment in sodium and potassium indicate that magmas were silica undersaturated basalt. These alkali basalts have abundant white quartzite (cortical) xenoliths, which shown mm to cm reaction rims. The rims are composed of zoned clinopyroxenes, the core of diopside (Wo= 50.13–51.74; En= 44.89–48.67; Fs= 0.30–4.96) with greenish Na-rich rims (aerigine-augite, Q= 71.06–86.31; Ae= 21.99–27.41; Jd= 0.89–1.55), Al-rich saponite (Al2O3 9.38–12.74 wt%), quartz, carbonates, and potassium feldspars (sanidine). The reaction zone produces also olivine alteration by iddingsite (denoting the highly oxidizing character of the environment). In addition to the drastic mineralogical changes, the reaction zone is characterized by depletion in potassium and enrichment (oversaturation) in silica.
Funding
This research was supported by the Autonomous Community of Valencia through the CIAICO/2023/179 project.
How to cite: Campos-Gómez, M., Blanco-Quintero, I. F., and González-Jiménez, J. M.: Direct evidence of crustal contamination of mantle-derived alkaline magma in the Campos de Calatrava Volcanic Field (SW Spain), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11401, https://doi.org/10.5194/egusphere-egu26-11401, 2026.
The Longgang volcanic field (LVF), one of the most active volcanic areas in Northeast China, is a continental monogenetic volcanic zone located about 100 km west of the Tianchi volcano in the Changbaishan volcanic field. Since the Early Pleistocene, the LVF has experienced multiple eruptive episodes from several centers, forming over 160 spatter cones, scoria cones, and maar lakes. The most recent eruption occurred around 1,700 years ago at the Jinhongdingzi (JLDZ) volcano, which produced a subplinian-style eruption. The LVF is bounded by the NNE-trending Dunhua-Mishan and Yalyjiang faults, with the Hunjiang fault also transecting the area.
The region exhibits significant seismic activity and rapid surface uplift, particularly in its northeastern part. Seismicity has been shallowing over time, suggesting a potential link to deep magmatic processes.
Using GNSS and leveling data, we investigated three-dimensional crustal movements. Horizontal velocities relative to the Eurasian plate are generally below 10 mm/year toward the southeast. Stations east of the Dunhua-Mishan fault show postseismic effects from the 2011 Tohoku earthquake. The fault currently displays extensional behavior. Vertical motion has been dominantly uplift over the past 60 years, consistent with InSAR observations from 2014–2019 in the Jingyu area.
Magnetotelluric profiling reveals a crustal high-resistivity structure beneath the LVF, interpreted as solidified magma. These bodies vary in depth: >18 km in the west, shallowest beneath JLDZ, >40 km in the central region (early volcanic centers), and >20 km near Fusong in the east. A large-scale low-resistivity zone beneath these high-resistivity bodies is interpreted as a mid-to-lower crustal magma system. Notably, a low-resistivity anomaly below 10 km beneath JLDZ likely represents a magma conduit connected to the deeper system. The eastern magma source is relatively shallow (~30 km). We propose that mantle upwelling and intermittent magma migration contribute to the observed uplift and seismicity in the LVF.
How to cite: Hu, Y., Zhao, L., Zhang, W., Liu, C., and Zhuang, W.: Analysis of Deformation Characteristics and Uplift Mechanism in the Longgang Volcanic Field, China, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1714, https://doi.org/10.5194/egusphere-egu26-1714, 2026.
We present results from a magnetotelluric (MT) study conducted as a pilot project, investigating the electrical structure of the partial melt at the crust-mantle boundary beneath central Iceland. With an ongoing thinning of the Vatnajökull ice cap, located above the mantle plume head, the lithosphere experiences uplift and decompression. Due to the unloading, the promotion of partial melting in the upper mantle is expected, potentially increasing volcanic activity. This partial melt zone in the asthenosphere generates a conductive zone that long-period MT methods can detect. These results could provide new perspectives on partial melt at the crust-mantle boundary beneath Iceland, complementing existing seismic and gravity observations, and contributing to the discussion of plume-lithosphere interactions.
Long-period MT data were acquired during a field campaign in August-September 2025 along a ~200 km east-west profile, perpendicular to the plate boundary, with ~50 km station spacing. Time-series data from four stations were processed using single-station and remote-reference techniques following the Frankfurt MT (FFMT) software in MATLAB. The preliminary results show two conductive layers, one indicating the deep conductive layer at depths of 5-20 km, previously identified in Icelandic MT studies. A second, deeper low-resistivity zone is observed and interpreted as a possible signature of the crust-mantle transition or partial melt accumulation in the upper mantle. 3D forward models of the data will be conducted to display how the responses would change with anomalies at different depths. In addition, a literature study on the petrophysical properties of magma in porous rocks will be carried out to constrain our interpretations, linking resistivity and porosity under varying pressure and temperature conditions. Together, these results will evaluate whether a decompressional-induced partial melting beneath central Iceland is detectable using long-period MT methods, with implications for mantle plume dynamics.
How to cite: Sverrisdóttir, E. B., Kalscheuer, T., Árnason, K., Junge, A., Kiyan, D., and Tryggvason, A.: Magnetotelluric Imaging of the Upper Mantle Conductivity in Iceland: Investigating Signs of Partial Melt Due to Glacial Uplift, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19957, https://doi.org/10.5194/egusphere-egu26-19957, 2026.
Complete images of magma plumbing systems are fundamental for understanding volcanic activity. Earthquake hypocenter distributions, their migration, and geodetically inferred pressure sources provide valuable constraints, but these dynamic signals are usually spatially localized and temporally short-lived (days to tens of years). In contrast, petrological and geophysical studies often image large trans-crustal magma plumbing systems beneath volcanoes, inferred to occupy volumes of ~1000 km³ and to develop over the long lifetime of a volcano. This discrepancy highlights a key gap between short-lived, small-volume magma involved in unrest and eruptions (<0.1 km³) and long-lived, large-scale magmatic reservoirs.
To bridge this gap, we integrate recent geophysical observations at active volcanoes in Japan and propose a unified magma plumbing framework linking long-lived and short-lived magmatic processes. We present electrical resistivity structures beneath Kirishima, Sakurajima, and Hakone volcanoes derived from dense broadband magnetotelluric (MT) observations. All three volcanoes have experienced significant crustal deformation, seismicity, and eruptions within the past 15 years.
Beneath each volcano, inclined columnar-shaped conductive bodies with volumes exceeding ~1000 km³ are imaged beneath active craters, extending from depths of a few kilometers to the lower crust. Common features include: (1) tectonic earthquake hypocenters are largely distributed outside the conductive bodies, and (2) geodetically inferred pressure sources and deep low-frequency earthquakes are concentrated along their edges. At Kirishima volcano, the conductor geometry corresponds closely to a low-VSV region imaged by surface-wave tomography. At Sakurajima volcano a magmatic dike intrusion on 15 August 2015 occurred near the top of the conductor.
We interpret the large conductive bodies as long-lived magmatic reservoirs dominated by crystal mush, within which sill complexes are developed. In contrast, small and transient magma pockets likely form along reservoir margins. We propose an edge-ascent model in which magma and volatiles preferentially migrate along conductor boundaries, feeding normal small eruptions, whereas magma stored in the large reservoirs may only be mobilized during large eruptions.
How to cite: Aizawa, K., Koyama, T., Uyeshima, M., Muramatsu, D., and Shigematsu, H.: Linking Long-Lived and Transient Magma Plumbing Systems Beneath Volcanoes Using Dense Magnetotelluric Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3753, https://doi.org/10.5194/egusphere-egu26-3753, 2026.
Extensive magmatism and the formation of Large Igneous Provinces (LIPs) along continental margins are commonly attributed to anomalously high mantle temperatures and/or mantle fertility, such as plume activity. However, the role of lithospheric strength in controlling magmatic productivity remains poorly explored. Using 2-D thermo-mechanical numerical models, we identify a new mechanism for syn-breakup magmatic surges that does not require anomalous mantle properties. Instead, enhanced asthenospheric upwelling is triggered by the gravitational collapse of elevated rift flanks, a process that occurs only when lithospheric strength is sufficiently high. Multidisciplinary observations from the Labrador Sea–Baffin Bay rift system—including tectonic, magmatic, and geophysical constraints—are consistent with this mechanism and link excessive magmatism to a strong lithosphere. Our results highlight the overlooked influence of lithospheric strength on melt production rates during rifting and continental breakup. This study offers a complementary framework for understanding volcanism and LIP formation along continental margins, without requiring anomalously hot or fertile mantle, while not excluding such contributions where independently supported.
How to cite: Wang, S. and Leng, W.: Breakup of strong cratonic lithosphere causes extensive magmatism by rift shoulder subsidence, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5200, https://doi.org/10.5194/egusphere-egu26-5200, 2026.
Louisville Ridge in the southwest Pacific Ocean is a ~4200-km-long chain of submarine volcanoes generated at a hotspot presently located between the Heezen and Tula Fracture Zones, ~550 km northwest of the Pacific-Antarctic spreading ridge. Swath bathymetry surveys reveal the Louisville Ridge comprises seamounts, a number of which are guyots and so were once ocean islands. Seamount age increases progressively along the ridge, such that the youngest (unnamed) seamount is near the Pacific-Antarctic ridge while the oldest, Osbourn (~77-81 Ma), is located near the intersection of the ridge with the Tonga-Kermadec trench. Plate kinematic studies show a) the smooth trend of the ridge is copolar with the Hawaiian-Emperor seamount chain in the northwest Pacific Ocean, b) the ages at the main bends in the two chains are similar (~47 Ma), c) the difference in distance between same age seamounts in the two chains and the expected distance based on their present hotspot separation is small (±2°) and, d) the Pacific plate as a whole has behaved rigidly for at least the past 50 Myr as it migrated northwest over fixed the Hawaii and Louisville hotspots. Studies of plate rigidity immediately beneath the Louisville Ridge, however, have yielded conflicting results. Previous studies suggest the elastic thickness, Te, a proxy for the long-term flexural rigidity of the plates, is relatively high north of the main bend (~20-22 km) and relatively low (~16-18 km) to the south. However, seismic refraction data acquired north of the main bend along a ‘dip’ line during SONNE cruise SO195 at the 27.6° S seamount yielded a low Te (~10 km). Here, we use seismic refraction data acquired north of the bend along a ‘strike’ line, Profile C, during SONNE cruise SO215, together with ~1900 estimates of Te derived from gravity data, to show that Te is indeed low (6-10 km) at the northern end of the Louisville Ridge and then increases to ~26 km in the vicinity of the main bend at distance ~1309 km. These observations are consistent with the hypothesis that Te is dependent on age, and hence thermal structure of the Pacific plate, at the time of volcano loading. However, the isotherm that controls Te (276±10oC) along the whole ridge is lower than at the Hawaiian-Emperor seamount chain (336±18 oC) and, interestingly, the bend-fault region of the proximal Tonga-Kermadec trench – outer rise system (342±35oC). We examine here the implications of a ‘weak’ zone within an otherwise rigid Pacific plate for deformation models of brittle and ductile flow at lithospheric conditions based on extrapolations of data from experimental rock mechanics and for subduction initiation models where large downward flexures (up to 3.7 km) of oceanic and mantle crust may extend some thousands of km from a trench almost to a ridge.
How to cite: Xu, C. and Watts, A.: Gravity and seismic constraints on plate flexure and mantle rheology along the whole Louisville Ridge, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5032, https://doi.org/10.5194/egusphere-egu26-5032, 2026.
The Cerro de Agrás volcanic cone (Cofrentes, Spain) is a ~2 Ma monogenetic effusive edifice, approximately 1 km wide and ~100 m high. It is dominated by pyroclastic deposits with subordinate meter-sized fragments of alkali basaltic lava, such as spatter flows, suggestive of a Strombolian eruptive style. The alkali basalts are aphanitic and display a porphyritic texture, with prevailing olivine as phenocrysts partially altered to iddingsite. The alkali basalts host small (0.5-4 cm) rounded-to-irregularly shaped ultramafic xenoliths of medium-grained spinel lherzolites with a protogranular texture, characterized by coarse olivine and orthopyroxene crystals (2–3 mm) and finer clinopyroxene and spinel grains (250–300 µm). Olivine shows homogeneously high Mg# [(Mg/Mg+Fe) = 0.90 to 0.94], whereas clinopyroxene diopside display slightly lower Mg# (0.91 to 0.92) and low Al (0.16-0.22 apfu) but noticeable Ca (0.85 to 0.95 apfu). Orthopyroxenes are enstatites with Mg# varying from 0.90 to 0.94. Spinels are Al- and Mg-rich, with Al# (Al/(Al+Cr)) ranging from 0.77 to 0.79 and Mg# ranging from 0.69-0.77. Thermobarometric calculation using the mineral compositions suggests temperatures between 1100 to 1150 °C and pressures ranging 15 to 18 kbar; very likely related with partial melting at ca. 50 km depth. Typically, the rims of the xenoliths, exhibit spongy textures where orthopyroxene is partially replaced by olivine + clinopyroxene. Here, newly-formed olivine grains yield lower Mg# 0.77-0.88 wheras clinopyroxene is augite with lower Ca (0.56 -0.83 apfu) and Mg# (0.95 to 1.00). These features seem to suggest the reaction of preexisting orthopyroxene with a non-equilibrium incoming host alkali basalt during xenolith ascent to surface.
How to cite: Blanco-Quintero, I. F., Campos-Gómez, M., García-Martínez, N., Benavente, D., Cañaveras, J. C., and González-Jiménez, J. M.: Orthopyroxene breakdown at lherzolite–melt contacts, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18824, https://doi.org/10.5194/egusphere-egu26-18824, 2026.
An increasing number of studies identify craton boundaries marked by the transitions from thick to thin lithosphere as favorable regions for magmatism-derived mineralization. Similarly, numerous Cenozoic intraplate volcanic provinces are clustered or aligned with thick-to-thin lithosphere transitions, as observed in the Circum-Mediterranean region.
Proposed explanations for the origin of this magmatism invoke mantle flow patterns modulated by lithospheric steps or lithosphere-asthenosphere boundary (LAB) topography. These steps have been proposed to trigger edge-driven convection patterns potentially leading to decompression melting. Other hypotheses suggest that asthenospheric flow guided by LAB topography and directed toward adjacent thinner lithosphere produces decompression melting. However, recent studies suggest that these mechanisms are inefficient in generating long-lived high-volume magmatism.
This presentation explores convection patterns associated with thick-to-thin lithosphere transitions and investigates how they are modulated by asthenospheric thermal anomalies and/or extensional boundary conditions. We use numerical two-dimensional thermo-mechanical modelling to explore combined scenarios including variable buoyancy of the continental root, upwelling of mantle plumes, and distributed asthenospheric heating. The impact of each setting on mantle flow and melt production is assessed using the ASPECT open-source code, which employs a visco-plastic formulation. Preliminary results indicate that anomalous asthenospheric heating, likely associated with secondary mantle plumes, strongly enhances magmatism near the transition to thick lithosphere.
How to cite: Rodríguez-Batista, M. P., Negredo, A. M., and Pastor-Galán, D.: Magmatism at Thick–Thin Lithosphere Transitions: Mantle Flow and Melt Generation from Numerical Modelling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5108, https://doi.org/10.5194/egusphere-egu26-5108, 2026.
Magmatism along divergent continental margins is mainly controlled by adiabatic decompression induced by the divergent motion of the continental lithosphere and the consequent upwelling of the asthenospheric mantle. Additionally, the mantle potential temperature, fertility, and volatile content also affect the rate of magmatism. Due to the complexity of the geodynamic evolution of the margin with the concomitant magmatism, the use of numerical models represents an appropriate approach. To quantify the rate of magmatism through time, since the onset of lithospheric stretching, during and after the rifting phases, we performed a series of numerical simulations considering different stretching rates, rheological structures for the lithosphere and mantle potential temperature. To perform the numerical simulations, we used the thermomechanical numerical code Mandyoc, considering recent implementations of calculation of melt fractions, incorporation of latent heat in the energy conservation equation, and influence of melt depletion on density and viscosity. The volume of magmatism obtained in the numerical simulations is compared with different segments of the Brazilian margin with variable degree of magmatism, based on interpreted seismic data published for these portions of the continental margin.
How to cite: Monteiro e Silva, M., Sacek, V., and Macedo Silva, J. P.: Rate of magmatism as a function of stretching rate and mantle potential temperature during and after continental rifting: insights from thermomechanical numerical models , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14011, https://doi.org/10.5194/egusphere-egu26-14011, 2026.
Intraplate volcanic events provide important insights into the dynamic evolution of the Earth's interior. In the ocean, an age-progressive seamount chain is traditionally attributed to the lithosphere moving over a stationary mantle plume. However, many seamounts are spatially scattered without clear age progression, and their relationships to deep mantle processes remain contentious. Here we argue that all seamounts, either with or without age progression, were produced by deep plume-related activities. By developing high-resolution mantle convection models with data assimilation, we predict the present mantle plume structures consistent with recent seismic tomography. In addition, we reproduce the age trends of major hotspot tracks since the Cretaceous. In our model, most Cretaceous seamounts in the Pacific Ocean formed above major plume heads ponding beneath the young oceanic plate, where the resulting hotspot zones fueled widespread intraoceanic volcanism without age progression. Subsequently, the aging and expanding Pacific plate covers more plume conduits from the shrinking neighboring plates, forming the observed Cenozoic age-progressive hotspot tracks above the narrow plume tails. We further show that the widespread and long-lived residual thermal anomalies, which we refer to as seamount brewing zones, eventually form small-volumed seamounts far away from hotspots.
How to cite: Dong, H., Cao, Z., Li, Y., Liu, L., Li, S., Liu, J., Dai, L., and Zhu, R.: Seamounts Formation due to Deep Mantle Plume Heating, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8571, https://doi.org/10.5194/egusphere-egu26-8571, 2026.
