Orals: Wed, 30 Apr | Room 0.16
Phanerozoic intraplate magmatism has frequently been observed in association with ancient sutures, palaeorifts and strike-slip fault zones across multiple ancient cratons, including Laurentia, Baltica, Australia, Siberia. However, it is still unclear whether these lithospheric discontinuities were passive conduits for the melts generated in the asthenosphere, or if their tectonic reactivations acted as a primary control on melt production and distribution. In the Superior province of the Canadian shield, we explore the relationship between intraplate tectonic and magmatic activity along two segments of the Proterozoic St. Lawrence failed rift system, which hosts two Jurassic kimberlite fields (Kirkland Lake, Timiskaming) and a Cretaceous alkaline province (Monteregian Hills). Our goals are 1) to examine the structural settings of these provinces and 2) investigate the potential role of these lithospheric structures in melt production and channelling under the Mesozoic stress regime.
Basement fault structures associated with kimberlite pipes and alkaline intrusions were identified using available aeromagnetic data from Timiskaming and Montérégie. Magnetic data were employed to construct a constrained 3-D inversion of the magnetic susceptibility distribution using Oasis montaj VOXI software package. Additionally, the regional stress field in the Superior province in the Mesozoic was reconstructed based on 542 measurements of joints, shear fractures, veins and dykes taken at 36 sites across the Palaeozoic cover of St. Lawrence lowlands. The Right Dihedron and Rotational Optimisation methods implemented in WinTensor 5.9.2 were used to compute stress tensors for structural associations of different relative ages.
The results demonstrate that Kimberlite pipes of the Timiskaming and Kirkland Lake fields tend to cluster around the intersections of two fault families: 1) thrust faults of Neoarchean Destor-Porcupine and Esker – Larder Lake sutures (trending W–E), and 2) normal faults of the Proterozoic Timiskaming graben (trending NNW – SSE). Intrusions of the Monteregian Hills alkaline province are also emplaced at the intersection of two fault families: 1) normal faults of the Proterozoic Ottawa – Bonnechere graben (trending W–E), and 2) a N–S trending set of faults of unclear kinematics or age. Reconstructed stress tensors for the Mesozoic are indicative of an extensional regime and a progressive counter-clockwise rotation of the stress-field throughout the Mesozoic (subhorizontal σ3 trend shifts from 86 to 306).
The spatial distribution of intrusions within the Timiskaming and Ottawa-Bonnechere grabens, indicates that intraplate magmatism was strongly controlled by St. Lawrence paleorift structures. However, intrusions are preferentially localized in areas where the paleorift is intersected by other fault systems. We speculate that these local fault systems are transfer faults oriented perpendicular to the normal faults of St. Lawrence system, creating pull-apart-like structures that accommodated intraplate magmatism. This emplacement model aligns with geochronological data, which indicate Jurassic intrusions of the Timiskaming and Kirkland Lake fields were emplaced along NNW–SSE-trending graben under a SW–NE trending σ3 , while the Cretaceous Monteregian Hills were emplaced along the W–E-trending Ottawa–Bonnechere graben under a N–S trending σ3.
How to cite: Koptev, E., Peace, A., and Boyce, J.: Tectono-magmatic reactivation in cratonic settings: a case study from the Superior province, Canada, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-708, https://doi.org/10.5194/egusphere-egu25-708, 2025.
The Miocene epoch on Svalbard is characterized by volcanic activity and tectonic uplift, but the causes and relationship between these two processes remain debated. The evidence of coeval basaltic magmatism has probably affected a large area including Svalbard. The Seidfjellet Formation, a series of basaltic lava flows, represents a unique late Miocene subaerial magmatic event (5–10 Ma) in northwestern Spitsbergen. These flows, covering more than 200 km2, are exposed on top of numerous mountains in Andrée Land overlying Devonian sedimentary rocks. This study investigates the structure, composition and origin of this underexplored igneous province within a tectonomagmatic context, focusing on defining the magnitude, paleoenvironment, and chronology of the volcanism and contributing to our understanding of the Miocene evolution in Svalbard and adjacent Arctic regions.
In the summer of 2023, we systematically mapped and sampled (n = 83) well-exposed outcrops along Woodfjorden, logging basaltic lava flows from an elevation of approximately 600 to over 1000 m above sea level. Additionally, we acquired photospheres and photographs using unmanned aerial vehicles (UAVs). Photographs were processed to obtain high-resolution georeferenced digital outcrop models (DOMs) for systematic mapping of the Seidfjellet Formation and its relationship with the pre-basal emplacement paleosurface. To enhance the consistency of our dataset, 13 legacy samples collected in 2014 were analyzed for standard geochemical characterization, including major and trace element concentrations, isotopic ratios, and 40Ar/39Ar age determination.
The mapped lava flow sequences have variable thicknesses, with 400 m being the observed local maximum, indicating significant magma accumulation. A massive 50 m thick olivine-rich sheet-flow unit is present in the lower part of the formation. Locally, a distinct hyaloclastic unit documents subaqueous lava emplacement. In contrast, the upper sections provide clear evidence of subaerial emplacement, with pahoehoe lava flow features. The interpretation of DOMs, the distribution of the lava flows as well as GIS-based thickness and volume estimates suggest that the igneous province extends more widely than what is evident from the existing remnant outcrops. The Seidfjellet Formation shows variable sediment-basalt transitions, including sharp valley infill profiles and erosion surfaces above Devonian sandstones. Thickness estimates and remnant outcrop distributions point towards an eruption center near Scott Keltiefjellet, where hyaloclastites and dolerite layers are also exposed. Geochemical analysis reveals both silica-saturated 'tholeiitic' and silica-undersaturated 'alkaline' magmas, with isotopic evidence of crustal-contaminated mantle-derived magmas, reflecting a complex geological setting. Six Ar/Ar ages document a timespan of over 1 million years between 8 and 10 Ma, whereas one sample has an age of about 5 Ma refining earlier estimates.
The Seidfjellet Fm. represents the only subaerial expression of Miocene volcanic activity in Svalbard. Linking this event to similar and coeval features in the Arctic, both in terms of geochemistry and paleoenvironmental studies, provides an opportunity to identify a significant magmatic event potentially linked to the region's vertical motion history.
How to cite: Telmon, M., Betlem, P., Grundvåg, S. A., Kenji Horota, R., Minakov, A., Planke, S., Senger, K., Tegner, C., and Zastrozhnov, D.: The Seidfjellet Formation in NW Spitsbergen: A Window into Miocene Volcanism and Tectonics of Arctic-Atlantic Gateway , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3700, https://doi.org/10.5194/egusphere-egu25-3700, 2025.
The Northeast Atlantic Igneous Province (NAIP) formed during the Paleocene/Early Eocene, driven by the Iceland hotspot. Its volcanic margins show a positive correlation between igneous thickness (H) and lower-crustal P-wave velocity (VP), indicating that high-temperature is driving excess mantle melting. However, previous studies have argued for large variations in structure and magmatic volumes between the conjugate margins of the Vøring Plateau and East Greenland, and there are inconsistencies in defining the conjugate continent-ocean transition zones (COTs). In this study, we use the H-VP correlation from various wide angle seismic studies, where a positive trend identifies igneous crust, while a rapid transition to a strong negative trend marks the increased presence of continental crust to redefine the COTs on conjugate Vøring Plateau and East Greenland margins. This definition gives consistent COTs in plate reconstruction to opening. Our results show that the total magmatic volume of the East Greenland margin (8.23 × 10⁵ km³) is only slightly larger than for the Vøring Plateau (7.51 × 10⁵ km³). Later secondary magmatism in East Greenland (Late Eocene to Miocene) occurred during the separation between East Greenland and the Jan Mayen Microcontinent. Assuming symmetric magmatic volumes on each plate after breakup between the East Greenland margin and the Vøring Plateau, the difference can be used to estimate secondary magmatic volume in East Greenland (0.72 × 10⁵ km³), which is less than 10% of the initial breakup magmatism. In addition, other post-breakup mid-to-late Cenozoic events including Logi Ridge, Jan Mayen Plateau, Vesteris Seamount, Jan Mayen Island and Vøring Spur, contribute an estimated total volume of 2.2 × 10⁵ km³. While quite visible, the igneous volume of these events is thus far less than the Early Eocene breakup magmatism.
How to cite: Tan, P. and Breivik, A.: Break up and Post-Breakup Magmatism between the conjugate margins of the Vøring Plateau and East Greenland, NE Atlantic, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4037, https://doi.org/10.5194/egusphere-egu25-4037, 2025.
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 has been attributed to lateral flow of plume material into thin-lithosphere areas, but evidence for such flow is scarce. Here, we use new seismic data and new 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 dramatic 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 has 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.
How to cite: Bonadio, R., Lebedev, S., Chew, D., Xu, Y., Fullea, J., and Meier, T.: Volcanism and long-term seismicity controlled by plume-induced plate thinning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10558, https://doi.org/10.5194/egusphere-egu25-10558, 2025.
Age-progressive volcanic “hotspot” chains result from the passage of a tectonic plate over a deep-rooted thermochemical plume, thereby sampling the otherwise-inaccessible lowermost mantle. A common feature of oceanic hotspot tracks is the occurrence of two parallel volcanic chains. For example, the Hawaiian Loa and Kea chains are separated by a gap of 50 km, and likely sample the same ~100-km wide mantle melting zone. Several other tracks (including Tristan-Gough, Shona, the Wake seamounts, Tuvalu and Cook-Australs) are made up of a double chain with a 200-400 km spacing, but the origin of such widely-spaced double hotspots remains unknown.
Here, we explore 3D Cartesian geodynamic models of thermochemical plume ascent through the upper mantle. We investigate the effects of the lateral distribution of intrinsically-dense eclogitic material across the plume stem on upwelling style. For small eclogite contents, the plume rises as a “classical” columnar upwelling. For a wide range of intermediate eclogite contents in in the plume, the plume spreads laterally in the depth range of 300~410 km, where the excess density of eclogite is greater than above and below, as also predicted by [1]. This “Deep Eclogitic Pool” then splits up into two lobes that feed two separate shallow plumelets, particularly for significantly higher eclogite contents in the center than the periphery of the underlying plume stem. These two plumelets sustain two separate melting zones at the base of the lithosphere, which are elongated in the direction of plate motion due to interaction with small-scale convection. Such a “forked plume” morphology can account for hotspot chains with two widely-spaced (200~350 km) tracks and with long-lived (>5 Myr) coeval activity along each track. Some cases can even account for intermittent tripe-chain hotspot volcanism. Forked plumes may provide an ideal opportunity to study geochemical zonation of the lower-mantle plume stem, because each of the two plumelets robustly samples a distinct sector of the underlying deep plume stem, preserving chemical heterogeneity from the lowermost mantle.
We compare our model predictions to geochemical asymmetry evident along the Wake, Tuvalu and Cook-Austral double-chain segments, which together make up the extensive (>100 Ma) Rurutu-Arago hotspot track. The preservation of a long-lived NE-SW geochemical asymmetry along the Rurutu-Arago double chain indicates a deep origin, likely originating from the southern margin of the Pacific large low shear-velocity province. Our findings highlight the potential of the ocean-island basalt geochemical record to map lower-mantle structure over space and time, thus complementing seismic-tomography snapshots.
[1] Ballmer et al., 2013 (doi:10.1016/j.epsl.2013.06.022)
How to cite: Ballmer, M. and Finlayson, V.: Widely-spaced Double Hotspot Chains due to Forked Plumes sample Lower Mantle Geochemical Structure, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12410, https://doi.org/10.5194/egusphere-egu25-12410, 2025.
The Rodrigues Ridge (Indian Ocean) is a N100°E oriented submarine volcanic structure stretching eastward of the Mascarene Plateau and toward the Central Indian Ridge (CIR). The geodynamic origin of Rodrigues’ volcanism is a matter of debate because the ridge neither follows the track of the Réunion hotspot nor the fabric of the oceanic lithosphere. To decipher the origin of this volcanism, we investigated the construction history of Rodrigues Island (i.e., the emerged portion of the ridge), by means of geomorphology, field observations, geochronology, and geochemistry. The morphology of Rodrigues Island’s slopes, the shape of the coral shelf, and unconformities observed in the field suggest that the island was constructed in two stages, including formation of a subcircular shield edifice, followed by formation of a N070°E ridge. This scenario is confirmed by K-Ar dating of groundmass and (U-Th)/He dating of zircon from volcanic rocks, suggesting that the circular edifice grew from 2.7 Ma to 2.5 Ma. Then, after a ca. 0.3 Myr hiatus and subsidence of the island, volcanic activity resumed from 2.2 Ma to 1.1 Ma, resulting in formation of the present-day ridge shape of Rodrigues Island. These ages are much younger than the unpublished ages ranging from 9.7 to 7.5 Ma reported for submarine volcanic rocks dredged on the flank of the Rodrigues Ridges.
Major/trace element and Sr-Nd-Pb isotopic analyses of the samples further show that the two stages of subaerial volcanism are chemically relatively homogenous, but much more enriched in incompatible elements than samples from the submarine ridge. Rodrigues Island was thus built by rejuvenescent volcanism of the submarine ridge. Available bathymetric and paleomagnetic data show that the Rodrigues Ridge propagates toward the east onto a less than 3 Ma old oceanic lithosphere (Demets et al., 2005) toward the CIR as en-échelon N070°E segments, called the Three Magi and the Gasitao ridges. The subaerial ridge shape of Rodrigues Island may thus belong to this array of en-échelon segments formed in the past 3 Ma.
Collectively, all the pieces of information suggest that the N100°E Rodrigues Ridge grew by protracted volcanism from ca. 10 Ma to ≤7 Ma, then from ca. 3.5 Ma to ca. 1 Ma by the propagation toward the CIR and coalescence of en-échelon N070°E segments of rejuvenated volcanism. Intriguingly, this temporality is coeval with the volcanic activity of Mauritius and Réunion Islands along the track of the Réunion hotspot, and particularly with the rejuvenescent volcanism of Mauritius since ca. 3.5 Ma. This coincidence favors a scenario of Rodrigues volcanism formed by capture of the Réunion plume ascending material by the CIR. We will discuss our results and their implications on the volcanic, structural and geomorphology history of the Rodrigues Ridge.
How to cite: Seghi, J., Famin, V., Quidelleur, X., Gourbet, L., Danisik, M., Nauret, F., Révillon, S., Michon, L., and Arnould, M.: History of the Rodrigues Ridge, Indian Ocean: implications of the Réunion hotspot and the Central Indian Ridge, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12411, https://doi.org/10.5194/egusphere-egu25-12411, 2025.
Hotspots create linear volcanic features on Earth’s crust as tectonic plates migrate over and thus are often used to trace absolute plate motion. The effectiveness of a hotspot reference frame depends on the hotspot’s fixity or constraints on its motion history. Studies of Pacific hotspots revealed distinct hotspot motions that were variously attributed to shallow and/or deep mantle convection processes, but knowledge of hotspot movements elsewhere remains limited. Here we report robust and high-precision 40Ar/39Ar ages for the Ninetyeast Ridge, a >5000-km long linear volcanic ridge generated by the Kerguelen hotspot during the Indian Plate’s northward drift towards Eurasia. New ages suggest changing volcanic progression rates along the ridge, in contrast to a constant rate as previously documented. Combined with independent constraints on the Indian Plate motion and seafloor spreading, we reveal two periods of northward hotspot migration together with the Indian-Antarctic spreading ridge, and two periods of rapid southward motion of the hotspot when it was disconnected from and re-captured by separate spreading ridge segments. These rapidly changing motion histories affected by spreading ridges suggest that mantle plume lateral flows are susceptible to changes in shallow mantle convection processes due to the existence of horizontal ponding zones and vertical conduits as revealed by recent seismic tomography images of mantle plumes.
How to cite: Jiang, Q., Olierook, H., Jourdan, F., Carmona Hoyos, D., Merle, R., Mervine, E., and Sager, W.: Motions of the Kerguelen hotspot constrained by high-precision 40Ar/39Ar ages of the Ninetyeast Ridge, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6674, https://doi.org/10.5194/egusphere-egu25-6674, 2025.
The origin, processes, and significance of intra-plate magmatism have long been debated, with the spotlight predominantly directed to oceanic volcanism. However, on continental margins the mechanisms that can generate or sustain prolonged magmatism throughout vast regions remains puzzling, with hotspot (s.s.), mantle plumes or edge-driven convection being invoked to explain these noteworthy manifestations.
Based on the age of emplacement and the present-day location of the magmatic occurrences, across the Central-East Atlantic Alkaline Province (CEAAP; Southwest Iberian Margin - SWIM, Morocco, Canarias and Madeira), the crustal paleogeographic location of emplacement was investigated. In parallel we analysed their relative motion paths relative to a stationary mantle reference and its associated tectonic plates.
Magmatism in this province, is revealed to be derived from a stationary super-plume ponded at the 660 km discontinuity at least since the late Cretaceous. Additionally, the recent discovery of new magmatic manifestation on the SWIM shows that magmatism in the region is more pervasive than anticipated. Our models indicate that this active mantle upwelling resulted in three main periods of activity and has been responsible for the irregular spatial-temporal distribution of magmatism. As tectonic plates wandered, alkaline magmatism that was initially emplaced within the Southwest Iberian Margin (103-70 Ma), was subsequently affecting continental Morocco (57-45 Ma), Canarias and Madeira (< 32 Ma), resulting in episodic and dispersed intra-plate magmatic activity, both on oceanic and continental crust. We estimate the position of the stationary mantle upwelling located between 20-30ºN and 10-20ºW.
Our models unravel prominent paleogeographic affinities of a common mantle source, linking late Cretaceous SWIM magmatism (e.g., Tore NW, Tore N, Ormonde, Sintra, Monchique) with present day Canarias and continental Morocco (e.g., Taourirt, Rekkame, Tamazert). Contrastingly, the motion paths from the occurrences on the SWIM (e.g., Torillon, Ampère and Unicorn), relate with the more recent magmatism at Madeira. Older magmatism from southern Canarias (e.g., Bisabuelas, Henry, Tropic) is revealed affine to the present-day location of the Sahara seamounts and Cape Verde. Younger magmatism in the High Atlas (e.g., Siroua, Sarrho, Oujda) appears to be as unrelated with the inherited SWIM mantle upwelling.
Results suggest that the intermittent emission of secondary mantle plumes (plumelets) ascended to the crust to form, as a whole, a cluster of dominantly non-aligned magmatism manifestations, including laccoliths, seamounts and volcanoes. Moreover, the spatial-temporal analysis of the magmatism on the CEAAP indicates a relative N-NW rejuvenation of emplacement. This is considered to have resulted from post-Cretaceous induced drag, as the plumelets progressively interacted with the base of the Nubian plate.
Acknowledgments: RP is supported Fundação para a Ciência e a Tecnologia, I.P. (FCT), Portugal, through the research unit UIDB/04035/2020 - GeoBioTec. JCD is supported by an FCT contract CEEC Inst. 2018, CEECINST/00032/2018/CP1523/CT0002.
How to cite: Pereira, R., Araújo, B., Duarte, J. C., and Mata, J.: Tracking a common mantle plume, from Iberia to Canarias-Madeira, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13333, https://doi.org/10.5194/egusphere-egu25-13333, 2025.
Proterozoic massif-type anorthosites are large plutons, predominantly composed of plagioclase, emplaced between 2.7 and 0.5 Ga. The Mesoproterozoic Kunene Complex is the largest massif-type anorthosite complex in the world, with an estimated area of ∼ 42,500 km², emplaced in southern Angola and northern Namibia. Recent geochronological studies on the main lithologies indicate ages between 1.50 and1.36 Ga, with the anorthosite dating between 1.43 and 1.37 Ga.
The anorthosite suite of the Kunene Complex locally hosts irregular pegmatoidal enclaves (a few meters-long, one meter-wide), primarily composed of large grains of orthopyroxene, clinopyroxene, Fe-Ti oxides, apatite, and plagioclase, with minor quartz, zircon, titanite and sulphide. The mineralogy and pegmatitic texture suggest that these enclaves represent evolved residual melts, occurring during the final stages of the liquid line of descent of parental magmas to the anorthosite. However, a U-Pb zircon date at ∼1.50 Ga obtained from an enclave is 60 Myr older than the oldest age measured on the Kunene anorthosite so far.
In this study, we provide new U-Pb dates and mineral trace element chemistry for zircon, apatite, and titanite in a set of enclaves and their direct host anorthosites. Samples were collected in two quarries in the central region of the complex in Angola, where these enclaves are well exposed.
Zircon dates from anorthosites and hosted enclaves range between 1.52 and 1.40 Ga. This establishes the beginning of the Kunene magmatism at around 1.5 Ga, testifies to coeval crystallisation of enclaves and host anorthosite, and indicates a prolonged zircon resetting due to the magmatism extending more than 130 Myr.
Both the subhedral cm-scale apatite observed in the enclaves and the smaller grains (max 200 µm) show textural features suggesting they are primary phases. Their trace element signature (relative enrichment in light rare earth elements) agrees with a magmatic origin. With no Pb loss after crystallisation, the igneous age would have been preserved. However, no ages at 1.5 Ga were documented for apatite, as they range between 1.41 and 1.35 Ga and overlap with the youngest zircon dates. We attribute these ages to partial resetting of the parent-daughter system during prolonged thermal activity and fluid circulation triggered by the long-lived Kunene magmatism, which resulted in apparent or mixed apatite ages.
Titanite in the enclaves crystallised as a secondary phase, appearing as clusters of minute anhedral grains closely associated with other alteration minerals. The U-Pb dates for titanite range from 1.41 to 1.37 Ga, overlapping with those for apatite. Titanite records the greenschist facies assemblages observed in the enclaves, providing key evidence of fluid-rock interactions during the post-magmatic stage.
The prolonged magmatic history of the Kunene Complex testifies to extended interaction between crystallisation processes, thermal reworking, and fluid-induced alteration. The new findings indicate that the enclave and host anorthosite are coeval, place the beginning of the anorthosite magmatism at 1.5 Ga, with metasomatic and thermal overprint at 1.42–1.35 Ga. The new data refine the temporal framework of the Kunene Complex emplacement and provide new fascinating insights into the magma dynamics of massif-type anorthosites.
How to cite: Ngomane, G., Lekoetje, T., Milani, L., Bybee, G. M., Hayes, B., Owen-Smith, T. M., Lehmann, J., and Jelsma, H.: Prolonged (>100 Myr) magmatic and thermal evolution in the world’s largest massif-type anorthosite complex (Kunene Complex, Angola and Namibia), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10002, https://doi.org/10.5194/egusphere-egu25-10002, 2025.
Nyamuragira volcano is an active volcano near the city of Goma in the Democratic Republic of the Congo, situated about 25 kilometers north of Lake Kivu. It has been described as Africa's most active volcano and has erupted over 40 times since 1885. on 2 January 2010 Nyamuragira began spewing out lava flows. Extensive lava flows from the 2010 eruption can be seen on satellite photographs reaching 25 kilometers south-west to Lake Kivu, about 22 kilometers north-west and 35 kilometers north-north-east. The volcano erupted again on 5 November 2011.That eruption produced a 400-meter-high column of lava, and it is said to have been its largest eruption in 100 years. Volcanic activity attributed to The Kivu rift resulted from a sub-equatorial extensional motion and normal faulting and accompanied with seismological activities. It suggests a complicated lower and upper crust tectonic patten and old neo tectonic settings.
It is a challenge to determine active tectonic and geologic structure attributed to magma eruption. Shallow and deep geologic structures around the volcanic area. Heterogeneities of the lithosphere and its impact on the volcanic activities. Old and neo tectonics responsible for volcanic and seismic activities. quantitatively predict the position and direction of dike intrusions and resulting eruptive fissures at volcanoes, because they are governed by the interplay between several factors, such as a heterogeneous regional stress field, preexisting discontinuities and heterogeneous and anisotropic properties of rocks.
Radar altimetry data has been used to derive gravity and its variations over the world's oceans and an excellent tool for mapping sea floor structures, including tectonics, sea mounts and rifts. On the other hand, the Gravity Recovery and Climate Experiment (GRACE) satellite mission has widely demonstrated its sensitivity to ongoing mass redistribution within the various sub-systems of the earth. Finally, GOCE (Gravity field and steady-state Ocean Circulation Explorer) satellite is the first satellite mission that observes gradient of the Earth gravity field from space. Integrated satellite gravity data have been used to delineate the tectonic settings, magma referred pathway, magma reservoirs and vertical dikes.
How to cite: Zahran, K.: Volcanic activity at the East African Rift System as seen from space, case study Nyamuragira Volcano, D.R. Congo., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17876, https://doi.org/10.5194/egusphere-egu25-17876, 2025.
Posters on site: Wed, 30 Apr, 16:15–18:00 | Hall X2
Cold slab subduction and hot plume burst are generally envisaged as independent triggers for convergent margin and intraplate magmatisms, respectively. However, descending oceanic plates occasionally encounter ascending mantle plumes, leading to contrasting hypotheses that plumes interrupt subduction processes and/or slabs choke plume pathways. This study used 2-D numerical simulation to reproduce a Paleozoic scenario in Central Asia where a subduction-induced plume head is invoked to interpret the formation of the Tarim large igneous province (LIP). The model assumes a long-lived mantle plume beneath the South Tianshan oceanic plate adjacent to the trench. As subduction initiated, plume materials spread first under the moving oceanic lithosphere, which developed a sequence of seamounts. Subsequently, the continual subduction drove a strong downwelling flow that stalled or restricted plume ascent in the upper mantle and caused the accumulation of hot materials in the uppermost lower mantle. Ultimately, the slab break-off after collision provided an opening pathway allowing for the accumulated hot materials to reach the surface, resulting in the development of a concurrent plume head and the formation of LIP on the overriding Tarim craton. Bending and rollover of the subducted oceanic lithosphere beneath an implemented stationary trench may contribute slab components to the LIP source, which can reasonably explain the slab-like geochemical fingerprints of basaltic rocks. Our work offers a tentative interpretation for the paradox that seamount formation preceded the LIP eruption in Tianshan and highlights possible slab effects, where subduction can stall the plume tail, causing heat accumulation that triggers a LIP.
How to cite: Wang, K.: Subduction-stalled plume tail triggers Tarim large igneous province, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1969, https://doi.org/10.5194/egusphere-egu25-1969, 2025.
The Mascarene Basin, between Madagascar, the Seychelles Plateau, and the Réunion hotspot track, is an ocean lithosphere whose geodynamic evolution remains enigmatic in many aspects. Part of the enigma concerns the unexplained extinction of the Mascarene mid-ocean ridge ca. 62 Ma ago and the shift of oceanic accretion to a new ridge (i.e., the Carlsberg Ridge) further north. The presence and timing of the Amirante aborted subduction trench (between Madagascar and the Seychelles) is another enigmatic aspect of the regional geodynamics (e.g., Rodriguez, CRGEOS 352, 235-245, 2020).
To shed light on these conundrums, we investigated the architecture of the Mascarene Basin during the MD245 “MASC” oceanographic cruise onboard the Marion Dufresne II research vessel. Bathymetric surveying revealed numerous seamounts at the axis of the paleo-ridge, along paleo-transform faults, and some also on the southern flank of the paleo-ridge. Interestingly, all the seamounts are located in the continuity of the Amirante paleo-subduction trench. Dredging operations on the seamounts recovered a suite of highly differentiated magmatic rocks ranging from biotite-rich basalts to rhyolites and granodiorites. Zircon and apatite (U-Th)/He data from these igneous rocks suggest that the seamounts formed during a protracted period between ca. 67 Ma and ca. 43 Ma.
Does this highly differentiated magmatism at 67-43 Ma reflect a residual activity of the ridge under extinction? Or, a nascent arc magmatism associated with the Amirante subduction? Further geochemical analyses are required to answer this question. Regardless, we note that the 67 Ma date coincides with the first magmatic manifestation of the Réunion plume as the Deccan traps, whilst the 43 Ma date corresponds to the deceleration of India and the passage of the Somalia Plate over the Réunion plume. We thus posit that differentiated magmatism, ridge extinction, and subduction initiation and abortion could be all related to the Réunion plume. Indeed, the Réunion plume is suspected to have pushed the Indian Plate toward Asia, causing its drastic acceleration and slowdown from 67 to 43 Ma (Cande and Stegman, Nature 475, 47-52, 2011). We further propose that the Réunion plume had a symmetric push effect on the Somalia Plate, converting oceanic spreading into compression, hampering spreading of the Mascarene Ridge, and eventually leading to the Amirante subduction. Compression (and differentiated magmatism) vanished when the Somalia Plate passed over the Réunion hotspot.
How to cite: Famin, V., Danišík, M., Révillon, S., Zaragosi, S., Beaufort, L., Sauter, D., Tzevahirtzian, A., Lebeau, G., Seghi, J., Leduc, G., Bassinot, F., Eude, A., Vinet, N., Quidelleur, X., Nauret, F., Michon, L., and Bachèlery, P. and the MASC Team: Ridge extinction in the Mascarene Basin due to the Réunion hotspot: preliminary results of the MASC Cruise, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17727, https://doi.org/10.5194/egusphere-egu25-17727, 2025.
Iceland has long been a focal point of geophysical research due to its potential association with a mantle plume. While earlier studies generally supported a plume originating from the core-mantle boundary with minimal lateral displacement during ascent, recent high-resolution tomographic images have indicated the presence of a curved, ascending mantle plume beneath Iceland. Consequently, the detailed source region and morphology of the Iceland plume remain debated. In this study, we provide new constraints on the Iceland mantle plume by examining the structure of the mantle transition zone (MTZ) using SS precursor imaging. We collected a large SS precursor dataset from 1976 to 2023 and adopted a recently proposed multi-dimensional reconstruction method to enhance the weak SS precursor phases for improved probing of the MTZ.
Our seismic observations reveal substantial thinning (~230 km) of the MTZ beneath Iceland compared to the regional average of 238 km and the global average of 242 km. This thinning is characterized by a slight depression of the 410 km discontinuity (~5 km) and a pronounced uplift of the 660 km discontinuity (~12 km). Temperature anomalies estimated using Clapeyron slopes suggest respective perturbations of +50 K and +300 K at the 410 and 660 discontinuities beneath Iceland. The former estimate is significantly lower compared to the reported thermal anomalies at major hotspots, e.g., ΔT410 ≈ +200 K west of Hawaii. This large temperature contrast suggests that either strong thermal heterogeneities exist across the MTZ or an alternative mechanism is required to explain the thinning of the MTZ beneath Iceland. We suggest that the mildly depressed 410 may be partly attributed to the influence of water during the ascent of the mantle plume. The presence of water effectively reduces pressures for the phase transition from olivine to wadsleyite, causing upward displacement of the 410 km discontinuities. This result suggests that variations in water distribution and content play a critical role in the structural anomalies observed in the MTZ beneath Iceland. The observed thinning of the MTZ supports the existence of a deep mantle plume, potentially supplying material to the shallow hotspots near the Iceland-Mid-Atlantic Ridge.
How to cite: Jiang, X., Chen, Y., Oboue, Y. A. S. I., Wang, J., Fei, H., and Thomas, C.: Seismic Imaging of Mantle Transition Zone Suggests Hot Deep Plume Underneath Iceland-Mid-Atlantic Ridge Region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16914, https://doi.org/10.5194/egusphere-egu25-16914, 2025.
The Makbal Complex is located within the western Tien Shan mountain range in NW-Kyrgyzstan. It’s central part comprises high-pressure (HP) and ultrahigh-pressure (UHP) metasedimentary and metabasaltic rocks of continental and oceanic origin, respectively.
Within the eastern part of the Makbal complex, abundunt 0.5 to 5 meter wide NW-SE oriented sills occur mainly within the Neldy group, but were also found in the Chymynsai and Kaindy groups.
The sampled rocks are altered to different extents with a dark to medium gray-green fine grained matrix comprising mainly chlorite and one to three millimeter sized porphyroclasts of amphibole, biotite, feldspar and carbonate, the latter most likely of secondary origin. Chlorite is not only the dominating matrix phase due to low grade alteration, it often replaces other mafic minerals such as amphibole, biotite and clinopyroxene. Although the majority of samples are highly altered, some phenocrysts are still fresh and include: (1) amphibole (kaersutite), (2) Mg-rich augite, (3) biotite of intermediate Fe-Mg content, (4) plagioclase of andesine to labradorite composition, and in some cases (5) K-feldspar. Based on the observed porphyritic texture and distribution of observed phenocrysts, the dikes can be classified as lamprophyres belonging mainly to the spessartite and to a lesser extent to the minette and vogesite groups.
Within the Nb/Y–Zr/Ti as well as the TAS diagrams (Pearce, 1996, Le Bas et al, 1986), the samples plot in the basalt, basaltic andesite, trachyandesite, and andesite fields. They all fall into the subalkaline field and most follow a shoshonitic or high-K calcalkaline trend in the SiO2-K2O diagram (Peccerillo and Taylor 1976). According to the Ti-Zr classification diagram after Pearce and Cann (1973) and the Nb/Yb−Th/Yb diagram (Pearce 2008), the lamprophyres were clearly emplaced within a compressional/continental arc setting. The chondrite normalized rare earth element pattern display a 100 times enrichment in light rare earth elements and a nearly constant 10 to 20 times enrichment of the middle and heavy rare earth elements excluding a deep-seated garnet bearing mantle as source of the lamprophyre melt. The patterns neither show a pronounced negative Nb-Ta anomaly nor any Eu anomaly.
Zircons could be extracted from an altered lamprophyre sample with kaersutite and plagioclase phenocrysts. The zircons are elongated with magmatic oscillatory zoning in CL image. The weighted mean 206Pb/238U age is 457 +/- 1 Ma, but a trend towards younger ages down to 440 Ma is observed. This age is similar to the intrusion age of a calcalkaline granodiorite body exposed approximately 5 to10 km to the west of the lamprophyre dikes. Both magmatic intrusives post-date the UHP event in the Makbal complex and bear important information to understand the full tectonic evolution. A genetic relationship of the lamprophyres and mafic enclaves found within the granodiorite is postulated.
How to cite: Gallhofer, D., Rechberger, J., Skrzypek, E., Orozbaev, R., and Hauzenberger, C. A.: Petrology, Geochemistry and Geochronology of Lamprophyres from the UHP Makbal Complex, NW-Kyrgystan, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12274, https://doi.org/10.5194/egusphere-egu25-12274, 2025.
Multiple magmatic and metamorphic events occurred in northeast Asia during the Orosirian period. Orosirian multiple magmatic and metamorphic events are also known to provide information about the amalgamation and break-up of the Columbia/Nuna supercontinent. The Yeongnam Massif, one of the Paleoproterozoic tectonic provinces in the Korean Peninsula, is known to have undergone two magmatic activities during ca. 2.02-1.86 Ga. This study focused on the Orosirian metagranitoid and amphibolite in the Gangjin-Wando-Jangheung area in the southwestern part of the Yeongnam Massif. In this study, we conducted the zircon Lu-Hf isotope analysis, the whole-rock geochemical analysis, and zircon U-Pb dating for metagranitoid and mafic xenoliths. Our study, a detailed investigation into the emplacement timing and petrogenesis of the Orosirian metagranitoid and mafic xenoliths in the study area, can provide crucial insights into the Orosirian multiple magmatic activities in the Yeongnam Massif along with their tectonic implications.
How to cite: Ko, K.: Zircon U-Pb-Hf isotope and whole-rock geochemical analysis of the Paleoproterozoic Orosirian metagranitoid and mafic xenolith in the southwestern part of the Yeongnam Massif, South Korea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3561, https://doi.org/10.5194/egusphere-egu25-3561, 2025.
Granitoids are prevalent in southeastern China and are associated with numerous renowned polymetallic deposits. The mineralization is thought to have a close genetic linkage with granitic magmatism in this region. However, the petrogenesis of these granites remains a subject of debate. Dengfuxian granites in the eastern Hunan Province, a representative granitic pluton, formed during this geological period and are linked with tungsten deposits. To constrain their magmatic origins and petrogenesis, analyses were conducted, including whole-rock geochemistry, SIMS zircon geochronology, oxygen isotope studies, and LA-ICPMS zircon Lu–Hf isotopic analyses on selected samples of Dengfuxian granites.The Dengfuxian granitic pluton predominantly consists of biotite granite, two-mica granite, and muscovite granite. Age determinations of the various granite types indicate the existence of two distinct episodes: the Late Triassic (221–226 Ma) and the Late Jurassic (150–151 Ma). Granites from both periods consistently exhibit high concentrations of SiO₂, Al₂O₃, total alkalis, K₂O, and P₂O₅, while showing low levels of MgO, TiO₂, and MnO₂, exhibiting a range from weak to strong peraluminous characteristics. Geological and geochemical evidence supports that the Dengfuxian granites are highly fractionated I-type granites, although some features typical of S-type granites are present, likely due to significant magmatic fractionation.Zircon Hf and O isotopic data reveal that the granites from both episodes originated from ancient crustal material, undergoing partial melting and substantial fractionation. The Late Triassic granites, in particular, appear to have incorporated a greater proportion of ancient crustal material into their magma.
How to cite: Liu, Q. and Zhang, H.: Petrogenesis of Dengfuxian granites in Hunan Province, SE China: Insights from U-Pb zircon ages and geochemistry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5901, https://doi.org/10.5194/egusphere-egu25-5901, 2025.
During the Lower Cretaceous, a significant tectonomagmatic activity around the South Atlantic Rift System led to the formation of numerous sedimentary basins, continental volcanism (basaltic and silicic), dike swarms, sill complexes, alkaline intrusions, and volcanic margins. In the northern Mantiqueira Province (Espírito Santo, Brazil), the Vitória-Ecoporanga belt is characterized by intense NW-SE-oriented faulting and fracturing zone, that hosts the Vitória Dikes, the northernmost low-Ti tholeiitic plumbing system of the Paraná Magmatic Province. These dikes exhibit microgabbroic textures and mineralogy composed mostly of plagioclase, clinopyroxenes, and Fe-Ti oxides. Geochemically, they have MgO = 3.83-7.2 wt.%, aligning with subalkaline tholeiitic basalts to basaltic andesites (total alkalis = 2.4-4.8 wt.%). These tholeiites are enriched in large ion lithophile elements, showing pronounced negative anomalies of Nb(-Ta) in comparison to Rb, Ba, U, Th, K, La, Ce, and Pb. They have 87Sr/86Sr(i) ranging from 0.70994 to 0.70575, and εNd(i) varying from -0.95 to -11.4, combined with heterogeneous values of Pb isotopes: 206Pb/204Pb(m) (18.2-16.7), 207Pb/204Pb(m) (15.6-15.4), and 208Pb/204Pb(m) (38.9-37.6), thus suggesting some degree of lithospheric/crustal contribution. New 40Ar/39Ar and K-Ar geochronology confirms an Early Cretaceous filiation to the Vitória Dikes. After comparing the multidata types of the Vitória tholeiites with the existing dataset of the Riacho do Cordeiro Dikes of the Equatorial Atlantic Province, it is possible to suggest that both were interconnected during the Early Cretaceous. This reinforces therefore that the Vitória and Riacho do Cordeiro Dikes would constitute one of the largest low-Ti tholeiitic plumbing systems in the South Atlantic area associated with the Cretaceous breakup of the West Gondwana supercontinent. In this context, a parental E-MORB magma mixed with melts derived from the West Gondwanan lithosphere to form the low-Ti tholeiites. Although tracing a mantle plume as a direct geochemical contributor to low-Ti basalts is challenging and not straightforward, it cannot be completely dismissed. A smaller contribution from the plume may have been involved in the formation of potential parental liquids with signatures analogous to E-MORBs.
How to cite: Avelino de Macedo Filho, A., Janasi, V., Oliveira, A., Hollanda, M. H., Dantas, E., and Lino, L.: The Vitória Dike Swarm: A Key Piece in the Puzzle of Low-Ti Tholeiitic Magmatism Related to the South Atlantic Rift System, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12432, https://doi.org/10.5194/egusphere-egu25-12432, 2025.
Enigmatic fayalite and orthopyroxene-bearing quartz-monzonite, locally named bauchite, is identified at the lowest exposed structural level of the Pan-African basement in Nigeria. This very iron-rich rock challenges the typical Bowen's reaction series, which suggests that olivine and quartz should not coexist. Nigeria's Precambrian basement consists of a series of metamorphosed magmatic and sedimentary rocks including schists, quartzites, amphibolites, and calc-silicates, transitioning into a granitoid-gneiss complex, designated as the Bauchi complex, in the north-central region. The lowest structural level of this complex consists, from bottom to top, in bauchite, hornblende-biotite granite and biotite granite, which is in contact with granulite facies migmatites. Earlier studies attributed bauchite formation to the impregnation of granites by iron-rich fluids and argued that the coexistence of ortho- and clino-pyroxenes with fayalite and quartz suggests deep-crustal magmatic emplacement (≈30 km depth).
Our field investigations indicate that bauchite and surrounding granite, crosscuts the regional scale NW-SE trending foliation of the host migmatites, which is consistent with an intrusive plutonic body. The preferred orientation of feldspar phenocrysts in bauchite but also in granites, delineates a shallow-dipping magmatic foliation and a regional-scale domal structure. Bauchite, exposed in the core of the dome, has a granular texture, with microcline and albite phenocrysts in a matrix of fayalite, ortho- and clino- pyroxenes, hornblende, biotite, and quartz. The accessory minerals present are zircon, apatite, magnetite, ilmenite, and titanite. At the lowest structural level, green bauchite dominated by fayalite and pyroxenes grades in brown bauchite characterized by a larger amount of hornblende and biotite. Textural analysis indicates a magmatic layering delineated by the alternation of fayalite-pyroxenes and microcline-albite layers. Interstitial quartz shows no signs of intracrystalline deformation, consistent with late crystallization from a melt. Hornblende shows lobate contacts with feldspars and typically forms a corona around fayalite and pyroxenes. Biotite is present as euhedral crystals in contact with hornblende. Microcline is typically bordered by myrmekite. These textures point to a reaction between fayalite-pyroxenes and microcline-albite layers leading to the crystallization of hornblende, biotite and quartz. Bauchite samples have an average SiO2 content of 65%, a high FeO/MgO ratio (14-17), and low Mg/(Fe+Mg) ratios (0.09-0.12). Their average K/(Na+K) is 0.49, with K2O exceeding 4%, making them highly potassic. The SiO2 content negatively correlates with most major oxides except K2O and Na2O, which show positive correlation. Trace elements data show high concentrations of Rb, Ba, K, and Zr, along with negative anomalies in Nb, Sr, P, Ti, Gd, Lu, and Y but positive anomalies in Zr, pointing to a deep-seated, alkaline magma. These features are consistent with an origin of bauchite resulting from interaction between an exotic iron-rich mantle derived alkaline magma and a felsic hydrous crustal one.
How to cite: Yahuza, I., Vanderhaeghe, O., Grégoire, M., and Isah Haruna, A.: The Pan-African fayalite quartz-monzonite from north-central basement of Nigeria, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8869, https://doi.org/10.5194/egusphere-egu25-8869, 2025.
Classification of silica-undersaturated igneous rocks represents of one long-standing problems in igneous petrology. Mineralogical classification of foid-bearing rocks has been formally set [1,2] but no continuously applicable systematics and universal classification criteria have been developed for alkaline ultramafic rocks including melilite-bearing varieties and special rock groups [3,4,5]. Chemical classification is primarily based on the total-alkali – silica (TAS) diagram [2], but condensation of multiple components (CaO, MgO, MnO, FeO, Fe2O3, Al2O3, TiO2, P2O5) in the diagram’s origin precludes its effective use for descriptive classification and petrogenetic interpretation involving mafic and ultramafic rocks. Universal availability and accuracy of whole-rock geochemical data together with fine-grained or glassy character of many volcanic rocks on one hand and historical origin of petrographic classifications in mineral mode and involvement of mineral-melt relations in magma evolution and crystallization on the other hand require consistent and universal link between the chemical and mineralogical approaches. This is a component transformation problem, which can be approached from several different perspectives: (i) component transformation sensu stricto preserving the composition space dimensionality, (ii) reduction of space dimensionality involving projecting or condensing components, usually for graphical applications or for condensation of complex natural compositions into simplified synthetic (e.g., experimental) systems, and (iii) subsection of the space leading to multiple combinations of new components; this approach is embodied in norm calculations. The widely applied tool – the CIPW norm [6,7] – suffers from several inadequacies when applied to silica-undersaturated rocks: (i) persistence of anorthite to critically undersaturated state, (ii) absence of melilite or its end-members, and (iii) incomplete or incorrect feldspar-foid compatibility relations. In this contribution we develop a condensed composition space to represent principal chemical variations in silica-undersaturated rocks. The condensation offers uniform treatment of diverse heteromorphic relations in dependence on temperature, pressure or water activity. The breakdown of plagioclase to aluminous clinopyroxene with decreasing silica activity and subsequent transformation of clinopyroxene to melilite is visualized in chemographic projections via olivine and nepheline, involving thermodynamically based phase relations as a function of silica activity. Finally, we define intermediate members of feldspar, nepheline, clinopyroxene and melilite solid solutions and develop a more comprehensive, quasimodal normative calculation for anhydrous silica-undersaturated igneous assemblages. This approach offers successive, rigorous steps for (i) overall classification and interpretation of chemical variations independently of mineral assemblages, (ii) projective analysis for comparison of chemical variations with experimental or thermodynamic phase relations, and (iii) algorithm for normative calculation approaching modal associations. This provides a uniform basis for both descriptive classification as well as genetic interpretation of silica-undersaturated magmas and rocks.
References: [1] Streckeisen A., 1965. Geol. Rundsch. 55, 478-494; [2] Le Maitre R.W., ed., 2002. Igneous Rocks. A Classification and Glossary of Terms, Cambridge Univ. Press; [3] Woolley A.R., et al., 1996. Can. Mineral. 34, 175-186; [4] Dunworth E.A., Bell K., 1998. Can. Mineral. 36, 895-903; [5] Tappe S., et al., 2005. J. Petrol. 46, 1893-1900; [6] Cross W., et al., 1902. J. Geol. 10, 555-690; [7] Janoušek V., et al., 2016. Geochemical Modelling of Igneous Processes, Springer.
How to cite: Dolejs, D.: Chemographic projections and normative calculations for silica-undersaturated igneous rocks, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13724, https://doi.org/10.5194/egusphere-egu25-13724, 2025.
