Recent advances in geophysical imaging, dredging and drilling-based exploration have evidenced features like dykes, sills, and Seaward-Dipping Reflectors and tectonic structures such as folds, brittle faults, and shear zones, revealing details of large crustal transects offshore.
We welcome contributions from all fields of geoscience that relate to the extent of continental, oceanic, and hybrid crust beneath continental shelves and in the oceans. Contributions may be based on observations, numerical modelling or theory, and may derive from any part of the world. We also welcome contributions focusing on the long-term processes from orogenesis to rifting and transform faulting, and bring new perspectives to disputed areas.
From classic microcontinents to Rifted Oceanic Magmatic Plateau (ROMP) - the spectrum of continental crust found within the ‘oceanic’ realm is diverse. The tectonic mechanisms responsible for emplacing continental fragments in the ocean also generate a wealth of sedimentary and structural geology, which we show can be prospective for geothermal, carbon capture and storage, and hydrocarbon exploitation. The emplacement mechanisms and examples of continental crust in the oceanic realm therefore merit further investigation. In this presentation, three mechanisms of emplacing continental crust into the oceanic realm will be explored, with specific reference to the geothermally rich Afar and Iceland ROMPs, Jan Mayen microcontinent and Davis Straight proto-microcontinent, as well as the newly recognised Davie Ridge strike-slip continental allochthon, which hosts one of the largest natural gas reserves on Earth. During the emplacement of continental material into the oceanic realm, we identify particular roles for lithospheric rheology during rifting, offsets along a rift system and strike-slip tectonics (in particular transpressional tectonics), and changes in plate motion. This talk also diversifies on the traditional viewpoint that continental crust is often emplaced in the oceanic realm due to hotspot activity.
How to cite: Phethean, J. J. J., Schiffer, C., Rime, V., and Longley, L.: Diverse tectonic mechanisms emplace continental crust in the ‘oceanic’ realm, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4395, https://doi.org/10.5194/egusphere-egu25-4395, 2025.
The whole North Atlantic region has highly anomalous topography and bathymetry. Observations show evidence for anomalously shallow bathymetry in the ocean as well as recent rapid topographic change with onshore uplift close to the Atlantic coast and simultaneous subsidence of basins on the continental shelves, most likely throughout the Mesozoic. We present a geophysical interpretation of the whole region with emphasis on data relevant for assessing hypsometric change
Most of the North Atlantic Ocean has anomalously shallow bathymetry by up-to 4 km compared to other oceans. Bathymetry is elevated by up-to 2 km and follows the square-root-of-age model, except for the region between Greenland Iceland Faroe Ridge (GIF) and the Jan Mayen Fracture Zone as well as in the Labrador Sea to Baffin Bay. Heat flow follows with large scatter the square-root-of-age model in parts of the ocean and is anomalously low on the Reykjanes and Mohns spreading ridges. Near-zero free-air gravity anomalies indicate that the oceanic areas are generally in isostatic equilibrium except along the mid-oceanic ridges, whereas anomalously low Bouguer anomalies in the oceanic areas indicate low density in the uppermost mantle. Anomalously thick crust is observed along GIF and extends into the Davies Strait. There is no correlation between bathymetry and heat flow, which indicates that the anomalous bathymetry mainly is caused by compositional variation and isostatic compensation of low density continental lithosphere within the oceanic regions. The location of major oceanic fracture zones and continental fragments appears to be controlled by onshore structures.
The onshore circum-Atlantic areas show rapid uplift close to the coast with rates of up-to 3 cm/yr. This is surprisingly mainly associated with strong positive free-air gravity anomalies, which would predict isostatic subsidence. Some parts of the high topography, however, appear supported by low-density anomalies below the seismic Moho. It is enigmatic that the presumed Archaean-Proterozoic continental Barents Sea region is submerged and includes deep sedimentary basins.
How to cite: Thybo, H. and Artemieva, I.: The anomalous North Atlantic region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20626, https://doi.org/10.5194/egusphere-egu25-20626, 2025.
Major sites of currently active serpentinization production are slow and ultra-slow mid-ocean ridges (MORs). At magma-poor margins, serpentinization takes place during mantle exhumation at the Continent Ocean Transition (COT), a phase occurring after continental breakup and before the establishment of a steady-state oceanic ridge. During this process, mantle rocks become intensely serpentinized as they interact with seawater that percolates through cracks and faults. However, the precise sequence of serpentinization formation in these regions remains still a topic of debate.
In this study, we examine two well-known examples of mantle exhumation: the West Iberia margin, using the FRAME-P3 profile, and the Tyrrhenian back-arc basin, analyzed through the MEDOC-6 profile. Both profiles were recently acquired with high-resolution multi-channel seismic (MCS) data and are complemented by previously modelled wide-angle seismic (WAS) data. This integration significantly enhances the P-wave velocity model, providing a more detailed and refined view of the basement structure and challenging previous interpretations. The improved model offers better velocity resolution, particularly in regions with complex subsurface structures, and delivers a comprehensive characterization of the transition zone between the oceanic crust and exhumed mantle.
This analysis revealed unprecedented details such as the extent of serpentinization and the detection of a continuous reflector indicative of a hydration front. They also highlight significant fluid-rock interactions and serpentinization processes in the region. In addition, the time-migrated MCS seismic section provides a detailed view of the tectonostratigraphic framework of the COT transition.
How to cite: Merino, I., R. Ranero, C., Prada, M., Sallarès, V., and Pérez-Gussinyè, M.: Mantle Serpentinization at Rifted Margins: insights from West Iberia and the Tyrrhenian Sea using seismic imaging and Vp tomography, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4717, https://doi.org/10.5194/egusphere-egu25-4717, 2025.
Since the earliest debates on continental drift theory, the African-Arabian rift system and the Afar region have been used as typical examples for extensional processes and the rift-to-drift transition. New findings suggest that the classical evolution model proposing a linear evolution from continental rifting in the Main Ethiopian Rift to advanced rifting in the Afar and oceanic spreading in the Red Sea is an oversimplification. Instead, the style of rifting seems to have a more important control on the structure and composition of each region than the magnitude or the age of the extension. In particular, the Central Afar region shows important extension, but it is far from showing normal, Penrose-like oceanic spreading. As such, it is considered as a precursor of some types of oceanic plateaus, such as the Greenland-Iceland-Faroe Ridge. This suggests that some features found far offshore and usually considered as purely oceanic might represent an extreme type of passive margin, hyperextended and magma ultra-rich. Conversely, the Danakil Depression, adjacent to Central Afar, shows a typical magma-rich structure on seismic data with well-defined Seaward Dipping Reflector (SDR) packages. However, outcrop data shows that they chiefly consist of sediments with only a small volume of magmatic products. This questions the composition of other margins worldwide that were often assumed to be made of magmatic material solely based on the recognition of SDR.
These new findings suggest that the position, composition, and structure of the continent-ocean transitions might be more complex and diverse than previously assumed.
How to cite: Rime, V., Keir, D., Phethean, J., Kidane, T., and Foubert, A.: The complex rift-to-drift transition: surprises and lessons from the Afar region, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4330, https://doi.org/10.5194/egusphere-egu25-4330, 2025.
In the early stages of continental rifting, a considerable volume of both mafic and felsic magmas can be formed. These magmas originate from the mantle and lower crust respectively, and their composition and volume are related to the localization and potential jumps of the rifting centers. An excellent illustration of these magmatic and tectonic processes are the aborted rift systems along the South Africa and Namibia volcanic passive margins and the eastern Afar area. In order to investigate these processes, we have used a thermo-mechanical numerical modelling approach based on the marker-in-cell method. Our experiments reveal that under the combined presence of far-field tectonic extension and thermal anomalies, partial melting in the upper mantle first generates large amounts of erupted basalt that forms traps and early conjugate SDRs (Seaward-Dipping Reflectors). Subsequently, melting of the lower crust and re-melting of mantle-derived intrusions produce felsic magmas at a later stage of rifting shortly preceding the lithospheric break-up phase. As the lithosphere thins, the rifting center may migrate laterally and crustal anatexis becomes inactive. As a result, the SDRs packages are laterally continuous and the early rift systems subsides, hosting the latest felsic magma extrusives. Throughout the evolution of the magmatic rift system, the production of mafic melts is primarily controlled by the location of thermal anomalies in the upper mantle.
How to cite: Wang, T., Geoffroy, L., Koptev, A., and Foulger, G.: Exploring the earliest stage of magmatic break-up through numerical simulations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9996, https://doi.org/10.5194/egusphere-egu25-9996, 2025.
“Oceanic” magnetic anomalies were “calibrated”, on Iceland, for just the last 4 million years. They extrapolated to 84 Ma (20x!) in the South Atlantic (Heirtzler et al., 1968), where there are 34 magnetic stripes west of the Mid Atlantic ridge. They extend back to 84 Ma and Cretaceous “Quiet Period” crust. This crust, however, is continental, not oceanic, and was not a 37 million year episode when Earth forgot to reverse its magnetic field.
There are 57 magnetic lineaments in the SE Pacific (140 Ma?), never discussed.
During the birth of Plate Tectonics Vine & Mathews (1963) famously related magnetic stripes to geomagnetic reversals. They noted, however, that alternations of ridges of high intensity and valleys of low intensity could result from presence of strongly magnetized material adjacent to weakly magnetized material. This qualification does not appear in subsequent literature.
In their paper Heirtzler et al., (op. cit.) qualified their work, writing: “the possible error in extrapolation cannot be overemphasized; if the Vine & Mathews (1963) theory is in error, the conclusions of this paper do not apply”. Thus, if the Vine & Mathews (op. cit.) qualification, above, is correct, extrapolation in the S Atlantic is incorrect.
What is “oceanic crust”? Karner (2008) described thinning of continental passive margin from 30 – 40 k to10 km, followed by rupture. Extension (100s percent) forms zones 100s km wide with organized magnetic anomalies from serpentinization. Correlatable magnetic anomalies do not unambiguously define “oceanic crust”.
Serpentinization involves reaction of peridotite with water at less than 500oC. The reaction is exothermic and results in volume increase as much as 45%. Magnetite forms.
Southern Pacific Ocean magnetic striping is symmetric between extended and largely subsided continent Zealandia and South America.
Onshore, thick basinal prisms, elongated parallel to the Andes, have steep western (Liassic deep water shales) and gentle eastern (Upper Triassic shallow water carbonates) boundaries. The basins shallow up to carbonates, red beds and evaporites. The ages correspond to Pangaean breakup.
The asymmetric basins were uplifted from the Pacific via transpression along the N-S, dextral strike-slip plate boundary (Liquiñe Fault).
They came from the Pacific.
Triassic-Jurassic rifting marked initiation of Pangaean breakup along the NW margin of Colombia, also a zone dextral strike-slip faulting (Romeral suture: oceanic rocks to the west, continental rocks to the east). Transpression shortened the Jurassic-late Cretaceous passive margin into metasediments (graphitic schists and black marbles in the western and central Andean Cordillera).
Further northwards the striping pattern becomes complex. The spreading ridge approaches the Americas and evolves into the San Andreas dextral strike-slip fault.
Seismic data record seaward-dipping wedges in the eastern Pacific.
So, in view of all this, how much “oceanic” crust is there in the Southern Pacific?
How to cite: James, K.: How much oceanic crust in the Southern Pacific?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3826, https://doi.org/10.5194/egusphere-egu25-3826, 2025.
Seamounts provide a unique record of volcanic processes in the oceans. In the Pacific Ocean, where seamounts are especially abundant, understanding their age and spatial distributions offers valuable insights into tectonic history, melt-extraction processes, and crustal provenance. However, detailed constraints on seamount formation history remain limited by sparse age data and age-dependent preservation, as older seamounts are progressively lost to subduction.
To address these challenges, we develop a data-driven approach to estimate seamount ages by analyzing relationships among multiple variables. Our analysis reveals that features such as crustal age, seamount height, and proximity to proposed “hotspots” illuminate the complex interactions between plate tectonics and magmatic processes. Using these relationships, we estimate ages for previously undated seamounts including uncertainty assessments. By adjusting volumetric measurements for ancient crustal area and subduction losses, we identify distinct phases in Pacific volcanism: (1) an Early Cretaceous period dominated by Large Igneous Provinces, (2) a Mid-Late Cretaceous transition marked by increasing non-hotspot seamount volcanism, and (3) a Cenozoic regime characterized by variable spreading rates and evolving ridge-seamount relationships.
This reconstruction provides new insights into the relative contributions of clearly plate-related- and other processes to Pacific volcanism through time, suggesting a more complex interplay between lithospheric and sub-lithospheric dynamics than previously recognized. Similar methods could be applied to other oceans, including the Atlantic and Indian Oceans, where they might also be adapted to discriminate crustal types.
How to cite: Zhao, Y., Riel, B., Zhang, J., and Foulger, G.: Data-driven Reconstruction of Pacific Seamount Ages: New Insights into Ocean Basin Volcanic Evolution, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3960, https://doi.org/10.5194/egusphere-egu25-3960, 2025.
The Eastern Continental Margin of India (ECMI) is a passive, magma-poor margin that formed during India’s separation from Antarctica in the Early Cretaceous period. The margin extends for approximately 2000 kilometres from the Cauvery Basin in the south to the Mahanadi Basin in the north, encompassing multiple river-fed sedimentary basins, including the Bengal, Mahanadi, Krishna–Godavari, Palar, and Cauvery basins. Geophysical methods, such as seismic, gravity, and magnetic surveys, have been instrumental in analysing the ECMI's nature and evolution. While detailed multichannel seismic imaging, particularly along the ION1000 profile in the Krishna-Godavari offshore basin, has enhanced our understanding of ECMI’s crustal structure, significant gaps remain in comprehending its rift architecture in relation to the surrounding geology. Additionally, critical thermal characteristics, such as Curie point depths and heat flow patterns have not been investigated in the ECMI till date.
In this study, we utilized magnetic, gravity, and multichannel seismic data to investigate the rifting processes, subsurface structure, and thermal characteristics of the Krishna-Godavari offshore basin and surrounding areas. In addition to reinterpreting the ION1000 profile, we conducted a thorough analysis along the ION1200 and ION1240 profiles using both qualitative and quantitative methods. This allowed us to refine the structural framework of the region. Radially averaged spectral analysis of magnetic data was used to estimate Curie depths, from which heat flow values were derived, providing insight into the geothermal framework of the margin. Gravity data analysis enabled us to estimate Moho depths through non-linear inversion, giving a more precise configuration of the crust-mantle boundary.
Qualitative analysis of the ION1200 and ION1240 profiles helped us to identify structural domains associated with rifting processes, while quantitative analysis revealed the patterns of tectonic subsidence and depth anomalies. These findings indicate significant subsidence and outer margin collapse in the exhumed domain, with no evidence of crustal thickening during rifting. Variations in heat flow values are attributed to substantial sediment accumulation that acts as a thermal insulator over old oceanic crust. This study presents a comprehensive model for the evolution of the ECMI, illustrating how deep crustal processes, mapped through seismic, gravity, and magnetic methods, influence the overlying sedimentary structure and thermal characteristics of the passive margin, ultimately shaping its geological and geothermal framework.
How to cite: Khan, S. A., Jacob, J., Desa, M. A., and Nelson, R.: Unveiling Crustal Dynamics and Thermal Structure in the Krishna-Godavari offshore Basin using Seismic, Magnetic, and Gravity Data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-431, https://doi.org/10.5194/egusphere-egu25-431, 2025.
In recent years there have been diverse reports of material in the lithosphere under the oceans, away from continental shelves, that does not comprise classical oceanic crust underlain by progressively mantle lithosphere that thickens according to plate-cooling models. These reports come from multiple different research approaches including:
- Marine geophysical surveying and sampling, identifying microcontinents, e.g., the Jan Mayen Microcontinent Complex, and ”orogenic bridges”, e.g., the Davis Strait;
- Deep seismic profiling detecting continental material beneath surface basalts, e.g., the Alpha-Mendeleev Rise;
- Large-scale seismic imaging using teleseismic earthquakes, identifying lithosphere with continental characteristics, e.g., in the South Atlantic;
- Aeromagnetic surveying revealing the extent of seafloor-spreading-related anomalies, e.g., in the Fram Strait;
- Broad cross-disciplinary work identifying crust inconsistent with a purely basaltic composition, e.g. the Greenland-Iceland-Faroe Ridge;
- Direct observation, e.g., on the Rio Grande Rise;
- Geochemistry, e.g., on the South West Indian Ridge;
- Dating of zircons from igneous rocks in the oceans that pre-date the time of formation of the local oceanic crust, e.g., Mauritius.
Understanding the extent of continental material in the oceans, and acceptance that hybrid continental/oceanic crust may exist – a third kind of crust – is an emerging field. At present no systematic review has been done of potential continental or hybrid regions in the oceans away from continental margins. It is thus unknown how widespread it might be and there is no broad understanding of or how it got there and why. It is timely for a systematic review of the subject aimed at identifying key research targets for the future.
How to cite: Foulger, G., Koehl, J.-B., and Peace, A.: Continental Material in the Oceans, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3329, https://doi.org/10.5194/egusphere-egu25-3329, 2025.
Two major styles of Mesozoic rifting occurred in the SW Atlantic. Along the eastern coast, north of Rio de Janeiro, oceanic crust formed shortly after the initial extensional phase with little lithospheric stretching. In contrast, along the southeastern coast, a high degree of lithospheric stretching occurred, leading to a large area of now-subsided stretched continental crust before the final rupture and oceanic crust formation.
Numerical modeling of rifting processes indicates that a prolonged stretching phase can result from a low-strength lithospheric lid or a more ductile lower crust. A lower crust with a more felsic composition (higher quartz content) tends to be more ductile. We compiled previously published bulk Vp/Vs ratio results from receiver function studies to investigate a potential systematic compositional difference between the eastern and southeastern continental coasts. However, no systematic difference was identified that could explain the two distinct rifting styles.
On the other hand, recent continental-scale seismic tomography maps consistently show that the lithospheric lid (100–150 km depth) in the eastern continental margin has higher seismic velocities compared to the southeastern margin. This suggests that the high degree of lithospheric stretching in the southeastern margin may be attributed to a low-strength lithospheric mantle.
New thermomechanical numerical simulations of lithospheric stretching are presented, taking into account lateral compositional inheritances and initial thermal anomalies. These simulations quantify how variations in lithospheric mantle rigidity can influence the architecture of the margin, controlling its width and asymmetry. The numerical results are compared with different segments of the margin to evaluate whether compositional or thermal inheritances in the mantle (e.g., related to the influence of the Tristan da Cunha mantle plume) can partially explain the differences in rifting styles.
How to cite: Sacek, V., Assumpção, M., Gosling, G., Monteiro da Silva, R., Rocha, M., Nascimento, A., and Affonso, G.: Rifting style of the SW Atlantic margin determined by lithospheric strength, as revealed by seismic tomography and receiver functions, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5053, https://doi.org/10.5194/egusphere-egu25-5053, 2025.
In order to investigate the deep structure along the transect Ligurian Sea - Northern Apennines - Po Basin, a new gravity model was constructed on the composite cross-section (465 km long) derived from published seismic profiles, geophysical data and surface (marine and onland) geology.
Along the transect, the gravity field shows great changes: 160 mGal offshore in the Ligurian Sea; a wide minimum of -160 mGal onshore in the Po Basin. The corresponding density model was constrained by: the structure of the sedimentary successions and basement-crystalline crust, the offshore-onshore WARR (wide-angle reflection and refraction), reflection seismic profiles and Moho depth derived from European Moho compilations. A shear-wave seismic tomography model was used to constrain the upper mantle; the derived seismic velocity model was converted into density one. At the end, the calculated gravity effect was compared with the observed gravity.
The modelled density transect shows an oceanic crust, a continental crust, and an Ocean Continent Transition (OCT) zone; the crustal thickness varying from ~15.5 km in the Ligurian Sea to ≤40-km (including 18 km of meta-sedimentary and sedimentary successions) in the Po Basin. The latter causes the mentioned gravity minimum. The OCT is abruptly separated from the oceanic crust by a block, ~40 km wide and with steep flanks marked by local magnetic anomaly, which we relate to exhumed HP/LT alpine metamorphic ocean-derived rocks. Specifically, the OCT zone is ~ 120 km wide and it affects the Northern Apennines orogenic wedge made of basement (Tuscan metamorphic unit) overlain by Mesozoic carbonate rocks, Oligocene-Miocene foredeep siliciclastic sediments and Ligurian ophiolite-bearing units which, as a whole, form a transitional crust up to 25 km thick. A peculiar feature of this OCT is a wedge-shaped sub-Moho body which is ~ 7 km thick maximum, deepens and thins northeastwards and has velocity/density value higher than lower crust and lower than upper mantle.
All these features are indicative of the complex nature of this OCT, which was affected by different geodynamic processes during the long-lived history of the Europe and Adria plates convergence since the Late Cretaceous. These processes include the Cretaceous-Eocene subduction of European plate underneath Adria with the closure of the ancient Piedmont-Ligurian Ocean and formation of the northernmost segment of the “Mediterranean Alps”. The exhumation of the inner portion of the wedge between West-Liguria and Corsica and the post-Eocene rifting associated to asthenospheric flow resulted in the dismemberment of the Alpine orogenic wedge during the early Apennines deformation history which enhanced the formation of the modern Ligurian Sea at the northeastern tip of the Liguro-Provencal Basin (Western Mediterranean Sea) and at the northern tip of the Tyrrhenian Sea. In the offshore-onshore part of the OCT, the astenopheric zones are recorded as low-velocity layers (from S-wave tomography) in the subcrustal region and in the upper mantle where they correspond to zones of low density. The distribution of the high heat flow zones strictly corresponds to the low-velocity upper mantle heterogeneities confirming their recent origin associated with magmatic activity.
How to cite: Yegorova, T., Artoni, A., Torelli, L., Molli, G., Storti, F., Murovskaya, A., Qadir, A., Chizzini, N., and Cioce, S.: Ocean-continent transition zone on the updated lithospheric transect from the Ligurian Sea to the Po Basin (Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9056, https://doi.org/10.5194/egusphere-egu25-9056, 2025.
The crustal structure of the Newfoundland-West Iberian conjugate margins has been extensively studied with seismic data and drilling legs. Recent surveys in the West Iberian margin have revealed a complex crustal architecture with continental, oceanic and exhumed mantle domains that change along the margin. In contrast, the Newfoundland margin, with lower seismic and drilling information available, remains comparatively more poorly understood. The main wide-angle and streamer SCREECH survey was acquired in 2000 and was modelled with comparative computational limitations at the time. The resulting images and model have been debated and did not unequivocally characterize the nature of the basement domains along the margin. Thus, the evolution of the deformation during rifting and the symmetry or asymmetry of the conjugate pair of margins are still discussed.
The SCREECH data acquisition parameters are similar to modern data, and we took advantage of their quality to re-process, image the structure and model the seismic phases with methodologies that have been refined during the last decade. Recent developments in parallel computing and novel geophysical approaches provide now the means to obtain a new look at the structure with enhanced resolution seismic models and a mathematically-robust analysis of the data uncertainty, that was formerly difficult, if not unfeasible, to achieve.
We use the SCREECH original field data, formed by three transects with coincident multichannel seismic (MCS) reflection data acquired with a 6-km streamer and wide-angle data recorded by short-period OBS and OBH spaced at ~15 km. We reprocessed the streamer data and also performed the joint inversion of streamer and wide-angle OBS/OBH seismic data, using reflections and refraction arrivals, which improved the definition of the geological units and the spatial resolution of the velocity model for each unit. We performed a statistical uncertainty analysis of the resulting model, supporting the improved reliability of the observed features.
Our results reveal previously unrecognized crustal heterogeneity, including variations in crustal thickness and composition along the margin. In particular, the crustal domain classification and the COT location were done considering the existence of a deep reflector, interpreted as the Moho and defining a 4-5 km crust that was interpreted as oceanic. Our results suggest that this reflector may not represent the Moho, as the observed crustal properties are not consistent with typical oceanic crust. The integration of the MCS images with the velocity models allowed us to re-interpret the crustal structure of this margin and integrate all the observations in a refined evolution model for the West Iberian – Newfoundland conjugate margins.
How to cite: Gómez de la Peña, L., Ranero, C., Prada, M., Shillington, D., and Sallarès, V.: Are all deep reflectors Moho? A case study of the Newfoundland margin, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9761, https://doi.org/10.5194/egusphere-egu25-9761, 2025.
The International Ocean Discovery Program Expedition 402 in the Tyrrhenian Sea was conducted from February 9 to April 8, 2024. The Tyrrhenian is the youngest basin in the western Mediterranean Sea. It formed from the Middle Miocene to the Recent by lithospheric thinning associated with slab rollback and with the east-southeast to southeast retreat of the Apennine subduction system. Continental breakup was followed by mantle exhumation in the Vavilov Basin after Messinian (5.33 Ma ago), central Tyrrhenian. Mantle exhumation was not followed by seafloor spreading, providing an exceptional opportunity to zoom in on the early stages of the exhumation process.
The samples and data collected during Exp. 402 provide an extensive new data set to constrain the geometry and timing of the deformation that led to mantle exhumation and elucidate the processes that unroofed the deep mantle forming the continent-ocean transition. Sediments collected at the basement contact constrain the minimum age of emplacement of mantle rocks, which occurred in the Pliocene. Drilling has provided conclusive evidence that the basement of the Magnaghi-Vavilov Basin consists of serpentinized upper mantle peridotites and that mantle exhumation was not followed by the formation of a magmatic oceanic crust. The oldest sediments above the basement were biostratigraphically dated to 2.82-3.56 Ma at Site U1612 and 3.56-3.85 Ma at Site U1616. The oldest biostratigraphic dates at Site U1614 were younger, 1.71-1.95 Ma. This information, placed in the context of knowledge of the basin, will allow us to reconstruct the geometry of the Tyrrhenian basin before, during, and after crustal extension and to follow its kinematic evolution over time until mantle exhumation.
How to cite: Loreto, M. F. and Zitellini, N. and the Exp. 402 Science Party: Zooming into the early stages of the exhumation process in the Tyrrhenian Basin by IODP Exp. 402, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11249, https://doi.org/10.5194/egusphere-egu25-11249, 2025.
The transformation of magnetic anomalies to magnetic potential or pseudo-gravity simplifies the complexities of magnetic anomaly interpretation. We present new pseudo-gravity maps, derived from EMAG2v3 data, for the South Atlantic Ocean and adjacent continent to reveal insights into crust and lithosphere composition.
The pseudo-gravity transformation of the full-field magnetic anomaly consists of three steps: (i) reduction to the pole (RTP); (ii) integration to determine magnetic potential; and (iii) scaling to determine the pseudo-gravity, assuming a constant ratio of density contrast to magnetization. This transformation produces a gravity-like anomaly that would be observed if the magnetization were replaced by a density distribution of proportional magnitude. We use magnetic data from the public domain EMAG2 v3 as the primary input. The South Atlantic region was divided into 90 tiles of 5º to account for regional variations in magnetic inclination and declination. An important assumption for the transformation is that the magnetization is induced. The pseudo-gravity mapping shows large amplitude positive anomalies consistent with the assumption of induced magnetization; negative anomalies identify areas of remnant magnetization. In the oceanic domain, alternating positive and negative anomalies reflect magnetic reversals and are not an artifact.
On the South American plate, the Rio-Grande-Rise exhibits three distinct high positive pseudo-gravity anomalies, reflecting thick magmatic crust. The São-Paulo-Plateau in the Santos Basin, Florianópolis-Ridge and Torres-High also show high positive anomalies. The Campos Basin has lower-amplitude positive anomalies, suggesting localized magmatic crust. In the continents, high-amplitude positive anomalies correlate with magmatic intrusion. The high positive pseudo-gravity anomalies form an NW-SE arc from magmatic material in the Paraná Basin to the São-Paulo-Plateau, continuing through the Florianópolis-Ridge and Rio-Grande-Rise.
Strong positive anomalies along the Namíbia-Ridge, Walvis-Ridge, and southwestern African margin form a "7"-shaped uniform anomaly, corresponding to magmatic crust. In contrast, the oceanic crust offshore Orange Basin shows a north-south region of negative anomalies. No significant anomalies are seen in the Tristan-Gough Guyot Province (nor are they seen on the Vitória-Trindade or Tristan-Gough Guyot Province hot-spot tracks).
A comparison of the pseudo-gravity map with crustal thickness from gravity inversion shows that many large, high-amplitude positive pseudo-gravity anomalies in the oceanic domain correlate strongly with anomalously thick crust (>12.5 km thickness) on the Rio-Grande-Rise, São-Paulo-Plateau, Florianópolis-Ridge, Namíbia-Ridge and Walvis-Ridge. Plate reconstruction of pseudo-gravity anomalies and crustal thickness suggest that the Namíbia-Ridge and western Florianópolis-Ridge, both with thick magmatic crust, have a common origin at approximately 110 Ma but were later separated by the Florianópolis-Fracture-Zone. The spatial relationship of observed high positive pseudo-gravity anomalies on magmatically intruded crust in the South American and African continents, the hybrid or magmatic crust on their rifted margins and thickened magmatic crust within the South Atlantic shows the major role of mantle inheritance in their origin.
How to cite: Graça, M., Kusznir, N., and Gusmão, R.: Pseudo-Gravity Transformation of Magnetic Anomaly Data for the South Atlantic and Adjacent Continent: Implications for Crust and Lithosphere Composition, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13445, https://doi.org/10.5194/egusphere-egu25-13445, 2025.
The Tyrrhenian Sea is a young back-arc basin that has been shaped by various complex geologic processes, such as crustal thinning, mantle exhumation, and localized magmatism. For the last half-century, the basement of the Tyrrhenian basin was sampled during several ocean-drilling campaigns. The past expedition DSDP 42 and ODP107 revealed that that in addition to continental rocks of the passive margins, the Tyrrhenian basement also includes mafic rocks characteristic of an oceanic domain, and serpentinized peridotites indicative of exhumed mantle. In 2024, the IODP Expedition 402 returned to the Tyrrhenian Sea with the primary objective of sampling the transition between different tectonic domains in the Vavilov basin.
The basement rocks recovered during the IODP Expedition 402 ranged from felsic to ultramafic. Our results confirmed the continental affiliation of the conjugate Cornaglia and Campania terraces on the margins of the Vavilov basin. In the center of the basin, we recovered peridotites, mafic basalts and diorites, and granitoids in relatively close sites, revealing the apparent heterogeneity of the basement framework. In this paper, we summarize the physical properties of different basement lithologies of the Vavilov basin. We report average values of bulk density, porosity, grain density, compressional velocity, magnetic susceptibility, gamma-radiation, and thermal conductivity for different rock types. These parameters are crucial for geological, geophysical, geochemical, and geodynamic models of the study area, which will help to constrain the tectonic evolution of this complex geologic region.
How to cite: Filina, I., Loreto, F., Shuck, B., Abe, N., and Pezard, P. and the IODP Exp.402 Science Party: Physical properties of hard rocks collected in Tyrrhenian Basin during the IODP Expedition 402 , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14000, https://doi.org/10.5194/egusphere-egu25-14000, 2025.
We present a Curie point depth map that casts light on the deep crustal temperature structure and can provide insights into the mechanisms of Iceland's formation. We used high-precision aeromagnetic anomaly data and a robust inversion algorithm. Curie point depth ranges from 4 to 28 km. The shallowest depths occur over the Reykjanes Peninsula and west and central Iceland. Curie point depth is relatively deep in north-central, south-central and eastern Iceland. The average thermal conductivity of the crustal magnetic layer, K, is 2.9 W/(m˚C). There is a weak inverse correlation between Curie point depth and 1026 heat flow measurement points. Mean heat flow is 170 mW/m2. The base of the seismogenic layer from earthquakes in Iceland is generally slightly deeper than the Curie depth point. The supra-Curie point depth temperature gradient in Iceland is 20-80˚C/km. This may be compared with the average thermal gradient of oceanic crust of ~ 65˚C/km. In contrast, the sub-Curie point depth temperature gradient in the thick lower portion of the crust is significantly reduced – 10-35˚C/km, which is more typical of continental crust which has a median gradient of ~ 34˚C/km. Our results support the hypothesis that the 20-30 km thick lower crust of Iceland contains a substantial amount of continental material.
How to cite: Meng, L., Liu, S., Xu, S., Foulger, G. R., and Hu, X.: Temperature Structure of the Icelandic Crust from Curie Point Depth, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14416, https://doi.org/10.5194/egusphere-egu25-14416, 2025.
The Tyrrhenian Sea, a Neogene back-arc basin in the central Mediterranean, is a site of active debate regarding its crustal affiliation as both oceanic basalts and gabbroic rocks, as well as exhumed mantle peridotites were recovered throughout the Tyrrhenian Sea. Interestingly, the recent IODP Expedition 402 revealed granitoids and serpentinized peridotites in close proximity drill sites within the Vavilov basin. These apparent heterogeneous mantle rocks warrant further research using an integrated geophysical approach, incorporating all available geophysical data to understand the spatial distribution of crustal domains across the Tyrrhenian seafloor.
The crustal heterogeneity in the study area results from the interplay of back-arc extension processes, including localized mantle exhumation, crustal thinning, and magmatic intrusions driven by the eastward retreat of the Calabrian-Apennine subduction system. This study investigates the tectonic affinity of the crust in the region via joint analysis of published seismic reflection and refraction data from MEDiterraneo OCcidental (MEDOC) 4 and 6 surveys, topography data, and potential fields (gravity and magnetic). Drilling results from DSDP 373, ODP Leg 107 and IODP Exp. 402 served as geological constraints for geophysical interpretations.
We present two 2D subsurface models along the MEDOC-4 and MEDOC-6 profiles that reveal the geometry of crustal and mantle structures and explain variations in the observed gravity and magnetic anomalies through differences in their physical properties. The models highlight the variations in densities and magnetic susceptibilities in all prominent geologic structures that profiles transect, including the Baronie, Magnaghi, Vavilov, and Flavio Gioia Seamounts. We also present a map delineating the spatial distribution of rock types in the central Tyrrhenian Sea, which outlines continental, oceanic and exhumed mantle domains using all data blended in the analysis.
How to cite: Onyebum, T., Filina, I., and Loreto, F. and the IODP Exp. 402 Science Party: Integrated Geophysical Modeling of Tectonic and Crustal Structures across the Tyrrhenian Sea, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16886, https://doi.org/10.5194/egusphere-egu25-16886, 2025.
The Rio Grande Rise and Valdivia Bank are significant bathymetric and geological features in the South Atlantic Ocean, situated on the South American and African plates, respectively. Most models agree that the interaction with the Tristan-Gough mantle plume and mid-ocean ridge has influenced the formation of these plateaus. However, the role of rifting and continental breakup driving their formation remains controversial. In this study, we integrate geological, geophysical, and geochemical data to determine the nature of the crust within the Rio Grande Rise and Valdivia Bank and develop a plate tectonic model to contextualise their formation within the breakup of Southwest Gondwana and the time-dependent interaction with the Tristan-Gough mantle plume in the Late Cretaceous. Our approach includes analysing the tectonic provenance of dredged continental rock samples from the Rio Grande Rise, DSDP borehole data for sedimentation history, seismic imaging for magmatic rift structures, and Ce/Pb and Nb/U ratios for continental crust contamination. Gravity anomaly data provided insights into crustal thickness and structural fabric across the region. A regional cross-section linking the magmatic rifted margin of the Pelotas Basin and the Rio Grande Rise provided insights into the geological processes, and their relative timing, that influenced the region. Our study classifies the Rio Grande Rise and Valdivia Bank as microcontinents characterised as magmatic transitional crust with complex tectonic histories shaped by mantle plume activity during the breakup of Southwest Gondwana. We present a plate motion model that captures the evolution of a microplate and related seafloor spreading. It incorporates the temporal evolution of the Rio Grande and Valdivia microcontinents, including their final separation around 72 million years ago. Geochemical analysis confirmed continental crust contamination, supporting previous interpretations of Proterozoic continental rock samples dredged in the Rio Grande Rise. Seismic interpretation pointed to similar magmatic rift structures involving rifted continental crust in these geological features and their conjugate rifted margins, highlighting their common tectonic history. Initial off-axis spreading ridges and the inheritance of major continental tectonic fabric conditioned the creation of microcontinent and rift-related structures within a magmatic setting. Relative rotations (100 – 72 Ma), recognised by internal structures and curved fracture zones, support the existence of a microplate in the South Atlantic. Under the influence of the mantle plume, spreading ridges to the east and west of the microplate were aborted, and a new ridge linking the Central and Southern South Atlantic mid-ocean ridge became established by this time. Our kinematic plate model challenges existing ideas by linking these features to a combination of continental and plume-related processes and demonstrating their formation through magma-rich continental rifting rather than simple oceanic plateau formation. This study contributes to the understanding of microcontinent dynamics in plume-influenced rift settings, offering a new perspective on the geodynamic history of the South Atlantic. It provides a foundation for future research to explore the physiographic evolution of these structures, their roles in ocean circulation and climate, and how they influence sedimentation processes in the adjacent rifted margins.
How to cite: Rigoti, C., Zahirovic, S., Seton, M., and Dehler, N.: Plate-plume interaction driving microcontinent formation in the South Atlantic: The Rio Grande and Valdivia microcontinents , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8811, https://doi.org/10.5194/egusphere-egu25-8811, 2025.
The Walvis transform marginal plateau constitutes a key geodynamic node in the evolution of the South Atlantic Ocean. It is the conjugate of the Santos transform marginal plateau. Both plateaus formed associated successively with: (1) the Austral South Atlantic rifting marking the separation of the southwestern Gondwana during the end of the Late Jurassic and Early Cretaceous with a northward propagating breakup between 133-124 Ma (M11 à M2). This stage was narrowly associated with the mantle plume of the Tristan Da Cunha Hot spot, at the origin of the Paranà-Etendeka Trapp (135-132 Ma). It is associated with the divergent opening of the North Pelotas magma-rich margin. (2) The later opening of the Central Atlantic segment (113 Ma) between Angola and Brazil. The Walvis and Santos plateaus separated during this stage along the Florianopolis Transform Zone in the Albian.
In this context, the Walvis Plateau probably marks a dynamic and persistent mantle-influenced complex. This system not only controlled the tectonic, volcanic, and topographic local processes, but also played a critical role as a rift propagation barrier toward the north, preserving a magmatic landbridge between continents, disturbing the establishment of the oceanic connection between the austral et central segments of the South Atlantic Ocean, and therefore the deep oceanic circulations. A detailed description of these multi-scale interactions is essential for understanding the links between regional dynamics, magmatism, and oceanic evolution at the start of the formation of the South Atlantic.
In this study, we propose a multi-sequential tectono-magmatic description of the Walvis Ridge. Through the interpretation of deep penetrating multi-channel seismic reflection profiles and wide-angle refraction lines, combined with magnetic and gravimetric anomalies, we describe the structuration of the Walvis Plateau. The analysis of these data enables us to identify and delineate several key aspects: major seismic/geologic units, crustal architecture, the structural genetic passive margin domains from Moho interface inflections, and the spatial-temporal sequencing of effusive magmatic events, called Seaward Dipping Reflectors (SDRs). Most of those SDRs evolve gradually from east to west. Between magnetic anomaly M4 and M0, a notable feature of this evolution is the appearance of a preserved proto-magmatic center, identifiable by a double verging structure, oriented N-S and turning E-W to the south, probably signing a magmatic reorganization at some stage. Within the overall relative westward motion of the effusive systems, we show that it gradually orients towards the north in the direction of the core of the Walvis Plateau together with the development of a large lava delta prograding southward. At a later stage, the plateau is affected by large normal faults forming a graben in the thinned domain, coevally to the formation of the Florianopolis Transform Fault.
This study highlights the complex interactions between tectonic and magmatic processes in a polyphased breakup and oceanisation setting, integrating the influence of the mantle plume and geological inheritance of Gondwana Supercontinent. It provides new perspectives on the Walvis Plateau dynamics and, more generally, on the formation and rupture of marginal magmatic transform plateaus.
How to cite: Poirrier, S., Sapin, F., Loncke, L., Graindorge, D., and Nielsen, C.: Tectono-magmatic evolution of the Walvis plateau: Multi-scale and polyphased interactions between mantle plume, rifting and transform activity, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17424, https://doi.org/10.5194/egusphere-egu25-17424, 2025.
