Olivier Galland

• Galland, Olivier; Chiacchiera, Sabina; Cal, Hernán de la; Jerram, Dougal Alexander; Lombardo, Ezequiel & Palma, J. Octavio [Show all 12 contributors for this article] (2026). The impacts of volcanism on hydrocarbon-bearing sedimentary basins - Examples from the world-class Neuquén Basin case study, Argentina. Global and Planetary Change. ISSN 0921-8181. 257. doi: 10.1016/j.gloplacha.2025.105218. Full text in Research Archive Show summary

  The last two decades of research have highlighted that volcanism occurring in sedimentary basins can have substantial effects on sedimentary formations. In particular, igneous intrusions can trigger the generation of large amounts of greenhouse gases in organic-rich host rocks, leading to dramatic climate change and mass extinctions. Volcanism can also have significant impacts on hydrocarbon-bearing sedimentary basins. The Neuquén Basin, Argentina, is a well-studied example of a hydrocarbon-producing sedimentary basin hosting massive volcanism. The combination of substantial industry subsurface data and high-quality outcrops makes the Neuquén Basin an exceptional geological object to study magma-sedimentary rock interactions and their implications to hydrocarbon systems. This contribution reviews well-studied examples from the Neuquén Basin that illustrate: (1) thermal effects of sills on maturation of the organic matter of the source rock, (2) fracturing processes in igneous intrusions and the host rock, (3) sills as producing fractured reservoirs, (4) intrusion-induced doming as structural trap or as potential fractured reservoir, (5) fluid migration along igneous intrusions, (6) reservoir compartmentalization induced by dykes, (7) generation of bitumen dykes in vicinity of intrusions, and (8) improvement of geophysical imaging using large-scale outcrops. All in all, our review documents various effects of magma-rock interactions in hydrocarbon-bearing sedimentary basins, and highlights the significant scientific value of the Neuquén Basin as a world-class case study for unravelling processes of magma-rock interactions in hydrocarbon-bearing sedimentary basins.

• Biswas, Uddalak; Galland, Olivier & Carlson, Andreas (2026). Laponite® RD and hydroxyethyl cellulose as host rock and magma analogue to simulate a wide range of rheological combinations in the volcanic plumbing system. Tectonophysics. ISSN 0040-1951. 937. doi: 10.1016/j.tecto.2026.231351. Full text in Research Archive Show summary

  Analogue modelling is essential for understanding magma emplacement in the Earth’s crust and requires strict geometric, kinematic and dynamic scaling. Therefore, material selection must satisfy the scaling laws to reproduce the natural rheological variability. Although often represented by end-member rheologies, crustal rocks in nature exhibit complex rheological behaviour. In this study, we analysed two complex materials, Laponite® RD (LRD) and hydroxyethyl cellulose (HEC), to assess their effectiveness as geological analogues for country rock and magma in dyke emplacement experiments. We provide a detailed characterisation of LRD, highlighting its tuneable rheological properties via curing time (t_c). To characterise the complex rheology of the LRD gels, rotational and oscillatory tests, including flow, amplitude, frequency sweep, and creep and recovery tests, were performed at curing times (t_c) ranging from 30 to 240 min. We tested the rheology of aqueous HEC solutions at concentrations of 0.50, 0.75, and 1.00 wt%. Additionally, this study highlights the significant role of surface tension in laboratory analogue experiments, demonstrating the need to minimise interfacial tension by selecting an appropriate magma analogue fluid when using a viscoelastic host. The rheological test results showed that the storage modulus (G^') and yield stress (τ_y) increased systematically with increasing t_c. The flow and surface tension test results indicate that HEC hydrous solutions serve as robust magma analogues, offering variable viscosities with minimal alterations in surface tension and density. Combining the rheological analysis results of LRD and HEC, we propose a new methodology for simulating a wide range of rheological conditions by systematically varying the LRD curing time and employing different concentrations of HEC as a magma analogue. Our approach emphasises precise rheological characterisation together with control of magma-analogue density and surface tension, minimising the interfacial tension and buoyancy contrast with the host for accurate scaling in analogue models of volcanic plumbing systems.

• Senger, Kim; Ammerlaan, Fenna; Betlem, Peter; Gaina, Carmen; Galland, Olivier & Grundvåg, Sten-Andreas [Show all 21 contributors for this article] (2026). A Field Guide to the High Arctic Large Igneous Province in and Around Isfjorden, Svalbard. Tektonika. 3(2), p. 176–216. doi: https:/tektonika.online/index.php/home/article/view/124/197. Full text in Research Archive Show summary

  The High Arctic Large Igneous Province (HALIP) is a major tectono-magmatic element that affected large parts of the Arctic during the Cretaceous (magmatism occurred from 126 to 78 million years ago [Ma]). In Svalbard, HALIP intrusive and extrusive rocks are grouped and classified as the Diabasodden Suite. Sills and dykes are present throughout Svalbard, emplaced in units stratigraphically ranging from crystalline basement to Jurassic-Cretaceous siliciclastics. Time-equivalent lava flows are exposed on Kong Karls Land in eastern Svalbard. In this contribution, we firstly define and introduce major features of the circum-Arctic HALIP. Secondly, we zoom into Svalbard where we document and summarize the attributes of HALIP outcrops (i.e., the Diabasodden Suite) located in and around Isfjorden, the most accessible location that is reachable on day trips using boats from Longyearbyen. For each of the 15 sites we focus on specific aspects of HALIP characterization, including geochronology, geochemistry and geometry of volcanic and intrusive rocks. We complement field descriptions of the sites with digital geoscientific data, including digital outcrop models and photospheres. Finally, we synthesize the Isfjorden study area in the context of data and knowledge gaps for the HALIP in general. We hope that this contribution will stimulate further HALIP research in Isfjorden and beyond.

• Johannesen, Rakul Maria Ingunardóttir; Galland, Olivier; Kjøll, Hans Jørgen; Ólavsdóttir, Jana; Eidesgaard, Óluva & Planke, Sverre (2026). Impact of fractures on basaltic reservoirs - Field characterisation of fracture distribution in lava flows, Faroe Islands. International Journal of Greenhouse Gas Control. ISSN 1750-5836. 151. doi: 10.1016/j.ijggc.2026.104620. Full text in Research Archive
• Greiner, Sonja H.M.; Galland, Olivier; Sigmundsson, Freysteinn; Burchardt, Steffi; Geirsson, Halldór & Pedersen, Rikke [Show all 7 contributors for this article] (2025). The Influence of Variable Host Rock Cohesion and Magma Viscosity on Intrusion-Fault Interaction: Insights From Laboratory Models. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 130(4). doi: 10.1029/2024JB029870. Full text in Research Archive Show summary

  Magma transport through the Earth's shallow crust can be affected by pre-existing weaknesses like faults. Consequently, fault-channeled magma may reach the surface in unexpected locations. Hence, better understanding of magma-fault interaction is needed to improve hazard assesment. We investigate the effect of host rock cohesion and magma viscosity on intrusion-fault interaction using laboratory experiments. Vegetable oil and glucose syrup, serving as low- and high-viscosity analogue magmas, were injected into intact and faulted granular materials with variable cohesion (mixtures of silica flour and micro-glass beads), serving as a brittle plastic model crust. High-cohesion models produced sheet intrusions, that propagated along fault segments upon intersection. Low-cohesion models produced low-aspect ratio intrusions low width/thickness ratio. Without tectonic stresses, the cohesion strongly controls intrusion-fault interaction, while tested model magma viscosities exerted a weaker control. Our findings show that intrusion-fault interaction is a highly complex process and important to consider at active volcanoes.

• Kjøll, Hans Jørgen; Scheiber, Thomas & Galland, Olivier (2025). Rapid viscous flow of crustal rocks controls dyke emplacement in the ductile crust. Nature Communications. 17(1). doi: 10.1038/s41467-025-67464-3. Full text in Research Archive Show summary

  Abstract Magmatic dykes are the main pathways for magma through Earth’s crust. They are often assumed to be magma-filled fractures that propagate as thin, tapered sheet intrusions through mode I tensile opening at the fracture tip and elastic bending of the host rock along the dyke walls. Here, we present field evidence from northern Sweden, showing that deep-crustal dyke emplacement was, despite high strain rates, associated with significant ductile deformation of the host rocks. On average, 25% of the dyke thickness was accommodated by ductile flow of the immediate host rock. Modelling magma cooling times suggests average ductile strain rates of 10 −3 s −1 to 10 −6 s −1 , i.e. 6 to 10 orders of magnitude faster than typical tectonic ductile strain rates in the middle crust. These results have major implications for understanding ductile crustal strength and the interpretation of geophysical signals used to mitigate geohazards in volcanically active areas.

• Giro, João Paulo; Zanella, Alain; Mourgues, Regis; Galland, Olivier & Ramirez, Mariano Martín (2025). A novel adaptable analog material for simulating transversely isotropic rocks: mechanical properties and applications. International Journal of Rock Mechanics And Mining Sciences. ISSN 1365-1609. 192. doi: 10.1016/j.ijrmms.2025.106145. Full text in Research Archive Show summary

  Transversely isotropic rocks (TIRs) are widespread in geological formations, and understanding their mechanical behavior is crucial for geotechnical and geoengineering applications. This study presents the development of a novel analog material that reproduces the directional mechanical properties of TIRs. The material is composed of quartz sand, mica flakes, and gelatin in adjustable proportions, allowing control over strength and stiffness anisotropy. Uniaxial compressive strength (UCS) and direct shear tests were conducted to evaluate mechanical responses across different anisotropy angles. Results show that the analog material replicates key features of natural TIRs, including directional variations in strength and fracture modes. In UCS tests, the anisotropy angle (β) governs the transition between tensile and shear failure. In direct shear tests, the orientation angle (α) significantly affects shear strength. Higher gelatin concentrations increase cohesion and Young's modulus without changing the internal friction angle, while mica content reduces overall strength and stiffness. Comparisons with published data on sedimentary and metamorphic rocks confirm the mechanical representativeness of the material. Its simplicity, tunability, and reproducibility make it a useful tool for scaled physical modeling of anisotropic rock behavior in the laboratory. This approach supports the experimental investigation of deformation and failure mechanisms in layered rock masses under controlled conditions.

• Sartell, Anna Marie Rose; Söderlund, U.; Senger, Kim; Kjøll, H. J. & Galland, Olivier (2025). A Review of the Spatiotemporal Evolution of the High Arctic Large Igneous Province, and a New U‐Pb Age of a Mafic Sill Complex on Svalbard. Geochemistry Geophysics Geosystems. 26(12). doi: 10.1029/2024gc011842. Full text in Research Archive Show summary

  The High Arctic Large Igneous Province (HALIP) formed in the circum‐Arctic during the Cretaceous. The timing and duration of emplacement of these mafic magmas are important for understanding the climatic and environmental effects, yet many uncertainties remain. The dating methods used vary greatly between different regions. For example, the mafic intrusions in Svalbard have mainly been dated using the 40 K/ 40 Ar method, which is more sensitive to overprinting at lower temperatures. This is problematic especially in the Arctic, where the Eocene Eurekan orogeny has impacted the intrusions post‐emplacement. Meanwhile, in the Canadian Arctic, 206 Pb/ 238 U dating on zirconium minerals has been the most common method employed, which requires much higher temperatures to be reset. We present a new compilation of ages for HALIP igneous and volcanic rocks in the circum‐Arctic, derived from a thorough review and reassessment of previously reported data. This compilation applies rigorous, method‐specific criteria to evaluate the reliability of existing HALIP age determinations, ensuring traceability and applicability for future data sets. By establishing a robust framework for assessing age data, this approach enhances the reliability of geological interpretations of HALIP magmatism, and highlights, for example, the spatial migration of peak magmatic activity through time in the High Arctic. To improve our understanding of the temporal evolution of the HALIP, we also present a new 206 Pb/ 238 U baddeleyite isotopic dilution thermal ionization mass spectrometry age from Svalbard. The new weighted mean 206 Pb/ 238 U age from Svalbard, 123.3 ± 1.6 Ma, is based on six samples belonging to one large sill. This age is in perfect agreement with existing published 206 Pb/ 238 U and 40 Ar/ 39 Ar ages, and suggests magma emplacement on Svalbard between 124.7 ± 0.3 and 120.2 ± 1.9 Ma ago.

• Lombardo, E.F.; Jerram, Dougal Alexander; Yagupsky, D. & Galland, Olivier (2025). Seismic imaging of sub-vertical dykes and dyke/sill transitions in sedimentary basins: A case study from miocene volcanic complexes in the Neuquén Basin, Argentina. Global and Planetary Change. ISSN 0921-8181. 255. doi: 10.1016/j.gloplacha.2025.105126. Full text in Research Archive Show summary

  Seismic reflection has proven to be a powerful tool for imaging sub-horizontal or inclined magma conduits emplaced in sedimentary basins; however, the imaging of subvertical dykes remains significantly more challenging. Nevertheless, imaging dykes in sedimentary basins is essential, as these structures are fundamental components of volcanic plumbing systems and can exert a substantial influence on subsurface fluid migration. This study introduces a novel seismic interpretation workflow designed to enhance the three-dimensional imaging of subvertical igneous dykes within sedimentary basins. The proposed approach utilizes seismic attributes, specifically Ant Tracking applied to Variance and Amplitude Contrast volumes. The workflow was applied to a 3D seismic reflection dataset from the El Trapial hydrocarbon concession, Neuquén Basin, Argentina, enabling the extraction of thin, three-dimensional geobodies interpreted as dykes. Furthermore, the integration of 3D imaging and mapping of associated sills within the same basin yields new insights into the three-dimensional relationships between sills and their feeder dykes. The interpretation of subsurface dykes and dyke/sill transitions is validated by satellite imagery and direct field observations. This workflow is applicable to other sedimentary basins with buried volcanic plumbing systems.

• Lombardo, Ezequiel Felipe; Jerram, Dougal Alexander; Yagupsky, Daniel & Galland, Olivier (2025). Seismic Imaging of Sub-Vertical Dykes and Dyke/Sill Transitions in Sedimentary Basins: A Case Study from Miocene Volcanic Complexes in the Neuquén Basin, Argentina. Social Science Research Network (SSRN). doi: 10.2139/ssrn.5281335. Full text in Research Archive Show summary

  Dykes and sills are fundamental elements of volcanic plumbing systems. When emplaced in sedimentary basins, igneous dykes and sills have significant implications for the structural integrity of the basin, can permanently re-modify basin geometries and effect key properties influencing a basins fluid migration pathways. Seismic reflection data have proved powerful to image sub-horizontal or inclined sills emplaced in sedimentary basins, whereas imaging sub-vertical dykes is much more challenging. As such the role of dykes in sub-surface data can be underestimated and our understanding of the connections between dykes feeding sills and visa-versa within the magma plumbing system is poorly constrained. This study presents a novel seismic interpretation method aimed at enhancing the three-dimensional imaging of subvertical igneous dykes emplaced within sedimentary basins. The proposed workflow implements seismic attributes Ant Tracking applied to Variance and Amplitude Contrast. We applied the workflow to a 3D seismic reflection volume from the El Trapial hydrocarbon concession, Neuquén Basin, Argentina, and show how 3D vertical thin geobodies of interpreted dykes can be extracted. When combined with 3D imaging and mapping of related sills within the same basin, we are able to provide new insights into the 3-dimensional relationship between sills and their feeder dykes. The Interpreted subsurface dykes and dyke/sill transitions are ground-truthed by both satellite imagery and direct field observations. The workflow proposed in this study can be applied to numerous other sedimentary basins hosting buried volcanic plumbing systems.

• Galland, Olivier; Chiacchiera, Sabina; Cal, Hernán de la; Jerram, Dougal Alexander; Lombardo, Ezequiel & Palma, J. Octavio [Show all 12 contributors for this article] (2025). The impacts of volcanism on hydrocarbon-bearing sedimentary basins - Examples from the world-class Neuquén Basin case study, Argentina. EarthArXiv preprint platform. 257. doi: 10.31223/x5c16f. Full text in Research Archive Show summary

  The last two decades of research have highlighted that volcanism occurring in sedimentary basins can have substantial effects on sedimentary formations. In particular, igneous intrusions can trigger the generation of large amounts of greenhouse gases in organic-rich host rocks, leading to dramatic climate change and mass extinctions. Volcanism can also have significant impacts on hydrocarbon-bearing sedimentary basins. The Neuquén Basin, Argentina, is an outstanding example of hydrocarbon-producing sedimentary basin hosting massive volcanism. The combination of substantial industry subsurface data and outstanding outcrops makes the Neuquén Basin a world-class geological object to study magma-sedimentary rock interactions and their implications to hydrocarbon systems. This contribution reviews well-studied examples from the Neuquén Basin that illustrate: (1) thermal effects of sills on maturation of the organic matter of the source rock, (2) fracturing processes in igneous intrusions and the host rock, (3) sills as producing fractured reservoirs, (4) intrusion-induced doming as structural trap or as potential fractured reservoir, (5) fluid migration along igneous intrusions, (6) reservoir compartmentalization induced by dykes, (7) generation of bitumen dykes in vicinity of intrusions, and (8) improvement of geophysical imaging using large-scale outcrops. All in all, our review (1) documents various effects of magma-rock interactions in hydrocarbon-bearing sedimentary basins, and (2) highlights the great scientific value of the Neuquén Basin as a world-class case study for unravelling processes of magma-rock interactions in hydrocarbon-bearing sedimentary basins.

• Galland, Olivier; Sartell, Anna Marie Rose; Horota, Rafael Kenji; Kjøll, Hans Jørgen; Runge, Jonathan J. S. & Midtkandal, Ivar [Show all 7 contributors for this article] (2025). Stratigraphic Influence on Emplacement and 3‐Dimensional Structure of a Large Mafic Sill in Sedimentary Strata. Basin Research. ISSN 0950-091X. 37(4). doi: 10.1111/bre.70047. Full text in Research Archive Show summary

  Sills are fundamental elements of volcanic plumbing systems emplaced in sedimentary basins. Even though sills are commonly considered simple, planar concordant igneous sheets, they are actually complex 3‐dimensional objects. Detailed knowledge of the 3D structure of sills and their host rocks is of primary relevance to better constrain the emplacement mechanisms and the impacts of sills on sedimentary basins. This study describes the results of 3‐dimensional geological mapping of a large (~14 × 9 km), well‐exposed Early Cretaceous dolerite sill in Central Spitsbergen, Svalbard, Arctic Norway, using a combination of digital outcrop modelling and field mapping. The sill was emplaced within Upper Palaeozoic sedimentary formations of Svalbard. It is made of distinct segments emplaced at different stratigraphic levels of the host rock stratigraphy. The mapping shows a clear stratigraphic control on the intrusion morphology. Sill segments emplaced at the boundary between two formations, which mark a strong lithological and rheological boundary, are straight and concordant. Conversely, segments emplaced within a more homogeneous formation exhibit more irregular, locally discordant shapes. The sill segments emplaced at distinct stratigraphic levels are connected by steeply dipping steps, which formed through dilatant shearing between the tips of the sill segments. The preferred NW‐SE orientation of the steps and the thinning of the sill towards the SE suggests a propagation direction of the magma towards the SE. Our study shows how 3‐dimensional knowledge of igneous intrusions is key for revealing their emplacement mechanisms.

• Greiner, Sonja H. M.; Sigmundsson, Freysteinn; Geirsson, Halldór; Burchardt, Steffi & Galland, Olivier (2025). Tectonic Stress as the Driving Mechanism for Dike Opening in an Oblique Rift Setting: A Deformation Model of the 2021 Fagradalsfjall Dike, Iceland. Geophysical Research Letters. ISSN 0094-8276. 52(8). doi: 10.1029/2024GL113970. Full text in Research Archive Show summary

  Repeated dike-intrusions often occur in zones where extensional stress has accumulated. Still, geodetic modeling of observed dike-induced ground deformation often ignores the contribution of tectonic stress. On the obliquely spreading Reykjanes Peninsula, Iceland, tectonic strain build-up had been geodetically documented for three decades when a magmatic dike formed at Fagradalsfjall in 2021. We explore the contribution of tectonic stress on dike emplacement in a viscoelastic three-dimensional Finite-Element deformation model. Tectonic stress accumulation is initially simulated through plate motion, and later partially released by opening of a segmented rectangular dike. We find that surface deformation can be largely reproduced by releasing 60% of the accumulated tectonic stress. Partial stress release and low magma overpressure are consistent with successive dike intrusions and low-intensity eruptions in the area. Our model provides an approach to consistently model stress-release constrained by surface deformation.

• Johannesen, Rakul Maria Ingunardóttir; Ólavsdóttir, Jana; Boldreel, Lars Ole; Eidesgaard, Óluva; Senger, Kim & Galland, Olivier (2025). Revisiting the Stratigraphy and Structure of the Faroe Islands Flood Basalts for Large-Scale CO<inf>2</inf> Storage in Basalt Reservoirs. Basin Research. ISSN 0950-091X. 37(3). doi: 10.1111/bre.70032. Full text in Research Archive Show summary

  Comprehensive mapping of the stratigraphy and structures is essential when exploring basaltic reservoirs for CO2 storage. A major task in analysing the storage potential of the reservoir is to bring all relevant geological data within a single framework for integration and joint interpretation. In this study, we illustrate how data integration facilitates an improved understanding of the geological evolution of the Faroe Islands, the North Atlantic Igneous Province, and how the data integration forms a foundation for future carbon capture and storage campaigns. We have integrated new and existing data including geological field observations, digital elevation models, digital outcrop models, lithological logs, seismic profiles, and bathymetry in a single, consistent, and quality-controlled toolbox. Two key findings are that (a) we have mapped stratigraphic markers in the central Faroe Islands across the islands, and there is no indication of large-scale strike-slip faults that offset the volcanic stratigraphy; (b) our analysis provides no clear onshore evidence of transfer zones in the Faroe Islands. We show that a high density of data and integration of data types across different vertical and horizontal scales is crucial for mapping the highly heterogeneous basaltic reservoir.

• Lombardo, Ezequiel F.; Galland, Olivier; Yagupsky, Daniel & Jerram, Dougal Alexander (2024). Characterization of a structural trap associated with an intrusive complex: the El Trapial oilfield, Neuquén Basin, Argentina. Geological Society Special Publication. ISSN 0305-8719. 547(1), p. 291–320. doi: 10.1144/SP547-2023-98. Full text in Research Archive
• Palma, J. Octavio; Rabbel, Ole; Spacapan, Juan B.; Ruiz, Remigio & Galland, Olivier (2024). The Cara Cura intrusive complex, Neuquén Basin, Argentina: a field analogue of a whole igneous petroleum system. Geological Society Special Publication. ISSN 0305-8719. 547, p. 261–290. doi: 10.1144/SP547-2023-119. Full text in Research Archive
• Palma, Octavio Joakim; Burchardt, Steffi; Schmiedel, Tobias; Guerriero, Lucas; Jerram, Dougal Alexander & Mair, Karen [Show all 8 contributors for this article] (2024). Stratigraphy and structure of Chachahuén volcanic complex, southern Mendoza province, Argentina. Journal of South American Earth Sciences. ISSN 0895-9811. 140. doi: 10.1016/j.jsames.2024.104900. Full text in Research Archive
• Galland, Olivier; Villar, Héctor J.; Mescua, José; Jerram, Dougal Alexander; Messager, Gregoire Eugene Philippe & Medialdea, Adrian [Show all 11 contributors for this article] (2024). Structural control of igneous intrusions on fluid migration in sedimentary basins: the case study of large bitumen seeps at Cerro Alquitrán and Cerro La Paloma, northern Neuquén Basin, Argentina. Geological Society Special Publication. ISSN 0305-8719. 547(1), p. 231–259. doi: 10.1144/SP547-2023-115. Full text in Research Archive
• Greiner, Sonja H.M.; Burchardt, Steffi; Sigmundsson, Freysteinn; Óskarsson, Birgir V.; Galland, Olivier & Geirsson, Halldór [Show all 7 contributors for this article] (2023). Interaction between propagating basaltic dikes and pre-existing fractures: A case study in hyaloclastite from Dyrfjöll, Iceland. Journal of Volcanology and Geothermal Research. ISSN 0377-0273. 442. doi: 10.1016/j.jvolgeores.2023.107891. Full text in Research Archive
• Sæter, Torstein; Galland, Olivier; Feneuil, Blandine; Haugen, Håvard Jostein & Carlson, Andreas (2023). Growth of a viscoplastic blister underneath an elastic sheet. Journal of Fluid Mechanics. ISSN 0022-1120. 964, p. 1–16. doi: 10.1017/jfm.2023.320. Full text in Research Archive Show summary

  Inspired by geological structures formed by magmatic intrusions that deform the Earth's crust, we investigate the elastohydrodynamic growth of a viscoplastic blister under an elastic sheet resting on a prewetted substrate. By combining experiments, scaling analysis and numerical simulations, we reveal new regimes for the elastoviscoplastic growth dynamics of the blister. The blister height and its apparent radius grow as h(0,t)∼t5/9 and R(t)∼t2/9 if the fluid pressure is set by bending of the sheet, and as h(0,t)∼t5/13 and R(t)∼t4/13 if the fluid pressure is set by stretching of the sheet. A plug-like flow inside the blister dictates its dynamics, whereas the blister takes a self-similar shape given by a balance of the fluid's yield stress and the pressure gradient induced by the deformation of the elastic sheet.

• Rabbel, Ole; Hasenclever, Jörg; Galerne, Christophe Yann; Galland, Olivier; Mair, Karen & Palma, Octavio (2023). Impact of permeability evolution in igneous sills on hydrothermal flow and hydrocarbon transport in volcanic sedimentary basins. Solid Earth (SE). ISSN 1869-9510. 14(6), p. 625–646. doi: 10.5194/se-14-625-2023. Full text in Research Archive Show summary

  Sills emplaced in organic-rich sedimentary rocks trigger the generation and migration of hydrocarbons in volcanic sedimentary basins. Based on seismic and geological observations, numerical modeling studies of hydrothermal flow around sills show that thermogenic methane is channeled below the intrusion towards its tip, where hydrothermal vents nucleate and transport methane to the surface. However, these models typically assume impermeable sills and ignore potential effects of permeability evolution in cooling sills, e.g., due to fracturing. Here, we combine a geological field study of a volcanic basin (Neuquén Basin, Argentina) with a hybrid finite-element–finite-volume method (FEM–FVM) of numerical modeling of hydrothermal flow around a sill, including hydrocarbon generation and transport. Our field observations show widespread veins within sills composed of graphitized bitumen and cooling joints filled with solid bitumen or fluidized shale. Raman spectroscopy indicates graphitization at temperatures between 350 and 500 ∘C, suggesting fluid flow within the intrusions during cooling. This finding motivates our modeling setup, which investigates flow patterns around and through intrusions that become porous and permeable upon solidification. The results show three flow phases affecting the transport of hydrocarbons generated in the contact aureole: (1) contact-parallel flow toward the sill tip prior to solidification, (2) upon complete solidification, sudden vertical “flushing” of overpressured hydrocarbon-rich fluids from the lower contact aureole towards and into the hot sill along its entire length, and (3) stabilization of hydrocarbon distribution and fading hydrothermal flow. In low-permeability host rocks, hydraulic fracturing facilitates flow and hydrocarbon migration toward the sill by temporarily elevating porosity and permeability. Up to 7.5 % of the generated methane is exposed to temperatures >400 ∘C in the simulations and may thus be permanently stored as graphite in or near the sill. Porosity and permeability creation within cooling sills may impact hydrothermal flow, hydrocarbon transport, and venting in volcanic basins, as it considerably alters the fluid pressure configuration, provides vertical flow paths, and helps to dissipate overpressure below the sills.

• Galland, Olivier; Villar, Héctor J.; Mescua, José; Jerram, Dougal Alexander; Midtkandal, Ivar & Palma, J. Octavio [Show all 8 contributors for this article] (2023). The long-term legacy of subvolcanic intrusions on fluid migration in sedimentary basins: The Cerro Alquitrán case study, northern Neuquén Basin, Argentina. Basin Research. ISSN 0950-091X. 35(5), p. 1840–1855. doi: 10.1111/bre.12782. Full text in Research Archive Show summary

  Abstract Cooling subvolcanic igneous intrusions are known to have a substantial impact on fluid flow in the shallow Earth's crust, for example activation of geothermal systems, circulation of mineralized fluids in ore deposits, fast maturation of organic matter in sedimentary rocks and the potential release of large volumes of greenhouse gases, which have triggered mass extinctions during the Earth's history. However, the long‐term post‐cooling legacy of subvolcanic intrusions on fluid flow received much less attention. Here we describe a demonstrative geological example in the Andean foothills, Argentina, showing that igneous intrusions have long‐term effects on fluid flow after their emplacement and cooling. The case study is a ca. 11‐million‐year‐old, eroded subvolcanic conduit, at the rims of which large volumes of bitumen are naturally seeping out on the Earth's surface. This contribution highlights that intense syn‐emplacement fracturing of the magma has created high‐permeability pathways that affect the regional fluid circulations, even millions of years after cooling. Our observations reveal how extinct subvolcanic intrusions have long‐term consequences on subsurface fluid circulations, which need to be accounted for in the exploration of geothermal energy, drinkable groundwater, hydrocarbons and CO 2 sequestration in volcanic basins and regions hosting ancient shallow magma intrusions.

• Senger, Kim & Galland, Olivier (2022). Stratigraphic and Spatial Extent of HALIP Magmatism in Central Spitsbergen. Geochemistry Geophysics Geosystems. 23(11). doi: 10.1029/2021GC010300. Full text in Research Archive Show summary

  Rapid extensive magmatism may have a profound effect on global climate by liberating and releasing greenhouse gases to the atmosphere through contact metamorphism of lithologically heterogeneous host rocks and degassing of magma and associated lava flows. The high Arctic Archipelago of Svalbard offers accessible, superbly exposed outcrops revealing Early Cretaceous magmatism associated with the High Arctic Large Igneous Province (HALIP). In this contribution, we investigate the onshore-offshore intrusive complex of central Spitsbergen formed due to HALIP activity, that is, the Diabasodden Suite. This is the most “data-rich” part of Svalbard due to past petroleum exploration and research drilling. In this area, the predominantly dolerite intrusions are emplaced in a range of host rocks ranging from Permian carbonate-dominated successions to organic-rich shale-dominated successions of Middle Triassic and Late Jurassic-Early Cretaceous age. Two hundred sixty five individual igneous intrusions, covering 72 km2, are exposed onshore in the study area. This equates to approximately 0.14–2.5 km3 of emplaced magma. In addition, subsurface characterization using borehole, seismic and magnetic data indicates that an area of additional ca. 3,000 km2 is affected by magmatism (magma volume 3.2–195.2 km3). Wireline logs in boreholes characterize both intrusions and associated aureoles. Aureoles with very low resistivity indicate occurrence of organic-rich shales suggesting past fluid circulation and de-gassing. This study forms the foundation for quantifying HALIP-related magmatism in the data-poorer parts of Svalbard, and other circum-Arctic basins.

• Galland, Olivier; Cal, Hernán de la; Mescua, José & Rabbel, Ole (2022). 3-dimensional trapdoor structure of laccolith-induced doming and implications for laccolith emplacement, Pampa Amarilla, Mendoza Province, Argentina. Tectonophysics. ISSN 0040-1951. 836. doi: 10.1016/j.tecto.2022.229418. Full text in Research Archive
• Reutz, Elisabeth Hoffstad & Galland, Olivier (2022). The effect of weak Mohr–Coulomb layers on the onset of caldera collapse - A limit analysis modelling approach. Journal of Volcanology and Geothermal Research. ISSN 0377-0273. 433. doi: 10.1016/j.jvolgeores.2022.107727. Full text in Research Archive Show summary

  Calderas are subcircular volcanic depressions that can occur due to drainage of a subsurface magma reservoir. Numerous models simulating the initiation and growth of caldera collapse consider homogeneous overburden of the magma reservoir. This study describes plastic models implementing limit analysis to investigate the effects of weak layers (low cohesion and low friction) on caldera formation and structure. Our models show that the presence of weak layers within the crust favours the onset of caldera collapse, as it reduces the critical magma underpressure within the magma chamber to initiate roof failure. This effect is more pronounced with greater cumulated thickness of weak layers. In homogeneous models, the onset of caldera collapse is accommodated by a simple, localized outward dipping reverse damage band (caldera fault), whereas in layered models caldera collapse is accommodated by more complex damage structures. Weak layers confine damage underneath the layers, limiting the growth of the caldera fault toward the surface. Calculated stress trajectories are rotated across weak layers, showing that weak layers act as stress barriers. The effect of weak layers is stronger when the layer is closer to the magma reservoir, where layer-parallel damage form underneath the layer, interpreted as a potential detachment level. Multiple layers trigger more distribution of the damage and several layer-parallel damage bands. The subsurface distribution of damage due to weak layers may lead to more distributed surface subsidence, enhancing sagging before a caldera fault reaches the surface. Finally, internal detachments due to weak layers are likely important for observed episodic transient subsurface collapse episodes before collapse occurs at surface. All in all, our models that implement plastic deformation predict significant stress perturbations as a result of varying Mohr–Coulomb properties only. Our study thus shows that widely used static elastic models are not sufficient for physically relevant stress analyses of geological systems. In addition, our study shows that plastic (or elasto-plastic) models are necessary to predict the location and extent of inelastic damage accommodating volcano deformation and failure.

• Lescoutre, Rodolphe; Almqvist, Bjarne; Koyi, Hemin; Berthet, Théo; Hedin, Peter & Galland, Olivier [Show all 9 contributors for this article] (2022). Large-scale, flat-lying mafic intrusions in the Baltican crust and their influence on basement deformation during the Caledonian orogeny. Geological Society of America Bulletin. ISSN 0016-7606. 134(11-12), p. 3022–3048. doi: 10.1130/B36202.1. Full text in Research Archive Show summary

  Abstract The Fennoscandian Shield in central Sweden displays a complex structural and compositional architecture that is mainly related to the Proterozoic history of the Baltica paleocontinent. In its western parts, the Precambrian basement is covered by the allochthonous rocks of the Caledonide orogen, and direct information about the underlying crust is restricted to a few unevenly distributed basement windows in western Sweden and Norway. In this study, we use preliminary results from the second borehole of the Collisional Orogeny in the Scandinavian Caledonides project (COSC-2), new gravity data, forward gravity, and magnetic modeling and interpretation of seismic reflection profiles to assess the 3-D architecture of the basement. Our results reveal a wide (~100 km) and dense network of mainly flat-lying and saucer-shaped dolerites intruding the volcanic and granitic upper crustal rocks of the Transscandinavian Igneous Belt. Similar intrusion geometries related to 1.2 Ga dolerites can be recognized in the Fennoscandian Shield. We discuss that the formation of these sill complexes occurred in a lithologically and structurally heterogeneous crust during transtension, which is in disagreement with the current understanding of sill emplacement that involves crustal shortening, layering, or anisotropy of the host rock. Our seismic interpretation and the structural observations from the COSC-2 drilling show that part of the Caledonian-related basement deformation was localized along the margins of the dolerite sheets. We propose that the dolerite intrusion geometry, akin to a flat-ramp geometry, guided the basement deformation during the Caledonian orogeny.

• Rincón, M.; Márquez, A.; Herrera, R.; Galland, Olivier; Sánchez-Oro, J. & Concha, D. [Show all 7 contributors for this article] (2022). Monitoring Volcanic and Tectonic Sandbox Analogue Models Using the Kinect v2 Sensor. Earth and Space Science. 9(6). doi: 10.1029/2020EA001368. Full text in Research Archive Show summary

  The measurement of surface deformation in analogue models of volcanic and tectonic processes is an area in continuous development. Properly quantifying topography change in analogue models is key for a useful comparison between experiment results and nature. The aim of this work is to evaluate the capabilities of the simple and cheap Microsoft® Kinect v2 sensor for monitoring analogue models made of granular materials. Microsoft® Kinect v2 is a video-gaming RedGreenBlue-Depth device combining an optical camera and an infrared distance measurement sensor. The precision of the device for model topography measurements has been quantified using 64 experiments, with variable granular materials materials and distance to the model. Additionally, we tested the capabilities of averaging several distance images to increase the precision. We have developed a specific software to facilitate the acquisition and processing of the Kinect v2 data in experiment monitoring. Our results show that measurement precision is material dependent: with clear-colored and fine-grained materials, a precision ∼1.0 mm for digital elevation models with a 1.6 mm pixel size can be obtained. We show that by averaging ≥5 consecutive images the distance precision can reach values as low as 0.5 mm. To show the Kinect v2 capabilities, we present monitoring results from case study experiments modeling tectonics and volcano deformation. The Kinect v2 achieves lower spatial resolutions and precision than more sophisticated techniques such as photogrammetry. However, Kinect v2 provides a cheap, straightforward and powerful tool for monitoring the topography changes in sandbox analogue models.

• Schmiedel, Tobias; Burchardt, Steffi; Mattsson, Tobias; Guldstrand, Frank Bo Buster; Galland, Olivier & Palma, Octavio [Show all 7 contributors for this article] (2021). Emplacement and Segment Geometry of Large, High-Viscosity Magmatic Sheets. Minerals. 11(10). doi: 10.3390/min11101113. Full text in Research Archive Show summary

  Understanding magma transport in sheet intrusions is crucial to interpreting volcanic unrest. Studies of dyke emplacement and geometry focus predominantly on low-viscosity, mafic dykes. Here, we present an in-depth study of two high-viscosity dykes (106 Pa·s) in the Chachahuén volcano, Argentina, the Great Dyke and the Sosa Dyke. To quantify dyke geometries, magma flow indicators, and magma viscosity, we combine photogrammetry, microstructural analysis, igneous petrology, Fourier-Transform-Infrared-Spectroscopy, and Anisotropy of Magnetic Susceptibility (AMS). Our results show that the dykes consist of 3 to 8 mappable segments up to 2 km long. Segments often end in a bifurcation, and segment tips are predominantly oval, but elliptical tips occur in the outermost segments of the Great Dyke. Furthermore, variations in host rocks have no observable impact on dyke geometry. AMS fabrics and other flow indicators in the Sosa Dyke show lateral magma flow in contrast to the vertical flow suggested by the segment geometries. A comparison with segment geometries of low-viscosity dykes shows that our high-viscosity dykes follow the same geometrical trend. In fact, the data compilation supports that dyke segment and tip geometries reflect different stages in dyke emplacement, questioning the current usage for final sheet geometries as proxies for emplacement mechanism.

• Mattsson, Tobias; Petri, Benoît; Almqvist, Bjarne S.G.; McCarthy, William; Burchardt, Steffi & Palma, Octavio [Show all 8 contributors for this article] (2021). Decrypting Magnetic Fabrics (AMS, AARM, AIRM) Through the Analysis of Mineral Shape Fabrics and Distribution Anisotropy. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 126(6). doi: 10.1029/2021JB021895. Full text in Research Archive Show summary

  Anisotropy of magnetic susceptibility (AMS) and anisotropy of magnetic remanence (AARM and AIRM) are efficient and versatile techniques to indirectly determine rock fabrics. Yet, deciphering the source of a magnetic fabric remains a crucial and challenging step, notably in the presence of ferrimagnetic phases. Here we use X-ray micro-computed tomography to directly compare mineral shape-preferred orientation and spatial distribution fabrics to AMS, AARM and AIRM fabrics from five hypabyssal trachyandesite samples. Magnetite grains in the trachyandesite are euhedral with a mean aspect ratio of 1.44 (0.24 s.d., long/short axis), and >50% of the magnetite grains occur in clusters, and they are therefore prone to interact magnetically. Amphibole grains are prolate with magnetite in breakdown rims. We identified three components of the petrofabric that influence the AMS of the analyzed samples: The magnetite and the amphibole shape fabrics and the magnetite distribution anisotropy. Depending on their relative strength, orientation and shape, these three components interfere either constructively or destructively to produce the AMS fabric. If the three components are coaxial, the result is a relatively strongly anisotropic AMS fabric (P' = 1.079). If shape fabrics and/or magnetite distribution anisotropy are non-coaxial, the resulting AMS is weakly anisotropic (P' = 1.012). This study thus reports quantitative petrofabric data that show the effect of magnetite distribution anisotropy on magnetic fabrics in igneous rocks, which has so far only been predicted by experimental and theoretical models. Our results have first-order implications for the interpretation of petrofabrics using magnetic methods.

• Bertelsen, Håvard Svanes; Guldstrand, Frank Bo Buster; Sigmundsson, Freysteinn; Pedersen, Rikke; Mair, Karen & Galland, Olivier (2021). Beyond elasticity: Are Coulomb properties of the Earth's crust important for volcano geodesy? Journal of Volcanology and Geothermal Research. ISSN 0377-0273. 410. doi: 10.1016/j.jvolgeores.2020.107153. Full text in Research Archive
• Poppe, Sam; Holohan, Eoghan P.; Rudolf, Michael; Rosenau, Matthias; Galland, Olivier & Delcamp, Audray [Show all 7 contributors for this article] (2021). Mechanical properties of quartz sand and gypsum powder (plaster) mixtures: Implications for laboratory model analogues for the Earth's upper crust. Tectonophysics. ISSN 0040-1951. 814. doi: 10.1016/j.tecto.2021.228976. Full text in Research Archive
• Rabbel, Ole; Palma, Octavio; Mair, Karen; Galland, Olivier; Spacapan, Juan Bautista & Senger, Kim (2021). Fracture networks in shale-hosted igneous intrusions: Processes, distribution and implications for igneous petroleum systems. Journal of Structural Geology. ISSN 0191-8141. 150. doi: 10.1016/j.jsg.2021.104403. Full text in Research Archive Show summary

  Igneous intrusions in sedimentary basins can influence basin-scale fluid flow and petroleum systems in various ways. They may act as barriers, preferential pathways or even reservoirs for fluids. The fracture networks of intrusions usually represent the main control of their hydraulic properties. However, our understanding of different fracturing mechanisms and their quantitative effect on fracture network properties remains limited, and good field examples are sparse. Here, we present a comprehensive field study from the Neuquén Basin, Argentina, using a reservoir-scale outcrop of a sill complex emplaced in organic-rich shale, which constitutes a direct analogue of oil-producing fractured igneous reservoirs. We provide field evidence of various fracturing mechanisms affecting the fracture network, including cooling joints, bituminous dykes, hydrothermal veins, and tectonic faults. Using high-resolution digital fracture network quantification, we then tie these fracture mechanisms to spatial variations of fracture orientation, intensity and connectivity. Our results indicate that all observed fracture types are involved in hydrocarbon migration and/or storage. Bitumen of very high thermal grade within the intrusions implies migration of hydrocarbons into the sills in a destructive high-temperature environment. Importantly, bitumen dykes and faults locally alter the fracture network, creating zones of strongly increased fracture intensity and connectivity and therefore improved reservoir properties.

• Pierdominici, Simona; Millet, John M.; Kück, Jochem K. M.; Thomas, Donald; Jerram, Dougal Alexander & Planke, Sverre [Show all 9 contributors for this article] (2020). Stress Field Interactions Between Overlapping Shield Volcanoes: Borehole Breakout Evidence From the Island of Hawai'i, USA. Journal of Geophysical Research (JGR): Earth Surface. ISSN 2169-9003. 125(8). doi: 10.1029/2020JB019768. Full text in Research Archive Show summary

  Knowledge of the in situ stress state of the Earth's crust plays a key role in understanding geological processes including plate tectonics, earthquakes, slope failure, and igneous emplacement. In this paper, we determine the in situ stress orientation from the PTA2 borehole on the island of Hawai'i, drilled into a lava flow dominated sequence between Mauna Kea and Mauna Loa. High‐resolution acoustic images were collected from the open hole interval 886 m to 1,567 m. Based on identification of 371 borehole breakouts for a total length of 310 m, the mean orientation of the minimum horizontal principal stress is N106° and remains constant across different volcanic rock fabrics. Changes in borehole breakout shape are linked to the different strength of volcanic facies and intra‐facies. The orientation of the present‐day stress field at Mauna Kea deviates from the plate forces and regional tectonic stress field. We interpret the compressive stress regime at the PTA2 site as resulting from the competing gravitational fields of the large topographic highs of Mauna Kea and Mauna Loa. Our study reveals that the mass accumulation associated with shield volcano growth imparts significant local variations to the subsurface stress state on volcanic islands consisting of overlapping shield volcanoes. The results have significant implications for stress accumulation leading to brittle failure and flank collapse, along with potentially influencing magma accumulation and ascent pathways during volcanic island evolution. This study provides the first insights into the orientation of the present‐day stress field between the major island forming shield volcanoes of Hawai'i.

• Senger, Kim; Betlem, Peter; Birchall, Thomas; Buckley, Simon John; Coakley, Bernard & Eide, Christian Haug [Show all 23 contributors for this article] (2020). Using digital outcrops to make the high Arctic more accessible through the Svalbox database. Journal of Geoscience Education (JGE). ISSN 1089-9995. doi: 10.1080/10899995.2020.1813865. Full text in Research Archive Show summary

  The high Arctic is a remote place, where geoscientific research and teaching require expensive and logistically demanding expeditions to make use of the short field seasons. The absence of vegetation facilitates the use of modern photogrammetric techniques for the cost-effective generation of high-resolution digital outcrop models (DOMs). These georeferenced models can be used in pre-fieldwork activities to help prepare for traditional geological fieldwork, during fieldwork to record observations, and post-fieldwork to conduct quantitative geological analyses. Analyses of DOMs range in scale from mm-cm (e.g., size and spacing of dinosaur footprints), to hundreds of meters (e.g., seismic modeling of outcrops and outcrop-well-seismic correlations) and can advance research objectives. This integration is strengthened if key geoscientific data, like geological and topographical maps, subsurface profiles, borehole data, remote sensing data, geophysical data and DOMs can be integrated through a common database, such as the Svalbox database that we present in this commentary. Svalbox geographically targets the Svalbard archipelago, where fieldwork is challenging due to the harsh polar environment, risk of polar bear encounters and demanding transport to the field area. The University Centre in Svalbard nonetheless relies on utilizing the natural Svalbard environment for its field-based education, and now makes use of Svalbox to make geological fieldwork more efficient and post-fieldwork analyses more quantitative. Experience and usage of such tools in geoscientific education, particularly in the polar regions, is not well documented. Therefore, we share experiences on both developing and optimizing Svalbox, and on student and lecturer usage. Svalbox includes a web-based interface through which DOMs are shared and displayed together with relevant public-domain geoscientific data sets. Svalbox also serves as a platform to share student and teacher experiences on the entire DOM workflow, from acquisition to data distribution. For the Svalbox users questioned by the project group, DOMs were found to provide many benefits, including quantitative analyses, extended field season, appreciation of scale and data sharing that significantly outweigh present-day challenges, such as the need for expensive hardware and lack of easily accessible interpretation software, the latter being surmountable within the near-term

• Sleveland, Arve; Midtkandal, Ivar; Galland, Olivier & Leanza, Hector Armando (2020). Sedimentary Architecture of Storm-Influenced Tidal Flat Deposits of the Upper Mulichinco Formation, Neuquén Basin, Argentina. Frontiers in Earth Sciences. ISSN 1863-4621. 8. doi: 10.3389/feart.2020.00219. Full text in Research Archive Show summary

  This study reports on the Lower Cretaceous upper Mulichinco Formation in the Neuquén Basin, west-central Argentina. The studied succession comprises shallow marine strata, deposited in a mixed wave and tidal flat environment where ebb-tidal currents dominated. We describe mixed storm- and tide-influenced deposits within progradationally stacked high-frequency sequences and discuss process interaction, sediment dispersal, and preservation potential. These storm and tidal deposits mix spatially on bed, bedset, and sequence scales, suggesting multi-scale process interactions. The study investigates a 12-km-long continuous outcrop, oriented sub-parallel to the paleocoastline. The succession comprises subtidal flat and meandering tidal channel complexes, with interbedding and interfingering of storm and tidal deposits. The tidal deposits are widespread and comprise moderately sorted sandstones with bimodal paleocurrent directions, single and double mud drapes, reactivation surfaces, and inclined heterolithic stratification. Varying bimodal paleocurrent directions suggest that the paleocoastline was irregular, consisting of both protrusions and bays. Storm deposits are mainly found erosively interbedded with subtidal flat sandstones, and exhibit decimeter-thick, well-sorted hummocky and swaley cross-stratified sandstones. These storm deposits show systematic lateral variations in abundance, from dominant to absent, which are linked to subtle variations in water depth along the irregular paleocoastline. As the tidal deposits are widespread across the study area, and with no significant facies change, the varying dispersal of storm-influenced deposits is considered a product of wave refraction, with converging and diverging wave energy at interpreted positions of coastal protrusions and embayments, respectively. Consequently, the irregular paleocoastline morphology caused spatial variability in wave impact and controlled preservation of interbedded storm and tidal deposits at the coastal protrusions while facilitating complete tidal remobilization of sediments in the embayments. With no evidence for fluvial influence, ebb-tidal currents are considered as the main drivers for sediment dispersal onto the subtidal flat, through the meandering tidal channels.

• Poppe, Sam; Galland, Olivier; Winter, N. J. de; Goderis, S.; Claeys, P. & Debaille, V. [Show all 8 contributors for this article] (2020). Structural and Geochemical Interactions Between Magma and Sedimentary Host Rock: The Hovedøya Case, Oslo Rift, Norway. Geochemistry Geophysics Geosystems. 21(3). doi: 10.1029/2019GC008685. Full text in Research Archive Show summary

  Two end‐member conceptual models are used to describe deformation of the Earth's crust induced by magma intrusion. “Mode I” fracturing assumes tensile or opening‐mode, elastic deformation, while “Mode II” fracturing assumes plastic shear‐mode deformation around a viscous indenter. Field observations of both mechanisms exist, but it remains unclear which mechanism dominates in which conditions. We describe intrusion geometries, host rock deformation, and geochemical magma‐host rock interactions around 53 exceptionally preserved, tephrite‐basanite Permian dike segments of 0.5‐ to 30‐cm thickness. These thin dikes, that is, “dikelets,” intruded Late‐Ordovician carbonate‐rich sedimentary rocks on Hovedøya island, Oslo Rift, Norway. Dikelets emplaced in preexisting fractures dominantly created cavities ahead of their narrow, tapering tips and are associated with bent host rock, broken bridges, and stepped segmented geometries. Other tips are blunt with dense brittle fracturing around them. Also, cross‐sectional intrusion segment opening profiles deviate from parabola‐shaped profiles typical for elastic media. The observations demonstrate that dominant opening‐mode host rock deformation can coexist with shear‐mode deformation locally. Alignment of most dikelet segments along the dominant host rock fracture directions highlights the control of local structural orientations on magma emplacement. Analysis of bulk major and trace element compositions, in situ micro‐XRF sample analysis and carbon and oxygen stable isotope compositions, suggests that thermochemical interactions between magma and the carbonate‐rich host rock produced a low‐viscosity mixture of magma, pore water, and gas. We propose that such low‐viscosity hybrid fluid may assist in the intrusion of magma in sedimentary rocks by filling the cavity ahead of propagating sheet intrusion tips.

• Rabbel, Ole; Mair, Karen; Galland, Olivier; Grühser, Carina & Meier, Tobias (2020). Numerical Modeling of Fracture Network Evolution in Organic‐Rich Shale With Rapid Internal Fluid Generation. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 125. doi: 10.1029/2020JB019445. Full text in Research Archive Show summary

  When low‐permeability and organic‐rich rocks such as shale experience sufficient heating, chemical reactions including shale dehydration and maturation of organic matter lead to internal fluid generation. This may cause substantial pore fluid overpressure and fracturing. In the vicinity of igneous intrusions emplaced in organic‐rich shales, temperatures of several hundred degrees accelerate these processes and lead to intense fracturing. The resulting fracture network provides hydraulic pathways, which allow fluid expulsion and affect hydrothermal fluid flow patterns. However, the evolution of these complex fracture networks and controls on geometry and connectivity are poorly understood. Here, we perform a numerical modeling study based on the extended finite element method to investigate coupled hydromechanical fracture network evolution due to fast internal fluid generation. We quantify the evolution of different initial fracture networks under varying external stresses by analyzing parameters including fracture length, opening, connectivity, and propagation angles. The results indicate a three‐phase process including (1) individual growth, (2) interaction, and (3) expulsion phase. Magnitude of external stress anisotropy and degree of fracture alignment with the largest principal stress correlate with increased fracture opening. We additionally find that although the external stress field controls the overall fracture orientation distribution, local stress interactions may cause significant deviations of fracture paths and control the coalescence characteristics of fractures. Establishing high connectivity in cases with horizontally aligned initial fractures requires stress anisotropy with σV > σH, while the initial orientation distribution is critical for connectivity if stresses are nearly isotropic.

• Souche, Alban; Galland, Olivier; Haug, Øystein Thorden & Dabrowski, Marcin (2019). Impact of host rock heterogeneity on failure around pressurized conduits: Implications for finger-shaped magmatic intrusions. Tectonophysics. ISSN 0040-1951. 765, p. 52–63. doi: 10.1016/j.tecto.2019.05.016. Full text in Research Archive Show summary

  Rock failure accommodating the emplacement of magmatic intrusions is controlled by the local stress regime within the host rock. Most of the mechanical models addressing rock failure conditions (e.g., for a given tectonic regime or magma overpressure) simplify the stress calculation by assuming the homogeneity of the host rock properties. In this study, we highlight the importance of local heterogeneities in controlling the localization of the deformation and the failure mechanism around a magmatic intrusion. We numerically model the elastoplastic deformation of a heterogeneous host rock intruded by an overpressurized magmatic body of cylindrical or finger-shaped geometry. The plastic component of the deformation is considered with a mixed mode mechanism allowing dilatant and shear displacements to act simultaneously. Our simulations are performed for small strain amplitudes that reflect the pre-failure conditions of the host. We assess the subsequent failure mechanism of the system based on the development of the localized strain patterns. The heterogeneity in the model is introduced by a stochastic perturbation of the host rock cohesion with characteristic wavelength and amplitude. We show that a relatively small perturbation of ±10% of the cohesion field can efficiently localize the plastic deformation and control the subsequent emplacement mechanism. We further investigate a more realistic geological scenario in which the intrusion resides within sedimentary layers of contrasting strength, resulting in both heterogeneity and anisotropy of mechanical properties in the host rock. Our model reproduces similar deformation patterns as observed around finger-shaped magma intrusions within the Vaca Muerta shales in the Neuquén basin, Argentina. We conclude that heterogeneities within the host rock may locally “seed” dilatant shear faults around magmatic conduits and finger-shaped intrusions and result in the development of a process zone of length scale in order with the intrusion radius length scale.

• Schmiedel, Tobias; Galland, Olivier; Haug, Øystein Thorden; Dumazer, Guillaume Henri & Breitkreuz, Christoph (2019). Coulomb failure of Earth's brittle crust controls growth, emplacement and shapes of igneous sills, saucer-shaped sills and laccoliths. Earth and Planetary Science Letters. ISSN 0012-821X. 510, p. 161–172. doi: 10.1016/j.epsl.2019.01.011. Full text in Research Archive Show summary

  Tabular intrusions are common features in the Earth's brittle crust. They exhibit a broad variety of shapes, ranging from thin sheet intrusions (sills, saucer-shaped sills, cone sheets), to more massive intrusions (domed and punched laccoliths, stocks). Such a diversity of intrusion shapes reflects different emplacement mechanisms caused by contrasting host rock and magma rheologies. Most current models of tabular intrusion emplacement assume that the host rock behaves purely elastically, whereas numerous observations show that shear failure plays a major role. In this study, we investigate the effects of the host rock's Coulomb properties on magma emplacement by integrating (1) laboratory models using dry Coulomb granular model hosts of variable strength (cohesion) and (2) limit analysis numerical models. Our results show that both sheet and massive tabular intrusions initiate as a sill, which triggers shear failure of its overburden along an inclined shear damage zone at a critical sill radius, which depends on the emplacement depth and the overburden's cohesion. Two scenarios are then possible: (1) if the cohesion of the overburden is significant, opening of a planar fracture along the precursory weakened shear damage zones to accommodate magma flow, leads to the formation of inclined sheets, or (2) if the cohesion of the overburden is negligible, the sill inflates and lifts up the overburden, which is dissected by several faults that control the growth of a massive intrusion. Finally, we derive a theoretical scaling that predicts the thickness-to-radius aspect ratios of the laboratory sheet intrusions. This theoretical prediction shows how sheet intrusion morphologies are controlled by a mechanical equilibrium between the flowing viscous magma and Coulomb shear failure of the overburden. Our study suggests that the emplacement of sheet and massive tabular intrusions are parts of the same mechanical regime, in which the Coulomb behavior of the Earth's brittle crust plays an essential role.

• Kjøll, Hans Jørgen; Galland, Olivier; Labrousse, Loic & Andersen, Torgeir Bjørge (2019). Emplacement mechanisms of a dyke swarm across the brittle-ductile transition and the geodynamic implications for magma-rich margins. Earth and Planetary Science Letters. ISSN 0012-821X. 518, p. 223–235. doi: 10.1016/j.epsl.2019.04.016. Full text in Research Archive Show summary

  gneous dykes are the main magma transport pathways through the Earth’s crust, and they are considered to mainly accommodate for tectonic extension in volcanic rifts. Dykes are typically considered to result from brittle fracturing, even in the ductile crust. A common assumption is that dyke orientation is controlled by tectonic stresses, such that dykes in rifts are expected to be vertical and perpendicular to extension. Here we report on detailed field observations of a spectacularly well-exposed dyke swarm to show that dykes were not systematically emplaced by purely brittle processes and that dyke orientation may differ from the dominant tectonic stress orientations. The dyke complex formed near the brittle-ductile transition during opening of the Iapetus Ocean and is now exposed in the Scandinavian Caledonides. Distinct dyke morphologies related to different emplacement mechanisms has been recognized: 1) Brittle dykes that exhibit straight contacts with the host rock, sharp tips, en-echelon segments with bridges exhibiting angular fragments; 2) Brittle-ductile dykes that exhibit undulating contacts, rounded tips, ductile folding in the host rock and contemporaneous brittle and ductile features;3) Ductile “dykes” that exhibit rounded shapes and mingling between the soft ductile host rock and the intruding mafic magma. The brittle dykes exhibit two distinct orientations separated by c. 30◦ that are mutually cross-cutting, suggesting that the dyke swam did not consist of only vertical sheets perpendicular to regional extension, as expected in rifts. We were able to use the well-exposed host rock layers as markers to perform a kinematic restoration to quantify the average strain accommodating the emplacement of the dyke complex: it accommodated for >100% extension, but counter-intuitively it also accommodated for 27% crustal thickening. We infer that the magma influx rate was higher than the tectonic stretching rate, implying that magma was emplaced forcefully, as supported by field observations. Finally, our observations suggest that the fast emplacement of the dyke swarm triggered a rapid shallowing of the brittle-ductile transition, and lead to a considerable weakening of the crust. Our study can potentially have large implications significant for surface topography and seismicity in active rifts and volcanic areas around the world.

• Galland, Olivier; Spacapan, Juan Bautista; Rabbel, Ole; Mair, Karen; Soto, Frederico Gonzalez & Eiken, Trond [Show all 8 contributors for this article] (2019). Structure, emplacement mechanism and magma-flow significance of igneous fingers ? Implications for sill emplacement in sedimentary basins. Journal of Structural Geology. ISSN 0191-8141. 124, p. 120–135. doi: 10.1016/j.jsg.2019.04.013. Full text in Research Archive Show summary

  Field and seismic observations show that numerous sills exhibit lobate morphologies. Each lobe corresponds to a distinct igneous segment exhibiting a finger-like shape, the long axis of which is commonly interpreted as a magma-flow indicator. Robust understanding of the emplacement mechanisms of finger-shaped sills, and direct observations supporting finger orientation as magma-flow indicator are lacking. In this paper, we present the results of detailed structural mapping on an exceptional, easily accessible 1-km long outcrop in the Neuquén Basin, Argentina, that exhibits a sill, its contacts and the structures in the finely layered sedimentary host rock. We show that the sill is made of distinct segments that grew, inflated or coalesced. We also demonstrate that the fingers were emplaced according to the viscoelastic fingering or viscous indenter models, with no field evidence of tensile elastic fracture mechanism as commonly assumed in mechanical models of sill emplacement. We identified new structural criteria at the intrusion's contacts for inferring magma flow direction during the magma emplacement. Our small-scale structural observations carried out on a seismic-scale outcrop have the potential to considerably aid the structural interpretation of seismic data imaging igneous sills, i.e. to fill the standard gap between outcrop-scale field observations and seismic-scale geophysical data.

• Burchardt, Steffi; Mattsson, Tobias; Palma, J Octavio; Galland, Olivier; Almqvist, Bjarne & Mair, Karen [Show all 9 contributors for this article] (2019). Progressive Growth of the Cerro Bayo Cryptodome, Chachahuen Volcano, Argentina?Implications for Viscous Magma Emplacement. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 124(8), p. 7934–7961. doi: 10.1029/2019JB017543. Full text in Research Archive
• Spacapan, Juan Bautista; D'Odorico, Alejandro; Palma, Octavio; Galland, Olivier; Senger, Kim & Ruiz, Remigio [Show all 8 contributors for this article] (2019). Low resistivity zones at contacts of igneous intrusions emplaced in organic-rich formations and their implications on fluid flow and petroleum systems: a case study in the northern Neuquén Basin, Argentina. Basin Research. ISSN 0950-091X. 32(1), p. 3–24. doi: 10.1111/bre.12363. Full text in Research Archive Show summary

  Igneous sills and laccoliths emplaced in sedimentary basins may significantly impact petroleum systems, both positively and negatively. Igneous intrusions provide heat to maturate regionally immature organic‐rich host rocks, act as fractured reservoirs hosting commercial accumulations of hydrocarbons, and form structures affecting fluid flow and trapping at different scales. Nevertheless, the petrophysical implications of igneous intrusions on their host rock are poorly known. In this study, we analyse 200 wells in the Río Grande Valley oil field, Neuquén basin, Argentina, where the main reservoirs are in fractured igneous sills. This dataset represents a globally unique possibility to characterize the igneous–host rock interaction using both wireline logs and core material. We identify a systematic Contact Low Resistivity Zone (CLRsZ) at both the upper and lower contacts of the sills emplaced in the organic‐rich Vaca Muerta and Agrio Formations. We characterize the nature of these CLRsZ and their petrophysical properties by integrating resistivity and gamma ray well logs, petrographic analyses, petrophysical tests and geochemical analyses. The low resistivity signal of the CLRsZ is dominantly carried by massive‐sulphide deposits, mainly pyrite, observed both in the host rock and the chilled margin of the sills. Well log images and porosity‐permeability analysis on core plugs show that both the sills and their associated CLRsZ can act as carrier for fluid flow and reservoir for hydrocarbons storage. The thickness of the upper and lower CLRsZ correlates linearly with the thickness of the sill, and the volume of both the upper and lower CLRsZ represents ca. 40% with respect to the volume of their associated sill. The thickness of the CLRsZ represents ca. 13% of the thickness of contact aureole induced by the sills. In the CLRsZ, a great proportion of kerogen was transformed to hydrocarbon, so that CLRsZ were restricted to the innermost contact aureole of the sills. Our results show that the CLRsZ can have major implications on fluid flow and should be considered in reservoir models in volcanic basins hosting sills emplaced in organic‐rich formations.

• Poppe, Sam; Holohan, Eoghan; Galland, Olivier; Buls, Nico; Gompel, Gert Van & Keelson, Benyameen [Show all 11 contributors for this article] (2019). An inside perspective on magma intrusion: Quantifying 3d displacement and strain in laboratory experiments by dynamic X-ray computed tomography. Frontiers in Earth Science. 7. doi: 10.3389/feart.2019.00062. Full text in Research Archive Show summary

  Magma intrusions grow to their final geometries by deforming the Earth's crust internally and by displacing the Earth's surface. Interpreting the related displacements in terms of intrusion geometry is key to forecasting a volcanic eruption. While scaled laboratory models enable us to study the relationships between surface displacement and intrusion geometry, past approaches entailed limitations regarding imaging of the laboratory model interior or simplicity of the simulated crustal rheology. Here we apply cutting-edge medical wide beam X-ray Computed Tomography (CT) to quantify in 4D the deformation induced in laboratory models by an intrusion of a magma analog (golden syrup) into a rheologically-complex granular host rock analog (sand and plaster). We extract the surface deformation and we quantify the strain field of the entire experimental volume in 3D over time by using Digital Volume Correlation (DVC). By varying the strength and height of the host material, and intrusion velocity, we observe how intrusions of contrasting geometries grow, and induce contrasting strain field characteristics and surface deformation in 4D. The novel application of CT and DVC reveals that distributed strain accommodation and mixed-mode (opening and shear) fracturing dominates in low-cohesion material overburden, and leads to the growth of thick cryptodomes or cup-shaped intrusions. More localized strain accommodation and opening-mode fracturing dominates in high-cohesion material overburden, and leads to the growth of cone sheets or thin dikes. The results demonstrate how the combination of CT and DVC can greatly enhance the utility of optically non-transparent crustal rock analogs in obtaining insights into shallow crustal deformation processes. This unprecedented perspective on the spatio-temporal interaction of intrusion growth coupled with host material deformation provides a conceptual framework that can be tested by field observations at eroded volcanic systems and by the ever increasing spatial and temporal resolution of geodetic data at active volcanoes.

• Haug, Øystein Thorden; Galland, Olivier; Souloumiac, Pauline; Souche, Alban; Guldstrand, Frank Bo Buster & Schmiedel, Tobias [Show all 7 contributors for this article] (2018). Shear Versus Tensile Failure Mechanisms Induced by Sill Intrusions: Implications for Emplacement of Conical and Saucer-Shaped Intrusions. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 123(5), p. 3430–3449. doi: 10.1002/2017JB015196. Full text in Research Archive Show summary

  Sills, saucer‐shaped sills, and cone sheets are fundamental magma conduits in many sedimentary basins worldwide. Models of their emplacement usually approximate the host rock properties as purely elastic and consider the plastic deformation to be negligible. However, many field observations suggest that inelastic damage and shear fracturing play a significant role during sill emplacement. Here we use a rigid plasticity approach, through limit analysis modeling, to study the conditions required for inelastic deformation of sill overburdens. Our models produce distinct shear failure structures that resemble intrusive bodies, such as cone sheets and saucer‐shaped sills. This suggests that shear damage greatly controls the transition from flat sill to inclined sheets. We derive an empirical scaling law of the critical overpressure required for shear failure of the sill's overburden. This scaling law allows to predict the critical sill diameter at which shear failure of the overburden occurs, which matches the diameters of natural saucer‐shaped intrusions' inner sills. A quantitative comparison between our shear failure model and the established sill's tensile propagation mechanism suggests that sills initially propagate as tensile fractures, until reaching a critical diameter at which shear failure of the overburden controls the subsequent emplacement of the magma. This comparison also allows us to predict, for the first time, the conditions of emplacement of both conical intrusions, saucer‐shaped intrusions, and large concordant sills. Beyond the application to sills, our study suggests that shear failure significantly controls the emplacement of igneous sheet intrusions in the Earth's brittle crust.

• Planke, Sverre; Rabbel, Ole; Galland, Olivier; Millet, John; Manson, Ben & Jerram, Dougal Alexander [Show all 8 contributors for this article] (2018). Seismic imaging and petroleum implications of igneous intrusions in sedimentary basins constrained by outcrop analogues and seismic data from the Neuquén Basin and the NE Atlantic. In Vernengo, Luis; Atencio, Mario; Branca, Marcela; Corti, Eduardo; D'Biassi, Tomás; Enrique, Jorge Dario; Torrejón, Maximiliano García; Pianelli, Luis; Ricardi, Alberto; Soubiés, Daniel & Späth, Federico (Ed.), 10 Congreso de Exploración y Desarrollo de Hidrocarburos - Simposio de Geofísica: La geofísica como vinculo entre el conocimiento de la tierra y la sociedad. Instituto Argentino del Petroleo y del Gas. ISSN 9789879139929. p. 343–366. Full text in Research Archive

View all works in NVA

• Galland, Olivier (2026). Beyond Elasticity – How inelastic properties of crustal rocks control the propagation of dykes and sills in volcanic plumbing systems. Full text in Research Archive
• Pinel, Virginie & Galland, Olivier (2026). Limitations of dislocation models for quantifying surface displacement induced by the buoyancy of ascending dikes. doi: https:/meetingorganizer.copernicus.org/EGU26/EGU26-5871.html. Full text in Research Archive Show summary

  Dislocation models, whether analytical or numerical, are widely used to interpret surface displacements induced by magmatic intrusions. Deep learning methods developed for interpreting InSAR data are also trained using synthetic data produced by dislocation models. While these models are well suited to describing the deformation and stresses induced by the emplacement of magma within a planar structure, they neglect buoyancy, which is the main driving mechanism for magma ascent within the crust. We use analog experiments to highlight the effect of buoyancy on dike-induced surface deformation. Finite volumes of air or silicone oil are injected into gelatin, which is characterized by elastic behavior. The fluid-filled crack rises vertically through the gelatin due to buoyancy. Its position, shape, and orientation are tracked by side cameras, and the surface displacement of the gelatin is measured simultaneously by photogrammetry and pixel shift tracking from images acquired by four synchronized cameras located at the top of the experimental setup. We compare the displacement field estimated from the dislocation model with the recorded displacement field in the laboratory. We show that while dislocation models with realistic opening distributions are able to reproduce the displacement field profile fairly accurately, they systematically underestimate vertical displacement in the near field and overestimate horizontal displacements for a buoyant ascending crack. Our study shows that buoyancy of dikes triggers upward displacement of the Earth’s surface, which is not accounted by dislocation models. We discuss in more detail the potential consequences of this bias in dislocation models for the interpretation of geodetic data in volcanic areas.

• Biswas, Uddalak; Galland, Olivier & Carlson, Andreas (2026). Formation of various geometry by viscous magma intruding into visco-elasto-plastic deep crust: a 2D analogue experiment. Full text in Research Archive Show summary

  Magma ascends to the Earth's surface for eruption by traversing the crust, which is the uppermost layer above the mantle, where the magma originates. As this substantial volume of magma moves through the crust, it deforms the crustal rocks, facilitating its progression toward the surface and subsurface. The resulting geometry, which may manifest as thin sheets, branching fingers, or blunt lobes, is set by the competition between the intruding fluid and the mechanical response of the host material. These deformation mechanisms, which control the geometry of the magmatic bodies, are essential for assessing hazards related to volcanic eruptions, seismic activity due to volcanism, and the localisation of economically valuable ore deposits. As the deformation of the crustal rocks by the intruding magma occurs at a certain depth and natural exposures record only the end state of this strongly dynamic process, the mechanics behind this process can’t be inferred directly. To address this gap, researchers have employed analogue modelling as a tool to simulate a simplified analogous intrusion process of magma at a laboratory scale for decades. Conventionally, in these analogue experiments, crustal rocks have been modelled using elastic or plastic Coulomb materials, whereas magma has been represented as a viscous fluid by previous researchers. However, recent studies have shown that deep crustal rocks exhibit a complex visco-elastic to visco-elasto-plastic rheology in nature. To simulate the crustal rocks more accurately, in this study, we approached the problem by injecting a viscous fluid as a magma analogue into an aqueous Laponite® RD (LRD) gel, which acted as a model host rock, confined in a two-dimensional Hele-Shaw cell. The LRD gel exhibits diverse rheological properties, transitioning progressively from a viscous liquid to a viscoelastic state, and ultimately to an elastico-viscous solid, as its curing time (tc) increases. Considering this property of the LRD gel, we used tc = 30, 60, 90, 150, and 240 min to represent crustal rock under different physical and chemical conditions. On the other hand, magma in nature exhibits variable viscosity depending on its composition, temperature and volatile content. In parallel, we varied the injected fluid using water and hydroxyethyl cellulose solutions at 0.50 and 0.75wt%, to span the range of viscosity. Injection was carried out at a fixed volumetric flow rate of 10 ml/min up to a maximum injected volume of 50 ml, so that the flow rate is held constant while the rheology of the host and viscosity of the fluid are varied. Additionally, polyamide tracer particles with a diameter of 60 μm were embedded in the gel, enabling particle image velocimetry (PIV) to simultaneously resolve the deformation field of the host as the intrusion expanded. The experiments produced distinct intrusion geometries that systematically depended on host rheology and the viscosity of the injected fluid. The velocimetry fields from the PIV analysis further show that intrusions of broadly similar shapes can be accommodated by clearly different velocity and strain distributions within the host. Combining the evolving geometry with the accompanying strain pattern therefore offers a route toward identifying which deformation mechanism accommodated a given volume of magma, and this diagnostic can in principle be applied to interpret the intrusion patterns observed in the field.

• Biswas, Uddalak; Galland, Olivier & Carlson, Andreas (2026). Magma emplacement mechanism in visco-elasto-plastic crustal rock: an insight from quantitative 2D analogue experiments. doi: 10.5194/egusphere-egu26-18980. Full text in Research Archive Show summary

  Magma generated at depth ascends through the crust and erupts at the surface. In this process, the magma volume creates space by deforming the crustal rock. To study this process, researchers have employed analogue experiments for decades. Conventionally, most analogue models assume the crustal rock as a purely elastic, brittle (Coulomb), or viscous material. However, natural rocks exhibit more complex visco-elasto-plastic behaviours, with rheological properties transitioning from elastic-plastic to visco-elasto-plastic with increasing depth. Conversely, magma itself behaves as a Newtonian fluid, exhibiting a range of viscosities influenced by factors such as silica and volatile content. In this study, we conducted scaled 2D analogue magma emplacement experiments using Laponite® RD (LRD), a complex visco-elasto-plastic rheological material, as a host rock analogue. The rheological properties of LRD were systematically varied by changing the curing time (tc) from tc = 30 min to tc = 240 min to simulate a broad range of crustal rheological behaviours, corresponding to different depths from viscous to visco-elasto-plastic regimes. Food-coloured water and hydroxyethyl cellulose (HEC) aqueous solutions, with concentrations of 0.50 wt% and 0.75 wt%, are used to simulate magma with varying viscosities. Polyamide seeding particles (PSPs) of 60µm diameter were incorporated inside the LRD solution to quantify host-rock deformation during magma emplacement via particle image velocimetry (PIV). Our experimental results show that magma intrusions exhibit various shapes, ranging from straight-edged fractures in the case of low-viscosity water and viscoelastic LRD of high tc to bulbous, rounded forms in high-viscosity HEC and viscous LRD of low tc. Furthermore, PIV data enabled the identification of domains exhibiting distinct deformation types, thereby delineating changes in deformation regimes attributable to variations in the rheological properties of the host rock. Finally, by integrating geometric and PIV analyses, we established a relationship between the intrusion morphology and host rock rheology, and propose a mechanical model that elucidates the deformation mechanisms operative within the host during magma emplacement across different rheological combinations of host and magma materials.

• Tjoflot, Gunn Kristin; Kjøll, Hans Jørgen; Galland, Olivier & Scheiber, Thomas (2026). The pressure from magma can fold solid rock in less than one day. [Internet]. partner.sciencenorway.no. doi: https:/partner.sciencenorway.no/geology-mineralogy-natural-sciences/the-pressure-from-magma-can-fold-solid-rock-in-less-than-one-day/2658836. Full text in Research Archive Show summary

  The consequences of volcanic eruptions can be severe. Researchers have now made a surprising discovery. They found the evidence on a mountainside.

• Tjoflot, Gunn Kristin; Kjøll, Hans Jørgen; Galland, Olivier & Scheiber, Thomas (2026). Magmatrykket kan folde solid fjell på under én dag. [Internet]. forskning.no. doi: https:/www.forskning.no/geofag-geologi-partner/magmatrykket-kan-folde-solid-fjell-pa-under-en-dag/2659015. Full text in Research Archive Show summary

  Konsekvensene av vulkanutbrudd kan være enorme. Nå har UiO-forskere gjort en overraskende oppdagelse. Beviset fant de i en fjellside.

• Kjøll, Hans Jørgen; Scheiber, Thomas & Galland, Olivier (2026). Magma på vei mot overflaten knøvler fjell - Institutt for geofag. Full text in Research Archive Show summary

  Vulkanutbrudd viser naturens rå krefter, fra historiske kjempeutbrudd til ferske lavastrømmer på Island. En ny studie fra UiO-forskere i prosjektet «Beyond Elasticity» ved Institutt for geofag og Njord-senteret gir ny kunnskap om de enorme kreftene som kan oppstå dypt nede i jordskorpen.

• Kjøll, Hans Jørgen; Scheiber, Thomas & Galland, Olivier (2026). Rapid viscous flow of crustal rocks controls dyke emplacement in the ductile crust. doi: 10.5194/egusphere-egu26-19107. Full text in Research Archive Show summary

  In the upper crust, dykes are commonly assumed to propagate as elastic fractures, exhibiting thin, tapered geometries, and propagating through mode I, tensile opening at the fracture tip. In the lower ductile crust, which is often assumed to have a Maxwell-type rheology, the fast strain rates associated with dyke emplacement are thought to embrittle the host rock. This reasoning has led to the assumption that ductile deformation of the host rock is negligible during dyke emplacement in the deep crust. In Sarek National Park, northern Sweden, a dyke complex was emplaced during a ca 608 Ma continental rifting event at depths of 10–15 km and temperatures reaching ca 650 °C. The dyke swarm was emplaced into carbonate and sandstone host rocks. Detailed field observations from glacially polished outcrops demonstrate that significant ductile deformation of the host rock accommodated dyke emplacement. We quantify that approximately 25% of the dyke thickness is accommodated by ductile folding of the host rock. Thermal modelling is used to estimate magma crystallization times, which in turn allow estimating ductile strain rates on the order of 10-3 to 10-6 s-1. These strain rates are 6 to 10 orders of magnitude higher than typical tectonic ductile strain rates in the middle crust (10-12 - 10-15 s-1). Furthermore, we document how the weak rheology of the host rock influenced the shape and geometry of the mafic dykes. These results have implications for our understanding of dyke emplacement as well as general deformation and rock strength in the ductile crust, which constitute a significant part of the pathway for magma to reach the surface.

• Kleven, Alette; Barras, Fabian & Galland, Olivier (2025). Tensile versus shear failure of the host rocks at the tip of a pressurized dyke. Full text in Research Archive Show summary

  Sheet intrusions are the most fundamental magma pathways through the crust. Field observations suggest a variety of dyke propagation modes, ranging from tensile failure of the host rock in agreement with the Linear Elastic Fracture Mechanics (LEFM) theory, to shear failure of the host rock in agreement with the viscous indenter model. Under which conditions tensile versus shear failure occur at the propagating dyke tips is currently unknown. This is a key question as the LEFM and viscous indenter dyke propagation mechanisms may produce drastically distinct geophysical and geodetic signals. Here we present a Finite Element Model (FEM) that simulates the elastoplastic behavior of crustal rocks following a Drucker-Prager yield criterion. The host rock is deformed by the increasing pressure in an elliptical dyke until failure is reached at its tip. In our elastoplastic model, either tensile or shear failure occurs, depending on the host rock cohesion, the dyke dimension and depth. By exploring the parameter space, we built phase diagrams to map under which conditions tensile versus shear failure occur at dyke tips. Our results show that shear failure is favored when (1) the host rock cohesion is low, and/or (2) the dyke tip is deep and/or (3) the thickness-to-length aspect ratio of the dyke is high. Our study and phase diagram provide insights for the interpretation of geophysical and geodetic data collected at active volcanoes.

• Galland, Olivier (2025). El Condór - A scientific expedition in the heart of the Andes (1st - 10th March 2025). [Internet]. YouTube. doi: https:/youtu.be/O10lHizhrSA. Full text in Research Archive Show summary

  Revealing the roots of volcanoes is key for (1) assessing volcanic hazards, (2) exploring for geothermal energy, (3) storing CO2 in igneous rocks, (4) exploring for critical raw materials such as Rare Earth Elements (REE) and (5) studying impacts of volcanism on hydrocarbons when the volcano's substratum is a sedimentary basin. These were the grand objectives of the El Condór expedition, co-organised by scientists from the Njord Centre (University of Oslo) and the Laboratoire de Planétologie et Géosciences of Université du Mans (LPG – UMR CNRS 6112). Located between 3000 and 4000 meters of elevation, in the wildest and most remote Andes mountains of the Mendoza Province, Argentina, reachable after three days of horse riding, this expedition was both a scientific and human adventure. The target of the expedition was chosen because volcanic roots emplaced in the sedimentary sequences of the Neuquén Basin, a historically prolific hydrocarbon-bearing sedimentary basin, are exceptionally well-exposed. The name of the expedition "El Condór" was inspired by the name of a remote asphaltite prospect located at almost 4000 metres altitude, in the confines of the Argentinian Andes. Asphaltite looks like coal, but its origin is very different as it resulted from the injection of large volumes of hydrocarbons along a fluid-filled fracture. However, the processes governing asphaltite formation remains to a great extent enigmatic. In addition, asphaltites contain high concentrations of Rare Earth Elements, such as Vanadium, which are critical raw materials for new technologies. The specific objectives of the expedition were three-fold: • mapping in great details the structure of eroded volcanic roots; • understanding the impacts of magma conduits on organic-rich sedimentary formations, and understanding whether they played a role in the formation of the asphaltite deposit; • constraining the processes leading to high concentrations of Rare Earth Elements in the asphaltite. The expedition team consisted of: • Prof. Olivier Galland (volcanology in sedimentary basins, Njord Centre, University of Oslo, Norway) • Dr. Alain Zanella (geology of organic-rich formations, Laboratoire de Planétologie et Géosciences, Université du Mans, France) • Prof. Régis Mourgues (Structural geology and mechanics, Laboratoire de Planétologie et Géosciences, Université du Mans, France) • João Paulo Giro (PhD student, Laboratoire de Planétologie et Géosciences, Université du Mans, France) • Amélie Leray (free-lance photographer) • Johnny Albino (guide, Choique Turismo Alternativo - Malargüe, Argentina) • Ricardo Funes (mountain guide, Mendoza, Argentina) • Federico Guajardo (gaucho) • Carlos Guajardo (gaucho) • 16 horses Due to severe logistical challenges and extreme access conditions, the expedition did not reach the El Condór asphaltite deposit. Nevertheless, the talent of the scientific team allowed adapting and collecting numerous scientific data that will be the foundation for future scientific publications.

• Biswas, Uddalak; Galland, Olivier & Carlson, Andreas (2025). Variable curing time of Laponite RD: a convenient way to simulate a wide range of crustal rheology. Full text in Research Archive Show summary

  Crustal rocks exhibit complex and highly variable rheological behaviors, which are challenging to account for in laboratory simulations of geological processes. The choice of relevant analogue materials is crucial for a successful laboratory experiment that can address such processes more accurately. The advent of new technologies and complex synthetic materials widens the window for the analogue experimentalist to revisit some of the problems for deeper understanding. Most of standard analogue materials used for simulating crustal rocks exhibit endmember rheology, i.e., viscous, elastic or coulomb (plastic). However,crustal rocks can exhibit a wide range of complex rheological properties, such as visco-elastic, visco-plastic, elasto-plastic and viscoelasto-plastic, during deformation under stress. In the last decade, a few researchers started using complex rheological materials, such as Carbopol, to simulate those processes more accurately. Laponite RD is one of such advanced complex rheological materials. Laponite RD is a synthetic sheet silicate mineral that resembles a natural clay mineral called hectorite. Laponite RD is used mostly as a rheological modifier in cosmetics, paint and the pharmaceutical industry. This material comes in powder form and transforms into gel when mixed with deionised water. This gel material was investigated previously by a few analogue modellers. However, these researches consist of rheological variation, either depending upon concentration (in terms of weight%, wt.%) or very long curing time. However, during the investigation of the rheological properties of Laponite RD materials, we identified that a variation in short (< 4 hours) curing time (tc) can simulate a wide range of complex rheological behaviour of crustal rock from viscous to visco-elastic to elastic. We ran rheometrical measurements (amplitude sweep test and frequency sweep test) on 3 wt.% Laponite RD gels with variable curing times from tc=30 min to tc=240 min. Note that the gels were cured within the rheometer. The test results show a consistent increase in both the storage modulus (G′) and Loss modulus (G″) of the samples with increasing tc (COULD BE GREAT TO SHOW A FIGURE). To test the reproducibility of these analyses, we ran the same analysis with fixed tc several times and found that each run yielded similar values for G′ and G″ for a specific tc. Our tests highlighted the effect of the thixotropic property of Laponite gel on its rheology: handling of the laponite to place it in the rheometer dramatically affects its rheology. Hence, our results show that it is crucial to cure the sample at the place of the experiment to simulate accurate rheological behaviour. Finally, taking an example of Laponite RD gel with variable tc as host in a magma emplacement experiment, we demonstrated the use of these gels to simulate a wide range of complex rheological behaviour of crustal rocks (refer to figure). Our study shows that Laponite RD gels are robust and easy-to-handle alternatives to Carbopol gels commonly used in analogue modelling.

• Biswas, Uddalak; Galland, Olivier & Carlson, Andreas (2025). 2D analogue models of magma emplacement in the visco-elastic crust. Full text in Research Archive Show summary

  The Earth’s crust exhibits very complex rheology depending upon several physio-chemical conditions like temperature, pressure and lithology. This complex rheology of the crustal rocks is challenging to model. Thus, most researchers model magma propagation through crustal rocks of end-member rheologies such as viscous, coulomb (plastic) and elastic materials. These models acquire crucial information regarding the magma emplacement mechanisms. However, they are not sufficient to capture the whole spectrum of rheological behaviours of the host rock during the emplacement process. In this work, we performed a series of 2D magma injection experiments in the laboratory considering laponite RD gels as crustal rock analogues, showing complex rheological behaviour during deformation. According to the rheological analysis using a rheometer (Anton Paar MCR 702), laponite in deionised water solution exhibits a range of rheological behaviours from purely viscous to visco-elastic to purely elastic depending upon varying concentration (weight percentage, wt%) in the water. We used laponite gels of 2 wt% to 3.5 wt% to test the effects of varying rheology (yield stress = 0.597 Pa to 10.6 Pa) of the crustal rock analogue in the laboratory. These experiments used dyed oil (viscosity= 65 mPa.s) and water (viscosity= 1 mPa.s) as magma equivalents. Our 2D experiments revealed a range of intrusion shapes, from thin liquid-filled cracks of simple shapes to more massive fluid intrusions of complex shapes, indicating their varied mechanism of formation from brittle fracturing to ductile flow. To reveal the gel deformation accommodating the emplacement of the magma analogue, we implemented image analysis combining the photoelastic properties of the laponite gel and Digital Image Correlation. The resulting quantitative results allow us correlating the intrusion morphologies with the deformation mechanisms within the gel. Finally, from the experimental observations, we propose a model that connects the host rheology with the magma emplacement mechanism.

• Greiner, Sonja; Sigmundsson, Freysteinn; Geirsson, Halldór; Burchardt, Steffi & Galland, Olivier (2025). Tectonic stress release through dike emplacement constrained by surface deformation: Finite Element modeling of the 2021 Fagradalsfjall dike, Iceland. Full text in Research Archive Show summary

  At divergent plate boundaries, tectonic stress accumulates due to plate motion over time and may be released through rifting episodes and dike emplacement. Although the importance of tectonic stress for magmatic intrusions in this context is well known, it is rarely directly considered in surface deformation models. In 2021, a magmatic dike formed in the Fagradalsfjall volcanic system, SW-Iceland, ending almost 800 years of volcanic quiescence on the obliquely spreading Reykjanes Peninsula. Dike emplacement was accompanied by intense seismicity and ground deformation, which was geodetically well documented. We implement a Finite Element deformation model to explore and quantify the contribution of tectonic stress as a driving mechanism for the emplacement dike, using the 2021 Fagradalsfjall dike as a case study. First, tectonic stress accumulates due to oblique plate motion in a viscoelastic model. Secondly, dike opening locally releases a part of the accumulated tectonic stress. We found that geodetic observations can be reproduced reasonably well when ca. 60% of the accumulated tectonic stress is released. In oblique tectonic settings, shearing above the dike may help to distinguish between dikes driven largely by tectonic stress or by magmatic overpressure. Tectonic stress as the dominant driving mechanism for dike emplacement at Fagradalsfjall in 2021 is consistent with low magma flow rates at the onset of the eruption and partial stress release is consistent with subsequent dike intrusions between 2021-2023. Our model helps to better understand volcano-tectonic interaction on the Reykjanes Peninsula and to consistently model stress release constrained by surface deformation.

• Kjøll, Hans Jørgen; Galland, Olivier & Scheiber, Thomas (2025). Fast ductile deformation during magma emplacement – Evidence for inelastic deformation of host rock surrounding dykes. Full text in Research Archive Show summary

  In the upper crust, dykes and are often assumed to propagate as elastic fractures exhibiting thin, tapered sheet shapes, and propagating through mode I, tensile opening at the fracture tip. In the lower ductile crust, which is often assumed to have a Maxwell-type rheology, the fast strain rates associated with dyke emplacement are envisaged to embrittle the host rock. This argument has been used to assume that ductile deformation of the host rock is negligible during dyke emplacement in the deep crust. However, recent work we conducted in Sarek national park, northern Sweden, describe spectacular outcrops of dykes emplaced in the ductile crust. Field observations show that significant ductile deformation of the host rock has accommodated the emplacement of the dykes. We quantify that c. 15% of the dyke thickness is accommodated by ductile folding of the host rock. Thermal modelling is used to estimate crystallization time for the magma, which allows estimating ductile strain rates on the order of 10-8 s-1. This strain rate estimate is orders of magnitude higher than typical tectonic ductile strain rates (10-12 - 10-15 s-1) in the middle crust. Furthermore, we document how the weak rheology of the host rock influenced the shape and geometry of the mafic dykes. These new results have implications for how we envisage dyke emplacement as well as general deformation and rock strength in the ductile crust, which constitute a significant part of the pathway for magma to reach the surface.

• Lombardo, Ezequiel; Yagupsky, Daniel; Cristallini, Ernesto; Jerram, Dougal Alexander & Galland, Olivier (2025). Crustal doming induced by the emplacement of volcanic plumbing systems: case studies at back-arc volcanoes in the Neuquén Basin, Argentina. Full text in Research Archive Show summary

  Volcanic edifices in textbooks are typically represented as local accumulations of volcanic products generally building up from a near flat substratum. In this contribution, we present three volcanoes case studies and show that their substratum has been systematically uplifted through crustal doming. These case studies formed in the compressional back-arc tectonic setting of the Neuquén Basin, Argentina. These volcanic complexes built upon, and their shallow plumbing systems were emplaced into, the Mesozoic sedimentary strata of the Neuquén Basin. Borehole data and 3-dimensional seismic data acquired for hydrocarbon exploration show that the strata of the Mesozoic substratum underneath each volcanic complex exhibits a large, gentle domal structure of 500 to 1000 metres amplitude. The domal structures correlate in position and dimension with those of the volcanoes, which consist of a thin cover of volcanic products coating the underlying crustal dome. The volcanoes also show evidence of lower amplitude localized doming around individual and nested shallow intrusions. Our study suggests that the injection of volcanic plumbing systems in back-arc settings contributes to crustal thickening and doming of the Earth's surface. Such doming may locally affect regional stresses, which may impact magma transport in the shallow crust and control the emplacement of radial dyke swarms, shallower sill intrusions, and enhance transport of magma to the surface. In general, our study highlights the effects of volcanic plumbing systems on the structure and stress in the Earth's crust, and the links from the deeper to the shallower parts of the system.

• Kjøll, Hans Jørgen; Galland, Olivier & Scheiber, Thomas (2025). Fast ductile rock deformation accommodating dyke emplacement in the middle crust. Full text in Research Archive Show summary

  Growth of magmatic sheet intrusions is generally assumed to occur through initial tensile fracturing and elastic bending of the host rock resulting in intrusion geometries characterized by straight segments and sharply tapered tips. In addition, most models assume that rates of dyke emplacement are too fast to be accommodated by ductile flow of the host rock, even at mid-crustal levels. There is, however, increasing field evidence that suggests that inelastic processes such as plastic deformation and/or partial melting of the host rock may play an important role in emplacement dynamics. We have studied a mafic dyke complex emplaced in the middle crust of an Ediacaran-aged magma-rich rifted margin in Northern Sweden. The host rocks in the field area are composed primarily of dolostone intercalated with silicic beds. The peak ambient temperature during dyke emplacement was approximately 500-700°C. Local partial melting of the host rock occurred contemporaneously with emplacement of the mafic dykes. Field observations show that the host rock beds are tightly folded (up to 30% shortening) close to the contacts of the surrounding dykes, and strain, i.e., the wavelength of the folds, decreases rapidly with increasing distance from the dykes. The axial planes of the folds next to the contacts are sub-parallel to the dyke contacts themselves, suggesting that the folds formed as a consequence of dyke emplacement and inflation. Estimates of dykes cooling times suggest that the magma reached its solidus temperature within one year. Our results suggest that the strain rate accommodating dyke emplacement was very rapid (on the order of 10-7 s-1) compared to typical tectonic strain rate estimates (ca 10-12 - 10-15s-1). Our data show that inelastic deformation is an important aspect during dyke emplacement in the middle crust, and that fast strain rates are possible.

• Johannesen, Rakul Maria Ingunardóttir; Galland, Olivier; Ólavsdóttir, Jana; Kjøll, Hans Jørgen; Eidesgaard, Óluva & Planke, Sverre (2025). Fractured basalts as reservoirs for permanent CO2 storage on the Faroe Islands. doi: 10.5194/egusphere-egu25-12801. Full text in Research Archive Show summary

  During the last decade, the pilot CarbFix project in the Iceland rift zone has provided highly promising results for permanently storing CO2 as carbonates in basalts. A key question is whether this method can be applied in other basaltic formations worldwide where the rocks are older, the porosities are lower, the chemical compositions are different, and/or the temperatures are lower. Storing CO2 in the subsurface necessitates injectivity, where two essential properties are permeability and porosity. In basaltic formations, porous volumes are typically found as vesicle zones, near lava flow boundaries and in flow tops, or fractures. Currently, it appears that the permeability necessary for injecting fluids in basalts is dominated by fractures. The Faroe Islands, in the North Atlantic, consist of layered basalts of Paleogene age. The aim of this study is to examine the potential of the Faroe Island Basalt Group (FIBG) as a CO2 reservoir. To evaluate the reservoir properties of the FIBG we interpret and integrate new and existing data at multiple scales, including satellite images, UAV photogrammetric surveys, and field mapping. We have determined the distribution of large-scale lineaments (faults and dykes), flow-scale fractures, and the interaction between them in three dimensions. Here, we focus on the Malinstindur Formation, a compound basalt sequence, which is a potential pilot injection sequence because of its permeability potential. Large-scale mapping of the FIBG volcanostratigraphy is used to map the depth of the Malinstindur Formation and to determine the presence of large strike-slip faults across the archipelago. In addition, large-scale structural lineaments exhibiting a preferred EW-trending orientation are mapped. In addition, fracture analyses on different scales (from islands to outcrops), have been conducted to investigate how lava flow architectures, regional stress, and faults control fracture distribution and connectivity. The results of these analyses show that (1) the fracture density decreases with flow thickness, (2) the orientation of the internal fractures follows the same as those of the sets of regional scale lineaments, and (3) there is no link between the fracture intensity in the basalts and the distance to the regional scale lineaments. This study will serve as a foundation for determining the subsurface distribution of the Malinstindur Formation and the fracture distribution and connectivity at potential injection sites in order to estimate the potential for permanent CO2 storage within the Faroe Islands.

• Salvioli, Melisa; Cal, Hernán de la; Lajoinie, M.; Galland, Olivier & Lanfranchini, M. (2024). Petrografía de intrusivos terciarios de Pampa Amarilla relacionados a los sistemas petroleros atípicos del sur de Mendoza, Cuenca Neuquina, Argentina. XXII Congreso Geológico Argentino. Full text in Research Archive
• Galland, Olivier & Jerram, Dougal Alexander (2024). Structural control of igneous intrusions on fluid migration in sedimentary basins. [Internet]. YouTube. doi: https:/youtu.be/AnRo85chr5Q. Full text in Research Archive Show summary

  This video is a brief summary of two publications describing the control of ancient magmatic intrusions on subsurface fluid migrations, here bitumen. The publications are: - Galland, O., Villar, H.J. et al. 2023. The long-term legacy of subvolcanic intrusions on fluid migration in sedimentary basins: The Cerro Alquitrán case study, northern Neuquén Basin, Argentina. Basin Research, 35, 1840-1855, https://doi.org/https://doi.org/10.1111/bre.12782. - Galland, O., Villar, H. et al. 2024. Structural control of igneous intrusions on fluid migration in sedimentary basins: the case study of large bitumen seeps at Cerro Alquitrán and Cerro La Paloma, northern Neuquén Basin, Argentina. In: Kilhams, B., Watson, D. and Holford, S. (eds) The Impacts of Igneous Systems on Sedimentary Basins and Their Energy Resources. Geological Society, London, Special Publications, https://doi.org/https://doi.org/10.1144/SP547-2023-115. The study shows that intense fracturing within the magmatic body, induced by the shearing of the magma during emplacement, represent high-permeability zones that channel subsurface fluid migrations. Our study highlights the high relevance of accounting for fractured subsurface magmatic intrusions in basin models, but also on geothermal energy exploration.

• Galland, Olivier; Kjøll, Hans Jørgen & Scheiber, Thomas (2024). Beyond Elasticity project - Fieldwork 2024 in Sarek National Park, northern Sweden. [Internet]. YouTube. doi: https:/youtu.be/3dpzyvERjqo. Full text in Research Archive Show summary

  August 2024, Prof. Olivier Galland, Drs. Hans Jørgen Kjøll and Thomas Scheiber conducted a geological field expedition at Sarek National Park, northern Sweden. The expedition was funded through the "Beyond Elasticity" project, a large research project funded through the very competitive FRIPRO program, Research Council of Norway. The aspiration of "Beyond Elasticity" is to revisit our understanding of propagation and emplacement of magmatic sheet intrusions, such as dykes, sills and cone sheets. The primary objective of this project is to establish novel mechanical understanding of dyke and sill emplacement that reconciles the distinct magma emplacement models. We aim to show that, and quantify how much, inelastic deformation contributes to dyke and sill propagation and emplacement. The field work is one part of this multidisciplinary project, which integrates laboratory modelling, numerical modelling and theory, and geophysics. The project gathers scientists from the Departments of Geosciences, Physics and Mathematics at the University of Oslo, as well as scientists from Iceland, Sweden, and UK. Music credits: Song: Shine On Music by: CreatorMix.com

• Sartell, Anna Marie Rose; Beier, Christoph P.; Söderlund, Ulf; Senger, Kim; Shephard, Grace & Kjøll, Hans Jørgen [Show all 7 contributors for this article] (2024). Geochemistry and geochronology of the High Arctic Large Igneous Province on Svalbard. Full text in Research Archive
• Senger, Kim & Galland, Olivier (2022). Early Cretaceous magmatism in central Spitsbergen: stratigraphic and spatial exten. Full text in Research Archive
• Galland, Olivier (2020). Farlige vulkaner i verden. [Radio]. NRK. Full text in Research Archive
• Kjøll, Hans Jørgen; Galland, Olivier; Labrousse, Loic & Andersen, Torgeir Bjørge (2020). Emplacement mechanisms of a dyke swarm across the Brittle- Ductile transition. Full text in Research Archive Show summary

  Dykes are the main magma transport pathways through the Earth’s crust and, in volcanic rifts, they are considered the main mechanism to accommodate tectonic extension. Most models consider dykes as hydro-fractures propagating as brittle tensile, mode I cracks opening perpendicular to the least principal stress. This implies that dykes emplaced in rifts are expected to be sub-vertical and accommodate crustal extension. Here we present detailed field observations of a well-exposed dyke swarm that formed near the brittle-ductile transition at a magma-rich rifted margin during opening of the Iapetus Ocean. It was related to a ca 600 million year-old large igneous province. Our observations show that dykes were not systematically emplaced by purely brittle deformation and that dyke orientation may differ from the typical mode 1 pattern. Distinct dyke morphologies related to different emplacement mechanisms have been recognized including: 1) Brittle dykes that exhibit straight contacts with the host rock, sharp tips, and en-echelon segments with bridges exhibiting angular fragments; 2) Brittle-ductile dykes with undulating contacts, rounded tips, folding of the host rock and contemporaneous brittle and ductile features; 3) Ductile “dykes” with rounded shapes and mingling between partially molten host rock and the intruding mafic magma. The brittle dykes exhibit two distinct orientations separated by ~30° that are mutually cross-cutting, demonstrating that the dyke swam did not consist of only vertical sheets oriented perpendicular to regional extension, as expected in rifts. By using the host-rock layers as markers, a kinematic restoration to quantify the average strain accommodating the emplacement of the dyke complex was performed. This strain estimate shows that the dyke swarm accommodated >100% horizontal extension, but also 27% vertical thickening. This suggests that the magma influx rate was higher than the tectonic stretching rate, which imply that magma was emplaced forcefully, as supported by field observations of the host-rock deformation. Finally, observations of typical “brittle” dykes that were subsequently deformed by ductile mechanisms as well as dykes that were emplaced by purely ductile mechanisms suggest that the fast emplacement of the dyke swarm triggered a rapid shallowing of the brittle-ductile transition. The abrupt dyke emplacement and associated heating resulted in weakening of the crust that probably facilitated the continental break-up, which culminated with opening of the Iapetus Ocean.

• Rabbel, Ole; Galland, Olivier; Mair, Karen; Lecomte, Isabelle; Spacapan, Juan Bautista & Palma, Octavio (2020). Integration of geological field observations and geophysical data: The El Manzano Sill Complex (Argentina) as a showcase of igneous intrusions emplaced in active petroleum systems. Full text in Research Archive
• Kjøll, Hans Jørgen; Galland, Olivier; Labrousse, Loic & Andersen, Torgeir Bjørge (2020). Emplacement Mechanisms of a Dyke Swarm Across the Brittle-Ductile Transition. Full text in Research Archive
• Haug, Øystein Thorden; Galland, Olivier; Souloumiac, Pauline; Souche, Alban; Guldstrand, Frank Bo Buster & Schmiedel, Tobias [Show all 7 contributors for this article] (2019). Shear versus tensile failure mechanisms induced by sill intrusions – Implications for emplacement of conical and saucer-shaped intrusions. Full text in Research Archive
• Poppe, Sam; Holohan, Eoghan; Galland, Olivier & Kervyn, Matthieu (2019). Magma-induced deformation of the Earth’s upper crust in nature and in laboratory experiments scanned by X-ray Computed Tomography. Full text in Research Archive
• Galland, Olivier; Cal, Hernán de la & Rabbel, Ole (2019). Laccolith-induced deformation – A case study integrating field mapping, 3D seismic and well data at Pampa Amarilla, Neuquén Basin, Argentina. Full text in Research Archive
• Galland, Olivier (2019). The Physical Geology of Subvolcanic Systems – Laccoliths, Sills and Dykes (LASI6). Full text in Research Archive
• Mattsson, Tobias; Burchardt, Steffi; Palma, Octavio; Galland, Olivier; Almqvist, Bjarne S.G. & Hammer, Øyvind [Show all 9 contributors for this article] (2019). Magmatic fabrics related to different growth stages of the Cerro Bayo Cryptodome. Full text in Research Archive
• Bertelsen, Håvard Svanes; Galland, Olivier; Rogers, Benjamin David; Dumazer, Guillaume Henri & Benanni, Alexandre Abbana (2019). Laboratory modeling of coeval brittle and ductile deformation during magma emplacement into viscoelastic rocks. Full text in Research Archive
• Kjøll, Hans Jørgen; Galland, Olivier; Labrousse, Loic & Andersen, Torgeir Bjørge (2019). Dyke emplacement mechanisms across the brittle-ductile transition. Full text in Research Archive Show summary

  Dyke emplacement mechanisms across the brittle-ductile transition Hans Jørgen Kjøll1, Olivier Galland2, Loic Labrousse3 & Torgeir Andersen1 1 Center for Earth Evolution and Dynamics (CEED), University of Oslo 2 Physics of Geological Processes, the Njord Center, Department of Geosciences, University of Oslo 3 Institut des Sciences de la Terre Paris, ISTeP, CNRS-INSU, Sorbonne Université Dyking is the main process of magma transport through the Earth’s lithosphere. Dykes are thin sheets exhibiting shapes similar to fractures, so that the main models of dyke emplacement assume that they form by mode I hydraulic fracturing following the σ1-σ2 plane. Because of the rapid strain rates accommodating dyking, it is assumed that dyke propagation and emplacement are only governed by brittle processes, even in the ductile crust. However, the contribution of ductile deformation in dyke emplacement has not been assessed. Here we report detailed and spectacular field observations from northern Sweden and Norway of a ~605 Ma old dyke complex emplaced near the brittle-ductile transition. The dyke complex formed during continental rifting and opening of the Iapetus Ocean, and is now exposed in the Scandinavian Caledonides. In northern Sweden, observations are made along a 1.5 km long continuously exposed cliff providing unique and exceptional overview images of the dyke complex. The detailed structural analysis of the dykes and of the structures related to their emplacement allows us to identify distinct dyke emplacement mechanisms, sub-divided into: 1) Brittle dykes that exhibit straight contacts with the host rock, sharp tips, en-echelon segments with either broken bridges or intact bridges between the segments. The dyke thicknesses follow a Weibull distribution, commonly applied to fracture mechanics; 2) Brittle-ductile dykes that exhibit ductile bridges with complex patterns. Both brittle-ductile and ductile-brittle features are observed, i.e. where ductile flow induced by inflating dykes overprint brittle structures associated with dyke emplacement and vice versa; 3) Ductile “dykes” that show mingling textures between the soft ductile host rock and the intruding mafic magma as well as irregular magmatic boudinage. The dykes exhibit two distinct orientations, and are mutually cross-cutting, suggesting that the dykes did not form as vertical sheets perpendicular to regional extension. Thanks to the well-exposed layering of the dykes’ host rock, we performed a kinematic restoration to quantify the strain induced by the dyke complex. As expected, the dyke complex accommodated >100% extension in agreement with the rifting. However, counter-intuitively it also accommodated 12% of crustal thickening, in agreement with local shortening structures near the dyke walls, showing the forceful mechanism of magma emplacement. Our observations underline the complexity of magma emplacement mechanisms near the brittle-ductile transition and show that dyke emplacement cannot be described as simple mode-I brittle fractures that are being passively filled and inflated by magma.

• Senger, Kim; Betlem, Peter; Rabbel, Ole; Galland, Olivier & Lecomte, Isabelle (2019). Early Cretaceous igneous intrusions in Svalbard: seismic modelling as a link between boreholes, outcrops and seismic data. Full text in Research Archive
• Galland, Olivier (2019). Geology guide for French school. Full text in Research Archive
• Souche, Alban; Galland, Olivier; Haug, Øystein Thorden & Dabrowski, Marcin (2019). Impact of host rock heterogeneity on failure around pressurized conduits: Implications for finger-shaped magmatic intrusions. Full text in Research Archive
• Schmiedel, Tobias; Galland, Olivier; Haug, Øystein Thorden; Dumazer, Guillaume & Breitkreuz, Christoph (2019). Coulomb failure of Earth’s brittle crust controls growth, emplacement and shapes of igneous sills, saucer-shaped sills and laccoliths. Full text in Research Archive
• Galland, Olivier & Sassier, Caroline (2019). Cover page photograph of magazine GeoExPro. GeoExpro. ISSN 1744-8743. 16(4), p. 1–1. Full text in Research Archive
• Galland, Olivier & Sassier, Caroline (2019). Photograph on cover page of the magazine GeoExPro. GeoExpro. ISSN 1744-8743. 16(4), p. 1–1. Full text in Research Archive
• Galland, Olivier (2019). Volcanology laboratory practicals for students at the French school in Oslo. Full text in Research Archive
• Kjøll, Hans Jørgen; Andersen, Torgeir Bjørge; Labrousse, Loic & Galland, Olivier (2019). From rift to drift - Construction of the magma-rich pre-Caledonian Iapetus margin of Baltica. Full text in Research Archive Show summary

  The northern part of the pre-Caledonian Iapetus margin, which now rests within nappes in the Scandinavian Caledonides, is generally characterized as a fossil magma-rich rifted margin. The margin developed in the late Ediacaran during the opening of the Iapetus Ocean. It was deformed and metamorphosed during the Caledonian orogeny, but large parts of the margin escaped the penetrative strain and regional metamorphism related to this event, and are now preserved in kilometer-scale boudins. The boudins preserve a several kilometer-thick sedimentary package mostly composed of siliciclastic and carbonaceous rocks. A key unit in the stratigraphy is a stromatolite-bearing dolomitic marble containing pure magnesite lenses as well as Cl-rich scapolite, both indicative of evaporite deposits. This unit can be found at several localities along the Scandinavian Caledonides. A recently described glaciogenic diamictite directly overlies the carbonates, which in turn is overlain by a > 1 km thick shallow marine sandstone succession, possibly marking the onset of rifting. The youngest detrital zircon from the sandstone unit is 698 Ma, providing a useful maximum deposition age. The sedimentary succession rests on top of a basement slice with top-W extensional shear indicators. The deformation has been dated to 637 Ma and corroborates the interpretation that Baltica and Laurentia was rifting at this time. The entire sedimentary succession is dissected by a dense network of mafic dikes, which has been dated to range from 596-608 Ma, providing a minimum estimate for the deposition of the sedimentary succession. This minimum age also rules out the Gaskiers glacial event to be responsible for the deposition of the diamictite. The emplacement of the dike swarm was short and intense and led to local partial melting of the host rocks. The rapid influx of magma exceeded the tectonic stretching rate, which together with their conjugate geometry allowed the dike emplacement to also cause a vertical thickening of the crust synchronous with extension. The diking event led to the break-up of Baltica and Laurentia in the Late Ediacaran after at least 30 million years of rifting and show that the magmatic event started late in the overall rifting history.

• Guldstrand, Frank Bo Buster; Galland, Olivier & Mair, Karen (2019). Learning-by-doing in the laboratory. Full text in Research Archive
• Måløy, Knut Jørgen; Eriksen, Jon Alm; Flekkøy, Eirik Grude; Toussaint, Renaud; Galland, Olivier & Sandnes, Bjørnar (2019). Pattern formation of frictional fingers in a gravitational potential. Full text in Research Archive
• Måløy, Knut Jørgen; Eriksen, Jon Alm; Flekkøy, Eirik Grude; Toussaint, Renaud; Galland, Olivier & Sandnes, Bjørnar (2019). Pattern formation of frictional fingers in a gravitational field. Full text in Research Archive
• Guldstrand, Frank Bo Buster; Bertelsen, Håvard Svanes; Souche, Alban; Galland, Olivier & Zanella, Alain (2019). Intrusion of Viscous Magma in a Cohesive Crust Visualized and Quantified from Quasi-2D Laboratory Experiments. Full text in Research Archive
• Kjøll, Hans Jørgen; Andersen, Torgeir Bjørge; Galland, Olivier; Corfu, Fernando; Labrousse, Loic & Tegner, Christian [Show all 7 contributors for this article] (2019). Deep section of a Neoproterozoic fossil magma rich rifted margin exposed. Full text in Research Archive Show summary

  Structures of rifted continental margins are the finite result of active processes when continents rift apart. During the convergent stages of Wilson cycle, remnants of rifted margins may be incorporated into orogens, especially the magma-poor end-member. The magma-rich margins, however, are commonly lost in subduction due to low buoyancy. The understanding of magma-rich margins is therefore mostly based on drill holes and geophysical observations. In this contribution, we explore the temporal evolution and the ambient conditions of a magma-rich rifted margin preserved within the Scandinavian Caledonides. The Scandinavian Dyke Complex was emplaced in a sedimentary basin during the opening of the Iapetus Ocean 615 to 590 million years ago. The dyke complex now constitutes 70-90% of the area and is locally well-preserved despite the complex Caledonian history. Five field seasons in northern Sweden and Norway provide new observations from regional to microscopic scale about the structural geometry, relative timing, and development of the margin. Jadeite in clinopyroxene geothermobarometry, titanium in biotite geothermometry and garnet isopleth modeling show that the ambient pressure and temperature conditions were similar for the entire dyke complex at 0.25 to 0.45 GPa, with contact metamorphic temperatures up to c. 700◦C. Using a photomosaic of a large and well-exposed cliff face we used layers in the metasediments as markers to restore the host-rock back to the pre-dike configuration, allowing us to quantify the average strain accommodated by the dyke swarm. It accommodated for >100% extension and for 27% crustal thickening. From this we infer that the magma influx rate was higher than the tectonic stretching rate, implying that magma was emplaced in a forceful manner, which is also supported by field observations. In the northern part of the study area, high precision dating of magmatic zircon shows that significant partial melting of the sedimentary host-rock, at relatively shallow levels, occurred at 613 ± 1 Ma. This shows that the crust was molten already 6 Ma before the dyke swarm was emplaced at 606 ± 2 Ma. We propose that the locally pervasive partial melting occurred due to high geothermal gradient and introduction of mafic melts in the lower crust. These processes caused a rapid shallowing of the brittle-ductile transition, which thereby significantly reduced the strength of the crust.

• Sleveland, Arve; Midtkandal, Ivar; Galland, Olivier & Leanza, Hector Armando (2019). Compensational stacking and architecture of mouth-bar deposits in a mixed-process deltaic environment; Mulichinco Formation, Neuquén Basin, Argentina. Full text in Research Archive
• Sleveland, Arve; Midtkandal, Ivar; Galland, Olivier & Leanza, Hector Armando (2019). Sedimentary architecture of mixed-process mouth bar deposits in the Mulichinco Formation, Neuquén Basin, Argentina. Full text in Research Archive
• Rabbel, Ole; Galland, Olivier; Palma, Octavio; Spacapan, Juan Bautista; Senger, Kim & Lecomte, Isabelle [Show all 7 contributors for this article] (2019). From field observations to seismic modeling: The El Manzano Sill Complex (Argentina) as a showcase of the influence of igneous intrusions on petroleum systems. Full text in Research Archive
• Kjøll, Hans Jørgen; Galland, Olivier; Labrousse, Loic & Andersen, Torgeir Bjørge (2019). Emplacement Mechanisms of a Dyke Swarm Across the Brittle-Ductile Transition. Full text in Research Archive
• Mair, Karen; Bertelsen, Håvard Svanes; Guldstrand, Frank Bo Buster & Galland, Olivier (2019). Learning by doing: Use of research based methods and novel laboratory experiments in teaching Earthquake and Volcanic Processes. Full text in Research Archive
• Galland, Olivier (2018). The impacts of igneous intrusions on the Vaca Muerta Fm., Neuquén Basin, Argentina. Full text in Research Archive
• Guldstrand, Frank Bo Buster; Galland, Olivier; Souche, Alban; Bertelsen, Håvard Svanes & Zanella, Alain (2018). Dyke induced Quasi-2D deformation in a Coulomb brittle host – the influence of host strength on propagation and emplacement. Full text in Research Archive
• Syversen, Lill Karoline; Augland, Lars Eivind; Galland, Olivier; Svensen, Henrik Hovland & Callegaro, Sara (2025). Using xenoliths as tracers of magmatic processes in the Oslo Rift. Universitetet i Oslo. Full text in Research Archive Show summary

  As magma travels through the Earth’s crust, it interacts with the host rock. During ascent, magma can entrain host rock xenoliths which may be preserved in the intrusions, providing important information of the magma ascent and subsurface constituents. In the Permian Oslo Rift, several dikes and sills contain xenoliths. This study aims to obtain a greater understanding of the magma ascent- and emplacement history during the Oslo Rift volcanism by studying these xenoliths. With a multidisciplinary approach using geochemistry, petrography, and photogrammetry, this study explores the mechanisms of xenolith-formation, and further how the dikes and sills are connected to the large-scale plumbing system of the Oslo Rift. Five localities across ~95 km in the Oslo Rift reveals several xenolith lithologies derived from different crustal depths: Lithologies from Lindøya and Bevøya comprises of gneisses, metamorphic quartz, and sandstones. Near Buhammeren, xenoliths of amphibole-gabbro and bytownite-anorthosite are observed. The variety in lithologies suggests a range of entrainment depths from gabbroic sources in the lower deep crust, the Precambrian basement, and Cambro-Devonian sediments. The angularity of xenoliths is averagely estimated as “rounded”, and the estimated 3D-shapes often occurs as near equant-shaped. An increase in roundness, possibly coupled with increasingly equant shapes, are interpreted as being indicative of a longer residence time in the magma. Near Buhammeren and in Jevnaker, amphibole- and pyroxene phenocrysts- and xenoliths reveal crystallization depths of 20–30 ± 3.02 km and 22–35 ± 5.1 km respectively, interpreted as corresponding to deep crustal magma chambers. This supports former studies on the large-scale Oslo Rift plumbing system, where the lower 30 – 20 km of the crust is interpreted as a gabbroic cumulate intrusive layer formed by a prolonged period of magma fractionation. The samples bulk-rock compositions also reveal significant similarities – both compared to the early B1-basalt and compared to one another. This is indicative of a similar magma source that ascended through the crust before significant magma fractional crystallization occurred. This thesis shows the importance of studying xenoliths in the Oslo Rift, as these can provide important information on both crustal compositions and magmatic processes. Further studies should focus on constraining better depth estimates for phenocryst crystallization, as well as acquiring more accurate xenolith entrainment depths for a better understanding of the magma ascent history.

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