Henrik Hovland Svensen

• Tegner, C.; Guo, P.; Chatterjee, S.; Lambart, S.; Jones, Morgan Thomas & Planke, Sverre [Vis alle 27 forfattere av denne artikkelen] (2026). A whole rock geochemical dataset for magmatic rocks drilled on the mid-Norwegian margin. Scientific Data. 13. doi: 10.1038/s41597-026-07073-x. Fulltekst i vitenarkiv Vis sammendrag

  The mid-Norwegian margin is one of the best studied volcanic rifted margins on Earth. Geophysical investigations have demonstrated the presence of well-developed inner and outer Seaward Dipping Reflectors (SDRs), landward flows, lava deltas, marginal highs, volcanic centers, ash layers, and sill complexes. These features have been proven to consist of magmatic rocks through the international Deep Sea Drilling Program (DSDP Leg 38, 1974), Ocean Drilling Program (ODP Leg 104, 1985), International Ocean Discovery Program (IODP Expedition 396, 2021), and commercial drilling. A total of fifteen drill cores penetrated magmatic rocks that formed between 57 and 50 million years ago (Ma). Here we provide (i) new ( n =  224) major and trace element compositions obtained by X-ray fluorescence (XRF), inductively-coupled plasma mass spectrometry (ICP-MS), and inductively-coupled optical emission spectrometry (ICP–OES) on whole rock powders of magmatic rocks for IODP Exp. 396 ( n  = 119), ODP Exp. 104 ( n =  79), DSDP Exp. 38 ( n  = 24); and (ii) a compilation of all new and published data for magmatic rocks in the fifteen drill cores ( n  = 563). Portable X-ray fluorescence (pXRF) data ( n  = 381) for the IODP Exp. 396 cores are also reported. These datasets provide a resource for examining the origin of magmatism associated with continental breakup and rifted margin formation, particularly the formation of excess magmatism compared to normal mid-oceanic spreading ridges, mantle-crust interaction, and the linkage of magmatism to global hyperthermal events on Earth’s surface.

• Neumann, Else Ragnhild; Callegaro, Sara; Jacobsen, Stein B; Hyung, Eugenia; Svensen, Henrik Hovland & Larsen, Bjørn Tore [Vis alle 7 forfattere av denne artikkelen] (2025). Geodynamic evolution of the first basaltic volcanism (B1) in the Oslo Rift (Southeast Norway). Lithos. ISSN 0024-4937. 512-513. doi: 10.1016/j.lithos.2025.108133. Fulltekst i vitenarkiv Vis sammendrag

  The Oslo Rift represents the northernmost part of the “The Skagerrak-Centered Large Igneous Province” (SCLIP) characterized by the initial phase of mafic volcanism (“B1” basalts) around 300 Ma. We present a rift-scale geochemical overview of the B1 lavas and discuss their origin and evolution. The B1 phase comprises lava piles reaching up to 1500 m thickness, emplaced in a short time (1–2 m.y.). The lavas are strongly alkaline in the south (Brunlanes melilitites) and decrease in alkalinity towards the north (Krokskogen tholeiites). A strong regional dependence is also evident in the trace element and radiogenic isotope geochemistry. The initial radiogenic isotope compositions of the B1 lavas imply that their formation involved at least four mantle sources. One source was unradiogenic in Srsingle bondNd isotopes (LoNd type) and gave rise to the southernmost, strongly alkaline Brunlanes series. This component has been interpreted as plume-derived. An alternative possibility is that it was located in metasomatized domains within the lower lithosphere, produced by low-Sr-Nd isotope melts/fluids at some stage just before, or during, the earliest SCLIP phase. We regard the plume model to be most likely. The second mantle source had HIMU-like Sr-Nd-Pb isotopes and was enriched in incompatible trace elements. The third source had the Sr-Nd-Pb isotope characteristics of enriched mantle (EM-type) and was less enriched in incompatible trace elements than the HIMU-like source. We propose that the lower lithosphere beneath the Skien-Vestfold-Jeløya area consisted of garnet peridotite with EM-type Sr-Nd-Pb isotope characteristics that at some stage, long before the SCLIP event, was metasomatized by melts/fluids forming veins strongly enriched in incompatible trace elements and with HIMU-like isotopes. The formation of the strongly to mildly alkaline Skien B1 series involved all these three mantle sources, whereas the mildly alkaline Vestfold and Jeløya B1 basalts were formed by mixing between HIMU-like and EM-type melts. The strongly to mildly alkaline B1 melts formed at ≥140 km depth before, or during, the earliest stages of stretching and thermal erosion of the lithosphere. The northernmost B1 series, the Krokskogen tholeiites, probably formed by partial melting of lithospheric mantle rocks (the fourth mantle source) relatively depleted in incompatible trace elements, that had not been affected by metasomatic processes. The Krokskogen tholeiites appear to have formed at lower pressures, possibly implying a short duration for the thermal erosion of the lithosphere. Reconstructing the petrogenetic evolution of the B1 lavas is important because CO2 degassing during this basaltic phase of the SCLIP may have impacted the global climate around the Carboniferous-Permian transition and further into the Permian.

• Frieling, Joost; Svensen, Henrik Hovland & Mather, Tamsin A. (2025). Mercury efficiently volatilized but not completely removed from sediments around igneous intrusions. Geology. ISSN 0091-7613. 53(2), s. 176–180. doi: 10.1130/g52622.1. Fulltekst i vitenarkiv Vis sammendrag

  The impact of large igneous province (LIP) volatile emissions from magmatic and thermogenic sources has been widely studied using sedimentary mercury (Hg). Igneous sill emplacement in sedimentary basins was a key component of several LIPs, generating environmentally significant amounts of thermogenic gases (e.g., CH4, CO2, Hg) and fluids by heating sedimentary rocks. Understanding these processes is key to realizing the promise of Hg in sedimentary archives to understand LIP impacts and track LIP carbon outputs. Published data show sedimentary rocks in contact aureoles of such LIP-related intrusions retain some Hg despite exposure temperatures above the stability limit of sedimentary Hg phases (>300 °C). We examine this unexpected Hg retention using Hg thermal desorption profiles (TDPs). The TDPs reveal a remarkable pattern in Hg speciation related to intrusions: with increasing aureole temperature, Hg release is progressively dominated by a low-temperature phase that could have formed only during or after cooling of the intrusion. We calculate a temperature-dependent Hg volatilization efficiency and show that 70%–100% of Hg was mobilized above 350 °C. Despite the efficient volatilization, only ~50% of the volatilized Hg was removed from the studied aureole. Mercury recapture in and around the thermal aureole likely extends into the associated hydrothermal vent systems, reduces the Hg:C ratios of emitted thermogenic gases, and may lead to underestimation of Hg-based LIP thermogenic CO2 and CH4 emissions estimates and their environmental impact.

• Whattam, Jack William; Midtkandal, Ivar; Jerram, Dougal Alexander; Callegaro, Sara & Svensen, Henrik Hovland (2024). The episodic onset of explosive and silicic-dominated volcanism in a continental rift; insights from the Permian Oslo Rift, Norway. Volcanica. 7(2), s. 925–951. doi: 10.30909/vol.07.02.925951. Fulltekst i vitenarkiv Vis sammendrag

  The nature of rifting episodes and their associated volcanism mark key stratigraphic events in the evolution of volcano-sedimentary basins. Following the final assemblage of Pangea, the European region was subject to rifting and magmatism during crustal re-equilibration throughout the Permian. The aborted, partially eroded Oslo Rift is an excellent archive of this Permian magmatism, but the late-stage volcanological evolution is poorly understood. We present the first detailed documentation of a succession covering this period, with mafic lavas and volcaniclastic (tuff breccia) deposits, trachy-andesitic tuffs, and rheomorphic to moderately welded ignimbrites. Contrary to previous ideas, we show evidence suggesting the development of Strombolian-type scoria-cones, silicic fissure-fed eruptions, and major periods of rift-wide volcanic quiescence. Our observations highlight episodic silicic volcanism characterised by rapid evolution from high-grade ignimbrites to moderately and poorly welded ignimbrites. We infer rapid emptying of large, shallow silicic reservoirs and frequent source switching is responsible for the observed characteristics.

• Svensen, Henrik Hovland; Jones, Morgan Thomas; Percival, Lawrence; Grasby, Stephen E. & Mather, Tamsin (2023). Release of mercury during contact metamorphism of shale: Implications for understanding the impacts of large igneous province volcanism. Earth and Planetary Science Letters. ISSN 0012-821X. 619. doi: 10.1016/j.epsl.2023.118306. Fulltekst i vitenarkiv Vis sammendrag

  Elevated mercury (Hg) in sedimentary strata are a widely used tracer for assessing the relationship between large igneous province (LIP) activity and global environmental change. A key unknown in applying this proxy is the extent to which Hg was sourced from contact metamorphism of sedimentary rocks during sill intrusions versus gaseous emissions of the magmas themselves. Here, we investigate Hg behaviour during contact metamorphism of shales. We show loss of 80–99% of the sedimentary Hg in contact aureoles in four case studies covering the interactions around dykes, sills and plutons associated the High Arctic LIP (Sverdrup Basin, Canada), the Karoo LIP (South Africa) and the Skagerrak-centred LIP (Oslo Rift, Norway). A combination of geochemical data and thermal modelling around a dyke from the High Arctic LIP shows 33% Hg volatilization in the aureole at 265–300 °C. The other cases show similar behaviours with significant lowering of organic-bound Hg, more significantly in the innermost 60% of the contact aureoles. We hypothesize that gaseous Hg is transported out of aureoles during metamorphism, together with CH4 and CO2. Furthermore, we estimate the thermogenic Hg mobilization from Karoo LIP aureoles as 72–192 t per km3 of aureole, which is between 1–3 times the estimated volumetric Hg release from Karoo magmas. When scaling our results to the size of the shale portions of the Karoo Basin affected by the LIP and a timescale of 100 kyr of sill emplacement, the average Hg flux is calculated to have been 78–207 t/y with maximum values up to ∼300 t/y. The pulsed nature of intrusive volcanism suggests that this thermogenic Hg flux could have dominated LIP Hg emissions during periods of their life span. Our results demonstrate that the global Hg cycle can be significantly perturbed following LIP-scale sill emplacement into organic-rich sedimentary rocks and our quantification of the emissions based on source-rock analysis provides important information for independent interpretation of the sedimentary Hg record.

• Berndt, Christian; Planke, Sverre; Zarikian, Carlos A. Alvarez; Frieling, Joost; Jones, Morgan Thomas & Millett, John M. [Vis alle 36 forfattere av denne artikkelen] (2023). Shallow-water hydrothermal venting linked to the Palaeocene–Eocene Thermal Maximum. Nature Geoscience. ISSN 1752-0894. 16, s. 803–809. doi: 10.1038/s41561-023-01246-8. Fulltekst i vitenarkiv Vis sammendrag

  The Palaeocene–Eocene Thermal Maximum (PETM) was a global warming event of 5–6 °C around 56 million years ago caused by input of carbon into the ocean and atmosphere. Hydrothermal venting of greenhouse gases produced in contact aureoles surrounding magmatic intrusions in the North Atlantic Igneous Province have been proposed to play a key role in the PETM carbon-cycle perturbation, but the precise timing, magnitude and climatic impact of such venting remains uncertain. Here we present seismic data and the results of a five-borehole transect sampling the crater of a hydrothermal vent complex in the Northeast Atlantic. Stable carbon isotope stratigraphy and dinoflagellate cyst biostratigraphy reveal a negative carbon isotope excursion coincident with the appearance of the index taxon Apectodinium augustum in the vent crater, firmly tying the infill to the PETM. The shape of the crater and stratified sediments suggests large-scale explosive gas release during the initial phase of vent formation followed by rapid, but largely undisturbed, diatomite-rich infill. Moreover, we show that these vents erupted in very shallow water across the North Atlantic Igneous Province, such that volatile emissions would have entered the atmosphere almost directly without oxidation to CO2 and at the onset of the PETM.

• Deegan, Frances M.; Callegaro, Sara; Davies, Joshua H.F.L. & Svensen, Henrik Hovland (2023). Driving Global Change One LIP at a Time. Elements. ISSN 1811-5209. 19(5), s. 269–275. doi: 10.2138/gselements.19.5.269. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland; Jones, Morgan Thomas & Mather, Tamsin A. (2023). Large Igneous Provinces and the Release of Thermogenic Volatiles from Sedimentary Basins. Elements. ISSN 1811-5209. 19(5), s. 282–288. doi: 10.2138/gselements.19.5.282. Fulltekst i vitenarkiv
• Jones, Morgan Thomas; Stokke, Ella Wulfsberg; Rooney, Alan D.; Frieling, Joost; Strandmann, Philip A. E. Pogge von & Wilson, David J. D. [Vis alle 15 forfattere av denne artikkelen] (2023). Tracing North Atlantic volcanism and seaway connectivity across the Paleocene-Eocene Thermal Maximum (PETM). Climate of the Past. ISSN 1814-9324. 19(8), s. 1623–1652. doi: 10.5194/cp-19-1623-2023. Fulltekst i vitenarkiv Vis sammendrag

  Abstract. There is a temporal correlation between the peak activity of the North Atlantic Igneous Province (NAIP) and the Paleocene–Eocene Thermal Maximum (PETM), suggesting that the NAIP may have initiated and/or prolonged this extreme warming event. However, corroborating a causal relationship is hampered by a scarcity of expanded sedimentary records that contain both climatic and volcanic proxies. One locality hosting such a record is Fur Island in Denmark, where an expanded pre- to post-PETM succession containing hundreds of NAIP ash layers is exceptionally well preserved. We compiled a range of environmental proxies, including mercury (Hg) anomalies, paleotemperature proxies, and lithium (Li) and osmium (Os) isotopes, to trace NAIP activity, hydrological changes, weathering, and seawater connectivity across this interval. Volcanic proxies suggest that NAIP activity was elevated before the PETM and appears to have peaked during the body of the δ13C excursion, but decreased considerably during the PETM recovery. This suggests that the acme in NAIP activity, dominated by flood basalt volcanism and thermogenic degassing from contact metamorphism, was likely confined to just ~200 kyr (ca. 56.0–55.8 Ma). The hundreds of thick basaltic ashes in the post-PETM strata likely represent a change from effusive to explosive activity, rather than an increase in NAIP activity. Detrital δ7Li values and clay abundances suggest that volcanic ash production increased basaltic reactive surface area, likely enhancing silicate weathering and atmospheric carbon sequestration in the early Eocene. Signals in lipid biomarkers and Os isotopes, traditionally used to trace paleotemperature and weathering changes, are used here to track seaway connectivity. These proxies indicate that the North Sea was rapidly cut off from the North Atlantic in under 12 kyr during the PETM recovery due to NAIP thermal uplift. Our findings reinforce the hypothesis that the emplacement of the NAIP had a profound and complex impact on Paleocene–Eocene climate, both directly through volcanic and thermogenic degassing, and indirectly by driving regional uplift and changing seaway connectivity.

• Deegan, Frances M.; Bédard, Jean H.; Grasby, Stephen E.; Dewing, Keith; Geiger, Harri & Misiti, Valeria [Vis alle 13 forfattere av denne artikkelen] (2022). Magma-Shale Interaction in Large Igneous Provinces: Implications for Climate Warming and Sulfide Genesis. Journal of Petrology. ISSN 0022-3530. 63(9), s. 1–10. doi: 10.1093/petrology/egac094. Fulltekst i vitenarkiv Vis sammendrag

  Large Igneous Provinces (LIPs) whose magma plumbing systems intersect sedimentary basins are linked to upheavals of Earth’s carbon and sulfur cycles and thus climate and life history. However, the underlying mechanistic links between these phenomena are elusive. We address this knowledge gap through short time-scale petrological experiments (1200 °C and 150 MPa) that explore interaction between basaltic melt and carbonaceous shale (mudstone) using starting materials from the Canadian High Arctic LIP and the Sverdrup Basin in which it intrudes. Here we show that entrainment of shale xenoliths in basaltic melt causes shale to shatter due to incipient thermal stress and devolatilization, which accelerates assimilation by increasing reactive surface area. Shale assimilation therefore facilitates transfer of sediment-derived volatile elements to the shallow parts of LIP plumbing systems, whereupon carbon dominates the vapor phase whilst sulfur is partitioned into sulfide melt droplets. This study reveals that although carbon and sulfur are efficiently mobilized as a consequence of shale assimilation, sulfides can sequester sulfur - an important climate cooling agent - thus enhancing net emissions of climate warming greenhouse gases by shale-intersecting LIPs.

• Gaynor, Sean P.; Svensen, Henrik Hovland; Polteau, Stephane & Schaltegger, Urs (2022). Local melt contamination and global climate impact: Dating the emplacement of Karoo LIP sills into organic-rich shale. Earth and Planetary Science Letters. ISSN 0012-821X. 579. doi: 10.1016/j.epsl.2022.117371. Fulltekst i vitenarkiv Vis sammendrag

  The emplacement of Large Igneous Provinces (LIPs) is commonly correlated with global climate change, and environmental and biological crises. To establish this complex causative link, chemical proxies from marine sedimentary sections must be temporally tied to LIP activity through high-precision geochronology. The temporal link is often ambiguous, especially as periods of environmental change are commonly shorter than the full duration of magmatic and volcanic activity in a LIP. Most importantly, temporal relations need to be established through precise and accurate U-Pb geochronology; however, mafic rocks are often undersaturated in zircon or baddeleyite. New U-Pb age determinations of pegmatitic pods from Karoo LIP dolerite sills into the Ecca Group of the Karoo Basin yield single crystal dates with uncertainties below 50 ka, which allow for a new, detailed assessment of this intrusive event. These samples yield complicated age spectra and Hf geochemistry, which indicate that localized assimilation of sedimentary rocks enabled zircon saturation within these mafic melts. Zircon crystallization age interpretations from these data indicate that sill emplacement within the Ecca Group was coeval across the basin within uncertainty of U-Pb dating, and therefore represents a period of particularly high magma flux. Since the Ecca Group is locally exceptionally rich in organic matter, the widespread and rapid sill-related contact metamorphism generated a significant volume of thermogenic volatiles. Given the temporal overlap of the emplacement of sills between 183.147 ± 0.059 Ma and 183.187 ± 0.133 Ma and the timing of the global Toarcian Oceanic Anoxic Event (TOAE), our data support a causal link between this discrete period of high flux emplacement of Karoo sills into the Ecca Group and the global climate change that took place during the Early Jurassic.

• Shen, Jun; Yin, Runsheng; Algeo, Thomas J.; Svensen, Henrik Hovland & Schoepfer, Shane D. (2022). Mercury evidence for combustion of organic-rich sediments during the end-Triassic crisis. Nature Communications. 13. doi: 10.1038/s41467-022-28891-8. Fulltekst i vitenarkiv Vis sammendrag

  Abstract The sources of isotopically light carbon released during the end-Triassic mass extinction remain in debate. Here, we use mercury (Hg) concentrations and isotopes from a pelagic Triassic–Jurassic boundary section (Katsuyama, Japan) to track changes in Hg cycling. Because of its location in the central Panthalassa, far from terrigenous runoff, Hg enrichments at Katsuyama record atmospheric Hg deposition. These enrichments are characterized by negative mass independent fractionation (MIF) of odd Hg isotopes, providing evidence of their derivation from terrestrial organic-rich sediments (Δ 199 Hg < 0‰) rather than from deep-Earth volcanic gases (Δ 199 Hg ~ 0‰). Our data thus provide evidence that combustion of sedimentary organic matter by igneous intrusions and/or wildfires played a significant role in the environmental perturbations accompanying the event. This process has a modern analog in anthropogenic combustion of fossil fuels from crustal reservoirs.

• Bajard, Manon Juliette Andree; Ballo, Eirik Gottschalk; Høeg, Helge Irgens; Bakke, Jostein; Støren, Eivind Wilhelm Nagel & Loftsgarden, Kjetil [Vis alle 11 forfattere av denne artikkelen] (2022). Climate adaptation of pre-Viking societies. Quaternary Science Reviews. ISSN 0277-3791. 278. doi: 10.1016/j.quascirev.2022.107374. Fulltekst i vitenarkiv Vis sammendrag

  Understanding how the Viking societies were impacted by past climate variability and how they adapted to it has hardly been investigated. Here, we have carried out a new multi-proxy investigation of lake sediments, including geochemical and palynological analyses, to reconstruct past changes in temperature and agricultural practices of pre-Viking and Viking societies in Southeastern Norway during the period between 200 and 1300 CE. The periods 200–300 and 800–1300 CE were warmer than the 300–800 CE period, which is known as the “Dark Ages Cold Period”. This cold period was punctuated by century-scale more temperate intervals, which were dominated by the cultivation of cereals and hemp (before 280 CE, 420–480 CE, 580–700 CE, and after 800 CE). In between, cold intervals were dominated by livestock farming. Our results demonstrate that the pre-Viking societies changed their agricultural strategy in response to climate variability during the Late Antiquity.

Se alle arbeider i NVA

• Konglevold, Laila; Christiansen, Stefan; Svensen, Henrik Hovland & Bjørshol, Anja (2023). Verdens navle. House of Foundation. ISBN 9788284170534. 255 s. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2022). Et land av stein. Bergartene som har formet Norge. Kagge Forlag AS. ISBN 9788248929901. 311 s. Fulltekst i vitenarkiv

Se alle arbeider i NVA

• Svensen, Henrik Hovland (2026). Om Oslofeltet og grunnen under føttene. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2026). Øygarden. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2026). Abels tårn - Hvor vakker er naturen? [Radio]. NRK P2. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2026). Åpent atelier. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2026). Lagring av CO2 i undergrunnen. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2026). Lagring av CO2 i undergrunnen. Fulltekst i vitenarkiv
• Polteau, Stephane; Kihle, Jan; Yarushina, Viktoriya M.; Kiss, Daniel; Svensen, Henrik Hovland & Callegaro, Sara (2026). Enigmatic occurrences of liquid oil in diabase intrusions and vesicular basalt. doi: https:/www.egu26.eu/. Fulltekst i vitenarkiv Vis sammendrag

  The presence of liquid petroleum trapped within low-permeability vesicular basalt or mafic intrusions is more than a scientific curiosity, as it also challenges the conventional fluid migration and storage models in porous media. Its presence is significant because it may suggest complex primary magmatic porosity development, low temperature alteration and resulting fluid pathways, nano-scale deformation, or other processes leading to secondary porosity development. Thus the cases offer insights into processes controlling hydrocarbon and fluid flow systems in volcanic areas. In this contribution, we present the study of a Permian dolerite dyke at Tvedestrand in Norway and a vesicular basalt sample from West Greenland, both of which contain liquid oil. The Tvedestrand dyke is emplaced in Precambrian gneiss that was previously overlain by Cambrian black shales. The Greenland basalt is part of the North East Atlantic igneous province, underlain by petroleum-bearing sedimentary strata. Organic geochemistry indicates both oils to be immature, hence suggesting migration through these rocks after emplacement and cooling. We also show ultrahigh-resolution photographs in natural and ultraviolet light to show the distribution of petroleum compounds and image the microstructures controlling fluid migration. The parameters controlling fluid migration in tight crystalline rocks are important to constrain, as these are directly relevant to hydrocarbon exploration in unconventional settings and for hydrogen or carbon storage. We discuss the most likely mechanisms enabling fluid migration in these systems and their broader implications.

• Andersen, Gard Lilledal; Svensen, Henrik Hovland; Deegan, Frances M.; Callegaro, Sara; Whattam, Jack William & Jeon, Heejin [Vis alle 8 forfattere av denne artikkelen] (2026). Small crystals, big eruptions: Quartz phenocrysts as archives of caldera-forming processes in the Permian Drammen Caldera, Oslo Rift, Norway. Fulltekst i vitenarkiv Vis sammendrag

  Caldera-forming eruptions are among the most dangerous and catastrophic volcanic phenomena, yet the related magma reservoir processes are poorly understood. In the Permo-Carboniferous Oslo Rift in Southeastern Norway, there are at least 15 calderas, several of which have preserved pyroclastic deposits. Here we focus on a >450 m thick rhyolitic ignimbrite succession in the 7 x 7 km Drammen Caldera, located 40 km southwest of Oslo. We present field observations, petrography, and geochemical analyses, with an emphasis on primary quartz phenocrysts. Ignimbrite stratigraphy in the Drammen Caldera comprises the high-grade, phenocryst-rich Lian Formation (25–30% crystals) and the moderate- to low-grade, phenocryst-poor Sørumlia Formation (1–2% crystals). The Lian Formation records a large, sustained pyroclastic eruption that tapped a crystal-rich part of the reservoir, whereas the Sørumlia Formation was deposited over several smaller, highly explosive eruptions sourced from crystal-poor magma batches. In both formations, primary quartz phenocrysts occur as euhedral, rounded, and embayed crystals, and range in size from 50 to 2000 μm. Cathodoluminescence (CL) imaging of primary quartz phenocrysts reveals widespread oscillatory zoning, and several crystals show a distinct core with resorption margin, indicating changing magma reservoir conditions during crystal growth. To investigate the origin of the zoning, we conducted in situ oxygen and silicon isotope analyses. The primary quartz has an average δ18O value of 8.03 ± 0.23‰, suggesting assimilation of high-δ18O Lower Palaeozoic sedimentary rocks surrounding the caldera. As most intracrystal values are indistinguishable within the analytical uncertainty, we interpret assimilation to have occurred prior to quartz growth. Quartz phenocrysts yield an average δ30Si value of -0.08 ± 0.43‰. Like oxygen, silicon isotopes show no significant inter- or intracrystal variation, indicating isotopic homogeneity of the melt prior to the ignimbrite-forming eruptions. The combination of textural complexity and isotopic homogeneity in primary quartz phenocrysts provides new insights into felsic magma reservoir processes in the Oslo Rift.

• Neumann, Else Ragnhild; Callegaro, Sara; Jacobsen, Stein B.; Hyung, E.; Svensen, Henrik Hovland & Larsen, Bjørn Tore [Vis alle 7 forfattere av denne artikkelen] (2026). Mantle heterogeneity beneath the Oslo Rift revealed by the early basaltic stage of the Skagerrak LIP. Fulltekst i vitenarkiv Vis sammendrag

  The Oslo Rift is the northernmost reach of the Skagerrak Large Igneous Province (SkLIP; Torsvik et al., 2008), where mafic volcanism began around 300 Ma with the emplacement of the so-called “B1” basalts. Erupted over a relatively brief interval of ca. 1-2 Myr, B1 lavas now form successions up to 1500 m thick and provide a precious window into early rift evolution and mantle dynamics at the onset of SkLIP activity. We present a rift-scale geochemical overview of B1 lavas from five main lava piles: Brunlanes, Skien, Vestfold, Jeløya, and Krokskogen. The lavas geochemistry displays a pronounced latitudinal gradient: highly alkaline products (melilitites to alkali basalts) dominate the southern sections, while tholeiitic compositions are found at Krokskogen in the north, despite broadly coeval emplacement across the region (Corfu et al., 2024). This transition is accompanied by changes in trace element abundances and radiogenic isotopes, implying contribution of up to four distinct mantle sources. The strongly alkaline Brunlanes lavas reflect are kimberlite-like, with low initial Sr–Nd isotope ratios (LoNd type; Hyung et al., 2023). We interpret this as a deep, mildly carbonated mantle plume source, although a role for metasomatic lithospheric domains cannot be entirely ruled out. A second mantle component shows HIMU-like Sr–Nd–Pb isotopic signatures and high incompatible-element contents, whereas a third, enriched-mantle (EM-type) source supplies a less incompatible-element-rich contribution. The Skien B1 series appears to record melting of a hybrid mantle involving all three components, while Vestfold and Jeløya basalts reflect mixing between HIMU-like and EM-type sources. We propose that the lower lithosphere beneath the Skien–Vestfold–Jeløya area consisted of EM-type garnet peridotite that was metasomatized by HIMU-like melts long before SkLIP initiation, forming enriched veins subsequently tapped during B1 volcanism. These melts likely originated at ≥140 km depths during or just prior to lithospheric thinning.

• Svensen, Henrik Hovland (2025). Om Oslos undergrunn. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2025). Ekskursjon i Oslo. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2025). Ekskursjon i Oslo. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland & Kongevold, Laila (2025). Linoworkshop. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2025). Et land av stein – hvordan landet vårt er bygget opp. doi: https:/puioslo.no/arrangement/et-land-av-stein-hvordan-landet-vart-er-bygget-opp/. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2025). Vinterutstillingen i Halden 2025. doi: https:/www.ostfoldbildendekunstnere.no/vinterutstillingen. Fulltekst i vitenarkiv
• Neumann, Else Ragnhild; Callegaro, Sara; Jacobsen, Stein B.; Hyung, E.; Svensen, Henrik Hovland & Larsen, Bjørn Tore [Vis alle 7 forfattere av denne artikkelen] (2025). Mantle complexity beneath the Oslo Rift: geochemical insights into the earliest phase of the Skagerrak-Centered LIP. Fulltekst i vitenarkiv Vis sammendrag

  The Oslo Rift marks the northernmost extent of the Skagerrak-Centered Large Igneous Province (SCLIP; Torsvik et al., 2008), where mafic volcanism first erupted around 300 Ma with the emplacement of the so called “B1” basalts. These lavas, deposited rapidly over ~1–2 million years, now form stacks up to 1500 meters thick and offer a unique glimpse into early rift evolution and mantle dynamics at the onset of SCLIP activity. We present a rift-scale geochemical portrait for the B1 lavas from five lava piles – from south to North: Brunlanes, Skien, Vestfold, Jeløya, Krokskogen. The lavas show a striking latitudinal gradient – from highly alkaline melilitites in the south (Brunlanes) to tholeiites in the north (Krokskogen), despite their roughly coeval emplacement in these different areas (Corfu et al., 2024). This chemical transition includes systematic variations in trace elements and radiogenic isotopes, pointing to the involvement of at least four distinct mantle sources. The southernmost, strongly alkaline lavas from Brunlanes derive from a plume-like, mildly carbonated, mantle component with low initial Sr-Nd isotope ratios (LoNd type; Hyung et al., 2023). We favor a deep seated (kimberlite-like) plume origin for this component, but we also consider the possibility of metasomatized lithospheric domains enriched by melts or fluids shortly before the onset of magmatism. A second source exhibits HIMU-like Sr-Nd-Pb isotope signatures and high incompatible element concentrations. A third, enriched mantle (EM-type) source contributes a less incompatible-element-rich component. The Skien B1 series reflects melting of a hybrid mantle involving all three components, while Vestfold and Jeløya basalts record mixing between HIMU-like and EM-type sources. We propose that the lower lithosphere beneath the Skien-Vestfold-Jeløya region was originally EM-type garnet peridotite, later metasomatized by HIMU-like melts that formed enriched veins long before SCLIP initiation. These B1 melts likely formed at ≥140 km depth, during or immediately before lithospheric thinning. A fourth, depleted mantle source that escaped metasomatic enrichment, was only tapped by the Krokskogen tholeiitic basalts in the north, and likely formed at shallower depths, suggesting rapid thermal erosion of the lithosphere in the north. Understanding the multi-source evolution of the B1 basalts is critical for reconstructing the earliest magmatic stages of the SCLIP and assessing their potential role, via CO₂ degassing, in Carboniferous–Permian climate perturbations (Wang et al., 2023).

• Kverndokk, Kyrre; Nielsen, May-Brith Ohman; Døving, Runar; Svensen, Henrik Hovland; Setten, Gunhild & Brochmann, Ragnhild [Vis alle 7 forfattere av denne artikkelen] (2025). Paradisets bakside. [TV]. Viten-TV. doi: https:/www.vitentv.no/media/Paradisets+bakside/0_jqcwwfvl. Fulltekst i vitenarkiv Vis sammendrag

  Dokumentarfilm

• Svensen, Henrik Hovland (2025). CO2 storage in volcanic-sedimentary systems. doi: https:/npf.no/konferansen/ccs-2025/. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland & Planke, Sverre (2025). Potensialet for lagring av CO2 i vulkanske bergarter i Norge. Fulltekst i vitenarkiv
• Andersen, Gard Lilledal; Svensen, Henrik Hovland; Augland, Lars Eivind; Callegaro, Sara; Whattam, Jack William & Deegan, Frances M. [Vis alle 8 forfattere av denne artikkelen] (2025). Unravelling the eruption history of the Drammen Caldera: A multidisciplinary study of caldera-forming processes in the Permian Oslo Rift, Norway. Fulltekst i vitenarkiv Vis sammendrag

  During the mature stages of the Permo-Carboniferous Oslo Rift, at least 15 calderas formed. Thick ignimbrite deposits are preserved in several of these calderas but remain poorly studied with modern methods. This study focuses on a rhyolitic ignimbrite succession in the 7x7 km Drammen Caldera, located 40 km southwest of Oslo. Here, we present field observations, petrographic results, and geochemical analyses of the deposits. Despite significant glacial erosion and partial Quaternary coverage, we show that over 450 m of ignimbrite stratigraphy is preserved in the Drammen Caldera. In addition, we have identified ashfall and lahar deposits interbedded between ignimbrite units. The ignimbrites range from high- to low-welding grade, and we interpret them to record at least five explosive eruptions resulting in two caldera collapse events. The ignimbrites are altered but retain primary volcanic textures. Cathodoluminescence (CL) reveals complex zoning patterns in quartz phenocrysts, indicating multiple growth and dissolution stages. Phenocrysts are heavily fragmented, with fractures healed by quartz cementation. Oxygen isotopes measured in-situ in zoned quartz phenocrysts suggest assimilation of high-δ18O Lower Palaeozoic sedimentary rocks surrounding the caldera. Ongoing work on silicon isotopes and U-Pb geochronology aims to further refine the timing and petrogenetic processes. We conclude that the ignimbrites preserved in the Drammen Caldera hold information about complex magma reservoir dynamics, leading to several explosive eruptions. We present a six-stage evolution model for the caldera. This study highlights the potential for detailed multidisciplinary ignimbrite studies in other Oslo Rift calderas, as well as other eroded calderas globally.

• Planke, Sverre; Berndt, Christian; Huismans, Ritske Sipke; Faleide, Jan Inge; Bünz, Stefan & Millett, John [Vis alle 8 forfattere av denne artikkelen] (2025). Understanding Volcanic Rifted Margins and Paleoclimate Implications from Scientific Drilling in the NE Atlantic. doi: https:/ui.adsabs.harvard.edu/abs/2024AGUFMPP44A..02P/abstract. Fulltekst i vitenarkiv
• Lundmark, Anders Mattias; Bakken, Kristian Bjelbøle; Anell, Ingrid; Augland, Lars Eivind; Conrad, Clinton Phillips & Dunkel, Kristina G [Vis alle 10 forfattere av denne artikkelen] (2025). Why don’t my students come to class? Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2025). Når kommer neste vulkanutbrudd på Island? Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2025). Et land av stein. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2025). VICCO og CO2-lagring. Fulltekst i vitenarkiv
• Lundmark, Anders Mattias; Bakken, Kristian Bjelbøle; Anell, Ingrid; Augland, Lars Eivind; Conrad, Clinton Phillips & Dunkel, Kristina G [Vis alle 10 forfattere av denne artikkelen] (2025). “Why don’t my students come to class?”. Fulltekst i vitenarkiv
• Lundmark, Anders Mattias; Bakken, Kristian Bjelbøle; Anell, Ingrid; Augland, Lars Eivind; Conrad, Clinton Phillips & Dunkel, Kristina G [Vis alle 10 forfattere av denne artikkelen] (2025). “Why don’t my students come to class?”. Fulltekst i vitenarkiv
• Nygaard, Madeleine Skov; Planke, Sverre; Berndt, Christian; Zastrozhnov, Dmitry; Faleide, Jan Inge & Jones, Morgan Thomas [Vis alle 18 forfattere av denne artikkelen] (2025). Mimir High Core-log-seismic Integration. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland; Callegaro, Sara; Kjøll, Hans Jørgen; Midtkandal, Ivar; Whattam, Jack William & Dalslåen, Bjørgunn Heggem [Vis alle 10 forfattere av denne artikkelen] (2024). Rhomb porphyry lavas from the Oslo Rift revisited: New insights from construction-related boreholes and cores. Fulltekst i vitenarkiv
• Andersen, Guro Lilledal; Svensen, Henrik Hovland; Augland, Lars Eivind; Callegaro, Sara & Whattam, Jack (2024). The explosive volcanism of the Oslo Rift – insights from the ignimbrites of the Drammen Caldera. Fulltekst i vitenarkiv
• Whattam, Jack; Svensen, Henrik Hovland; Midtkandal, Ivar; Jerram, Dougal Alexander & Callegaro, Sara (2024). Mafic volcaniclastic deposits in the Oslo Rift. Fulltekst i vitenarkiv
• Callegaro, Sara; Svensen, Henrik Hovland; Heimdal, Thea H.; Kjøll, Hans Jørgen; Harstad, Andreas Olaus & Augland, Lars Eivind [Vis alle 9 forfattere av denne artikkelen] (2024). Geochemistry of sills from the early stage of the Oslo Rift. Fulltekst i vitenarkiv
• Dalslåen, Bjørgunn Heggem; Planke, Sverre; Svensen, Henrik Hovland & Kirkeby, Terje Rogvi (2024). Conquering the sub-surface: Taking on the Oslo Rift lava pile and infrastructure development. Fulltekst i vitenarkiv
• Planke, Sverre; Berndt, Christian; Bünz, Stefan; Huismans, Ritske Sipke; Faleide, Jan Inge & Svensen, Henrik Hovland [Vis alle 11 forfattere av denne artikkelen] (2024). Understanding Volcanic Rifted Margins and Paleoenvironment by Scientific Drilling in the NE Atlantic. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Geologen som ble besatt av kunst. [Journal]. Apollon. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Vulkanutbrudd på Island og hvordan de kan påvirke oss. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Oppdatering om vulkanutbruddet på Island (januar 2024). [TV]. NRK Dagsrevyen. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Vulkanutbruddet på Island (januar 2024). [Radio]. NRK Nyhetsmorgen (radio/TV). Fulltekst i vitenarkiv
• Augland, Lars Eivind; Midtkandal, Ivar; Svensen, Henrik Hovland & Planke, Sverre (2024). Detrital zircons in reworked tephra deposits – a proxy for contourites? Fulltekst i vitenarkiv
• Nygaard, Madeleine Skov; Planke, Sverre; Berndt, Christian; Zastrozhnov, Dmitry; Faleide, Jan Inge & Jones, Morgan Thomas [Vis alle 24 forfattere av denne artikkelen] (2024). PALMAR – Paleogene Basin Development on the Vøring and Møre Margins. Fulltekst i vitenarkiv
• Nygaard, Madeleine Skov; Planke, Sverre; Berndt, Christian; Zastrozhnov, Dmitry; Faleide, Jan Inge & Jones, Morgan Thomas [Vis alle 24 forfattere av denne artikkelen] (2024). IODP Exp. 396 Drilling and High-Resolution 3D Seismic on the Mimir High. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Oslos mystiske fortid. Foredrag på fagdag hos Oslo katedralskole. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Excursion to Hovedøya for ECORD. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Hva skjer på Island? Foredrag på Frogner seniorsenter. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Kunstnersamtale: Inn i det ukjente: En samtale om kunsten, forskningen og en avgrunn av tid. Med Henrik Svensen, Geir Harald Ssamuelsen og Sigrid Espelid. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Obligen. Detlakelse på podcasten Real læring. [Internet]. Real læring. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Ekskursjon til Sognsvann for en gruppe fra NGI. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Guidet ekskursjon til Huk, Bygdøy, med elever fra St. Olavs videregående skole, Stavanger. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Dokumentarfilm (opptak) om hager og antropocen. [TV]. Leidar Norway. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Guidet tur i Oslo sentrum for bedriftslaget til Gjensidige forsikring. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Foredrag og vandring på Fossildagene i Slemmestad. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Plutselige endringer. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2024). Hva kan gå galt? Intervju til dokumentarserie. [TV]. Teddy TV. Fulltekst i vitenarkiv
• Callegaro, Sara; Whattam, Jack & Svensen, Henrik Hovland (2023). Eruption history through late-stage rift activity: the central volcanoes and caldera-related deposits of the Permian Oslo Rift, southern Norway. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland; John, Timm; Polozov, A.; Callegaro, Sara; Jones, Morgan Thomas & Newton, Robert [Vis alle 8 forfattere av denne artikkelen] (2023). Carbon, sulphur, and mercury geochemistry in a crater lake in the Siberian Traps. Fulltekst i vitenarkiv
• Callegaro, Sara; Svensen, Henrik Hovland; Heimdal, Thea Hatlen; Guarino, Vincenza; Deegan, Frances M. & Jerram, Dougal Alexander [Vis alle 8 forfattere av denne artikkelen] (2023). Dolerite sills from the Siberian Traps (Tunguska basin, Russia) bear evidence of halogens mobilization from evaporitic host rocks. Fulltekst i vitenarkiv
• Callegaro, Sara; Svensen, Henrik Hovland; Heimdal, Thea Hatlen; Deegan, Frances M.; Jerram, Dougal Alexander & Polozov, Alexander [Vis alle 7 forfattere av denne artikkelen] (2023). Magma-evaporite interaction in doleritic sills from the Siberian Traps: insights from whole-rock and mineral data. Fulltekst i vitenarkiv
• Deegan, Frances M.; Bédard, Jean H.; Grasby, Stephen E.; Dewing, Keith; Geiger, Harri & Misiti, Valeria [Vis alle 13 forfattere av denne artikkelen] (2023). Magma-Shale Interaction and Volatile Mobilization at LIPs: Insights from Kinetic Experiments. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2023). Du kan ofte se granitt og gneis når du går tur, men hvordan ble de til? [Internet]. forskning.no. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2023). Oslos geologiske historie. Fulltekst i vitenarkiv
• Bond, David; Callegaro, Sara; Davies, Joshua; Deegan, Frances; Galloway, Jennifer & Gaynor, Sean [Vis alle 14 forfattere av denne artikkelen] (2023). Meet the Authors. Elements. ISSN 1811-5209. 19(5), s. 265–266. doi: 10.2138/gselements.19.5.265. Fulltekst i vitenarkiv
• Whattam, Jack; Svensen, Henrik Hovland; Midtkandal, Ivar; Callegaro, Sara & Jerram, Dougal Alexander (2023). Intermittent cessation and renewal of volcanism in the Oslo Rift revealed through detailed mapping and stratigraphy. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2023). Om vulkanutbruddet på Island (desember 2023). [Radio]. NRK Nyhetsmorgen (radio/TV). Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2023). Om vulkanutbrudd og klimakonsekvenser. [Radio]. NRK Radio P2. Fulltekst i vitenarkiv
• Callegaro, Sara; Svensen, Henrik Hovland; Heimdal, Thea Hatlen; Kjøll, Hans Jørgen; Harstad, Andreas Olaus & Neumann, Else Ragnhild (2022). New insights on shallow intrusions from the early stage of the Oslo Rift. Fulltekst i vitenarkiv
• Callegaro, Sara; Svensen, Henrik Hovland; Deegan, Frances M.; Planke, Sverre & Polozov, Alexander (2022). Magma-host rock interaction in basaltic sills from the Siberian Traps (Tunguska basin, Russia): mineral scale and whole-rock perspectives. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2022). Østfolds vakre bergarter og mystiske fortid. Fulltekst i vitenarkiv
• Einevoll, Gaute & Svensen, Henrik Hovland (2022). Podcast #51 i Vett og vitenskap. [Internet]. Podcast "Vett og vitenskap". Fulltekst i vitenarkiv
• Svensen, Henrik Hovland & Torgersen, Eivind (2022). Norske byggeklosser – bergartene som bygget landet. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2022). Geologisk vandring i Oslo sentrum. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland & Müller, Reidar (2022). Lanseringssamtale, Et land av stein. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2022). Hva skjuler seg under asfalten i Oslo? Fulltekst i vitenarkiv
• Berndt, Christian; Planke, Sverre; Zarikian, Carlos A.; Bünz, Stefan; Karstens, Jens & Svensen, Henrik Hovland [Vis alle 8 forfattere av denne artikkelen] (2022). Shallow-water hydrothermal venting in the North Atlantic during the Paleocene Eocene Thermal Maximum. Fulltekst i vitenarkiv Vis sammendrag

  The Paleocene Eocene Thermal Maximum (PETM, ~56 Ma) was a rapid global warming of 5-6 ºC resulting from massive (>2000 Gigatons) carbon emissions. A potential release mechanism is thermogenic gas from contact metamorphism of carbon-bearing sediments due to magma intrusions into sedimentary basins. Here, we present seismic data and borehole information from the North Atlantic Igneous Province. They show that even in the center of the rift system, water depths were sufficiently shallow to allow most gas released from hydrothermal vent systems to bypass the water column. The shape of the vent craters and stratified infill suggest vigorous explosive gas release during the initial phase of vent formation and rapid shallow marine and largely undisturbed infill thereafter. The recorded negative carbon isotope excursion and occurrence of the index taxon Apectodinium augustum in the crater-infill support assignment to a latest Paleocene to earliest Eocene vent formation. The data support a scenario where magmatic sill emplacement and resulting hydrothermal activity rapidly injected thermogenic greenhouse gas into the atmosphere

• Svensen, Henrik Hovland (2022). Science and art: Experience from collaboration with artists - and using art in outreach. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2022). The Huken quarry and the resulting landscapes. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2022). Oslos naturhistorie gjennom to milliarder år - og vulkanene på Ullern. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2022). Under asfalten. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2022). Geologien i Oslo-området. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2022). Da Oslo eksploderte. Fulltekst i vitenarkiv
• Bjærke, Marit Ruge; Ekström, Anders; Hastrup, Frida & Svensen, Henrik Hovland (2022). Bridging an epistemological gap: Roundtable on the importance of cooperation between the humanities and the natural sciences. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland; Bøckmann, Petter & Bjorå, Charlotte Sletten (2022). Abels tårn. [Radio]. EKKO; NRK P2. Fulltekst i vitenarkiv
• Svensen, Henrik Hovland (2022). Ny bok om bergarter i Norge. [Radio]. NRK P1+ Holm. Fulltekst i vitenarkiv
• Solheim, Mari; Svensen, Henrik Hovland & Dunkel, Kristina G (2025). Evolution of Mafic Dykes in a Major Fault Zone, the Oslo rift Petrology and geochemistry of fluid-rock interaction along the Ekeberg Fault. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  This thesis investigates how magmatic intrusions in the Oslo Rift were modified by hydrothermal fluid circulation, with a focus on dykes intersected in the Ekeberg Fault zone. A continues drill core from Alna was studied using petrography, bulk-rock geochemistry, and stable isotopes to trace evolution of Permian dykes and their surrounding rocks. The dykes, originally composed of feldspar, pyroxene, and oxides, are now strongly altered. Away from the fault, alteration is dominated by albite, chlorite, and epidote, reflecting higher temperature fluids. Within the fault zone, the rocks are overprinted by dolomite, clays, barite and sulfides, consistent with lower temperature CO2- and sulfur-rich fluids linked to organic-rich alum shale and basement-derived fluids. Textures such as porous albite and zoned dolomite show that alteration progressed through fluid driven replacement reactions, which also created porosity and sustained fluid flow. Geochemical and isotopic data highlight the contribution of multiple fluid sources: magmatically heated seawater, shale derived volatiles, and basement fluids. The Alna dykes therefore express a complex history of overprinting by successive hydrothermal events.

• 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. Fulltekst i vitenarkiv Vis sammendrag

  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.

• Ballo, Eirik Gottschalk; Bajard, Manon; Bakke, Jostein & Svensen, Henrik Hovland (2025). Reconstructing climate, environmental and societal dynamics in southeastern Norway through the past 2000 years. Universitetet i Oslo. Fulltekst i vitenarkiv Vis sammendrag

  One of the key challenges we face today is the changing climate and its environmental impacts, affecting all life on Earth. Examining historical human responses to climate crises provides insights into resilience and adaptability. Robust data is essential for studying past climate and environmental changes effectively. European climate records covering the past 2000 years reveal a prolonged cooling period, known as the Dark Ages Cooling Period (c. 300–800 CE), punctuated by a pronounced cooling in the mid-6th century. Studies show that these cold intervals are more complex and regionally varied than previously believed. In the 6th century in Norway, archaeological evidence points to crop failures, famine, farm abandonment and changes in social organization in some regions, while others experienced minimal impact during these cold periods. However, southeastern Norway lacks detailed high-resolution paleoclimate and paleoenvironmental reconstructions, limiting our ability to fully understand these events. This thesis aims to enhance understanding of climate, environmental, and societal dynamics in southeastern Norway over the past 2000 years, focusing on the Dark Ages Cold Period (c. 300–800 CE), through sediment analysis from Lake Sagtjernet and Lake Ljøgottjern in southeastern Norway. We introduce a μCT scan method for varve counting for Lake Sagtjernet, establishing the first varve chronology from a Norwegian lake, covering c. 4023 years. This chronology enables the first paleoclimate and paleoenvironmental reconstruction from Norwegian varved lake sediments. This reconstruction reveals 2000 years of temperature variability, highlighting a major cooling event—the largest in 2000 years—that aligns with the 6th century cooling event. However, sparse settlements in the first millennium complicate climate impact interpretation at Lake Sagtjernet, while the last millennium shows increased human activities during both warm and cold periods. Reconstructed temperatures between 200 and 1300 CE from Lake Ljøgottjern indicate a notably colder period from 300 to 800 CE, compared to the periods before (200–300 CE) and after (800–1300 CE), identified as the Dark Ages Cold Period. Temperature fluctuations within this cold period significantly influenced agricultural strategies at the more populated Lake Ljøgottjern. Warmer intervals favoring crop cultivation and colder intervals prompting a shift towards livestock farming, illustrating the impact of climatic conditions on societal development.

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