Hans Jørgen Kjøll

• Turino, V.; Magni, Valentina; Kjøll, Hans Jørgen & Jakob, Johannes (2023). The Effect of Magma Poor and Magma Rich Rifted Margins on Continental Collision Dynamics. Journal of Geophysical Research (JGR): Solid Earth. ISSN 2169-9313. 128(12). doi: 10.1029/2023JB027173. Full text in Research Archive
• Kjøll, Hans Jørgen; Midtkandal, Ivar; Planke, Sverre; Millett, John; Manton, Ben & Anderskouv, Kresten (2023). The interplay between siliciclastic and carbonate depositional systems: Maastrichtian to Danian basin-floor sediments of the mid-Norwegian Møre Basin. Basin Research. ISSN 0950-091X. 36(1). doi: 10.1111/bre.12827. Full text in Research Archive
• Rosenqvist, Marija Plahter; Meakins, Max William John; Planke, Sverre; Millett, John M.; Kjøll, Hans Jørgen & Voigt, Martin J. [Show all 7 contributors for this article] (2023). Reservoir properties and reactivity of the Faroe Islands Basalt Group: Investigating the potential for CO<inf>2</inf> storage in the North Atlantic Igneous Province. International Journal of Greenhouse Gas Control. ISSN 1750-5836. 123. doi: 10.1016/j.ijggc.2023.103838. Full text in Research Archive
• Jakob, Johannes; Andersen, Torgeir Bjørge; Mohn, Geoffroy; Kjøll, Hans Jørgen & Beyssac, Olivier (2022). Revised tectono-stratigraphic scheme for the Scandinavian Caledonides and its implications for our understanding of the Scandian orogeny. In Kuiper, Yvette D. (Eds.), New Developments in the Appalachian-Caledonian-Variscan Orogen. The Geological Society of America. ISSN 978-0-8137-2554-3. p. 335–374. doi: 10.1130/2022.2554(14). Full text in Research Archive
• Jakob, Johannes; Kjøll, Hans Jørgen & Andersen, Torgeir Bjørge (2022). A Fossil Magma-rich Rifted Margin in the Scandinavian Caledonides, Continental Rifted Margins 2: Case examples. ISTE. ISSN 9781789450620. p. 185–202. Show summary

  Rifted margins mark the transition between continents and oceans, which are the two first-order types of land masses on Earth. Rifted margins contribute to our understanding of lithospheric extensional processes and are studied by various disciplines of Earth Science (geology, geophysics, geochemistry). Thanks to better and wider public access to high-quality data, our understanding in these areas has improved significantly over these last two decades. This book summarizes this knowledge evolution and details where we stand today, with a series of case examples included. It is structured in a practical way, with concise text descriptions and comprehensive diagrams. Continental Rifted Margins 2 is a useful resource for students and newcomers to the rifted margin community – a “cookbook” of sorts to facilitate the reading of scientific publications and provide basic definitions and explanations.

• Andersen, Torgeir Bjørge; Jakob, Johannes; Kjøll, Hans Jørgen & Tegner, Christian (2022). Vestiges in the Pre-Caledonian Passive Margin of Baltica in the Scandinavian Caledonides: Overview, Revisions and Control on the Structure of the Mountain Belt. Geosciences. ISSN 2076-3263. 12(57). doi: 10.3390/geosciences12020057. Full text in Research Archive Show summary

  Abstract: The Pre-Caledonian margin of Baltica has been outlined as a tapering wedge with increas- ing magmatism towards the ocean–continent transition. It is, however, well known that margins are complex, with different and diachronous evolution along and across strike. Baltica’s vestiges in the Scandes have complexities akin to modern margins. It included a microcontinent and magma-poor hyperextended and magma-rich segments. It was probably up to 1500 km wide before distal parts were affected by plate convergence. Characteristic features are exhumed mantle peridotites and their detrital equivalents, some exposed to the seafloor by the pre-orogenic hyperextension. A major change in the architecture of the mountain belt occurred across the NW–SE trending Sveconorwe- gian front in the Baltican basement. This coincided with the NE termination of the Jotun-Lindås- Dalsfjord basement nappes, the remains of the Jotun Microcontinent (JMC) formed by hyperexten- sion prior to the orogeny. Mantle with ophicalcite breccias exhumed by hyperextension are covered by deep-marine sediments and local conglomerates. Baltican basement slivers are common in the transitional crust basins. Outboard the JMC, the margin was magma-rich. The main break-up mag- matism at 605 ± 10 Ma was part of the vast Central Iapetus Magmatic Province. The along-strike heterogeneity of the margin controlled diachronous and contrasting tectonic evolution during the later Caledonian plate convergence and collision. Keywords: Scandinavian Caledonides; Baltica; passive margin; hyperextension; mantle exhuma- tion; microcontinent; magma-rich; magma-poor

• Kjøll, Hans Jørgen (2020). Late Neoproterozoic basin evolution of the magma rich Iapetus margin of Baltica. Norwegian Journal of Geology. ISSN 2387-5844. 100(1), p. 1–32. doi: 10.17850/njg100-1-6. 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 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.

• Kjøll, Hans Jørgen; Andersen, Torgeir Bjørge; Corfu, Fernando; Labrousse, Loic; Tegner, Christian & Abdelmalak, Mohamed Mansour [Show all 7 contributors for this article] (2019). Timing of break-up and thermal evolution of a pre-Caledonian Neoproterozoic exhumed magma-rich rifted margin. Tectonics. ISSN 0278-7407. 38(6), p. 1843–1862. doi: 10.1029/2018TC005375. Full text in Research Archive Show summary

  During the terminal stages of Wilson cycles, remnants of magma-poor margins may be incorporated into the orogens, whereas the magma-rich margins often are 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 Dike Complex was emplaced into a sedimentary basin during the initial break-up and opening of the Iapetus Ocean 615 to 590 million years ago. The dike complex constitutes 70-90% of the magma-rich, syn-rift basins and is locally well-preserved despite the complex Caledonian history. This contribution provides new observations about the 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 dike complex at 0.25 to 0.45 GPa, with contact metamorphic temperatures up to c. 700°C. In the northernmost part of the study area U-Pb dating of magmatic zircon shows that partial melting of the sedimentary host-rock, at relatively shallow levels, occurred at 612 Ma. This shows that the crust was molten already 6 million years before the northernmost dike swarm was emplaced at 605.7 ± 1.8 Ma. We propose that the locally pervasive partial melting occurred due to high geothermal gradients and introduction of mafic melt in the lower crust. These processes significantly reduced the strength of the crust, eventually facilitating continental break-up.

• Tegner, Christian; Andersen, Torgeir Bjørge; Kjøll, Hans Jørgen; Brown, Eric L.; Hagen-Peter, Graham & Corfu, Fernando [Show all 8 contributors for this article] (2019). A mantle plume origin for the Scandinavian Dyke Complex: a "piercing point" for 615 Ma plate reconstruction of Baltica? Geochemistry Geophysics Geosystems. ISSN 1525-2027. 20(2), p. 1075–1094. doi: 10.1029/2018GC007941. Full text in Research Archive Show summary

  Abstract The origin of Large Igneous Provinces (LIPs) associated with continental breakup and the reconstruction of continents older than c. 320 million years (pre-Pangea) are contentious research problems. Here we study the petrology of a 615 - 590 Myr dolerite dyke complex that intruded rift-basins of the magma-rich margin of Baltica and now is exposed in the Scandinavian Caledonides. These dykes are part of the Central Iapetus Magmatic Province (CIMP), a LIP emplaced in Baltica and Laurentia during opening of the Caledonian Wilson Cycle. The >1000 km long dyke complex displays lateral geochemical zonation from enriched to depleted basaltic compositions from south to north. Geochemical modelling of major and trace elements shows these compositions are best explained by melting hot mantle 75-250°C above ambient mantle. Although the trace element modelling solutions are non- unique, the best explanation involves melting a laterally zoned mantle plume with enriched and depleted peridotite lithologies, similar to present-day Iceland and to the North Atlantic Igneous Province. The origin of CIMP appears to have involved several mantle plumes. This is best explained if rifting and breakup magmatism coincided with plume generation zones at the margins of a Large Low Shear-wave Velocity Province (LLSVP) at the core mantle boundary. If the LLSVPs are quasi-stationary back in time as suggested in recent geodynamic models, the CIMP provides a guide for reconstructing the paleogeography of Baltica and Laurentia 615 million years ago to the LLSVP now positioned under the Pacific Ocean. Our results provide a stimulus for using LIPs as piercing points for plate reconstructions.

• Jakob, Johannes; Andersen, Torgeir Bjørge & Kjøll, Hans Jørgen (2019). A review and reinterpretation of the architecture of the South and South-Central Scandinavian Caledonides—A magma-poor to magma-rich transition and the significance of the reactivation of rift inherited structures. Earth-Science Reviews. ISSN 0012-8252. 192, p. 513–528. doi: 10.1016/j.earscirev.2019.01.004. Full text in Research Archive Show summary

  nterpretations of the pre-Caledonian rifted margin of Baltica commonly reconstruct it as a simple, tapering, wedge-shaped continental margin dissected by half graben, with progressively more rift-related magmas towards the ocean-continent transition zone. It is also interpreted to have had that simple architecture along-strike the whole length of the margin. However, present-day rifted margins show a more complex architecture, dominated by different and partly diachronous segments both along and across strike. Here, we show that the composition and the architecture of the Baltican-derived nappes of the South and South Central Scandinavian Caledonides are to a large extend rift-inherited. Compositional variations of nappes in similar tectonostratigraphic positions can be ascribed to variations along-strike the rifted margin, including a magma-rich, a magma-rich to magma-poor transition zone, and a magma-poor segment of the margin. The architecture of the nappe stack that includes the Baltican-derived nappes was formed as a result of the reactivation of rift-inherited structures and the stacking of rift domains during the Caledonian Orogeny.

• Kjøll, Hans Jørgen; Viola, Giulio; Menegon, Luca & Sørensen, Bjørn Eske (2015). Brittle-viscous deformation of vein quartz under fluid-rich lower greenschist facies conditions. Solid Earth (SE). ISSN 1869-9510. 6(2), p. 681–699. doi: 10.5194/se-6-681-2015. Full text in Research Archive

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• Tegner, Christian; Andersen, Torgeir Bjørge; Kjøll, Hans Jørgen; Brown, Eric L.; Graham-Hagen, Peter & Corfu, Fernando [Show all 8 contributors for this article] (2024). Dyke Complexes of the Scandinavian Caledonides. Show summary

  Dyke Complexes of the Scandinavian Caledonides Christian Tegnera, Torgeir B. Andersenb, Hans Jørgen Kjøllb, Eric L. Browna, Graham Hagen-Peterc, Fernando Corfub, Sverre Plankeb, and Trond H. Torsvikb aDepartment of Geoscience, Aarhus University, Denmark, christian.tegner@geo.au.dk; bDepartment of Geosciences, University of Oslo, Norway; cEarth Sciences, Vrije Universiteit Amsterdam, Netherlands Dyke complexes (c. 615 – 560 Ma) exposed in the Scandinavian Caledonides are part of the Central Iapetus Magmatic Province, a large igneous province related to the opening of the Iapetus Ocean and an earlier phase of the North Atlantic Wilson Cycle. These include a >1000 km long dyke complex preserved in the Särv, Seve and Corrovarre nappes (Andréasson et al., 1998; Hollocher et al., 2007; Tegner et al., 2019) and dykes of the Seiland Igneous Province preserved in the Kalak nappe (Robins and Takla, 1979; Reginiussen et al., 1995). The compositions of the >1000 km long dyke complex is mainly tholeiitic and displays lateral geochemical zonation from enriched to depleted basaltic compositions from south to north. In addition, the central part of this dyke complex (in Trøndelag, Norway and Jämtland, Sweden) displays alkali basalt compositions. In contrast, the dykes of the Seiland Igneous Province are entirely composed of alkali basalts including ankaramite, picrite and lamprophyres. In this talk we will review the geochemical details of the basaltic magmas in the Scandinavian dyke complexes and discuss their origin from heterogenous and most likely multiple mantle plumes, and from enriched subcontinental lithospheric mantle. References Andréasson, P.G., Svenningsen, O.M., Albrecht, L. (1998). Dawn of Phanerozoic orogeny in the North Atlantic tract; Evidence from the Seve-Kalak Superterrane, Scandinavian Caledonides. Journal of the Geological Society of Sweden GFF 120, 159–172. doi:10.1080/11035899801202159 Hollocher, K., Robinson, P., Walsh, E., Terry, M.P. (2007). The Neoproterozoic Ottfjället dike swarm of the Middle Allochthon, traced geochemically into the Scandian Hinterland, Western Gneiss Region, Norway. American Journal of Science 307, 901–953. doi:10.2475/06.2007.02 Reginiussen, H., Ravna, E.J.K., Berglund, K. (1995). Mafic Dykes from Øksfjord, Seiland Igneous Province, northern Norway: geochemistry and palaeotectonic significance. Geological Magazine 132, 667–681. Robins, B., Takla, M.H. (1979). Geology and geochemistry of a metamorphosed picrite-ankaramite dyke suite from the Seiland province, northern Norway. Norsk Geologisk Tidsskrift 59, 67-95. Tegner, C., Andersen, T.B., Kjøll, H.J., Brown, E.L., Hagen-Peter, G., Corfu, F., Planke, S., and Torsvik, T.H. (2019). A mantle plume origin for the Scandinavian Dyke Complex: a “piercing point” for 615 Ma plate reconstruction of Baltica? Geochemistry, Geophysics, Geosystems 20, 1075-1094. doi:10.1029/2018GC007941

• 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. .
• Tegner, Christian; Andersen, Torgeir Bjørge; Kjøll, Hans Jørgen; Brown, Eric L.; Hagen-Peter, Graham & Corfu, Fernando [Show all 8 contributors for this article] (2021). A mantle plume origin for the Scandinavian Dyke Complex: a “piercing point” for 615 Ma plate reconstruction of Baltica? Show summary

  The origin of Large Igneous Provinces (LIPs) associated with continental breakup and the reconstruction of continents older than c. 320 million years (pre-Pangea) are contentious research problems. Here we study the petrology of a 615 - 590 Myr dolerite dyke complex that intruded rift-basins of the magma-rich margin of Baltica and now is exposed in the Scandinavian Caledonides. These dykes are part of the Central Iapetus Magmatic Province (CIMP), a LIP emplaced in Baltica and Laurentia during opening of the Caledonian Wilson Cycle. The >1000 km long dyke complex displays lateral geochemical zonation from enriched to depleted basaltic compositions from south to north. Geochemical modelling of major and trace elements shows these compositions are best explained by melting hot mantle 75-250°C above ambient mantle. Although the trace element modelling solutions are non-unique, the best explanation involves melting a laterally zoned mantle plume with enriched and depleted peridotite lithologies, similar to present-day Iceland and to the North Atlantic Igneous Province. The origin of CIMP appears to have involved several mantle plumes. This is best explained if rifting and breakup magmatism coincided with plume generation zones at the margins of a Large Low Shear-wave Velocity Province (LLSVP) at the core mantle boundary. If the LLSVPs are quasi-stationary back in time as suggested in recent geodynamic models, the CIMP provides a guide for reconstructing the paleogeography of Baltica and Laurentia 615 million years ago to the LLSVP now positioned under the Pacific Ocean. Our results provide a stimulus for using LIPs as piercing points for plate reconstructions.

• Kjøll, Hans Jørgen; Galland, Olivier; Labrousse, Loic & Andersen, Torgeir Bjørge (2020). Emplacement Mechanisms of a Dyke Swarm Across the Brittle-Ductile Transition.
• Kjøll, Hans Jørgen; Galland, Olivier; Labrousse, Loic & Andersen, Torgeir Bjørge (2020). Emplacement mechanisms of a dyke swarm across the Brittle- Ductile transition. 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.

• Kjøll, Hans Jørgen (2020). Langs dette fjellet går geologene rett ned i jordas indre. [Internet]. Titan.no.
• Kjøll, Hans Jørgen; Galland, Olivier; Labrousse, Loic & Andersen, Torgeir Bjørge (2019). Emplacement Mechanisms of a Dyke Swarm Across the Brittle-Ductile Transition.
• Andersen, Torgeir Bjørge; Jakob, Johannes & Kjøll, Hans Jørgen (2019). The Jotun Microcontient.
• Andersen, Torgeir Bjørge; Jakob, Johannes & Kjøll, Hans Jørgen (2019). Exhumation of continental Mantle by Hyperextension, in passive continental margins: the Caledonian example” . Show summary

  Exhumation of Continental Mantle by Hyperextension in Passive Continental Margins:the Caledonian example The pre-Caledonian Baltican rifted margin has been outlined as a tapering wedge with increasing magmatism towards the ocean-continent transition (OCT), and with a similar structure along its entire length. It is, however, well-known that passive margins can be complex, with different and diachronous segment-evolutions along and across strike. The Baltican nappes in the Scandes preserve a complexity akin to modern margins, including an OCT, a micro-continent and continental slivers, hyperextended-to-embryonic oceanic basins with exhumed sub-continental mantle and a major magma-rich segment. The margin was probably up to 1500 km wide, before distal parts were affected by plate-convergence in the early to middle Ordovician. The margin vestiges, overprinted by Scandian and earlier fabrics now occur at low to middle structural levels in the mountain belt. Proximal parts comprise rift-basins with syn- to post-rift deposits of Cryogenian, Ediacaran and Lower Palaeozoic age. Its vestiges also comprise continental slivers, coarse- to fine-grained sediments as well as deep-marine deposits. A major change in the Caledonian structure occurs across a NW-SE transverse zone parallel to a fundamental basement structure within Baltica, the Sveconorwegian (Grenville) deformation front. The most prominent changes across this lineament are: 1) the coincidence with the NE-termination of the Jotun-Microcontinent (JMC) and 2) the transition from a magma-rich segment in the NE to a hyperextended, magma-poor segment inboard the JMC in the SW. The latter comprises numerous (>100) solitary meta-peridotites and detrital serpentinites. These mantle-fragments, mostly original harzburgites to dunites, were emplaced tectonically and were variably hydrated and carbonated prior to the Caledonian orogeny. Where exhumed to the seafloor some produced detrital serpentinites. The mantle fragments were covered by deep-basin fine-grained sediments and local breccias and conglomerates. Metasomatic alteration and ophicalcite breccias are commonly developed. Other important features in these OCT basins are Baltican basement slivers (up to 40 x 1.5 km). The magma-poor OCT segment is now overlain by a huge basement nappe complex (Jotun, Lindås, Dalsfjord, Eikefjord NC), which after rifting, but prior to Scandian collision, was positioned outboard the hyperextended OCT basin as the Jotun-Microcontinent (JMC). The JMC´s distal margin have mafic dykes and lavas and was affected by early-Caledonian deformation/metamorphism. The magma-rich segment (Seve-Kalak NC) also hosts exhumed mantle peridotites and detrital serpentinites (locally w/fossils), but its most prominent characteristic is the Scandinavian Dyke Complex (SDC) forming parts of a ~615-595 Ma Large Igneous Province that probably assisted opening of the Iapetus Ocean. The magma-poor SW segment inboard the JMC, formed an OCT basin similar to the present North Atlantic rifted margin system between Ireland and the Hatton-Rockall ribbons.

• Andersen, Torgeir Bjørge; Jakob, Johannes & Kjøll, Hans Jørgen (2019). The pre-Caledonian Margin of Baltica.
• 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. 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.

• Andersen, Torgeir Bjørge; Jakob, Johannes; Kjøll, Hans Jørgen & Tegner, Christian (2019). A new look at the Scandinavian Caledonides and the significance of Hyper-extension in the pre-Caledonian passive margin of Baltica . Show summary

  The pre-Caledonian Baltican rifted margin has been outlined as a tapering wedge with increasing magmatism towards the ocean-continent transition (OCT), and with a mostly similar structure along its length. It is, however, well-known that passive margins can be complex, with different and diachronous segment-evolutions along and across strike. The Baltican nappes in the Scandes preserve a complexity akin to modern margins, including an OCT, a micro-continent and continental slivers, hyperextended-to-embryonic oceanic basins as well as a major magma-rich segment. The margin was several hundred-, probably up to 1500 km wide, before distal parts were affected by plate-convergence between ~480 and 450 Ma. The margin vestiges, overprinted by Scandian and earlier fabrics as well as the late/post-orogenic extension, now occur at low to middle structural levels in the mountain belt. Proximal parts comprise continental to marine rift-basins with syn- to post-rift deposits of Late Cryogenian, Ediacaran and Lower Palaeozoic age. Its vestiges also comprise continental slivers, coarse- to fine-grained sediments as well as deep-marine deposits. A major change in the nappe-structure occurs across a NW-SE transverse zone parallel to a fundamental basement structure within Baltica, the Sveconorwegian (Grenville) deformation front. The most prominent changes across this lineament are: 1) the coincidence with the NE-termination of the Jotun-Lindås-Dalsfjord nappe complexes, interpreted as the Jotun-Microcontinent (JMC) and 2) the transition from a magma-rich segment in the NE to a hyperextended, magma-poor segment in the SW. The latter has numerous (>100) solitary meta-peridotites and detrital serpentinites (some fossiliferous). The mantle-fragments w/ophicalcite breccias were emplaced tectonically and are covered mostly by deep-basin sediments and local breccias and conglomerates. This ‘mixed’ (mélange) unit was locally affected by pre-Caledonian metasomatism and intruded by gabbros and granitoids (at ~487±1 to 471±2 Ma); also reflected by clastic zircons (>468 Ma) present in the sediments. Other important features are Baltican basement slivers (up to 40 x 1.5 km). The magma-poor SW segment is overlain by a huge basement/cover nappe complex, which after rifting, but prior to Scandian collision, was positioned outboard the hyperextended domain as the Jotun-Microcontinent (JMC). JMC´s most distal parts have mafic dykes and lavas and were affected by early-Caledonian deformation/metamorphism. The SW margin segment was ~400 km long, hyperextended- and magma-poor, and received sediments as late as the Middle Ordovician (and possibly until the onset of the mid-Silurian Scandian orogeny?). The NE magma-rich segment also has mantle peridotites and detrital serpentinites (locally w/fossils), but its most prominent characteristic is the Scandinavian Dyke Complex (SDC) forming parts of a ~615-595 Ma Large Igneous Province that probably assisted opening of the Iapetus Ocean. In the SW segment there is so far no evidence of Late Proterozoic magmatism, but Baltican basement was locally truncated by mafic dykes at ~850 to 830Ma and 615 Ma. The magma-poor SW segment, inboard the JMC, formed a transitional-crust basin opening to an ocean basin, similar to the present North Atlantic rift system between Ireland and the Hatton-Rockall ribbons. The margin of Baltica probably has its best modern analogue in the North-Atlantic and Norwegian-Greenland Sea margins.

• 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. 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.

• Kjøll, Hans Jørgen; Galland, Olivier; Labrousse, Loic & Andersen, Torgeir Bjørge (2019). Dyke emplacement mechanisms across the brittle-ductile transition. 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.

• Andersen, Torgeir Bjørge; Jakob, Johannes; Kjøll, Hans Jørgen; Quintela, Orlando; Corfu, Fernando & Torsvik, Trond Helge [Show all 9 contributors for this article] (2019). Hyperextension in magma-poor and magma-rich domains along the pre-Caledonian passive margin of Baltica . Show summary

  Hyperextension in magma-poor and magma-rich domains along the pre-Caledonian passive margin of Baltica Torgeir B. Andersen, Johannes Jakob, Hans-Jørgen Kjøll, Orlando Quintela, Fernando Corfu, Trond H. Torsvik, 1)Christian Tegner, 2)Loic Labrousse and 3)Geoffroy Mohn CEED, Univ. Oslo; 1)Århus Univ.; 2)Sorbonne Univ, ISTeP-Paris; 3)Univ. Cergy-Pontoise Email: t.b.andersen@geo.uio.no The pre-Caledonian Baltican rifted margin has been outlined as a tapering wedge with increasing magmatism towards the ocean-continent transition (OCT), and with a mostly similar structure along its length. It is, however, well-known that passive margins can be complex, with different and diachronous segment-evolutions along and across strike. The Baltican nappes in the Scandes preserve a complexity akin to modern margins, including an OCT, a micro-continent and continental slivers, hyperextended-to-embryonic oceanic basins as well as a major magma-rich segment. The margin was several hundred-, probably up to 1500 km wide, before its distal parts were affected by convergence between ~480 and 450 Ma. Its vestiges, overprinted by Scandian and earlier fabrics as well as the late/post-orogenic extension, now occur at low to middle structural levels in the mountain belt. Proximal parts comprise continental to marine rift-basins with syn- to post-rift deposits of Late Cryogenian, Ediacaran and Lower Palaeozoic age. Its vestiges also comprise continental slivers, coarse- to fine-grained sediments as well as deep-marine deposits. A major change in the nappe-structure occurs across a NW-SE transverse zone parallel to a fundamental basement structure within Baltica, the Sveconorwegian front. The most prominent changes across this lineament are: 1) the coincidence with the NE-termination of the Jotun-Lindås-Dalsfjord nappe complex, interpreted as the Jotun- Lindås-Dalsfjord microcontinent (JMC) and 2) the transition from the magma-rich segment in the NE to the hyperextended, magma-poor segment in the SW. The latter has numerous (>100) solitary meta-peridotites and detrital serpentinites (some fossiliferous). The mantle-fragments w/ophicalcite breccias were emplaced tectonically and are covered mostly by deep-basin sediments and local breccias and conglomerates. This ‘mixed’ (mélange) unit was locally affected by pre-Caledonian metasomatism and intruded by gabbros and granitoids (at ~487±1 to 471±2 Ma); this magmatism is also reflected by clastic zircons (>468 Ma) present in the sediments. Other important features are Baltican basement slivers (up to 40 x 1.5 km). The magma-poor SW segment is overlain by a huge basement/cover nappe complex, which after rifting, but prior to Scandian collision, was positioned outboard the hyperextended domain as the Jotun-Lindås-Dalsfjord Microcontinent (JMC). JMC´s distal parts at Atløy, have mafic dykes and lavas in the Høyvik Gp, and were affected by early-Caledonian event(s). The SW margin segment was ~400 km long, hyperextended- and magma-poor, and received sediments as late as the Middle Ordovician (and perhaps until the onset of the mid-Silurian Scandian orogeny?). The NE magma-rich segment also has mantle peridotites and detrital serpentinites (locally w/fossils), but its most prominent characteristic is the Scandinavian Dyke Complex (SDC) forming parts of a ~615-595 Ma Large Igneous Province that probably assisted opening of the Iapetus Ocean. In the SW segment there is so far no evidence of Late Proterozoic magmatism, but Baltican basement was locally truncated by mafic dykes at ~850 to 830Ma and 615 Ma. The magma-poor SW segment, inboard the JMC, formed a transitional-crust basin opening to an ocean basin, similar to the present North Atlantic rift system between Ireland and the Hatton-Rockall ribbons. The margin of Baltica probably has its best modern analogue in the North-Atlantic and Norwegian-Greenland Sea margins.

• Andersen, Torgeir Bjørge; Jakob, Johannes; Kjøll, Hans Jørgen; Corfu, Fernando; Torsvik, Trond Helge & Tegner, Christian [Show all 8 contributors for this article] (2018). Architecture and Palaeography of the per-Caldonian Margin of Baltica.
• Kjøll, Hans Jørgen; Andersen, Torgeir Bjørge; Tegner, Christian; Labrousse, Loic; Corfu, Fernando & Planke, Sverre (2018). Defining a magma-rich rifted margin fossil analogue in the Scandinavian Caledonides. Show summary

  The Iapetus Ocean opened ca 610 Ma ago possibly due to the interaction with a mantle plume at the base of the lithosphere. Stretching of the conjoined crystalline crust started prior to break-up and provided accommodation for continental and shallow marine syn-rift sediments. An early non-magmatic phase with discrete and localized deformation was followed by pervasive mafic magmatism where dyke-emplacement accounted for the bulk of the stretching. During the Caledonian orogeny, the Iapetan margin was thrusted onto Baltica as the Iapetus closed. To- day, vestiges of the magma-rich margin reside within nappes from central Sweden to northern Norway. Although overprinted by Caledonian deformation fabrics and metamorphism, there are localities where pre-Caledonian mag- matic and sedimentary structures are well-preserved, thereby allowing for detailed studies of deep to intermediate processes at magma-rich rifted margins. Three field seasons have yielded observations on the outcrop and micro- scopic scale that provide information about relative timing and development of the margin, both the early non- magmatic stage and the subsequent magmatic stage. In particular, dyke geometries and morphologies have been assessed from photogrammetric 3D models to constrain the active mechanisms during dyke emplacement. Jadeite in clinopyroxene geobarometry constrain the crystallization pressure of clinopyroxenes of the different intrusion levels and coupled with U/Pb geochronology constrain the timing of intrusion. Furthermore, dense sampling of mafic intrusions for geochemistry reveals a similar lateral geochemical signature as observed across the Iceland plume. Based on these new observations we argue that the well-preserved parts of the margin comprise: 1) Parts of an early lower crustal magmatic complex consisting of coronitic gabbros and granites; 2) Strongly stretched and attenuated crystalline basement intruded by mafic dykes; 3) Highly intruded pre- to syn-rift sediments, locally forming sheeted dyke complexes and 4) Extrusive mafic lavas, including pillow basalts, interlayered with metased- iments. Such a complete fossil magma-rich rifted margin analogue has never been recognized in the field before and provides unique opportunities to study processes occurring at deep levels in the crust even at the microscopic scales and may thus reform our understanding of the architecture, evolution, and processes at magma-rich rifted margins.

• Tegner, Christian; Andersen, Torgeir Bjørge; Kjøll, Hans Jørgen; Brown, Eric L.; Hagen-Peter, Graham & Corfu, Fernando [Show all 8 contributors for this article] (2018). The pre-Caledonian Scandinavian Dyke Complex and 600 Ma plate reconstructions of Baltica. Show summary

  A spectacular dyke complex is surprisingly well preserved along c. 1000 km in the Caledonian nappes of central and northern Scandinavia. This dyke complex was originally emplaced into continental sedimentary basins along the rifted margin of Baltica, it is part of the Central Iapetus Magmatic Province (CIMP), and it has U-Pb ages of 615-590 Ma. To constrain its origin and to potentially guide plate reconstructions of Baltica we: (1) re-visited the dyke complexes of the Ottfjället, Sarek, Kebnekaise, Tornetrask and Indre Troms mountains of Sweden and Norway; (2) produced new and compiled published geochemical data; (3) modeled mantle sources and melting dynamics; and (4) extended reconstructions of the paleo-position of Baltica back to 600 Ma. The compiled dataset includes c. 600 analyses that forms a coherent suite dominated by tholeiitic ferrobasalt, but including alkali basalts in the central portion. The tholeiitic dykes display lateral variations in geochemical enrichment (e.g. delta-Nb, La/Sm(N) and Sr isotopes) in the southern and central portions, grading to more depleted compositions in the north. Our petrological modeling suggests melting of asthenospheric mantle involving at least two source compositions at temperatures elevated about 100 °C above ambient mantle, consistent with melting of a zoned mantle plume originating from a plume generation zone at the core-mantle boundary. If the position of the present plume generation zone in the Pacific can be viewed as stationary back to 600 Ma, we entertain the idea that the Scandinavian Dyke Complex may be used to guide plate reconstructions.

• Andersen, Torgeir Bjørge; Jakob, Johannes; Kjøll, Hans Jørgen; Corfu, Fernando; Planke, Sverre & Torsvik, Trond Helge [Show all 9 contributors for this article] (2018). The Pre-Caledonian Margin of Baltica: overview and research in progress. Show summary

  The Caledonian margin of Baltica formed by continental break-up of Rodinia in the Late Proterozoic to Ediacaran. With exception of the dike-swarm near Egersund in SW Norway, the Fennoscandian basement including the autochthonous basement windows along the axis of the mountain belt were little affected by the magmatism associated with the break-up. The distal parts, however, were strongly attenuated, hyper-extended and a 1000 km long segment, intensively intruded by a Large Igneous Province (LIP), the Pre-Caledonian LIP (PC-LIP). Here, we provide glimpses of our work in progress from the vestiges of the margin. More details on several aspects of the margin evolution are presented by co-authors. Here we present a regional model for the pre-Caledonian margin suggesting it was highly complex and included micro-continental sliver(s) and both a hyperextended, magma-poor domain with transition(s) to attenuated embryonic oceanic and magma-rich margin domains. The break-up related PC-LIP magmatism lasted from approximately 615 to 570 Ma, but the most intense activity appears to have been at ~600 Ma. Our ongoing work suggests that the impingement of a mantle plume on the Ediacaran continental lithosphere was associated with a temperature anomaly of ~100oC, causing widespread melting of the asthenosphere and dyke-intrusion of the continental crust and sediments of the margin. We suggest that the pre-Caledonian margin of the Iapetus preserved in the Scandes comprise most of the elements of passive continental margins, and that it probably represents one of the best exposed field analogue for the deeper and least known parts of passive margins.

• Kjøll, Hans Jørgen; Andersen, Torgeir Bjørge; Labrousse, Loic & Corfu, Fernando (2018). A new tectonic model for the Seve Nappe Complex in Norrland, Sweden. Show summary

  A new tectonic model for the Seve Nappe Complex in Norrland, Sweden Hans Jørgen Kjøll, Torgeir B. Andersen, Loic Labrousse, Fernando Corfu 1) CEED 2) Paris The Seve Nappe Complex (SNC) in Norrbotten, Sweden has classically been mapped as a series of nappes formed by the telescoping of the rifted margin of Baltica. Typically, the SNC is sub-divided into the lower, middle and upper nappe-series. The lower Seve generally constitute slivers of basement, such as the Akkajaure nappe and are overlain by meta-sedimentary and meta-igneous rocks representing both the middle and upper Seve nappes. The peak metamorphism varies considerably within the Seve from local eclogite facies to a more regional amphibolite facies and domains where original pre-Caledonian contact metamorphism related to dolerite intrusions are preserved. This has led to the norm of subdividing the SNC in different thrust nappes. We propose, however, a model where the Seve in Norrbotten represents a more continuous section through the magma-rich, attenuated margin of Baltica and that the metamorphic overprint, rather than representing decoupling and re-stacking, represent differential reactivity of individual lithologies with different reaction potential. High strain zones are present throughout Seve but the need for large internal thrusts juxtaposing older rocks on top of younger is not present internally in the Seve. This has dramatic consequences for, not only the understanding of the mountain building in the Caledonides, but may also open a new interest for the Seve as a place to study the deep processes of magma-rich passive margins, which are often lost in subduction and in general difficult to study in seismic lines due to masking of high velocity mafic intrusive and extrusive rocks.

• Kjøll, Hans Jørgen; Andersen, Torgeir Bjørge; Tegner, Christian; Labrousse, Loic & Planke, Sverre (2018). A fossil magma-rich margin revealed. Show summary

  A fossil magma-rich rifted margin revealed Hans Jørgen Kjøll, Torgeir B. Andersen, Christian Tegner, Loic Labrousse and Sverre Planke 1) CEED 2) Aarhus Universite 3) Paris 4) CEED/VBPR The Iapetus opened ~610 Myr ago, when a plume impinged on the lower crust of Baltica and Laurentia. Stretching of the conjoined crystalline crust started in the Neoproteozoic, prior to break-up and provided accommodation for continental and shallow marine syn-rift sediments. An early a-magmatic phase with discrete and localized deformation was followed by pervasive mafic magmatism where dike-emplacement accounted for the majority of the stretching. During the Caledonian orogeny the Baltican margin was thrusted onto Baltica as the Iapetus closed. Now, vestiges of the magma-rich margin resides within nappes from central Sweden to northern Norway. Although, overprinted by Caledonian fabrics, there are localities where pre-Caledonian structures are well-preserved, thereby allowing for detailed studies of deep to intermediate processes at magma-rich rifted margins. We propose the architecture of the magma-rich margin of Baltica and magma-rich rifted margins in general can be studied in the Caledonides. The well-preserved parts of the margin comprise: 1) Parts of a lower crustal magmatic complex w/gabbros and mafic dykes intruding stretched crystalline basement; 2) Strongly stretched and attenuated crystalline basement intruded by mafic dikes; 3) Highly intruded pre- to syn-rift sediments and 4) Extrusive mafic lavas, including pillow basalts, interlayered with metasediments. Together these levels represent a nearly continuous section through a magma-rich rifted margin, with some never-before described levels, such as the lower crustal magmatic complex.

• Andersen, Torgeir Bjørge; Jakob, Johannes; Kjøll, Hans Jørgen; Corfu, Fernando; Planke, Sverre & Torsvik, Trond Helge [Show all 8 contributors for this article] (2017). The Pre-Caledonian Margin of Baltica. Show summary

  The pre-Caledonian margin of Baltica formed by the rifting and eventual continental break-up of Rodinia in the Late Proterozoic to Ediacaran. With exception of the ca. 615 Ma dolerite dike-swarm near Egersund in SW Norway, the Fennoscandian basement including the mostly autochthonous basement windows in western Scandinavia (Lofoten, Western Gneiss Region, etc.) were surprisingly little affected by the rifting and the subsequent magmatism associated with the break-up. The distal parts of the margin, however, were strongly attenuated, hyper-extended and in a more than 1000 km long segment, intensively intruded by a break-up related Large-Igneous Province (LIP), here referred to as the Pre-Caledonian LIP (PC-LIP). In this presentation, we provide glimpses of new results and observations as well as work in progress from a large part of the nappe-stack of Scandinavian Caledonides containing the vestiges of the pre-Caledonian margin. More details on several aspects of the Pre-Caledonian margin evolution are presented by co-workers during this meeting. Based on our recent and some previous work, we propose a regional paleogeography model for the pre-Caledonian passive margin as it evolved from the Ediacaran into the late-Cambrian to the early-Ordovician, when the Iapetus Ocean started closing. We suggest that the distal margin architecture was highly complex and included micro-continental sliver(s) and a hyperextended, magma-poor domain with transition(s) to highly attenuated embryonic oceanic and magma-rich passive margin domains. The break-up related PC-LIP magmatism lasted from approximately 615 to 570 Ma, but the most intense dyke-emplacement appears to have been around 600 Ma. Our ongoing structural and metamorphic petrology studies, combined with geochronology, geochemical analyses and petrological modelling suggest that the impingement of a mantle plume on the Ediacaran continental lithosphere may have been associated with a temperature anomaly of up to 100oC, causing widespread melting of the asthenosphere as well as partial melt-generation in highly attenuated and intensely dike-intruded parts of the continental crust and sediments of the margin. It is our opinion that the pre-Caledonian distal margin rocks of the Iapetus as preserved in nappes of Scandinavian Caledonides preserve most of the elements of wide passive margins, and that it probably represents one of the best exposed field analogue for the deeper and least known parts of passive margins.

• Andersen, Torgeir Bjørge; Jakob, Johannes; Kjøll, Hans Jørgen; Corfu, Fernando; Tegner, Christian & Mohn, Geoffroy [Show all 9 contributors for this article] (2017). The Magma-poor and Magma-rich settings; the onshore perspective: The Caledonian case.
• Tegner, Christian; Andersen, Torgeir Bjørge; Brown, Eric L.; Corfu, Fernando; Planke, Sverre & Kjøll, Hans Jørgen [Show all 7 contributors for this article] (2017). The pre-Caledonian Scandinavian Dyke Complex and 600 Ma plate reconstructions of Baltica. Show summary

  Magmatism of the first known rifting phase of the North Atlantic Wilson cycle is surprisingly well preserved in the Cale- donian nappes of central and northern Scandinavia. Along c. 1000 km the Särv and Seve Nappes are characterised by spectacular dyke complexes and other intrusive forms origi- nally emplaced into continental sedimentary basins along the rifted margin of Iapetus. We refer to this as the magma-rich segment of the pre-Caledonian margin of Baltica, in contrast to the hyper-extended and magma-poor segment exposed in southern Norway (Andersen et al., Jakob et al., this meeting). In the larger picture the Scandinavian Dyke Complex is part of the Central Iapetus Magmatic Province ( ). The intensity, volume and structure of the Scandinavian Dyke Complex is comparable to that of the present passive margins of the North Atlantic large igneous province (Kjøll et al., this meeting) and U-Pb ages suggest magmatism was short-lived at 610-590 Ma. To constrain the origin of the Scandinavian Dyke Complex and to potentially guide plate reconstructions of Baltica we: (1) re-visited the dyke complexes of the Särv, Sarek, Kebnekaise, Tornetrask and Indre Troms mountains of Sweden and Norway; (2) compiled new and published geochemical data for the entire dyke complex; (3) modeled mantle sources and melting dy- namics; and (4) extended reconstructions of the paleo-position of Baltica back to 600 Ma. Although the appearance of the dykes ranges from garnet amphibolite gneiss to pristine mag- matic intrusions, all bulk rock compositions largely reflect the original magmatic rock. The compiled dataset includes c. 600 analyses that essentially forms a coherent suite dominated by tholeiitic ferrobasalt akin to the North Atlantic large igneous province, but including alkali basalts in the central portion where meta-carbonatite is also reported. A few samples (<30) are significantly contaminated with crust, but most are largely uncontaminated. The tholeiitic dykes display systematic lateral variations over c. 1000 km in trace element compositions suggesting geochem- ical enrichment (e.g. delta-Nb and La/Sm(N) relative to mid- ocean ridge basalt) in the southern and central portions, grad- ing to more depleted compositions in the north. The most enriched tholeiites occur in the central portion that also in- cludes alkali basalts. The lateral geochemical zoning is com- parable to e.g. the North Atlantic large igneous province and around Iceland today. Our petrological modeling suggests melting of asthenospheric mantle involving at least two source compositions at temperatures elevated above ambiant mantle. We therefore speculate that the Scandinavian Dyke Complex formed by melting of a zoned mantle plume originating from a plume generation zone (margins of large low shear-wave velocity provinces) at the core-mantle boundary. If the posi- tion of the present plume generation zone in the Pacific can be viewed as stationary back to 600 Ma, we entertain the idea that the Scandinavian Dyke Complex may be used to guide plate reconstructions.

• Kjøll, Hans Jørgen; Andersen, Torgeir Bjørge & Tegner, Christian (2017). Constraining dike emplacement conditions from virtual outcrop modelling .
• Andersen, Torgeir Bjørge; Kjøll, Hans Jørgen; Jakob, Johannes; Corfu, Fernando & Tegner, Christian (2017). The pre-Caledonian margin of Baltica.
• Kjøll, Hans Jørgen; Andersen, Torgeir Bjørge; Tegner, Christian; Corfu, Fernando & Planke, Sverre (2017). Wilson cycle-kick-off: Constraining the influence of a LIP during the Neoproterozoic evolution of the pre-Caledonian margin of Baltica and Laurentia.
• Tegner, Christian; Andersen, Torgeir Bjørge; Brown, Eric L.; Corfu, Fernando; Planke, Sverre & Kjøll, Hans Jørgen [Show all 7 contributors for this article] (2017). The pre-Caledonian Scandinavian Dyke Complex and 600 Ma plate reconstructions of Baltica.
• Andersen, Torgeir Bjørge; Jakob, Johannes; Kjøll, Hans Jørgen; Corfu, Fernando & Tegner, Christian (2017). A new look at the pre-Caledonian margin of Baltica. Show summary

  From the long history of previous work, most recently compiled by Nystuen and co-workers (2008, Episodes), it is well-documented that the pre-Caledonian margin of Baltica must have constituted a several hundred km wide and a more than 2000 km long passive continental margin. The vestiges of the margin now occur in the nappes at low- to intermediate tectono-stratigraphic levels in the mountain belt. The lower and originally proximal parts of the margin are dominated by continental rift basins mostly filled with coarse-grained siliciclastic sediments deposited in the late Proterozoic through the Ediacaran and into the Lower Palaeozoic, where the youngest dated clastic zircons are ~470 Ma (Slama & Pedersen 2015 JGS). At higher levels, and originally in more distal positions of the original margin, the nappes commonly comprise both basement and cover as well as deep-marine basin deposits. A major change in the architecture of the tectonic units that originally formed in the passive margin takes place across a NW-SE trending zone, which is roughly parallel to the present-day Gudbrandsdalen of South Norway. The transition zone is also roughly parallel to the major basement lineament of the Sveconorwegian orogenic front in south Norway. The most important change across this transverse lineament is that the NE segment is magma-rich, characterized by abundant basaltic magmatism. The basalts, mostly now seen mostly as dykes and gabbroic intrusions can be identified from Corrovarre in the north (Zwaan & van Roermund 1990, NGT) to Otta in the south (e.g. Sturt et al. 1991). Where dated, they were apparently emplaced during a relatively short time span between ~615 and 595 Ma (e.g. Baird et al. 2015, GFF; Nystuen et al. 2016, & Kumpulainen et al. 2016, both Abstracts, Nordic Winter meeting). This magmatism constitutes a large igneous province (LIP see presentation by Tegner et al. and Kjøll et al. this abstract volume). The SW segment is magma-poor and largely devoid of magmatic rocks of Ediacaran age (~540-635 Ma), except for the important Egersund dolerites cutting in-situ Baltican basement at 616±3 Ma (Bingen et al. 1998, The Journal of Geology; Walderhaug et al. 2007, Geophysical Jl. International). Instead the SW segment is characterised by numerous (>100) solitary meta-peridotites, mostly meta-dunites and meta-harzburgites as well as a number of detrital serpentinites and soapstones. These are interpreted as fragments of exhumed mantle and their erosion products, respectively. The meta-peridotites were originally exhumed and emplaced structurally, and covered by dominantly deep-basin sediments, but also by coarse sedimentary breccias and conglomerates, as part of the rifted margin development. The mélange was intruded locally by Early Ordovician gabbro to granitic rocks and was affected by initial metasomatism before the main Scandian metamorphism and deformation (Jakob et al. JGS in press and this abstract volume). Another important feature of the sedimentary and ultra-mafic mélange unit is the common presence of elongate (up to ~40 km), mostly thin (<100 m) deformed basement slivers of Baltican affinity (Jakob et al. JGS, in press). The magma-poor SW segment is structurally overlain by huge crystalline basement nappes (Jotun, Bergsdalen, Lindås, Dalsfjord Nappes) of Baltican basement, which after rifting, but prior to the Scandian Caledonian shortening were positioned outboard of the hyperextended segment. These nappes probably constituted a micro-continental sliver comparable in size to the Jan Mayen microcontinent in the present Greenland-Norwegian Sea. The SW segment represented by the 'melange' is interpreted to have constituted an approximately 400 km long, hyperextended- and magma-poor basin, which received sediments into the Early Ordovician and perhaps until the onset of the Scandian orogeny?

• Kjøll, Hans Jørgen; Andersen, Torgeir Bjørge; Corfu, Fernando & Tegner, Christian (2016). Constraining the influence of a LIP on the Neoproterozoic break-up of Baltica and Laurentia.
• Kjøll, Hans Jørgen (2016). Dette er de fem vakreste bergartene. [Journal]. https://titan.uio.no/node/1773.
• Kjøll, Hans Jørgen; Andersen, Torgeir Bjørge; Tegner, Christian; Corfu, Fernando & Planke, Sverre (2016). Wilson-cycle “kick-off”: Constraining the influence of a Large Igneous Province during the Neoproterozoic evolution of the pre-Caledonian margin of Baltica.
• Tegner, Christian; Andersen, Torgeir Bjørge; Corfu, Fernando; Planke, Sverre; Kjøll, Hans Jørgen & Torsvik, Trond Helge (2016). The pre-Caledonian Large Igneous Province and the North Atlantic Wilson Cycle.
• Andersen, Torgeir Bjørge; Jakob, Johannes; Kjøll, Hans Jørgen; Corfu, Fernando; Tegner, Christian & Alsaif, Manar [Show all 8 contributors for this article] (2016). Hyperextension, micro-continents, magma-poor and magma-rich segments in the pre-Caledonian margin of Baltica: research in progress .
• Kjøll, Hans Jørgen (2016). Modums geologiske historie.
• Fellman, Tuva & Kjøll, Hans Jørgen (2016). Jordskjelv. [Radio]. NRK P3.
• Kjøll, Hans Jørgen; Torgersen, Espen & Viola, Giulio (2014). Caledonian shortening by combined folding and thrusting in the immediate footwall of the Caledonian sole thrust: The example of the Repparfjord Tectonic Window, northern Norway. Show summary

  The Repparfjord Tectonic Window (RTW) is a window through the Caledonian nappes in northern Norway that exposes a package of greenschist facies metasedimentary and metavolcanic rocks of Paleoproterozoic age. These were deformed and metamorphosed during the Svecofennian orogeny producing km-wavelength upright NE-SW folds. Pervasive effects of a later Caledonian overprint, caused by the emplacement of the Kalak Nappe Complex during the Silurian, are limited and confined to the northwestern edge of the window, where NW-SE shortening caused the development of a compressional imbricate stack. Individual imbricates exploit preexisting, progressively tightening upright to overturned folds and are bound by generally very steep to sub-vertical discrete faults. One of these structures, the Skinnfjellet Fault Zone (SFZ), truncates the large doloarenite-hosted Nussir Cu deposit and has a present-day orientation that makes reverse displacement mechanically difficult. This study aims at a better understanding of the mechanical and temporal evolution of these steep thrusts. The SFZ strikes roughly NS, is sub-vertical and bears dip-slip lineations. It separates greenstones in the west from arcosic sandstones, conglomerates and the Nussir Cu deposit in the east. Kinematic indicators give east block up. Faulting occurred mostly under brittle conditions producing an approximately eight meter thick damage zone and a 40 cm thick fault gouge core. A second prominent fault is the Nussirjavrri Fault Zone (NFZ). The main fault plane dips moderately toward the NNE, bears a NW plunging lineation and a number of kinematic indicators indicate top-to-the-SSE thrusting. The fault trace is mappable for c. one km, but high-resolution geophysics indicates an ENE-WSW continuation. Mapping shows that the fault zone is folded openly with a fold axis trending NNE/SSW, consistent with the geometry of a subregional folding phase of inferred Caledonian age. The fault affects greenstones, graphitic slates and dolomites. The mylonitic thrust core thickness varies from 10 to 40 cm and is composed by alternating dark and light bands of chlorite, muscovite and graphite, together with quartz and carbonates. Interspersed within the foliation are interstitial euhedral pyrite and cm to dm scale dolomite clasts. Dolomite decarbonation is locally observed. Synkinematic quartz veins occur subparallel to the tectonic foliation. Quartz is dynamically recrystallized by SGRR and has an average grain size of c. 35um. Thin sections show two distinct and strong LPO’s. One is preserved within the core grains whereas the other is found within arrays of the recrystallized subgrains, whose distribution appears to be controlled by healed brittle fractures. Mapping indicates that the NFZ is cut by the SFZ and its overall transport direction to the SSE, in addition to its structural location at the front of the imbricate, strengthen its interpretation as a Caledonian structure (also consistent with dated and similarly oriented faults from the RTW). We suggest that the SFZ formed as an antithetic back thrust within the Caledonian imbricate stack, possibly exploiting the limbs of a preexisting large-scale antiform. During Caledonian shortening this Paleoproterozoic megafold was tightened, leading to a progressive steepening of the fold limbs and of the SFZ, while NFZ was progressively folded around the fold hinge.

• Kjøll, Hans Jørgen & Viola, Giulio (2015). Structural Evolution of the Porsa Imbricate Stack (Finnmark, northern Norway) - Based on field mapping and microstructural analysis. NTNU.

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