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  • 1.
    Bender, H.
    et al.
    Department of Geological Sciences, Stockholm University, Stockholm, Sweden.
    Ring, U.
    Department of Earth Sciences, Geophysics, Uppsala University, Uppsala, Sweden.
    Almqvist, B.S.G.
    Department of Earth Sciences, Geophysics, Uppsala University, Uppsala, Sweden.
    Grasemann, B.
    Department of Geodynamics and Sedimentology, University of Vienna, Vienna, Austria.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Metamorphic Zonation by Out‐of‐Sequence Thrusting at Back‐Stepping Subduction Zones: Sequential Accretion of the Caledonian Internides, Central Sweden2018Inngår i: Tectonics, ISSN 0278-7407, E-ISSN 1944-9194, Vol. 37, nr 10, s. 3545-3576Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Exhumation of the high‐grade metamorphic Seve Nappe Complex and its emplacement between lower‐grade nappes has been related to wedge extrusion in the central Scandinavian Caledonides. To test this hypothesis, the kinematic evolution of the Caledonian nappe pile is studied by systematic structural mapping in central and northern Jämtland, Sweden. Structural data, combined with petrological and quartz microstructure observations, document pervasive top‐to‐the‐ESE, foreland‐directed shearing under progressively decreasing metamorphic grade across the entire nappe pile. Mylonitic foliation, foliation‐parallel boudinage, and abundant top‐to‐the‐ESE and rare, scattered top‐to‐the‐WNW shear‐sense indicators imply foreland‐directed general shear. This deformation regime caused exhumation by concurrent thrusting and vertical ductile thinning. We propose a specific succession of in‐ and out‐of‐sequence thrusts that generated the metamorphic zonation. Our model envisions in‐sequence propagation of thrusts during exhumation of the Seve Nappe Complex, related to subduction of Baltica beneath a volcanic arc within Iapetus. Concurrently, Iapetus subducted beneath Laurentia farther to the west. When Iapetus was closed, Baltica subduction stepped westward and continued beneath Laurentia. The back stepping of subduction at the onset of continental collision caused out‐of‐sequence propagation of the orogenic wedge. Thrusting cut downsection across the existing tectonostratigraphy, emplacing units of lower metamorphic grade above the high‐grade Seve Nappe Complex. This imbrication generated the present metamorphic zonation of the Caledonian nappe pile during sustained convergence between Laurentia and Baltica.

  • 2.
    Bergström, Ulf
    et al.
    Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Wahlgren, Carl-Henric
    Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden.
    Polyphase (1.6–1.5 and 1.1–1.0 Ga) deformation and metamorphism of Proterozoic (1.7–1.1 Ga) continental crust, Idefjorden terrane, Sveconorwegian orogen2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 397-434Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    Crust generated during an accretionary orogeny at 1.66–1.52 Ga (Gothian), and later during crustal extension at c. 1.51–1.49, c. 1.46, c. 1.34–1.30 Ga and after c. 1.33 Ga, dominate the Idefjorden terrane. Metamorphism under greenschist to, locally, high-pressure granulite facies, emplacement of syn-orogenic pegmatite and granite, and polyphase deformation followed at 1.05–1.02 Ga (Agder tectonothermal phase, Sveconorwegian orogeny). Sinistral transpressive deformation, including foreland-directed thrusting, preceded top-to-the-west movement and large-scale open folding along north–south axial trends during the younger orogeny. Crustal extension with emplacement of dolerite and lamprophyre dykes, norite–anorthosite, and a batholithic granite took place at c. 0.95–0.92 Ga (Dalane phase, Sveconorwegian orogeny). Ductile shear zones divide the Idefjorden terrane into segments distinguished by the character of the Gothian crustal component. Orthogneisses with c. 1.66 and c. 1.63–1.59 Ga protoliths occur in the Median segment; c. 1.59–1.52 Ga gneissic intrusive rocks and 1.6 Ga paragneisses with relicts of Gothian deformation and migmatization at c. 1.59 Ga and at c. 1.56–1.55 Ga occur in the Western segment. Mineral resources include stratabound Cu–Fe sulphides hosted by sandstone deposited after c. 1.33 Ga, and polymetallic quartz vein mineralization locally containing Au.

  • 3.
    Brojerdi, Fatemeh Sharifi
    et al.
    Department of Earth Sciences, Uppsala University.
    Juhlin, Christopher
    Department of Earth Sciences, Uppsala University.
    Stephens, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Malehmir, Alireza
    Department of Earth Sciences, Uppsala University.
    Reflection seismic imaging of the deeper structures at the Forsmark spent nuclear fuel repository site, central Sweden2013Inngår i: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 89, s. 21-34Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Forsmark area belongs to the Paleoproterozoic Svecokarelian orogen (c. 1.9-1.8 Ga), the principal geological entity inside the Fennoscandian Shield, and is the site where Sweden has proposed to store its spent nuclear fuel. Three major sub-vertical (at the surface), composite ductile and brittle deformation zones that strike in a WNW or NW direction are present in the area. In between these zones the bedrock is less deformed and considered suitable for a repository. We present reprocessed reflection seismic data from seven profiles in which we have focused on improving the images in the depth range 1–5 km by passing lower frequencies through the processing flow at the cost of poorer resolution in the near-surface realm. The new images indicate that sub-horizontal to moderately dipping structures are possibly more extensive at depth than previously thought. Three main deeper reflective zones have been identified, one that is sub-horizontal and two that dip moderately to the southwest. The sub-horizontal reflective zone may represent a 1.27-1.26 Ga dolerite sill at about 3 km depth. One of the moderately dipping reflective zones may originate either from another dolerite sill or from a brittle fault system. The other moderately dipping structure may be present throughout most of the area and could cut all three sub-vertical deformation zones at depth. The new images and corresponding interpretation do not require a re-evaluation of the Forsmark site for storage of spent fuel, but they do influence how to interpret the deeper structures and, as a consequence, the tectonic evolution of the area.

  • 4.
    Gee, David G.
    et al.
    Department of Earth Sciences, Uppsala University, Villavägen 16, Uppsala, Sweden.
    Klonowska, Iwona
    Department of Earth Sciences, Uppsala University, Villavägen 16, Uppsala, Sweden.
    Andréasson, Per-Gunnar
    Department of Geology, Lund University, Sölvegatan 12, Lund, Sweden.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Middle thrust sheets in the Caledonide orogen, Sweden: the outer margin of Baltica, the continent–ocean transition zone and late Cambrian–Ordovician subduction–accretion2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 517-548Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    Nappes of continental outer and outermost margin affinities (Middle Allochthon) were transported from locations west of the present Norwegian coast and thrust eastwards onto the Baltoscandian foreland basin and platform. They are of higher metamorphic grade than underlying thrust sheets and most are more penetratively deformed. These allochthons are treated here in three groups. The lower thrust sheets comprise Paleoproterozoic crystalline basement (e.g. Tännäs Augen Gneiss Nappe) and greenschist facies, Neoproterozoic, siliciclastic metasedimentary rocks (e.g. Offerdal Nappe). These are overthrust by a Cryogenian−Ediacaran succession intruded by c. 600 Ma dolerites (Baltoscandian Dyke Swarm) with an affinity to mid-ocean ridge basalt containing normal to enriched incompatible element contents (Särv Nappes). The upper sheets are dominated by higher-grade allochthons (Seve Nappe Complex) with similar, mainly siliciclastic sedimentary protoliths, more mafic magmatism and some solitary ultramafic bodies. Within this early Ediacaran continent−ocean transition zone (COT) assemblage, generally metamorphosed in amphibolite facies, some nappes experienced migmatization, and eclogites are present. Evidence of ultrahigh-pressure metamorphism has been obtained from garnet peridotites and eclogites; recently, microdiamonds have been discovered in paragneisses. Subduction of the COT started by the late Cambrian and accretion continued through the Ordovician, prior to the Baltica–Laurentia collision. Thrusting of all these Middle allochthons onto the foreland basin exceeds a distance of 400 km.

  • 5.
    Gee, David G.
    et al.
    Department of Earth Sciences, Uppsala University, Villavägen 16, SE-752 36 Uppsala, Sweden.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Lower thrust sheets in the Caledonide orogen, Sweden: Cryogenian–Silurian sedimentary successions and underlying, imbricated, crystalline basement2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 495-515Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    The Jämtlandian Nappes and their equivalents further north, belonging to the lower thrust sheets in the Caledonide orogen of Sweden, comprise a mega-duplex of Cryogenian–Silurian sedimentary rocks sandwiched between structurally higher allochthons and a basal décollement. Further west towards the hinterland, crystalline basement is increasingly involved in this thrusting, imbricate stacking occurring beneath the décollement in antiformal windows. The sedimentary successions were derived from the Cryogenian rifted margin of Baltica, the Ediacaran–Cambrian drifted margin, and Ordovician and Silurian foreland basins. During the Early–Late Ordovician (Floian–Sandbian), hinterland-derived turbidites were deposited in response to early Caledonian accretion of subducted complexes belonging to the outermost margin of Baltica, now preserved in the higher allochthons. Following a quiescent period during the Late Ordovician (Hirnantian) and early part of the Llandovery, collision of Laurentia and Baltica reactivated the foreland basins, with flysch and molasse deposition during the Llandovery–Wenlock. Collisional shortening during this Scandian orogenic episode continued into the Devonian. High- and ultrahigh-pressure (HP/UHP) metamorphism accompanied Baltica's underthrusting of Laurentia in the deep hinterland, and prominent basement-cored antiforms developed towards the foreland during the advance of the orogenic wedge over the foreland basin onto the Baltoscandian platform.

  • 6.
    Gee, David G.
    et al.
    Department of Earth Sciences, Uppsala University, Villavägen 16, SE-752 36 Uppsala, Sweden.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Regional context and tectonostratigraphic framework of the early–middle Paleozoic Caledonide orogen, northwestern Sweden2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 481-494Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    The Scandian mountains in northwestern Sweden are dominated by the eastern part of the Scandinavian Caledonides, an orogen that terminated during the middle Paleozoic with Himalayan-style collision of the ancient continents of Baltica and Laurentia. In this foreland region, far-transported higher allochthons from an exotic continental margin (Rödingsfjället Nappe Complex) and underlying mostly oceanic-arc basin character (Köli Nappe Complex) were emplaced at least 700 km onto the Baltoscandian margin of Baltica. The thrust sheets below the Iapetus Ocean terranes were derived from the transition zone to Baltica (Seve Nappe Complex), comprising mainly siliciclastic metasedimentary rocks, hosting abundant metamorphosed c. 600 Ma mafic intrusions. They preserve evidence of subduction (eclogites, garnet peridotites and microdiamonds in host paragneisses), starting in the late Cambrian; exhumation continued through the Ordovician. Underlying allochthons derived from the outer margin of Baltica are less-metamorphosed Neoproterozoic sandstone-dominated successions, also intruded by Ediacaran dolerite dykes (Särv Nappes); they are located tectonically above similar-aged metasandstone and basement slices, devoid of dykes (Offerdal and Tännäs Augen Gneiss nappes and equivalents). Lowermost allochthons (Jämtlandian Nappes and equivalents), from the inner Baltoscandian margin, provide evidence of Cryogenian rifting, Ediacaran–Cambrian drifting and platformal sedimentation, followed by foreland basin development in the Ordovician and Silurian.

  • 7.
    Johansson, Åke
    et al.
    Swedish Museum of Natural History, Department of Geosciences.
    Stephens, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Timing of magmatism and migmatization in the 2.0–1.8 Ga accretionary Svecokarelian orogen, south-central Sweden2017Inngår i: International journal of earth sciences, ISSN 1437-3254, E-ISSN 1437-3262, Vol. 106, nr 3, s. 783-810Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Palaeoproterozoic (2.0–1.8 Ga) Svecokarelian orogen in central Sweden consists of a low-pressure, predominantly medium-grade metamorphic domain (central part of Bergslagen lithotectonic unit), enclosed to the north and south by low-pressure migmatite belts. Two periods of metamorphism (1.87–1.85 and 1.83–1.79 Ga) are known in the migmatite belts. In this study, new U–Th–Pb ion microprobe data on zircon and monazite from twelve samples of locally migmatized gneisses and felsic intrusive bodies determine both protolith and metamorphic ages in four sample areas north of Stockholm, inside or immediately adjacent to the medium-grade metamorphic domain. Two orthogneiss samples from the Rimbo area yield unusually old protolith ages of 1909 ± 4 and 1908 ± 4 Ma, while three orthogneisses from the Skutskär and Forsmark areas yield more typical protolith ages between 1901 ± 3 and 1888 ± 3 Ma. Migmatized paragneiss samples from this and two earlier studies contain a significant detrital component sourced from this 1.9 Ga magmatic suite. They are interpreted to be deposited contemporaneously with or shortly after this magmatism. Migmatization of the paragneiss at Rimbo was followed by intrusion of leucogranite at 1846 ± 3 Ma. Even in the other sample areas to the north (Hedesunda-Tierp, Skutskär and Forsmark), metamorphism including migmatization is constrained to the 1.87–1.85 Ga interval and penetrative ductile deformation is limited by earlier studies in the Forsmark area to 1.87–1.86 Ga. However, apart from a metamorphic monazite age of 1863 ± 1 Ma, precise ages were not possible to obtain due to the presence of only partially reset recrystallized domains in zircon, or highly discordant U-rich metamict and altered metamorphic rims. Migmatization was contemporaneous with magmatic activity at 1.87–1.84 Ga in the Bergslagen lithotectonic unit involving a mantle-derived component, and there is a spatial connection between migmatization and this magmatic phase in the Hedesunda-Tierp sample area. The close spatial and temporal interplay between ductile deformation, magmatism and migmatization, the P–T metamorphic conditions, and the continuation of similar magmatic activity around and after 1.8 Ga support solely accretionary rather than combined accretionary and collisional orogenic processes as an explanation for the metamorphism. The generally lower metamorphic grade and restricted influence of the younger metamorphic episode, at least at the ground surface level, distinguishes the central part of the Bergslagen lithotectonic unit from the migmatite belts further north and south.

  • 8.
    Kampmann, Tobias Christoph
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Jansson, Nils F.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Olin, Paul H.
    CODES ARC Centre of Excellence and TMVC ARC Research Hub, University of Tasmania.
    Gilbert, Sarah
    CODES ARC Centre of Excellence and TMVC ARC Research Hub, University of Tasmania.
    Wanhainen, Christina
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Syn-tectonic sulphide remobilization and trace element redistribution at the Falun pyritic Zn-Pb-Cu-(Au-Ag) sulphide deposit, Bergslagen, Sweden2018Inngår i: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 96, s. 48-71Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mineralization types at the Palaeoproterozoic Falun base metal sulphide deposit are predominantly pyritic Zn-Pb-Cu-rich massive sulphide mineralization, disseminated to semi-massive Cu-Au mineralization, auriferous quartz veins, and mineralized shear zones of talc-chlorite-dominated schist. The massive and disseminated to semi-massive sulphide mineralization types were subject to polyphase ductile deformation (D1 and D2) and metamorphism under low-P, lower-amphibolite facies conditions, which led to the development of ore textures and paragenetic relationships indicating both mechanical and chemical remobilization of sulphides. In the massive sulphide mineralization, rare inclusion-rich pyrite occurs as relic cores inside inclusion-poor metamorphosed pyrite. Imaging and spot analysis using multielement laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) reveal that inclusion-poor pyrite was depleted in trace elements, which were originally present as non-stoichiometric lattice substitutions or in mineral inclusions. The inclusion-rich pyrite was shielded from depletion and, at least partly, retained its initially higher trace element concentrations, including Au.

    Gold is also associated with chalcopyrite in the disseminated to semi-massive Cu-Au mineralization and in the system of auriferous quartz veins hosted therein, the latter being also affected by the D2 ductile strain. It is inferred that emplacement of the vein system took place after the peak of metamorphism, which occurred between D1 and D2, but prior to and possibly even shortly after completion of the D2 deformational event. Similarities in trace element signatures in chalcopyrite are compatible with the interpretation that the quartz veins formed by local chemical remobilization of components from the Cu-Au mineralization. Transport of liberated Au from pyrite during grain growth in the massive sulphide mineralization may have upgraded the Au endowment in the quartz veins, leading to the additional formation of native gold in the veins. A strong correspondence between elements liberated from pyrite (e.g. Pb, Bi, Se and Au) and those forming discrete and characteristic mineral phases in the quartz veins (Pb-Bi sulphosalts, native gold) supports this hypothesis.

    Trace element signatures for the main sulphide minerals pyrite, chalcopyrite, sphalerite and galena are similar to previously published data from other metamorphosed massive sulphide deposits. The association of the Falun mineralization with elevated Bi is reflected by its occurrence in sulphide minerals (e.g. galena) and in abundant mineral inclusions of Pb-Bi sulphosalts (e.g. weibullite), especially in the disseminated to semi-massive Cu-Au mineralization. Elevated Sn concentrations in the lattice and/or as cassiterite inclusions in chalcopyrite, sphalerite and galena are compatible with a hot, acidic and reducing fluid during formation of the syn-volcanic, base metal sulphide mineralization and associated host-rock alteration.

  • 9.
    Kampmann, Tobias Christoph
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Jansson, Nils
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Stephens, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Majka, Jarosław
    Uppsala universitet, AGH University of Science and Technology, Mickiewicza.
    Lasskogen, Jonas
    Boliden Mineral AB.
    Systematics of Hydrothermal Alteration at the Falun Base Metal Sulfide Deposit and Implications for Ore Genesis and Exploration, Bergslagen ore district, Fennoscandian Shield, Sweden2017Inngår i: Economic geology and the bulletin of the Society of Economic Geologists, ISSN 0361-0128, E-ISSN 1554-0774, Vol. 112, nr 5, s. 1111-1152Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Paleoproterozoic Falun Zn-Pb-Cu-(Au-Ag) pyritic sulfide deposit in the Bergslagen ore district, Sweden, is enveloped by hydrothermally altered rocks metamorphosed to the lower amphibolite facies. Immobile-element ratios suggest that the alteration precursors were volcanic rocks of mainly rhyolitic to dacitic composition. Least altered examples of these rocks plot along magmatic fractionation trends outlined by late- to post-ore feldspar-phyric metadacite dikes and post-ore granitoid plutons, consistent with a comagmatic relationship between these calc-alkaline, coeval (<10-m.y.) suites. Dolomite or calcite marble, as well as diopside-hedenbergite or tremolite skarn, form subordinate but important lithologic components in the hydrothermally altered zone. Marble occurs as fragments in the massive pyritic sulfide mineralization, suggesting that at least some mineralization formed by carbonate replacement.

    Mass-change calculations suggest that the hydrothermally altered volcanic rocks gained Mg and Fe and generally lost Ca, K, and Na. Proximal, quartz-anthophyllite-rich altered rocks additionally gained Si, whereas several types of biotite-rich altered rocks lost this element. These mass changes along with mineral chemical data for anthophyllite, biotite, cordierite, and garnet, and the common occurrence of quartz indicate that chloritization, sericitization, and silicification were the dominant premetamorphic alteration styles. A zonation from distal sericitized and silicified volcanic rocks to intermediate sericitized rocks, partly overprinted by chloritization (Mg-rich chlorite), and proximal siliceous and intensely chloritized (Fe-rich chlorite) rocks has been identified. Furthermore, mass changes in more peripheral parts of the altered zone toward the southeast of the deposit suggest that the alteration weakens gradationally toward the volcanic and subvolcanic rocks surrounding the deposit. These patterns represent vectors toward mineralization.

    Intensely chloritized rocks, largely represented by a single, rhyolitic precursor, envelop the central pyritic massive sulfide bodies to the east, south, and west, supporting a structural model in which the massive sulfide mineralization formed the stratigraphically highest preserved unit in the center, surrounded in a tubular manner by stratigraphic footwall rocks. The northern side represents a portion of the footwall, which was separated by a major shear zone. These spatial relationships also have implications for near-mine exploration, since quartz-rich footwall rocks locally host disseminated to semimassive stockwork Cu-Au mineralization.

    Cooling of a hot (300°–400°C), acidic (pH ≤4) and reducing fluid carrying metals and sulfur is suggested for formation of stockwork Cu-Au vein mineralization and hydrothermal alteration in the stratigraphic footwall. The Zn-Pb-Cu-rich massive sulfide mineralization is inferred to have formed by fluid neutralization upon interaction with carbonates and mixing with cooler seawater upon fluid entry into porous pumice breccia in a subseafloor setting. Dissolution processes, primary porosity in the pumice breccia, and secondary porosity produced during synvolcanic faulting are all suggested to have contributed to the creation of space necessary for the formation of the massive sulfide mineralization. Falun differs from other deposits of the same type in Bergslagen mainly in the high pyrite content of the massive sulfide mineralization, the absence of related Fe oxide deposits, as well as the dominant replacement of volcaniclastic sediments compared to carbonates. The types of host rocks, the inferred premetamorphic feldspar-destructive alteration types, and the style of mineralization and alteration zonation at the deposit are reminiscent of pyritic volcanogenic massive sulfide (VMS) deposits. However, the importance of chemical trapping by fluid-limestone interaction, as well as the spatial association with subordinate skarn alteration constitute important differences to a classic VMS model.

  • 10.
    Kampmann, Tobias Christoph
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Stephens, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Structural geology and spatial patterns of hydrothermal alteration at the Falun pyritic Zn-Pb-Cu-(Au-Ag) sulphide deposit, Bergslagen region, south-central Sweden2014Konferansepaper (Fagfellevurdert)
  • 11.
    Kampmann, Tobias Christoph
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Stephens, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    3D modelling and sheath folding at the Falun Zn-Pb-Cu-(Au-Ag) massive sulphide deposit and implications for exploration in a 1.9 Ga ore district, Fennoscandian Shield, Sweden2016Inngår i: Mineralium Deposita, ISSN 0026-4598, E-ISSN 1432-1866, Vol. 51, nr 5, s. 665-680Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Falun pyritic Zn-Pb-Cu-(Au-Ag) deposit, situated in the Palaeoproterozoic (1.9–1.8 Ga) Bergslagen lithotectonic unit in the south-western part of the Fennoscandian Shield, is one of the major base metal sulphide deposits in Sweden. Altered rocks and ore types at Falun have been metamorphosed and deformed in a heterogeneous ductile manner, strongly modifying mineral assemblages in the original hydrothermal alteration system and the geometry of the deposit. Using a combined methodological approach, including surface mapping of lithologies and structures, drill core logging and microstructural investigation, the polyphase character (D1 and D2) of the ductile deformation is demonstrated and a 3D model for the deposit created. F2 sheath folding along axes that plunge steeply to the south-south-east, parallel to a mineral stretching lineation and the dip direction of the S2 foliation, is suggested as a key deformation mechanism forming steeply plunging, rod-shaped ore bodies. This is in contrast to previous structural models involving fold interference and, in turn, has implications for near-mine exploration, the occurrence of hanging-wall components to the ore body being questioned. Typical rock-forming minerals in the Falun alteration aureole include quartz, biotite/phlogopite, cordierite, anthophyllite and minor almandine, andalusite and chlorite, as well as dolomite, tremolite and actinolite. Where observable, the silicate minerals in the alteration rocks show growth patterns during different phases of the tectonothermal evolution, considerable static grain growth occurring between D1 and D2 and even after D2. A major high-strain zone, characterized by the mineral assemblage talc-chlorite-(quartz-biotite/phlogopite) defines a boundary between northern and southern structural domains at the deposit, and is closely spatially associated with the polymetallic massive sulphide ores. A possible role as a metal-bearing fluid conduit during ore genesis is discussed.

  • 12.
    Kampmann, Tobias Christoph
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Stephens, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Hydrothermal alteration, 3D modeling and sheath folding at the volcanic-hosted Falun Zn-Pb-Cu-(Au-Ag) deposit – implications for exploration in a 1.9 Ga ore district, Fennoscandian Shield, central Sweden2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The Paleoproterozoic (1.9 Ga), volcanic-hosted Zn-Pb-Cu-(Au-Ag) sulfide deposit at Falun is located in the Bergslagen lithotectonic unit, central Sweden, which includes one of the major ore districts in the Fennoscandian Shield, northern Europe. The Falun deposit is known mainly as one of the world’s leading copper suppliers over many centuries. During the 20th century, the mine was a major base (Zn, Pb, Cu) and precious (Ag, Au) metal producer until it closed during 1992.This study has the following four aims: (i) Identify the style and spatial distribution of hydrothermal alteration; (ii) determine the geometry of the different types of ore bodies; (iii) provide a mechanism for the structure of the deposit; and (iv) address broader implications for the Bergslagen ore district. Petrographic and structural data were collected during surface mapping and microscope work; modeling of the different ore bodies in 3D space was completed using available mine level maps and data collected during new logging of available drill cores. The Falun deposit is affected by polyphase ductile deformation and metamorphism under amphibolite facies conditions. The metamorphosed alteration rocks are dominated by distal quartz-mica-cordierite-(anthophyllite) and proximal quartz-anthophyllite assemblages, interpreted to represent Si-, Fe-, Mg-metasomatism of felsic volcanic rocks. Dolomite and calc-silicate (tremolite, actinolite, diopside)-skarn assemblages are interpreted as the equivalent alteration of carbonate rocks. Surface mapping in the open pit indicates that the ore bodies are completely enveloped by these altered rocks. Structural data suggest the presence of a reclined F2 fold that plunges steeply to the southeast, with a stretching component defined by a linear grain-shape fabric sub-parallel to the fold axis. Modeling in 3D space reveals the presence of several rod-shaped ore bodies that also plunge steeply to the southeast and thicken and merge upwards into a single ore body that is up to 270 m in diameter at the ground surface. The ore body close to this surface is zoned in a concentric pattern, from a massive, pyritic Zn-Pb-Cu-sulfide core in the inner part to a more Cu-rich sulfide zone and then a semi-massive to disseminated Cu-Au mineralization in the outer part. The cone-shaped and zoned ore bodies are interpreted as steeply-plunging megascopic sheath folds, formed in a ductile, high-strain tectonic regime. The viscosity contrast between competent, strongly silicified and metamorphosed felsic volcanic host rock and softer massive sulfide ore is suggested to have enhanced the development of these sheath folds. Steeply plunging, rod-shape geometries have commonly been reported for several volcanic-hosted sulfide and Fe oxide ore deposits in the Bergslagen lithotectonic unit and megascopic sheath folds have been identified in a high-strain belt in the northern part of this unit. If sheath fold formation can be confirmed as a key deformation mechanism for ore bodies in this mineral district, in contrast to the classical model of dome and basin fold interference structure, this will influence near-mine exploration strategies. Previous structural concepts and models for footwall/hanging wall relationships will need radical revision and areas previously considered as barren hanging wall lithologies may have a higher exploration potential.

  • 13.
    Kampmann, Tobias Christoph
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Structural investigation and 3D modelling of the Falun pyritic Zn-Pb-Cu-(Au-Ag) sulphide deposit, Bergslagen region, south-central Sweden2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    One of the prominent ore deposits of the Bergslagen region in south-central Sweden is located in Falun in the northern part of this mining district. A belt of 1.91-1.89 Ga metavolcanic rocks hosts both the ores and an alteration aureole of several hundreds to thousands of metres in extent at the ground surface. Analysis of the structures in the area reveals a polyphase ductile deformational history and a major, steeply plunging F2 reclined fold. 3D modelling of the boundary surface to the pyritic Zn-Pb-Cu sulphide ore has been used to visualize the geometry of this ore body at depth, constraining its steeply plunging rod-like and NW-SE elongate shape and a geometric control by the F2 fold structure.

  • 14.
    Kampmann, Tobias
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Jansson, Nils
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Stephens, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Majka, Jarosław
    Uppsala universitet.
    Systematics of hydrothermal alteration at the volcanic-hosted Falun Zn-Pb-Cu-(Au-Ag) deposit: implications for ore genesis, structure and exploration in a 1.9 Ga ore district, Fennoscandian Shield, Sweden2016Inngår i: Geophysical Research Abstracts, ISSN 1029-7006, E-ISSN 1607-7962, Vol. 18Artikkel i tidsskrift (Fagfellevurdert)
  • 15.
    Kampmann, Tobias
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Stephens, Michael
    Sveriges Geologiska Undersökning.
    Ripa, Magnus
    Sveriges Geologiska Undersökning.
    Hellström, Fredrik
    Sveriges Geologiska Undersökning.
    Timing of magmatism and mineralisation at Falun, a major base metal sulphide deposit in the Fennoscandian Shield, Sweden2015Konferansepaper (Fagfellevurdert)
  • 16.
    Kampmann, Tobias
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Stephens, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik. Sveriges Geologiska Undersökning.
    Ripa, Magnus
    Sveriges Geologiska Undersökning.
    Hellström, Fredrik
    Sveriges Geologiska Undersökning.
    Majka, Jarosław
    Uppsala universitet.
    Time constraints on magmatism, mineralisation and metamorphism at the Falun base metal sulphide deposit, Sweden, using U-Pb geochronology on zircon and monazite2016Inngår i: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 278, s. 52-68Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    U–Th–Pb (zircon and monazite) ion probe data have provided constraints on the timing of emplacement and metamorphism of magmatic rocks close to the Palaeoproterozoic, Falun base metal sulphide deposit in the Bergslagen lithotectonic unit, Fennoscandian Shield, Sweden, and, thereby the timing of mineralisation. Hydrothermal alteration and mineralisation at Falun are constrained to a short interval of several million years between a 207Pb/206Pb weighted average age of 1894 ± 3 Ma for a rhyolitic sub-volcanic rock in the felsic volcanic to sub-volcanic host rock suite, and a 207Pb/206Pb weighted average age of 1891 ± 3 Ma for a post-sulphide, porphyritic dacite dyke. Magmatism also included the emplacement of granite plutons with igneous crystallization ages of 1894 ± 3, 1894 ± 2 Ma and 1893 ± 3 Ma. The felsicsub-volcanic to volcanic activity and the emplacement of dacite dykes and granite plutons overlap in age within their respective analytical uncertainties, indicating hydrothermal alteration and sulphide mineralisation inside a narrow time span of intense magmatic activity, and burial of the supracrustal rocks.Two distinct patchy and homogeneous metamorphic monazite types in a felsic volcanic rock around and hydrothermally altered rocks at the Falun deposit yield 207Pb/206Pb weighted average ages of 1831 ± 8 Ma and 1822 ± 5 Ma, respectively. These ages fall well within the temporal range of a younger1.84–1.81 Ga (M2) metamorphic episode during the 2.0–1.8 Ga Svecokarelian orogeny, with the older episode (M1) inside the Bergslagen lithotectonic unit at around 1.86 Ga. This shows the major influence of the M2 event in the north-western part of this unit, leading to a complete resetting of the U–Th–Pb isotopesystem in monazite.

  • 17.
    Möller, Charlotte
    et al.
    Department of Geology, University of Lund.
    Bingen, Bernard
    Geological Survey of Norway, Trondheim.
    Andersson, Jenny
    Geological Survey of Sweden.
    Stephens, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Viola, Giulio
    Geological Survey of Norway, Trondheim.
    Scherstén, Anders
    Department of Geology, University of Lund.
    A non-collisional, accretionary Sveconorwegian orogen: comment2013Inngår i: Terra Nova, ISSN 0954-4879, E-ISSN 1365-3121, Vol. 25, nr 2, s. 165-168Artikkel i tidsskrift (Fagfellevurdert)
  • 18.
    Petersson, Jesper
    et al.
    Vattenfall Research & Development.
    Stephens, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Mattsson, Håkan
    Geovista AB.
    Möller, Charlotte
    University of Lund.
    Albitization and quartz dissolution in Paleoproterozoic metagranite, central Sweden: implications for the disposal of spent nuclear fuel in a deep geological repository2012Inngår i: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 148, s. 10-26Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydrothermal alteration resulting in albitization and quartz dissolution has been identified in Paleoproterozoic metagranites down to − 1000 m elevation at Forsmark, Sweden. The alteration features were discovered during investigations to locate a site for the disposal of spent nuclear fuel in a deep geological repository. In general, albitization occurs extensively, but it is also observed locally adjacent to minor intrusive bodies of amphibolite. The altered rocks show a marked decrease in K-feldspar and an increase in quartz relative to the unaltered equivalents, resulting in an epitonalitic composition. Plagioclase is metamorphic in character and generally richer in albite than in the unaltered rocks. It is inferred that albitization was triggered by the input of basic or intermediate melts into the crust during igneous activity close to the peak of regional metamorphism at 1.87–1.86 Ga. The mineralogy of the epitonalites gives rise to an increased thermal conductivity and, thereby, a positive influence for the design and safety of a deep geological repository for spent nuclear fuel. However, the increased frequency of low conductive amphibolite in the albitized volumes, consistent with the proposed mechanism for alteration, gives a negative influence. In sharp contrast to the albitization, a majority of the occurrences of quartz dissolution, which resulted in the formation of episyenite, are located along fracture zones. Quartz dissolution took place between or after 1.8–1.7 Ga, when the bedrock was able to respond to deformation in a brittle manner. Most of the vugs left after the removal of quartz are, to a variable extent, refilled by hydrothermal assemblages, including quartz, albite, K-feldspar, hematite, chlorite and calcite. The geometry and spatial distribution of episyenite argue against an extreme fluid/rock ratio and it is inferred that the fluids had at least a moderate salinity with a temperature in excess of 300 °C. The dissolution process was promoted by the generation of secondary permeability localized in columnar or pipe-like volumes. The close spatial connection to fracture zones provides a basis to avoid bedrock affected by this type of alteration and, thereby, reduce the negative mechanical and hydrogeological aspects for a deep geological repository.

  • 19.
    Ripa, Magnus
    et al.
    Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Continental magmatic arc and siliciclastic sedimentation in the far-field part of a 1.7 Ga accretionary orogen2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 253-268Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    Trachyandesitic to trachybasaltic lavas, interlayered siliciclastic sedimentary rocks and subaerial ignimbrites with a rhyolitic to trachydacitic composition lie unconformably above metamorphic rocks in west-central Sweden. These volcanic rocks erupted at 1711 + 7/−6 to 1691 ± 5 Ma and belong to a high-K, calc-alkaline to shoshonitic suite deposited in a continental arc setting. Positive ɛNd values and Nb/Yb ratios in the trachyandesitic to trachybasaltic rocks indicate an enriched mantle source. Coeval, 1710 ± 11 to 1681 ± 16 Ma plutonic and subvolcanic rocks are mainly granitic or quartz syenitic in composition. Subordinate components include quartz monzonite, quartz monzodiorite and monzogabbro or gabbro. ɛNd values in the range −1.0 to + 1.1 overlap with those in the inferred 1.9–1.8 Ga source rocks. All these rocks belong to the youngest phase of the lithodemic unit referred to as the Transscandinavian Igneous Belt. This magmatic province extends in a roughly NNW direction for at least 900 km, variably deformed and metamorphosed equivalents occurring inside and beneath younger orogenic belts to the south (Sveconorwegian) and north (Caledonian). The part of the province in west-central Sweden addressed here represents a far-field and shallow crustal component in this 1.7 Ga accretionary orogenic system.

  • 20.
    Ripa, Magnus
    et al.
    Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Dolerites (1.27–1.25 Ga) and alkaline ultrabasic dykes (c. 1.14 Ga) related to intracratonic rifting2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 315-323Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    Doleritic sills, lopoliths and dykes were emplaced into the Paleoproterozoic craton in central Sweden at 1271–1264, 1259–1256 and c. 1247 Ma, a complex temporal zonation occurring in a WSW–ENE direction. The dolerites are subalkaline to alkaline and show predominantly gabbroic, with a trend towards monzogabbroic and quartz monzodioritic, compositions. Positive ɛNd and ɛHf values suggest a significant depleted mantle component in the source volume of the parental magmas. Dyke orientations indicate extension, at least locally, in a northwesterly direction, consistent with a magma flow direction determined using the anisotropy of magnetic susceptibility values. Intracratonic rifting linked to the break-up of the supercontinent Columbia, back-arc extension above a subduction boundary in a westwards-retreating mode or a mantle plume tail above a continental hotspot have all been proposed for the tectonic setting. Renewed intracratonic rifting at c. 1.14 Ga in the coastal area in northeasternmost Sweden resulted in the emplacement of alkaline ultrabasic dykes, including carbonatites (beforsites), silico-carbonatites and lamprophyres, in a north–south direction along an older shear belt. The broader tectonic setting of this extensional event is not known.

  • 21.
    Ripa, Magnus
    et al.
    Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Swede.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Magmatism (1.6–1.4 Ga) and Mesoproterozoic sedimentation related to intracratonic rifting coeval with distal accretionary orogenesis2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 269-288Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    Separate pulses of magmatic activity involving the emplacement of plutons with predominantly granitic or bimodal granitic and gabbroic composition, as well as dolerite dykes, occurred in a cratonic setting in eastern Sweden at c. 1.59–1.58 Ga, c. 1.53–1.50 Ga and c. 1.47–1.44 Ga; anorthosite, monzodiorite and syenitoid rocks are locally present. Most of the granites have been compared with rapakivi granites in Finland and elsewhere. Isotopic data (Hf in zircons and ɛNd values) from the plutons in north-central Sweden show contamination by an Archean source. Siliciclastic rocks dominated by aeolian or deltaic sandstones overlie c. 1.58 Ga or c. 1.50 Ga plutons, are intercalated with 1.46 Ga basaltic lavas and were deposited prior to the emplacement of 1.27–1.25 Ga dolerites. The magmatic rocks are subalkaline (tholeiitic) to alkaline and the mafic components have been compared with continental flood basalts, suggesting an intracratonic, rift-related tectonic setting for the magmatism and sand deposition. These rocks constitute the westerly part of a late Paleoproterozoic to early Mesoproterozoic magmatic province in northern Europe, located along roughly north–south- and WSW–ENE-trending linear belts. This tectonic development was coeval with accretionary orogenic activity further to the west and SW.

  • 22.
    Ripa, Magnus
    et al.
    Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Siliciclastic sedimentation in a foreland basin to the Sveconorwegian orogen and dolerites (0.98–0.95 Ga) related to intracratonic rifting2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 325-333Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    Sub-ophitic, equigranular or plagioclase-phyric dolerite dykes, referred to as the Blekinge–Dalarna dolerite (BDD) swarm, were emplaced during the time span 0.98–0.95 Ga and trend NNE–NNW in an arcuate fashion, parallel to and east of the Sveconorwegian orogen. Dolerite sills are locally present. These rocks are subalkaline to alkaline with a monzogabbroic or gabbroic composition and show a predominantly within-plate tectonic affinity. ɛNd and ɛHf values fall in the range −2 to +4 and +1 to +5, respectively. Siliciclastic sedimentary rocks (Almesåkra Group) in a small outlier in southern Sweden were deposited in an aeolian to fluviatile or lacustrine environment and an arid or semi-arid warm palaeoclimate, coevally with the dolerite sills. Smaller occurrences of sandstone with peperitic field relationships to the BDD dykes are known from other localities. The spatial distribution, orientation and age of the BDD magmatic suite suggest roughly east–west extension in the eastern, cratonic foreland to the Sveconorwegian orogen during the latest phase of this mountain-building event, the age data tentatively suggesting a younging to the east. The siliciclastic sedimentary rocks represent an erosional relict of a larger and spatially much more extensive early Tonian foreland basin to this orogen, as proposed earlier on the basis of fission-track thermochronology.

  • 23.
    Saintilan, Nicholas J.
    et al.
    Section of Earth and Environmental Sciences, University of Geneva.
    Stephens, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Spikings, Richard A.
    Section of Earth and Environmental Sciences, University of Geneva.
    Schneider, Jens C.
    Department of Mineralogy, Technische Universität Bergakademie Freiberg.
    Chiaradia, Massimo
    Section of Earth and Environmental Sciences, University of Geneva.
    Spangenberg, Jorge E.
    Institute of Earth Surface Dynamics, University of Lausanne.
    Ulianov, Alexey
    Institute of Earth Sciences, University of Lausanne.
    Fontboté, Lluis
    Section of Earth and Environmental Sciences, University of Geneva.
    Polyphase vein mineralization in the Fennoscandian Shield at Åkerlandet, Järvsand, and Laisvall along the erosional front of the Caledonian orogen, Sweden2017Inngår i: Mineralium Deposita, ISSN 0026-4598, E-ISSN 1432-1866, Vol. 52, nr 6, s. 823-844Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Åkerlandet, Järvsand, and Laisvall deposits in Sweden are calcite-fluorite-sulfide vein deposits and occurrences located close to the current erosional front of the Caledonian orogen and hosted by crystalline basement rocks in the Fennoscandian Shield. At Laisvall, basement-hosted veinlets occur beneath Ediacaran to Cambrian sandstones that host a strata-bound Pb-Zn deposit. The mineralized fractures at Åkerlandet and Järvsand occur along fault systems oriented N–S to NNW–SSE. Veins or veinlets strike NNW–SSE and NW–SE at Åkerlandet, NNE–SSW at Järvsand, and NNW–SSE and NNE–SSW to NE–SW at Laisvall. At Åkerlandet and Järvsand, fractures acted as conduits for hydrothermal fluids of variable composition and formed during separate tectonic events. At Åkerlandet, the fault zone with NNW–SSE strike shows kinematic indicators consistent with ~NE–SW bulk horizontal extension. At Järvsand, the calcite-fluorite-galena veins formed along R-Riedel shears related to the host N–S to NNW–SSE fault system. The kinematic indicators are consistent with ~NW–SE bulk horizontal extension, similar to the extensional deformation during the later part of the Caledonian orogeny (Silurian to Devonian). At Åkerlandet, adularia-quartz deposition was followed by sphalerite ± galena and finally by precipitation of fluorite and calcite. 40Ar-39Ar thermochronology of a single adularia sample did not yield a well-defined plateau age but the gas released at higher temperatures suggests an early Tonian (980 to 950 Ma) crystallization age, i.e., during the later part of the Sveconorwegian orogeny, although the data do not exclude other less likely interpretations. Previous fluid inclusion microthermometry and geochronological studies and new petrographic and geochemical results suggest that sphalerite ± galena mineralization formed from saline, relatively oxidizing, moderate-temperature, and slightly acidic hydrothermal fluids, either during the Ediacaran or the Middle Ordovician. Metals and H2S were derived from local basement rocks. Based on petrographic evidence, rare earth element composition, and S, C, and O isotope data, fluorite and calcite precipitated under near neutral and relatively reducing conditions. Occurrence of solid bitumen in veins at Åkerlandet and C and O isotope data of calcite at Åkerlandet and in the Laisvall basement veinlets suggest that the precipitation of calcite and fluorite was triggered by interaction of hot and evolved hydrothermal fluids (87Sr/86Sr = 0.718–0.732) with organic matter. Structural, petrographic, and geochemical data at Laisvall suggest that the basement structures hosting calcite-fluorite ± pyrite veinlets were utilized in the Middle Ordovician as the plumbing system for the oxidizing, slightly acidic, metal-bearing brines that caused the economic Pb-Zn mineralization in the overlying sandstones

  • 24.
    Saintilan, Nicolas J. D
    et al.
    University of Geneva, Department of Earth and Environmental Sciences, Section of Earth and Environmental Sciences, University of Geneva.
    Schneider, Jens C.
    Department of Mineralogy, Technische Universität Bergakademie Freiberg.
    Stephens, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Chiaradia, Massimo
    Section of Earth and Environmental Sciences, University of Geneva.
    Kouzmanov, Kalin
    Section of Earth and Environmental Sciences, University of Geneva.
    Wälle, Marküs
    Institute of Geochemistry and Petrology, ETH Zürich.
    Fontboté, Lluís
    Section of Earth and Environmental Sciences, University of Geneva.
    A middle ordovician age for the laisvall sandstone-hosted Pb-Zn deposit, Sweden: A response to early caledonian orogenic activity2015Inngår i: Economic geology and the bulletin of the Society of Economic Geologists, ISSN 0361-0128, E-ISSN 1554-0774, Vol. 110, nr 7, s. 1779-1801Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ten sphalerite separates isolated from mineralized samples in proximal and distal positions relative to the proposed main feeder fault systems at the Laisvall deposit were used to obtain an absolute age determination of this world-class Pb-Zn deposit hosted by autochthonous Ediacaran to Lower Cambrian sandstone and located currently along the erosional front of the Scandinavian Caledonides in northern Sweden. Residue and leachate fractions of each separate were obtained using the crush-leaching technique. All samples correspond to sphalerite formed using reduced sulfur derived from thermochemical sulfate reduction, three of them from disseminated ore in the Lower Sandstone, two from the disseminated ore in the Upper Sandstone, and five from steeply dipping galena-sphalerite-calcite veinlets interpreted in previous works as remobilization of disseminated ores. The isotope dilution-thermal ionization mass spectrometry (ID-TIMS) data yield an overall complex Rb-Sr isotope pattern with two distinct trends in the 87Sr/86Sr vs. 87Rb/86Sr isochron diagram. The three sphalerite residues of disseminated mineralization from the Lower Sandstone orebody show Rb-Sr isotope systematics indicative of undisturbed primary precipitates, and yield an isochron model age of 467 ± 5 Ma (mean square weighted deviation, MSWD, 1.4). Since the isochron is based on three points, the obtained age is to be considered as preliminary. Yet, the obtained age is fully consistent with geologic evidence reported by previous authors and pointing to Middle Ordovician timing of ore formation. The ID-TIMS data were complemented by laser ablation-inductively coupled plasma mass spectrometry (LA-ICPMS) analyses on the same sphalerite samples. The data support the hypothesis that the measured ID-TIMS Rb and Sr contents in these sphalerite residues are held in the sphalerite structure itself and are not related to micro-inclusions. The most viable hypothesis, in agreement with published work, is that during rapid growth, sphalerite may incorporate Rb and Sr ions from the hydrothermal fluids in its structure, most probably in octahedral voids. By contrast, the second trend in the 87Sr/86Sr vs. 87Rb/86Sr space defined by most other sphalerite residues and corresponding inclusion fluid leachates from the Upper Sandstone orebody and the veinlet samples is too steep to account for a realistic isochron age determination. This steep linear trend is interpreted to represent a postmineralization disturbance involving fluids rich in Sr. This disturbance of the Rb-Sr isotope system is consistent with the presence of the steeply dipping galena-sphalerite-calcite veinlets and the fact that the Upper Sandstone is, in places, tectonically disrupted because of its proximity to the basal Caledonian décollement. The attempt to date the Granberget deposit, located in tectonically disrupted allochthonous units inside the Caledonian orogen, failed because the Rb-Sr isotope systematics of the three analyzed sphalerite samples are also disturbed. The obtained Middle Ordovician (467 ± 5 Ma) mineralization age at Laisvall can be interpreted as a far-field foreland response to an early Caledonian arc-continent collision and the subsequent development of a foreland basin. Basinal brines formed in the foredeep of the orogen could be conveyed cratonward, interact with permeable Baltica crystalline basement rocks, and resurge as metal-bearing fluids in sandstone at Laisvall along reactivated Paleoproterozoic crystalline basement faults. Mixing of metal-bearing brines with hydrocarbon and H2S-rich fluids in Ediacaran to Lower Cambrian sandstone may explain the initial Sr isotope signature (87Sr/86Sr = 0.715900 ± 60) of the isochron intersect

  • 25.
    Saintilan, Nicolas J. D
    et al.
    University of Geneva, Department of Earth and Environmental Sciences.
    Spangenberg, Jorge E.
    Institute of Earth Surface Dynamics, University of Lausanne.
    Samankassou, Elias
    University of Geneva, Department of Earth and Environmental Sciences.
    Kouzmanov, Kalin
    Section of Earth and Environmental Sciences, University of Geneva, University of Geneva, Department of Earth and Environmental Sciences.
    Chiaradia, Massimo
    Section of Earth and Environmental Sciences, University of Geneva, University of Geneva, Department of Earth and Environmental Sciences.
    Stephens, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Fontboté, Lluís
    University of Geneva, Department of Earth and Environmental Sciences, Section of Earth and Environmental Sciences, University of Geneva.
    A refined genetic model for the Laisvall and Vassbo Mississippi Valley-type sandstone-hosted deposits, Sweden: constraints from paragenetic studies, organic geochemistry, and S, C, N, and Sr isotope data2016Inngår i: Mineralium Deposita, ISSN 0026-4598, E-ISSN 1432-1866, Vol. 51, nr 5, s. 639-664Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The current study has aimed to refine the previously proposed two-fluid mixing model for the Laisvall (sphalerite Rb-Sr age of 467 ± 5 Ma) and Vassbo Mississippi Valley-type deposits hosted in Ediacaran to Cambrian sandstone, Sweden. Premineralization cements include authigenic monazite, fluorapatite, and anatase in the Upper Sandstone at Laisvall, reflecting anoxic conditions during sandstone burial influenced by the euxinic character of the overlying carbonaceous middle Cambrian to Lower Ordovician Alum Shale Formation (δ 13Corg = −33.0 to −29.5 ‰, δ 15Norg = 1.5 to 3.3 ‰, 0.33 to 3.03 wt% C, 0.02 to 0.08 wt% N). The available porosity for epigenetic mineralization, including that produced by subsequent partial dissolution of pre-Pb-Zn sulfide calcite and barite cements, was much higher in calcite- and barite-cemented sandstone paleoaquifers (29 % by QEMSCAN mapping) than in those mainly cemented by quartz (8 %). A major change in the Laisvall plumbing system is recognized by the transition from barite cementation to Pb-Zn sulfide precipitation in sandstone. Ba-bearing, reduced, and neutral fluids had a long premineralization residence time (highly radiogenic 87S/86Sr ratios of 0.718 to 0.723) in basement structures. As a result of an early Caledonian arc-continent collision and the development of a foreland basin, fluids migrated toward the craton and expelled Ba-bearing fluids from their host structures into overlying sandstone where they deposited barite upon mixing with a sulfate pool (δ 34Sbarite = 14 to 33 ‰). Subsequently, slightly acidic brines initially residing in pre-Ediacaran rift sediments in the foredeep of the early Caledonian foreland basin migrated through the same plumbing system and acquired metals on the way. The bulk of Pb-Zn mineralization formed at temperatures between 120 and 180 °C by mixing of these brines with a pool of H2S (δ 34S = 24 to 29 ‰) produced via thermochemical sulfate reduction (TSR) with oxidation of hydrocarbons in sandstone. Other minor H2S sources are identified. Upward migration and fluctuation of the hydrocarbon-water interface in sandstone below shale aquicludes and the formation of H2S along this interface explain the shape of the orebodies that splay out like smoke from a chimney and the conspicuous alternating layers of galena and sphalerite. Intimate intergrowth of bitumen with sphalerite suggests that subordinate amounts of H2S might have been produced by TSR during Pb-Zn mineralization. Gas chromatograms of the saturated hydrocarbon fraction from organic-rich shale and from both mineralized and barren sandstone samples indicate that hydrocarbons migrated from source rocks in the overlying Alum Shale Formation buried in the foredeep into sandstone, where they accumulated in favorable traps in the forebulge setting.

  • 26.
    Saintilan, Nicolas J. D
    et al.
    University of Geneva, Department of Earth and Environmental Sciences.
    Stephens, Michael
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Lundstam, Erik
    Boliden AB.
    Fontboté, Lluís
    University of Geneva, Department of Earth and Environmental Sciences.
    Control of Reactivated Proterozoic Basement Structures on Sandstone-Hosted Pb-Zn Deposits along the Caledonian Front, Sweden: Evidence from Airborne Magnetic Data, Structural Analysis, and Ore-Grade Modeling2015Inngår i: Economic geology and the bulletin of the Society of Economic Geologists, ISSN 0361-0128, E-ISSN 1554-0774, Vol. 110, nr 1, s. 91-117Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Strata-bound, nonstratiform, epigenetic galena-sphalerite-cement mineralization in Ediacaran-Cambrian sandstone, including the previously mined deposits at Laisvall and Vassbo, occurs along the eastern erosional front of the Caledonian orogen in Sweden. The sandstone is part of an autochthonous siliciclastic sedimentary sequence that rests unconformably on top of Proterozoic crystalline basement beneath the Caledonian thrust nappes. Linear anomalies have been identified in high-resolution airborne magnetic data that correspond to geologic features in the Proterozoic basement. Furthermore, the Laisvall and Vassbo strata-bound Pb-Zn deposits are both spatially associated with areas of change in the trend of the magnetic lineaments. Magnetic anomalies, trending either N-S to NE-SW and WNW-ESE to NW-SE in the Laisvall area, and NNE-SSW to NNW-SSE and NW-SE to W-E in the Vassbo area, were identified. In the Laisvall area, some magnetic minima and edges along magnetic gradients can be correlated with faults in the Proterozoic basement. The reactivation of these basement structures is expressed in the Ediacaran-Cambrian sedimentary cover rocks as newly formed faults with Phanerozoic displacement. Along individual faults belonging to two sets (NE-SW to N-S and WNW-ESE to NW-SE), synsedimentary block movement has been recognized. The highest Pb and Zn grades in Laisvall delineate orebodies and orebody trends that follow these faults. Areas where the faults change strike contain some of the largest and richest orebodies. In the Vassbo area, the orebody footprint reflects a folded dolerite dike in the underlying Proterozoic basement. The dike, modeled on the basis of borehole data, is recognized by a magnetic maximum and an edge along a magnetic gradient. No faults have been mapped at the ground surface as being related to the location of dolerite dikes in the basement. However, it is considered that the basement dikes illustrate a structural control, emplacement either producing a local fracture network or being driven by preexisting basement structures. The main orebodies in both deposits display funnel-shape geometry, fault-rooted in Laisvall and located close to the hinges of the folded dolerite dike in the basement at Vassbo. Metal distribution patterns are similar in both deposits and are characterized by Pb-rich cores proximal to the basement-steered structures while Zn-rich shells are distal from these structures. The funnel-shaped ore geometry is interpreted to reflect a fault-rooted migration path and the metal precipitation mechanism. In both deposits, the highest Pb and Zn grades occur at the top of sandstone paleoaquifers. Similar mineralization footprints, variation in grades, and paleoaquifer settings were recognized in several carbonate-hosted Mississippi Valley-type (MVT) Zn-Pb deposits (e.g., San Vicente deposit, Peru; Topla-Mežica deposits, Slovenia). This geometry is suggestive of a sour gas trap that accumulated by density at the top of paleoaquifers. This gas could have provided H2S by thermogenic sulfate reduction to the metal-bearing fluids and triggered precipitation of Pb-Zn sulfides. The combined evidence from the airborne magnetic data, the structural analysis and the geometry of the orebodies, and metal distribution suggests that the basement faults reactivated during the Ediacaran-Cambrian sedimentation, acted at a later time as feeders for the metal-bearing fluids to fertile horizons for mineralization, and localized deformation during postsedimentary and postmineralization tectonics.

  • 27.
    Saintilan, Nicolas J.
    et al.
    Department of Earth Sciences, University of Geneva, Geneva, Switzerland.
    Spangenberg, Jorge E.
    Institute of Earth Surface Dynamics, University of Lausanne, Lausanne, Switzerland.
    Chiaradia, Massimo
    Department of Earth Sciences, University of Geneva , Geneva, Switzerland.
    Chelle-Michou, Cyril
    Department of Earth Sciences, University of Geneva, Geneva, Switzerland.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik. Formerly Geological Survey of Sweden (SGU), Uppsala, Sweden.
    Fontboté, Lluís
    Department of Earth Sciences, University of Geneva, Geneva, Switzerland.
    Petroleum as source and carrier of metals in epigenetic sediment-hosted mineralization2019Inngår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, artikkel-id 8283Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Sediment-hosted ore deposits contribute a significant amount (up to 65%) of the global resources of lead and zinc. Among them, the Mississippi-Valley type deposits and related oil fields often comprise large-scale hydrothermal systems where regional host rocks are stained with disseminated liquid petroleum (crude oil) and other organic compounds. Current models for the formation of those epigenetic Pb-Zn sulphide deposits consider that metals are mostly leached from basement rocks and their detrital erosional products, and transported by oxidized basinal hydrothermal fluids as chloride complexes. Sulphide precipitation mainly occurs when these basinal brines interact with fluids rich in reduced sulphur species produced mostly by thermochemical sulphate reduction (TSR) mediated by hydrocarbons. Here, using organic geochemistry and Pb isotopes, we provide evidence that petroleum and associated water were key for the formation of sulphide mineralization in the world-class sandstone-hosted ore deposit at Laisvall, not only by supplying reduced sulphur but also by contributing metals in significant amounts. The lead originally found in bitumen of the Alum Shale Formation was transported —during an arc-continent collisional event— by liquid petroleum and associated water to the site of sulphide mineralization. The alteration of petroleum by TSR made lead available for precipitation as sulphide. The petroleum-associated lead represents 40 to 60% of the metal budget in the deposit, the remainder being sourced by leaching of basement rocks.

  • 28.
    Skyttä, Pietari
    et al.
    Department of Geography and Geology, University of Turku.
    Weihed, Pär
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Högdahl, Karin
    Department of Earth Sciences, Uppsala University. Department of Geology and Mineralogy, Åbo Akademi University.
    Bergman, Stefan
    Geological Survey of Sweden.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Paleoproterozoic (2.0–1.8 Ga) syn-orogenic sedimentation, magmatism and mineralization in the Bothnia–Skellefteå lithotectonic unit, Svecokarelian orogen2020Inngår i: Sweden: Lithotectonic framework, tectonic evolution and mineral resources. / [ed] Stephens, M.B. and Bergman Weihed, J,, Geological Society of London, 2020, s. 83-130Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    The Bothnia–Skellefteå lithotectonic unit is dominated by turbiditic wacke and argillite (Bothnian basin), deposited at 1.96 (or older)–1.86 Ga, metamorphosed generally under high-grade conditions and intruded by successive plutonic suites at 1.95–1.93, 1.90–1.88, 1.87–1.85 and 1.81–1.76 Ga. In the northern part, low-grade and low-strain, 1.90–1.86 Ga predominantly magmatic rocks (the Skellefte–Arvidsjaur magmatic province) are enclosed by the basinal components. Subduction-related processes in intra-arc basin and magmatic arc settings, respectively, are inferred. Changes in the metamorphic grade and the relative timing of deformation and structural style across the magmatic province are linked to major shear zones trending roughly north–south and, close to the southern margin, WNW–ESE. Zones trending WNW–ESE and ENE–WSW dominate southwards. Slip along the north–south zones in an extensional setting initiated synchronously with magmatic activity at 1.90–1.88 Ga. Tectonic inversion steered by accretion to a craton to the east, involving crustal shortening, ductile strain and crustal melting, occurred at 1.88–1.85 Ga. Deformation along shear zones under lower-grade conditions continued at c. 1.8 Ga. Felsic volcanic rocks (1.90–1.88 Ga) host exhalative and replacement-type volcanogenic massive sulphide deposits (the metallogenic Skellefte district). Other deposits include orogenic Au, particularly along the ‘gold line’ SW of this district, porphyry Cu–Au–Mo, and magmatic Ni–Cu along the ‘nickel line’ SE of the ‘gold line’.

  • 29.
    Stephens, Michael
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Andersson, Jenny
    Sveriges Geologiska Undersökning, Geological Survey of Sweden.
    Migmatization related to mafic underplating and intra- or back-arc spreading above a subduction boundary in a 2.0−1.8 Ga accretionary orogen, Sweden2015Inngår i: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 264, s. 235-257Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Absolute ages of migmatization and protolith formation, and constraints on the timing of ductile deformation in two major lithotectonic units in the south-western part of a 2.0–1.8 Ga orogenic belt in the Fennoscandian Shield, south-eastern Sweden, have been determined using U-Pb ion probe analysis of different generations of zircon in veined gneisses and leucocratic granite. Detrital and xenocrystic zircon in paragneiss and garnet-bearing leucogranite, respectively, in the Bergslagen lithotectonic unit show ages of 2.1–2.0 Ga and 1.9 Ga. Deposition of the sedimentary material occurred during or after a subduction-related magmatic event at 1.91–1.87 Ga. Two orthogneiss protoliths formed during this magmatic event around 1.88 Ga while most zircon in the leucosome in a third migmatitic orthogneiss was inherited from a 1.85 Ga igneous protolith. A polyphase tectonothermal evolution with anatexis under low-P metamorphic conditions around 1.86 Ga (M1) and 1.84–1.81 Ga (M2) is inferred for the migmatitic gneisses in the Bergslagen unit; garnet-bearing leucogranite crystallized around 1.84–1.83 Ga, close in time to major folding of the M1 gneissic fabric. A previously unrecognised 1.86–1.85 Ga ductile deformational event under medium-grade metamorphic conditions has been identified in the adjacent lithotectonic unit to the south (Småland lithotectonic unit), close in time to the M1 event in the Bergslagen unit to the north.By constraining the timing of anatexis and comparing with information bearing on crustal thickness, excess mass at depth and the character and age of magmatic activity, it is inferred that anatexis in the Bergslagen lithotectonic unit is related to pulses of mafic underplating, during the early stages of two separate, subduction-related magmatic episodes after the 1.91–1.87 Ga magmatic event. It is suggested that each pulse was related to intra- or back-arc spreading above a subduction boundary, which had entered a retreating mode with separate, long periods (20–50 Ma) of extension or transtension. This study challenges the need to invoke crustal thickening related to plate collision at 1.9–1.8 Ga as a mechanism to explain high-grade metamorphism in the southern part of the 2.0–1.8 Ga orogen. Instead, a solely accretionary tectonic model involving an overriding plate along an active continental margin with significant extensional or transtensional crustal deformation is preferred.

  • 30.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Introduction to the lithotectonic framework of Sweden and organization of this Memoir2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 1-15Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    The solid rock geology of Sweden comprises three principal components: (1) Proterozoic and (locally) Archean rocks belonging to the western part of the Fennoscandian Shield; (2) Phanerozoic and (locally) Neoproterozoic sedimentary cover rocks deposited on top of this ancient crust; and (3) the early to mid-Paleozoic (0.5–0.4 Ga) Caledonide orogen. Earlier compilations have applied different principles for the subdivision of the geology in the Fennoscandian Shield and the Caledonide orogen. A uniform lithotectonic framework has been developed here. Crustal segments affected by orogenesis have been identified and their ages determined by the youngest tectonothermal event. Four ancient mountain belts and six orogenies are preserved. Solid rocks outside the orogens have been assigned to different magmatic complexes or sedimentary successions based on their time of formation and tectonic affiliation. This approach allows relicts of older mountain-building activity to be preserved inside a younger orogen – for example, the effects of the Archean (2.8–2.6 Ga) orogeny inside the 2.0–1.8 Ga Svecokarelian orogen and Paleo–Mesoproterozoic (1.7–1.5 and 1.5–1.4 Ga) mountain-building processes inside the 1.1–0.9 Ga Sveconorwegian orogen. Sweden's five largest mineral districts are addressed in the context of this new lithotectonic framework, which forms the architecture to the contents of the chapters in this Memoir.

  • 31.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Outboard-migrating accretionary orogeny at 1.9–1.8 Ga (Svecokarelian) along a margin to the continent Fennoscandia2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 237-250Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    An intimate lithostratigraphic and lithodemic connection between syn-orogenic rock masses inside the different lithotectonic units of the 2.0–1.8 Ga (Svecokarelian) orogen, Sweden, is proposed. A repetitive cyclic tectonic evolution occurred during the time period c. 1.91–1.75 Ga, each cycle lasting about 50–55 million years. Volcanic rocks (c. 1.91–1.88 Ga) belonging to the earliest cycle are host to most of the base metal sulphide and Fe oxide deposits inside the orogen. Preservation of relict trails of continental magmatic arcs and intra-arc basins is inferred, with differences in the depth of basin deposition controlling, for example, contrasting types of base metal sulphide deposits along different trails. The segmented geometry of these continental magmatic arcs and intra-arc basins is related to strike-slip movement along ductile shear zones during transpressive events around and after 1.88 Ga; late orogenic folding also disturbed their orientation on a regional scale. A linear northwesterly orogenic trend is suggested prior to this structural overprint, the strike-slip movement being mainly parallel to the orogen. A solely accretionary orogenic model along an active margin to the continent Fennoscandia, without any trace of a terminal continent–continent collision, is preferred. Alternating retreating and advancing subduction modes that migrated progressively outboard and southwestwards in time account for the tectonic cycles.

  • 32.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Upper and uppermost thrust sheets in the Caledonide orogen, Sweden: outboard oceanic and exotic continental terranes2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 549-575Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    Three separate stacks of thrust sheets (Köli Nappe Complex) constitute the Upper Allochthon in the Caledonide orogen, Sweden. This thrust complex is dominated by late Cambrian–Ordovician successions deposited in subduction-related, marginal oceanic basins. Magmatic activity at c. 488 Ma (Lower Köli) and c. 492–476 Ma (Middle Köli) is linked to rifted volcanic arcs and Zn–Cu–Fe–(Pb–Au–Ag) sulphide mineralization; serpentinite bodies with talc deposits are also conspicuous. Renewed magmatic activity, both plutonic (Upper and Middle Köli) and mafic volcanic (Middle and Lower Köli), occurred at c. 440–434 Ma during crustal extension. Late Ordovician shallow-marine sedimentation, deepening upwards into an early Silurian succession also prevailed (Lower Köli). Silurian (c. 430 Ma and later) folding, eastwards-vergent thrusting and greenschist or lower amphibolite facies metamorphism preceded upright, orogen-parallel and orogen-transverse open folding. Juxtaposition of an arc-related terrane to an ancient continental margin, comprising slices of gneiss and marble, in the Middle Köli occurred prior to c. 437 Ma and the eastwards-vergent thrusting; remnants of an Ordovician amphibolite facies tectonothermal event are also preserved in the Upper Köli. The tectonic roof to the Köli complex contains amphibolite facies mica schist, gneiss and marble, derived from the Laurentian continental margin, and a major gabbroic pluton (Rödingsfjället Nappe Complex, Uppermost Allochthon).

  • 33.
    Stephens, Michael B.
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Bergman, Stefan
    Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden.
    Regional context and lithotectonic framework of the 2.0–1.8 Ga Svecokarelian orogen, eastern Sweden2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 19-26Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    Six separate lithotectonic units, referred to from north to south as the Överkalix, Norrbotten, Bothnia–Skellefteå, Ljusdal, Bergslagen and Småland units, are identified inside the western part of the 2.0–1.8 Ga Svecokarelian orogen, Fennoscandian Shield, Sweden. Apart from the boundary between the Norrbotten and Bothnia–Skellefteå lithotectonic units in northern Sweden, which is defined on the basis of a change in crustal basement from Neoarchean (and possibly older) in the NE (Norrbotten) to juvenile Paleoproterozoic crust further south (Bothnia–Skellefteå), all the boundaries are defined by shear zones or combinations of zones that, in places, form broader shear belts up to several tens of kilometres thick. The identification of lithotectonic units provides a necessary foundation for a more detailed synthesis of the tectonic evolution of the 2.0–1.8 Ga orogeny in northern Europe, emphasizing in particular the allochthoneity between most of these units inside this part of the orogen.

  • 34.
    Stephens, Michael B.
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Wahlgren, Carl-Henric
    Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden.
    Accretionary orogens reworked in an overriding plate setting during protracted continent–continent collision, Sveconorwegian orogen, southwestern Sweden2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 435-448Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    The Eastern Segment in the Sveconorwegian orogen, southwestern Sweden, is dominated by 2.0–1.8, 1.7 and 1.5–1.4 Ga crust; and the overlying Idefjorden terrane by 1.6–1.5 Ga crust. Assuming reorganization of a subduction system prior to 1.5–1.4 Ga and applying a sinistral transpressive component of disruption during the subsequent Sveconorwegian orogeny (1.1–0.9 Ga), the Idefjorden terrane is inferred to be indigenous outboard rather than exotic with respect to the continental plate Fennoscandia (Baltica). The geological record then records successive westwards shift of accretionary orogens along a convergent plate boundary for at least 500 million years. Sveconorwegian foreland-younging tectonic cycles at c. 1.05 (or older)–1.02 Ga (Idefjorden terrane) and at c. 0.99–0.95 Ga (Eastern Segment) prevailed. Crustal thickening and exhumation during oblique convergence preceded migmatization, magmatic activity and a changeover to an extensional regime, possibly triggered by delamination of continental lithosphere, in each cycle. Convergence after 0.95 Ga involved antiformal doming with extensional deformation at higher crustal levels (Eastern Segment) and continued magmatic activity (Idefjorden terrane). An overriding plate setting is inferred during either accretionary orogeny or, more probably, protracted continent–continent collision. Continuity of the erosional fronts in the Grenville and Sveconorwegian orogens is questioned.

  • 35.
    Stephens, Michael B.
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Wahlgren, Carl-Henric
    Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden.
    Polyphase (1.9–1.8, 1.5–1.4 and 1.0–0.9 Ga) deformation and metamorphism of Proterozoic (1.9–1.2 Ga) continental crust, Eastern Segment, Sveconorwegian orogen2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 351-396Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    The Eastern Segment in the Sveconorwegian orogen comprises Paleoproterozoic–Mesoproterozoic magmatic suites, which formed along an active continental margin, and Mesoproterozoic suites emplaced during intracratonic extension. Zn–Pb sulphide and Fe oxide mineralizations in 1.9 Ga metavolcanic rocks form a significant mineral resource cluster in the northeastern part. Deformation and metamorphism under low-pressure (≤5 kbar) and variable-temperature conditions, including anatexis and granulite facies, prevailed during 1.9–1.8 Ga (Svecokarelian) and 1.5–1.4 Ga (Hallandian) accretionary orogenies. Sveconorwegian tectonothermal reworking initiated at c. 0.99–0.98 Ga in structurally lower levels. Crustal shortening, underthrusting with eclogite facies metamorphism (18 kbar), exhumation by eastwards thrusting (D1) during continued shortening and high-pressure granulite (8–12 kbar) to upper amphibolite facies metamorphism prevailed. Anatexis and folding around east–west axial surfaces with west-northwesterly constrictional strain (D2) followed at c. 0.98–0.95 Ga, being consanguineous with crustal extension. Structurally higher levels, northwards and eastwards, consist of high-pressure (10–12 kbar) orthogneisses, not affected by anatexis but also showing polyphase deformation. Sveconorwegian convergence ceased with upright folding along north–south axial surfaces and, in the uppermost frontal part, greenschist facies shearing with top-to-the-foreland normal followed by reverse displacement after 0.95 Ga. The normal shearing detached the upper compartment from the underlying gneisses.

  • 36.
    Stephens, Michael B.
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Wahlgren, Carl-Henric
    Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden.
    Regional context and lithotectonic framework of the 1.1–0.9 Ga Sveconorwegian orogen, southwestern Sweden2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 337-349Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    The 1.1–0.9 Ga Sveconorwegian orogen in southwestern Scandinavia belongs to the global system of mountain belts established during the assembly of the supercontinent Rodinia. An overall north–south structural trend and five lithotectonic units bounded by crustal-scale shear zones characterize this orogen. In Sweden, the Eastern Segment abuts the orogen's cratonic foreland eastwards and is separated from the Idefjorden terrane westwards by a ductile shear zone, up to 5 km thick, displaying a sinistral transpressive component. These two lithotectonic units differ on the basis of their pre-Sveconorwegian accretionary tectonic evolution, and the timing of Sveconorwegian high-pressure metamorphism, anatexis and polyphase deformation. High-pressure granulites and migmatites formed at c. 1.05–1.02 Ga in the Idefjorden terrane; eclogites, high-pressure granulites and migmatites at c. 0.99–0.95 Ga in the Eastern Segment. Magmatic activity and crustal extension progressed westwards at c. 0.98–0.92 Ga. Prior to or at 0.93–0.91 Ga, greenschist facies shear deformation with top-to-the-foreland movement affected the frontal part of the orogen. Geodynamic uncertainties concern the affinity of the Idefjorden terrane relative to Fennoscandia (Baltica), the character of the Sveconorwegian orogenesis, and the contiguous or non-contiguous nature of the erosional fronts of the late Mesoproterozoic–early Neoproterozoic orogens in Sweden and Canada.

  • 37.
    Stephens, Michael B.
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Weihed, J. BergmanTellurit AB, Sweden.
    Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources2020Collection/Antologi (Annet vitenskapelig)
    Abstract [en]

    The solid rock mass of Sweden forms a natural field laboratory revealing insight into the westward growth and reworking of one of the planet's ancient continental nuclei. Three major geological units are exposed in different parts of the country: the western part of the Fennoscandian Shield, mainly sedimentary rocks deposited on this crystalline rock mass and the Caledonide orogen. This volume synthesizes the tectonic evolution of Sweden over more than 2500 million years from the Neoarchean to the Neogene. Following an introduction describing the lithotectonic framework of the country and the organization of the volume, the tectonic evolution is addressed essentially chronologically. Different phases of intracratonic rifting, accretionary orogeny, continent–continent collisional orogeny and platformal sedimentation are identified. Sweden is one of Europe's major suppliers of metals, and the country's mineral resources are also presented in the context of the lithotectonic framework. Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources has been designed to interest a professional geoscientific audience and advanced students of Earth Sciences.

  • 38.
    Stephens, Michael
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Follin, Sven
    SF GeoLogic AB, Domherrevägen 9, SE-183 51 Täby.
    Petersson, Jesper
    Norconsult AB, Box 8774, SE-402 76 Göteborg.
    Isaksson, Hans
    Geovista AB.
    Juhlin, Christopher
    Department of Earth Sciences, Uppsala University, Uppsala universitet.
    Simenonov, Assen
    Swedish Nuclear Fuel and Waste Management Company.
    Review of the deterministic modelling of deformation zones and fracture domains at the site proposed for a spent nuclear fuel repository, Sweden, and consequences of structural anisotropy2015Inngår i: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 653, s. 68-94Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents a review of the data sets and methodologies used to construct deterministic models for the spatial distribution of deformation zones and intervening fracture domains in 3-D space at Forsmark, Fennoscandian Shield, Sweden. These models formed part of the investigations to characterize this site, recently proposed as a repository for the storage of spent nuclear fuel in Sweden. The pronounced spatial variability in the distribution of bedrock structures, formed under ductile (lower amphibolite- or greenschist-facies) and subsequently brittle conditions, was controlled by two factors; firstly, the multiphase reactivation, around and after 1.8 Ga, of older ductile structures with a strong anisotropy formed under higher-temperature conditions at 1.87–1.86 Ga; and, secondly, by the release of rock stresses in connection with loading and unloading cycles, after 1.6 Ga. The spatial variability in bedrock structures is accompanied by a significant heterogeneity in the hydraulic flow properties, the most transmissive fractures being sub-horizontal or gently dipping. Although the bedrock structures at Forsmark are ancient features, the present-day aperture of fractures and their hydraulic tranmissivity are inferred to be influenced by the current stress state. It is apparent that the aperture of fractures can change throughout geological time as the stress field evolves. For this reason, the assessment of the long-term (up to 100,000 years) safety of a site for the storage of spent nuclear fuel in crystalline bedrock requires an evaluation of all fractures at the site, not only the currently open fractures that are connected and conductive to groundwater flow. This study also highlights the need for an integration of structural data from the ground surface and boreholes with magnetic field and seismic reflection data with high spatial resolution, during the characterization of structures at a possible site for the storage of spent nuclear fuel in crystalline bedrock.

  • 39.
    Stephens, Michael
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Jansson, Nils
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik. Luleå University of Technology.
    Paleoproterozoic (1.9–1.8 Ga) syn-orogenic magmatism, sedimentation and mineralization in the Bergslagen lithotectonic unit, Svecokarelian orogen2020Inngår i: Sweden: Lithotectonic framework, tectonic evolution and mineral resources / [ed] Stephens, M.B., Bergman Weihed, J, London: Geological Society of London, 2020, 1, s. 155-206Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    Felsic volcanic rocks (c. 1.91–1.89 Ga) and interlayered limestone, hosting Zn–Pb–Ag ± Cu ± Au ± Fe sulphide and Fe oxide deposits, characterize the Bergslagen lithotectonic unit, Svecokarelian orogen, south-central Sweden. Three sulphide mines are currently in operation. Siliciclastic sedimentary rocks stratigraphically envelop this volcanic succession and all the rocks are intruded by a dominant calc-alkaline, c. 1.91–1.87 Ga plutonic suite. Fabric development associated with folding and localized shear deformation followed at c. 1.87–1.86 Ga (D1) and was succeeded by strongly partitioned strain (D2). Dextral transpression along steeply dipping, WNW–ESE or NW–SE shear zones prevailed in the northern and southern domains, whereas major folding with east to northeasterly axial surface traces and shearing along limbs occurred in the central domain. Open folding (D3) subsequently affected the western areas. Polyphase metamorphism under low-pressure and variable temperature conditions included anatexis at c. 1.86 Ga (M1) and 1.84–1.80 Ga (M2). More alkali–calcic magmatic activity, combined with the emplacement of anatectic granite and pegmatite, overlapped and succeeded the M1 and M2 migmatization events at c. 1.87–1.83 Ga and c. 1.82–1.75 Ga, respectively. The younger granites are genetically linked in part to W skarn deposits and host Mo sulphide mineralization. Switching between retreating and advancing subduction systems during three separate tectonic cycles along a convergent, active continental plate margin is inferred.

  • 40.
    Wahlgren, Carl-Henric
    et al.
    Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Reworking of older (1.8 Ga) continental crust by Mesoproterozoic (1.5–1.4 Ga) orogeny, Blekinge–Bornholm orogen, southeastern Sweden2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 291-312Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    The Blekinge–Bornholm orogen in southeastern Sweden consists of calc-alkaline to alkali–calcic intrusive rocks, rhyolites and dacites (1.8 Ga) that were structurally reworked under amphibolite facies conditions, affected by migmatization at mid-crustal levels at c. 1.44 Ga and intruded at c. 1.47–1.43 Ga by ferroan alkali–calcic plutons. This Mesoproterozoic orogen is bordered westwards by the Sveconorwegian orogen and northwards, along the boundary with well-preserved 1.8 Ga magmatic rocks in the Svecokarelian orogen, by a stitching c. 1.45 Ga pluton and steeply dipping ductile zones with a south-side-up, dip-slip shear component. A variably developed gneissic fabric (S1) dips gently to moderately northwards and is affected by asymmetrical F2 folds with a southerly vergence. Ductile high-strain zones with top-to-the south shear sense are suggested to correspond at depth to anomalously reflective zones along seismic profile BABEL line A. Open folding of the gneissosity around gently, north-plunging fold axes (F3) completed the ductile deformational evolution. Uncertainty remains about the timing of the amphibolite facies ductile fabric and the D2 folding, which is either late-stage Svecokarelian (c. 1.77–1.75 Ga) or Hallandian (c. 1.47–1.43 Ga). Non-collisional, accretionary orogenic systems are suggested to have operated during both time periods, radical reorganization of the subduction trend accompanying the Mesoproterozoic event.

  • 41.
    Wahlgren, Carl-Henric
    et al.
    Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Småland lithotectonic unit dominated by Paleoproterozoic (1.8 Ga) syn-orogenic magmatism, Svecokarelian orogen2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 207-235Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    The Småland lithotectonic unit in the 2.0−1.8 Ga Svecokarelian orogen, southeastern Sweden, is dominated by a c. 1.81−1.77 Ga alkali–calcic magmatic suite (the Transscandinavian Igneous Belt or TIB-1). At least in its central part, the TIB-1 suite was deposited on, or emplaced into, c. 1.83–1.82 Ga calc-alkaline magmatic rocks with base metal sulphide mineralization and siliciclastic sedimentary rocks (the Oskarshamn–Jönköping Belt). Ductile deformation and metamorphism under low- to medium-grade conditions affected the Oskarshamn–Jönköping Belt prior to c. 1.81 Ga. Both suites were subsequently affected by low-grade ductile deformation, mainly along steeply dipping, east–west to NW–SE shear zones with dip-slip and dextral strike-slip displacement. Sinistral strike-slip NE–SW zones are also present. In the northern part of the lithotectonic unit, 1.9 Ga magmatic rocks, c. 1.87–1.81 Ga siliciclastic sedimentary rocks and basalt, and c. 1.86–1.85 Ga granite show fabric development, folding along steep NW–SE axial surfaces and medium- or high-grade metamorphism prior to c. 1.81 Ga and, at least partly, at c. 1.86–1.85 Ga; base metal sulphide, Fe oxide and U or U–REE mineralizations also occur. Magmatism and siliciclastic sedimentation along an active continental margin associated with subduction-related, accretionary tectonic processes is inferred over about 100 million years.

  • 42.
    Wickström, Linda M.
    et al.
    Geological Survey of Sweden, Box 670, SE-751 28 Uppsala, Sweden.
    Stephens, Michael B.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik.
    Tonian–Cryogenian rifting and Cambrian–Early Devonian platformal to foreland basin development outside the Caledonide orogen2020Inngår i: Sweden: Lithotectonic Framework, Tectonic Evolution and Mineral Resources / [ed] M. B. Stephens and J. Bergman Weihed, Geological Society of London, 2020, s. 451-477Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    Different parts of a Tonian–Early Devonian sedimentary succession, covering Proterozoic crystalline basement, occur along the erosional front to the Caledonide orogen, as outliers and coastal strips on land, and as more continuous strata in offshore areas. Rift-related Tonian–Cryogenian siliciclastic sedimentation preceded the break-up of the supercontinent Rodinia, the birth of Baltica and surrounding oceanic realms during the Ediacaran, and a marine transgression across Baltica during the Cambrian. An Ediacaran alkaline and carbonatite intrusive complex in central Sweden formed in connection with the extensional activity. Subsequently, during the Cambrian–Early Devonian, Baltica drifted northwards in the southern hemisphere to the equator, and six different lithofacies associations containing both siliciclastic and carbonate sedimentation were deposited in platformal shelf and Caledonian foreland basin settings. Bentonites in Ordovician and early Silurian successions were coupled to closure of the surrounding oceanic realms. Tectonic processes during the Caledonian orogeny around the margins to Baltica, the distance to different crustal components in this continent and climatic changes steered variations in lithofacies. Resultant fluctuations in sea-level gave rise to hiatuses and palaeo-karsts. Uranium and other metals in kerogen-rich black shales (Cambrian–Early Ordovician), hydrocarbons, stratabound Pb–Zn sulphide deposits in Cambrian (–Ediacaran?) sandstone, and limestone constitute the main resources.

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