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Haakon Fossen - One of the best experts on this subject based on the ideXlab platform.
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the influence of structural inheritance and multiphase extension on rift development the northernnorth sea
Tectonics, 2019Co-Authors: Thomas B Phillips, Hamed Fazlikhani, Rebecca E Bell, Jan Inge Faleide, Haakon Fossen, Robert L. Gawthorpe, Christopher A L Jackson, Atle RotevatnAbstract:The northern North Sea rift evolved through multiple rift phases within a highly heterogeneous crystalline basement. The geometry and evolution of syn‐rift depocentres during this multiphase evolution, and the mechanisms and extent to which they were influenced by pre‐existing structural heterogeneities remain elusive, particularly at the regional scale. Using an extensive database of borehole‐constrained 2D seismic reflection data, we examine how the physiography of the northern North Sea rift evolved throughout late Permian‐Early Triassic (RP1) and Late Jurassic‐Early Cretaceous (RP2) rift phases, and assess the influence of basement structures related to the Caledonian Orogeny and subsequent Devonian extension. During RP1, the location of major depocentres, the Stord and East Shetland basins, was controlled by favorably oriented Devonian shear zones. RP2 shows a diminished influence from structural heterogeneities, activity localises along the Viking‐Sogn graben system and the East Shetland Basin, with negligible activity in the Stord Basin and Horda Platform. The Utsira High and the Devonian Lomre Shear Zone form the eastern barrier to rift activity during RP2. Towards the end of RP2, rift activity migrated northwards as extension related to opening of the proto‐North Atlantic becomes the dominant regional stress as rift activity in the northern North Sea decreases. Through documenting the evolving syn‐rift depocentres of the northern North Sea rift, we show how structural heterogeneities and prior rift phases influence regional rift physiography and kinematics, controlling the segmentation of depocentres, as well as the locations, styles and magnitude of fault activity and reactivation during subsequent events.
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The influence of structural inheritance and multiphase extension on rift development, the northern North Sea
2019Co-Authors: Thomas Phillips, Hamed Fazlikhani, Rebecca Bell, Jan Inge Faleide, Haakon Fossen, Robert L. Gawthorpe, Christopher A L Jackson, Atle RotevatnAbstract:The northern North Sea rift evolved through multiple rift phases within a highly heterogeneous crystalline basement. The geometry and evolution of syn-rift depocentres during this multiphase evolution, and the mechanisms and extent to which they were influenced by pre-existing structural heterogeneities remain elusive, particularly at the regional scale. Using an extensive database of borehole-constrained 2D seismic reflection data, we examine how the physiography of the northern North Sea rift evolved throughout late Permian-Early Triassic (RP1) and Late Jurassic-Early Cretaceous (RP2) rift phases, and assess the influence of basement structures related to the Caledonian Orogeny and subsequent Devonian extension. During RP1, the location of major depocentres, the Stord and East Shetland basins, was controlled by favorably oriented Devonian shear zones. RP2 shows a diminished influence from structural heterogeneities, activity localises along the Viking-Sogn graben system and the East Shetland Basin, with negligible activity in the Stord Basin and Horda Platform. The Utsira High and the Devonian Lomre Shear Zone form the eastern barrier to rift activity during RP2. Towards the end of RP2, rift activity migrated northwards as extension related to opening of the proto-North Atlantic becomes the dominant regional stress as rift activity in the northern North Sea decreases. Through documenting the evolving syn-rift depocentres of the northern North Sea rift, we show how structural heterogeneities and prior rift phases influence regional rift physiography and kinematics, controlling the segmentation of depocentres, as well as the locations, styles and magnitude of fault activity and reactivation during subsequent events.
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basement structure and its influence on the structural configuration of the northern north sea rift
Tectonics, 2017Co-Authors: Hamed Fazlikhani, Jan Inge Faleide, Haakon Fossen, Robert L. Gawthorpe, Rebecca E BellAbstract:The northern North Sea rift basin developed on a heterogeneous crust comprising structures inherited from the Caledonian Orogeny and Devonian post-orogenic extension. Integrating two-dimensional regional seismic reflection data and information from basement wells we investigate the pre-rift structural configuration in the northern North Sea rift. Three seismic facies have been defined below the base rift surface: 1) relatively low-amplitude and low-frequency reflections, interpreted as pre-Caledonian metasediments, Caledonian nappes and/or Devonian clastic sediments; 2) packages of high-amplitude dipping reflections (>500 ms thick), interpreted as basement shear zones; and 3) medium-amplitude and high frequency reflections interpreted as less sheared crystalline basement of Proterozoic and Paleozoic (Caledonian) origin. Some zones of Seismic Facies 2 can be linked to onshore Devonian shear zones whereas others are restricted to the offshore rift area. Interpreted offshore shear zones dip S, ESE and WNW in contrast to W to NW dipping shear zones onshore W Norway. Our results indicate that Devonian strain and ductile deformation was distributed throughout the Caledonian orogenic belt from central South Norway to the Shetland Platform. Most of the Devonian basins related to this extension are, however, removed by erosion during subsequent exhumation. Basement shear zones reactivated during the rifting and locally control the location and geometry of rift depocenters, e.g. in the Stord and East Shetland basins. Pre-rift structures with present-day dips >15° were reactivated, although some of the basement shear zones are displaced by rift faults regardless of their orientation relative to rift extension direction.
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From the early Paleozoic platforms of Baltica and Laurentia to the Caledonide orogen of Scandinavia and Greenland
Episodes, 2008Co-Authors: D. G. Gee, Nils Henriksen, Haakon Fossen, A. K. HigginsAbstract:The Caledonide Orogen in the Nordic countries is exposed in Norway, western Sweden, westernmost Finland, on Svalbard and in northeast Greenland. In the mountains of western Scandinavia, the structure is dominated by E-vergent thrusts with allochthons derived from the Baltoscandian platform and margin, from outboard oceanic (Iapetus) terranes and with the highest thrust sheets having Laurentian affinities. The other side of this bivergent orogen is well exposed in northeastern Greenland, where W-vergent thrust sheets emplace Laurentian continental margin assemblages onto the platform. Svalbard's Caledonides are disrupted by late Caledonian faults, but have close affinity with the Laurentian margin in Northeast Greenland. Only Svalbard's Southwestern terrane is foreign to this margin, showing affinity to the Pearya terrane of northern Ellesmere Island in arctic Canada. Between the margins of western Scandinavia and eastern Greenland, the wide continental shelves, now covered by late Paleozoic and younger successions, are inferred to be underlain by the Caledonide hinterland, probably incorporating substantial Grenville-age basement. In northernmost Norway, the NE-trending Caledonian thrust front truncates the NW-trending Neoproterozoic Timanide orogen of northwest Russia. Much of the central and eastern parts of the Barents Shelf are thought to be underlain by Caledonian-deformed Timanide basement. Caledonian Orogeny in Norden resulted from. the closure of the Iapetus Ocean and Scandian collision of continent Baltica with Laurentia. Partial subduction of the Baltoscandian margin beneath Laurentia in the mid-late Silurian was followed by rapid exhumation of the highly metamorphosed hinterland in the early Devonian, and deposition of Old Red Sandstones in intramontane basins. Late Scandian collapse of the orogen occurred on major extensional detachments, with deformation persisting into the late Devonian.
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the role of extensional tectonics in the caledonides of south norway
Journal of Structural Geology, 1992Co-Authors: Haakon FossenAbstract:Abstract Detailed and regional structural-kinematic analyses of the Caledonides of south Norway show evidence for a crustal extension that is far more widespread and substantial than previously thought. Two different modes of extension are recognized. The first (Mode I) involved kilometer-scale back movement of the Caledonian nappes. The back movement resulted in extensive shear deformation within the decollement zone between the nappe wedge and the basement as seen by abundant asymmetric mylonite structures indicating translation of the Caledonian nappes towards the northwest. A second mode (Mode II) involved extension of the Baltic Shield by the formation of large-scale, normal-sense oblique shear zones. Mode II extension occurred partly during and partly after the back movement of the overlying nappes. The extensional deformation consistently overprints the contractional Caledonian deformation in the whole region, and is therefore interpreted as a distinct (Devonian) event post-dating the Ordovician-Upper Silurian construction of the Caledonian orogenic wedge. The uniform and regional-scale back movement of the orogenic wedge towards the central parts of the orogen indicates that the extension at the end of the Caledonian Orogeny was closely related to post-collisional, Lower to Middle Devonian plate divergence.
R A Strachan - One of the best experts on this subject based on the ideXlab platform.
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Evidence for 930 Ma metamorphism in the Shetland Islands, Scottish Caledonides: implications for Neoproterozoic tectonics in the Laurentia–Baltica sector
2016Co-Authors: Of Rodinia, R A Strachan, K. A. Cutts, M. Hand, D. E. Kelsey, B. Wade, C. Clark, A. NettingAbstract:Abstract: Zircon and monazite laser-ablation inductively coupled plasma mass spectrometry U–Pb geochronological data for two metasediment samples from the Westing Group, northern Shetland Islands, Scottish Caledonides yield ages between 938 8 and 925 10 Ma (Tonian) for upper amphibolites-facies metamorphism. Texturally early metamorphism is recorded by a migmatitic garnet + sillimanite + plagioclase + muscovite + biotite assemblage, which formed at c. 650–700 8C and 7 kbar. Subsequent reworking resulted in the growth of a secondary garnet + kyanite + plagioclase + muscovite + biotite assemblage at c. 650 8C and 8–9 kbar. In situ electron probe microanalysis (EPMA) U–Th–Pb chemical dating of monazite hosted within garnet grains and the matrix of one sample also give Tonian ages, apparently indicating that all the metamorphism occurred during the Neoproterozoic. However, the dominant structural fabrics appear to have formed during the Ordovician–Silurian Caledonian Orogeny, suggesting that the reworking was substantially younger despite the apparent absence of Caledonian monazite or zircon ages. Detrital zircons are consistent with Laurentia–Baltica provenance. Deposition of the Westing Group is constrained to between c. 1030 and 930 Ma. The timing of Tonian metamorphism suggests possible correlations with sequences elsewhere in the northern Caledonides, including the Krummedal Succession of East Greenland and Laurentian-derive
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Evidence for 930 Ma metamorphism in the Shetland Islands, Scottish Caledonides: implications for Neoproterozoic tectonics in the Laurentia–Baltica sector of Rodinia
2016Co-Authors: K. A. Cutts, R A Strachan, M. Hand, D. E. Kelsey, B. Wade, C. Clark, A. NettingAbstract:Zircon and monazite laser-ablation inductively coupled plasma mass spectrometry U–Pb geochronological data for two metasediment samples from the Westing Group, northern Shetland Islands, Scottish Caledonides yield ages between 938 ± 8 and 925 ± 10 Ma (Tonian) for upper amphibolites-facies metamorphism. Texturally early metamorphism is recorded by a migmatitic garnet + sillimanite + plagioclase + muscovite + biotite assemblage, which formed at c. 650–700 °C and 7 kbar. Subsequent reworking resulted in the growth of a secondary garnet + kyanite + plagioclase + muscovite + biotite assemblage at c. 650 °C and 8–9 kbar. In situ electron probe microanalysis (EPMA) U–Th–Pb chemical dating of monazite hosted within garnet grains and the matrix of one sample also give Tonian ages, apparently indicating that all the metamorphism occurred during the Neoproterozoic. However, the dominant structural fabrics appear to have formed during the Ordovician–Silurian Caledonian Orogeny, suggesting that the reworking was substantially younger despite the apparent absence of Caledonian monazite or zircon ages. Detrital zircons are consistent with Laurentia–Baltica provenance. Deposition of the Westing Group is constrained to between c. 1030 and 930 Ma. The timing of Tonian metamorphism suggests possible correlations with sequences elsewhere in the northern Caledonides, including the Krummedal Succession of East Greenland and Laurentian-derived successions in Svalbard and northern Norway.
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contrasting magma emplacement mechanisms within the rogart igneous complex nw scotland record the switch from regional contraction to strike slip during the Caledonian Orogeny
Geological Magazine, 2014Co-Authors: H Kocks, Jane Evans, R A Strachan, Mike FowlerAbstract:The Rogart igneous complex is unique within the northern Scottish Caledonides because it comprises an apparent continuum of magma types that records a progressive change in emplacement mechanisms related to large-scale tectonic controls. Syn-D2 leucogranites and late-D2 quartz monzodiorites were emplaced during crustal thickening and focused within the broad zone of ductile deformation associated with the Naver Thrust. In contrast, emplacement of the post-D2 composite central pluton was controlled by development of a steeply dipping dextral shear zone along the Loch Shin Line, interpreted as an anti-Riedel shear within the Great Glen Fault system. The mantle-derived nature of the late-to-post-D2 melts implies that the Naver Thrust and the Loch Shin Line were both crustal-scale structures along which magmas were channelled during deformation. A U–Pb zircon age of 425±1.5 Ma for the outer component of the central pluton provides an upper limit on regional deformation and metamorphism within host Moine rocks. These findings are consistent with the view that a fundamental change in tectonic regime occurred in the Scottish Caledonides at c. 425 Ma, corresponding to the switch from regional thrusting that resulted from the collision of Baltica and Laurentia, to the development of the orogen-parallel Great Glen Fault system.
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lu hf and sm nd dating of metamorphic garnet evidence for multiple accretion events during the Caledonian Orogeny in scotland
Journal of the Geological Society, 2013Co-Authors: Anna Bird, R A Strachan, M F Thirlwall, Christina ManningAbstract:Caledonian orogenesis in Scotland is currently interpreted in terms of a Mid-Ordovician arc–continent collision (Grampian event) followed by the Silurian collision of Laurentia with Baltica (Scandian event). Lu–Hf and Sm–Nd garnet ages of c . 475–460 Ma obtained from prograde garnets in metasedimentary successions and metabasic intrusions within the Northern Highland and Grampian terranes confirm that the Mid-Ordovician Grampian orogenic event was approximately synchronous in the two terranes. Lu–Hf and Sm–Nd ages of c . 450 Ma obtained from prograde garnets within the Moine Nappe of the Northern Highland terrane provide evidence for a hitherto unrecognized Late Ordovician regional metamorphic event. The existing two-stage Grampian–Scandian model for Caledonian orogenesis in northern Scotland is thus an oversimplification, and the new ages imply a more complex structural evolution. The restriction of the Late Ordovician and Silurian events to the Northern Highland terrane reinforces the suggestion that it was far removed from the Grampian terrane until juxtaposition following major end-Caledonian (Devonian) sinistral displacement along the Great Glen Fault. A similar record of Mid- and Late Ordovician metamorphic events within the Laurentian-derived Uppermost Allochthons of Norway has been attributed to episodic accretion significantly prior to Silurian continent–continent collision and closure of the Iapetus Ocean. Supplementary materials: Results of trace element analysis of the garnets by laser ablation inductively coupled plasma mass spectrometry are available at www.geolsoc.org.uk/SUP18583.
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progressive fold and fabric evolution associated with regional strain gradients a case study from across a scandian ductile thrust nappe scottish caledonides
Geological Society London Special Publications, 2010Co-Authors: G I Alsop, D Cheer, R A Strachan, Maarten Krabbendam, P D Kinny, R E Holdsworth, A G LeslieAbstract:Fold and fabric patterns developed within a major Caledonian thrust nappe in NW Scotland reflect a progressive increase in regional D2 strain towards the basal ductile detachment. Within the upper greenschist to lower amphibolite facies thrust sheet, the main gently east-dipping foliations and SE-plunging transport-parallel lineations maintain a broadly similar orientation over c. 600 km2. Associated main phase, thrust-related folds (F2) are widely developed, and towards the base of the thrust sheet display progressive tightening and increasing curvilinearity of fold hinges ultimately resulting in sheath folds. Secondary folds (F3) are largely restricted to high-strain zones and are interpreted as flow perturbation folds formed during non-coaxial, top-to-the-NW ductile thrusting. These features are consistent with a structural model that incorporates plane strain pure-shear flattening with a superimposed and highly variable simple shear component focused into high-strain zones. The increase in strain over a distance of 30 km across strike is similar to the increasing deformation observed when structures are traced along strike to the north, and which are apparently related to proximity to basement-cover contacts. A U–Pb zircon age of 415±6 Ma obtained from a syn-D2 meta-granite confirms that regional deformation occurred during the Scandian phase of the Caledonian Orogeny.
Hakon Austrheim - One of the best experts on this subject based on the ideXlab platform.
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evidence for a Caledonian amphibolite to eclogite facies pressure gradient in the middle allochthon lindas nappe sw norway
Contributions to Mineralogy and Petrology, 2012Co-Authors: C Roffeis, Fernando Corfu, Hakon AustrheimAbstract:The Proterozoic anorthosite–mangerite–charnockite complex dominating the Lindas Nappe in the Scandinavian Caledonides was locally eclogitized in the southwestern part of the nappe during the Caledonian Orogeny, whereas only amphibolite facies assemblages are recorded in the rest of the nappe. Sveconorwegian granulites of anorthositic to jotunitic composition in the northernmost eclogite-free exposures of the nappe exhibit large garnet phenoblasts (ca. 900°C) that are fractured and partly replaced by a Caledonian symplectitic amphibolite facies assemblage (ca. 515°C). Metamorphic zircon attributed to this garnet breakdown is dated by ID-TIMS U–Pb at 430 ± 3 Ma, suggesting that the amphibolite facies overprint was coeval with the formation of eclogite 30 km further south, probably implying that the section across the nappe represents a Caledonian pressure gradient. The rocks also preserve a complex Sveconorwegian history including an age of 969 ± 6 Ma, which we interpret as dating magmatic emplacement of jotunitic–anorthositic portions of the complex, 936 ± 12 Ma reflecting the granulite facies metamorphism, and 908 ± 16 Ma, representing a late generation of zircon best explained as having formed by metasomatic processes. Caledonian shearing severely deformed zircon grains in an amphibolite facies shear zone, resetting their U–Pb systems, and forming new ones, hereby also demonstrating a case of resetting and recrystallization of low-U zircon. Our data, gained from diverse lithologies, illustrate several processes involved in making and resetting zircon as well as indicate the contemporaneous evolution and similar origin of the Lindas Nappe and the Jotun Nappe Complex.
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geochronology of fluid induced eclogite and amphibolite facies metamorphic reactions in a subduction collision system bergen arcs norway
Contributions to Mineralogy and Petrology, 2008Co-Authors: Johannes Glodny, Alexander Kuhn, Hakon AustrheimAbstract:Rb–Sr multimineral isochron data for metamorphic veins allow to date separate increments of the mineral reaction history of polymetamorphic terranes. Granulite facies rocks of the Lindas nappe, Bergen Arcs, Norway, were subducted and exhumed during the Caledonian Orogeny. The rocks show petrographic evidence for two distinct events of local fluid infiltration and vein formation, along fractures and shear zones. The first occurred at eclogite facies (15–21 kbar, 650–750°C) and a later one at amphibolite facies conditions (8–10 kbar, 600°C). The presence of fluids enabled local metamorphic equilibration only near fluid pathways. In fluid-absent domains, preexisting assemblages were metastably preserved. This resulted in a heterogeneity of metamorphic signatures on meter to μm-scales. Well-preserved granulite facies rocks preserve their Proterozoic Rb–Sr mineral ages, as does the U–Pb system of zircon in most lithologies. Six Rb/Sr multimineral isochron ages for eclogite facies veins and their immediate wallrocks date the fluid-induced eclogitization at 429.9 ± 3.5 Ma (2σ, weighted average, MSWD = 0.39). An eclogite facies vein has yielded metamorphic zircon with concordant U–Pb ages of 429 ± 3 Ma, identical to the U–Pb age of 427.4 ± 0.9 Ma for zircon xenocrysts in an amphibolite facies vein. Seven Rb/Sr mineral isochron ages date amphibolite-facies fluid infiltration at 414.2 ± 2.8 Ma (MSWD = 1.5), an age value testifying to residence of the rocks in the deep orogenic crust at temperatures >600°C for nearly 15 Ma. The new data show that Rb–Sr mineral isochron ages effectively date fluid-induced (re)crystallization events rather than stages of cooling. The direct link between isotopic ages and distinct petrographic equilibrium assemblages aids to constrain the evolution of rocks in the P–T-reaction-time space, which is essential for understanding exhumation histories and the internal dynamics of orogens in general.
Robin A Strachan - One of the best experts on this subject based on the ideXlab platform.
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evidence in north east greenland for late silurian early devonian regional extension during the Caledonian Orogeny
Geology, 1994Co-Authors: Robin A StrachanAbstract:Crustal extension during and immediately following continental collision is recognized as a fundamental process within many orogenic belts. In the North Atlantic region, Caledonian (Ordovician-Devonian) orogenesis resulted from continental collision of Laurentia and Baltica. In North-East Greenland (Laurentia), regional extension occurred during the Late Silurian to Early Devonian, probably as a response to crustal thickening at an earlier stage in the Orogeny. Extension resulted in a crustal geometry analogous to that of a metamorphic core complex. Recognition of this process in North-East Greenland substantially increases the area of the Caledonides known to have been affected by such extension, and provides additional evidence that this Paleozoic collisional orogen evolved in a manner similar to Mesozoic and Cenozoic examples.
N J Soper - One of the best experts on this subject based on the ideXlab platform.
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laurentian margin evolution and the Caledonian Orogeny a template for scotland and east greenland
Geological Society of America Memoirs, 2008Co-Authors: Graham A Leslie, Martin Smith, N J SoperAbstract:The orthotectonic Scottish Caledonides constitute only a small fragment of the Neoproterozoic to Paleozoic margin of Laurentia, albeit one which lies at a prominent bend in that margin. Sequences exposed in the Scottish outcrop include Mesoproterozoic, Neoproterozoic and Cambro-Ordovician strata which record sedimentation, volcanism and deformation related to the latter stages of the amalgamation of Rodinia, the subsequent breakout of Laurentia, and growth of the Iapetus Ocean. Metamorphic and tectonic overprints then record the destruction of that ocean through Ordovician arc accretion and mid-to-late Silurian collision of Laurentia, Baltica and Avalonia with the final closure of Iapetus by end-Silurian time. New isotopic data and recent advances in the understanding of the late Mesoproterozoic (Stenian) to Cambro-Ordovician stratigraphical framework now better constrain the sequence and timing of events across the ‘Scottish Corner’ and invite a dynamic comparison with the current research into the East Greenland Caledonides summarised in this volume. Although many broad similarities exist, the comparisons described here reveal for the first time a number of significant contrasts in the spatial arrangement of depocentres, location of rifting, patterns and timing of magmatism, metamorphism and contractional deformation. This expanded understanding of the late Neoproterozoic evolution of these adjacent sectors of Laurentia provides an important basis for reconstructions of the subsequent lower Paleozoic Caledonian orogenic evolution of the present North Atlantic region.
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the neoproterozoic hekla sund basin eastern north greenland a pre iapetan extensional sequence thrust across its rift shoulders during the Caledonian Orogeny
Journal of the Geological Society, 2001Co-Authors: A. K. Higgins, A G Leslie, N J Soper, M P Smith, Jan A Rasmussen, Martin SonderholmAbstract:The Vandredalen thrust sheet forms the allochthonous Caledonian front in Kronprins Christian Land, eastern North Greenland. It transported Neoproterozoic shallow marine, arkosic sediments of the Rivieradal Group and shelf sediments of the Hagen Fjord Group across parautochthonous Neoproterozoic–Ordovician sediments on the foreland. The thrust sheet roots to the east along the Brede Spaerregletscher–Hekla Sund lineament and has a demonstrable westwards displacement of c. 40 km. A large part of that displacement ( c . 22 km) is achieved on a single structure, the Vandredalen thrust, but this is only one of a linked system of thrusts which involve parautochthonous thin-skinned thrust sheets to the west and thicker skinned thrust sheets now exposed in the east. Conodont geothermometry suggests that the thick-skinned thrust sheets formerly extended westwards above the Vandredalen thrust sheet at higher structural levels. Restoration of the displacement on the thin-skinned thrusts reveals the Rivieradal Group to be a Neoproterozoic syn-rift sequence deposited in an eastwards-facing extensional half-graben (Hekla Sund Basin) which originally lay immediately to the east of the Brede Spaerregletscher–Hekla Sund lineament. The transgressive Hagen Fjord Group represents a period of post-rift thermal re-equilibration in latest Riphean time and the youngest units in the group overstep the original rift shoulder. The Hekla Sund Basin represents another example of the rift-sag episodes which are an important feature of the pre-Iapetan evolution of the Laurentian margin successions and comparisons are made with coeval basins in Scotland and Svalbard.
