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This paper provides a novel classification scheme for magma-induced subsurface vent complexes based on morphometric data and stacking patterns. The study area is the Naglfar Dome in the Vøring Basin where the interaction between magmatic intrusions and vent complexes is well known. Seismic interpretation, characterization and morphometric analyses of 35 vent complexes observed within the Palaeocene-Eocene strata were done from a high-quality, three-dimensional seismic reflection data. The vent complexes have dome-shaped, eye-shaped, fault-controlled and reactivated upper termini, and are linked to their root zones by columnar, downward-tapered and fault-related fluid conduits or pipes. Statistical analyses and cross plots of L-A and Dmax-Hmax allowed the discrimination of vents and pipes into their genetic types. A new classification scheme based on the morphometric sub-division and structures of subsurface vent complexes is introduced to include S-P-V, S-P-F, V-P-V and V-P-F types. These combinations freshly demonstrate the importance of morphometric data at deciphering the nature, timing, classification and activity of subsurface fluid vent complexes. [ABSTRACT FROM AUTHOR]

Pre-existing faults may facilitate subsurface magma transport and sill trangression in sedimentary basins. Although widely recognized, interaction between faults and intrusion networks in sedimentary basins remains poorly imaged by seismic reflection data. To understand how sills interact with pre-existing faults in sedimentary basins, we use high-resolution 3-D seismic reflection data from the Naglfar Dome, Vøring Basin to examine the seismic expression of sills, interpret fault geometries and displacement patterns, and characterize sill-fault interactions. The sills are expressed as tuned reflection packages, meaning they are below ∼<50 ± 5 m thick, with saucer-shaped, transgressive, and strata-concordant morphologies that range in area from 6 km2 to 180 km2. The interconnected sills form a sill-complex, which was emplaced during the Eocene and cross-cuts three main stratigraphic intervals (i.e. the Nise, Tang, and Brygge Formations). Faults are of Early Paleocene to Early Eocene age, tectonic in origin and dominated by normal faults that are up to 28 km long. Fault and sill interactions define a spectrum, which we sub-divide into five categories (i.e. Type 1a, 1b, 2, 3 and 4); the two main end-member fault-sill relationships documented here are (a) sills stepping up stratigraphy short distances via faults and (b) those with inclined limbs intruded along fault planes. Whilst interactions between the faults and the sills are common, quantitative displacement analysis reveals fault displacement did not influence where sills exploited faults. In the study, the intricate interaction of fault and magmatic sills and its broader implications to structural compartmentalization and outcrop-scale studies in many magma-rich continental margins are demonstrated. • Sills here have saucer-, transgressive, and strata-concordant morphologies. • Faults are tectonic in origin and dominated by normal faults. • First end-member fault-sill relationship are sills stepping stratigraphy. • Other sills have their inclined segments intruded along fault planes. • Sill intrusion into fault planes do not influence fault displacement character. [ABSTRACT FROM AUTHOR]

A key aspect on the evolution of rifted terranes and the prospectivity of the overlying sedimentary basins is heat. Temperature determines the deformation regime of crustal and mantle rocks and, thus, the style of rifting and geometry of rift basins. The generation of hydrocarbons from organic-rich rocks and reservoir conditions depend primarily on temperature. In this study, we model the thermal–burial history of the southern Vøring Basin (Mid-Norway Margin) along a regional transect (2-D), integrating basin- and lithospheric-scale processes. A model that accounts for the main extensional pulses that shaped the Mid-Norway Margin is in good general agreement with the present–past geothermal gradients inferred from borehole temperature and maturity data and the surface heat flux measurements in the proximal and intermediate margin. This supports a near steady-state, post-rift margin setting, following the break-up in the early Eocene. Significant discrepancies are, however, observed in the distal margin, where the borehole temperatures suggest (much) higher thermal gradients than model predicted and implied by the average surface heat flux. We speculate that the higher thermal gradients may result from deep-seated (mantle dynamics) thermal anomalies and/or recurrent hydrothermalism during periods of greater tectonic stress (regional compression and glacial loading rebound) and test the implications for the maturity of the Vøring Basin. The modelling results show, for example, that, depending on the thermal model assumptions, the depth and age of the optimal mid-Late Cretaceous source-rock horizons may vary by more than 2 km and 10 Ma, respectively.

Abstract: Mass wasting is triggered on many continental slopes by a number of mechanisms, including seismic shaking, high sedimentation rates, the presence of weak geological units and gas hydrate dissociation. In this study, the morphology of a Late Miocene–Early Pliocene mass‐transport complex (MTC) on the Utgard High is unravelled and discussed in relation to possible trigger mechanisms. The approach used here includes 3D seismic interpretation and the analysis of variance attribute maps. The interpreted MTC is located on the crest and flanks of the Utgard High and is composed of three mass‐transport deposits with seismic characters varying from transparent and chaotic seismic facies at the base to slightly deformed layers composed of mounds and rafted blocks in the middle and chaotic to transparent reflections at the top. Lithologically, the MTC consists predominantly of claystone with high gamma ray and low density and resistivity values, demonstrating that the associated mounds represent remobilized ooze sediments. A vertical stack of six magmatic sills emplaced from 55.6 to 56.3 Ma into the Upper Cretaceous shales is interpreted at depths of 3,000–5,500 ms two‐way travel time (TWTT). In association with these magmatic sills are several hydrothermal vent complexes that interacted with the top MTC horizon, signifying that episodic and secondary fluid‐venting events might be the principal mechanism facilitating mass wasting in the study area. In addition, the remobilization of ooze sediments into mounds is hypothesized to be dependent on fluids and clayey layers. As a corollary of this work, the importance of relict and recurrent episodes of fluid flow in the Vøring Basin and their influence on the geotechnical integrity of the overburden and later mass wasting is established. [ABSTRACT FROM AUTHOR]

Here, we document a suite of radial faults associated with hydrothermal vent complexes in the Vøring Basin, offshore Norway. These complexes have pyramid-shaped, cylindrical- and conical-shaped conduits, with a dome-, or eye-shaped morphology at their summit, intruding on Paleogene sedimentary rocks. Hydrothermal vents are intimate with the tips of magmatic sills that were emplaced at depths ranging between 1800 and 5800 ms Two Way Travel Time (TWTT). At shallower depths of 1800 to 3000 ms TWTT and intermediate depths of 3000 to 5000 ms TWWT, magmatic sills regularly intersect the lower parts of the vent conduits, which are characterized here as pipes. An important parameter that is used to characterize the morphology of a hydrothermal vent conduit is the width of the conduit, which is defined as the longest axis marking the extent of the vents' conduit within the surrounding host-rock strata. Our findings reveal that radial faults are commonly associated with the summits of hydrothermal vents, implying the existence of local stress fields around the vents, where the maximum compressive stress is radial and minimum stress is circumferential, which overrides the regional stress field and indicate variable stress regimes as opposed to tectonic faults. Importantly, circumferential stretching due to catastrophic plumbing of hydrothermal fluids, differential compaction and intensive fracturing enabled the polygonal faults to realign in a radial pattern resulting in the formation of radial faults at the vent summit. As a corollary of this work, we hypothesize that pyramid-shaped hydrothermal conduits are possibly markers of protracted sill emplacement in sedimentary basins. [ABSTRACT FROM AUTHOR]

A highly conductive body (0.1–0.8 Ω·m) is identified at mid-crustal depth (8–13 km) in the north Gjallar Ridge from magnetotelluric (MT) data and further investigated in light of other remote-sensing geophysical data (seismic reflection, gravity, aeromagnetic). A commercial 3D controlled-source electromagnetic survey was conducted in the Vøring Basin in 2014 and, although primarily designed for hydrocarbon exploration, good quality MT data were extracted at periods ranging from 10 0 to 10 3 s. Dimensionality analysis indicates clear 1D to 2D characteristics in the MT data. 2D inversion was carried out on four profiles (totalling ~ 94 km) oriented perpendicular to the electromagnetic strike and one profile along strike (~ 45 km), using a 1D subset of the data. All inversions converged quickly to RMS values close to unity and display a very good agreement with borehole resistivity data from well 6705/10-1 located in the survey area. A striking feature on all profiles is a highly conductive (0.1–0.8 Ω·m) body at 8–13 km depth. To explain the prominent conductive anomaly, integration of geophysical data favours the hypothesis of electrical conduction across well-connected mineral network in pre-Cretaceous sediments. Seismic interpretation suggests a link between the conductor and intruded sedimentary successions below a detachment level and associated low-angle faults. In the Vøring Basin, low magnetic signal and temperature at the conductor's depth indicate that such thick mineral deposits could display non-magnetic behaviour while occurring well below the magnetite Curie isotherm (~ 585 °C). Natural occurrences and magnetic properties of common iron-sulphide minerals favour a geological interpretation of mid-crustal conductivity as thick pyrrhotite deposits formed in intrusion's contact metamorphic aureoles. [ABSTRACT FROM AUTHOR]

In this study, three-dimensional seismic reflection and borehole data from the Vøring Basin, offshore Norway have been used to characterize a supra-sill related forced fold to understand its evolution and relevance in the context of regional tectonics. Magmatic sills were recognised to be positive high-amplitude anomalies with similar polarity to the seabed reflection. The seismic dataset reveals two groups of sills in the study area comprising interconnected sills beneath the regional forced fold, and those intruded into the overburden. Magmatic sills forming the interconnected sill complex are emplaced at a depth of about 5.5 s TWTT below the modern seafloor. Aspect ratio (length/width), A for the sills ranges from 1.63–6.90. The regional forced fold is interpreted based on its bathymetric and seismic-stratigraphic expression on horizon H7, which is part of the Palaeocene to Eocene Tang Formation. Amplitude of the accommodation fold is about 780 km 2 . Hydrothermal vent complexes and fluid-flow conduits in the study area develop above the sill edges and on the flanks of the interconnected sill complex extending from the lower part of the Tang Formation to the uppermost section of the Brygge Formation evidencing vertically focussed fluid flow in the study area. The overlying overburden is in turn deformed and structurally compartmentalized through forced folding and Late Cenozoic tectonics. We demonstrate that accommodation folding is formed in response to the emplacement of several interconnected sills during the opening of the Norwegian-Greenland Seas. Sill emplacement in the study area causes uplift of the Cretaceous to Palaeocene depocentre prior to further restructuration during Cenozoic tectonic inversion. Magmatic intrusions documented in this study have wider implications for understanding supra-sill deformations along volcanic margins with well-developed emplaced sills at depth and likewise hydrocarbon prospectivity in the study area. [ABSTRACT FROM AUTHOR]

Rich assemblages of dinoflagellate cysts from two sections in the Norwegian Sea provide a solid basis for a palynostratigraphic framework for the upper Albian to upper Maastrichtian succession in this area. The framework is based on a unique composite section combining samples from the shallow stratigraphic core 6711/4-U-1 and core-samples from well 6707/10-1, the latter filling in data from the intervals represented by hiatuses in core 6711/4-U-1. Seven previously described, and one new palynostratigraphic zone, are recognised. These are based on the relative abundances of prominent taxa together with top and base occurrences of selected age-diagnostic dinoflagellate cyst taxa. The zones and their ages in ascending order from the oldest to youngest comprise: the intra late Albian to intra early Cenomanian Subtilisphaera kalaalliti Interval Zone sensu Nøhr-Hansen (1993a); the intra early Cenomanian to intra late Cenomanian Palaeohystrichophora infusorioides – Palaeohystrichophora palaeoinfusa Interval Zone sensu Radmacher et al. (2014b); the Turonian to ?intra early Coniacian Heterosphaeridium difficile Interval Zone sensu Nøhr-Hansen (2012); the ?intra early Coniacian to late Santonian Dinopterygium alatum Interval Zone sensu Radmacher et al. (2014b); the early Campanian Palaeoglenodinium cretaceum Interval Zone sensu Radmacher et al. (2014b); the new intra Campanian Hystrichosphaeridium dowlingii – Heterosphaeridium spp. Interval Zone; the intra late Campanian Chatangiella bondarenkoi Interval Zone sensu Radmacher et al. (2014b) and the intra late Maastrichtian Wodehouseia spinata Range Zone sensu Nøhr-Hansen (1996). Comparison of the palynological events with records in adjacent regions enables correlation across similar paleolatitudes in the Northern Hemisphere. [ABSTRACT FROM AUTHOR]

Abstract: The Giant Gjallar Vent (GGV), located in the Vøring Basin off mid-Norway, is one of the largest (~5×3km) vent systems in the North Atlantic. The vent represents a reactivated former hydrothermal system that formed at about 56Ma. It is fed by two pipes of 440m and 480m diameter that extend from the Lower Eocene section up to the Base Pleistocene Unconformity (BPU). Previous studies based on 3D seismic data differ in their interpretations of the present activity of the GGV, describing the system as buried and as reactivated in the Upper Pliocene. We present a new interpretation of the GGV's reactivation, using high-resolution 2D seismic and Parasound data. Despite the absence of geochemical and hydroacoustic indications for fluid escape into the water column, the GGV appears to be active because of various seismic anomalies which we interpret to indicate the presence of free gas in the subsurface. The anomalies are confined to the Kai Formation beneath the BPU and the overlying Naust Formation, which are interpreted to act as a seal to upward fluid migration. The seal is breached by focused fluid migration at one location where an up to 100m wide chimney-like anomaly extends from the BPU up to the seafloor. We propose that further overpressure build-up in response to sediment loading and continued gas ascent beneath the BPU will eventually lead to large-scale seal bypass, starting a new phase of venting at the GGV. [Copyright &y& Elsevier]

Abstract: The diagenetic transformation of biogenic silica from opal-A to opal-CT was recognised on seismic reflection data over an area of 78 × 103 km2 on the mid-Norwegian margin. The opal-A/CT diagenetic boundary appears as a positive, high amplitude reflection that generally cross-cuts the hosting stratigraphy. We demonstrate that it is not a sea bottom simulating reflection (BSR) and also that is not in thermal equilibrium with the present day isotherms. We present arguments that three styles of deformation associated with the opal-A/CT reflection – polygonal faulting, regional anticlines and synclines and differential compaction folding – indicate that the silica diagenesis reaction front is fossilised at a regional scale. Isochore maps demonstrate the degree of conformity between the opal-A/CT reflection and three seismic horizons of Late Miocene to Early Pliocene age that potentially represent the paleo-seabed when ‘fossilisation’ of the reaction front took place. The seismic interpretational criteria for recognition of a fossilised diagenetic front are evaluated and the results of our study are integrated with previous studies from other basins of the NE Atlantic in order to determine if the arrest of silica diagenesis was diachronous along this continental margin. [ABSTRACT FROM AUTHOR]

Abstract: Ichnofabrics are applied in concert with sedimentological data to discriminate sub-environments within a Campanian deep-sea fan system in the Norwegian Sea. Seven ichnofabric types are recognised in the studied cores, which correspond to specific architectural elements of the fan system, including amalgamated channels, lobate sand sheets, proximal and distal overbank, fan fringe, and hemipelagic basin plain environments. A unique observation is an ultra-deep Chondrites ichnofabric, interpreted to result from the activity of a chemosymbiotic tracemaker, possibly utilising hydrothermal vents or hydrocarbon seeps in the near vicinity of an active rift system. Mapping and inter-well correlation of ichnofabrics allow a better control of lateral and vertical facies changes, which are important to exploration and production strategies. This study demonstrates that ichnofabric analysis is proving to be a valuable tool for the characterisation and prediction of reservoir quality, the recognition of potential flow barriers and prediction of lateral depositional trends in deep-sea fan deposits. [Copyright &y& Elsevier]

Abstract: The Late Cretaceous to Early Tertiary sequence of the Vøring and Møre Basins from the Norwegian Sea has been examined with respect to mineralogy based on 319 cutting samples from five wells. A clear relationship between mineralogy and well log data is demonstrated. A significant change with respect to velocity, porosity and density occurs within the depth interval corresponding to 80–90°C. At shallow depths/temperatures (<2.0km/70°C), compaction is mainly mechanical and the physical properties are similar to what has been measured by experimental compaction of mudstones. At greater depths, however, the log derived velocities and densities are higher than those produced by experimental compaction indicating significant chemical compaction. XRD analyses show a progressive alteration of smectite to illite (S–I) within this depth/temperature interval which results in the release of significant amounts of silica into solution. Detrital silt and fine-grained quartz showed no secondary quartz overgrowths. These grains are isolated within a clay matrix and surrounded by clay minerals, thus limiting the available surface area and pore space for quartz overgrowths. Chemical analyses (XRF) indicate that silica is conserved within this depth interval, and the amount released from S–I alteration was locally precipitated. Field emission gun-scanning electron microscopy (FEG-SEM) and cathode luminescence (CL) identified authigenic micro-crystalline quartz cement within the clay matrix at temperatures above ∼85°C. This is accompanied by an increase in velocity and density indicating that the S–I reaction and the precipitation of authigenic quartz caused a significant change in the rock stiffness. [Copyright &y& Elsevier]

The geological evolution of the volcanic passive margin off mid-Norway, NE Atlantic, and the active volcanic arc in northern Honshu, related to the subduction of the Pacific plate beneath Japan, are similar in the sense that long periods of extensional deformation has shifted to recent compression with formation of domal structures. Seismic wide-angle data have been acquired across six contractional domes in the Vøring Basin, mid-Norwegian Margin, and over the Ou Backbone Range ‘pop-up’ structure, northern Honshu. The models derived from the seismic data reveal that the location of all investigated structures in the Vøring Basin is between, or in the vicinity of pre-Eocene high-velocity structures, which may act as rigid blocks during compression. It is proposed that the existence and trend of these structures, subject to mild NW–SE compression, is the most important factor controlling the formation, spatial distribution and trend of the domes. Structures in the high-velocity lower crust may be the single most important element in controling the domal formation; all modelled highs in the lower crustal early Tertiary intrusive layer seem to be related to the formation of domes in the NW–SE direction. The Ou Backbone Range pop-up structure is localised at a low rigidity zone mapped as low upper crustal seismic velocities. The structure coincides with the present day volcanic front, which may be interpreted as the main reason for the existence of low velocities and the main factor controling the localization of compressional deformation. The Ou Backbone Range is squeezed between a high velocity upper crustal block to the east and a high velocity lower crustal block to the west, and it is speculated that the corresponding lateral and vertical variations in crustal rigidity may have contributed to the actual localization of the present day volcanic front. [Copyright &y& Elsevier]

The geologic setting of the formerly glaciated mid-Norwegian continental margin exerts specific controls on the formation of a bottom-simulating reflector (BSR) and the inferred distribution of gas hydrates. On the continental slope the lithology of glacigenic debris flow deposits and pre-glacial basin deposits of the Kai Formation prevent gas-hydrate formation, because of reduced pore size, reduced water content and fine-grained sediment composition. Towards the continental shelf, the shoaling and pinch-out of the gas-hydrate stability zone terminates the area of gas-hydrate growth. These geological controls confine the occurrence of gas hydrates and ensuing formation of a BSR to a small zone along the northern flank of the Storegga submarine slide and the slide area itself. A BSR inside the slide area indicates a dynamically adjusting gas-hydrate system to post-slide pressure–temperature equilibrium conditions. These observations, together with widespread evidence for fluid flow and deep-seated hydrocarbon reservoirs, suggest that the formation of BSR and gas hydrates on the mid-Norwegian continental margin is dominated by an advection of gas from the strata distinctly beneath the gas-hydrate stability zone. Fluids migrate upward within the Naust Formation and are deflected laterally by hydrated sediments and less permeable layers. Gases continually accumulate at the top of the slope, where overpressure eventually results in the formation of blow-out pipes and consequent pockmark development on the seabed. [Copyright &y& Elsevier]

During the summer of 1996, five profiles with a total length of 892.5 km and 30 recovered Ocean Bottom Seismographs (OBSs) were acquired along the southern part of the Vøring Margin, mid-Norway. These profiles are oriented in both strike and dip direction, mapping the crustal structure along the western-most part of this area. By performing both forward and inverse velocity travel-time modelling of the vertical components of the OBSs (P-waves) regional models have been established. The thickness of the Cenozoic sediments ranges from 0.5 km at the structural highs (Møre Marginal High) to more than 3 km in the Vigrid Syncline. The Cretaceous layers vary considerably in thickness, from 1.7 km close to the Jan Mayen Fracture Zone, increasing to approximately 8 km below the Helland Hansen Arch. Several intrusions are found in the Cretaceous layers and they individually range in thickness from 0.1 to 0.6 km. These intrusions can be followed through crossing profiles, in both in the models presented in this paper, and in the models inferred from earlier OBS surveys along this margin. The pre-Cretaceous sediments are modelled as a layer with P-wave velocity of more than 5 km/s. The thickness of this layer is generally less than 5 km, but locally a thickness of 6.5 km is modelled. The crystalline basement is modelled as a 6+ km/s refractor with a general trend shallowing towards south- and northwest. Along a strike-profile, the transition from continental to oceanic crust is modelled by increased P-wave velocity from 6.2 to 7.3 km/s, as the profile crosses the Jan Mayen Lineament towards the Møre Marginal High. The thickness of the continental crystalline basement is largest landward towards the Helland Hansen Arch where it exceeds 10 km. Towards the SW and NW, where the crystalline basement is elevated, the thickness decreases to less than 5 km. In the lower crust, a high velocity 7+ km/s body, interpreted as magmatic underplating, is found along three of the profiles in the present work. The SE boundary of this magmatic underplated layer is located beneath the Helland Hansen Arch and towards the Møre Marginal High. The southwestward termination is less certain, but the Jan Mayen Fracture Zone seems to control the emplacement of intrusions in the southern Vøring Basin. The depth to Moho varies from 12 to 28 km, deepening landwards. [Copyright &y& Elsevier]

High-quality seismic data document a Maastrichtian-Paleocene rift episode on the Vøring margin lasting for ∼20 m.y. prior to continental breakup. The rift structures are well imaged in the Fenris Graben and Gjallar Ridge region in the western Vøring Basin, and are characterized by low-angle detachment faults with variable fault geometries from south to north. The structural restoration has facilitated the division of pre- and syn-rift sediments across the extensional terrain, which is subsequently used to evaluate mode and mechanism for the lithospheric deformation. Extension estimates based on the structural restoration, subsidence analysis and crustal thickness evaluations yield stretching factors ranging between 1.5 to 2.3 across the main fault zone just landward of the early Tertiary flood basalts. The structural restoration also shows that a middle crustal dome structure, observed beneath the low-angle faults, can be explained by extensional unroofing. Thus, the dome structure may represent a possible metamorphic core complex. Calculations of the effects on vertical motion, assuming uniform and two-layer differential stretching models combined with the arrival of the Iceland mantle plume during rifting, indicate that the uniform extension model may account for both observed early rift subsidence and subsequent late rift uplift and erosion. Although the differential model can not be excluded, it implies early rift uplift which is not compatible with our seismic interpretation. The direct and indirect effects of the Iceland mantle plume may have caused as much as 1.2 km of late rift uplift. Comparison of the volcanic Vøring margin and the non-volcanic West Iberian margin shows similarities in terms of structural style as well as in mode and distribution of extension. [ABSTRACT FROM AUTHOR]

A key aspect on the evolution of rifted terranes and the prospectivity of the overlying sedimentary basins is heat. Temperature determines the deformation regime of crustal and mantle rocks and, thus, the style of rifting and geometry of rift basins. The generation of hydrocarbons from organic-rich rocks and reservoir conditions depend primarily on temperature. In this study, we model the thermal–burial history of the southern Vøring Basin (Mid-Norway Margin) along a regional transect (2-D), integrating basin- and lithospheric-scale processes. A model that accounts for the main extensional pulses that shaped the Mid-Norway Margin is in good general agreement with the present–past geothermal gradients inferred from borehole temperature and maturity data and the surface heat flux measurements in the proximal and intermediate margin. This supports a near steady-state, post-rift margin setting, following the break-up in the early Eocene. Significant discrepancies are, however, observed in the distal margin, where the borehole temperatures suggest (much) higher thermal gradients than model predicted and implied by the average surface heat flux. We speculate that the higher thermal gradients may result from deep-seated (mantle dynamics) thermal anomalies and/or recurrent hydrothermalism during periods of greater tectonic stress (regional compression and glacial loading rebound) and test the implications for the maturity of the Vøring Basin. The modelling results show, for example, that, depending on the thermal model assumptions, the depth and age of the optimal mid-Late Cretaceous source-rock horizons may vary by more than 2 km and 10 Ma, respectively. [ABSTRACT FROM AUTHOR]

Extensional settings with multiple phases of rifting are often intermitted by compressional tectonics or inversion. Differentiating compressional structures/phases in such settings become difficult when magma-induced forced folds are also present. This study uses a high-quality 3D seismic data to interpret tectonic inversion structures in the Naglfar Dome of the Norwegian North Sea. Cenozoic tectonic inversion in the Naglfar Dome is clearly observed in the area as (a) snakehead reflections and (b) trains of fault propagation anticlines along inverted normal faults. These structures selectively affect strata of Early Eocene to Oligocene age, indicating that both basin-wide and localised tectonic inversion have occurred in the Naglfar Dome. Early Miocene inversion in the study area occurred along reactivated, main and boundary faults between the Hel Graben and the Nyk High. Tectonic inversion in a purely extensional domain such as the Naglfar Dome post-dated the formation of a regional magma-induced forced fold. These inversion structures are cumulative consequences of the interaction of a NW-SE compression associated with a reconfiguration of plate motion during the opening of the Norwegian-Greenland Sea in the Eocene to Oligocene, active ridge push from both the Mohns Ridge and the Iceland insular margin, and far-field plate tectonic stresses associated with late stages of the Alpine orogeny. The results presented here demonstrate the rare occurrence of contractional structures within a purely extensional domain, with further implications for understanding the dynamics and evolution of faults along continental margins. Image 1 • Classic evidence for tectonic inversion includes snakehead folds and reverse faults. • The main phase of tectonic inversion occurred in Early Eocene to Oligocene. • A secondary inversion event is related an Early Miocene fault-related uplift. • Tectonic inversion in the area is caused by contractional and far-field stresses. • A clarification is provided here between inverted structures and a basin-wide forced fold. [ABSTRACT FROM AUTHOR]

The outer Vøring Basin, Norwegian Sea, is an abnormally deep and distal part of the Norwegian passive margin, known as "magma-rich". Yet, the lastest borehole drilled in its northernmost part led to a drastic change in the interpretation of seismic reflection data. This update motivates a new model for the entire Mesozoic-Eocene rifting period. Here I evaluate the link between tectonics, serpentinization and magmatism in the Norwegian margin from the Ryazanian-Valanginian to the Palaeocene-Eocene magmatic breakup. Maps of the regional Nise sandstones and main regional unconformities specifically highlight the fundamental role of the Nyk-Vema Structure to understand the basin and to question the deformation timing related to deep structures. The top of partially serpentinized mantle is supported by high-amplitude reflectors clearly visible on certain seismic lines, known as "T-Reflector", covered with gravity-driven pre-exhumation sediments and further deposits. A new structural scheme based on the interpretation of 2D and 3D seismic data shows the complex organization of fault networks and constrains a major deformation period between the Late Campanian and the Late Palaeocene. Ocean-scale complementary arguments are in good agreement with Lower-Cretaceous mantle exhumation. Before becoming a volcanic margin in the Palaeocene, this segment of the Norwegian margin appears as amagmatic until the Late Campanian, at least. I propose an integrated model since the onset of hyperextension in the end of the Jurassic until the cessation of activity of the Aegir Ridge in the Miocene. This model has implications regarding the context-dependent interpretation of lower-crustal bodies, the ubiquity of serpentinization and mantle exhumation worldwide, and on the hydrocarbon system. Unlabelled Image • Before becoming a volcanic margin in the Palaeocene, this segment of the Norwegian margin appears as amagmatic until the Late Campanian, at least; • Mantle exhumation occurred in the outer Vøring Basin during the Cretaceous and crustal lineaments likely reveal lithospheric-scale fracturing; • The magmatic breakup is shifted > 100 km from the continental breakup; • So-called "lower crustal bodies" are interpreted differently in magma-poor and magma-rich margins although they have similar properties; • Serpentinization is likely to reach the brittle-ductile transition, as observed for subduction-related bending faults or ultra-slow spreading ridges. [ABSTRACT FROM AUTHOR]