The stratigraphy and structure of the Faroese continental margin

This paper presents a summary of the stratigraphy and structure of the Faroese region. As the Faroese area is mostly covered by volcanic material, the nature of the pre-volcanic geology remains largely unproven. Seismic refraction data provide some indications of the distribution of crystalline basement, which probably comprises Archaean rocks, with the overlying cover composed predominantly of Upper Mesozoic (Cretaceous?) and Cenozoic strata. The Cenozoic succession is dominated by the syn-break-up Faroe Islands Basalt Group, which crops out on the Faroe Islands (where it is up to 6.6 km thick) and shelf areas; post-break-up sediments are preserved in the adjacent deep-water basins, including the Faroe–Shetland Basin. Seismic interpretation of the post-volcanic strata shows that almost every sub-basin in the Faroe–Shetland Basin has been affected by structural inversion, particularly during the Miocene. These effects are also observed on the Faroe Platform, the Munkagrunnur Ridge and the Fugloy Ridge, where interpretation of low-gravity anomalies suggests a large-scale fold pattern. The structure of the Iceland–Faroe Ridge, which borders the NW part of the Faroe area, remains ambiguous. The generally thick crust, together with the absence of well-defined seawards-dipping reflectors, may indicate that much of it is underlain by continental material

Ambient noise tomography reveals basalt and sub-basalt velocity structure beneath the Faroe Islands, North Atlantic

© 2017 Elsevier B.V. Ambient noise tomography is applied to seismic data recorded by a portable array of seismographs deployed throughout the Faroe Islands in an effort to illuminate basalt sequences of the North Atlantic Igneous Province, as well as underlying sedimentary layers and Precambrian basement. Rayleigh wave empirical Green's functions between all station pairs are extracted from the data via cross-correlation of long-term recordings, with phase weighted stacking implemented to boost signal-to-noise ratio. Dispersion analysis is applied to extract inter-station group travel-times in the period range 0.5–15 s, followed by inversion for period-dependent group velocity maps. Subsequent inversion for 3-D shear wave velocity reveals the presence of significant lateral heterogeneity (up to 25%) in the crust. Main features of the final model include: (i) a near-surface low velocity layer, interpreted to be the Malinstindur Formation, which comprises subaerial compound lava flows with a weathered upper surface; (ii) a sharp velocity increase at the base of the Malinstindur Formation, which may mark a transition to the underlying Beinisvørð Formation, a thick laterally extensive layer of subaerial basalt sheet lobes; (iii) a low velocity layer at 2.5–7.0 km depth beneath the Beinisvørð Formation, which is consistent with hyaloclastites of the Lopra Formation; (iv) an upper basement layer between depths of 5–9 km and characterized by S wave velocities of approximately 3.2 km/s, consistent with low-grade metamorphosed sedimentary rocks; (v) a high velocity basement, with S wave velocities in excess of 3.6 km/s. This likely reflects the presence of a crystalline mid-lower crust of Archaean continental origin. Compared to previous interpretations of the geological structure beneath the Faroe Islands, our new results point to a more structurally complex and laterally heterogeneous crust, and provide constraints which may help to understand how continental fragments are rifted from the margins of newly forming ocean basins

An Iceland hotspot saga

Is Iceland a hotspot, with ridge-centered plume? In Iceland vigorous volcanism has built up a plateau 3.0 km higher than at a normal mid-ocean ridge with 3 to 4 times thicker crust than average oceanic crust. This volcanism can be associated with anomalous volcanism for 56–61 Ma in the form of aseismic ridges that stretch across the North Atlantic Ocean through Iceland, i.e. the Greenland-Iceland-Ridge (GIR) and the Faeroe-Iceland-Ridge (FIR). Iceland is a “meltspot” and an hotspot and the GIR and FIR may be hotspot trails. The trends or age progressions of the GIR and FIR are too uncertain to conclude if the Iceland hotspot can be a fixed reference point. There is a large seismic low-velocity anomaly (LVA) in the mantle under Iceland at least down to 400–450 km depth and with globally low velocities down to 200 km depth. The center of the LVA is at 64◦40’N and 18◦10’W between the glaciers Hofsjökull and Vatnajökull. The shape of the LVA is approximately that of a cylinder in the depth range 100–450 km, but at certain depths elongated in the northsouth direction. The LVA extends at least up to 30–40 km depth beneath Central Iceland and the rift zones. The shallower part of the LVA (i.e. above 150 km depth) extends at least 700 km outside of Iceland to the southwest, along the Reykjanes Ridge. The LVA has been numerically modelled with geodynamic methods by several authors as a ridge-centered convecting plume. They try to fit crustal thickness of the Iceland hotspot and neighbouring ridge, and the magnitude and shape of the LVA. The latest of these models find a best fit: A plume 135–150◦C hotter than background mantle, retaining in general 1% partial melt in a maximum 90 km thick melting zone, but reaching up to 2–3% partial melt in the shallowest mantle. The rest of produced melt goes into forming the crust. Considerable work has been carried out on various plume models to explain these and other observations in Iceland, but the models are still some way from reaching a mature state. As long as important observations are lacking and some key questions remain unanswered, alternatives to the plume model or more realistic variants of it in a larger tectonic framework, including heterogeneous mantle, should not be discouraged.Er Ísland heitur reitur (hotspot) sem dregur orku sína frá möttulstróki undir úthafshrygg? Þarna hefur öflug eldvirkni myndað hásléttu sem rís 3,0 km upp yfir úthafshrygginn í Norður-Atlantshafi, og jarðskorpu sem er 3–4 sinnum þykkari heldur en venjulegur úthafshryggur hefur. Þessa umfram eldvirkni Íslands má rekja 56–61 milljón ára aftur í tímann í óvirkum hryggjum sem teygja sig eftir Norður- Atlantshafinu, þ.e. í Grænlands-Íslands hryggnum (GÍH) og Færeyja-Íslands hryggnum (FÍH). Ísland er heitur reitur, svæði með óvenju mikinn kvikubúskap (meltspot), og áðurnefnda hryggi má líta á sem spor eða eftirstöðvar heita reitsins (hotspot trails). Stefna GÍH og FÍH og aldursdreifing bergs í þeim er hins vegar of óviss til þess að slá megi því föstu að íslenski heiti reiturinn sé einn af föstum viðmiðunarpunktum jarðarinnar. Undir Íslandi er stórt svæði sem tefur jarðskálftabylgjur meira en gerist annars staðar vegna lághraðasvæðis í möttlinum (LSM). LSM nær a.m.k. niður á 400–450 km dýpi. Miðja þess er staðsett 64◦40’N og 18◦10’V, það er á milli Hofsjökuls og Vatnajökuls. Í stórum dráttum hefur LSM sívalningslögun á dýpinu 100–450 km, en það teygist úr svæðinu í N-S stefnu sums staðar á þessu dýpi. Undir miðju Íslands og undir gosbeltunum nær LSM að komast næst yfirborði jarðar eða upp að 30–40 km. Grynnri hluti LSM (þ.e. 150 km) nær a.m.k. 700 km út fyrir Ísland eftir Reykjaneshryggnum. Með aflfræðilegum reiknilíkönum hefur verið hermt eftir áhrifum möttulstóks. Nýjustu líkönin og þau sem herma best eftir LSM og þykkt jarðskorpunnar undir heita reitnum og nálægum úthafshryggjum reikna með flæði efnis sem er 135–150◦C heitara en bakgrunnsmöttullinn. Í 90 km þykku (lóðrétt) bræðslusvæði stróksins er að meðaltali 1% hlutbráð. Mest nær hlutbráðin 2–3% í grynnsta hluta svæðisins. Umframbráðin stígur upp og myndar jarðskorpuna. Möttulstrókslíkön hafa þróast, en hafa ekki enn náð nægilegri fullkomnun. Á meðan ekki hefur verið lagður grunnur að öllum grundvallareiginleikum möttulstróka, ætti ekki að letja hugmyndavinnu sem sækir á önnur mið til þess að útskýra uppruna heitra reita. Möttulstrókslíkön framtíðarinnar taka væntanlega mið af stærri tektónískri heild og mismunandi efnafræðilegri gerð möttulsins.Peer Reviewe

Variations in amount and direction of seafloor spreading along the northeast Atlantic Ocean and resulting deformation of the continental margin of northwest Europe

International audienceThe NE Atlantic Ocean opened progressively between Greenland and NW Europe during the Cenozoic. Seafloor spreading occurred along three ridge systems: the Reykjanes Ridge south of Iceland, the Mohns Ridge north of the Jan Mayen Fracture Zone (JMFZ), and the Aegir and Kolbeinsey Ridges between Iceland and the JMFZ. At the same time, compressional structures developed along the continental margin of NW Europe. We investigate how these compressional structures may have resulted from variations in the amount and direction of seafloor spreading along the ridge system. Assuming that Greenland is rigid and stationary, we have used a least squares method of palinspastic restoration to calculate differences in direction and rate of spreading along the Reykjanes, Kolbeinsey/Aegir and Mohns Ridges. The restoration generates relative rotations and displacements between the oceanic segments and predicts two main periods of left-lateral strike slip along the main oceanic fracture zones: (1) early Eocene to late Oligocene, along the Faeroe Fracture Zone and (2) late Eocene to early Oligocene and during the Miocene, along the JMFZ. Such left-lateral motion and relative rotation between the oceanic segments are compatible with the development of inversion structures on the Faeroe-Rockall Plateau and Norwegian Margin at those times and probably with the initiation of the Fugløy Ridge in the Faeroe-Shetland Basin during the Eocene and Oligocene. The Iceland Mantle Plume appears to have been in a position to generate differential seafloor spreading along the NE Atlantic and resulting deformation of the European margin

EuCRUST-07: A new reference model for the European crust

We present a new digital model ( EuCRUST-07) for the crust of Western and Central Europe and surroundings ( 35 degrees N - 71 degrees N, 25 degrees W - 35 degrees E). Available results of seismic reflection, refraction and receiver functions studies are assembled in an integrated model at a uniform grid ( 15 ' x 15 '). The model consists of three layers: sediments and two layers of the crystalline crust. Besides depth to the boundaries, we provide average P-wave velocities in the upper and lower parts of the crystalline crust. The new model demonstrates large differences in the Moho depth compared to previous compilations, over +/- 10 km in some specific areas ( e. g. the Baltic Shield). Furthermore, the velocity structure of the crust is much more heterogeneous than in previous maps. EuCRUST-07 offers a starting point for numerical modeling of deeper structures by allowing correction for crustal effects beforehand and to resolve trade-off with mantle heterogeneities

Frontier exploration and the North Atlantic Igneous Province : new insights from a 2.6 km offshore volcanic sequence in the NE Faroe–Shetland Basin

Acknowledgements and Funding This work was funded by Chevron. The authors would like to acknowledge the Chevron West of Shetlands team along with the Joint Venture partners OMV, Faroe Petroleum and Indemitsu for access to data along with permission to publish this study. PGS is thanked for access to the Corona Ridge Regional Geostreamer (CRRG) data and permission to publish the seismic line. The paper was improved thanks to insightful reviews by S. M. Jones and A. Saunders, which substantially improved an earlier draft. J. Still and F. Thompson gave invaluable technical support at the University of Aberdeen, and K. Wall helped with real-time cuttings analysis.Peer reviewedPostprin

Moho and basement depth in the NE Atlantic Ocean based on seismic refraction data and receiver functions

Seismic refraction data and results from receiver functions were used to compile the depth to the basement and Moho in the NE Atlantic Ocean. For interpolation between the unevenly spaced data points, the kriging technique was used. Free-air gravity data were used as constraints in the kriging process for the basement. That way, structures with little or no seismic coverage are still presented on the basement map, in particular the basins off East Greenland. The rift basins off NW Europe are mapped as a continuous zone with basement depths of between 5 and 15 km. Maximum basement depths off NE Greenland are 8 km, but these are probably underestimated. Plate reconstructions for Chron C24 (c. 54 Ma) suggest that the poorly known Ammassalik Basin off SE Greenland may correlate with the northern termination of the Hatton Basin at the conjugate margin. The most prominent feature on the Moho map is the Greenland–Iceland–Faroe Ridge, with Moho depths >28 km. Crustal thickness is compiled from the Moho and basement depths. The oceanic crust displays an increased thickness close to the volcanic margins affected by the Iceland plume

Regional Magma Plumbing and emplacement mechanisms of the Faroe-Shetland Sill Complex : Implications for magma transport and petroleum systems within sedimentary basins

Acknowledgement We extend our gratitude to the reviewers, Simon Kattenhorn and David Moy, whose careful reviews and comments greatly improved the paper. The editor is also thanked for clear guidance. This paper is dedicated to the memory of Dr Ken Thomson, who pioneered early work looking at intrusions within the Faroe-Shetland Basin. PGS are thanked for the generous donation of the FSB MegaSurveyPlus data set, which made this study possible, and for permission to publish this work. The Rosebank Joint Venture Project (Chevron North Sea Limited, OMV (U.K.) Limited, and DONG EandP (UK) Limited) is thanked for making Fig. 12 available. Spectral decomposition was carried out using Foster Findlay Associates’ (FFA) GeoTeric software. Seismic Interpretation was undertaken using IHS Kingdom Software. NS would like to acknowledge support and generous research funding for “Regional Emplacement of the Faroe-Shetland Sill Complex” from STATOIL FÆRØYENE AS, Chevron North Sea limited, Hess Limited, DONG E&P (U.K.) and OMV (U.K.) Limited. Richard Lamb, Steve Morse, Mike Keavney and David Iacopini are thanked for discussions and suggestions.Peer reviewedPostprin

Controls on the location of compressional deformation on the NW European margin

The distribution of Cenozoic compressional structures along the NW European margin has been compared with maps of the thickness of the crystalline crust derived from a compilation of seismic refraction interpretations and gravity modelling, and with the distribution of high-velocity lower crust and/or partially serpentinized upper mantle detected by seismic experiments. Only a subset of the mapped compressional structures coincide with areas susceptible to lithospheric weakening as a result of crustal hyperextension and partial serpentinization of the upper mantle. Notably, partially serpentinized upper mantle is well documented beneath the central part of the southern Rockall Basin, but compressional features are sparse in that area. Where compressional structures have formed but the upper mantle is not serpentinized, simple rheological modelling suggests an alternative weakening mechanism involving ductile lower crust and lithospheric decoupling. The presence of pre-existing weak zones (associated with the properties of the gouge and overpressure in fault zones) and local stress magnitude and orientation are important contributing factors

A review of the NE Atlantic conjugate margins based on seismic refraction data

The NE Atlantic region evolved through several rift episodes, leading to break-up in the Eocene that was associated with voluminous magmatism along the conjugate margins of East Greenland and NW Europe. Existing seismic refraction data provide good constraints on the overall tectonic development of the margins, despite data gaps at the NE Greenland shear margin and the southern Jan Mayen microcontinent. The maximum thickness of the initial oceanic crust is 40 km at the Greenland–Iceland–Faroe Ridge, but decreases with increasing distance to the Iceland plume. High-velocity lower crust interpreted as magmatic underplating or sill intrusions is observed along most margins but disappears north of the East Greenland Ridge and the Lofoten margin, with the exception of the Vestbakken Volcanic Province at the SW Barents Sea margin. South of the narrow Lofoten margin, the European side is characterized by wide margins. The opposite trend is seen in Greenland, with a wide margin in the NE and narrow margins elsewhere. The thin crust beneath the basins is generally underlain by rocks with velocities of >7 km s−1 interpreted as serpentinized mantle in the Porcupine and southern Rockall basins; while off Norway, alternative interpretations such as eclogite bodies and underplating are also discussed