North Atlantic Igneous Province Research Articles

Paleogene volcanic rocks in the northern Faroe–Shetland Basin and Møre Marginal High: understanding lava field stratigraphy

Abstract Onshore exposures of the North Atlantic Igneous Province have been studied in detail for over 200 years, whereas the more extensive offshore volcanic stratigraphy is significantly less well constrained with the exception of a small number of boreholes. Within this study we integrate seismic and well data across the northern Faroe–Shetland Basin and Møre Marginal High to improve understanding of the volcanic stratigraphy and its relationship to rifting in the NE Atlantic. Volcanic seismic facies, including compound and tabular lavas and hyaloclastites (representing subaerial and subaqueous emplacement), are interpreted across the study area, calibrated by the Lagavulin borehole. The volcanic sequence was erupted between c. 56.1 and 55.2 Ma, when subaerial conditions dominated in the region, but extensive lava deltas developed in a seaway east of the main lava field. Geochemical and thickness variations within the volcanic pile have important implications for the regional rifting history. MORB-like lavas at the base of Lagavulin, which thicken substantially northward, support an early onset of rifting near the Møre Marginal High prior to major thinning associated with continental breakup to the south and north. Following a period of erosion, smaller-degree melting caused the eruption of higher-TiO 2 /Zr lavas, marking the final ‘pre-breakup’ volcanism before emplacement of seaward-dipping reflectors.

Large Igneous Province thermogenic greenhouse gas flux could have initiated Paleocene-Eocene Thermal Maximum climate change

Large Igneous Provinces (LIPs) are associated with the largest climate perturbations in Earth’s history. The North Atlantic Igneous Province (NAIP) and Paleocene-Eocene Thermal Maximum (PETM) constitute an exemplar of this association. As yet we have no means to reconstruct the pacing of LIP greenhouse gas emissions for comparison with climate records at millennial resolution. Here, we calculate carbon-based greenhouse gas fluxes associated with the NAIP at sub-millennial resolution by linking measurements of the mantle convection process that generated NAIP magma with observations of the individual geological structures that controlled gas emissions in a Monte Carlo framework. These simulations predict peak emissions flux of 0.2–0.5 PgC yr–1 and show that the NAIP could have initiated PETM climate change. This is the first predictive model of carbon emissions flux from any proposed PETM carbon source that is directly constrained by observations of the geological structures that controlled the emissions.

Temporal evolution of primordial tungsten-182 and 3He/4He signatures in the Iceland mantle plume

Studies of short-lived radiogenic isotope systems and noble gas isotopic compositions of plume-derived rocks suggest the existence of primordial domains in Earth's present-day mantle. Tungsten-182 anomalies together with high 3He/4He in Phanerozoic rocks from large igneous provinces and ocean island basalts demonstrate the preservation of early-formed (within the first 60 Ma of solar system history) mantle domains tapped by modern mantle plumes. It has proven difficult to link the evidence for primordial domains with geochemical evidence for more recent processes, such as recycling. The Greenland-Iceland plume system, starting with eruptions of the Paleocene North Atlantic Igneous Province, is later manifested in the mid-Miocene to modern volcanic products of Iceland. Here, we report Pb isotopic compositions, μ182W (deviations in 182W/184W of a sample from a laboratory reference standard in parts per million), and 3He/4He, as well as highly siderophile element concentrations and Re-Os isotopic systematics of basaltic samples erupted at different times during the ~60 Ma history of the Greenland-Iceland plume. Paleocene samples from Greenland, representing the early stage of the mantle plume, are characterized by variable 3He/4He ranging from 7 to 48 R/RA (measured 3He/4He normalized to the atmospheric ratio) and an average μ182W of −4.0 ± 3.6 (2SD), within modern upper mantle-like values of 0 ± 4.5. The basalts from Iceland can be divided into two groups based on their Pb isotope compositions. One group, consisting mostly of Miocene basalts, is characterized by 206Pb/204Pb ranging from ~18.4 to 18.5, 3He/4He ranging from 17.8 to 40.2 R/RA, and μ182W values ranging from +1.7 to −9.1 ± 4.5. The other group, consisting mainly of Pleistocene and Holocene basalts, is characterized by higher 206Pb/204Pb, ranging from ~18.7 to 19.2, 3He/4He ranging from 7.9 to 25.7 R/RA, and μ182W values ranging from −0.6 to −11.7 ± 4.5. Collectively, the Greenland-Iceland suite examined requires mixing between a minimum of three mantle source domains characterized by distinct Pb-He-W isotopic compositions, in order to account for this range of isotopic data. The temporal changes in the isotopic data for these rocks appear to track the dominant contributing plume components as the system evolved. One of the domains is indistinguishable from the ambient upper oceanic mantle and contributed substantial material throughout the time progression. The other two domains are most likely primordial reservoirs that underwent limited de-gassing. Given the negative μ182W values in some rocks, one of these domains likely formed within the first 60 Ma of solar system history and is a major contributor to the youngest basalts. The isotopic characteristics of Greenland-Iceland plume-derived rocks reveal episodic changes in the source component proportions.

Two deep-mantle sources for Paleocene doming and volcanism in the North Atlantic

The North Atlantic Igneous Province (NAIP) erupted in two major pulses that coincide with the continental breakup and the opening of the North Atlantic Ocean over a period from 62 to 54 Ma. The unknown mantle structure under the North Atlantic during the Paleocene represents a major missing link in deciphering the geodynamic causes of this event. To address this outstanding challenge, we use a back-and-forth iterative method for time-reversed global convection modeling over the Cenozoic Era which incorporates models of present-day tomography-based mantle heterogeneity. We find that the Paleocene mantle under the North Atlantic is characterized by two major low-density plumes in the lower mantle: one beneath Greenland and another beneath the Azores. These strong lower-mantle upwellings generate small-scale hot upwellings and cold downwellings in the upper mantle. The upwellings are dispersed sources of magmatism and topographic uplift that were active on the rifted margins of the North Atlantic during the formation of the NAIP. While most studies of the Paleocene evolution of the North Atlantic have focused on the proto-Icelandic plume, our Cenozoic reconstructions reveal the equally important dynamics of a hot, buoyant, mantle-wide upwelling below the Azores.

A High‐Fidelity Benthic Stable Isotope Record of Late Cretaceous–Early Eocene Climate Change and Carbon‐Cycling

AbstractThe Late Cretaceous–Early Paleogene is the most recent period in Earth history that experienced sustained global greenhouse warmth on multimillion year timescales. Yet, knowledge of ambient climate conditions and the complex interplay between various forcing mechanisms are still poorly constrained. Here we present a 14.75 million‐year‐long, high‐resolution, orbitally tuned record of paired climate change and carbon‐cycling for this enigmatic period (~67–52 Ma), which we compare to an up‐to‐date compilation of atmospheric pCO2 records. Our climate and carbon‐cycling records, which are the highest resolution stratigraphically complete records to be constructed from a single marine site in the Atlantic Ocean, feature all major transient warming events (termed “hyperthermals”) known from this time period. We identify eccentricity as the dominant pacemaker of climate and the carbon cycle throughout the Late Maastrichtian to Early Eocene, through the modulation of precession. On average, changes in the carbon cycle lagged changes in climate by ~23,000 years at the long eccentricity (405,000‐year) band, and by ~3,000–4,500 years at the short eccentricity (100,000‐year) band, suggesting that light carbon was released as a positive feedback to warming induced by orbital forcing. Our new record places all known hyperthermals of the Late Maastrichtian–Early Eocene into temporal context with regards to evolving ambient climate of the time. We constrain potential carbon cycle influences of Large Igneous Province volcanism associated with the Deccan Traps and North Atlantic Igneous Province, as well as the sensitivity of climate and the carbon‐cycle to the 2.4 million‐year‐long eccentricity cycle.

Mercury anomalies across the Palaeocene–Eocene Thermal Maximum

Abstract. Large-scale magmatic events like the emplacement of the North Atlantic Igneous Province (NAIP) are often coincident with periods of extreme climate change such as the Palaeocene–Eocene Thermal Maximum (PETM). One proxy for volcanism in the geological record that is receiving increased attention is the use of mercury (Hg) anomalies. Volcanic eruptions are among the dominant natural sources of Hg to the environment; thus, elevated Hg∕TOC values in the sedimentary rock record may reflect an increase in volcanic activity at the time of deposition. Here we focus on five continental shelf sections located around the NAIP in the Palaeogene. We measured Hg concentrations, total organic carbon (TOC) contents, and δ13C values to assess how Hg deposition fluctuated across the PETM carbon isotope excursion (CIE). We find a huge variation in Hg anomalies between sites. The Grane field in the North Sea, the most proximal locality to the NAIP analysed, shows Hg concentrations up to 90 100 ppb (Hg∕TOC = 95 700 ppb wt %−1) in the early Eocene. Significant Hg∕TOC anomalies are also present in Danish (up to 324 ppb wt %−1) and Svalbard (up to 257 ppb wt %−1) sections prior to the onset of the PETM and during the recovery period, while the Svalbard section also shows a continuous Hg∕TOC anomaly during the body of the CIE. The combination with other tracers of volcanism, such as tephra layers and unradiogenic Os isotopes, at these localities suggests that the Hg∕TOC anomalies reflect pulses of magmatic activity. In contrast, we do not observe clear Hg anomalies on the New Jersey shelf (Bass River) or the Arctic Ocean (Lomonosov Ridge). This large spatial variance could be due to more regional Hg deposition. One possibility is that phreatomagmatic eruptions and hydrothermal vent complexes formed during the emplacement of sills led to submarine Hg release, which is observed to result in limited distribution in the modern era. The Hg∕TOC anomalies in strata deposited prior to the CIE may suggest that magmatism linked to the emplacement of the NAIP contributed to the initiation of the PETM. However, evidence for considerable volcanism in the form of numerous tephra layers and Hg∕TOC anomalies post-PETM indicates a complicated relationship between LIP volcanism and climate. Factors such as climate system feedbacks, changes to the NAIP emplacement style, and/or varying magma production rates may be key to both the onset and cessation of hyperthermal conditions during the PETM. However, processes such as diagenesis and organic matter sourcing can have a marked impact on Hg∕TOC ratios and need to be better constrained before the relationship between Hg anomalies and volcanic activity can be considered irrefutable.

A Mantle Plume Origin for the Scandinavian Dyke Complex: A “Piercing Point” for 615 Ma Plate Reconstruction of Baltica?

AbstractThe origin of Large Igneous Provinces (LIPs) associated with continental breakup and the reconstruction of continents older than ca. 320 million years (pre‐Pangea) are contentious research problems. Here we study the petrology of a 615–590 Ma dolerite dyke complex that intruded rift basins of the magma‐rich margin of Baltica and now is exposed in the Scandinavian Caledonides. These dykes are part of the Central Iapetus Magmatic Province (CIMP), a LIP emplaced in Baltica and Laurentia during opening of the Caledonian Wilson Cycle. The >1,000‐km‐long dyke complex displays lateral geochemical zonation from enriched to depleted basaltic compositions from south to north. Geochemical modelling of major and trace elements shows these compositions are best explained by melting hot mantle 75–250 °C above ambient mantle. Although the trace element modelling solutions are nonunique, the best explanation involves melting a laterally zoned mantle plume with enriched and depleted peridotite lithologies, similar to present‐day Iceland and to the North Atlantic Igneous Province. The origin of CIMP appears to have involved several mantle plumes. This is best explained if rifting and breakup magmatism coincided with plume generation zones at the margins of a Large Low Shear‐wave Velocity Province (LLSVP) at the core mantle boundary. If the LLSVPs are quasi‐stationary back in time as suggested in recent geodynamic models, the CIMP provides a guide for reconstructing the paleogeography of Baltica and Laurentia 615 million years ago to the LLSVP now positioned under the Pacific Ocean. Our results provide a stimulus for using LIPs as piercing points for plate reconstructions.

Contrasting TiO<sub>2</sub> Compositions in Early Cenozoic Mafic Sills of the Faroe Islands: An Example of Basalt Formation from Distinct Melting Regimes

The Paleocene lava succession of the Faroe Islands Basalt Group (FIBG), which is a part of the North Atlantic Igneous Province (NAIP), is intruded by numerous basaltic sills. These can be grouped into three main categories according to their geochemical characteristics: A low-TiO₂ sill category (TiO₂ = 0.7-0.9), a relatively high-TiO₂ sill category (TiO₂ = 1.95-2.6) and an intermediate-TiO₂ sill that displays major element compositions lying between the other two categories. Mantle normalised plots for the high-TiO₂ and low-TiO₂ sills display relatively uniform flat LREE trends and slightly steeper HREE slopes for high-TiO₂ relative to low-TiO₂ sills. The intermediate-TiO₂ Morskranes Sill is LREE depleted. Mantle normalised trace elements of low-TiO₂ sill samples define positive Eu and Sr anomalies, whereas high-TiO₂ sill samples display negative anomalies for these same lements. Different Nb and Ta anomalies (positive versus negative) in many high-TiO₂ versus low-TiO₂ sill samples suggest various metasomatism of their sources prior to partial melting. The intermediate-TiO₂ sill displays noticeably lower ⁸⁷Sr/⁸⁶Sr, ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb ratios relative to both the high-TiO₂ and the low-TiO₂ sill samples. Pb isotope compositions displayed by local contaminated basaltic lavas imply that some of these assimilated distinct crustal material from E Greenland or basement from NW Britain, while others probably assimilated only distinct E Greenland type of crustal material. A third crustal source of E Greenland or Rockall-type basement could be required in order to explain some of the range in lead isotopes displayed by the intermediate-TiO₂ Morskranes Sill. Geochemical modelling suggest that Faroese high-TiO₂ sills, could have formed by ~4 to 7.5% batch melting of moderately fertile lherzolites, while 16 to 21% batch melting fertile mantle sources could explain geochemical compositions of Faroese low-TiO₂ sills. The intermediate-TiO₂ sill samples could have formed by a range of 6 to 7% batch melting of a depleted mantle source, probably with a composition comparable to sources that gave rise to local low-TiO₂ and intermediate-TiO₂ host-rocks. Most Faroese sill samples probably developed outside the garnet stabilitry field and probably formed by batch melting of mantle materials comparable in composition to those reported for the sub-continental lithospheric mantle (SCLM) previously at depths of ≤ 85 km. Relative enrichments in LREE (and LILE in general), and their varying Nb and Ta anomalies point to sources affected by metasomatism.

Thinking about LIPs: A brief history of ideas in Large igneous province research

Large igneous provinces (LIPs) are extraordinary igneous and tectonic events that have influenced the planet in profound ways, including the major turnovers in the history of life. The LIP concept, definitions, and terminology first nucleated in a 1990 workshop jointly arranged by Joint Oceanographic Institutions and U.S. Science Support Program, subsequently presented in a series of seminal papers by Millard F. Coffin and Olav Eldholm in the early 1990's. They combined existing data and information from continental flood basalts with the emerging geophysical understanding of oceanic plateaus and rifted continental margins. The new terminology had major implications within the geosciences and beyond. However, when investigating how geoscientists described and interpreted these vast provinces prior to the 1990's, we are left with a series of questions. Who first realized that LIPs represent extraordinary events in the history of the Earth, what terminology was used, and why were geologists interested in this type of events? Here we discuss some of the key developments in LIP research, including mapping projects, expeditions, international programs, correlations across continents, and the history of the terminology. We focus our discussion on four cases, the Karoo LIP, the Siberian Traps, the North Atlantic Igneous Province, and the Ontong Java Plateau, comprising key examples of LIPs with long histories of study and exploration. We conclude that the past 150 years of LIP-related research and endeavor was largely driven by a need to understand fundamental aspects of Earth evolution, including continental drift, plate tectonic reconstructions, the origin of basalt, mantle processes and plumes, and the role of volcanism in driving mass extinctions and climatic changes.

LIP formation and protracted lower mantle upwelling induced by rifting and delamination

Large Igneous Provinces (LIPs) are commonly attributed to mantle plumes, hot upwellings from the deep lower mantle, apparently unrelated to plate motions. However, LIPs often form in association with rifting and breakup. Using numerical modelling, we introduce a novel idea that explains plume-like mantle upwelling by plate tectonic processes. Our model indicates that rifting-induced delamination of orogenic lithosphere can perturb the thermochemical mantle stratification and induce lower mantle upwelling which causes syn-rift LIP formation followed by protracted and enhanced mid ocean ridge basalt (MORB) generation. Our model provides an explanation for the geographical correlation between the Caledonian suture, the North Atlantic Igneous Province (NAIP) and present-day Icelandic magmatism.

The extraterrestrial impact evidence at the Palaeocene–Eocene boundary and sequence of environmental change on the continental shelf

We have identified clear evidence of an extraterrestrial impact within the onset of the carbon isotope excursion (CIE) that defines the Palaeocene-Eocene (P-E) boundary hyperthermal event (approx. 56 Ma) from several sites on the eastern Atlantic Coastal Plain and offshore. We review and update the state of the evidence for an impact at the P-E boundary, including a K-Ar cooling age of the ejecta that is indistinguishable from the depositional age at the P-E, which establishes the ejecta horizon as an isochronous stratigraphic indicator at the P-E. Immediately above the ejecta peak at the base of the coastal plain Marlboro Clay unit, we identify a sharp increase in charcoal abundance coincident with the previously observed dramatic increase in magnetic nanoparticles of soil pyrogenic origin. We therefore revisit the observed sequence of events through the P-E boundary on the western Atlantic Coastal Plain, showing that an extraterrestrial impact led to wildfires, landscape denudation and deposition of the thick Marlboro Clay, whose base coincides with the spherule horizon and CIE onset. The Sr/Ca ratio of the spherules indicates that the carbon responsible for the onset may be vaporized CaCO3 target rock mixed with isotopically light carbon from the impactor or elsewhere. Crucially, we do not argue that the impact was responsible for the full manifestation of the CIE observed globally (onset to recovery approx. 170 kyr), rather that a rapid onset was triggered by the impact and followed by additional carbon from other processes such as the eruption of the North Atlantic Igneous Province. Such a scenario agrees well with recent modelling work, though it should be revisited more explicitly.This article is part of a discussion meeting issue 'Hyperthermals: rapid and extreme global warming in our geological past'.

The Interplay Between the Eruption and Weathering of Large Igneous Provinces and the Deep‐Time Carbon Cycle

AbstractAlthough many sources of atmospheric CO2 have been estimated, the major sinks are poorly understood in a deep‐time context. Here we combine plate reconstructions, the eruption ages and outlines of Large Igneous Provinces (LIPs), and the atmospheric CO2 proxy record to investigate how their eruptions and weathering within the equatorial humid zone impacted global atmospheric CO2 since 400 Ma. Wavelet analysis reveals significant correlations between the eruption of the Emeishan LIP (259 Ma), the Siberian Traps (251 Ma), the Central Atlantic Magmatic Province (201 Ma), the second pulse of the North Atlantic Igneous Province (55 Ma), the High Arctic LIP (130 Ma), and the Deccan Traps (65 Ma) and perturbations in atmospheric CO2. Our analysis also reveals a clear relationship between the weathering of the Central Atlantic Magmatic Province (~200–100 Ma), the Deccan Traps (50–35 Ma), and the Afar Arabian LIP (30–0 Ma) and a significant atmospheric CO2 drawdown. Our results illustrate the significant role of subaerial LIP emplacement and weathering in modulating atmospheric CO2 and Earth's surface environments.

Environmental changes during the Cretaceous-Paleogene mass extinction and Paleocene-Eocene Thermal Maximum: Implications for the Anthropocene

The Cretaceous-Paleogene boundary (KPB) mass extinction (~66.02Ma) and the Paleocene-Eocene Thermal Maximum (PETM) (~55.8Ma) are two remarkable climatic and faunal events in Earth's history that have implications for the current Anthropocene global warming and rapid diversity loss. Here we evaluate these two events at the stratotype localities in Tunisia and Egypt based on climate warming and environmental responses recorded in faunal and geochemical proxies. The KPB mass extinction is commonly attributed to the Chicxulub impact, but Deccan volcanism appears as a major culprit. New mercury analysis reveals that major Deccan eruptions accelerated during the last 10ky and reached the tipping point leading up to the mass extinction. During the PETM, climate warmed rapidly by ~5°C, which is mainly attributed to methane degassing from seafloor sediments during global warming linked to the North Atlantic Igneous Province (NAIP). Biological effects were transient, marked by temporary absence of most planktic foraminifera due to ocean acidification followed by the return of the pre-PETM fauna and diversification. In contrast, the current rapid rise in atmospheric CO2 and climate warming are magnitudes faster than at the KPB or PETM events leading to predictions of a PETM-like response as best case scenario and rapidly approaching sixth mass extinction as worst-case scenario.

Discovery of a meteoritic ejecta layer containing unmelted impactor fragments at the base of Paleocene lavas, Isle of Skye, Scotland

Evidence for meteorite impacts in the geological record may include the presence of shocked minerals, spherule layers, and geochemical anomalies. However, it is highly unusual to find unmelted crystals from the actual impactor within an ejecta layer. Here we detail the first recorded occurrence of vanadium-rich osbornite (TiVN) on Earth, from two sites on Skye, northwest Scotland, which are interpreted as part of a meteoritic ejecta layer. TiVN has only previously been reported as dust from comet Wild 2, but on Skye it has been identified as an unmelted phase. Both ejecta layer sites also contain niobium-rich osbornite (TiNbN), which has not previously been reported. An extraterrestrial origin for these deposits is strongly supported by the presence of reidite (a high-pressure zircon polymorph), which is only found naturally at sites of meteorite impact. Barringerite [(Fe,Ni)2P], baddeleyite (ZrO2), alabandite (MnS), and carbon-bearing native iron spherules, together with planar deformation features and diaplectic glass in quartz, further support this thesis. We demonstrate through field relationships and Ar-Ar dating that the meteorite strike occurred during the mid-Paleocene. This is the first recorded mid-Paleocene impact event in the region and is coincident with the onset of magmatism in the British Palaeogene Igneous Province (BPIP). The Skye ejecta layer deposits provoke important questions regarding their lateral extent at the base of the BPIP and the possibility of their presence elsewhere beneath the much larger North Atlantic Igneous Province.

The ‘Clay-with-Flints’ deposit in Northern Ireland: reassessment of the evidence for an early Paleocene ignimbrite

AbstractReassessment of key geological sections, field relationships and petrographical characteristics of the Northern Ireland ‘Clay-with-Flints’ and ‘Donald's Hill Ignimbrite Formation’ show they formed dominantly by sedimentary processes. The involvement of a previously postulated pyroclastic flow during early Paleocene time is not recognized and, as such, the Donald's Hill Ignimbrite Formation stratigraphic term is discounted. Instead a multistage model of formation by sedimentary accumulation and remobilization is presented and the term Clay-with-Flints is retained. Regionally, two dominant facies are recognized in most Clay-with-Flints sections. Facies 1 was formed by an initial accumulation of flints on a chalk landscape undergoing karstification, and involved deposition of a clay matrix derived predominantly from contemporaneous erosion of subtropical soil horizons formed mainly on basalt. In Facies 2, evidence is observed for widespread remobilization of Facies 1 deposits by high-density mudflows driven by the advancement of the Antrim Lava Group, which caused the blockage of subsurface and marginalization of surface drainage. A stratigraphical constraint imposed by the presence of a supposed ignimbrite in this part of the North Atlantic Igneous Province has been problematic, but this is resolved by its identification as a diachronous, sedimentary deposit that formed until buried by either the lower or upper formations of the Antrim Lava Group.

Age and petrogenesis of the Lundy granite: Paleocene intraplate peraluminous magmatism in the Bristol Channel, UK

The Lundy granite forms part of the Lundy Igneous Complex, which is the southernmost substantive expression of magmatism within both the British Cenozoic Igneous Province and the wider North Atlantic Igneous Province. Its Qz + Pl + Kfs + Bt ± Grt ± Tpz mineralogy and peraluminous character contrast with other British Cenozoic Igneous Province granites farther north but are similar to the granites of the adjacent Early Permian Cornubian Batholith. We present the results of mapping, petrographical and mineral chemical analysis, and the first U–Pb zircon ages for the granite (59.8 ± 0.4 – 58.4 ± 0.4 Ma) and cross-cutting basic dykes (57.2 ± 0.5 Ma), which confirm a Paleocene age for magmatism. Zircon inheritance is limited but two cores imply the presence of Early Palaeozoic igneous rocks in the unexposed basement of SW England. The anomalous southerly location of the Lundy Igneous Complex is a consequence of mantle melting arising from the superimposition of localized lithospheric extension, related to intraplate strike-slip tectonics, with the distal ancestral Icelandic plume. Granite generation primarily reflects crustal partial melting during the emplacement of mantle-derived melts. The change in geochemical character between the Lundy granite (peraluminous) and other British Cenozoic Igneous Province granites (metaluminous or subalkaline) indicates a fundamental crustal source control between contrasting peri-Gondwanan and Laurentian basement provinces. Supplementary material: Sample locations, petrographic summaries, mineral chemistry data and secondary ionization mass spectrometry U–Pb analytical data are available at https://doi.org/10.6084/m9.figshare.c.3886783

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

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 0.5–15s, 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 2.5–7.0km depth beneath the Beinisvørð Formation, which is consistent with hyaloclastites of the Lopra Formation; (iv) an upper basement layer between depths of 5–9km and characterized by S wave velocities of approximately 3.2km/s, consistent with low-grade metamorphosed sedimentary rocks; (v) a high velocity basement, with S wave velocities in excess of 3.6km/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.

Mafic intrusions, hydrothermal venting, and the basalt-sediment transition: Linking onshore and offshore examples from the North Atlantic igneous province

The emplacement of large intrusive complexes into sedimentary basins can have profound effects on host sedimentary rocks including deformation, thermal aureole metamorphic reactions, alteration of fluid-flow pathways, and the formation of associated hydrothermal vent complexes (HVCs). These processes can in turn have major implications for petroleum systems on the local and regional scale, and can contribute to global climate change due to the production and outgassing of greenhouse gases, such as [Formula: see text] and [Formula: see text]. Imaging these features and assessing their implications from seismic data beneath extrusive volcanic cover is challenging due to heterogeneities in the volcanic pile and at the basalt-sediment transition. We have evaluated combined field and laboratory petrophysical data from the Isle of Skye, Scotland, where we identify a seismic-scale example of extensive intrusions interacting with the base-basalt transition. We have also evaluated a unique onshore example of a linked sill and associated HVC cutting up through the lava sequence. We compare these field results with HVCs from reflection seismic data across the Vøring Marginal High, offshore Norway, where subbasalt saucer-shaped intrusions are also seen associated with HVCs cutting the lava sequence. Seismic imaging problems associated with the velocity heterogeneity of volcanic sequences, along with a historical lack of high-quality 3D data in volcanic regions worldwide, is suggested as having largely precluded the identification of these features in the past. The under-representation of these hydrothermal vents in the literature has key implications for the future appraisal of intrusion-related outgassing effects on the global climate such as those related to the Palaeocene Eocene Thermal Maximum, along with subbasalt petroleum prospectivity where they may alter maturation and migration pathways.

Very large release of mostly volcanic carbon during the Palaeocene-Eocene Thermal Maximum.

Global warming during the Palaeocene-Eocene Thermal Maximum1,2 (PETM, ~56 Ma) is commonly interpreted as being primarily driven by the destabilization of carbon from surficial sedimentary reservoirs such as methane hydrates3. However, the source(s) of carbon remain controversial1,3–5. Resolving this is key to understanding the proximal cause, as well as quantifying the roles of triggers versus feedbacks in driving the event. Here we present new boron isotope data – a proxy for seawater pH – that demonstrate the occurrence of persistently suppressed surface ocean pH across the PETM. Our pH data, alongside a paired carbon isotope record, are assimilated in an Earth system model to reconstruct the unfolding carbon cycle dynamics across the event6,7. We find strong evidence for a much larger (>10,000 PgC) and on average isotopically heavier carbon source than considered previously8,9. This leads us to identify volcanism associated with the North Atlantic Igneous Province, rather than carbon from a surficial reservoir, as the main driver of the PETM10,11. We also find that, although amplifying organic carbon feedbacks with climate likely played only a subordinate role in driving the event, enhanced organic matter burial was important in ultimately sequestering the released carbon and accelerating the recovery of the Earth system12.

A new tectono-magmatic model for the Lofoten/Vesterålen Margin at the outer limit of the Iceland Plume influence

The Early Eocene continental breakup was magma-rich and formed part of the North Atlantic Igneous Province. Extrusive and intrusive magmatism was abundant on the continental side, and a thick oceanic crust was produced up to a few m.y. after breakup. However, the extensive magmatism at the Vøring Plateau off mid-Norway died down rapidly northeastwards towards the Lofoten/Vesterålen Margin. In 2003 an Ocean Bottom Seismometer profile was collected from mainland Norway, across Lofoten, and into the deep ocean. Forward/inverse velocity modeling by raytracing reveals a continental margin transitional between magma-rich and magma-poor rifting. For the first time a distinct lower-crustal body typical for volcanic margins has been identified at this outer margin segment, up to 3.5km thick and ∼50km wide. On the other hand, expected extrusive magmatism could not be clearly identified here. Strong reflections earlier interpreted as the top of extensive lavas may at least partly represent high-velocity sediments derived from the shelf, and/or fault surfaces. Early post-breakup oceanic crust is moderately thickened (∼8km), but is reduced to 6km after 1m.y. The adjacent continental crystalline crust is extended down to a minimum of 4.5km thickness. Early plate spreading rates derived from the Norway Basin and the northern Vøring Plateau were used to calculate synthetic magnetic seafloor anomalies, and compared to our ship magnetic profile. It appears that continental breakup took place at ∼53.1Ma, ∼1m.y. later than on the Vøring Plateau, consistent with late strong crustal extension. The low interaction between extension and magmatism indicates that mantle plume material was not present at the Lofoten Margin during initial rifting, and that the observed excess magmatism was created by late lateral transport from a nearby pool of plume material into the lithospheric rift zone at breakup time.