In the Bushveld complex of South Africa, the world's largest A-type granite (Nebo Granite) directly overlies the world's largest layered mafic intrusion (Rustenburg Layered Suite, RLS). For decades, Sr isotopes have been utilized to identify magma replenishment events and intervals of closed-system fractionation. Yet, the bulk rock Rb-Sr isotopes for the granites are known to be offset to unrealistically low age-corrected values, rendering direct comparisons to the RLS difficult. Here, we combine Sr isotopes for plagioclase feldspar measured by laser ablation (LA) ICP-MS with trace elements for bulk rock, clinopyroxene, amphibole and plagioclase and previously published bulk rock Sr isotopes across the mafic-felsic transition (Transition Zone) in the Bushveld complex. We show that the disturbance of bulk rock Sr isotope systematics coincides with the appearance of alkali feldspar and that the unrealistically low initial Sr isotopic values inferred from bulk rocks are not a feature of plagioclase. Instead, the Sr isotope compositions of plagioclase are very similar within uncertainty across the mafic-felsic transition. This supports a genetic link between mafic and felsic rocks. High initial 87Sr/86Sr values (at 2055 Ma) found for some plagioclase with high-Rb/Sr is likely an analytical artifact. We argue that the small spatial distance between undisturbed RLS diorites and disturbed granites precludes different thermal or hydrothermal histories for the two lithologies. Rather, we propose that the perthitic texture of alkali feldspar that existed during most of the Bushveld complex's more than 2 billion-year history made this phase more susceptible to Sr re-mobilization. Furthermore, the abundance of exsolved clinopyroxene and magnetite in rocks of the RLS Upper Zone that likely experienced similar hydrothermal conditions as the granite could have been the source of metals that mineralized the granites.

Abstract The mid‐Norwegian Margin, part of the North Atlantic Igneous Province (NAIP), is a well‐studied volcanic rifted margin formed during the breakup between Greenland and Eurasia ∼56 Ma, with the largest accumulation of magmatic material hosted by the Vøring Margin section. Despite extensive study in the area, the main controls on magmatic productivity during continental breakup remain debated. To constrain the drivers of breakup magmatism, we developed an inverse Monte Carlo statistical melting model that infers source mineralogy from basalt chemistry. When applied to basalts recently recovered on the Vøring Margin, our results reveal a clear shift in source mineralogy during rifting, with peak magmatism coinciding with clinopyroxene enrichment, despite mantle potential temperatures likely being capped below 1500°C. We also establish that, while the proto‐Iceland mantle plume played a role during the emplacement of the NAIP, the main driver for the continental breakup magmatism is lithospheric thinning as a consequence of continent breakup. This study provides new insights into the magmatic and geodynamic evolution of the mid‐Norwegian Margin, emphasizing the role of lithospheric refertilization in driving breakup magmatism.

The textures and chemistry of zircon in the Eocene Skaergaard intrusion, related to the East Greenland flood basalts and opening of the North Atlantic Ocean, are used to unravel a wide range of competing physicochemical processes in a shallow magma reservoir that cooled and crystallized as a closed system. This study involved detailed microscopy, SEM-cathodoluminescence imaging and LA-ICP-MS trace element analysis of zircon from mineral separates and directly in thin sections. Samples represent all major components of the Skaergaard intrusion, a suite of late granophyres and granophyric sills (Tinden, Sydtoppen), and hosting Precambrian gneiss. Zircon occurs primarily within interstitial crystalline pockets characterized by two distinct mineral assemblages that are related to crystallization from late-stage conjugate immiscible Si- and Fe-rich melts. Marked variations in zircon morphology occur throughout the intrusion. Large skeletal crystals, acicular needles, euhedral zircon with stubby or prismatic terminations, and wafer grains with feathery internal textures are typical of the Upper Border Series and Sandwich Horizon. In contrast, anhedral zircon with sector zoning is found throughout the Layered Series. Apatite, rutile, and thorite inclusions are abundant in Skaergaard zircon. Titanium-in-zircon temperatures for Skaergaard cumulates (total range = 579–861°C; Q1–Q3 = 711–777°C) and MELTS-modelled zircon saturation temperatures (790–845°C) for variable initial Zr concentrations indicate crystallization from highly fractionated near-solidus melts. The extremely variable abundance, morphology, and trace element chemistry (e.g. Th/U, Nb/Yb, Eu/Eu*, Ce/Nd, Yb/Dy) of Skaergaard zircon result from the combined effects of numerous processes. These include (1) crystallization of primocryst phases prior to zircon saturation, (2) extensive fractionation of interstitial melt, (3) late-stage liquid immiscibility in the consolidating cumulate pile, (4) disequilibrium crystallization triggered by late vapour saturation and volatile loss, (5) co-crystallization of accessory phases, and (6) secondary zircon growth as a result of the intrusion of the 660-m-thick Basistoppen sill above the just-solidified Sandwich Horizon. The remarkable morphological and geochemical diversity of zircon in the Skaergaard intrusion, unprecedented in the plutonic environment, demonstrates the critical role of distinct crystallization environments between the floor, walls, roof, and centre of the magma body during closed-system solidification of this sub-volcanic magma reservoir.

Throughout the Phanerozoic, temporal coincidence between Large Igneous Provinces (LIPs) and climate perturbations points to a potential causality via volcanic and thermogenic emissions. The best documented example of this association consists in the North Atlantic Igneous Province (NAIP) and the Paleocene–Eocene Thermal Maximum (PETM), which represents the most recent natural analogue for anthropogenic greenhouse gas emissions flux [1]. The NAIP extends from Greenland to the Scandinavian Peninsula and the British Isles, but the East Greenland margin preserves one of the most studied magmatic systems: the Skaergaard intrusion and its overlying 6-8 km thick lava pile, close to the centre of the province [2]. Melt and fluid inclusions within intrusive and effusive rock samples from East Greenland were screened and selected to investigate their volatile content by confocal Raman microspectroscopy. In the effusive rock samples, phenocrysts of olivine, clinopyroxene and sometimes plagioclase host primary melt inclusions containing gas bubbles. On the contrary, in the intrusive rock samples, most of primary melt inclusions within olivine crystals do not contain any gas bubble. However, in these rock samples, quartz often occurs as interstitial subhedral crystals or forms graphic textures with alkali feldspar, and hosts abundant multiphase (i.e., gaseous ± liquid ± solid phases) fluid inclusions. In general, the investigation of volatile species preserved by melt and fluid inclusions within magmatic minerals allows the reconstruction of volcanic and thermogenic emissions from LIPs [3; 4]. Here, we present preliminary data of this ongoing project that aims to constrain the role of volatiles from the NAIP in driving the synchronous PETM. [1] Jones et al. (2019), Nat. Commun. 10, 5547.[2] Larsen & Tegner (2006), Lithos 92, 181–197.[3] Capriolo et al. (2020), Nat. Commun. 11, 1670.[4] Capriolo et al. (2021), Nat. Commun. 12, 5534.

Large igneous provinces (LIPs) are thought to be the drivers of numerous Mesozoic episodes of dramatic environmental perturbation due to massive influx of volcanically sourced CO2 and subsequent enhanced global weathering rates. Two such episodes studied here are the Pliensbachian-Toarcian (Pl/To) event, closely followed by the Toarcian oceanic anoxic event (T-OAE), both of which have been temporally linked to eruption phases of the Karoo and Ferrar LIPs (KFLIP). Here we present high-precision platinum-group element (PGE) data for the sedimentary succession spanning across the Pl/To and the T-OAE from the Toarcian Global Stratotype Section and Point (GSSP) at Peniche, Portugal. The concentrations of PGEs peak across both Pl/To and the T-OAE, and correlate with Hg enrichment and negative carbon-isotope excursions reported from these intervals. They are also positively correlated with siliciclastic content (e.g., Al, Zr and Ti) and weathering proxy variations from these intervals (i.e., Os-187/Os-188 and Sr-87/Sr-86), although there are still enrichments in PGE/Al at both intervals. Pd/Ir and Pt/Ir ratios are slightly higher than in continental crust (similar to 30-80 for Peniche samples and similar to 22 for UCC), but similar to basalts from KFLIP. These observations, together with Hg concentrations, Os-187/Os-188 and Sr-87/Sr-86 ratios, are best explained by elevated continental weathering and additional volcanic input. These results support the hypothesis that KFLIP eruptions were responsible for both Pl/To and T-OAE, and further show that PGEs are a powerful proxy for fingerprinting volcanism and weathering.

The Danish subsurface ash series within the Eocene-aged Fur and Ølst Formations has a large theoretical CO2 storage capacity through carbon mineralisation, a potential that is the main motivation behind the C·ASH project initiated by researchers from the Department of Geoscience, Aarhus University. The potential carbon storage is achieved by injection of CO2 into the closely spaced volcanic ash beds in the Danish subsurface to accelerate silicate dissolution, leading to carbon fixation by mineralisation of CO2 as carbonate minerals. This provides a valuable alternative to conventional CO2 storage technologies that typically aim to store CO2 as a supercritical phase in deep porous aquifers. One of the essential requirements for the mineralisation technology is the identification of ash beds that contain enough reactive divalent cations (Ca2+, Fe2+, Mg2+) to sustain the silicate dissolution – carbonate precipitation reactions. This study aims to provide a geochemical proxy to identify and locate suitable ash beds with high CO2 sequestration potential. For this purpose, the shallow Harre borehole drilled in 1980 in northwestern Denmark is analysed using high-resolution XRF and SEM-EDS. In the Harre well the ash beds are most abundant within a five meters thick interval in the uppermost part of the Ølst Formation between 191 and 196 meters below surface. The XRF data show that titanium (Ti) is the most reliable elemental proxy for identifying the volcanic ash beds and that calcium (Ca), which is an important divalent cation for carbon mineralisation, is mostly enriched in the volcanic ash beds within the five meters interval. However, Ca may also be associated with gypsum (CaSO4·2H2O) and carbonates (CaCO3), suggesting that part of the Ca have already leached from silicates within the ash beds. This fraction is believed to be low and that the ash beds’ suitability for carbon mineralisation remain high.

A major outstanding question concerning the Bushveld Complex of South Africa is the genetic relationship between the granites (Lebowa Granite Suite, LGS) and granophyres (Rashoop Granophyre Suite, RGS), and their relation to the underlying layered mafic-ultramafic intrusion (Rustenburg Layered Suite, RLS). Here, we present new bulk rock major and trace elements, as well as Nd and Hf isotopes for 35 samples from the LGS (Nebo Granite) and RGS (Stavoren Granophyre and Zwartbank Pseudogranophyre) and combine this with published data to form a comprehensive dataset. The LGS and RGS range from ferroan to peraluminous compositions. Relative to the bulk continental crust, the granite and granophyres are depleted in Sc, V, Ti, P, Cr, and Sr, and either similar or enriched in other trace elements. epsilon Hf and epsilon Nd values (at 2055 Ma) show narrow ranges between -9.1 +/- 0.8 to -6.8 +/- 0.7 and - 6.0 +/- 0.3 to -5.1 +/- 0.6, respectively, across hundreds of kilometres, although higher epsilon Nd values have been reported previously (up to +5.2). These isotopic compositions correspond to published values for the RLS. Thus, the major element and isotopic composition as well as general trace element trends observed for LGS and RGS are consistent with derivation through fractional crystallization of basaltic magmas. A Rayleigh fractionation model for trace elements and major element mass balance suggest that c. 20% granite can be produced from fractional crystallization of such magmas. Multiple lines of evidence suggest that the granitic magmas mainly evolved in underlying, staging magma chambers rather than in the RLS chamber itself. This includes evidence for magma mixing in a newly identified transition zone separating RLS and LGS, the finding of zircon antecrysts in LGS and RGS, and the replenished and tapped nature of the RLS chamber.

Abstract While basaltic volcanism is dominant during rifting and continental breakup, felsic magmatism may be a significant component of some rift margins. During International Ocean Discovery Program (IODP) Expedition 396 on the continental margin of Norway, a graphite‐garnet‐cordierite bearing dacitic unit (the Mimir dacite) was recovered in two holes within early Eocene sediments on Mimir High (Site U1570), a marginal high on the Vøring Transform Margin. Here, we present a comprehensive textural, petrological, and geochemical study of the Mimir dacite in order to assess its origin and discuss the geodynamic implications. The major mineral phases (garnet, cordierite, quartz, plagioclase, alkali feldspar) are hosted in a fresh rhyolitic, vesicular, glassy matrix that is locally mingled with sediments. The major element chemistry of garnet and cordierite, the presence of zircon inclusions with inherited cores, and thermobarometric calculations all support an upper crustal metapelitic origin. While most magma‐rich margin models favor crustal anatexis in the lower crust, thermobarometric calculations performed here show that the Mimir dacite was produced at upper‐crustal depths (<5 kbar, 18 km depth) and high temperature (750–800°C) with up to 3 wt% water content. In situ U‐Pb analyses on zircon inclusions give a magmatic crystallization age of 54.6 ± 1.1 Ma, consistent with emplacement that post‐dates the Paleocene‐Eocene Thermal Maximum. Our results suggest that the opening of the Northeast Atlantic was associated with a phase of low‐pressure, high‐temperature crustal anatexis preceding the main phase of magmatism.

The Late Eocene-Oligocene post-breakup magmatism of the North Atlantic Igneous Province (NAIP) in East Greenland, is represented by sub-volcanic intrusions associated with a NE-SW oriented magmatic lineament, the Werner Bjerge Rift. This onshore magmatism extends for more than 100 km from eastern Traill & Oslash; to Werner Bjerge. In the same region, strike-slip post-breakup faulting is documented along N-S trending faults extending more than 300 km from Traill & Oslash; up to the north, along the Loch Fyne Fault Zone. Offshore East Greenland, the NW-SE trending East Jan Mayen Fracture Zone, has represented the northern boundary of the Jan Mayen Micro Continent in the Eocene-Oligocene, and extended westward, toward Traill & Oslash;. The Werner Bjerge Rift, the Loch Fyne Fault Zone and the East Jan Mayen Fracture Zone were active during the Late Eocene-Oligocene and intersected in eastern Traill & Oslash; with a 120 degrees angle, resembling a triple junction. This study presents the onshore deformation and magmatism associated with a failed triple junction that was active between 40 and 25 Ma, highlighting the importance of inherited structures in response to stress variations and plate tectonics modifications. The tectonic trends of the Fault-Fault-Ridge Traill & Oslash; triple junction are inherited structures from the Caledonian Orogeny and from multi-stage rifting episodes that characterized the East Greenland basin system since the Late Carboniferous. New age and geochemistry of the magmatism in the Werner Bjerge Rift, combined with structural analyses of fault systems suggest that the Traill & Oslash; triple junction was generated by plate tectonics configuration and not by a mantle plume. Triple junctions, the place where three tectonic plates meet, are often associated with mantle plumes. However, the hypothesis of divergent triple junctions linked to the initial doming of continental lithosphere above a mantle plume-head has been questioned by recent geological, geophysical, and numerical modeling studies. In this paper we describe structures and magmatism associated with a failed triple junction in Traill & Oslash; (East Greenland), that was active in the Late Eocene-Oligocene, between 40 and 25 Ma ago. The triple junction formed in the aftermath of mantle plume action within the North Atlantic Igneous Province and appears primarily controlled by lithosphere structure and inherited structural trends. The data indicate that pre-existing thermal and mechanical heterogeneities in the lithosphere could significantly impact the propagation, orientation, localization, and distribution of continental rifts and triple junctions. The N-S trending Loch Fyne Fault Zone, characterized by left-lateral strike slip faults, represents the failed arm of a triple junction The Werner Bjerg Rift is a Late Eocene-Oligocene failed rift characterized by alkaline magmatism similar to the East African rift Inherited structural trends, stress variations, and plate tectonics modifications primarily control the failed triple junction in Traill & Oslash;

Microscopic images of discrete samples were acquired using a scanning electron microscope (SEM) and captured as image files. These files were uploaded along with a brief description and a record of the microscopic conditions when the image was taken.

Figure F1.Multichannel Seismic Profile HV-7-96

The Palaeocene–Eocene Thermal Maximum (PETM) was a global warming event of 5–6 °C around 56 million years ago caused by input of carbon into the ocean and atmosphere. Hydrothermal venting of greenhouse gases produced in contact aureoles surrounding magmatic intrusions in the North Atlantic Igneous Province have been proposed to play a key role in the PETM carbon-cycle perturbation, but the precise timing, magnitude and climatic impact of such venting remains uncertain. Here we present seismic data and the results of a five-borehole transect sampling the crater of a hydrothermal vent complex in the Northeast Atlantic. Stable carbon isotope stratigraphy and dinoflagellate cyst biostratigraphy reveal a negative carbon isotope excursion coincident with the appearance of the index taxon Apectodinium augustum in the vent crater, firmly tying the infill to the PETM. The shape of the crater and stratified sediments suggests large-scale explosive gas release during the initial phase of vent formation followed by rapid, but largely undisturbed, diatomite-rich infill. Moreover, we show that these vents erupted in very shallow water across the North Atlantic Igneous Province, such that volatile emissions would have entered the atmosphere almost directly without oxidation to CO 2 and at the onset of the PETM.

Magnetic susceptibility was measured on whole-round sections (and rarely section halves) on the Whole-Round Multisensor Logger (WRMSL) and/or Special Task Multisensor Logger (STMSL) using a Bartington MS2 meter and a 90 mm or 80 mm MS2C loop. As volume of the sample is not controlled for this experiment, susceptibility units are recorded in instrument units and are not volume-corrected.

Laser ablation multi‐collector mass spectrometry (LA‐MC‐ICP‐MS) has emerged as the technique of choice for in situ measurements of Sr isotopes in geological minerals. However, the method poses analytical challenges and there is no widely adopted standardised approach to collecting these data or correcting the numerous potential isobaric inferences. Here, we outline practical analytical procedures and data reduction strategies to help establish a consistent framework for collecting and correcting Sr isotope measurements in geological materials by LA‐MC‐ICP‐MS. We characterise a new set of plagioclase reference materials, which are available for distribution to the community, and present a new data reduction scheme for the Iolite software package to correct isobaric interferences for different materials and analytical conditions. Our tests show that a combination of Kr‐baseline subtraction, Rb‐peak‐stripping using βRb derived from a bracketing glass reference material, and a CaCa or CaAr correction for plagioclase and CaCa or CaAr + REE2+ correction for rock glasses, yields the most accurate and precise 87Sr/86Sr measurements for these materials. Using the analytical and correction procedures outlined herein, spot analyses using a beam diameter of 100 μm or rastering with a 50–65 μm diameter beam can readily achieve < 100 ppm 2SE repeatability ("internal") precision for 87Sr/86Sr measurements for materials with < 1000 μg g‐1 Sr.

APC cores (N): 6 APC cores (N): 3 APC cores (N): 2 HLAPC cores (N): 1 HLAPC cores (N): 0 HLAPC cores (N): 0 XCB cores (N): 16 XCB cores (N): 7

The Skaergaard intrusion is a layered, ferrobasaltic intrusion emplaced during the Early Eocene into the rifting volcanic margin of East Greenland. The magma chamber crystallised in response to cooling from the roof and margins upwards and inward, forming upper, marginal and bottom series, the latter referred to as the Layered Series. The phase layering in the bottom series suggests an evolved, olivine-normative tholeiitic melt saturated in plagioclase and olivine, followed by augite, and then simultaneously by ilmenite and magnetite forming primocrysts. Pigeonite appears in the lower parts and continues until the centre of the series. Apatite appears in the upper part concurrently with liquid immiscibility. Cryptic variations of the individual primocrysts record a systematic upward increase in iron and decrease in magnesium for the mafic minerals and a systematic increase in sodium and decrease in calcium for plagioclase. The appearance of pigeonite is caused by reactions and crystallisation in the trapped melt and by subsolidus adjustments without this phase reaching liquidus saturation. The high mode of olivine at the base of the upper part with the appearance of apatite is interpreted to mark the onset of liquid immiscibility. This may have led to the separation of conjugate melts with granophyre migrating upward and the basic component largely staying stationary or sinking. Petrologic and geochemical observations indicate differentiation in the lower part of the intrusion, principally controlled by crystal fractionation with the efficiency of fractionation controlled by the evolution and escape of liquid from the solidifying mush. During the final stages of solidification, the onset of liquid immiscibility and termination of melt convection impeded differentiation. Modelling by perfect Rayleigh fractionation shows that major and included trace elements conform reasonably to observations, while excluded elements deviate from model predictions. This decoupling is caused by the mobility of a granophyre component formed in the trapped melt and in the main residual magma chamber. Consequently, the sampled gabbros may not be representative of the final solid-melt mush. By restoring the gabbros to their original mush compositions, it is possible to constrain granophyre migration pathways. We suggest that the granophyre formed in the trapped melt in the lower part of the intrusion mostly migrated laterally through pressure release pathways to form lenses and pockets with only limited upward migration into the main magma reservoir. Near the end stage of differentiation, the residual magma exsolved and formed complex mixtures of ferrobasaltic and granophyric melts. Estimates predict that a substantial amount of the granophyric melt penetrated as sills into the downward crystallising, upper part of the body as well as into the host rocks. The redistribution of granophyric melts within the solidifying crystal mush complicates predictions of trapped-melt content and mass-balance calculations but helps to explain apparent decoupling of included and excluded trace elements, especially towards the end stages of evolution. Final crystallisation was controlled mostly by in situ crystallisation leaving complex mixtures of ferrodiorite and granophyre components.

The end-Triassic mass extinction (ETME; c. 201.6 Ma), one of the so-called “big-five” mass extinctions in the Phanerozoic era, is associated with widespread marine anoxia, ocean acidification, global warming, carbon cycle perturbations (δ13C) and an extinction of diverse marine and terrestrial groups. This extinction is frequently linked to the volcanic activity in the Central Atlantic Magmatic Province (CAMP) which is often cited to explain e.g., the correlative negative carbon excursions across many sections, mutagenesis of land plants by Hg-toxicity, and enrichment of Hg/TOC. Despite this, the exact identification of a volcanic signal in many of these sections is not well constrained. In this study we present high-precision platinum group element (PGE: Ir, Ru, Pt, Pd) and Re data for the Triassic-Jurassic boundary succession at the Kuhjoch section (Austria). These are the first results from our new analytical setup using high-pressure asher digestion, isotope dilution and multi-collector inductively-coupled plasma mass spectrometry for precise determination in low concentration (e.g. ppt) samples such as sediments. The PGE and Re concentrations and patterns vary significantly with stratigraphy. The c. 13 m of clayey sediments above the onset of the extinction (marked by the c. 16 cm thick T-bed) show pronounced enrichment in Pt, Pd and Ir concentrations relative to the under- and overlying carbonate dominated stratigraphy. Their PGE patterns are non-chondritic with Pd/Ir and Pt/Ir similar to CAMP basalts. Normalised for lithology (Al2O3), however, there are no significant variations in Pt, Pd and Ir values below, within and above the clayey sediments. Re and Ru are, however, depleted compared to the other PGEs in the clayey interval, something also observed in some CAMP basalts. One possibility is therefore to interpret the PGE-rich, clayey sediments, including the main extinction interval in the basal portion, as recording increased weathering of CAMP basalts. As the PGE enrichment increases up through the T-bed, this could show that the onset of CAMP weathering and mass extinction would have therefore coincided. However, further work is needed to identify the relative role of CAMP volatile emission during volcanic activity versus post-eruption weathering of basalts.