| 1. |
- Barker, Abigail, et al.
(författare)
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Disequilibrium in historic volcanic rocks from Fogo, Cape Verde traces carbonatite metasomatism of recycled ocean crust
- 2023
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Ingår i: Lithos. - : Elsevier. - 0024-4937 .- 1872-6143. ; , s. 107328-107328
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Tidskriftsartikel (refereegranskat)abstract
- Fogo, Cape Verde, located upon thick oceanic lithosphere, provides a window into processes occurring in the mantle where recycled ocean crust in an upwelling mantle plume interacts with ambient mantle. Our objective is to investigate the nature of the lithologies of the mantle sources involved in the petrogenesis of historic volcanic rocks from Fogo. We observe enclaves and mingling textures in the lavas combined with oxygen isotope disequilibrium between olivine and clinopyroxene phenocrysts. Olivine δ18O values display positive correlations with Zr/Hf and Zr/Y and a negative correlation with U/Th, whereas clinopyroxene δ 18O values correlate positively with Ba/Nb. Heterogeneity between crystal populations and within the groundmass indicates that multiple magma batches are mixed beneath Fogo. In terms of mantle endmembers and source lithologies, a HIMU endmember was generated by melting of carbonated eclogite as indicated by low δ 18O values, Zr/Hf, Ba/Nb and high U/Th ratios. In contrast, we show the EM1 endmember has high δ 18O, Zr/Hf, Ba/Nb and low U/Th ratios, derived from melting of variably carbonated peridotite. Additionally, Ba/Th ratio are high, indicating that carbonatite melts have contributed to alkaline magma compositions at Fogo.
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| 2. |
- Bedard, Jean H., et al.
(författare)
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Basaltic sills emplaced in organic-rich sedimentary rocks : Consequences for organic matter maturation and Cretaceous paleo-climate
- 2024
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Ingår i: Geological Society of America Bulletin. - : Geological Society of London. - 0016-7606 .- 1943-2674. ; 136:5-6, s. 1982-2006
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Tidskriftsartikel (refereegranskat)abstract
- Many continental large igneous provinces coincide with climate perturbations and mass extinctions. When basaltic plumbing systems traverse carbon-rich sedimentary rocks, large volumes of greenhouse gases may be generated. We document how intrusive sills of the Mesozoic High Arctic Large Igneous Province affected surrounding fine-grained, organic-rich siliciclastic rocks of the Sverdrup Basin in the Canadian Arctic Archipelago. Petrographic and X-ray diffraction data from samples located near sills show the presence of high-temperature metamorphic phases (diopside, andalusite, garnet, and cordierite). Raman thermometry on organic matter yields peak temperatures of 385-400 degrees C near sill contacts, tailing off to far-field temperatures of <= 230 degrees C. Samples located >20 m from sills show no systematic change in vitrinite reflectance and have a VRo eq% value of similar to 2.5%, which indicates a temperature of similar to 210 degrees C. The finite element thermal modeling tool SUTRAHEAT was applied to the 17-m-thick Hare Sill, emplaced at 3 km depth at 1105 degrees C. SUTRAHEAT results show that contact-proximal rocks attain temperatures of >700 degrees C for a brief period (similar to 1 year). By 5 years, the Hare Sill is completely solidified (<730 degrees C), and the temperature anomaly collapses rapidly thereafter as the thermal pulse propagates outward. By 10 years, all rocks within 10 m of the Hare Sill are between 450 degrees C and 400 degrees C, rocks at 20 m from the contact attain 200 degrees C, yet far-field temperatures (>50 m) have barely changed. When multiple sills are emplaced between 4 km and 6 km depth, all rocks between sills reach similar to 250 degrees C after 100 years, showing that it is possible to raise regional-scale background temperatures by similar to 150 degrees C for the observed High Arctic Large Igneous Province sill density. Vitrinite reflectance data and pyrolysis results, together with SILLi thermal modeling, indicate that much of the hydrocarbon-generating potential was eliminated by High Arctic Large Igneous Province intrusions. The SILLi model yields similar to 20 tonnes/m(2) of organic equivalent CO2 (all carbon gas is reported as CO2) from the Hare Sill alone when emplaced into Murray Harbour Formation rocks with 5.7 wt% organic carbon, and similar to 226 tonnes/m(2) by emplacement of multiple sills throughout the 2-km-thick Blaa Mountain Group with 3 wt% organic carbon. On a basin scale, this yields a total of similar to 2550 Gt CO2 from the Hare Sill, with similar to 13,000 Gt CO2 being generated by the multiple sill scenario, similar to estimates from other large igneous provinces. Much of the Blaa Mountain Group rocks now have organic carbon contents of <1 wt%, which is consistent with large volumes of carbon-species gas having been generated, likely a mixture of CO2, CH4, and other species. However, organic-rich Murray Harbour Formation rocks show no obvious reduction in organic carbon content toward the Hare Sill intrusive contacts, which suggests that not all of the carbon was lost from the sedimentary package hosting High Arctic Large Igneous Province magmas. We suggest that some of the gas generated by contact metamorphism failed to drain out for lack of high-permeability conduits, and then back-reacted to form calcite cements and pyrobitumen during cooling.
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| 3. |
- Bedard, Jean H., et al.
(författare)
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Geochemical Systematics of High Arctic Large Igneous Province Continental Tholeiites from Canada-Evidence for Progressive Crustal Contamination in the Plumbing System
- 2021
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Ingår i: Journal of Petrology. - : Oxford University Press. - 0022-3530 .- 1460-2415. ; 62:9
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Tidskriftsartikel (refereegranskat)abstract
- Cretaceous High Arctic large igneous province (HALIP) sub-alkaline magmatic rocks in Canada are mostly evolved (MgO 2-7 wt%), sparsely plagioclase + clinopyroxene +/- olivine-phyric tholeiitic basalts. There were two main HALIP continental flood basalt (CFB) eruption episodes: 135-120 Ma (Isachsen Fm.) and 105-90 Ma (Strand Fiord Fm.), both associated with cogenetic doleritic sills and dykes. Building on a large modern database, 16 HALIP tholeiite types are defined and grouped into genetic series using Ce vs Sm/Yb-NMORB distributions. Comparison with model melting curves implies that higher-Sm/Yb HALIP basalt types record low-degree melting of garnet-bearing mantle sources. More voluminous intermediate- and low-Sm/Yb HALIP basalt types separated from the mantle at shallower levels after further extensive melting in the spinel-peridotite field. Within a given Sm/Yb range, increases in incompatible elements such as Ce are coupled with progressive clockwise rotation of normalized incompatible trace element profiles. Trace element modeling implies this cannot be due to closed-system fractional crystallization but requires progressive and ubiquitous incorporation of a component resembling continental crust. The fractionation models imply that low-Sm/Yb HALIP basalts (similar to 7 wt% MgO) initially crystallized olivine gabbro assemblages, with lower-MgO basalts successively crystallizing gabbro and ilmenite-gabbro assemblages. In contrast, higher-Sm/Yb basalts fractionated more clinopyroxene and ilmenite, but extensive plagioclase fractionation is still required to explain developing negative Sr-Eu anomalies. Backfractionation models require about 40% addition of olivine to bring the most primitive HALIP basalts (similar to 7% MgO) into equilibrium with Fo(89) mantle. Inverse fractionation-assimilation modeling shrinks the CFB signature, making decontaminated model parental melts more similar to enriched mid-ocean ridge basalt. The progressive increase of the contamination signature within each HALIP tholeiitic differentiation series is not consistent with models involving derivation of HALIP basalts from a mantle source previously enriched by subduction. Strong interaction of basalt with Sverdrup Basin sedimentary rocks may cause localized over-enrichment in K-Rb-Th-U, but cannot explain strong Ba enrichment in the absence of concomitant K-Rb-Th-U enrichment. The localized Ba enrichment could reflect either a Ba-rich lithospheric mantle component that is strongly manifested in the coeval HALIP alkaline suites, or syn- to post-emplacement fluid-mediated transfer from Ba-rich host rocks.
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| 4. |
- Bedard, Jean H., et al.
(författare)
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High Arctic Large Igneous Province Alkaline Rocks in Canada : Evidence for Multiple Mantle Components
- 2021
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Ingår i: Journal of Petrology. - : Oxford University Press. - 0022-3530 .- 1460-2415. ; 62:9
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Tidskriftsartikel (refereegranskat)abstract
- The Cretaceous High Arctic Large Igneous Province (HALIP) in Canada, although dominated by tholeiites (135-90 Ma), contains two main groups of alkaline igneous rocks. The older alkaline rocks (similar to 96 Ma) scatter around major fault and basement structures. They are represented by the newly defined Fulmar Suite alkaline basalt dykes and sills, and include Hassel Formation volcanic rocks. The younger alkaline group is represented by the Wootton Intrusive Complex (92.2-92.7 Ma), and the Audhild Bay Suite (83-73 Ma), both emplaced near the northern coast of Ellesmere Island. Fulmar Suite rocks resemble EM-type ocean island basalts (OIB) and most show limited crustal contamination. The Fulmar Suite shows increases of P2O5 at near-constant Ba-K-Zr-Ti that are nearly orthogonal to predicted fractionation- or melting-related variations, which we interpret as the result of melting composite mantle sources containing a regionally widespread apatite-bearing enriched component (P1). Low-P2O5 Fulmar Suite variants overlap compositionally with enriched HALIP tholeiites, and fall on common garnet Iherzolite trace element melting trajectories, suggesting variable degrees of melting of a geochemically similar source. High-P2O5 Hassel Formation basalts are unusual among Fulmar rocks, because they are strongly contaminated with depleted lower crust; and because they involve a high-P2O5-Ba-Eu mantle component (P2), similar to that seen in alkali basalt dykes from Greenland. The P2 component may have contained Ba-Eu-rich hawthorneite and/or carbonate minerals as well as apatite, and may typify parts of the Greenlandic sub-continental lithospheric mantle (SCLM). Mafic alkaline Audhild Bay Suite (ABS) rocks are volcanic and hypabyssal basanites, alkaline basalts and trachy-andesites, and resemble HIMU ocean island basalts in having high Nb, low Zr/Nb and low Sr-87/Sr-86(i). These mafic alkaline rocks are associated with felsic alkaline lavas and syenitic intrusions, but crustally derived rhyodacites and rhyolites also exist. The Wootton Intrusive Complex (WIC) contains geochemically similar plutonic rocks (alkali gabbros, diorites and anatectic granites), and may represent a more deeply eroded, slightly older equivalent of the ABS. Low-P2O5 ABS and WIC alkaline mafic rocks have flat heavy rare earth element (HREE) profiles suggesting shallow mantle melting; whereas High-P2O5 variants have steep HREE profiles indicating deeper separation from garnet-bearing residues. Some High-P2O5 mafic ABS rocks seem to contain the P1 and P2 components identified in Fulmar-Hassel rocks, whereas other samples trend towards possible High-P2O5 + Zr (PZr) and High-P2O5 + K2O (PK) components. We argue that the strongly alkaline northern Ellesmere Island magmas sampled mineralogically heterogeneous veins or metasomes in Greenlandic-type SCLM, which contained trace phases such as apatite, carbonates, hawthorneite, zircon, mica or richterite. The geographically more widespread apatite-bearing component (P1) could have formed part of a heterogeneous plume or upwelling mantle current that also generated HALIP tholeiites when melted more extensively, but may also have resided in the SCLM as relics of older events. Rare HALIP alkaline rocks with high K-Rb-U-Th fall on mixing paths implying strong local contamination from either Sverdrup Basin sedimentary rocks or granitic upper crust. However, the scarcity of potassic alkaline HALIP facies, together with the other trace element and isotopic signatures, provides little support for a ubiquitous fossil sedimentary subduction-zone component in the HALIP mantle source.
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| 5. |
- Bindeman, I. N., et al.
(författare)
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Diverse mantle components with invariant oxygen isotopes in the 2021 Fagradalsfjall eruption, Iceland
- 2022
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Ingår i: Nature Communications. - : Nature. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- The basalts of the 2021 Fagradalsfjall eruption were the first erupted on the Reykjanes Peninsula in 781 years and offer a unique opportunity to determine the composition of the mantle underlying Iceland, in particular its oxygen isotope composition (δ18O values). The basalts show compositional variations in Zr/Y, Nb/Zr and Nb/Y values that span roughly half of the previously described range for Icelandic basaltic magmas and signal involvement of Icelandic plume (OIB) and Enriched Mid-Ocean Ridge Basalt (EMORB) in magma genesis. Here we show that Fagradalsfjall δ18O values are invariable (mean δ18O = 5.4 ± 0.3‰ 2 SD, N = 47) and indistinguishable from “normal” upper mantle, in contrast to significantly lower δ18O values reported for erupted materials elsewhere in Iceland (e.g., the 2014–2015 eruption at Holuhraun, Central Iceland). Thus, despite differing trace element characteristics, the melts that supplied the Fagradalsfjall eruption show no evidence for 18O-depleted mantle or interaction with low-δ18O crust and may therefore represent a useful mantle reference value in this part of the Icelandic plume system.
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| 6. |
- Callegaro, S., et al.
(författare)
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Geochemistry of deep Tunguska Basin sills, Siberian Traps : correlations and potential implications for the end-Permian environmental crisis
- 2021
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Ingår i: Contributions to Mineralogy and Petrology. - : Springer Nature. - 0010-7999 .- 1432-0967. ; 176:7
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Tidskriftsartikel (refereegranskat)abstract
- A vast portion of the plumbing system of the Siberian Traps Large Igneous Province (STLIP) is emplaced in the Tunguska Basin, where borehole data reveal ubiquitous and abundant sills with great lateral extension. These intrusions intersect Cambrian-Ordovician evaporite, carbonate and siliciclastic series, and locally coal-bearing Permian host rocks, with a high potential for thermogenic gas generation. Here we present new geochemical data from 71 magmatic and 4 sedimentary rock samples from the Tunguska Basin center and periphery, recovered from 15 deep sills intercepted by boreholes. The studied samples are all low-Ti basalt and basaltic andesites, confirming absence of high-Ti and alkaline STLIP magmatism in the Tunguska Basin. The sills derive from picritic parental melts produced by extensive melting of a mantle source with recycled crustal components below a thinned lithosphere (50-60 km), within the spinel stability field. The mantle source was dominantly peridotitic, with enriched pyroxenitic domains formed by recycled lower crust, in agreement with previous models for the main tholeiitic STLIP phase. Limited amounts (up to 5%) of highly radiogenic granitoids or moderately radiogenic metapelites were assimilated in upper crustal magma reservoirs. After emplacement, sills intruded in Cambrian evaporites assimilated marlstones and interacted with the evaporitic host rocks, probably via fluids and brines. This is the first time that such process is described in subvolcanic rocks from all across the volcanic basin. The sills are correlated geochemically with the established chemostratigraphy for the on-craton STLIP lava piles and intrusions (Norilsk region). Sills correlated with the Morongovsky-Mokulaevsky Fm. and the Norilsk-type intrusions are the most voluminous, present all across the central Tunguska Basin, and bear the strongest evidence of interaction with evaporites. Massive discharge of thermogenic volatiles is suggested by explosive pipes and hydrothermal vent structures throughout the Tunguska Basin. We propose that this voluminous pulse of magmatism is a good candidate for the hitherto unidentified early intrusive phase of the STLIP, and may link the deep Tunguska basin sills to the end-Permian environmental crisis.
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| 7. |
- Darmawan, Herlan, et al.
(författare)
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Hidden mechanical weaknesses within lava domes provided by buried high-porosity hydrothermal alteration zones
- 2022
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Ingår i: Scientific Reports. - : Springer Nature. - 2045-2322. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Catastrophic lava dome collapse is considered an unpredictable volcanic hazard because the physical properties, stress conditions, and internal structure of lava domes are not well understood and can change rapidly through time. To explain the locations of dome instabilities at Merapi volcano, Indonesia, we combined geochemical and mineralogical analyses, rock physical property measurements, drone-based photogrammetry, and geoinformatics. We show that a horseshoe-shaped alteration zone that formed in 2014 was subsequently buried by renewed lava extrusion in 2018. Drone data, as well as geomechanical, mineralogical, and oxygen isotope data suggest that this zone is characterized by high-porosity hydrothermally altered materials that are mechanically weak. We additionally show that the new lava dome is currently collapsing along this now-hidden weak alteration zone, highlighting that a detailed understanding of dome architecture, made possible using the monitoring techniques employed here, is essential for assessing hazards associated with dome and edifice failure at volcanoes worldwide.
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| 8. |
- Day, James M. D., et al.
(författare)
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Mantle source characteristics and magmatic processes during the 2021 La Palma eruption
- 2022
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Ingår i: Earth and Planetary Science Letters. - : Elsevier. - 0012-821X .- 1385-013X. ; 597
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Tidskriftsartikel (refereegranskat)abstract
- The 2021 eruption of La Palma (September 19-December 13) was the first subaerial eruption in the Canary Islands in 50 years. Approximately 0.2 km3 of lava erupted from a newly formed, broadly basaltic composite volcanic edifice on the northwestern flank of the Cumbre Vieja volcanic ridge. Comprehensive sampling of the olivine-and clinopyroxene-phyric lavas over the eruption period reveals temporal changes in mineralogy and bulk rock geochemistry from tephrite to basanite. Initial tephrite lavas have low MgO (-6 wt.%) and elevated TiO2 (-4 wt.%) and contain amphibole crystals and gabbroic micro -xenoliths. In contrast, lavas with progressively more mafic compositions erupted to approximately day 20 of the eruption and thereafter remained as basanite (-8 wt.% MgO; 3.7 wt.% TiO2) until eruption termination. Temporal changes in lava chemistry reflect initial eruption of fractionated magmas that crystallized 5-10% olivine and clinopyroxene, as well as minor spinel, sulfide, and magnetite, followed by later eruption of deeper-sourced and more primitive magma. Vanadium-in-olivine oxybarometry indicates parental magmas were oxidized (fO2 = +1.5 to +2 FMQ) with 8.2 +/- 0.8 wt.% MgO and were generated from between 2.5-3% partial melting of a mantle source potentially containing a pyroxenite component (Xpx = 0.31 +/- 0.12). Day 1-20 tephrites have more radiogenic 187Os/188Os (0.143-0.148) and lower Pd, Pt, Ir and Os contents than post day 20 basanites (187Os/188Os = 0.141-0.145). Combined with available seismic data, the lavas provide a high-resolution record of eruptive evolution. Initial fractionated tephrite magma was stored in the upper lithosphere up to four years prior to eruption, consistent with pre-cursor seismicity and the presence of partially reacted amphibole and micro-xenoliths. The later lavas of the eruption were fed by more primitive basanitic parental magmas that were likely sourced from the deeper portion of the magma storage system that is underplating the island. Precursor events to the 2021 La Palma eruption involved seismicity and magma emplacement, storage and differentiation, which was followed by mobilisation, eruption, and eventual exhaustion of stored magma and partial melts. This magmatic progression is similar to that documented from the 1949 and 1971 Cumbre Vieja eruptions. Ocean islands with limited basaltic magma supply show similarities to the magmatic evolution observed in large silicic systems, where initial magma emplacement and differentiation is followed by later magma remobilisation that induces volcanic activity.
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| 9. |
- Dayton, Kyle, et al.
(författare)
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Deep magma storage during the 2021 La Palma eruption
- 2023
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 9:6
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Tidskriftsartikel (refereegranskat)abstract
- The 2021 La Palma eruption provided an unpreceded opportunity to test the relationship between earthquake hypocenters and the location of magma reservoirs. We performed density measurements on CO2-rich fluid in-clusions (FIs) hosted in olivine crystals that are highly sensitive to pressure via calibrated Raman spectroscopy. This technique can revolutionize our knowledge of magma storage and transport during an ongoing eruption, given that it can produce precise magma storage depth constraints in near real time with minimal sample prep-aration. Our FIs have CO2 recorded densities from 0.73 to 0.98 g/cm3, translating into depths of 15 to 27 km, which falls within the reported deep seismic zone recording the main melt storage reservoir.
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| 10. |
- Deegan, Frances, et al.
(författare)
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Age and Geochemistry of High Arctic Large Igneous Province Tholeiitic Magmatism in NW Axel Heiberg Island, Canada
- 2023
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Ingår i: Geochemistry Geophysics Geosystems. - : American Geophysical Union (AGU). - 1525-2027. ; 24:11
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Tidskriftsartikel (refereegranskat)abstract
- The Cretaceous High Arctic Large Igneous Province (HALIP) in Canada involved extrusion of continental flood basalts (CFBs) at 130-120 Ma and 100-95 Ma and emplacement of an extensive sill and dike network that intersected the Carboniferous to Paleogene Sverdrup Basin. In this paper, we present new Ar-40/Ar-39 ages, major and trace elements, and Sr-Nd-Pb isotope ratios for HALIP lava, dikes, and sills from Bukken Fiord, NW Axel Heiberg Island, Canadian Arctic Islands. Our best constrained Ar-40/(39) ages yield a weighted average of 124.1 +/- 1 (2 sigma) Ma, coincident with the first pulse of tholeiitic CFB magmatism in the Arctic-wide HALIP as exemplified by Isachsen Formation flood basalts on Axel Heiberg Island. The Bukken Fiord samples are plagioclase and clinopyroxene-phyric tholeiitic basalts, are relatively evolved (3.2-6.5 wt% MgO), and share similar major and trace element compositions to typical HALIP tholeiites. Initial Nd-143/Nd-144 ranges from 0.51260 to 0.51291 and initial Sr-87/Sr-86 ranges from 0.70362 to 0.70776, while measured Pb-206/Pb-204, Pb-207/Pb-204, and Pb-208/Pb-204 range from 18.614 to 19.199, 15.534 to 15.630, and 38.404 to 39.054, respectively. The most primitive sample in this study has Sr-Nd-Pb isotope signatures that suggest an enriched plume-derived mantle source for HALIP tholeiites. Most samples, however, possess relatively radiogenic isotope signatures that can be explained by moderate degrees of assimilation of Sverdrup Basin sedimentary rocks. Magma-crust interaction in the HALIP plumbing system was likely widespread and may have increased the environmental impact of the HALIP, particularly if crustal carbon was volatilized.
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