| 1. |
- Andersson, Stefan S., et al.
(författare)
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Apatite as a tracer of the source, chemistry and evolution of ore-forming fluids : The case of the Olserum-Djupedal REE-phosphate mineralisation, SE Sweden
- 2019
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Ingår i: Geochimica et Cosmochimica Acta. - : PERGAMON-ELSEVIER SCIENCE LTD. - 0016-7037 .- 1872-9533. ; 255, s. 163-187
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Tidskriftsartikel (refereegranskat)abstract
- This study explores the suitability of apatite as a tracer of the source(s), chemistry, and evolution of ore-forming hydrothermal fluids. This is tested by analysing the halogen (F, Cl, Br, and I), stable Cl isotopic, and trace element compositions of fluorapatite from the regional-scale Olserum-Djupedal rare earth element (REE) phosphate mineralisation in SE Sweden, which is dominated by monazite-(Ce), xenotime-(Y), and fluorapatite. The primary hydrothermal fluid flow system is recorded in a sequence from proximal granite-hosted to distal metasediment-hosted fluorapatite. Along this sequence, primary fluorapatite shows a gradual increase of Cl and Br concentrations and in (Gd/Yb)N, a decrease of F and I concentrations, a decrease in δ37Cl values, in (La/Sm)N, and partly in (La/Yb)N and (Y/Ho)N. Local compositional differences of halogen and trace element concentrations have developed along rims and in domains adjacent to fractures of fluorapatite due to late-stage partial reaction with fracture fluids. These differences are insignificant compared to the larger deposit-scale zoning. This suggests that apatite can retain the primary record of the original ore-forming fluid despite later overprinting fluid events. The agreement between Br/Cl and I/Cl ratios of apatite and those of co-existing fluid inclusions at lower temperatures indicates that only a minor fractionation of Br from I occurs during apatite precipitation. The halogen ratios of apatite can thus be used as a first-order estimate for the composition of the ore-forming fluid. Taking the small fractionation factors for Cl isotopes between apatite and co-existing fluid at high temperatures into account, we propose that the Cl isotopic composition of apatite and the halogen ratios derived from the apatite composition can be used jointly to trace the source(s) of ore-forming fluids. By contrast, most trace elements incorporated in apatite are affected by the host rock environment and by fluid-mineral partitioning due to growth competition between co-crystallising minerals. Collectively, apatite is sensitive to changing fluid compositions, yet it is also able to record the character of primary ore-forming fluids. Thus, apatite is suitable for tracing the origin, chemistry, and evolution of fluids in hydrothermal ore-forming settings.
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| 2. |
- Budd, David A., et al.
(författare)
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Magma reservoir dynamics at Toba caldera, Indonesia, recorded by oxygen isotope zoning in quartz
- 2017
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- Quartz is a common phase in high-silica igneous rocks and is resistant to post-eruptive alteration, thus offering a reliable record of magmatic processes in silicic magma systems. Here we employ the 75 ka Toba super-eruption as a case study to show that quartz can resolve late-stage temporal changes in magmatic δ18O values. Overall, Toba quartz crystals exhibit comparatively high δ18O values, up to 10.2‰, due to magma residence within, and assimilation of, local granite basement. However, some 40% of the analysed quartz crystals display a decrease in δ18O values in outermost growth zones compared to their cores, with values as low as 6.7‰ (maximum ∆core−rim = 1.8‰). These lower values are consistent with the limited zircon record available for Toba, and the crystallisation history of Toba quartz traces an influx of a low-δ18O component into the magma reservoir just prior to eruption. Here we argue that this late-stage low-δ18O component is derived from hydrothermally-altered roof material. Our study demonstrates that quartz isotope stratigraphy can resolve magmatic events that may remain undetected by whole-rock or zircon isotope studies, and that assimilation of altered roof material may represent a viable eruption trigger in large Toba-style magmatic systems.
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| 3. |
- Connelly, J. N., et al.
(författare)
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Calibrating volatile loss from the Moon using the U-Pb system
- 2022
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier. - 0016-7037 .- 1872-9533. ; 324, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- Previous isotope studies of lunar samples have demonstrated that volatile loss was an important part of the early history of the Moon. The radiogenic U-Pb system, where Pb has a significantly lower T50% condensation temperature than U, has the capacity to both recognize and calibrate the extent of volatile loss but this approach has been hindered by terrestrial Pb contamination of samples. We employ a novel method that integrates analyses of individual samples by Ion Microprobe and Thermal Ionization mass spectrometry to correct for ubiquitous common Pb contamination, a method that results in significantly higher estimates for mu-values (238U/204Pb) than previously reported. Using this method, six of seven samples of low-Ti basaltic meteorites return mu-values between 1900 and 9600, values that are consistent with a re-evaluation of published results that return mu-values of 510-2900 for both low-and high-Ti basalts. While some degree of fractionation during partial melting may increase mu-values, we infer that the source region(s) for the basalts must also have had elevated mu-values by the time the lunar magma ocean solidified. Models to account for the available initial Pb isotopic compositions of lunar basalts in light of timing constraints from thermal modelling imply that their source regions had a mu-value of at least 280, consistent with the elevated mu-values of lunar basalts and that inferred for their sources. Such high mu-values are attributed to the preferential loss of more than 99% of the Pb over U relative to a precursor with a Mars-like composition in the aftermath of the giant impact. Such an extensive loss of Pb is consistent with previously reported losses of other elements with comparable volatility, namely Zn, Rb, Ga and CrO2. Finally, our modelling of highly-radiogenic lunar Pb isotopes assuming crystallization of the lunar magma ocean over 100s of millions of years shows that the elevated mu-values allows for, but does not require, a young Moon formation age.
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| 4. |
- Deegan, Frances, et al.
(författare)
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Boron isotope fractionation in magma via crustal carbonate dissolution.
- 2016
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 6
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Tidskriftsartikel (refereegranskat)abstract
- Carbon dioxide released by arc volcanoes is widely considered to originate from the mantle and from subducted sediments. Fluids released from upper arc carbonates, however, have recently been proposed to help modulate arc CO2 fluxes. Here we use boron as a tracer, which substitutes for carbon in limestone, to further investigate crustal carbonate degassing in volcanic arcs. We performed laboratory experiments replicating limestone assimilation into magma at crustal pressure-temperature conditions and analysed boron isotope ratios in the resulting experimental glasses. Limestone dissolution and assimilation generates CaO-enriched glass near the reaction site and a CO2-dominated vapour phase. The CaO-rich glasses have extremely low δ11B values down to −41.5‰, reflecting preferential partitioning of 10B into the assimilating melt. Loss of 11B from the reaction site occurs via the CO2 vapour phase generated during carbonate dissolution, which transports 11B away from the reaction site as a boron-rich fluid phase. Our results demonstrate the efficacy of boron isotope fractionation during crustal carbonate assimilation and suggest that low δ11B melt values in arc magmas could flag shallow-level additions to the subduction cycle.
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| 5. |
- Deegan, Frances M., et al.
(författare)
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Pyroxene standards for SIMS oxygen isotope analysis and their application to Merapi volcano, Sunda arc, Indonesia
- 2016
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Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 447, s. 1-10
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Tidskriftsartikel (refereegranskat)abstract
- Measurement of oxygen isotope ratios in common silicate minerals such as olivine, pyroxene, feldspar, garnet, and quartz is increasingly performed by Secondary Ion Mass Spectrometry (SIMS). However, certain mineral groups exhibit solid solution series, and the large compositional spectrum of these mineral phases will result in matrix effects during SIMS analysis. These matrix effects must be corrected through repeated analysis of compositionally similar standards to ensure accurate results. In order to widen the current applicability of SIMS to solid solution mineral groups in common igneous rocks, we performed SIMS homogeneity tests on new augite (NRM-AG-1) and enstatite (NRM-EN-2) reference materials sourced from Stromboli, Italy and Webster, North Carolina, respectively. Aliquots of the standard minerals were analysed by laser fluorination (LF) to establish their δ18O values. Repeated SIMS measurements were then performed on randomly oriented fragments of the same pyroxene crystals, which yielded a range in δ18O less than ± 0.42 and ± 0.58‰ (2σ) for NRM-AG-1 and NRM-EN-2, respectively. Homogeneity tests verified that NRM-AG-1 and NRM-EN-2 do not show any crystallographic orientation bias and that they are sufficiently homogeneous on the 20 μm scale to be used as routine mineral standards for SIMS δ18O analysis. We subsequently tested our new standard materials on recently erupted pyroxene crystals from Merapi volcano, Indonesia. The δ18O values for Merapi pyroxene obtained by SIMS (n = 204) agree within error with the LF-derived δ18O values for Merapi pyroxene but differ from bulk mineral and whole-rock data obtained by conventional fluorination. The bulk samples are offset to higher δ18O values as a result of incorporation of mineral and glass inclusions that in part reflects crustal contamination processes. The Merapi pyroxene SIMS data, in turn, display a frequency peak at 5.8‰, which allows us to estimate the δ18O value of the primary mafic magma at Merapi to ~ 6.1‰ when assuming closed system differentiation.
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| 6. |
- Fassmer, K., et al.
(författare)
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Middle Ordovician subduction of continental crust in the Scandinavian Caledonides - an example from Tjeliken, Seve Nappe Complex, Sweden.
- 2017
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Ingår i: Contributions to Mineralogy and Petrology. - : Springer Science and Business Media LLC. - 0010-7999 .- 1432-0967. ; 172
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Tidskriftsartikel (refereegranskat)abstract
- The Seve Nappe Complex of the Scandinavian Caledonides is thought to be derived from the distal passive margin of Baltica which collided with Laurentia in the Scandian Phase of the Caledonian Orogeny at 430–400 Ma. Parts of the Seve Nappe Complex were affected by pre-Scandian high- and ultrahigh-pressure metamorphism, in a tectonic framework that is still unclear, partly due to uncertainties about the exact timing. Previous age determinations yielded between ~ 505 and ~ 446 Ma, with a general trend of older ages in the North (Norrbotten) than in the South (Jämtland). New age determinations were performed on eclogite and garnet–phengite gneiss at Tjeliken in northern Jämtland. Thermodynamic modelling yielded peak metamorphic conditions of 25–27 kbar/680–760 °C for the garnet–phengite gneiss, similar to published peak metamorphic conditions of the eclogite (25–26 kbar/650–700 °C). Metamorphic rims of zircons from the garnet–phengite gneiss were dated using secondary ion mass spectrometry and yielded a concordia age of 458.9 ± 2.5 Ma. Lu–Hf garnet-whole rock dating yielded 458 ± 1.0 Ma for the eclogite. Garnet in the eclogite shows prograde major-element zoning and concentration of Lu in the cores, indicating that this age is related to garnet growth during pressure increase, i.e. subduction. The identical ages from both rock types, coinciding with published Sm–Nd ages from the eclogite, confirm subduction of the Seve Nappe Complex in Northern Jämtland during the Middle Ordovician in a fast subduction–exhumation cycle.
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| 7. |
- Ivarsson, Magnus, et al.
(författare)
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Exceptional Preservation of Fungi as H2-Bearing Fluid Inclusions in an Early Quaternary Paleo-Hydrothermal System at Cape Vani, Milos, Greece
- 2019
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Ingår i: Minerals. - : MDPI. - 2075-163X. ; 9:12, s. 1-33
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Tidskriftsartikel (refereegranskat)abstract
- The production of H-2 in hydrothermal systems and subsurface settings is almost exclusively assumed a result of abiotic processes, particularly serpentinization of ultramafic rocks. The origin of H-2 in environments not hosted in ultramafic rocks is, as a rule, unjustifiably linked to abiotic processes. Additionally, multiple microbiological processes among both prokaryotes and eukaryotes are known to involve H-2-production, of which anaerobic fungi have been put forward as a potential source of H-2 in subsurface environments, which is still unconfirmed. Here, we report fungal remains exceptionally preserved as fluid inclusions in hydrothermal quartz from feeder quartz-barite veins from the Cape Vani Fe-Ba-Mn ore on the Greek island of Milos. The inclusions possess filamentous or near-spheroidal morphologies interpreted as remains of fungal hyphae and spores, respectively. They were characterized by microthermometry, Raman spectroscopy, and staining of exposed inclusions with WGA-FITC under fluorescence microscopy. The spheroidal aqueous inclusions interpreted as fungal spores are unique by their coating of Mn-oxide birnessite, and gas phase H-2. A biological origin of the H-2 resulting from anaerobic fungal respiration is suggested. We propose that biologically produced H-2 by micro-eukaryotes is an unrecognized source of H-2 in hydrothermal systems that may support communities of H-2-dependent prokaryotes.
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| 8. |
- Jastrzebski, Miroslaw, et al.
(författare)
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Geochronology, petrogenesis and geodynamic significance of the Visean igneous rocks in the Central Sudetes, northeastern Bohemian Massif
- 2018
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Ingår i: Lithos. - : Elsevier BV. - 0024-4937 .- 1872-6143. ; 316-317, s. 385-405
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Tidskriftsartikel (refereegranskat)abstract
- New sensitive high-resolution ion microprobe (SHRIMP) UPb zircon geochronologic data, whole-rock geochemical and Sr-Nd-Pb isotopic data, and zircon and quartz Ύ18O isotopic data from the Staré Město granitoids (SMG), Jawornik granitoids (JG), and Kłodzko-Złoty Stok granitoids (KZSG) and associated mafic and ultramafic rocks are examined. This study provides new insights into the processes of magma generation, transport and emplacement during the Variscan development of the contact zone of the Saxothuringia, Teplá-Barrandia and Brunovistulia in the Central European portion of the Variscan belt. The results of this study, combined with existing geochemical and isotopic data, imply that the parental magmas of these intrusions share a close affinity and suggest that these intrusions formed in a subduction-related tectonic setting. The SMG, JG and KZSG magmas represent hybrids that formed from the contamination of partial melts from the lower crust and/or subducted sediments with various proportions of enriched mantle-derived melts. These mainly sheeted plutons intruded along the main geological boundaries during the Visean and recorded the vertical and lateral displacements between the major tectono-stratigraphic units (microplates) in the NE Bohemian Massif. In the Central Sudetes, these granitoid magmas were first emplaced along the northern continuation of the Moldanubian Zone. The SHRIMP UPb dating of zircons indicates that the SMG intruded the reactivated suture zone between the Brunovistulia and Saxothuringia at 344–341 Ma. Sills of the JG were emplaced between c. 347 and c. 334 Ma. The composite Kłodzko-Złoty Stok Pluton, which includes the KZSG and accompanying mafic enclaves and pyroxenite and lamprophyre dykes, was mainly emplaced at 340–333 Ma. The magmas of the KZSG possibly facilitated the final amalgamation of the Sudetic counterparts of the Teplá-Barrandia and Saxothuringia microplates during the orogenic uplift of the latter. Petrologic and oxygen isotopic data further indicate partial post-magmatic hydrothermal and/or alteration processes. Our new data further stress the connection of magma transfer and active shear zones, which could manifest as crustal-scale magma-ascent conduits.
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| 9. |
- Nemchin, A. A., et al.
(författare)
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U-Pb isotope systematics and impact ages recorded by a chemically diverse population of glasses from an Apollo 14 lunar soil
- 2022
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier. - 0016-7037 .- 1872-9533. ; 321, s. 206-243
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Tidskriftsartikel (refereegranskat)abstract
- Glass beads formed by ejection of impact-melted lunar rocks and soils are an important component of lunar soils. These glasses range from 100s of microns to up to a few cm in diameter and contain variable, but usually relatively low (several hundred ppb to a few ppm), quantities of U. Because Pb is a volatile element, it tends to be lost from the melts, so individual impact glasses can be dated by the U-Th-Pb isotopic systems. The presence of two additional Pb components in lunar glasses, likely linked to addition of lunar Pb to the beads during their residence on the lunar surface and from terrestrial laboratory contamination, require corrections to the data before accurate formation ages of the glasses can be determined. Here we report a U-Th-Pb isotopic and geochemical study of impact glasses from the Apollo 14 soil 14163, which documents multiple impacts into chemically diverse targets that can be linked to the main groups of rocks found on the Moon, i.e., mare basalts, highlands plagioclase-rich rocks, and KREEP (from high contents of K, REE and P) enriched rocks. The impact ages show a bimodal distribution with peaks at ~3500-3700 Ma and < 1000 Ma, similar to that obtained previously by Ar-40-Ar-39 dating of other suites of lunar regolith glasses. Our data suggest two predominant age peaks at ~100 Ma and ~500 Ma, with other statistically definable clusters of ages also possible. As Pb is relatively resistant to subsolidus diffusive loss in these glasses, the age clusters probably represent primary formation ages during impact events, although processes such as preferential preservation of young glasses and impact conditions necessary for production of regolith glasses need further quantification. (C) 2021 The Authors. Published by Elsevier Ltd.
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| 10. |
- Svedäng, Henrik, et al.
(författare)
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Compensatory Feeding in Eastern Baltic Cod (Gadus morhua) : Recent Shifts in Otolith Growth and Nitrogen Content Suggest Unprecedented Metabolic Changes
- 2020
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Ingår i: Frontiers in Marine Science. - : FRONTIERS MEDIA SA. - 2296-7745. ; 7
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Tidskriftsartikel (refereegranskat)abstract
- The productivity of the Eastern Baltic cod (EBC) has been severely reduced over the last 25 years, for reasons that remain unclear. The size distribution of EBC has become increasingly truncated, condition and health status have deteriorated, and sexual maturation has started to occur at increasingly smaller sizes. Despite an increasing trend in recruitment during this period, reduced growth or increased mortality rates after the recruitment phase have resulted in decreasing landing levels and low profitability in the cod fishery, whereas the scientific community has difficulties in disentangling the causes of the decline of EBC. We studied changes in metabolic status in EBC between the capture years of 1995 and 2015, by investigating two aspects of fish metabolism that can be extracted retrospectively from otolith (earstone) morphometry and nitrogen content. Changes in relative otolith size to fish size are related to the metabolic history of the individual fish, and the otolith nitrogen content reveals the level of protein synthesis and feeding rate. Because otoliths accrue continuously on their surface and are biological stable (inert), the chemical content of the otolith trajectory reflects the timeline of the fish. We measured the N/Ca ratio as a proxy for protein content in EBC otolith along distal radius traverses from the core to the edge of the otolith by using secondary ion mass spectrometry (SIMS). Here we show that the otoliths have become smaller at a given fish size, and the ratio of N/Ca has increased over the studied period. These proxies reveal significant metabolic changes during the same period as the condition, and stock productivity has declined. We discuss potential mechanisms behind the metabolic changes, including elevated temperature and compensatory feeding due to nutrient deficiencies. Such changes in food quality may, in turn, relate to still unrecognized but on-going ecosystem shifts, where climate change could be the ultimate driver.
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