| 1. |
- Drake, Henrik, 1979-, et al.
(författare)
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Unprecedented S-34-enrichment of pyrite formed following microbial sulfate reduction in fractured crystalline rocks
- 2018
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Ingår i: Geobiology. - : Wiley. - 1472-4677 .- 1472-4669. ; 16:5, s. 556-574
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Tidskriftsartikel (refereegranskat)abstract
- In the deep biosphere, microbial sulfate reduction (MSR) is exploited for energy. Here, we show that, in fractured continental crystalline bedrock in three areas in Sweden, this process produced sulfide that reacted with iron to form pyrite extremely enriched in S-34 relative to S-32. As documented by secondary ion mass spectrometry (SIMS) microanalyses, the S-34(pyrite) values are up to +132 parts per thousand V-CDT and with a total range of 186 parts per thousand. The lightest S-34(pyrite) values (-54 parts per thousand) suggest very large fractionation during MSR from an initial sulfate with S-34 values (S-34(sulfate,0)) of +14 to +28 parts per thousand. Fractionation of this magnitude requires a slow MSR rate, a feature we attribute to nutrient and electron donor shortage as well as initial sulfate abundance. The superheavy S-34(pyrite) values were produced by Rayleigh fractionation effects in a diminishing sulfate pool. Large volumes of pyrite with superheavy values (+120 +/- 15 parts per thousand) within single fracture intercepts in the boreholes, associated heavy average values up to +75 parts per thousand and heavy minimum S-34(pyrite) values, suggest isolation of significant amounts of isotopically light sulfide in other parts of the fracture system. Large fracture-specific S-34(pyrite) variability and overall average S-34(pyrite) values (+11 to +16 parts per thousand) lower than the anticipated S-34(sulfate,0) support this hypothesis. The superheavy pyrite found locally in the borehole intercepts thus represents a late stage in a much larger fracture system undergoing Rayleigh fractionation. Microscale Rb-Sr dating and U/Th-He dating of cogenetic minerals reveal that most pyrite formed in the early Paleozoic era, but crystal overgrowths may be significantly younger. The C-13 values in cogenetic calcite suggest that the superheavy S-34(pyrite) values are related to organotrophic MSR, in contrast to findings from marine sediments where superheavy pyrite has been proposed to be linked to anaerobic oxidation of methane. The findings provide new insights into MSR-related S-isotope systematics, particularly regarding formation of large fractions of S-34-rich pyrite.
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| 2. |
- Drake, Henrik, et al.
(författare)
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Extreme fractionation and micro-scale variation of sulphur isotopes during bacterial sulphate reduction in deep groundwater systems
- 2015
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Ingår i: Geochimica Et Cosmochimica Acta. - : Elsevier BV. - 0016-7037 .- 1872-9533. ; 161, s. 1-18
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Tidskriftsartikel (refereegranskat)abstract
- This study conducted at the Aspo Hard Rock Laboratory, SE Sweden, determines the extent and mechanisms of sulphur-isotope fractionation in permanently reducing groundwater in fractured crystalline rock. Two boreholes > 400 m below the ground surface were investigated. In the 17-year-old boreholes, the Al instrumentation pipes had corroded locally (i.e., Al[oxy] hydroxides had formed) and minerals (i.e., pyrite, iron monosulphide, and calcite) had precipitated on various parts on the equipment. By chemically and isotopically comparing the precipitates on the withdrawn instrumentation and the borehole waters, we gained new insight into the dynamics of sulphate reduction, sulphide precipitation, and sulphur-isotope fractionation in deep-seated crystalline-rock settings. An astonishing feature of the pyrite is its huge variability in delta S-34, which can exceed 100 parts per thousand in total (i.e., -47.2 to +53.3 parts per thousand) and 60 parts per thousand over 50 mu m of growth in a single crystal. The values at the low end of the range are up to 71 parts per thousand lower than measured in the dissolved sulphate in the water (20-30 parts per thousand), which is larger than the maximum difference reported between sulphate and sulphide in pure-culture experiments (66 parts per thousand) but within the range reported from natural sedimentary settings. Although single-step reduction seems likely, further studies are needed to rule out the effects of possible S disproportionation. The values at the high end of the range (i.e., high delta S-34(py)) are much higher than could be produced from the measured sulphate under any biogeochemical conditions. This strongly suggests the development of closed-system conditions near the growing pyrite, i.e., the rate of sulphate reduction exceeds the rate of sulphate diffusion in the local fluid near the pyrite, causing the local aqueous phase (and thus the forming pyrite) to become successively enriched in heavy S (S-34). Consequently, the delta S-34 values of the forming pyrite become exceptionally high and strongly decoupled from the delta S-34 values of the sulphate in the bulk fluid. The Al-(oxy) hydroxide and calcite precipitates are explained by a combination of deposit and galvanic corrosion initiated by Al corrosion by H2S produced by sulphate-reducing microorganisms. (C) 2015 Elsevier Ltd. All rights reserved.
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| 3. |
- 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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| 4. |
- Lewerentz, Alexander, et al.
(författare)
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Baddeleyite formation in zircon by Ca-bearing fluids in silica-saturated systems in nature and experiment : resetting of the U-Pb geochronometer
- 2019
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Ingår i: Contributions to Mineralogy and Petrology. - : Springer Science and Business Media LLC. - 0010-7999 .- 1432-0967. ; 174:8
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Tidskriftsartikel (refereegranskat)abstract
- Intergrowths of baddeleyite have been found in zircon grain interiors from amphibolite- and granulite-facies felsic rocks from southwest Greenland. The zircon grains are either close to or in direct contact with quartz. A series of experiments has been conducted using natural, unaltered zircon grains +/- SiO2 in H2O-CaCl2, and H2O-Ca(OH)(2) solutions with varying molar proportions of Ca to Si at 900 degrees C; 1000MPa and 600 degrees C; 400MPa for 4-50days. Experimental results indicate that baddeleyite formed in the reacted zircon if the molar amount of Ca was close to or greater than Si in the system. The baddeleyite primarily takes the form of bead-like trails along the reaction front between the altered and unaltered zircon. Uranium, Th, and Y+REE were detected in both the newly formed baddeleyite and in the altered zircon, while Pb was effectively absent in both phases. Formation of baddeleyite from zircon in the silica-saturated rocks only appears to be possible when Ca saturates the system, such that the Si is tied up as CaSiO3 lowering the silica activity to <1. This highly localized (mu m to nm scale) effect in natural quartz-bearing rocks, where baddeleyite forms in the interiors of zircon grains in contact with quartz, implies that metastability in natural rock-forming systems can occur on a very small scale. Non-incorporation of Pb in the newly formed baddeleyite, or in areas of the zircon altered by fluids, implies that either could be used to date the metasomatic event responsible for their formation.
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| 5. |
- Logan, Leslie, 1992-, et al.
(författare)
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Energy Drive for the Kiruna Mining District Mineral System(s): Insights from U-Pb Zircon Geochronology
- 2022
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Ingår i: Minerals. - : MDPI. - 2075-163X. ; 12:7
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Tidskriftsartikel (refereegranskat)abstract
- The Kiruna mining district, Sweden, known for the type locality of Kiruna-type iron oxide-apatite (IOA) deposits, also hosts several Cu-mineralized deposits including iron oxide-copper-gold (IOCG), exhalative stratiform Cu-(Fe-Zn), and structurally controlled to stratabound Cu +/- Au. However the relationship between the IOA and Cu-systems has not been contextualized within the regional tectonic evolution. A broader mineral systems approach is taken to assess the timing of energy drive(s) within a regional tectonic framework by conducting U-Pb zircon geochronology on intrusions from areas where Cu-mineralization is spatially proximal. Results unanimously yield U-Pb ages from the early Svecokarelian orogeny (ca. 1923-1867 Ma including age uncertainties), except one sample from the Archean basement (2698 +/- 3 Ma), indicating that a distinct thermal drive from magmatic activity was prominent for the early orogenic phase. A weighted average Pb-207/Pb-206 age of 1877 +/- 10 Ma of an iron-oxide-enriched gabbroic pluton overlaps in age with the Kiirunavaara IOA deposit and is suggested as a candidate for contributing mafic signatures to the IOA ore. The results leave the role of a late energy drive (and subsequent late Cu-mineralization and/or remobilization) ambiguous, despite evidence showing a late regional magmatic-style hydrothermal alteration is present in the district.
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| 6. |
- Klawonn, Isabell, et al.
(författare)
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Untangling hidden nutrient dynamics : rapid ammonium cycling and single-cell ammonium assimilation in marine plankton communities
- 2019
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Ingår i: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 13:8, s. 1960-1974
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Tidskriftsartikel (refereegranskat)abstract
- Ammonium is a central nutrient in aquatic systems. Yet, cell-specific ammonium assimilation among diverse functional plankton is poorly documented in field communities. Combining stable-isotope incubations (15N-ammonium, 15N2 and 13C-bicarbonate) with secondary-ion mass spectrometry, we quantified bulk ammonium dynamics, N2-fixation and carbon (C) fixation, as well as single-cell ammonium assimilation and C-fixation within plankton communities in nitrogen (N)-depleted surface waters during summer in the Baltic Sea. Ammonium production resulted from regenerated (≥91%) and new production (N2-fixation, ≤9%), supporting primary production by 78–97 and 2–16%, respectively. Ammonium was produced and consumed at balanced rates, and rapidly recycled within 1 h, as shown previously, facilitating an efficient ammonium transfer within plankton communities. N2-fixing cyanobacteria poorly assimilated ammonium, whereas heterotrophic bacteria and picocyanobacteria accounted for its highest consumption (~20 and ~20–40%, respectively). Surprisingly, ammonium assimilation and C-fixation were similarly fast for picocyanobacteria (non-N2-fixing Synechococcus) and large diatoms (Chaetoceros). Yet, the population biomass was high for Synechococcus but low for Chaetoceros. Hence, autotrophic picocyanobacteria and heterotrophic bacteria, with their high single-cell assimilation rates and dominating population biomass, competed for the same nutrient source and drove rapid ammonium dynamics in N-depleted marine waters.
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| 7. |
- Nisson, D.M., et al.
(författare)
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Hydrogeochemical and isotopic signatures elucidate deep subsurface hypersaline brine formation through radiolysis driven water-rock interaction
- 2023
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Ingår i: Geochimica et Cosmochimica Acta. - : Elsevier. - 0016-7037 .- 1872-9533. ; 340, s. 65-84
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Tidskriftsartikel (refereegranskat)abstract
- Geochemical and isotopic fluid signatures from a 2.9–3.2 km deep, 45–55 °C temperature, hypersaline brine from Moab Khotsong gold and uranium mine in the Witwatersrand Basin of South Africa were combined with radiolytic and water–rock isotopic exchange models to delineate brine evolution over geologic time, and to explore brine conditions for habitability. The Moab Khotsong brines were hypersaline (Ca-Na-Cl) with 215–246 g/L TDS, and Cl− concentrations up to 4 mol/L suggesting their position as a hypersaline end-member significantly more saline than any previously sampled Witwatersrand Basin fluids. The brines revealed low DIC (∼0.266–∼1.07 mmol/L) with high (∼8.49–∼23.6 mmol/L) DOC pools, and several reduced gaseous species (up to 46 % by volume H2) despite microoxic conditions (Eh = 135–161 mV). Alpha particle radiolysis of water to H2, H2O2, and O2 along with anhydrous-silicate-to-clay alteration reactions predicted 4 mol/L Cl− brine concentration and deuterium enrichment in the fracture waters over a period > 1.00 Ga, consistent with previously reported 40Ar noble gas-derived residence times of 1.20 Ga for this system. In addition, radiolytic production of 7–26 nmol/(L × yr) H2, 3–11 nmol/(L × yr) O2, and 1–8 nmol/(L × yr) H2O2 was predicted for 1–100 g/g 238U dosage scenarios, supporting radiolysis as a significant source of H2 and oxidant species to deep brines over time that are available to a low biomass system (102–103 cells/mL). The host rock lithology was predominately Archaean quartzite, with minerals exposed on fracture surfaces that included calcite, pyrite, and chlorite. Signatures of 18Ocalcite, 13Ccalcite, Δ33Spyrite, 34Spyrite and 87Sr/86Sr obtained from secondary ion mass spectrometry (SIMS) microanalyses suggest several discrete fluid events as the basin cooled from peak greenschist conditions to equilibrium with present-day brine temperatures. The brine physiochemistry, geochemistry, and cellular abundances were significantly different from those of a younger, shallower, low salinity dolomitic fluid in the same mine, and both were different from the mine service water. These results indicate the discovery of one of few long-isolated systems that supports subsurface brine formation via extended water–rock interaction, and an example of a subsurface brine system where abiotic geochemistry may support a low biomass microbial community.
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| 8. |
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| 9. |
- Bezenjani, R. Nasiri, et al.
(författare)
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Detrital zircon geochronology and provenance of the Neoproterozoic Hammamat Group (Igla Basin), Egypt and the Thalbah Group, NW Saudi Arabia : Implications for regional collision tectonics
- 2014
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 245, s. 225-243
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Tidskriftsartikel (refereegranskat)abstract
- Detrital zircon U-Pb SIMS dating is used to evaluate the provenance of two correlative basins in the Arabian-Nubian Shield (ANS). The Wadi Igla Formation in the Central Eastern Desert (CED) of Egypt and the Thalbah Group in the Midyan Terrane (MT) of NW Saudi Arabia are considered to be post-amalgamation terrestrial basins, developed during closure of the Mozambique Ocean and amalgamation of the ANS in Cryogenian-early Ediacaran time. The analytical results indicate that the upper-part of the Wadi Igla Formation has a maximum depositional age of 628 +/- 6 Ma, contains 98% Neoproterozoic zircon with ages between 815 and 628 Ma, and has two distinct peaks at 690 Ma and 652 Ma. A rhyolite clast from the upper-part of the Wadi Igla Formation gives a U-Pb age of 700 +/- 6 Ma. This age significantly predates Dokhan volcanism, indicating that the dominant rhyolitic clasts within the Wadi Igla Formation are not from the Dokhan Volcanics, as previously believed. Analytical results from the Thalbah Group suggest multiphase basin formation and development. The lower part of the Thalbah Group is intruded by monzogranites of the Liban complex, has a minimum depositional age of 635 +/- 5 Ma, resembling that of the Wadi Igla Formation. Its middle part has a maximum age of 612 +/- 7 Ma and is comprised of 90% Neoproterozoic zircon with ages ranging from 820 to 612 Ma. The upper part of the Thalbah Group has a maximum age of 596 +/- 10 Ma and contains a wider range of Neoproterozoic detritus with ages between 985 and 596 Ma. The basement of the Thalbah Group is represented by metasediments and metavolcanics of the Zaam Group. The sample collected from the uppermost part of the Zaam Group (Um Ashsh Formation) contains zircon of mostly Cryogenian age (ca. 812-697 Ma) and has a maximum age of 700 +/- 4 Ma, suggesting that the Zaam Group might be correlative with the subduction-related metavolcanic and metasedimentary rocks that are overlain unconformably by the Wadi Igla Formation in the CED. The Wadi Igla basin and the lower and middle parts of the Thalbah basin have similar provenance, record a Cryogenian-early Ediacaran age, and represent syn-subduction (rather than post-amalgamation) basins. The upper part of the Thalbah Group, in contrast, has a distinct provenance representing an Ediacaran syn-collisional basin. The narrow age range of the Wadi Igla Formation and the lower and middle parts of the Thalbah Group indicates a restricted source from the CED and MT island arc basement, whereas the wide age range for the upper part of the Thalbah Group indicates a contribution from other parts of the ANS. The sediment sources and the age patterns of detrital zircons change abruptly at ca. 596 Ma. This may coincide with the onset of collision of the CED and MT basements with the older Hijaz-Gebeit terrane (850-680 Ma) to the south along the Yanbu-Onib-Sol Hamed-Gerf-Allaqi-Heiani (YOSHGAH) suture in the ANS during the East African Orogeny.
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| 10. |
- 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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