| 1. |
- Drake, Henrik, 1979-, et al.
(author)
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Ancient microbial activity in deep hydraulically conductive fracture zones within the Forsmark target area for deep geological nuclear waste disposal, Sweden
- 2018
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In: Geosciences. - : MDPI AG. - 2076-3263. ; 8
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Journal article (peer-reviewed)abstract
- Recent studies reveal that organisms from all three domains of life—Archaea, Bacteria, and even Eukarya—can thrive under energy-poor, dark, and anoxic conditions at large depths in the fractured crystalline continental crust. There is a need for an increased understanding of the processes and lifeforms in this vast realm, for example, regarding the spatiotemporal extent and variability of the different processes in the crust. Here, we present a study that set out to detect signs of ancient microbial life in the Forsmark area—the target area for deep geological nuclear waste disposal in Sweden. Stable isotope compositions were determined with high spatial resolution analyses within mineral coatings, and mineralized remains of putative microorganisms were studied in several deep water-conducting fracture zones (down to 663 m depth), from which hydrochemical and gas data exist. Large isotopic variabilities of 13Ccalcite (?36.2 to +20.2‰V-PDB) and 34Spyrite (?11.7 to +37.8‰V-CDT) disclose discrete periods of methanogenesis, and potentially, anaerobic oxidation of methane and related microbial sulfate reduction at several depth intervals. Dominant calcite–water disequilibrium of 18O and 87Sr/86Sr precludes abundant recent precipitation. Instead, the mineral coatings largely reflect an ancient archive of episodic microbial processes in the fracture system, which, according to our microscale Rb–Sr dating of co-genetic adularia and calcite, date back to the mid-Paleozoic. Potential Quaternary precipitation exists mainly at ~400 m depth in one of the boreholes, where mineral–water compositions corresponded.
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| 2. |
- Neubeck, Anna, et al.
(author)
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Carbon isotopic composition of Frutexites in subseafloor ultramafic rocks
- 2021
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In: Biogeochemistry. - : Springer. - 0168-2563 .- 1573-515X. ; 154:3, s. 525-536
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Journal article (peer-reviewed)abstract
- Micrometer sized stromatolitic structures called Frutexites are features observed in samples from the deep subsurface, and hot-spring environments. These structures are comprised of fine laminations, columnar morphology, and commonly consist of iron oxides, manganese oxides, and/or carbonates. Although a biological origin is commonly invoked, few reports have shown direct evidence of their association with microbial activity. Here, we report for the first time the occurrence of subsurface manganese-dominated Frutexites preserved within carbonate veins in ultramafic rocks. To determine the biogenicity of these putative biosignatures, we analyzed their chemical and isotopic composition using Raman spectroscopy and secondary ion mass spectroscopy (SIMS). These structures were found to contain macromolecular carbon signal and have a depleted 13C/12C carbon isotopic composition of – 35.4 ± 0.50‰ relative to the entombing carbonate matrix. These observations are consistent with a biological origin for the observed Frutexites structures.
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| 3. |
- Drake, Henrik, Docent, 1979-, et al.
(author)
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Biosignatures of ancient microbial life are present across the igneous crust of the Fennoscandian shield
- 2021
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In: Communications Earth & Environment. - : Springer Nature. - 2662-4435. ; 2:1
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Journal article (peer-reviewed)abstract
- Earth’s crust contains a substantial proportion of global biomass, hosting microbial life up to several kilometers depth. Yet, knowledge of the evolution and extent of life in this environment remains elusive and patchy. Here we present isotopic, molecular and morphological signatures for deep ancient life in vein mineral specimens from mines distributed across the Precambrian Fennoscandian shield. Stable carbon isotopic signatures of calcite indicate microbial methanogenesis. In addition, sulfur isotope variability in pyrite, supported by stable carbon isotopic signatures of methyl-branched fatty acids, suggest subsequent bacterial sulfate reduction. Carbonate geochronology constrains the timing of these processes to the Cenozoic. We suggest that signatures of an ancient deep biosphere and long-term microbial activity are present throughout this shield. We suggest that microbes may have been active in the continental igneous crust over geological timescales, and that subsurface investigations may be valuable in the search for extra-terrestrial life.
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| 4. |
- Drake, Henrik, Docent, 1979-, et al.
(author)
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Fossilized anaerobic and possibly methanogenesis-fueling fungi identified deep within the Siljan impact structure, Sweden
- 2021
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In: Communications Earth & Environment. - : Springer Science and Business Media LLC. - 2662-4435. ; 2:1, s. 1-11
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Journal article (peer-reviewed)abstract
- Recent discoveries of extant and fossilized communities indicate that eukaryotes, including fungi, inhabit energy-poor and anoxic environments deep within the fractured igneous crust. This subterranean biosphere may constitute the largest fungal habitat on our planet, but knowledge of abyssal fungi and their syntrophic interactions with prokaryotes and their concomitant metabolisms is scarce. Here we report findings of fossilized, chitin-bearing fungal hyphae at ~540 m depth in fractured bedrock of the Siljan impact structure, the largest crater in Europe. Strong 13C-enrichment of calcite precipitated with and on the fungi suggests formation following methanogenesis, and that the anaerobic fungi decomposed dispersed organic matter producing for example H2 that may have fueled autotrophic methanogens. An Eocene age determined for the calcite infers the first timing constraint of fossilized fungi in the continental igneous crust. Fungi may be widespread decomposers of organic matter and overlooked providers of H2 to autotrophs in the vast rock-hosted deep biosphere.
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| 5. |
- Drake, Henrik, Docent, 1979-, et al.
(author)
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In Situ Rb/Sr Geochronology and Stable Isotope Geochemistry Evidence for Neoproterozoic and Paleozoic Fracture-Hosted Fluid Flow and Microbial Activity in Paleoproterozoic Basement, SW Sweden
- 2023
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In: Geochemistry Geophysics Geosystems. - : American Geophysical Union (AGU). - 1525-2027. ; 24:5
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Journal article (peer-reviewed)abstract
- Recent studies have shown that biosignatures of ancient microbial life exist in mineral coatings in deep bedrock fractures of Precambrian cratons, but such surveys have been few and far between. Here, we report results from southwestern Sweden in an area of 1.6-1.5 Ga Paleoproterozoic rocks heavily reworked by the 1.14-0.96 Ga Sveconorwegian orogeny, a terrane previously scarcely explored for ancient microbial biosignatures. Calcite-pyrite-adularia-illite-coated fractures were analyzed for stable isotopes via Secondary Ion Mass Spectrometry (delta C-13, delta O-18, delta S-34) and in situ Rb/Sr geochronology via Laser-ablation inductively coupled plasma mass spectrometry. The Rb/Sr ages for calcite-adularia and calcite-illite show that several fluid flow events can be discerned (797 +/- 18-769 +/- 7, 391 +/- 5-387 +/- 6, 356 +/- 5-347 +/- 4, and 301 +/- 7 Ma). The delta C-13, delta O-18 and Sr-87/Sr-86 values of different calcite growth zones further confirmed episodic fluid flow. Pyrite delta S-34 values down to -49.9% V-CDT, together with systematically increased delta S-34 from crystal core to rim, suggest formation following microbial sulfate reduction under semi-closed conditions. Assemblages involving MSR-related pyrite generally have Devonian to Permian Rb/Sr ages, indicating an association to extension-related fracturing and fluid mixing during foreland-basin formation linked to Caledonian orogeny in the northwest. An assemblage with an age of 301 +/- 7 Ma is potentially related to Oslo Rift extension, whereas the Neo-Proterozoic ages relate to post-Sveconorwegian extensional tectonics. Remnants of short-chained fatty acids in the youngest calcite coatings further indicate a biogenic origin, while the absence of organic molecules in older calcite is in line with thermal degradation, potentially related to heating during Caledonian foreland basin burial. Plain Language Summary This study investigates mineral coatings in Proterozoic basement fractures of Southwestern Sweden, within the Precambrian Fennoscandian shield, to gain insights into ancient microbial life and paleo-fluid flow. Isotopic signatures of these mineral coatings suggest that microbial sulfate reducers have been present in the system as also indicated by preserved organic molecules. Microanalytical geochronology determinations reveal that the fracture system has been activated several times in the Neoproterozoic, Devonian-Early Carboniferous, and Late Carboniferous/Early Permian. These activations are associated with extension events following the Sveconorwegian and Caledonian orogenies as well as formation of the Oslo Rift. The signs of microbial activity are related to the youngest of these events, post-dating burial in the Caledonian foreland basin, when bedrock temperatures became habitable.
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| 6. |
- Drake, Henrik, 1979-, et al.
(author)
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Incorporation of Metals into Calcite in a Deep Anoxic Granite Aquifer
- 2018
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In: Environmental Science & Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851 .- 1086-931X .- 1520-6912. ; 52:2, s. 493-502
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Journal article (peer-reviewed)abstract
- Understanding metal scavenging by calcite in deep aquifers in granite is of importance for deciphering and modeling hydrochemical fluctuations and water rock interaction in the upper crust and for retention mechanisms associated With underground, repositories for toxic wastes. Metal scavenging into calcite has generally been established in the laboratory or in natural environments that cannot be unreservedly applied to conditions in deep crystalline rocks, an environment of broad interest, for nuclear waste repositories. Here, we report a microanalytical study: of calcite precipitated over a period of 17 years from anoxic, low-temperature (14 degrees C), neutral (pH: 7.4-7.7), and brackish (Cl: 1700-7100 mg/L) groundwater flowing in fractures at >400 m depth in granite rock. This enabled assessment of the trace metal uptake by calcite under these deep-seated conditions. Aquatic speciation modeling was carried out to assess influence of metal complexation on the partitioning into calcite. The resulting environment-specific partition coefficients were for several divalent ions in line with values obtained in controlled laboratory experiments, whereas for several other ions they differed substantially. High absolute uptake of rare earth elements and U(IV) suggests that coprecipitation into calcite can be an important sink for these metals and analogousactinides in the vicinity of geological repositories.
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| 7. |
- Drake, Henrik, 1979-, et al.
(author)
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Unprecedented S-34-enrichment of pyrite formed following microbial sulfate reduction in fractured crystalline rocks
- 2018
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In: Geobiology. - : Wiley. - 1472-4677 .- 1472-4669. ; 16:5, s. 556-574
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Journal article (peer-reviewed)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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| 8. |
- Jastrzebski, Miroslaw, et al.
(author)
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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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In: Lithos. - : Elsevier BV. - 0024-4937 .- 1872-6143. ; 316-317, s. 385-405
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Journal article (peer-reviewed)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. |
- Lewerentz, Alexander, et al.
(author)
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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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In: Contributions to Mineralogy and Petrology. - : Springer Science and Business Media LLC. - 0010-7999 .- 1432-0967. ; 174:8
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Journal article (peer-reviewed)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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| 10. |
- Robinson, Frank A., et al.
(author)
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Preliminary detrital zircon signatures from the southern Asir terrane, Saudi Arabia : A link to Yemen or the Nubian Shield?
- 2018
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In: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 311, s. 247-261
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Journal article (peer-reviewed)abstract
- The Arabian Shield comprises early Neoproterozoic to Cambrian (similar to 850-530 Ma) tectonostratigraphic terranes formed by the closure and accretion of juvenile volcanic arcs and back-arc basins associated with Gondwana assembly. Unlike the Nubian Shield which preserves crustal isotopic signatures, the Arabian Shield is distinctly juvenile with the exception of the Paleoproterozoic (similar to 1800-1670 Ma) Khida subterrane in Saudi Arabia and the terranes of Yemen. This study presents the first combined zircon U-Pb, O and Hf isotope data of metavolcanic and metasedimentary rocks from southwestern most Saudi Arabia, near the Yemen border - a region thought to contain some of the oldest (>815 Ma) lithologies in Saudi Arabia, including the Atura Formation and the Tayyah Belt. One volcaniclastic metasediment sample from the Atura Formation yields zircon U-Pb age peaks of 741, 672, 646 Ma (n = 131), delta O-18((V-SMOW)) ranging from 4.6 to 8.3 parts per thousand and epsilon(Hf) (t) from +7.7 to +12.5. Two samples from the Tayyah Belt include an older metasandstone and a late intruding granitic dyke which provides a minimum age for the Tayyah Belt. The former yields two significant U-Pb peaks of 812 (n = 8) and 999 (n = 6) Ma, delta O-18 and epsilon(Hf) (t) values ranging from 4.4 to 9.6 parts per thousand and -10.1 to +12.4, respectively; the later yields a concordia age of 645.8 [+/- 1.7] Ma (n = 29), delta O-18 ranging from 5.7 to 6.6 parts per thousand, and epsilon(Hf) (t) of +5.9 to +9.6. The zircon age and juvenile Hf signatures from the Atura Formation are consistent with the synorogenic phase in the Shield. Sedimentation was likely associated with arc volcanism during the previously documented eastward phase of accretion at similar to 740-640 Ma and the closure of the Mozambique Ocean. In contrast, the data from the texturally more mature Tayyah Belt metasediment indicate a more distal, and more evolved crustal input at the time of sediment deposition which is unusual for the Saudi Arabian Shield. Consequently, the Tayyah metasediments are likely sourced from areas with greater continental affinity, such as the cratonic basement and/or reworked crust of the Sahara metacraton in NE Africa.
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