| 1. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Ancient microbial activity in deep hydraulically conductive fracture zones within the Forsmark target area for deep geological nuclear waste disposal, Sweden
- 2018
-
Ingår i: Geosciences. - : MDPI AG. - 2076-3263. ; 8
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 2. |
- Drake, Henrik, Docent, 1979-, et al.
(författare)
-
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
-
Ingår i: Geochemistry Geophysics Geosystems. - : American Geophysical Union (AGU). - 1525-2027. ; 24:5
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 3. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Isotopic evidence for microbial production and consumption of methane in the upper continental crust throughout the Phanerozoic eon
- 2017
-
Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 470, s. 108-118
-
Tidskriftsartikel (refereegranskat)abstract
- Microorganisms produce and consume methane in terrestrial surface environments, sea sediments and, as indicated by recent discoveries, in fractured crystalline bedrock. These processes in the crystalline bedrock remain, however, unexplored both in terms of mechanisms and spatiotemporal distribution. Here we have studied these processes via a multi-method approach including microscale analysis of the stable isotope compositions of calcite and pyrite precipitated in bedrock fractures in the upper crust (down to 1.7 km) at three sites on the Baltic Shield. Microbial processes have caused an intriguing variability of the carbon isotopes in the calcites at all sites, with delta C-13 spanning as much as -93.1 parts per thousand (related to anaerobic oxidation of methane) to +36.5 parts per thousand (related to methanogenesis). Spatiotemporal coupling between the stable isotope measurements and radiometric age determinations (micro-scale dating using new high spatial methods: LA-ICP-MS U-Pb for calcite and Rb-Sr for calcite and co-genetic adularia) enabled unprecedented direct timing constraints of the microbial processes to several periods throughout the Phanerozoic eon, dating back to Devonian times. These events have featured variable fluid salinities and temperatures as shown by fluid inclusions in the calcite; dominantly 70-85 degrees C brines in the Paleozoic and lower temperatures (<50-62 degrees C) and salinities in the Mesozoic. Preserved organic compounds, including plant signatures, within the calcite crystals mark the influence of organic matter in descending surficial fluids on the microbial processes in the fracture system, thus linking processes in the deep and surficial biosphere. These findings substantially extend the recognized temporal and spatial range for production and consumption of methane within the upper continental crust. (C) 2017 Elsevier B.V. All rights reserved.
|
|
| 4. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Unprecedented S-34-enrichment of pyrite formed following microbial sulfate reduction in fractured crystalline rocks
- 2018
-
Ingår i: Geobiology. - : Wiley. - 1472-4677 .- 1472-4669. ; 16:5, s. 556-574
-
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.
|
|
| 5. |
- Guenthner, William R., et al.
(författare)
-
Zircon, titanite, and apatite (U-Th)/He ages and age-eU correlations from the Fennoscandian Shield, southern Sweden
- 2017
-
Ingår i: Tectonics. - : John Wiley & Sons. - 0278-7407 .- 1944-9194. ; 36:7, s. 1254-1274
-
Tidskriftsartikel (refereegranskat)abstract
- Craton cores far from plate boundaries have traditionally been viewed as stable features that experience minimal vertical motion over 100-1000Ma time scales. Here we show that the Fennoscandian Shield in southeastern Sweden experienced several episodes of burial and exhumation from similar to 1800Ma to the present. Apatite, titanite, and zircon (U-Th)/He ages from surface samples and drill cores constrain the long-term, low-temperature history of the Laxemar region. Single grain titanite and zircon (U-Th)/He ages are negatively correlated (104-838Ma for zircon and 160-945Ma for titanite) with effective uranium (eU=U+0.235xTh), a measurement proportional to radiation damage. Apatite ages are 102-258Ma and are positively correlated with eU. These correlations are interpreted with damage-diffusivity models, and the modeled zircon He age-eU correlations constrain multiple episodes of heating and cooling from 1800Ma to the present, which we interpret in the context of foreland basin systems related to the Neoproterozoic Sveconorwegian and Paleozoic Caledonian orogens. Inverse time-temperature models constrain an average burial temperature of similar to 217 degrees C during the Sveconorwegian, achieved between 944Ma and 851Ma, and similar to 154 degrees C during the Caledonian, achieved between 366Ma and 224Ma. Subsequent cooling to near-surface temperatures in both cases could be related to long-term exhumation caused by either postorogenic collapse or mantle dynamics related to the final assembly of Rodinia and Pangaea. Our titanite He age-eU correlations cannot currently be interpreted in the same fashion; however, this study represents one of the first examples of a damage-diffusivity relationship in this system, which deserves further research attention.
|
|
| 6. |
- Rogers, Paul, et al.
(författare)
-
Moderniserad dagsljusstandard
- 2018
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This report is the account of SBUF project 13209 “Moderniserad dagsljusstandard” (Modernized daylight standard). This is a continuation of the SBUF project 12966 “Förstudie dagsljusstandard” (Pre-study daylight standard) published in 2015. SBUF and the Swedish Energy Agency are the two sources of this project’s funding. The task has been to freely describe and interpret history, day-to-day and future development needs for daylight in buildings within the framework of the Swedish National Board of Housing, Building and Planning. The project has been a feasibility study in order to design a proposal on how to proceed towards creating an improved and modernized interpretation of BBR section 6: 322. The ultimate goal is a daylight standard applicable to the construction industry and functioning.
|
|
| 7. |
- Tillberg, Karin, 1983-
(författare)
-
The Outsider in Our Midst : A Study of Language and Norms Concerning the “Outsider” in Persian Period Yehud
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The topic for the present study concerns how values and norms are conveyed through language. I explore two texts set in the Persian period—Isaiah 56:1–8 and Nehemiah 13:1–3, 23–31—and how these texts discuss those literary figures described as not belonging to the community. The investigation is conducted through a method inspired by Pierre Bourdieu’s work in social anthropology. Bourdieu’s notions are turned into heuristic tools for literary analysis. By systematically examining the literary figures that appear in the texts—how they can be interpreted as agents, possessing different forms of capital, which situate them in various fields—the analysis consists of studying the power dynamic between the “in-group” and those on the outside. Thus, the implicit values and tacit knowledge of the agents are highlighted, which in turn means that an understanding is gained as to what affects the language used by the agents. This doxa affects the agents and their position in the fields. I interpret Deuteronomic theology—particularly in the form of Deuteronomy 23:2–9— and imperial ideology as doxic, as notions common to everyone.At the end of the investigation, the results of the analysis are discussed by critically engaging with the theoretical notion of hospitality. This discussion is included in order to situate the agents in the fields as host and guest, to examine the power dynamic further.One of the primary aims of the present study is to challenge the position among scholars that these texts contradict each other, where the former is viewed as inclusivist and the latter considered exclusivist. I arrive at a different conclusion, that Isaiah 56 and Nehemiah 13 could be read in dialogue with one another. Nehemiah 13 can be seen as an embodiment of Isaiah 56 through the character of Nehemiah as an image of utmost loyalty, similar to the sārîs and the ben-nēkār, which both emerge as tropes conveying loyalty.
|
|
| 8. |
- Tillberg, Mikael
(författare)
-
Constraining the timing of veins, faults and fractures in crystalline rocks by in situ Rb-Sr geochronology
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Precambrian cratons are continent cores archiving the oldest crustal histories on Earth. The crystalline basement of cratons is typically characterized by complex arrays of multiple fracture and fault generations hosting minerals formed by fluids flowing through fracture networks. Disentangling absolute chronologies of the various fracturing, faulting and fluid flow events have to date been difficult given the micro-scale mineral intergrowths and zonations, inhibiting conventional dating techniques. In the general lack of age constraints, deformation and mineralization mechanisms cannot be attributed to specific tectonic regimes, hampering reconstruction of local and regional events of fluid flow and mineral precipitation, and ultimately of the geological evolution of cratons. This thesis presents diverse studies utilizing the radiogenic decay of fracture, fault and shear zone mineral assemblages sampled from the crystalline basement of the Fennoscandian Shield, aiming at detecting episodic fracturing reactivation, mineralization and microbial processes throughout the craton history.The analytical procedures involve, foremost, Rb-Sr geochronology, along with U-Pb and (U-Th)/He geochronology, stable isotope and trace element geochemistry, fluid inclusion thermometry and biomarkers. The in situ age determinations enabled 1) linking of greisen and distal veins to magmatic and post-magmatic fluid circulation, 2) slickenfibre growth to distinct faulting episodes, and 3) mineral precipitation in fractures, veins and shear zones to regionally extending deformation events across the Fennoscandian Shield. In addition, dating of mineralization related to deep fracture-hosted microbial life constrained the timing of such activity at several sites. The precipitation episodes stretch from Paleoproterozoic to Jurassic times with overgrowth generations separated in time by up to one billion years in single veins and even within individual crystals. The findings of the thesis demonstrate that the methodological protocol has potential to directly date a wide range of mineral assemblages in fractures, faults, veins and shear zones given that the isochron requirements are fulfilled. Fulfillment is ensured through detailed petrological and structural characterization followed by geochronological analysis and thorough data reduction allowing validation of isotopic data down to submicrometer level. The outcomes have implications for tectonic reconstructions at various scales, for the tracing of the deep ancient biosphere and for comprehending hydrothermal ore deposition, with direct societal relevance in the detection of ancient microbial activity and fracture reactivation at the candidate site for a spent nuclear fuel repository in Sweden.
|
|
| 9. |
- Tillberg, Mikael, et al.
(författare)
-
Fractionation of Rare Earth Elements in Greisen and Hydrothermal Veins Related to A-Type Magmatism
- 2019
-
Ingår i: Geofluids. - : Hindawi Limited. - 1468-8115 .- 1468-8123. ; 2019
-
Tidskriftsartikel (refereegranskat)abstract
- This study focuses on concentrations and fractionation of rare earth elements (REE) in a variety of minerals and bulk materials of hydrothermal greisen and vein mineralization in Paleoproterozoic monzodiorite to granodiorite related to the intrusion of Mesoproterozoic alkali- and fluorine-rich granite. The greisen consists of coarse-grained quartz, muscovite, and fluorite, whereas the veins mainly contain quartz, calcite, epidote, chlorite, and fluorite in order of abundance. A temporal and thus genetic link between the granite and the greisen/veins is established via high spatial resolution in situ Rb-Sr dating, supported by several other isotopic signatures (delta S-34, Sr-87/Sr-86, delta O-18, and delta C-13). Fluid-inclusion microthermometry reveals that multiple pulses of moderately to highly saline aqueous to carbonic solutions caused greisenization and vein formation at temperatures above 200-250 degrees C and up to 430 degrees C at the early hydrothermal stage in the veins. Low calculated Sigma REE concentration for bulk vein (15ppm) compared to greisen (75ppm), country rocks (173-224ppm), and the intruding granite (320ppm) points to overall low REE levels in the hydrothermal fluids emanating from the granite. This is explained by efficient REE retention in the granite via incorporation in accessory phosphates, zircon, and fluorite and unfavorable conditions for REE partitioning in fluids at the magmatic and early hydrothermal stages. A noteworthy feature is substantial heavy REE (HREE) enrichment of calcite in the vein system, in contrast to the relatively flat patterns of greisen calcite. The REE fractionation of the vein calcite is explained mainly by fractional crystallization, where the initially precipitated epidote in the veins preferentially incorporates most of the light REE (LREE) pool, leaving a residual fluid enriched in the HREE from which calcite precipitated. Fluorite occurs throughout the system and displays decreasing REE concentrations from granite towards greisen and veins and different fractionation patterns among all these three materials. Taken together, these features confirm efficient REE retention in the early stages of the system and minor control of the REE uptake by mineral-specific partitioning. REE-fractionation patterns and fluid-inclusion data suggest that chloride complexation dominated REE transport during greisenization, whereas carbonate complexation contributed to the HREE enrichment in vein calcite.
|
|
| 10. |
- Tillberg, Mikael, 1990, et al.
(författare)
-
In situ Rb-Sr dating of fine-grained vein mineralizations using LAICP-MS
- 2017
-
Ingår i: Procedia Earth and Planetary Science. 15th Water-Rock Interaction International Symposium (WRI), 16-21 Oct 2017, Evora, Portugal.. - Amsterdam : Elsevier. - 1878-5220. ; , s. 464-467
-
Konferensbidrag (refereegranskat)abstract
- Direct mineral dating is critical for thorough understanding of the genesis of hydrothermal mineralizations, ore forming processes and events of fracturing and related fluid-rock interaction. Since minerals of suitable type and sample volume for conventional techniques can be rare, development of high-precision in situ Rb-Sr dating of common rock-forming minerals such as micas, feldspars and calcite offers possibilities to gain temporal constraints of a wide variety of geological features with detailed spatial and depth resolution. This technique separates Sr-87 from Rb-87 by introducing a reaction gas between two quadropoles in a LAICP- MS system. In this study, in situ Rb-Sr geochronology distinguishes the timing of several different fracture-controlled hydrothermal events: 1 and 2) greisen mineralizations and associated far-field hydrothermal veins adjacent to a granite intrusion, 3) reactivation events within a mylonite shear zone and 4) low-temperature precipitation from saline organic-rich brines in thin veinlets. We demonstrate that in situ Rb-Sr dating is feasible for a broad range of mineral assemblages, textures, temperatures and ages, emphasizing the impending use of this new method in ore deposit exploration and many other research fields.
|
|
| 11. |
- Tillberg, Mikael, et al.
(författare)
-
In situ Rb-Sr dating of slickenfibres in deep crystalline basement faults
- 2020
-
Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 10:1, s. 1-12
-
Tidskriftsartikel (refereegranskat)abstract
- Establishing temporal constraints of faulting is of importance for tectonic and seismicity reconstructions and predictions. Conventional fault dating techniques commonly use bulk samples of syn-kinematic illite and other K-bearing minerals in fault gouges, which results in mixed ages of repeatedly reactivated faults as well as grain-size dependent age variations. Here we present a new approach to resolve fault reactivation histories by applying high-spatial resolution Rb-Sr dating to fine-grained mineral slickenfibres in faults occurring in Paleoproterozoic crystalline rocks. Slickenfibre illite and/or K-feldspar together with co-genetic calcite and/or albite were targeted with 50 µm laser ablation triple quadrupole inductively coupled plasma mass spectrometry analyses (LA-ICP-MS/MS). The ages obtained disclose slickenfibre growth at several occasions spanning over 1 billion years, from at least 1527 Ma to 349 ± 9 Ma. The timing of these growth phases and the associated structural orientation information of the kinematic indicators on the fracture surfaces are linked to far-field tectonic events, including the Caledonian orogeny. Our approach links faulting to individual regional deformation events by minimizing age mixing through micro-scale analysis of individual grains and narrow crystal zones in common fault mineral assemblages.
|
|
| 12. |
- Tillberg, Mikael, 1990, et al.
(författare)
-
Re-Evaluating the Age of Deep Biosphere Fossils in the Lockne Impact Structure
- 2019
-
Ingår i: Geosciences. - Basel : MDPI AG. - 2076-3263. ; 9:5
-
Tidskriftsartikel (refereegranskat)abstract
- Impact-generated hydrothermal systems have been suggested as favourable environments for deep microbial ecosystems on Earth, and possibly beyond. Fossil evidence from a handful of impact craters worldwide have been used to support this notion. However, as always with mineralized remains of microorganisms in crystalline rock, certain time constraints with respect to the ecosystems and their subsequent fossilization are difficult to obtain. Here we re-evaluate previously described fungal fossils from the Lockne crater (458 Ma), Sweden. Based on in-situ Rb/Sr dating of secondary calcite-albite-feldspar (356.6 +/- 6.7 Ma) we conclude that the fungal colonization took place at least 100 Myr after the impact event, thus long after the impact-induced hydrothermal activity ceased. We also present microscale stable isotope data of C-13-enriched calcite suggesting the presence of methanogens contemporary with the fungi. Thus, the Lockne fungi fossils are not, as previously thought, related to the impact event, but nevertheless have colonized fractures that may have been formed or were reactivated by the impact. Instead, the Lockne fossils show similar features as recent findings of ancient microbial remains elsewhere in the fractured Swedish Precambrian basement and may thus represent a more general feature in this scarcely explored habitat than previously known.
|
|
| 13. |
|
|
| 14. |
- Tillberg, Mikael, 1990, et al.
(författare)
-
Reconstructing craton-scale tectonic events via in situ Rb-Sr geochronology of poly-phased vein mineralization
- 2021
-
Ingår i: Terra Nova. - : Wiley. - 0954-4879 .- 1365-3121. ; 33:5, s. 502-510
-
Tidskriftsartikel (refereegranskat)abstract
- Fault- and fracture-hosted multi-stage mineral assemblages that formed by fracture reactivation and fluid migration, constitute archives of the tectonic evolution of Precambrian cratons. Complex intergrowth patterns of these mineral records often hinder absolute dating of mineralization events for geological models. We apply LA-ICP-MS/MS in situ Rb-Sr dating of single crystal growth zones in sub-mm-wide vein mineralization assemblages including illite, K-feldspar, albite, calcite, mica, zeolites, fluorite and/or epidote at three Palaeoproterozoic crystalline bedrock sites over 300 km apart in the Fennoscandian Shield. The dating campaign reveals multiple age clusters between ca. 1757 +/- 15 and 355 +/- 12 Ma correlating with fluid flow and fracture reactivation events initiated by far-field orogens and their foreland basin evolution. This new approach for reconstructing geological histories of Precambrian cratons connects micro-scale age determinations of different mineral growth zones in fractures with regional-scale crustal dynamic responses to tectonic events.
|
|
| 15. |
- Tillberg, Mikael, et al.
(författare)
-
The deep geothermal energy potential of Kalmar and Nybro municipalities
- 2024
-
Rapport (övrigt vetenskapligt/konstnärligt)abstract
- The potential for enhanced geothermal energy production in the Kalmar and Nybro municipalities is investigated by reviewing existing data on the regional geothermal gradient and the extent of fracture zones with depth of the crystalline crust in the research area. Existing geophysical and hydrological models along with bedrock maps and results of earlier studies in the nearby region are integrated in this report. The geothermal gradient in the Kalmar-Nybro area is currently not quantified, but proximal measurements indicate that the temperature is not likely to increase significantly more than 16-17°C/km considering local bedrock properties. Target depths would in this scenario be up to 6-7 km for production drilling. The only major deformation zone in the area stretches in a WNW direction from Kalmar and has potential for containing deep open fractures. The Boda-Örsjö area appears to host an extensive fracture network of multiple converging fracture zones. However, prediction of fracture occurrence at depths of several kilometres is highly speculative since no deep drill data has been produced in the area. Suggestions for further studies required in order to develop a deep geothermal project in the region are provided, with emphasis on locating favourable structural settings and bedrock stress conditions. Nevertheless, technical method developments regarding drilling and fluid injection are likely required for enabling deep geothermal energy production in the relatively cold depths of the exposed crystalline bedrock characterizing both the examined area in this report and the predominant parts of Scandinavia.
|
|
| 16. |
- Yu, Changxun, 1983-, et al.
(författare)
-
A Combined X-ray Absorption and Mössbauer Spectroscopy Study on Fe Valence and Secondary Mineralogy in Granitoid Fracture Networks : Implications for Geological Disposal of Spent Nuclear Fuels
- 2020
-
Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 54:5, s. 2832-2842
-
Tidskriftsartikel (refereegranskat)abstract
- Underground repository in crystalline bedrock is a widely accepted solution for long-term disposal of spent nuclear fuels. During future deglaciations, meltwater will intrude via bedrock fractures to the depths of future repositories where O2 left in the meltwater could corrode metal canisters and enhance the migration of redox-sensitive radionuclides. Since glacial meltwater is poor in reduced phases, the quantity and (bio)accessibility of minerogenic Fe(II) in bedrock fractures determine to what extent O2 in future meltwater can be consumed. Here, we determined Fe valence and mineralogy in secondary mineral assemblages sampled throughout the upper kilometer of fractured crystalline bedrock at two sites on the Baltic Shield, using X-ray absorption and Mössbauer spectroscopic techniques that were found to deliver matching results. The data point to extensive O2-consuming capacity of the bedrock fractures, because Fe(II)-rich phyllosilicates were abundant and secondary pyrite was dispersed deep into the bedrock with no overall increase in Fe(II) concentrations and Fe(II)/Fe(III) proportions with depth. The results imply that repeated Pleistocene deglaciations did not cause a measurable decrease in the Fe(II) pool. In surficial fractures, largely opened during glacial unloading, ferrihydrite and illite have formed abundantly via oxidative transformation of Fe(II)-rich phyllosilicates and recently exposed primary biotite/hornblende.
|
|
