| 1. |
- Marks, Michael A. W., et al.
(författare)
-
The F, Cl, Br and I Contents of Reference Glasses BHVO-2G, BIR-1G, BCR-2G, GSD-1G, GSE-1G, NIST SRM 610 and NIST SRM 612
- 2017
-
Ingår i: Geostandards and Geoanalytical Research. - : Wiley. - 1639-4488 .- 1751-908X. ; 41:1, s. 107-122
-
Tidskriftsartikel (refereegranskat)abstract
- Halogen contents for the widely distributed reference glasses BHVO-2G, BIR-1G, BCR-2G, GSD-1G, GSE-1G, NIST SRM 610 and NIST SRM 612 were investigated by pyrohydrolysis combined with ion chromatography, total reflection X-ray fluorescence analysis, instrumental neutron activation analysis, the noble gas method, electron probe microanalysis and laser ablation-inductively coupled plasma-mass spectrometry. Glasses BHVO-2G, GSD-1G and GSE-1G have halogen contents that can be reproduced at the 15% level by all bulk techniques and cover a significant range in halogen mass fractions for F (~ 20–300 μg g−1), Cl (~ 70–1220 μg g−1) and Br (~ 0.2–285 μg g−1) and I (~ 9–3560 ng g−1). The BIR-1G glass has low F (< 15 μg g−1), Cl (~ 20 μg g−1), Br (15 ng g−1) and I (3 ng g−1). The halogen contents for the silica-rich NIST SRM 610 and 612 glasses were poorly reproduced by the different techniques. The relatively high Cl, Br and I abundances in glasses GSD-1G and GSE-1G mean that these glasses are well suited for calibrating spatially resolved micro-analytical studies on silicate glasses, melt and fluid inclusions. Combined EPMA and laser ablation-inductively coupled plasma-mass spectrometry data for glass GSE-1G demonstrate homogeneity at the 10% level for Cl and Br.
|
|
| 2. |
- Pabst, Sonja, et al.
(författare)
-
Evidence for boron incorporation into the serpentine crystal structure
- 2011
-
Ingår i: American Mineralogist. - 0003-004X. ; 96:7, s. 1112-1119
-
Tidskriftsartikel (refereegranskat)abstract
- Serpentinite mud volcanoes from the Mariana forearc comprise B-rich mantle wedge peridotites serpentinized by slab fluids. The major component of these rocks are serpentine group minerals [Mg(3)Si(2)O(5)(OH)(4)], showing highly variable textural and geochemical features. Micro-Raman spectroscopy reveals that the serpentine minerals are well-crystallized lizardite and chrysotile. In situ SIMS spot analyses and element mapping via ToF-SIMS show that B is evenly distributed across serpentine grains, suggesting that serpentine, both lizardite and chrysotile in different textural regions, can host significant amounts of B (up to similar to 200 mu g/g) into its crystal structure. As such structurally bound B can only be released during recrystallization or serpentine breakdown, our results have implications for modeling of the efficiency of cross-arc fluid mobile element recycling in subduction zones and stress the importance of the hydrated forearc mantle as a reservoir for fluid mobile elements.
|
|
| 3. |
|
|
| 4. |
- Andersson, Stefan S., et al.
(författare)
-
Mineral paragenesis and sulphide trace element distribution in the metamorphosed Lovisa Zn-Pb deposit, Bergslagen (Sweden), as revealed by 3D X-ray tomography, ore petrography and LA-ICP-MS analysis
- 2022
-
Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 140
-
Tidskriftsartikel (refereegranskat)abstract
- This study encompasses the ore mineralogy, textures and sulphide trace element chemistry of the Palaeoproterozoic Lovisa stratiform Zn-Pb deposit and the stratigraphically underlying Lovisa Fe Formation in the Bergslagen ore province (Sweden). We investigate the relative timing of formation and subsequent modifications of its ores in relation to the c. 1.87-1.80 Ga Svecokarelian orogeny. The Lovisa Zn-Pb deposit consists of several different ore types. The massive sphalerite-galena ore is distinctly deformed, exhibiting a multiple-scale "ball ore" texture with rounded silicate clasts within a deformed, fine-grained sulphide matrix. Underlying the massive ore is a locally folded, sphalerite-rich laminated ore, interpreted to represent a metamorphosed relict primary lamination. Several generations of sphalerite-galena fracture fillings and veins occur adjacent to the main ore zones and they cross-cut early ductile structures and metamorphic features. The trace element signatures of the sphalerite-galena infillings generally mimic those of the two main ore zones, thus supporting an origin by localised remobilisation of the primary sulphide ore and demonstrating limited trace element redistribution during this process. In contrast, discrete sulphosalt-rich fracture fillings cross-cutting earlier galena-chalcopyriterich fracture fillings and veinlets in the Lovisa Fe Formation suggest a significant but still relatively localised redistribution of metals. Trace element mapping of sulphides from the Lovisa Zn-Pb deposit reveals that inclusion-free overgrowths on pyrite crystals are locally Co-enriched compared to the cores, which resulted from the redistribution of Co during late metamorphic processes. Combined textural and geochemical evidence suggest that the originally syngenetic exhalative sulphide ore at Lovisa was locally strongly affected by polyphase deformation and remobilisation. This was initiated during the first stage of amphibolite facies grade regional metamorphism and deformation (D1, c. 1.87-1.85 Ga) but is mostly evident from the later stages (D2) and the evolution to retrograde and brittle conditions (c. 1.83-1.80 Ga and later).
|
|
| 5. |
- Babaahmadi, Arezou, 1985, et al.
(författare)
-
Development of an electro-chemical accelerated ageing method for leaching of calcium from cementitious materials
- 2016
-
Ingår i: Materials and Structures. - : Springer Science and Business Media LLC. - 1359-5997 .- 1871-6873. ; 49:1-2, s. 705-718
-
Tidskriftsartikel (refereegranskat)abstract
- To facilitate the long term durability predictions of nuclear waste repositories, acceleration methods enhancing calcium leaching process from cementitious materials are needed, even though mechanisms not necessarily comparable to those predominant in a natural leaching process may be developed. In the previously published acceleration methods the samples are very small, which limits further physical or mechanical tests. In this paper, a new acceleration method based on electro-chemical migration is presented. The method although not driven with the same kinetics as in natural leaching, was designed in such a way that unnecessarily destructive by-effects could be minimized while promoting a higher leaching rate for a sample size suitable for further testing the mechanical and physical properties. It is shown that approximately 1x10^6 C of electrical charge per paste specimen of size Ø50 x 75 mm (approximately 230 g) is required to leach out the total amount of Portlandite. The chemical and mineralogical properties of leached samples are characterized by various techniques. It is concluded that aged samples are comparable to those leached in a natural leaching process as both are characterized by a layered system comprising an unaltered core delineated by total dissolution of Portlandite followed by a progressive decalcification of the calcium silicate hydrate gel.
|
|
| 6. |
- Baldermann, A., et al.
(författare)
-
Impact of green clay authigenesis on element sequestration in marine settings
- 2022
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 13:1
-
Tidskriftsartikel (refereegranskat)abstract
- Retrograde clay mineral reactions (reverse weathering), including glauconite formation, are first-order controls on element sequestration in marine sediments. Here, we report substantial element sequestration by glauconite formation in shallow marine settings from the Triassic to the Holocene, averaging 3 +/- 2 mmol.cm(-2).kyr(-1) for K, Mg and Al, 16 +/- 9 mmol.cm(-2).kyr(-1) for Si and 6 +/- 3 mmol.cm(-2).kyr(-1) for Fe, which is similar to 2 orders of magnitude higher than estimates for deep-sea settings. Upscaling of glauconite abundances in shallow-water (0-200 m) environments predicts a present-day global uptake of similar to <= 0.1 Tmol.yr(-1) of K, Mg and Al, and similar to 0.1-0.4 Tmol.yr(-1) of Fe and Si, which is similar to half of the estimated Mesozoic elemental flux. Clay mineral authigenesis had a large impact on the global marine element cycles throughout Earth's history, in particular during 'greenhouse' periods with sea level highstand, and is key for better understanding past and present geochemical cycling in marine sediments.
|
|
| 7. |
- Barros, R., et al.
(författare)
-
LA-ICP-MS Rb-Sr dating of LCT rare-element pegmatites and associated rocks of Leinster, Ireland
- 2017
-
Ingår i: 14th SGA Biennial Meeting on Mineral Resources to Discover. 993-996. - 9782981689801
-
Konferensbidrag (refereegranskat)abstract
- High technology metals such as lithium and tantalum are commonly hosted in pegmatites, leading to renewed interest in understanding their origin. Obtaining accurate and precise results from pegmatites can be challenging. We have applied a newly developed laser ablation Rb-Sr dating method using reaction gases in a quadrupole ICP-MS to spodumene pegmatites and country rocks, late Caledonian granodiorite and Ordovician schist, in southeast Ireland. Rb-Sr isochron ages and initial Sr-87/Sr-86 ratios obtained are: around 413 Ma and 0.7109 +/- 49 to 0.8348 +/- 82 for lithium pegmatites; around 413 Ma and 0.7054 +/- 50 to 0.7102 +/- 28 for barren pegmatites; 420.6 +/- 8.4 Ma and 0.7068 +/- 28 for granodiorite; 406.5 +/- 5.8 and 0.7160 +/- 58 for schist. The method is sufficiently accurate and precise to date pegmatites. Ages obtained are consistent with the emplacement age of the Leinster Granite. Age constraints from schist within a pegmatite exomorphic halo are shown to be a good tool to determine pegmatite age. Highly variable initial Sr-87/Sr-86 ratios in spodumene pegmatites emplaced near schists show evidence for country rock contamination.
|
|
| 8. |
- Cabral, A. R., et al.
(författare)
-
Distinguishing high-from low-temperature platinum nuggets through their trace-element pattern
- 2019
-
Ingår i: Economic Geology and The Bulletin of the Society of Economic Geologists. - : Society of Economic Geologists. - 0361-0128. ; 114:2, s. 201-206
-
Tidskriftsartikel (refereegranskat)abstract
- High- and lowerature platinum nuggets from two historical localities, Chocó in Colombia and Córrego Bom Sucesso in Brazil, are compared with respect to trace elements. Supergene platinum nuggets from Córrego Bom Sucesso are enriched in Se and Hg, but depleted in siderophile and chalcophile elements, and have fractionated platinum group element patterns, in comparison with magmatic platinum nuggets from Chocó. In particular, Se concentrations over ∼100 g/g Se and S/Se ratios above unity indicate Se recycling in a supergene environment with abundant organic matter. © 2019 Society of Economic Geologists; Economic Geology.
|
|
| 9. |
- Cabral, A. R., et al.
(författare)
-
Fluid-inclusion microthermometry and the Zr-in-rutile thermometer for hydrothermal rutile
- 2015
-
Ingår i: International Journal of Earth Sciences. - : Springer Science and Business Media LLC. - 1437-3254 .- 1437-3262. ; 104:2, s. 513-519
-
Tidskriftsartikel (refereegranskat)abstract
- The Zr-in-rutile thermometer is well established for the determination of metamorphic temperatures, particularly in high-grade metamorphic terrains, and for sedimentary provenance studies. The robustness of the rutile thermometry has not been tested on hydrothermal systems. Unlike quartz, a common hydrothermal mineral with abundant fluid inclusions, it is difficult to find fluid inclusions in rutile that are suitable for fluid-inclusion microthermometry. Here, we report fluid-inclusion microthermometric measurements in rutile from the auriferous quartz-kaolinite-hematite vein that typifies the gold deposit of Mil Oitavas in the southern Serra do Espinha double dagger o, Minas Gerais, Brazil. Primary fluid inclusions in the rutile record moderately saline (10-12 wt% NaCl equivalent), aqueous-carbonic fluids with a total homogenization temperature of similar to 250 A degrees C, which were likely trapped at about 300 A degrees C and 2.0 kbar. This temperature is approximately 200 A degrees C lower than that predicted by the Zr-in-rutile thermometer. For hydrothermal conditions of relatively low temperature, direct measurements of homogenization temperatures in rutile-hosted fluid inclusions should be preferred to the Zr-in-rutile thermometer.
|
|
| 10. |
- Chan, Phoebe, et al.
(författare)
-
Freshening of the Alaska Coastal Current recorded by coralline algal Ba/Ca ratios
- 2011
-
Ingår i: Journal of Geophysical Research-Biogeosciences. - 0148-0227. ; 116
-
Tidskriftsartikel (refereegranskat)abstract
- Arctic Ocean freshening can exert a controlling influence on global climate, triggering strong feedbacks on ocean-atmospheric processes and affecting the global cycling of the world's oceans. Glacier-fed ocean currents such as the Alaska Coastal Current are important sources of freshwater for the Bering Sea shelf, and may also influence the Arctic Ocean freshwater budget. Instrumental data indicate a multiyear freshening episode of the Alaska Coastal Current in the early 21st century. It is uncertain whether this freshening is part of natural multidecadal climate variability or a unique feature of anthropogenically induced warming. In order to answer this, a better understanding of past variations in the Alaska Coastal Current is needed. However, continuous long-term high-resolution observations of the Alaska Coastal Current have only been available for the last 2 decades. In this study, specimens of the long-lived crustose coralline alga Clathromorphum nereostratum were collected within the pathway of the Alaska Coastal Current and utilized as archives of past temperature and salinity. Results indicate that coralline algal Mg/Ca ratios provide a 60 year record of sea surface temperatures and track changes of the Pacific Decadal Oscillation, a pattern of decadal-to-multidecadal ocean-atmosphere climate variability centered over the North Pacific. Algal Ba/Ca ratios (used as indicators of coastal freshwater runoff) are inversely correlated to instrumentally measured Alaska Coastal Current salinity and record the period of freshening from 2001 to 2006. Similar multiyear freshening events are not evident in the earlier portion of the 60 year Ba/Ca record. This suggests that the 21st century freshening of the Alaska Coastal Current is a unique feature related to increasing glacial melt and precipitation on mainland Alaska.
|
|
| 11. |
- Chan, P., et al.
(författare)
-
Multicentennial record of Labrador Sea primary productivity and sea-ice variability archived in coralline algal barium
- 2017
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Accelerated warming and melting of Arctic sea-ice has been associated with significant increases in phytoplankton productivity in recent years. Here, utilizing a multiproxy approach, we reconstruct an annually resolved record of Labrador Sea productivity related to sea-ice variability in Labrador, Canada that extends well into the Little Ice Age (LIA; 1646 AD). Barium-to-calcium ratios (Ba/Ca) and carbon isotopes (delta C-13) measured in long-lived coralline algae demonstrate significant correlations to both observational and proxy records of sea-ice variability, and show persistent patterns of co-variability broadly consistent with the timing and phasing of the Atlantic Multidecadal Oscillation (AMO). Results indicate reduced productivity in the Subarctic Northwest Atlantic associated with AMO cool phases during the LIA, followed by a step-wise increase from 1910 to present levels-unprecedented in the last 363 years. Increasing phytoplankton productivity is expected to fundamentally alter marine ecosystems as warming and freshening is projected to intensify over the coming century.
|
|
| 12. |
- Cornell, David H., 1948, et al.
(författare)
-
Th-U-Pb zircon geochronology of the Palaeoproterozoic Hartley Formation porphyry by six methods, with age uncertainty approaching 1 Ma
- 2016
-
Ingår i: South African Journal of Geology. - : Geological Society of South Africa. - 0371-7208 .- 1012-0750. ; 119:3, s. 473-494
-
Tidskriftsartikel (refereegranskat)abstract
- The Palaeoproterozoic Hartley Formation in the Olifantshoek Group was deposited in one of the rift-related Waterberg (sensu lato) red bed basins which formed on the Kaapvaal Craton after the 2.05 Ga Bushveld intrusions and coeval thermal event. The age of these basins is not well constrained due to the shortage of directly dateable rock types. The Hartley Formation contains rare quartz-porphyry lavas interbedded with the dominant basalts and these provide the means to date the formation by analyses of zircon. In this work zircon from one sample has been dated by six Th-U-Pb methods, namely Laser Ablation ICP Quadrupole Mass Spectrometry, Laser Ablation ICP High-resolution Mass Spectrometry, Laser Ablation ICP Multicollector Mass Spectrometry U-Pb (also Lu-Hf), Nordsim Ion probe U-Pb and Th-Pb; and Krogh method ID-TIMS. Our precise ages give a combined age of 1915.2 ± 1.1 Ma. Including one published ion probe date from the only other known occurrence of quartz porphyry, the results only agree if the quoted analytical errors are increased by 20%, which gives a combined result of 1915.6 ± 1.4 Ma. This is considered a reliable, precise and accurate age for the Hartley Formation and supersedes the published Kober method 207Pb/206Pb age of 1928 ± 4 Ma. The new Lu-Hf zircon data, supported by published whole rock Sm-Nd and Rb-Sr data, suggests that both the dominant basalts and the rare quartz porphyries of the Hartley Formation were derived from mafic source rocks which had been in the crustal domain from Archaean times. By contrast with the intracratonic rifts of the other Waterberg Basins, the Olifantshoek Supergroup reflects the development of a western passive margin as the Archaean Kaapvaal Craton rifted and drifted. This was followed by accretion of the Rehoboth Province along the Kalahari Line, accompanied by the development of the east-vergent Kheis Province thrust complex. This created a larger cratonic block against which the 1.2 Ga collisions of Namaqua-Natal terranes impacted. The Kheis Province now yields ~1.17 Ma cooling ages, reflecting the Namaqua collisions, but the true age of the Kheis event is still enigmatic.
|
|
| 13. |
- Cornell, David H., 1948, et al.
(författare)
-
The Plat Sjambok Anorthosite and its tonalitic country rocks : mesoproterozoic pre-tectonic intrusions in the Kaaien Terrane, Namaqua-Natal Province, southern Africa
- 2013
-
Ingår i: International Geology Review. - : Informa UK Limited. - 0020-6814 .- 1938-2839. ; 55:12, s. 1471-1489
-
Tidskriftsartikel (refereegranskat)abstract
- The Plat Sjambok Anorthosite crops out near Prieska Copper Mines in the Namaqua-Natal Province of southern Africa. It is a massif-type anorthosite, previously regarded as a late-tectonic intrusion and part of the ca. 1100 Ma bimodal Keimoes Suite. Our new ion probe U-Pb zircon data show that the Plat Sjambok massif intruded at 1259 ± 5 Ma, before the 1220 Ma Namaqua collision events and is thus approximately 150 million years older than the Keimoes Suite. Despite the proximity to Prieska Mines, the anorthosite is located in the Kaaien Terrane close to the Brakbos Fault, which is the boundary with the Areachap Terrane in which Prieska Mines is situated. We dated the Nelspoortjie Tonalite, the main country rock of the Plat Sjambok Anorthosite, by laser ablation ICPMS at 1273 ± 13 Ma. Both intrusions thus originated concurrently with the 1286-1241 Ma volcanic rocks of the Areachap Group, which developed in a subduction-related arc setting, prior to its collision with the Kaaien Terrane and Kaapvaal Craton. Metamorphic zircon rims in the Plat Sjambok Anorthosite give an age of 1122 ± 7 Ma, a time that corresponds to a quiet period in the Areachap Terrane. We propose a tectonic model in which formation of the Nelspoortjie Tonalite and Plat Sjambok Anorthosite was driven by intrusions from the mantle into a back-arc related tensional environment within the Kaaien Terrane, possibly situated above an Archaean crustal tongue. This led to heating in a thickened crustal setting in which the tonalite originated as a partial melt of amphibolite. The anorthosite then formed as a mixture of mantle-derived gabbro and Archaean crustal rocks, which explains the 2100-2600 Ma zircon-Hf crustal residence ages and the Sm-Nd trend towards an old crustal source. The anorthosite and its country rocks were only juxtaposed with the Prieska Copper Mining District by late-tectonic uplift and transpressional movements on the Brakbos Fault towards the end of the Namaqua tectogenesis.
|
|
| 14. |
- Cruz-Uribe, Alicia, et al.
(författare)
-
A New LA-ICP-MS Method for Ti in Quartz: Implications and Application to HP Rutile-Quartz Veins from the Czech Erzgebirge
- 2017
-
Ingår i: Geostandards and Geoanalytical Research. - : Wiley. - 1639-4488 .- 1751-908X. ; 41:1
-
Tidskriftsartikel (refereegranskat)abstract
- Experimental determination of the pressure and temperature controls on Ti solubility in quartz provides a calibration of the Ti-in-quartz (TitaniQ) geothermometer applicable to geological conditions up to ~ 20 kbar. We present a new method for determining 48Ti mass fractions in quartz by LA-ICP-MS at the 1 μg g−1 level, relevant to quartz in HP-LT terranes. We suggest that natural quartz such as the low-CL rims of the Bishop Tuff quartz (determined by EPMA; 41 ± 2 μg g−1 Ti, 2s) is more suitable than NIST reference glasses as a reference material for low Ti mass fractions because matrix effects are limited, Ca isobaric interferences are avoided, and polyatomic interferences at mass 48 are insignificant, thus allowing for the use of 48Ti as a normalising mass. Average titanium mass fraction from thirty-three analyses of low temperature quartz from the Czech Erzgebirge is 0.9 ± 0.2 μg g−1 (2s) using 48Ti as a normalising mass and Bishop Tuff quartz rims as a reference material. The 2s average analytical uncertainty for individual analyses of 48Ti is 8% for 50 μm spots and 7% for 100 μm spots, which offers much greater accuracy than the 21–41% uncertainty (2s) incurred from using 49Ti as an analyte.
|
|
| 15. |
- Cruz-Uribe, A. M., et al.
(författare)
-
Trace element and isotopic zoning of garnetite veins in amphibolitized eclogite, Franciscan Complex, California, USA
- 2021
-
Ingår i: Contributions to Mineralogy and Petrology. - : Springer Science and Business Media LLC. - 0010-7999 .- 1432-0967. ; 176:5
-
Tidskriftsartikel (refereegranskat)abstract
- Here we present major element, trace element, and oxygen isotope data for garnet from an amphibolitized eclogite block from Ring Mountain, Franciscan Complex, California, USA. Garnetite veins 1-5 cm thick are laterally continuous up to 10 m within an Mg-rich blackwall zone of the eclogite block. Complex major and trace element zoning patterns reveal multiple stages of garnet growth in both the matrix and garnetite veins. Similarities in major and trace element zoning between matrix and vein garnet suggest that crystallization of the garnetite veins began toward the end of matrix garnet core growth, and continued throughout the garnet growth history of the rock. Oscillatory zoning in rare-earth elements suggests garnet growth in pulses, with matrix-diffusion-limited growth in between pulses. Oxygen isotope analyses of matrix and vein garnet have a range in delta O-18 values of 5.3-11.1 parts per thousand. Differences in delta O-18 values of up to similar to 4 parts per thousand between garnet core and rim are observed in both the matrix and vein; garnet cores range from 9.8 to 11.1 parts per thousand (median 10.4 parts per thousand), garnet mantles range from 8.3 to 10.0 parts per thousand (median 9.7 parts per thousand), and garnet rims range from 5.8 to 7.8 parts per thousand (median 6.7 parts per thousand). Late-stage vein crystallization appears as a garnet "cement" that fills in a network of small (typically 5-50 mu m) garnet cores, and likely crystallized from an amorphous phase. The low delta O-18 values of this latest stage of garnet growth are consistent with interaction with serpentinites, and likely represent the physical incorporation of the eclogite block into the serpentinite matrix melange.
|
|
| 16. |
|
|
| 17. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Incorporation of Metals into Calcite in a Deep Anoxic Granite Aquifer
- 2018
-
Ingår i: Environmental Science & Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851 .- 1086-931X .- 1520-6912. ; 52:2, s. 493-502
-
Tidskriftsartikel (refereegranskat)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.
|
|
| 18. |
- Drake, Henrik, 1979-, et al.
(författare)
-
Incorporation of trace elements into calcite precipitated from deep anoxic groundwater in fractured granitoid rocks
- 2017
-
Ingår i: Procedia Earth and Planetary Science. 15th Water-Rock Interaction International Symposium (WRI). Evora, Portugal, OCT 16-21, 2016.. - : Elsevier BV. - 1878-5220. ; , s. 841-844
-
Konferensbidrag (refereegranskat)abstract
- An extensive microanalytical study of calcite precipitated from groundwater flowing into boreholes at >400 m depth in the Aspo Hard Rock Laboratory, Sweden, has been carried out. Hydrochemical variations in packed-off sections, isolating water-conducting fractures intersected by two boreholes, were documented over a period of 17 years. The extraction of the borehole equipment revealed calcite precipitation on the equipment. This mineral material enabled unique assessment of uptake of different trace elements by calcite during precipitation from granitoid fracture groundwater, at anoxic, low-temperature (c.a 14 degrees C), and neutral (pH: 7.4-7.7) conditions, under variable salinity (Cl: 2500-7000 mg/L) prevailing at these depths. Temporal hydrochemical variations could be traced by detailed micro-analytical transects in the calcites and the influence of metal speciation and complexation on partitioning into calcite could be assessed (e.g. explaining unexpectedly low incorporation of REEs). The resulting environment-specific partition coefficients for a large number of metals are relevant in models of radionuclide retention around proposed deep nuclear waste repositories in this kind of environment, particularly because 1) elements such as REEs act as natural analogues to actinides, and 2) existing coefficients established in laboratory or in other natural environments cannot be unreservedly applied to conditions in deep crystalline rocks.
|
|
| 19. |
- 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.
|
|
| 20. |
- Fumes, R. A., et al.
(författare)
-
Petrochronology of high-pressure granulite facies rocks from Southern Brasilia Orogen, SE Brazil: Combining quantitative compositional mapping, single-element thermometry and geochronology
- 2022
-
Ingår i: Journal of Metamorphic Geology. - : Wiley. - 0263-4929 .- 1525-1314. ; 40:3, s. 517-552
-
Tidskriftsartikel (refereegranskat)abstract
- We use a combination of several in situ techniques to assess the P-T-t path of high-pressure granulites from the Passos Nappe in the Southern Brasilia Orogen (SE Brazil). Quantitative element mapping and single-element thermometers (Zr-in-rutile and Ti-in-quartz) are coupled with P-T pseudosections and monazite and rutile dating. Compositional and temperature maps, based on cathodoluminescence mapping and in situ analyses of Ti-in-quartz, are presented as a novel approach to evaluate crystallization temperature. The studied rocks have a pelitic protolith and record a peak pressure assemblage of garnet + kyanite + rutile + K-feldspar + quartz + melt +/- plagioclase that formed at similar to 830 degrees C and 1.2 GPa. Retrograde conditions of similar to 560 degrees C and 0.6 GPa are determined based on the grossular content of garnet and the crystallization of biotite and ilmenite. Metamorphic peak conditions occurred ca. 635 Ma, according to monazite dating, with a younger date of ca. 615 Ma associated with later kyanite crystallization. Rutile ages of ca. 590 Ma are linked to the late retrograde stage (at similar to 600 degrees C). Results show that the distribution of Ti-in-quartz is heterogeneous, decreasing in abundance towards the rim of crystals, though the higher temperatures constrained with Ti-in-quartz thermometry are broadly consistent with peak conditions. The peak pressure conditions are consistent with continental collision setting in the Southern Brasilia Orogen and were followed by an early cooling/decompression stage and then by a slow cooling during exhumation and transport to shallower crustal levels.
|
|
| 21. |
- Gamboa, G., et al.
(författare)
-
Mg/Ca ratios in coralline algae record northwest Atlantic temperature variations and North Atlantic Oscillation relationships
- 2010
-
Ingår i: Journal of Geophysical Research-Oceans. - 0148-0227. ; 115
-
Tidskriftsartikel (refereegranskat)abstract
- [1] Climate variability in the North Atlantic has been linked in part to the North Atlantic Oscillation (NAO). The NAO influences marine ecosystems in the northwestern Atlantic and transport variability of the cold Labrador Current. Understanding historic patterns of NAO variability requires long-term and high-resolution climate records that are not available from instrumental data. Here we present the first century-scale proxy record of sea surface temperature (SST) variability from the Newfoundland shelf, a region from which other annual-resolution shallow marine proxies are unavailable. The 116 year record was obtained from three sites along the eastern Newfoundland shelf using laser ablation inductively coupled mass spectrometry-determined Mg/Ca ratios in the crustose coralline alga Clathromorphum compactum. The alga is characterized by a high Mg-calcite skeleton exhibiting annual growth increments and a century-scale lifespan. Results indicate positive correlations between interannual variations in Mg/Ca ratios and both station-based and gridded instrumental SST. In addition, the record shows high spatial correlations to SST across the Newfoundland shelf and the Gulf of St. Lawrence. Before 1950 the Mg/Ca proxy record reveals significant departures from gridded temperature records. While the Newfoundland shelf is generally considered a region of negative correlations to the NAO, the algal time series as well as a recent modeling study suggest a variable negative relationship with the NAO which is strongest after similar to 1960 and before the mid-1930s.
|
|
| 22. |
- Halfar, J., et al.
(författare)
-
Coralline algal growth-increment widths archive North Atlantic climate variability
- 2011
-
Ingår i: Palaeogeography Palaeoclimatology Palaeoecology. - 0031-0182. ; 302:1-2, s. 71-80
-
Tidskriftsartikel (refereegranskat)abstract
- Over the past decade coralline algae have increasingly been used as archives of paleoclimate information. Encrusting coralline algae, which deposit annual growth increments in a high Mg-calcite skeleton, are amongst the longest-lived shallow marine organisms. In fact, a live-collected plant has recently been shown to have lived for at least 850 years based on radiometric dating. While a number of investigations have successfully used geochemical information of coralline algal skeletons to reconstruct sea surface temperatures, less attention has been paid to employ growth increment widths as a temperature proxy. Here we explore the relationship between growth and environmental parameters in Clathromorphum compactum collected in the subarctic Northwestern Atlantic. Results indicate that growth-increment widths of individual plants are poorly correlated with instrumental sea surface temperatures (SST). However, an averaged record of multiple growth increment-width time series from a regional network of C. compactum specimens up to 800 km apart reveals strong correlations with annual instrumental SST since 1950. Hence, similar to methods applied in dendrochronology, averaging of multiple sclerochronological records of coralline algae provides accurate climate information. A 115-year growth-increment width master chronology created from modern-collected and museum specimens is highly correlated to multidecadal variability seen in North Atlantic sea surface temperatures. Positive changes in algal growth anomalies record the well-documented regime shift and warming in the northwestern Atlantic during the 1990s. Large positive changes in algal growth anomalies were also present in the 1920s and 1930s, indicating that the impact of a concurrent large-scale regime shift throughout the North Atlantic was more strongly felt in the subarctic Northwestern Atlantic than previously thought, and may have even exceeded the 1990s event with respect to the magnitude of the warming. (C) 2010 Elsevier B.V. All rights reserved.
|
|
| 23. |
|
|
| 24. |
- Hamisi, J., et al.
(författare)
-
Hydrothermal footprint of the Birthday Reef, Reefton goldfield, New Zealand
- 2017
-
Ingår i: New Zealand Journal of Geology and Geophysics. - : Informa UK Limited. - 0028-8306 .- 1175-8791. ; 60:2, s. 59-72
-
Tidskriftsartikel (refereegranskat)abstract
- The Birthday Reef was the most productive gold producer during historic mining of the Reefton goldfield on the west coast of the South Island of New Zealand. Deep exploration drill holes (up to 1.6 km long) intersected the mineralised quartz vein zone and adjacent hydrothermal alteration halo beneath the historic mine workings. The Paleozoic metasedimentary host rocks contain between 0.5 and 8 ppb Au and between 4 and 30 ppm As, and metamorphic pyrite typically contains 0.1 to 1 ppm Au in solid solution. The Au and As halo, above these background values, extends < 20 m from the Birthday Reef, and other petrographic indicators of alteration are also confined to this narrow envelope. Porphyroblasts of pyrite and arsenopyrite, with minor Au enrichment, grew across the metamorphic cleavage in the alteration halo before emplacement of the Birthday Reef and associated shearing, and reflect an earlier, late metamorphic precursor to the main gold mineralisation phase.
|
|
| 25. |
- Hegner, E., et al.
(författare)
-
Mineral Ages and P-T Conditions of Late Paleozoic High-Pressure Eclogite and Provenance of M Lange Sediments from Atbashi in the South Tianshan Orogen of Kyrgyzstan
- 2010
-
Ingår i: American Journal of Science. - 0002-9599. ; 310:9, s. 916-950
-
Tidskriftsartikel (refereegranskat)abstract
- Ages derived from various isotope systems in high-pressure (HP) rocks of the western Tianshan orogen of NW China have been interpreted as evidence for late Carboniferous and/or Triassic collision of the accretionary margin of the Central Asian Orogenic Belt (CAOB) with the Tarim Craton. In order to elucidate this controversy, we present new P-T data as well as Sm-Nd and (40)Ar/(39)Ar cooling ages for an eclogite sample from Atbashi in the accretionary m lange of the South Tianshan suture in Kyrgyzstan, some 500 km along strike to the west of the controversial locality in the upper Akeyazhi River Valley in NW China. A clockwise P-T path for the eclogite with peak pressures of 18 to 24 kbar at 520 to 600 degrees C is consistent with near-isothermal decompression and exhumation in a subduction zone before collision of the CAOB with the Tarim Craton. Geochemical data and an initial epsilon Nd value of similar to +9 suggest an N-MORB protolith for the eclogite. The high-pressure mineral assemblage of the eclogite yielded a statistically robust Sm-Nd isochron age of 319 +/- 4 Ma (2 sigma, 5 data points, MSWD = 0.4) for equilibration and closure of the Sm-Nd system during HP metamorphism. (40)Ar/(39)Ar dating of phengite from the same sample yielded a cooling age of 316 +/- 3 Ma (2 sigma) implying rapid exhumation. Docking of the Tarim Craton with the southern margin of the Middle Tianshan-North Tianshan blocks in Kyrgyzstan during the late Carboniferous is supported by widespread emplacement of A-type granitoids of early Permian age that suggest a setting of consolidated crust. An tuunetamorphosed and little deformed molasse-type conglomerate of latest Carboniferous age, overlying the HP rocks, indicates that HP metamorphism, exhumation, and exposure of the HP m lange occurred from 320 to 300 Ma. The detrital zircon age spectrum of a metagraywacke sample from the accretionary melange suggests sources in the Tarim Craton and/or from the Middle and North Tianshan that possibly comprise rifted blocks from Tarim.
|
|
