Ändra sökning
Avgränsa sökresultatet
1 - 36 av 36
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1. Barnes, Christopher J..
    et al.
    Majka, Jarek
    Jeanneret, Pauline
    Ziemniak, Grzegorz
    Kooijman, Ellen
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Kośmińska, Karolina
    Kielman-Schmitt, Melanie
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Schneider, D.A.
    Using Th-U-Pb geochronology to extract crystallization ages of Paleozoic metamorphic monazite contaminated by initial Pb2021Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 582, s. 120450-120450, artikel-id 120450Artikel i tidskrift (Refereegranskat)
  • 2. Bellucci, J. J.
    et al.
    Herd, C. D. K.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Nemchin, A. A.
    Kenny, G. G.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Merle, Renaud E.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Insights into the chemical diversity of the martian mantle from the Pb isotope systematics of shergottite Northwest Africa 81592020Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 545, artikel-id 119638Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Shergottite Northwest Africa (NWA) 8159 is a basaltic rock derived from a mantle source with chemical characteristics that are unique in the martian meteorite suite. To further investigate this source reservoir, the Pb isotope compositions of plagioclase/maskelynite, pyroxene, phosphates, and shock melt-glass in NWA 8159 have been measured in situ by Secondary Ion Mass Spectrometry (SIMS). Due to the limited spread in Pb isotope data, these Pb isotope compositions have been used to calculate an imprecise PbPb isochron age of 3.4 ± 2.1 Ga (2σ), which is broadly consistent with the crystallization age of 2.37 ± 0.25 Ga determined previously by 147Sm143Nd. The lack of radiogenic in-growth within individual minerals since 2.4 Ga means that this sample is depleted in U, which is in agreement with NWA 8159's positive initial ε143Nd. An initial Pb composition was calculated using an x-y weighted average of the least radiogenic Pb isotope population measured in the sample. This initial Pb composition is not consistent with the model for Pb growth in the shergottite mantle at 2.4 Ga. This composition is, however, consistent with the model for the Nakhla-Chassigny mantle. Using the latter model, a source μ (238U/204Pb) of 2.6 ± 0.6 has been calculated. This μ-value is in contrast with the other depleted shergottites (1.4-1.5) and falls significantly off the array of source ε143Nd vs. μ defined by the rest of the martian meteorite suite and thus, necessitates a differentiation history distinct from the other martian meteorites. Sequestering Pb in sulphides during differentiation is the only mechanism to fractionate U from Pb and create a low-μ reservoir. Consequently, the relatively high μ-value of the source of NWA 8159 is in contrast with the positive initial ε143Nd and indicates that its mantle source region likely lacked significant sulphur. This is consistent with the lack of sulphides in the sample itself and could have played a role in its complicated oxidation history.

  • 3.
    Bellucci, Jeremy
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Nemchin, Alexander
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Ross, Kielman
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Snape, Joshua
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Pidgeon, Robert
    Geochronology of Hadean zircon grains from the Jack Hills, Western Australia constrained by quantitative scanning ion imaging2018Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 476, s. 469-480Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Five Hadean (> 4 Ga) aged zircon grains from the Jack Hills metasedimentary belt have been investigated by a secondary ion mass spectrometry scanning ion image technique. This technique has the ability to obtain accurate and precise full U-Pb systematics on a scale < 5 μm, as well as document the spatial distribution of U, Th and Pb. All five of the grains investigated here have complex cathodoluminescence patterns that correlate to different U, Th, and Pb concentration domains. The age determinations for these different chemical zones indicate multiple reworking events that are preserved in each grain and have affected the primary crystalized zircon on the scale of < 10 μm, smaller than conventional ion microprobe spot analyses. In comparison to the spot analyses performed on these grains, these new scanning ion images and age determinations indicate that almost half of the spot analyses have intersected several age and chemical domains in both fractured and unfractured parts of the individual crystals. Some of these unfractured, mixed domain spot analyses have concordant ages that are inaccurate. Thus, if the frequency of spot analyses intersecting mixed domains here is even close to representative of all other studies of the Jack Hills zircon population, it makes the interpretation of any trace element, Hf, or O isotopic data present in the literature tenuous. Lastly, all of the grains analysed here preserve at least two distinguishable 207Pb/206Pb ages. These ages are preserved in core-rim and/or complex internal textural relationships in unfractured domains. These secondary events took place at ca. 4.3, 4.2, 4.1, 4.0, 3.7, and 2.9 Ga, which are coincident with previously determined statistically robust age peaks present in this zircon population.

    Ladda ner fulltext (pdf)
    fulltext
  • 4.
    Bellucci, Jeremy
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Nemchin, Alexander
    Pidgeon, Robert
    Grange, Marion
    Reddy, Steven
    Timms, Nick
    A scanning ion imaging investigation into the micron-scale U-Pb systematics in a complex lunar zircon2016Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 438, s. 112-122Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The full U-Pb isotopic systematics in a complex lunar zircon ‘Pomegranate’ from lunar impact breccia 73235 have been investigated by the development of a novel Secondary Ion Mass Spectrometry (SIMS) scanning ion imaging (SII) technique. This technique offers at least a four-fold increase in analytical spatial resolution over traditional SIMS analyses in zircon. Results from this study confirm the hypothesis that the Pomegranate zircon crystallized at 4.302 ± 0.013 Ga and experienced an impact that formed, U-enriched zircon around primary zircon cores at 4.184 ± 0.007 Ga (2σ, all uncertainties). The increase in spatial resolution offered by this technique has facilitated targeting of primary zircon that was previously inaccessible to conventional spot analyses. This approach has yielded results indicating that individual grains with a diffusive distance of less than ~4 μm have been reset to the young impact age, while individual grains with a diffusive distance larger than ~6 μm have retained the old crystallization age. Assuming a broad range in cooling rate of 0.5–50 °C/year, which has been observed in a suite of similar lunar breccias, a maximum localized temperature generated by the impact that reset small prima- ry zircon and created new, high-U zircon is estimated to be between 1100 and 1280 °C.

    Ladda ner fulltext (pdf)
    fulltext
  • 5. Brengman, Latisha A.
    et al.
    Fedo, Christopher M.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Jabeen, Iffat
    Banerjee, Neil R.
    Evaluating the geochemistry and paired silicon and oxygen isotope record of quartz in siliceous rocks from the ~3 Ga Buhwa Greenstone Belt, Zimbabwe, a critical link to deciphering the Mesoarchean silica cycle2021Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 577, s. 120300-120300, artikel-id 120300Artikel i tidskrift (Refereegranskat)
  • 6. Chatterjee, Sukalpa
    et al.
    Mezger, Klaus
    Pandey, Om Prakash
    Kielman-Schmitt, Melanie
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Hofer, Alina
    Kooijman, Ellen
    Naturhistoriska riksmuseet, Enheten för geovetenskap. Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden.
    The Singhbhum Craton (India) records a billion year of continental crust formation and modification2023Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 641, s. 121772-121772, artikel-id 121772Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The petrogenesis of continental crust from its ultimate mantle source can be reconstructed from the element abundances and radiogenic isotope compositions of ideally pristine igneous rocks. The initial isotope compositions of igneous rocks provide geochemical constraints on the age, composition and evolution of their source(s). Determining initial isotope ratios for rock samples can be challenging, especially in rocks with a long and protracted thermal history. The Rb-Sr system is highly sensitive to parent-daughter element fractionation during magma differentiation. This makes the Rb-Sr isotope systematics ideal to trace the precursor composition of Archean felsic crust and constrain the time of element fractionation during the formation and subsequent modification of continental crust. Initial isotope compositions can be obtained directly from minerals that strongly prefer the daughter element and effectively exclude the parent element of the radio-isotope system of interest. Apatite, having a near zero Rb/Sr ratio, is ideal for preserving its initial 87Sr/86Sr and zircon records initial 176Hf/177Hf compositions. Combined modelling of Sr and Hf isotope data from granitoids of the Archean Singhbhum Craton, indicates that the older Paleoarchean granitoids, emplaced between 3.53 Ga and 3.44 Ga, were derived from a mafic precursor (∼52–54 wt% SiO2) sourced from a depleted mantle at ∼3.71 Ga. Initial 87Sr/86Sr isotope signatures of matrix apatite and apatite inclusions in zircon from the younger Paleoarchean granitoids (3.4–3.2 Ga) of the Singhbhum Craton indicate these younger granitoids were produced by mixing of magma generated from an older mafic source and partial melts derived from the older granitoids. The combined Sr-Hf isotope modelling links the timing of mantle extraction of the precursor material for Paleoarchean Singhbhum granitoids with a known mafic crust extraction event at ∼3.71 Ga. In combination, the new Sr isotope data from apatite combined with whole rock and zircon Hf isotope data from the literature reveal a ∼1 Ga protracted crustal growth and differentiation history of the nucleus of the Singhbhum Craton. By combining radio-isotope systems like 87Rb-87Sr and 176Lu-176Hf, the petrogenesis of Archean felsic crust from the extraction of mafic material from the mantle to reworking in an orogenic cycle to emplacement can be reconstructed. This approach can be applied to other greenstone-gneiss terranes to quantify the spatio-temporal and compositional evolution of voluminous felsic crust and the formation of cratons in the Archean.

  • 7. Crémière, A.
    et al.
    Lepland, A.
    Chand, S.
    Sahy, D.
    Kirsimäe, K.
    Bau, M.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Noble, S.R.
    Martma, T.
    Thorsnes, T.
    Brunstad, H.
    Fluid source and methane-related diagenetic processes recorded in cold seep carbonates from the Alvheim channel, central North Sea2016Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 432, s. 16-33Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Integrated petrography, mineralogy, geochronology and geochemistry of cold seep carbonate crusts and free gas from the Alvheim channel elucidate diagenetic carbonate precipitation and related seepage histories in the central North Sea. Free gas isotope characteristics coupled with carbonate δ13C values as low as − 66‰ VPDB, indicate a predominantly microbial methane source with minor thermogenic contribution. We estimate that ~ 70% of the carbon sequestered into carbonate precipitates was derived from local oxidation of methane. The early stage of crust growth is represented by microcrystalline aragonite and Mg-calcite (10 to 40% mol MgCO3) cementing seafloor sediments consisting of clays, quartz, feldspar, and minor detrital low Mg-calcite and dolomite. Typical association of aragonite cement with coarse-grained detritus may reflect elevated fluid flow and flushing of fine particles prior to cementation close to the seafloor. Middle rare earth element enrichment in early generation microcrystalline cements containing framboidal pyrite indicates diagenetic precipitation within the zone of anaerobic methane oxidation contiguous to iron reduction. The later generation diagenetic phase corresponds to less abundant radial fibrous and botryoidal aragonite which lines cavities developed within the crusts. In contrast to early generation cements, late generation cavity infills have rare earth elements and Y patterns with small negative Ce anomalies similar to seawater, consistent with carbonate precipitation in a more open, seawater dominated system. Aragonite U–Th ages indicate carbonate precipitation between 6.09 and 3.46 kyr BP in the northern part of the channel, whereas in the southern part precipitation occurred between 1.94 and 0.81 kyr BP reflecting regional changes in fluid conduit position.

  • 8. Deegan, F.M.
    et al.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Troll, V.R.
    Budd, D.A.
    Harris, C.
    Geiger, H.
    Hålenius, U.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Pyroxene standards for SIMS oxygen isotope analysis and their application to Merapi volcano, Sunda arc, Indonesia2016Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 447, s. 1-10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Measurement of oxygen isotope ratios in common silicate minerals such as olivine, pyroxene, feldspar, garnet, and quartz is increasingly performed by Secondary Ion Mass Spectrometry (SIMS). However, certain mineral groups exhibit solid solution series, and the large compositional spectrum of these mineral phases will result in matrix effects during SIMS analysis. These matrix effects must be corrected through repeated analysis of compositionally similar standards to ensure accurate results. In order to widen the current applicability of SIMS to solid solution mineral groups in common igneous rocks, we performed SIMS homogeneity tests on new augite (NRM-AG-1) and enstatite (NRM-EN-2) reference materials sourced from Stromboli, Italy and Webster, North Carolina, respectively. Aliquots of the standard minerals were analysed by laser fluorination (LF) to establish their δ18O values. Repeated SIMS measurements were then performed on randomly oriented fragments of the same pyroxene crystals, which yielded a range in δ18O less than ± 0.42 and ± 0.58‰ (2σ) for NRM-AG-1 and NRM-EN-2, respectively. Homogeneity tests verified that NRM-AG-1 and NRM-EN-2 do not show any crystallographic orientation bias and that they are sufficiently homogeneous on the 20 μm scale to be used as routine mineral standards for SIMS δ18O analysis. We subsequently tested our new standard materials on recently erupted pyroxene crystals from Merapi volcano, Indonesia. The δ18O values for Merapi pyroxene obtained by SIMS (n = 204) agree within error with the LF-derived δ18O values for Merapi pyroxene but differ from bulk mineral and whole-rock data obtained by conventional fluorination. The bulk samples are offset to higher δ18O values as a result of incorporation of mineral and glass inclusions that in part reflects crustal contamination processes. The Merapi pyroxene SIMS data, in turn, display a frequency peak at 5.8‰, which allows us to estimate the δ18O value of the primary mafic magma at Merapi to ~ 6.1‰ when assuming closed system differentiation.

  • 9.
    Dekov, Vesselin
    et al.
    University of Sofia.
    Boycheva, Tanya
    University of Sofia.
    Hålenius, Ulf
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Petersen, Sven
    Leibiz-Institut für Meeresforschung, IFM-GEOMAR.
    Billström, Kjell
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Stummeyer, Jens
    Bundesanstalt für Geowissenschaften und Rohstoffe, Hannover.
    Kamenov, George
    University of Florida.
    Shanks, Wayne
    U.S. Geological Survey, Denver.
    Atacamite and paratacamite from the ultramafic-hosted Logatchev seafloor vent field (14°45´ N, Mid-Atlantic Ridge)2011Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 286, s. 169-184Artikel i tidskrift (Refereegranskat)
  • 10.
    Dekov, Vesselin M.
    et al.
    IFREMER.
    Rouxel, Olivier
    Woods Hole Oceanographic Institution.
    Asael, Dan
    IFREMER.
    Hålenius, Ulf
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Munnik, Frans
    Helmoholz-Zentrum Dresden-Rossendorf.
    Native Cu from the oceanic crust: Isotopic insights into native metal origin2013Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 359, s. 136-149Artikel i tidskrift (Refereegranskat)
  • 11. Dekov, Vesselin
    et al.
    Vanlierde, E.
    Billström, Kjell
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Garbe-Schönberg, C-D.
    Weiss, D.J.
    Gatto Rotondo, G.
    Van Mee, K.
    Kuzmann, E.
    Fortin, D.
    Darchuk, L.
    Van Grieken, R.
    Ferrihydrite precipitation in goundwater-fed river systems (Nete and Demer river basins, Belgium): Insights from a combined Fe-Zn-Sr-Nd-Pb-isotope study.2014Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 386, s. 1-15Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Two groundwater-fed river systems (Nete and Demer, Belgium) carry red suspended material that settles on the river bed forming red sediments. The local aquifer that feeds these river systems is a glauconite-rich sand, which provides most of the dissolved Fe to the rivers. The solid component of these systems, i.e., the red suspended material and sediments, has a simple mineralogy (predominantly ferrihydrite), but shows a complex geochemistry pointing out the different processes contributing to the river chemistry: (1) the red sediments have higher transition metal (excluding Cu) and detrital element (e.g., Si, Al, K, Rb, etc.) concentrations than the red suspended matter because of their longer residence time in the river and higher contribution of the background (aquifer) component, respectively; (2) the red suspended material and sediments have inherited their rare earth element (REE) patterns from the aquifer; (3) the origin of Sr present in the red suspended matter and red sediments is predominantly marine (i.e., Quaternary calcareous rocks), but a small amount is geogenic (i.e., from detrital rocks); (4) Pb in both solids originates mostly from anthropogenic and geogenic sources; (5) all of the anthropogenic Pb in the red suspended material and sediments is hosted by the ferrihydrite; (6) Nd budget of the red riverine samples is controlled by the geogenic source and shows little anthropogenic component; (7) the signi- ficant Fe- and Zn-isotope fractionations are in line with the previous studies. Their fractionation patterns do not correlate, suggesting that the processes controlling the isotope geochemistry of Fe and Zn are different: oxidation/reduction most likely governs the Fe-isotope fractionation, whereas adsorption/desorption or admixing of anthropogenic sources controls the isotope fractionation of Zn.

  • 12.
    Dekov, V.M.
    et al.
    Department of Ocean Sciences, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo 108-8477, Japan.
    Kyono, K.
    Department of Ocean Sciences, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo 108-8477, Japan.
    Yasukawa, K.
    Frontier Research Center for Energy and Resources, School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan; Department of Systems Innovation, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
    Guéguen, B.
    CNRS, Univ Brest, UMR 6538 Laboratoire Géosciences Océan, F-29280 Plouzané, France; CNRS, Univ Brest, UMS 3113, F-29280 Plouzané, France.
    Ivarsson, Magnus
    Naturhistoriska riksmuseet, Enheten för paleobiologi.
    Kamenov, G.D.
    Department of Geological Sciences, University of Florida, 241 Williamson Hall, Gainesville, FL 32611, USA.
    Yamanaka, T.
    Department of Ocean Sciences, Tokyo University of Marine Science and Technology, 4-5-7 Konan, Minato-ku, Tokyo 108-8477, Japan.
    Asael, D.
    Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA.
    Ishida, M.
    Department of Systems Innovation, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
    Cavalcante, L.L.
    Naturhistoriska riksmuseet, Enheten för paleobiologi.
    Kato, Y.
    Frontier Research Center for Energy and Resources, School of Engineering, The University of Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan.
    Toki, T.
    Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan.
    Ishibashi, J.-I.
    Kobe Ocean-Bottom Exploration Center, Kobe University, 5-1-1 Fukaeminami-machi, Higashinada-ku, Kobe 658-0022, Japan.
    Mineralogy, geochemistry and microbiology insights into precipitation of stibnite and orpiment at the Daiyon-Yonaguni Knoll (Okinawa Trough) hydrothermal barite deposits2022Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 610, s. 121092-121092, artikel-id 121092Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Samples of active chimneys, chimney flanges and massive sulfides from the Daiyon-Yonaguni Knoll hydrothermal field are composed of major barite and minor stibnite and orpiment. Barite is inferred to precipitate from focused-discharge fluids composed of >40% hydrothermal end-member fluid at T = 100-240°C, whereas the stibnite and orpiment are later and lower temperature precipitates. The hydrothermal fluids from this field were subject of sub-seafloor boiling and phase separation and, consequently, are brine-rich depleted in volatile and enriched in non-volatile elements. Boiling and phase separation exerted major control on the rare earth elements (REE) partitioning in the vent fluids: high-chlorinity high-temperature fluids were enriched in light REE and low-chlorinity low-temperature fluids were enriched in heavy REE. Y/Ho molar ratio and Ce anomaly of the vent fluids suggest that the seawater has not completely reacted with the basement rocks and has not equilibrated with them. The trace element concentrations in the hydrothermal deposits suggest a complex interplay among hydrothermal, hydrogenetic and microbial processes. Sulfur isotope composition of the sulfides suggests that the sulfide S is a mixture of both basement rock and seawater S with a higher proportion of the basement rock S. The sulfate dissolved in the fluids was subjected to reduction during a slow mixing of hydrothermal fluid and seawater within the chimney walls of the Tiger and Abyss vents and this resulted in a heavy S-isotope composition of the vent fluid sulfate. Lead isotope composition of the hydrothermal deposits indicates mixing relationships suggesting that Pb and potentially other metals with similar geochemical behavior were derived from two or three sources. The Pb isotopes in the hydrothermal deposits imply that an enriched source, either sediments or extended continental lithosphere, and a depleted source, potentially back-arc mafic volcanics, are present in the area of Daiyon-Yonaguni Knoll. Filamentous orpiment found in the deposits is supposed to be either heavily mineralized fungal hyphae or pure abiogenic biomorphs. Presence of carbonaceous matter on and around the orpiment filaments suggests for microbial activity during filament formation. The filaments experienced temperature of 209.1±37.1°C which falls within the temperature range of the Daiyon-Yonaguni Knoll vent fluids. Stability phase diagrams modeling reveals that the stability of stibnite does not depend on the vent fluid chlorinity, but depends on the vent fluid temperature: the area of stibnite stability increases with decreasing vent fluid temperature and results in stibnite precipitation at low log10a of Sb2S42- and less reduced environment (Eh still <0). Orpiment is stable in a wide range of log10a of H2AsO4-, in reduced conditions and at high S activity. Barite is stable in wide range of log10a of Ba2+ and precipitates in slightly reduced to slightly oxic conditions.

    Ladda ner fulltext (pdf)
    fulltext
  • 13.
    Fehr, Manuela A.
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Andersson, Per S.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Hålenius, Ulf
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Gustafsson, Örjan
    Stockholms universitet.
    Mörth, Carl-Magnus
    Stockholms universitet.
    Iron enrichments and Fe isotopic compositions of surface sediments from the Gotland Deep, Baltic Sea2010Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 277, s. 310-322Artikel i tidskrift (Refereegranskat)
  • 14. Feng, Dong
    et al.
    Peckmann, Jörn
    Li, Niu
    Kiel, Steffen
    Naturhistoriska riksmuseet, Enheten för paleobiologi.
    Qiu, Jian-Wen
    Liang, Qianyong
    Carney, robert
    Peng, Yongbo
    Tao, Jun
    Chen, Duofu
    The stable isotope fingerprint of chemosymbiosis in the shell organic matrix of seep-dwelling bivalves2018Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 479, s. 241-250Artikel i tidskrift (Refereegranskat)
  • 15. Galic, A.
    et al.
    Mason, P.R.D.
    Mogollon, J.M.
    Wolthers, M.
    Vroon, P.Z.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Pyrite in a sulfate-poor Paleoarchean basin was derived predominantly from elemental sulfur: evidence from 3.2 Ga sediments in the Barberton Greenstone Belt, Kaapvaal Craton.2017Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 449, s. 135-146Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Multiple sulfur isotope variability in Archean sedimentary rocks provides constraints on the composition of the Earth’s earliest atmosphere. The magnitude and sign of mass-independent anomalies reflect not only atmospheric processes, but also transformations due to the Archean marine sulfur cycle prior to preservation into sedimentary pyrite. The processes affecting the Archean marine sulfur cycle and the role of microbial or abiotic redox reactions during pyrite formation remain unclear. Here we combine iron (Fe) and multiple sulfur (S) isotope data in individual pyrite grains with petrographic information and a one-dimensional reactive transport model, to investigate the sources of Fe and S in pyrite formed in a Paleoarchean sedimentary basin. Pyrites were selected from mudstones, sandstones and chert obtained from a drill core in the ca. 3.2 Ga Mapepe and Mendon Formations of the Fig Tree and Onverwacht Groups, respectively, in the Barberton Greenstone Belt, Kaapvaal Craton, South Africa. Pyrite textures and δ56Fe distinguish early-diagenetic pyrite formed with pore-water ferrous iron (disseminated grains with average δ56Fepyrite = 0‰) from late-diagenetic pyrite formed through sulfidation of iron oxide minerals (layered and aggregate forms with average δ56Fepyrite = + 1‰). Mass dependent S isotope variability in pyrite was small (δ34Spyrite ranged from − 1.1 to + 3.3‰) with a correspondingly minor spread in Δ33Spyrite (ranging from + 0.3 to + 2.1‰) and Δ36Spyrite (ranging from − 3.08 to + 0.27‰) that indicates a lack of post-depositional re-working with other distinct sulfur sources. Our combined Fe and S isotope data are most readily explained with pyrite sulfide derived from microbial-reworking of solid elemental S. Iron oxide minerals were necessary to buffer sulfide concentrations and provide favorable conditions for microbial sulfur disproportionation to proceed. The lack of a negative Δ33S signal indicates that pyrite from relatively deep marine diagenetic environments only partially records the products of atmospheric photolysis, consistent with low sulfate concentrations in the Paleoarchean ocean.

  • 16.
    Gdaniec, Sandra
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Roy-Barman, M
    Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ Université Paris-Saclay, Gif-sur-Yvette, France.
    Levier, M
    Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ Université Paris-Saclay, Gif-sur-Yvette, France.
    Valk, O
    Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany.
    Rutgers van der Loeff, M
    Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany.
    Foliot, L
    Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ Université Paris-Saclay, Gif-sur-Yvette, France.
    Dapoigny, A
    Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ Université Paris-Saclay, Gif-sur-Yvette, France.
    Missiaen, L
    Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ Université Paris-Saclay, Gif-sur-Yvette, France.
    Mörth, C-M
    Stockholm University.
    Andersson, P.S.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    231Pa and 230Th in the Arctic Ocean: Implications for boundary scavenging and 231Pa-230Th fractionation in the Eurasian Basin2020Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, s. 1-14, artikel-id 119380Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    231Pa, 230Th and 232Th were analyzed in filtered seawater (n=70) and suspended particles (n=39) collected along a shelf-basin transect from the Barents shelf to the Makarov Basin in the Arctic Ocean during GEOTRACE Ssection GN04 in 2015. The distribution of dissolved 231Pa and 230Th in the Arctic Ocean deviates from the linear increase expected from reversible scavenging. Higher 232Th concentrations were observed at the shelf, slope and in surface waters in the deep basin, pointing at lithogenic sources. Fractionation factors (FTh/Pa) observed at the Nansen margin were higher compared to FTh/Pa in the central Nansen Basin, possibly due to the residual occurrence of hydrothermal particles in the deep central Nansen Basin. Application of a boundary scavenging model quantitatively accounts for the dissolved and particulate 230Th distributions in the Nansen Basin. Modelled dissolved 231Pa distributions were largely overestimated, which was attributed to the absence of incorporation of water exchange with the Atlantic Ocean in the model. 231Pa/230Th ratios of the suspended particles of the Nansen Basin were below the 231Pa/230Th production ratio, but top-core sediments of the Nansen margin and slope have high 231Pa/230Th-ratios, suggesting that scavenging along the Nansen margin partly actsas a sink for the missing Arctic 231Pa.

    Ladda ner fulltext (pdf)
    fulltext
  • 17. Hammerli, Johannes
    et al.
    Kemp, Anthony I.S.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    In situ trace element and Sm-Nd isotope analysis of accessory minerals in an Eoarchean tonalitic gneiss from Greenland: Implications for Hf and Nd isotope decoupling in Earth’s ancient rocks2019Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 524, s. 394-405Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Some of the Earth’s oldest preserved continental crustal rocks, from southern West Greenland, contain contradictory radiogenic isotope signatures, whereby Hf isotope ratios are chondritic but Nd isotope ratios are distinctly super-chondritic. Models to explain this discrepancy are speculative and variously invoke deep magma ocean crystallisation, Hf-Nd decoupling in subduction zones, or metamorphic disturbance during younger thermal events. Determining the cause of this discrepancy is essential for understanding Eoarchean crust-mantle differentiation. We employ, for the first time, micro-analysis of REE-rich accessory minerals to shed light on the Nd isotope evolution of a key tonalitic gneiss sample from southern West Greenland that displays the apparent Hf-Nd isotope decoupling. The results show that the Sm-Nd isotope system was homogenized during a metamorphic event at ca. 2690 Ma. We suggest that metamorphic reactions involving consumption and re-crystallisation of REE-bearing phases were accompanied by LREE element mobility and the loss of unradiogenic Nd, shifting the bulk rock composition to a more radiogenic Nd isotope value. Our study provides the first direct evidence that the anomalous Nd isotope signatures in some Eoarchean gneisses are artefacts of the disturbance of the Sm-Nd isotope system, and not due to extensive differentiation of the bulk silicate Earth by magma ocean crystallisation or continental crust formation.

    Ladda ner fulltext (pdf)
    fulltext
  • 18. Jakubowicz, Michal
    et al.
    Dopieralska, Jolanta
    Kaim, Andrzej
    Skupien, Petr
    Kiel, Steffen
    Naturhistoriska riksmuseet, Enheten för paleobiologi.
    Belka, Zdzislaw
    Nd isotope composition of seep carbonates: towards a new approach for constraining subseafloor fluid circulation at hydrocarbon seeps2018Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 503, s. 40-51Artikel i tidskrift (Refereegranskat)
  • 19.
    Kielman, Ross
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap. Stockholm University.
    Nemchin, Alexander
    Curtin University.
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Pidgeon, Robert
    Curtin University.
    Bellucci, Jeremy
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    U-Pb age distribution recorded in zircons from Archean quartzites in the Mt. Alfred area, Yilgarn Craton, Western Australia2018Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 310, s. 278-290Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The U-Th-Pb isotopic data from detrital zircon grains from five samples of Archean quartzite from the Mt. Alfred area of the Illaara greenstone belt in the Yilgarn Craton of Western Australia are presented in this study. The zircon grains are typically fractured and contain both irregular and oscillatory zoned internal structures as revealed by cathodoluminescence imaging. Concordant 207Pb/206Pb ages range between 3109 ± 17 and 3918 ± 16 Ma (2σ), with three main age peaks at ca. 3640, 3690 and 3760 Ma. Older 207Pb/206Pb ages up to 4067 ± 5 Ma are strongly affected by at least one recent disturbance event, however one single-grain discordia yields an upper intercept age of 4107 ± 12 (MSWD = 1.2). A further sixteen zircon grains with multiple analyses define discordia that suggest U-Pb disturbance events in the Neoarchean and the Mesozoic, the latter as a result of invasive low temperature weathering solutions. The notable lack of grains with ages less than ∼3.6 Ga in the Mt. Alfred detrital zircon population differentiates it from other quartzite samples from both the Illaara Formation and the Eoarchean zircon-bearing metasedimentary rocks of the Narryer Terrane. Also, the limited spread of zircon ages between 3640 and 3760 Ma suggests a relatively uniform and possibly local source region. However, no rocks of this age have been found in the Youanmi Terrane. This implies either the distal transport of similarly aged clastic sediments at 3.1 Ga from the Narryer Gneiss Complex (NGC) to the Mt. Alfred area, or the previous existence of NGC-like rocks near the Illaara greenstone belt that are either not currently recognised or have since been destroyed.

  • 20.
    Kielman, Ross
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap. Stockholm University.
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Nemchin, Alexander
    Curtin University.
    Kemp, Anthony
    University of Western Australia.
    A tonalitic analogue to ancient detrital zircon2018Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 499, s. 43-57Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A zircon population from an Archean tonalite sample from southern West Greenland hasbeen used as a source analogue in order to test common methods and approaches applied toancient detrital zircon populations. Measurements of U-Th-Pb, oxygen and Lu-Hf isotopes aswell as rare earth element and Ti concentrations were made in these zircon crystals and,where possible, in multiple areas within a single grain. The population is dominated by oscillatory zoned cores aged 3.82 Ga with an isotopically and compositionally distinct rims that formed at 3.59 Ga. We demonstrate that multiple age components may be erroneously inferred from within these oscillatory zoned zircon cores, both from the total population and within individual grains. This has bearing on other zircon-hosted geochemical systems, as temporal correlations may be incorrectly assigned. Oxygen and Lu-Hf isotope compositions are relatively consistent through the population with only a small number of outliers. Ranges in rare earth element and Ti abundances are evident from the total population, from which apparent inverse cooling trends may be inferred. Additionally, we show that even with enhanced filtering of Ti concentrations using light rare earth element abundances,crystallisation temperatures derived from zircon grains of a single, hand sample sized rockcan yield both wide and bimodal results. Since even simple, single “source rock” zirconpopulations may, without careful scrutiny, portray artificially complex results, particular caremust be taken in the interpretation of complex ancient detrital zircon populations.

    Ladda ner fulltext (pdf)
    Kielman et al., 2018b
  • 21. Krall, Lindsay
    et al.
    Evins, Lena Z.
    Kooijman, Ellen
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Tullborg, Eva-Lena
    Tracing the palaeoredox conditions at Forsmark, Sweden, using uranium mineral geochronology2019Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 506, s. 68-78Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    U-Pb isotope systems have been used to constrain the timing of formation, alteration, and oxidation of U minerals from the meta-granitic bedrock at Forsmark, eastern Sweden. Secondary ion mass spectrometry (SIMS) has been used to collect U-Pb data from uraninite. Discordant data suggest a ~1.8 Ga emplacement of uraninite-bearing pegmatites and an event of uraninite alteration at ~1.6 Ga. The latter age is contemporaneous with the Gothian orogeny in Scandinavia, which was associated with hydrothermal fluid circulation in the Fennoscandian Shield. Ca-uranyl silicates haiweeite and uranophane predominately formed 1.3–1.2 Ga, contemporaneous with the emplacement of the Satakunta complex of the Central Scandinavian Dolerite Group. A Palaeozoic group of Ca-U(VI)-silicates is also present, which indicates that the geochemical composition of geologic fluids was heterogeneous throughout the fracture network during this time. Low Pb concentrations in the U(VI) silicates of several samples are compatible with a recent (<100 Ma) alteration or precipitation of these minerals in connection to reaction with carbonate-rich fluids. The results support a geologically early oxidation of U(IV) to U(VI) and provide insight into the palaeoredox conditions that may impart an on-going influence on the mobility of natural U in the Forsmark fracture network.

  • 22.
    Krall, Lindsey
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Augué-Sanz, L
    University of Zaragoza.
    Garcia-Orellana, J
    Universitat Autònoma de Barcelona.
    Trezzi, G
    Universitat Autònoma de Barcelona.
    Tullborg, E-L
    Terralogica AB.
    Suksi, Juhanni
    DecServis Consulting Company.
    Porcelli, D
    University of Oxford.
    Andersson, P.S.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Radium isotopes to trace uranium redox anomalies in anoxic groundwater2020Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 531, s. 1-18, artikel-id 119296Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    223Ra, 224Ra, 226Ra, and 228Ra isotopes have been measured in groundwaters from depths ranging 50–900 m in fractured crystalline bedrock (Forsmark, Sweden) to understand the reason for elevated (up to 150 μg/L) aqueous uranium (Uaq) at 400–650 m depth. Ra isotope data is interpreted alongside previously reported 222Rn, 234U, and 238U data, as well as PHREEQC geochemical modelling and uranium mineralogy. A novel, [223Ra/226Ra]GW-based approach (where brackets and “GW” subscript refer to expression of an activity ratio measured from groundwater) to groundwater residence time estimation shows that elevated [Uaq] is most common in Holocene-age groundwaters of marine origin. Although these groundwaters are geochemically reducing, the [223Ra/228Ra]corr (where “corr” subscript refers to a correction applied to compare [223Ra/228Ra]GW to the more commonly reported [226Ra/228Ra]GW) suggest that they interact with U-rich pegmatites containing Proterozoic- and Palaeozoic-age Ca-U(VI)-silicate minerals, which are undersaturated in the present groundwaters. Local aqueous U(VI) can be stabilized in Ca2UO2CO30 complexes at pe-values as low as −4.5 but is susceptible to reduction after a modest decrease in pe-value, alkalinity, or Ca concentration. The [223Ra/228Ra]corr and [224Ra/228Ra]GW also suggest that U(VI)aq precipitates as UO2+X at the interface betwee nmarine and non-marine groundwaters. From these data, local [Uaq] is proposed to be governed by on-going water-rock interaction involving old U(VI)-minerals.

    Ladda ner fulltext (pdf)
    fulltext
  • 23. Kusiak, Monika A.
    et al.
    Dunkley, Daniel J.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Wilde, Simon A.
    Sałacińska, Anna
    Konečný, Patrík
    Szopa, Krzysztof
    Gawęda, Aleksandra
    Chew, David
    Peak to post-peak thermal history of the Saglek Block of Labrador: A multiphase and multi-instrumental approach to geochronology2018Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 484, s. 210-223Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Saglek Block of coastal Labrador forms the western margin of the North Atlantic Craton, where Archean gneisses and granulites have been reworked during the Paleoproterozoic. Previous work has established that the block is a composite of Eoarchean to Mesoarchean protoliths metamorphosed to upper amphibolite and granulite facies at around 2.8–2.7Ga. New in-situ microbeam dating of accessory minerals in granoblastic gneisses reveals a complex peak to post-peak thermal history. Zircon growth at ca. 3.7–3.6Ga provides the age of formation of the tonalitic protoliths to the gneisses. Further zircon growth in syn-tectonic granitic gneiss and monazite growth in a variety of orthogneisses confirm peak metamorphic conditions at ca. 2.7Ga, but also reveal high-temperature conditions at ca. 2.6Ga and 2.5Ga. The former is interpreted as the waning stages of the 2.7Ga granulite event, whereas the latter is associated with a younger phase of granitic magmatism. In addition, apatite ages of ca. 2.2Ga may represent either cooling associated with the 2.5Ga event or a previously unrecognized greenschist-facies metamorphism event that predates the Torngat Orogeny.

    Ladda ner fulltext (pdf)
    fulltext
  • 24.
    Petersson, Andreas
    Naturhistoriska riksmuseet, Enheten för geovetenskap. University of Western Australia.
    A new 3.59 Ga magmatic suite and a chondritic source to the east Pilbara Craton2019Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, s. 51-70Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Pilbara Craton, Western Australia hosts one of the best-preserved Paleoarchean granite-greenstone terrains on Earth, and is inferred to have developed on an older (> 3.8 Ga), possibly Hadean, continental substrate. Such ancient crust has, however, never been identified in outcrop. Here, we show that metamorphosed gabbroic, leucogabbroic and anorthositic rocks of the South Daltons area, in the western part of the Shaw Granitic Complex, formed at 3.59–3.58 Ga and were intruded by granitic magma at 3.44 Ga. The 3.59–3.58 Ga gabbroic rocks, here named the Mount Webber Gabbro, represent the oldest, unambiguous igneous rock emplacement in the Pilbara Craton and significantly predate the oldest volcanic activity of the 3.53–3.23 Ga Pilbara Supergroup within the East Pilbara Terrane. We interpret the Mount Webber Gabbro samples to represent fragments of a dismembered layered mafic intrusion. Mantle-like zircon δ18O and Hf isotope signatures indicate derivation from a chondritic to near chondritic mantle at ~3.59 Ga, and do not support the existence of a>3.8 Ga basement to the East Pilbara Terrane. These results strengthen the notion of an approximately chondritic>3.5 Ga mantle beneath the Pilbara Craton, and provide further evidence that recent estimates of Archean stabilised continental volumes, based on the assumption of crust extraction from a global, convecting depleted mantle reservoir, may be overestimated.

    Ladda ner fulltext (pdf)
    fulltext
  • 25.
    Petersson, Andreas
    Naturhistoriska riksmuseet, Enheten för geovetenskap. University of Western Australia.
    Hickman, Arthur (Medarbetare/bidragsgivare)
    Whitehouse, Martin (Medarbetare/bidragsgivare)
    Naturhistoriska riksmuseet.
    Martin, Laure (Medarbetare/bidragsgivare)
    Grey, Chris (Medarbetare/bidragsgivare)
    A new 3.59 Ga magmatic suite and a chondritic source to the east Pilbara Craton2019Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, ISSN 0009-2541, s. 51-70Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The Pilbara Craton, Western Australia hosts one of the best-preserved Paleoarchean granite-greenstone terrains on Earth, and is inferred to have developed on an older (> 3.8 Ga), possibly Hadean, continental substrate. Such ancient crust has, however, never been identified in outcrop. Here, we show that metamorphosed gabbroic, leucogabbroic and anorthositic rocks of the South Daltons area, in the western part of the Shaw Granitic Complex, formed at 3.59–3.58 Ga and were intruded by granitic magma at 3.44 Ga. The 3.59–3.58 Ga gabbroic rocks, here named the Mount Webber Gabbro, represent the oldest, unambiguous igneous rock emplacement in the Pilbara Craton and significantly predate the oldest volcanic activity of the 3.53–3.23 Ga Pilbara Supergroup within the East Pilbara Terrane. We interpret the Mount Webber Gabbro samples to represent fragments of a dismembered layered mafic intrusion. Mantle-like zircon δ18O and Hf isotope signatures indicate derivation from a chondritic to near chondritic mantle at ~3.59 Ga, and do not support the existence of a>3.8 Ga basement to the East Pilbara Terrane. These results strengthen the notion of an approximately chondritic>3.5 Ga mantle beneath the Pilbara Craton, and provide further evidence that recent estimates of Archean stabilised continental volumes, based on the assumption of crust extraction from a global, convecting depleted mantle reservoir, may be overestimated.

  • 26.
    Petersson, Andreas
    Naturhistoriska riksmuseet, Enheten för geovetenskap. University of Western Australia.
    Kristinsdottir, Bara (Medarbetare/bidragsgivare)
    Kemp, Anthony (Medarbetare/bidragsgivare)
    Whitehouse, Martin (Medarbetare/bidragsgivare)
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Birimian crustal growth in the West African Craton: U-Pb, O and Lu-Hf isotope constraints from detrital zircon in major rivers2018Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, nr 479, s. 259-271Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Combined U-Pb, O and Lu-Hf isotope analyses of detrital zircon grains from five major rivers in Ghana are used to investigate the growth and evolution of the Birimian terrane of the West African Craton. The majority of the analysed zircon yields supra-chondritic εHf values, suggesting derivation from primarily juvenile host magmas. Zircon grains from the Birim River in southwestern Ghana deviate from the generally juvenile trend, where the sub-chondritic εHf but mantle-like δ18O of the 2.15 Ga population suggest reworking of ancient, but unweathered, meta-igneous crust. Hf-O isotope data from detrital zircons of the remaining rivers are consistent with sequential crust generation between ca. 2.2 and 2.1 Ga. Oxygen isotope data suggest that the contribution from Archaean sedimentary material to felsic magmas was below 30%, and in most cases below 10%. Zircon with strongly positive εHf values and elevated δ18O indicate rapid reworking of juvenile crust within southern Ghana. An increase towards heavier oxygen isotope signatures over time suggests a maturing arc system with rapid recycling of juvenile supracrustal material during the evolution of the Birimian terrane.

  • 27. Petersson, Andreas
    et al.
    Kemp, Anthony I.S.
    Gray, Chris M.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Formation of early Archean Granite-Greenstone Terranes from a globally chondritic mantle: Insights from igneous rocks of the Pilbara Craton, Western Australia2020Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 551, artikel-id 119757Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The continental crust grows via juvenile additions from the mantle. However, the timing of initial continent stabilisation and the rate of subsequent continental growth during the first billion years of Earth history is widely debated, in part due to uncertainty over the composition of the mantle source of new crust. Well-preserved Archean granite-greenstone terranes, as present within the Pilbara Craton (Western Australia), provide insights into the sources of felsic magmas and the processes of continental growth and evolution in the distant geological past at the regional scale. Here, we present zircon U-Pb, O and Hf isotope data from ancient gneissic and granitic rocks of the Pilbara Craton, to decipher magma sources and the timing and processes of craton growth. There is no evidence for depleted mantle compositions, and the simplest interpretation is that the crust of the Pilbara Craton was generated from mantle with a chondritic Hf isotope composition. Our results indicate crustal addition at ~3.59 Ga, represented by emplacement of gabbroic to anorthositic rocks. We suggest that the formation of these igneous rocks, and the foundering of the complementary residues, triggered extensive melting of hot, upwelling mantle, leading to the subsequent accumulation of the >12 km thick greenstone belt eruptive sequences from 3.53 Ga, with emplacement of coeval felsic magmas at depth. This process shaped the initial crustal configuration of the proto-craton, which subsequently underwent gravitationally driven overturn and reworking to generate stable, cratonic continental crust with the distinctive dome and keel architecture. The zircon Hf and O isotope signatures of the Pilbara igneous rocks from ~3.59–3.4 Ga do not support remelting of an ancient (> 3.8 Ga) basement, and reinforce the overwhelmingly chondritic to near-chondritic zircon Hf isotope composition of Eoarchean meta-igneous rocks from a number of different Archean cratons. A corollary of this remarkable global consistency is that a significant volume of the mantle maintained a chondritic composition for the Lu-Hf system from the formation of the Earth into the Paleoarchean (up to 3.6–3.5 Ga), as would be the case if stabilised volumes of felsic continental crust prior to 3.5 Ga were relatively small. One implication is that the common assumption of a linear evolution of depleted mantle from 4.5 Ga to the present day is inappropriate for determining the timing and volume of continental crust extraction in the Archean. The nearly identical early evolution of the Pilbara and Kaapvaal cratons suggests a common process to generate Archean granite-greenstone terranes that does not require extensive reworking of ancient crust, but rather involves juvenile crustal addition above persistent zones of upwelling, chondritic mantle.

  • 28. Pidgeon, R. T.
    et al.
    Nemchin, A. A.
    Roberts, M. P.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Bellucci, J. J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    The accumulation of non-formula elements in zircons during weathering: Ancient zircons from the Jack Hills, Western Australia2019Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 530Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this contribution we describe the influx of non-formula elements (Fe, Ca, Al, Y, U and Th) into fractures and selected zone lamellae in zircons from Jack Hills during recent weathering and discuss the effects of this on overlapping SIMS U-Th-Pb and oxygen isotope analyses. Previous research has recognised the importance of fractures in the generation of anomalous U-Th-Pb and oxygen isotope systems. In this report we show that besides fractures specific zones in euhedrally zoned zircon can act as pathways for the influx of weathering solutions and contain a similar range of trace element materials as do the fractures. Whereas zero-age discordant U-Pb systems of Jack Hills zircons have been explained by many authors in terms of Pb loss, present results confirm conclusions of our previous study that the main discordance mechanism of Jack Hills zircons is U-Th gain, due to overlap of SIMS analyses with mineralized fractures and zone lamellae with excess weathering-fluid-deposited U and Th. We explain the anomalously light and heavy oxygen isotopes and significant OH in SIMS analyses that overlap fractures and mineralized zones as due to the presence in the fractures of Ca, Fe, Al oxides and hydroxides with complexly fractionated oxygen isotopic systems. There is a suggestion in some of the elemental maps that there has been minor dispersion of trace elements away from fractures. But SIMS U-Th-Pb and oxygen isotope analyses on parts of the zircon away from fractures and mineralized zones show no evidence of interaction with weathering-fluid, indicating that penetration of weathering fluids into the body of the zircon at the location of the SIMS spots has not occurred. Results of this study have implications for other SIMS U-Th-Pb and oxygen isotope studies of zircons from rocks that have been subjected to weathering and also for early TIMS U-Pb measurements of bulk zircon samples that show zero Ma U-Pb discordance.

    Ladda ner fulltext (pdf)
    fulltext
  • 29. Rose-Koga, E.F.
    et al.
    Koga, K.T.
    Moreira, M.
    Vlastélic, I.
    Jackson, M.G.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Shimizu, N.
    Habib, N.
    Geochemical systematics of Pb isotopes, fluorine, and sulfur in melt inclusions from São Miguel, Azores.2017Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 485, s. 22-37Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pb isotopic measurements in olivine-hosted melt inclusions of ocean island basalts (OIBs) from São Miguel, Azores, reflect the high 207Pb/204Pb and 208Pb/204Pb at a given 206Pb/204Pb of their host lavas. The data are consistent with mixing between two endmembers: the first (the Central Group) has relatively high 208Pb/206Pb and is similar to the component sampled by Graciosa and Faial, and the second is a radiogenic endmember (with low 208Pb/206Pb) that we refer to as the Nordeste component. F and Cl concentrations measured in the same melt inclusions from São Miguel represent parental abundances unmodified by crustal assimilation. Based on undegassed F and Cl concentrations, the source beneath São Miguel is volatile-rich. Pb-isotope composition of the melt inclusions correlates positively with S concentration: we attribute this correlation to the dissolution of oceanic crust sulfides in the S-undersaturated basaltic melt of the Nordeste component. These blebs were then assimilated by the São Miguel magma and the magma droplets were later trapped in olivines.

    When comparing melt inclusions from worldwide OIBs representing mantle endmembers, we find an overall negative correlation between F/Nd and 208Pb/206Pb for volcanic glasses and melt inclusions. The high F/Nd (up to 40) endmember is represented by HIMU melt inclusions and the low F/Nd (down to 14) by EM1 Pitcairn glasses. São Miguel melt inclusions have an intermediate F/Nd of 23.1 ± 3.4.

  • 30. Rydland Pedersen, L.-E.
    et al.
    Staudigel, H.
    McLoughlin, N.
    Strauss, H.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    A multiple sulfur isotope study through the volcanic section of the Troodos ophiolite.2017Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 468, s. 49-62Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Multiple S isotope systematics (δ34S and Δ33S) and high resolution in-situ S isotope measurements offer new perspectives on the study of biological and abiotic cycling of sulfur in hydrothermal systems. We applied these techniques to the Tethyian Troodos ophiolite (91 Ma) from Cyprus, one of the best-preserved remnants of oceanic crust in the world, using materials from deep drill cores and surface sampling. We focused on the volcanic section of the ophiolite, including the hydrothermal massive sulfide deposit at Agrokipia, which represents a fossil zone of high-temperature fluid upwelling, and the Akaki river section which displays a range of lower temperature alteration types.

    The δ34S and Δ33S values of bulk and SIMS (secondary ion mass spectrometry) analyses from the Agrokipia sulfide deposits show that the sulfide minerals are largely derived from thermochemical reduction of entrained seawater sulfate and leached H2S from the “root zone” of hydrothermal upwelling. The contributions of these two sources can vary substantially within individual sulfide grains, indicating a very dynamic mixing between these sulfur sources. Microbial reworking of the sulfide mound is recorded in a sample with very elevated Δ33S values (0.22‰).

    The Akaki and Agrokipia volcanics experienced low temperature sulfur loss and removal of heavier sulfur isotopes due to partial oxidation by microbes. While some intervals gained sulfur, and have δ34S and Δ33S values indicative of microbial sulfate reduction. REE-data of vein quartz containing pyrite with δ34S = ~− 21‰ implies local ephemeral hydrothermal upwelling in the lower Akaki volcanics, possibly associated with the late stage boninitic magmatic activity in the Troodos ophiolite, suggesting that microbial sulfate reduction in oceanic crust may continue for 10–15 Ma in crustal sections with prolonged igneous activity such as Troodos.

  • 31.
    Sjöström, J.K.
    et al.
    Department of Geological Sciences, Stockholm University, Stockholm, Sweden.
    Bindler, R.
    Department of Ecology and Environmental Science, Umeå University, Umeå, Sweden.
    Martínez Cortizas, A.
    CRETUS, EcoPast (GI-1553), Universidad de Santiago de Compostela, Santiago de Compostela, Spai.
    Björck, S.
    Department of Geology, Lund University, Lund, Sweden.
    Hansson, S.V.
    Laboratoire écologie fonctionnelle et environnement, CNRS Université de Toulouse, Toulouse, France.
    Karlsson, Andreas
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Ellerton, D.T.
    Department of Geological Sciences, Stockholm University, Stockholm, Sweden.
    Kylander, Malin
    Department of Geological Sciences, Stockholm University, Stockholm, Sweden.
    Late Holocene peat paleodust deposition in south-western Sweden - exploring geochemical properties, local mineral sources and regional aeolian activity2022Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 602, s. 1-14, artikel-id 120881Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Atmospheric mineral dust not only interacts with the climate system by scattering incoming solar radiation and affecting atmospheric photochemistry, but also contributes critical nutrients to marine and terrestrial ecosystems. In a high-resolution analysis of paleodust deposition, peat development and soil dust sources, we assess the interplay between dust deposition and bog development of the Davidsmosse bog in south-western Sweden. Analyses of the 5400-year record (458 cm) included radiocarbon dating, bulk density, ash content, chemical and mineralogical composition and carbon stable isotopes, subsequently explored using principal component analysis. Fourteen dust events (DEs) were recorded (cal BP) in the peat sequence: 3580–3490; 3280; 3140; 3010–2840; 2740; 2610; 2480; 2340; 2240–2130; 1690; 1240; 960, 890–760, and 620–360. The majority of the DEs were coupled to increases in peat accumulation rates and increased nutrient content (N, P and K) suggesting that the DEs contributed with nutrients to the bog ecosystem, promoting increased accumulation. We also analyzed the chemical and mineral composition of potential mineral source deposits (separated into 6 grain-size fractions) from sites within a 4 km radius as well as aeolian dunes closer to the coast (25 km). The composition deposited on the present-day bog surface indicates that the bulk of the contemporary minerals have a local origin (<1.5 km), but the DEs may be of a more distant origin. The results also indicate that quartz and plagioclase feldspar content consistently increase with increasing grain-size, both in the source samples as well as in the peat sequence, and that the Si/Al ratio can be used to infer grain size changes in the peat. Two longer phases saw numerous DEs, between 2800 and 2130 cal BP and a stepwise increase from 960 towards 360 cal BP. The episodic character of the events, together with the inferred coarse grain size, suggest that the particles were deposited by (winter) storms. Future studies should include grain size analysis as well as a more in-depth comparison with regional paleo dust and storm records to increase knowledge on both transport processes (creep, saltation, suspension) and the climate processes driving late Holocene dust and storm events in Scandinavia.

    Ladda ner fulltext (pdf)
    fulltext
  • 32.
    Snape, Joshua
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Davids, Bart
    Nemchin, Alexander
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Bellucci, Jeremy
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Constraining the timing and sources of volcanism at the Apollo 12 landing site using new Pb isotopic compositions and crystallisation ages2018Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 482, s. 101-112Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The basaltic suites collected at the Apollo 12 landing site have been interpreted as representing a stratigraphic sequence of volcanic flows emplaced in the Oceanus Procellarum region between approximately 3100–3300 Ma. This study presents Secondary Ion Mass Spectrometry (SIMS) Pb isotopic analyses of samples from each of the basaltic suites, which have been used to constrain precise crystallisation ages and initial Pb isotopic composi- tions. The new crystallisation ages are consistent with the three main basaltic suites (olivine, pigeonite and ilmenite) being emplaced over a period of approximately 60 million years, and the improved precision of these ages has made it possible to reinterpret the stratigraphic sequence of basalt flows underlying the Apollo 12 landing site. Contrary to previous studies, the three ilmenite basalts are determined as having the oldest ages (with a weighted average of 3187 ± 6 Ma; 2σ) and are, therefore, interpreted as representing the lowest unit in the sequence, underlying the olivine and pigeonite basalts (with an age range constrained by the oldest and youngest pigeonite basalts; 3176 ± 6 Ma and 3129 ± 10 Ma; 2σ). The initial Pb isotopic compositions have been compared with recalculated initial Sr and Nd isotopic compositions, and are consistent with the three main basaltic suites originating from magmatic sources that incorporated different proportions of a common primitive mafic cumulate and the residual trapped liquid fraction remaining after a majority of the lunar magma ocean had crystallised. Our data also demonstrate that the feldspathic basalt (12038) is unique, both in terms of its crys- tallisation age (3242 ± 13 Ma) and its derivation from a distinct mantle reservoir.

    Ladda ner fulltext (pdf)
    fulltext
  • 33.
    Snape, Joshua
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Nemchin, Alexander
    Curtin University.
    Bellucci, Jeremy
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Whitehouse, Martin
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Pb isotopes in the impact melt breccia 66095: Association with the Imbrium basin and the isotopic composition of lithologies at the Apollo 16 landing site2017Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 466, s. 608-616Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recent in situ Secondary Ion Mass Spectrometry (SIMS) Pb isotope analyses of lunar basalts have provided precise crystallisation ages and initial Pb isotopic compositions for these samples. In this study, the same approach has been tested in the Apollo 16 impact melt breccia 66095, referred to as the “Rusty Rock” due to its enrichments in volatile elements, including Pb. Based on these analyses of the breccia, a Pb-Pb isochron age of 3909±17 Ma (at the 95% confidence level) and an initial Pb composition for 66095 have been determined. This age is interpreted as representing the time of breccia formation that, when combined with recent studies of lunar breccias, can be linked to the Imbrium basin forming impact. The directly measured initial Pb composition of the breccia from this work is similar a modelled compositions presented previously, and likely reflects an average value for the lithologies present at the Apollo 16 landing site at the time that the Imbrium ejecta was emplaced. The 66095 initial Pb isotopic composition is compared with the compositions in other lunar samples and the nature of the endmember lithologies in this mixture has been discussed within the framework of a multiple stage model of Pb isotope evolution on the Moon. This study demonstrates the effectiveness of this technique beyond its application in crystalline basalts, opening up the possibility of obtaining precise geochronological and Pb isotopic compositions from a broader sample set than was previously recognised.

    Ladda ner fulltext (pdf)
    fulltext
  • 34. Tual, Lorraine
    et al.
    Smit, Matthijs A.
    Cutts, Jamie
    Kooijman, Ellen
    Naturhistoriska riksmuseet, Enheten för geovetenskap. Department of Geosciences Swedish Museum of Natural History Stockholm Sweden.
    Kielman-Schmitt, Melanie
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Majka, Jarosław
    Foulds, Ian
    Rapid, paced metamorphism of blueschists (Syros, Greece) from laser-based zoned Lu-Hf garnet chronology and LA-ICPMS trace element mapping2022Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 607, s. 121003-121003, artikel-id 121003Artikel i tidskrift (Refereegranskat)
  • 35. Westhues, A.
    et al.
    Hanchar, J.M.
    Voisey, C.R.
    Whitehouse, Martin J.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Rossman, G.R.
    Wirth, R.
    Tracing the fluid evolution of the Kiruna iron oxide apatite deposits using zircon, monazite, and whole rock trace elements and isotopic studies.2017Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 466, s. 303-322Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The ore genesis of the Paleoproterozoic iron oxide apatite deposits in the vicinity of Kiruna in northern Sweden is poorly understood, despite a century-long mining history and 2500 Mt of iron ore with grades of 30 to 70 wt% Fe produced in the region to date. Zircon grains from the ore, recently dated at ca. 1874 Ma, show very different appearances compared to zircon from surrounding host rocks (ca. 1880 Ma) and related intrusions (ca. 1880 and ca. 1874 Ma), particularly an inclusion-rich rim. In contrast, zircon from the host rocks, and a proximal granite intrusion, exhibit typical igneous growth zoning. Electron microprobe results show near stoichiometric composition for Zr, Si, and Hf in the host rock zircon grains. The ore zircon crystals have low analytical totals with significant concentrations of Ca, Fe, Y, and P and infrared spectroscopy showed several weight percent of water. These ore zircon grains further show Fe-rich inclusions, zones and/or veins in elemental X-ray maps, and light rare earth elements (LREE) enrichment. Transmission electron microscopy (TEM) shows that the LREE are not due to micro- or nano-inclusions in the zircon, but are likely hosted as LREE oxides in amorphous regions of the grains. Based on these characteristics, the rims on ore zircon grains are interpreted to be of hydrothermal origin. Uranium-Pb in monazite from the ore, measured by SIMS, suggests a secondary event influencing the area at ca. 1624 Ma, a period of known geologic activity in Fennoscandia. Electron microprobe X-ray mapping of these monazite grains shows no zoning and relatively low U and Th concentrations.

    Stark contrasts are visible between the ore (depleted mantle influence) and host rocks (crustal influence) in the whole rock Lu-Hf and Sm-Nd data. The depleted mantle signature of the ore could be related to the Kiruna greenstone group as a potential source region for the iron. The Sm-Nd isotopic composition of monazite from the ore shows a crustal influence, and indicates that the younger event has not disturbed the whole rock Sm-Nd signature of the ore. The hydrothermal nature of the ore zircon grains and the isotopic signatures point to a hydrothermal influence on the ore formation, with a high temperature magmatic fluid related to the intrusions as most likely heat and fluid source.

  • 36.
    Whitehouse, Martin J.
    et al.
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Kemp, Anthony I.S.
    Petersson, Andreas
    Naturhistoriska riksmuseet, Enheten för geovetenskap.
    Persistent mildly supra-chondritic initial Hf in the Lewisian Complex, NW Scotland: Implications for Neoarchean crust-mantle differentiation2022Ingår i: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 606, s. 121001-121001, artikel-id 121001Artikel i tidskrift (Refereegranskat)
1 - 36 av 36
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf