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  • 101. El Albani, Abderrazak
    et al.
    Bengtson, Stefan
    Swedish Museum of Natural History, Department of Paleobiology.
    Canfield, Donald E.
    Riboulleau, Armelle
    Rollion Bard, Claire
    Macchiarelli, Roberto
    Ngombi Pemba, Lauriss
    Hammarlund, Emma
    Meunier, Alain
    Moubiya Mouele, Idalina
    Benzerara, Karim
    Bernard, Sylvain
    Boulvais, Philippe
    Chaussidon, Marc
    Cesari, Christian
    Fontaine, Claude
    Chi-Fru, Ernest
    Garcia Ruiz, Juan Manuel
    Gauthier-Lafaye, François
    Mazurier, Arnaud
    Pierson-Wickmann, Anne Catherine
    Rouxel, Olivier
    Trentesaux, Alain
    Vecoli, Marco
    Versteegh, Gerard J. M.
    White, Lee
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Bekker, Andrey
    The 2.1 Ga old Francevillian biota: biogenicity, taphonomy and biodiversity.2014In: PLoS ONE, ISSN 1932-6203, E-ISSN 1932-6203, Vol. 9, no 6:e99438, p. 1-18Article in journal (Refereed)
    Abstract [en]

    The Paleoproterozoic Era witnessed crucial steps in the evolution of Earth’s surface environments following the first appreciable rise of free atmospheric oxygen concentrations ~2.3 to 2.1 Ga ago, and concomitant shallow ocean oxygenation. While most sedimentary successions deposited during this time interval have experienced thermal overprinting from burial diagenesis and metamorphism, the ca. 2.1 Ga black shales of the Francevillian B Formation (FB2) cropping out in southeastern Gabon have not. The Francevillian Formation contains centimeter-sized structures interpreted as organized and spatially discrete populations of colonial organisms living in an oxygenated marine ecosystem. Here, new material from the FB2 black shales is presented and analyzed to further explore its biogenicity and taphonomy. Our extended record comprises variably sized, shaped, and structured pyritized macrofossils of lobate, elongated, and rodshaped morphologies as well as abundant non-pyritized disk-shaped macrofossils and organic-walled acritarchs. Combined microtomography, geochemistry, and sedimentary analysis suggest a biota fossilized during early diagenesis. The emergence of this biota follows a rise in atmospheric oxygen, which is consistent with the idea that surface oxygenation allowed the evolution and ecological expansion of complex megascopic life.

  • 102. Emo, Robert
    et al.
    Smit, Matthijs
    Schmitt, Melanie
    Swedish Museum of Natural History, Department of Geology.
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology.
    Scherer, Erik
    Sprung, Peter
    Bleeker, Wouter
    Mezger, Klaus
    Evidence for evolved Hadean crust from Sr isotopes in apatite within Eoarchean zircon from the Acasta Gneiss Complex2018In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 235, p. 450-462Article in journal (Refereed)
    Abstract [en]

    Current models for the properties of Hadean-Eoarchean crust encompass a full range of possibilities, involving crust that is anywhere from thick and differentiated to thin and mafic. New data are needed to test and refine these models, and, ultimately, to determine how continents were first formed. The Rb-Sr system provides a potentially powerful proxy for crustal evolution and composition. However, this system has thus far been underutilized in studies on early crustal evolution due to its susceptibility to re-equilibration. Overcoming this issue requires new analytical approaches to micro-sample ancient Sr-rich mineral relics that may retain primary Rb-Sr systematics, allowing for the precise and accurate determination of initial 87Sr/86Sr values. In this study, we used a novel application of laser-ablation multi-collector inductively coupled plasma mass spectrometry to determine the Sr isotope composition of apatite inclusions in >3.6 Ga zircon grains from Eoarchean granodiorite gneisses of the Acasta Gneiss Complex, Slave Province, Canada. The 87Rb-corrected 87Sr/86Sr values of these inclusions are largely identical and are distinctly different from values obtained from altered matrix apatite. The inclusion data provide the first direct estimate of initial 87Sr/86Sr for these ancient rocks. Combining this result with information on the protolith and source-extraction age yields estimates for the range of Rb/Sr values, and by extension composition, that the source of these rocks may have had. The data indicate that continental crust containing over 60 wt% of SiO2 was present in the ca. 4.2 Ga source of the Acasta Gneiss Complex. Thus vestiges of evolved crust must have existed within the primitive proto-continents that were present on the Hadean Earth.

  • 103.
    Esmaeilzadeh, Saeid
    et al.
    Stockholms universitet.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Valldor, Martin
    Technische Universität Braunschweig.
    Crystal growth, magnetic and optical properties of the ternary nitride MnSiN22006In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 18, p. 2713-2718Article in journal (Refereed)
  • 104. Eyal, Moshe
    et al.
    Be'eri-Shlevin, Yaron
    Eyal, Yehuda
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Litvinovsky, Boris
    Three successive Proterozoic island arcs in the Northern Arabian–Nubian Shield: Evidence from SIMS U–Pb dating of zircon2014In: Gondwana Research, ISSN 1342-937X, E-ISSN 1878-0571, Vol. 25, p. 338-357Article in journal (Refereed)
  • 105. Fassmer, K.
    et al.
    Klonowska, I.
    Walczak, K.
    Froitzheim, N.
    Majka, J.
    Fonseca, R.O.C.
    Münker, C.
    Janák, M.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Middle Ordovician subduction of continental crust in the Scandinavian Caledonides - an example from Tjeliken, Seve Nappe Complex, Sweden.2017In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 172, article id 103Article in journal (Refereed)
    Abstract [en]

    The Seve Nappe Complex of the Scandinavian Caledonides is thought to be derived from the distal passive margin of Baltica which collided with Laurentia in the Scandian Phase of the Caledonian Orogeny at 430–400 Ma. Parts of the Seve Nappe Complex were affected by pre-Scandian high- and ultrahigh-pressure metamorphism, in a tectonic framework that is still unclear, partly due to uncertainties about the exact timing. Previous age determinations yielded between ~ 505 and ~ 446 Ma, with a general trend of older ages in the North (Norrbotten) than in the South (Jämtland). New age determinations were performed on eclogite and garnet–phengite gneiss at Tjeliken in northern Jämtland. Thermodynamic modelling yielded peak metamorphic conditions of 25–27 kbar/680–760 °C for the garnet–phengite gneiss, similar to published peak metamorphic conditions of the eclogite (25–26 kbar/650–700 °C). Metamorphic rims of zircons from the garnet–phengite gneiss were dated using secondary ion mass spectrometry and yielded a concordia age of 458.9 ± 2.5 Ma. Lu–Hf garnet-whole rock dating yielded 458 ± 1.0 Ma for the eclogite. Garnet in the eclogite shows prograde major-element zoning and concentration of Lu in the cores, indicating that this age is related to garnet growth during pressure increase, i.e. subduction. The identical ages from both rock types, coinciding with published Sm–Nd ages from the eclogite, confirm subduction of the Seve Nappe Complex in Northern Jämtland during the Middle Ordovician in a fast subduction–exhumation cycle.

  • 106.
    Fehr, Manuela A.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Andersson, Per S.
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Gustafsson, Örjan
    Stockholms universitet.
    Mörth, Carl-Magnus
    Stockholms universitet.
    Iron enrichments and Fe isotopic compositions of surface sediments from the Gotland Deep, Baltic Sea2010In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 277, p. 310-322Article in journal (Refereed)
  • 107.
    Fehr, Manuela
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Andersson, Per S.
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Mörth, Carl-Magnus
    Stockholms universitet.
    Iron isotope variations in Holocene sediments of the Gotland deep, Baltic Sea2008In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 72, p. 807-826Article in journal (Refereed)
  • 108. Fisher, C.M.
    et al.
    Hanchar, J.M.
    Miller, C.M.
    Phillips, S.
    Vervoort, J.D.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Combining Nd isotopes in monazite and Hf isotopes in zircon to understand complex open-system processes in granitic magmas.2017In: Geology, Vol. 45, p. 267-270Article in journal (Refereed)
    Abstract [en]

    Mapping the age and trace element and Sm-Nd isotope compositions of monazite grains from a peraluminous Cretaceous granite using laser ablation–split stream analysis reveals a wide range in Nd isotope and rare earth element (REE) compositions within and between single grains. These data corroborate isotopic variability indicated by Hf isotope analysis of zircon in the same granite sample. The REE variations indicate that monazite grew during fractional crystallization. Hf and Nd isotopes indicate that the granitic magma was generated from at least two distinct Proterozoic sources of approximately the same age: one component that had highly radiogenic initial 176Hf/177Hf and 143Nd/144Nd and a second component that was notably less radiogenic. This study highlights the utility of in situ REE and Sm-Nd isotope data in monazite in magmatic systems. Further, it refines the zircon-based constraints on magmatic processes because of sensitivity of light REEs to fractional crystallization, lower probability of complications owing to inheritance, and smaller analytical volumes required.

  • 109. Fleming, E.J.
    et al.
    Flowerdew, Michael
    Smyth, H.R.
    Scott, R.A.
    Morton, A.C.
    Omma, J.E.
    Frei, D.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Provenance of Triassic sandstones on the southwest Barents Shelf and the implication for sediment dispersal patterns in northwest Pangaea.2016In: Marine and Petroleum Geology, ISSN 0264-8172, E-ISSN 1873-4073, Vol. 78, p. 516-535Article in journal (Refereed)
    Abstract [en]

    Thick Triassic siliciclastic units form major reservoir targets for hydrocarbon exploration on the Barents Shelf; however, poor reservoir quality, possibly associated with variation in provenance, remains a key risk factor in the area. In this study, sandstone dispersal patterns on the southwest Barents Shelf are investigated through petrographic and heavy mineral analysis, garnet and rutile geochemistry and zircon U-Pb geochronology. The results show that until the Early Norian Maximum Flooding Surface, two contrasting sand types were present: (i) a Caledonian Sand Type, characterised by a high compositional maturity, a heavy mineral assemblage dominated by garnet and low chrome-spinel:zircon (CZi) values, predominantly metapelitic rutiles and mostly Proterozoic and Archaean detrital zircon ages, interpreted to be sourced from the Caledonides, and (ii) a Uralian Sand Type, characterised by a low compositional maturity, high CZi values, predominantly metamafic rutiles and Carboniferous zircon ages, sourced from the Uralian Orogeny. In addition, disparity in detrital zircon ages of the Uralian Sand Type with contiguous strata on the northern Barents Shelf reveals the presence of a Northern Uraloid Sand Type, interpreted to have been sourced from Taimyr and Severnaya Zemlya. As such, a coincidental system is inferred which delivered sand to the Northern Barents Shelf in the late Carnian/early Norian. Following the Early Norian Maximum Flooding Surface, a significant provenance change occurs. In response to Late Triassic/Early Jurassic hinterland rejuvenation, supply from the Uralian Orogen ceased and the northern Scandinavian (Caledonian) source became dominant, extending northwards out on to the southwest Barents Shelf. The data reveal a link between reservoir quality and sand type and illustrate how provenance played an important role in the development of clastic reservoirs within the Triassic of the Barents Shelf.

  • 110. Fontorbe, G.
    et al.
    Frings, Patrick J
    Swedish Museum of Natural History, Department of Geology.
    De La Rocha, C. L.
    Hendry, K. R.
    Conley, D. J.
    A silicon depleted North Atlantic since the Palaeogene: Evidence from sponge and radiolarian silicon isotopes2016In: Earth and Planetary Science Letters, Vol. 453, p. 67-77Article in journal (Refereed)
    Abstract [en]

    Despite being one of Earth's major geochemical cycles, the evolution of the silicon cycle has received little attention and changes in oceanic dissolved silica (DSi) concentration through geologic time remain poorly constrained. Silicon isotope ratios (expressed as delta Si-30) in marine microfossils are becoming increasingly recognised for their ability to provide insight into silicon cycling. In particular, the delta Si-30 of siliceous sponge spicules has been demonstrated to be a useful proxy for past DSi concentrations. We analysed delta Si-30 in radiolarian tests and sponge spicules from the Blake Nose Palaeoceanographic Transect (ODP Leg 171B) spanning the Palaeocene-Eocene (ca. 60-30 Ma). Our delta Si-30 results range from +0.32 to +1.67 parts per thousand and -0.48 to +0.63 parts per thousand for the radiolarian and sponge records, respectively. Using an established relationship between ambient dissolved Si (DSi) concentrations and the magnitude of silicon isotope fractionation in siliceous sponges, we demonstrate that the Western North Atlantic was DSi deplete during the Palaeocene-Eocene throughout the water column, a conclusion that is robust to a range of assumptions and uncertainties. These data can constitute constraints on reconstructions of past-ocean circulation. Previous work has suggested ocean DSi concentrations were higher than modern ocean concentrations prior to the Cenozoic and has posited a drawdown during the Early Palaeogene due to the evolutionary expansion of diatoms. Our results challenge such an interpretation. We suggest here that if such a global decrease in oceanic DSi concentrations occurred, it must predate 60 Ma. (C) 2016 The Authors. Published by Elsevier B.V.

  • 111. Fontorbe, Guillaume
    et al.
    Frings, Patrick J
    Swedish Museum of Natural History, Department of Geology.
    De La Rocha, Christina
    Hendry, Kate
    Carstensen, Jacob
    Conley, Daniel
    Enrichment of dissolved silica in the deep equatorial Pacific during the Eocene-Oligocene2017In: Paleoceanography, ISSN 0883-8305, E-ISSN 1944-9186, Vol. 32, p. 848-863Article in journal (Refereed)
    Abstract [en]

    Silicon isotope ratios (expressed as δ30Si) in marine microfossils can provide insights into silica cycling over geologic time. Here we used δ30Si of sponge spicules and radiolarian tests from the Paleogene Equatorial Transect (Ocean Drilling Program Leg 199) spanning the Eocene and Oligocene (~50–23 Ma) to reconstruct dissolved silica (DSi) concentrations in deep waters and to examine upper ocean δ30Si. The δ30Si values range from 3.16 to +0.18‰ and from 0.07 to +1.42‰ for the sponge and radiolarian records, respectively. Both records show a transition toward lower δ30Si values around 37 Ma. The shift in radiolarian δ30Si is interpreted as a consequence of changes in the δ30Si of source DSi to the region. The decrease in sponge δ30Si is interpreted as a transition from low DSi concentrations to higher DSi concentrations, most likely related to the shift toward a solely Southern Ocean source of deep water in the Pacific during the Paleogene that has been suggested by results from paleoceanographic tracers such as neodymium and carbon isotopes. Sponge δ30Si provides relatively direct information about the nutrient content of deep water and is a useful complement to other tracers of deep water circulation in the oceans of the past. 

  • 112.
    Fornander, Elin
    et al.
    Stockholm University.
    Lidén, Kerstin
    Stockholm University.
    Eriksson, Gunilla
    Stockholm University.
    Andersson, Per
    Swedish Museum of Natural History, Department of Geology.
    Identifying mobility in populations with mixed marine/terrestrial diets: strontium isotope analyses of skeletal material from a passage grave in Resmo, Öland, Sweden2015In: Forging Identities. The Mobility of Culture in Bronze Age Europe: Report from a Marie Curie Project 2009-2012 with concluding conference at Aarhus University, Moesgaard, 2012, Volume 1 / [ed] Paulina Suchowska-Ducke, Samantha Scott Reiter, Helle Vandkilde, Oxford: British Archeological Reports , 2015, p. 183-192Chapter in book (Refereed)
    Abstract [en]

    Strontium isotope analysis of skeletal material as a means to reconstruct prehistoric residential patterns has previously mainly been applied to populations with terrestrial diets. Here we present a model for populations with mixed marine/terrestrial diets, which is based on two-component mixing of strontium isotopes. Applying this model, we can estimate the original strontium isotope value of the terrestrial component of the diet. Accordingly it is possible to identify non-local individuals even if they had a mixed marine/terrestrial diet. The model is applied to tooth enamel samples representing nine individuals recovered from a passage grave in Resmo, on the island of Öland in the Baltic Sea, where at least five non-local individuals, representing at least two different geographical regions of origin, were identified. Non-local individuals were more frequent during the Bronze Age than during previous phases.

  • 113.
    Forsström, Anna
    Swedish Museum of Natural History, Department of Geology. Linköping University.
    Extraction and determination of Hf in water using a chelating resin and ICP-AES2014Student paper other, 10 HE creditsStudent thesis
  • 114.
    Fregola, Rosa Anna
    et al.
    Università di Bari.
    Bosi, Ferdinando
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Cation ordering over short range and long range scales in the MgAl2O4-CuAl2O4 series2012In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 97, p. 1821-1827Article in journal (Refereed)
  • 115.
    Fregola, Rosa Anna
    et al.
    University of Bari.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Bosi, Ferdinando
    Swedish Museum of Natural History, Department of Geology.
    D'Ippolito, Veronica
    Sapienza University of Rome.
    Andreozzi, Giovanni
    Sapienza University of Rome.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Optical absorption spectroscopy study of the causes for color variations in natural Fe-bearing gahnite: insights from iron valency and site distribution data.2014In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 99, p. 2187-2195Article in journal (Refereed)
  • 116.
    Frings, Patrick J
    Swedish Museum of Natural History, Department of Geology.
    Revisiting the dissolution of biogenic Si in marine sediments: a key term in the ocean Si budget2017In: Acta Geochimica, ISSN 2096-0956, Vol. 36, no 3, p. 429-432Article in journal (Refereed)
    Abstract [en]

    Of the ~240 × 1012 mol year−1 of biogenic silica (bSi) produced by diatoms and other silicifying organisms, only roughly 3%–4% escapes dissolution to be permanently buried. At the global scale, how, where and why bSi is preserved in sediment is not well understood. To help address this, I compile 6245 porewater dissolved Si concentrations from 453 sediment cores, to derive the concentration gradient at the sediment–water interface and thus diffusive fluxes out of the sediment. These range from <0.002 to 3.4 mol m−2 year−1, and are independent of temperature, depth and latitude. When classified by sediment lithology, predominantly siliceous sediments unsurprisingly have higher mean diffusive fluxes than predominantly calcareous or clay-rich sediment. Combined with the areal extent of these lithologies, the ‘best-guess’ global sedimentary bSi recycling flux is 69 × 1012 mol year−1.

  • 117.
    Frings, Patrick J
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Clymans, W.
    Fontorbe, G.
    Gray, W.
    Chakrapani, G. J.
    Conley, D. J.
    De La Rocha, C.
    Silicate weathering in the Ganges alluvial plain2015In: Earth and Planetary Science Letters, Vol. 427, p. 136-148Article in journal (Refereed)
    Abstract [en]

    The Ganges is one of the world's largest rivers and lies at the heart of a body of literature that investigates the interaction between mountain orogeny, weathering and global climate change. Three regions can be recognised in the Ganges basin, with the Himalayan orogeny to the north and the plateaus of peninsular India to the south together delimiting the Ganges alluvial plain. Despite constituting approximately 80% of the basin, weathering processes in the peninsula and alluvial plain have received little attention. Here we present an analysis of 51 water samples along a transect of the alluvial plain, including all major tributaries. We focus on the geochemistry of silicon and its isotopes. Area normalised dissolved Si yields are approximately twice as high in rivers of Himalaya origin than the plain and peninsular tributaries (82, 51 and 32 kmol SiO2 km(-2) yr(-1), respectively). Such dissolved Si fluxes are not widely used as weathering rate indicators because a large but variable fraction of the DSi mobilised during the initial weathering process is retained in secondary clay minerals. However, the silicon isotopic composition of dissolved Si (expressed as delta Si-30) varies from +0.8 parts per thousand in the Ganges mainstem at the Himalaya front to +3.0 parts per thousand in alluvial plain streams and appears to be controlled by weathering congruency, i.e. by the degree of incorporation of Si into secondary phases. The higher delta Si-30 values therefore reflect decreasing weathering congruency in the lowland river catchments. This is exploited to quantify the degree of removal using a Rayleigh isotope mass balance model, and consequently derive initial silica mobilisation rates of 200, 150 and 107 kmol SiO2 km(-2) yr(-1), for the Himalaya, peninsular India and the alluvial plain, respectively. Because the non-Himalayan regions dominate the catchment area, the majority of initial silica mobilisation from primary minerals occurs in the alluvial plain and peninsular catchment (41% and 34%, respectively). (C) 2015 The Authors. Published by Elsevier B.V.

  • 118.
    Frings, Patrick J
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Clymans, Wim
    Conley, Daniel J.
    Amorphous Silica Transport in the Ganges Basin: Implications for Si Delivery to the Oceans2014In: Procedia Earth and Planetary Science, Vol. 10, no 0, p. 271-274Article in journal (Refereed)
    Abstract [en]

    Rivers transport ∽6 x1012 mol yr-1 of dissolved Si (DSi) from the continents to the oceans. They also carry amorphous silica (ASi), solid phases likely to dissolve in seawater. Unfortunately, the magnitude of this flux is poorly constrained at a global scale. We present 92 new ASi values from suspended particulate matter (SPM) from the Ganges basin. Bulk SPM is ∽1.2% ASi, and mean ASi concentrations are ∽65 μM, of comparable magnitude to DSi concentrations. Our results also indicate a) ASi is not evenly distributed in the water column of large rivers, b) the ASi is not a wholly biogenic Si endmember and c) the ASi flux is, to a first order, a function of the SPM load. Our results suggest that the ASi particulate load is much greater than previously believed, rivaling that of the DSi load with important implications for the global Si cycle and oceanic Si isotopic budget.

  • 119.
    Frings, Patrick J
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Clymans, Wim
    Jeppesen, Erik
    Lauridsen, Torben L
    Struyf, Eric
    Conley, Daniel J
    Lack of steady-state in the global biogeochemical Si cycle: emerging evidence from lake Si sequestration2014In: Biogeochemistry, ISSN 0168-2563, E-ISSN 1573-515X, Vol. 117, no 2-3, p. 255-277Article in journal (Refereed)
  • 120.
    Frings, Patrick J
    et al.
    Swedish Museum of Natural History, Department of Geology.
    De La Rocha, Christina
    Struyf, Eric
    van Pelt, Dimitri
    Schoelynck, Jonas
    Hudson, Mike Murray
    Gondwe, Mangaliso J.
    Wolski, Piotr
    Mosimane, Keotsheple
    Gray, William
    Schaller, Jörg
    Conley, Daniel J.
    Tracing silicon cycling in the Okavango Delta, a sub-tropical flood-pulse wetland using silicon isotopes2014In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 142, no 0, p. 132-148Article in journal (Refereed)
    Abstract [en]

    Chemical weathering of silicate minerals releases elements into solution whereas the neoformation of secondary minerals works in the opposite direction, potentially confounding estimates of silicate weathering rates. Silicon isotopes (δ30Si) may be a useful tool to investigate these processes. Here, we present 82 δ30Si measurements from surface waters, pore waters, biogenic silica (BSi), clays, sand and vegetation from the Okavango Delta, Botswana, a freshwater sub-tropical, flood-pulse wetland. Hydrologically, the Okavango is dominated by evapotranspiration water losses to the atmosphere. It receives an annual pulse of water that inundates seasonal floodplains, while river baseflow is sufficient to maintain a permanent floodplain. δ30Si in dissolved silica (DSi) in surface waters along a 300 km transect at near-peak flood show a limited range (0.36–1.19‰), implying the Delta is well buffered by a balance of processes adding and removing DSi from the surface water. A key control on DSi concentrations is the uptake, production of BSi and recycling of Si by aquatic vegetation, although the net isotopic effect is necessarily small since all BSi re-dissolves on short timescales. In the sediments, BSi δ30Si (n = 30) ranges from −1.49‰ to +0.31‰ and during dissolution, residual BSi tends towards higher δ30Si. The data permit a field-based estimate of the fractionation associated with BSi dissolution, ε30BSi-DSi = −0.26‰, though it is unclear if this is an artefact of the process of dissolution. Clay δ30Si ranges from −0.97‰ to +0.10‰, (n = 15, mean = −0.31‰) and include the highest values yet published, which we speculate may be due to an equilibrium isotope effect during diagenetic transformation of BSi. Two key trends in surface water DSi δ30Si merit further examination: declining δ30Si in an area roughly corresponding to the permanent floodplains despite net DSi removal, and increasing δ30Si in the area corresponding to the seasonal floodplains. We infer that evaporative enrichment of surface waters creates two contrasting regimes. Chemical weathering of low δ30Si phases releases low δ30Si DSi in the relatively dilute waters of the permanent floodplains, whereas silicon removal via clay formation or vegetation uptake is the dominant process in the more enriched, seasonal floodplains.

  • 121.
    Frings, Patrick J
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Fontorbe, G.
    Clymans, W.
    De La Rocha, C. L.
    Conley, D.J.
    The continental Si cycle and its impact on the ocean Si isotope budget2016In: Chemical Geology, Vol. 425, p. 12-36Article in journal (Refereed)
  • 122. Fritschle, Tobias
    et al.
    Daly, J. Stephen
    McConnell, Brian
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Menuge, Julian F.
    Buhre, Stephan
    Mertz-Kraus, Regina
    Döpke, Daniel
    Peri-Gondwanan Ordovician arc magmatism in southeastern Ireland and the Isle of Man: Constraints on the timing of Caledonian deformation in Ganderia2018In: GSA Bulletin, Vol. 130, no 11-12Article in journal (Refereed)
    Abstract [en]

    The timing of and tectonic controls on Ordovician magmatism and deformation within accreted terranes are key elements in reconstructing the generation of the Caledonian-Appalachian orogen. This paper addresses the topic through integrated geochronological, structural, and multi-isotope geochemical investigation of magmatic arc–related peri-Gondwanan rocks of Ganderian affinity in the Leinster-Lakesman terrane in SE Ireland and the Isle of Man.

    A basaltic andesite from a previously unrecognized volcaniclastic sequence in the Manx Group at Port-e-Vullen on the Isle of Man yielded an age of 472.7 ± 2.8 Ma (secondary ion mass spectrometry [SIMS] zircon U-Pb), and an arc-related rhyolite from the Avoca volcanic sequence in SE Ireland was dated at 463.6 ± 2.6 Ma. Two granitoids from Graiguenamanagh (SE Ireland) yielded ages of 462.0 ± 2.7 Ma (augen gneiss) and 460.5 ± 3.2 Ma (equigranular granite), whereas the Dhoon granite (Isle of Man) was dated at 457.2 ± 1.2 Ma. Each of the granitic rocks from Graiguenamanagh and Dhoon was previously considered to be of Silurian–Devonian age. In addition, two sheets of the Croghan Kinshelagh granite (SE Ireland) yielded indistinguishable ages of 456.9 ± 2.4 Ma and 455.4 ± 2.8 Ma.

    Multi-isotopic analyses (SIMS zircon oxygen, laser ablation–multi-collector–inductively coupled plasma–mass spectrometry [LA-MC-ICP-MS] zircon Lu-Hf, whole-rock Sm-Nd) on the rocks of the Leinster-Lakesman terrane suggest a significant source contribution from the Ganderian microcontinent, represented by the Early Ordovician metasedimentary Ribband and Manx Groups.

    Structural relationships at Graiguenamanagh demonstrate a late Middle Ordovician deformation event at ca. 460 Ma. This deformation appears to be equivalent to the widespread D1 event that affected Early Ordovician rocks in SE Ireland and corresponds to the early structures within the East Carlow deformation zone, previously interpreted as an exclusively Devonian structure. Along strike, the early deformation is spatially associated with serpentinite emplacement. The East Carlow deformation zone is interpreted as an intra-Ganderian suture along which separate fragments of a peri-Gondwanan magmatic arc were juxtaposed at ca. 460 Ma. This deformation represents a Caledonian tectonic event that has not been recognized within Ganderia in the Appalachian sector of the orogen.

  • 123. Galic, A.
    et al.
    Mason, P.R.D.
    Mogollon, J.M.
    Wolthers, M.
    Vroon, P.Z.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    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.2017In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 449, p. 135-146Article in journal (Refereed)
    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.

  • 124. Gallagher, M.
    et al.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Kamber, B.S.
    The Neoarchaean surficial sulphur cycle: an alternative hypothesis based on analogies with 20th century atmospheric lead.2017In: Geobiology, ISSN 1472-4677, E-ISSN 1472-4669, Vol. 15, p. 385-400Article in journal (Refereed)
    Abstract [en]

    We revisit the S-isotope systematics of sedimentary pyrite in a shaly limestone from the ca. 2.52 Ga Gamohaan Formation, Upper Campbellrand Subgroup, Transvaal, South Africa. The analysed rock is interpreted to have been deposited in a water depth of ca. 50–100 m, in a restricted sub-basin on a drowning platform. A previous study discovered that the pyrites define a nonzero intercept δ34SV-CDT–Δ33S data array. The present study carried out further quadruple S-isotope analyses of pyrite, confirming and expanding the linear δ34SV-CDT–Δ33S array with an δ34S zero intercept at ∆33S ca. +5. This was previously interpreted to indicate mixing of unrelated S-sources in the sediment environment, involving a combination of recycled sulphur from sulphides that had originally formed by sulphate-reducing bacteria, along with elemental sulphur. Here, we advance an alternative explanation based on the recognition that the Archaean seawater sulphate concentration was likely very low, implying that the Archaean ocean could have been poorly mixed with respect to sulphur. Thus, modern oceanic sulphur systematics provide limited insight into the Archaean sulphur cycle. Instead, we propose that the 20th-century atmospheric lead event may be a useful analogue. Similar to industrial lead, the main oceanic input of Archaean sulphur was through atmospheric raindown, with individual giant point sources capable of temporally dominating atmospheric input. Local atmospheric S-isotope signals, of no global significance, could thus have been transmitted into the localised sediment record. Thus, the nonzero intercept δ34SV-CDT–Δ33S data array may alternatively represent a very localised S-isotope signature in the Neoarchaean surface environment. Fallout from local volcanic eruptions could imprint recycled MIF-S signals into pyrite of restricted depositional environments, thereby avoiding attenuation of the signal in the subdued, averaged global open ocean sulphur pool. Thus, the superposition of extreme local S-isotope signals offers an alternative explanation for the large Neoarchaean MIF-S excursions and asymmetry of the Δ33S rock record.

  • 125. Gardiner, Nicholas J.
    et al.
    Searle, Michael P.
    Morley, Christopher K.
    Robb, Laurence J.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Roberts, Nick M.W.
    Kirkland, Christopher L.
    Spencer, Christopher J.
    The crustal architecture of Myanmar imaged through zircon U-Pb, Lu-Hf and O isotopes: Tectonic and metallogenic implications2018In: Gondwana Research, ISSN 1342-937X, E-ISSN 1878-0571, Vol. 62, p. 27-60Article in journal (Refereed)
    Abstract [en]

    The Tethys margin in central and eastern Asia is comprised of continental terranesseparated by suture zones, some of which remain cryptic. Determining the crustal architecture, and therefore the geological history, of the Eastern Tethyan margin remains challenging. Sited in the heart of this region, Myanmar is a highly prospective but poorly explored minerals jurisdiction. A better understanding of Myanmar's mineralization can only be realized through a better understanding of its tectonic history, itself reflected in at least four major magmatic belts. The Eastern and the Main Range Provinces are associated with the Late Permian to Early Triassic closure of Palaeo-Tethys. The Mogok–Mandalay–Mergui Belt and Wuntho–Popa Arc are a response to the Eocene closure of Neo-Tethys. However, magmatic ages outside these two orogenic events are also recorded. We present new zirconU-Pb, Lu-Hf and O isotope data from magmatic rocks across Myanmar, which we append to the existing dataset to isotopically characterize Myanmar's magmatic belts. Eastern Province Permian I-type magmatism has evolved εHf (−10.9 to −6.4), whilst Main Range Province Triassic S-type magmatism also records evolved εHf (−13.5 to −8.8). The Mogok-Mandalay-Mergui Belt is here divided into the Tin Province and the Mogok Metamorphic Belt. The Tin Province hosts ca. 77–50 Ma magmatism with evolved εHf (−1.2 to −15.2), and δ18O of 5.6–8.3‰. The Mogok Metamorphic Belt exhibits a more complex magmatic and metamorphic history, and granitoids record Jurassic, Late Cretaceous, and Eocene to Miocene phases of magmatism, all of which exhibit evolved εHf values between −4.6 and −17.6, and δ18O between 6.3 and 9.2‰. From the Tagaung-Myitkyina Belt, we report a magmatic age of 172 Ma and εHf of 18.1 to 10.8. To accommodate the geological evidence, we propose a tectonic model for Myanmar involving a greater Sibumasu – where the documented zircon isotopic variations reflect compositional variations in magmatic source – and invoke the role of a Tengchong Block. The Baoshan Block and Greater Sibumasu were likely assembled on or before the Triassic, a former Andean margin and suture which may lie across the Northern Shan Plateau, and reflected in isotopic differences between the northern and southern parts of the Mogok Metamorphic Belt. This contiguous Sibumasu–Baoshan Block then sutured onto the Indochina margin in the Late Triassic. We propose that a Tengchong Block within Myanmar provides for a southerly termination of the Meso-Tethys suture immediately north of the Mogok area. A discrete Tengchong Block may explain a discontinuous arc of Late Triassic to Jurassic I-type magmatism in central Myanmar, representing an Andean-type margin sited above a subducting Meso-Tethys on the margin of Sibumasu. The Tengchong Block sutured onto Greater Sibumasu before the Late Cretaceous, after which subduction of Neo-Tethys drove the magmatism of the Wuntho-Popa Arc and ultimately that of the Tin Province. The metallogenic character of granite belts in Myanmar reflects the crustal architecture of the region, which is remarkable for its prolific endowment of granite-hosted Sn-W mineralization in two quite distinct granite belts related to sequential Indosinian and Himalayan orogenesis.

  • 126. Gardiner, N.J.
    et al.
    Hawkesworth, C.J.
    Robb, L.J.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Roberts, N.M.W.
    Kirkland, C.L.
    Evans, N.J.
    Contrasting Granite Metallogeny through the Zircon Record: A Case Study from Myanmar2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 748Article in journal (Refereed)
    Abstract [en]

    Granitoid-hosted mineral deposits are major global sources of a number of economically important metals. The fundamental controls on magma metal fertility are tectonic setting, the nature of source rocks, and magma differentiation. A clearer understanding of these petrogenetic processes has been forged through the accessory mineral zircon, which has considerable potential in metallogenic studies. We present an integrated zircon isotope (U-Pb, Lu-Hf, O) and trace element dataset from the paired Cu-Au (copper) and Sn-W (tin) magmatic belts in Myanmar. Copper arc zircons have juvenile εHf (+7.6 to +11.5) and mantle-like δ18O (5.2–5.5‰), whereas tin belt zircons have low εHf (−7 to −13) and heavier δ18O (6.2–7.7‰). Variations in zircon Hf and U/Yb reaffirm that tin belt magmas contain greater crustal contributions than copper arc rocks. Links between whole-rock Rb/Sr and zircon Eu/Eu* highlight that the latter can monitor magma fractionation in these systems. Zircon Ce/Ce* and Eu/Eu* are sensitive to redox and fractionation respectively, and here are used to evaluate zircon sensitivity to the metallogenic affinity of their host rock. Critical contents of Sn in granitic magmas, which may be required for the development of economic tin deposits, are marked by zircon Eu/Eu* values of ca. ≤0.08.

  • 127. Gardiner, N.J.
    et al.
    Roberts, N.M.W.
    Morley, C.K.
    Searle, M.P.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Did Oligocene crustal thickening precede basin development in northern Thailand? A geochronological reassessment of Doi Inthanon and Doi Suthep2016In: Lithos, ISSN 0024-4937, E-ISSN 1872-6143, Vol. 240-243, p. 69-83Article in journal (Refereed)
    Abstract [en]

    The Doi Inthanon and Doi Suthep metamorphic core complexes in northern Thailand are comprised of amphibolite-grade migmatitic gneisses mantled by lower-grade mylonites and metasedimentary sequences, thought to represent Cordilleran-style core complexes exhumed through the mobilization of a low-angle detachment fault. Previous studies have interpreted two metamorphic events (Late Triassic and Late Cretaceous), followed by ductile extension between the late Eocene and late Oligocene, a model which infers movement on the detachment at ca. 40 Ma, and which culminates in a rapid unroofing of the complexes in the early Miocene. The Chiang Mai Basin, the largest such Cenozoic Basin in the region, lies immediately to the east. Its development is related to the extension observed at Doi Inthanon and Doi Suthep, however it is not definitively dated, and models for its development have difficulty reconciling Miocene cooling ages with Eocene detachment movement. Here we present new in-situ LA-ICP-MS and SIMS U–Pb age data of zircon and monazite grains from gneiss and leucogranite samples taken from Doi Inthanon and Doi Suthep. Our new zircon data exhibit an older age range of 221–210 Ma, with younger ages of ca. 72 Ma, and 32–26 Ma. Our monazite data imply an older age cluster at 83–67 Ma, and a younger age cluster of 34–24 Ma. While our data support the view of Indosinian basement being reworked in the Cretaceous, they also indicate a late Eocene–Oligocene tectonothermal event, resulting in prograde metamorphism and anatexis. We suggest that this later event is related to localized transpressional thickening associated with sinistral movement on the Mae Ping Fault, coupled with thickening at the restraining bend of the Mae Yuan Fault to the immediate west of Doi Inthanon. Further, this upper Oligocene age limit from our zircon and monazite data would imply a younger Miocene constraint on movement of the detachment, which, when combined with the previously recorded Miocene cooling ages, has implications for a model for the onset of extension and subsequent development of the Chiang Mai Basin in the early mid-Miocene.

  • 128. Gardiner, N.J.
    et al.
    Searle, M.P.
    Morley, C.K.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Spencer, C.J.
    Robb, L.J.
    The closure of Palaeo-Tethys in Eastern Myanmar and Northern Thailand: New insights from zircon U–Pb and Hf isotope data.2016In: Gondwana Research, ISSN 1342-937X, E-ISSN 1878-0571, Vol. 39, p. 401-422Article in journal (Refereed)
    Abstract [en]

    Two of the major granite belts of Southeast Asia are the Main Range and Eastern Province. Together, these are interpreted to represent the magmatic expression of the closure of Palaeo-Tethys during Late Palaeozoic to Early Mesozoic times. Recent geochronological and geochemical work has better delineated these belts within Peninsular Malaysia, thereby providing important constraints on the timing of Palaeo-Tethys suturing. However, the northern extension of this Palaeo-Tethyan suture is less well understood. Here we present new ion microprobe U–Pb zircon age data from northern Thailand and eastern Myanmar. Measured ages of 219 and 220 Ma from the Kyaing Tong granite imply northern extension of the Main Range Province into eastern Myanmar. The Tachileik granite in far eastern Myanmar yields an age of 266 Ma, consistent with published Eastern Province ages, and this therefore constrains the northern extension of the Palaeo-Tethys suture in eastern Myanmar. We further discuss how this suture may extend northwards into Yunnan. A Late Cretaceous age (70 Ma) measured in Thailand represents later magmatic activity, and is similar to published magmatic ages from central Myanmar. This younger magmatism is interpreted to be related to the subduction of Neo-Tethys prior to India–Asia collision. Further, we present new laser ablation zircon Hf isotope data from eastern Myanmar which suggest that Palaeoproterozoic crust underlies both the Main Range and Eastern Province granites. Our εHf model age of ca. 1750 Ma from Sibumasu, the basement underlying eastern Myanmar, lies within the range of other model ages reported thus far for the Baoshan Block north in Yunnan, interpreted by some to be the northern extension of Sibumasu.

  • 129. Gasser, D.
    et al.
    Jeřábek, P.
    Faber, P.
    Stünitz, H.
    Menegon, L.
    Corfu, F.
    Erambert, M.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Behaviour of geochronometers and timing of metamorphic reactions during deformation at lower crustal conditions: phase equilibrium modelling and U–Pb dating of zircon, monazite, rutile and titanite from the Kalak Nappe Complex, northern Norway.2015In: Journal of Metamorphic Geology, ISSN 0263-4929, E-ISSN 1525-1314, Vol. 33, p. 513-534Article in journal (Refereed)
    Abstract [en]

    This study investigates the behaviour of the geochronometers zircon, monazite, rutile and titanite in polyphase lower crustal rocks of the Kalak Nappe Complex, northern Norway. A pressure–temperature–time–deformation path is constructed by combining microstructural observations with P–T conditions derived from phase equilibrium modelling and U–Pb dating. The following tectonometamorphic evolution is deduced: A subvertical S1 fabric formed at ~730–775 °C and ~6.3–9.8 kbar, above the wet solidus in the sillimanite and kyanite stability fields. The event is dated at 702 ± 5 Ma by high-U zircon in a leucosome. Monazite grains that grew in the S1 fabric show surprisingly little variation in chemical composition compared to a large spread in (concordant) U–Pb dates from c. 800 to 600 Ma. This age spread could either represent protracted growth of monazite during high-grade metamorphism, or represent partially reset ages due to high-T diffusion. Both cases imply that elevated temperatures of >600 °C persisted for over c. 200 Ma, indicating relatively static conditions at lower crustal levels for most of the Neoproterozoic. The S1 fabric was overprinted by a subhorizontal S2 fabric, which formed at ~600–660 °C and ~10–12 kbar. Rutile that originally grew during the S1-forming event lost its Zr-in-rutile and U–Pb signatures during the S2-forming event. It records Zr-in-rutile temperatures of 550–660 °C and Caledonian ages of 440–420 Ma. Titanite grew at the expense of rutile at slightly lower temperatures of ~550 °C during ongoing S2 deformation; U–Pb ages of c. 440–430 Ma date its crystallization, giving a minimum estimate for the age of Caledonian metamorphism and the duration of Caledonian shearing. This study shows that (i) monazite can have a large spread in U–Pb dates despite a homogeneous composition; (ii) rutile may lose its Zr-in-rutile and U–Pb signature during an amphibolite facies overprint; and (iii) titanite may record crystallization ages during retrograde shearing. Therefore, in order to correctly interpret U–Pb ages from different geochronometers in a polyphase deformation and reaction history, they are ideally combined with microstructural observations and phase equilibrium modelling to derive a complete P–T–t–d path.

  • 130.
    Gatta, Diego
    et al.
    University of Milan, Italy.
    Bosi, Ferdinando
    Sapienza Università, Rome, Italy.
    Fernandez Diaz, Maria Teresa
    Institut Laue-Langevin, Grenoble, France.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    H-bonding scheme in allactite: a combined single-crystal X-ray and neutron diffraction, optical absorption spectroscopy, FTIR and EPMA-WDS study2016In: Mineralogical magazine, ISSN 0026-461X, E-ISSN 1471-8022, Vol. 80, no 5, p. 719-732Article in journal (Refereed)
    Abstract [en]

    The crystal chemistry of allactite from Långban, Värmland (Sweden) was investigated by single-crystal X-ray and neutron diffraction, optical absorption spectroscopy, Fourier-transform infra-red spectroscopy (FTIR) and electron microprobe analysis by wavelength-dispersive spectroscopy (EPMA-WDS). The optical spectra indicate the presence of Mn in valence state 2+ only. Assuming 16 O atoms per formula unit, arsenic as As5+ and the (OH) content calculated by charge balance, the resulting formula based on the EPMA-WDS data is (Mn6.732+Ca0.13Mg0.12Zn0.02)Σ7.00(As5+)2.00O16H8, very close to the ideal composition Mn7(AsO4)2(OH)8. In the unpolarized FTIR spectrum of allactite, fundamental (OH)-stretching bands are observed at 3236, 3288, 3387, 3446, 3484, 3562 and 3570 cm–1, suggesting that a number of OH environments, with different hydrogen bond strengths, occur in the structure. The neutron structure refinement shows that four independent H sites occur in allactite with full site occupancy, all as members of hydroxyl groups. The complex hydrogen-bonding scheme in the allactite structure is now well defined, with at least nine hydrogen bonds energetically favourable with mono-, bi- and trifurcated configurations.

  • 131.
    Gatta, G. D.
    et al.
    University of Milano.
    Bosi, Ferdinando
    Swedish Museum of Natural History, Department of Geology.
    McIntyre, G. J.
    Australian Nuclear Science and Technology Organisation.
    Henrik, Skogby
    Swedish Museum of Natural History, Department of Geology.
    First accurate location of two proton sites in tourmaline: A single-crystal neutron diffraction study of oxy-dravite2014In: Mineralogical magazine, ISSN 0026-461X, E-ISSN 1471-8022, Vol. 78, no 3, p. 681-692Article in journal (Refereed)
  • 132.
    Gatta, G. Diego
    et al.
    Università di Milano, Italy.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Bosi, Ferdinando
    Sapienza Università di Roma, Italy.
    Canadillas-Delgado, Laura
    Institut Laue-Langevin, Grenoble, France.
    Fernandez-Diaz, Maria Teresa
    Centro Universitario de la Defensa de Zaragoza, Spain.
    Minerals in cement chemistry: A single-crystal neutron diffraction study of ettringite. Ca6Al2(SO4)3(OH)12.27H2O2019In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 104, no 1, p. 73-78Article in journal (Refereed)
  • 133.
    Gatta, G.Diego
    et al.
    Università degli Studi de Milano.
    Bosi, Ferdinando
    Swedish Museum of Natural History, Department of Geology.
    McIntyre, Garry J.
    Australian Nuclear Science and Technology Organisation.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Static positional disorder in ulvöspinel: A single-crystal neutron diffraction study2014In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 99, p. 255-260Article in journal (Refereed)
  • 134.
    Gdaniec, Sandra
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Roy-Barman, Matthieu
    Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay,Gif-sur-Yvette, France.
    Foliot, Lorna
    Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay,Gif-sur-Yvette, France.
    Thil, Francois
    Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay,Gif-sur-Yvette, France.
    Dapoigny, Arnaud
    Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay,Gif-sur-Yvette, France.
    Burckel, Pierre
    Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, CEA-CNRS-UVSQ, Université Paris-Saclay,Gif-sur-Yvette, France.
    Garcia-Orellana, Jordi
    Institut de Ciència i Tecnologia Ambientals & Departament de Física, Universitat Autònoma de Barcelona, Bellaterra 08193, Spain.
    Masqué, Pere
    Institut de Ciència i Tecnologia Ambientals & Departament de Física, Universitat Autònoma de Barcelona, Bellaterra 08193, Spain.
    Mörth, Carl-Magnus
    Stockholm University, Department of Geological sciences, Stockholm, Sweden.
    Andersson, Per
    Swedish Museum of Natural History, Department of Geology.
    Thorium and Protactinium isotopes as tracers of marine particle fluxes and deep water circulation in the Mediterranean Sea2018In: Marine Chemistry, ISSN 0304-4203, E-ISSN 1872-7581, Vol. 199, p. 12-23Article in journal (Refereed)
    Abstract [en]

    231Pa, 230Th and 232Th were analyzed in unfiltered sea water samples (n = 66) and suspended particles (n = 19) collected in the Mediterranean Sea during the MedSeA-GA04-S cruise along the GEOTRACES section GA04S and used to investigate mechanisms controlling the distribution and fractionation of Pa and Th in an ocean margin environment. 231Pa and230Th are particle reactive radionuclides and are often used astracers of processes such as boundary scavenging, particle transport and ocean circulation. The depth profiles of total 231Pa and 230Th concentrations in the Mediterranean Sea displayed non-linear shapes. Higher total 232Th concentrations were observed at the straits and in deepwaters pointing at lithogenic sources. Fractionation factors FTh/Pa ranged from 1.4 to 9. Application of a box-model illustrated that 94 % of the 231Pa and almost all of the 230Th (99.9 %) produced in the Mediterranean Sea is removed to the sediment by scavenging. The negligible export of 230Th to the Atlantic Ocean, leads to a reevaluation of the mean settling speed of the filtered particles, which is now estimated to 500-1000 m/y. The low FTh/Pa fractionation factors are attributed to the efficient scavenging and lack of transport of 231Pa to the Atlantic Ocean.

  • 135. Ge, Rongfeng
    et al.
    Wilde, Simon
    Nemchin, Alexander
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Bellucci, Jeremy
    Swedish Museum of Natural History, Department of Geology.
    Erickson, Timmons
    Frew, Adam
    Thern, Eric
    A 4463 Ma apparent zircon age from the Jack Hills (Western Australia) resulting from ancient Pb mobilization2018In: Geology, ISSN 0091-7613, E-ISSN 1943-2682, Vol. 46, no 4, p. 303-306Article in journal (Refereed)
    Abstract [en]

    Hadean (≥4.0 Ga) zircon grains provide the only direct record of the first half-billion years of Earth’s history. Determining accurate and precise crystallization ages of these ancient zircons is a prerequisite for any interpretation of crustal evolution, surface environment, and geodynamics on the early Earth, but this may be compromised by mobilization of radiogenic Pb due to subsequent thermal overprinting. Here we report a detrital zircon from the Jack Hills (Western Australia) with 4486–4425 Ma concordant ion microprobe ages that yield a concordia age of 4463 ± 17 Ma (2σ), the oldest zircon age recorded from Earth. However, scanning ion imaging reveals that this >4.4 Ga apparent age resulted from incorporation of micrometer-scale patches of unsupported radiogenic Pb with extremely high 207Pb/206Pb ratios and >4.5 Ga 207Pb/206Pb ages. Isotopic modeling demonstrates that these patches likely resulted from redistribution of radiogenic Pb in a ca. 4.3 Ga zircon during a ca. 3.8 Ga or older event. This highlights that even a concordia age can be spurious and should be carefully evaluated before being interpreted as the crystallization age of ancient zircon.

  • 136. Glykou, Aikaterini
    et al.
    Eriksson, Gunilla
    Storå, J.
    Schmitt, Melanie
    Swedish Museum of Natural History, Department of Geology.
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology.
    Lidén, Kerstin
    Intra- and inter-tooth variation in strontium isotope ratios from prehistoric seals by laser ablation multi-collector inductively coupled plasma mass spectrometry2018In: Rapid Communications in Mass Spectrometry, ISSN 0951-4198, E-ISSN 1097-0231, Vol. 32, p. 1215-1224Article in journal (Refereed)
    Abstract [en]

    Rationale

    Strontium isotope ratios (87Sr/86Sr) in modern‐day marine environments are considered to be homogeneous (~0.7092). However, in the Baltic Sea, the Sr ratios are controlled by mixing seawater and continental drainage from major rivers discharging into the Baltic. This pilot study explores if variations in Sr can be detected in marine mammals from archaeological sites in the Baltic Sea.               

    Methods

    87Sr/86Sr ratios were measured in tooth enamel from three seal species by laser ablation multi‐collector inductively coupled plasma mass spectrometry (LA‐MC‐ICP‐MS). The method enables micro‐sampling of solid materials. This is the first time that the method has been applied to marine samples from archaeological collections.               

    Results

    The analyses showed inter‐tooth 87Sr/86Sr variation suggesting that different ratios can be detected in different regions of the Baltic Sea. Furthermore, the intra‐tooth variation suggests possible different geographic origin or seasonal movement of seals within different regions in the Baltic Sea through their lifetime.               

    Conclusions

    The method was successfully applied to archaeological marine samples showing that: (1) the 87Sr/86Sr ratio in marine environments is not uniform, (2) 87Sr/86Sr differences might reflect differences in ecology and life history of different seal species, and (3) archaeological mobility studies based on 87Sr/86Sr ratios in humans should therefore be evaluated together with diet reconstruction.

  • 137.
    Gori, Claudia
    et al.
    University of Parma, Italy.
    Tribaudino, Mario
    University of Parma, Italy.
    Mezzadri, Francesco
    University of Parma, Italy.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Co2+-doped diopside: crystal structure and optical properties2018In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 45, no 5, p. 443-461Article in journal (Refereed)
    Abstract [en]

    Synthetic clinopyroxenes along the CaMgSi2O6– CaCoSi2O6 join were investigated by a combined chemical-structuralspectroscopic approach. Single crystals were synthesized by flux growth methods, both from Ca-saturated and Ca-deficient starting compositions. Single crystal structure refinements show that the incorporation of Co2+ at the octahedrally coordinated cation sites of diopside, increases the unit-cell as well as the M1 and the M2 polyhedral volumes. Spectroscopic investigations (UV–VIS–NIR) of the Ca-rich samples reveal three main optical absorption bands, i.e. 4T1g4T2g(F), 4T1g 4A2g(F) and 4T1g4T1g(P) as expected for Co2+ at a six-coordinated site. The bands arising from the 4T1g4T2g(F) and the 4T1g4T1g(P) electronic transitions, are each split into two components, due to the distortions of the M1 polyhedron from ideal Oh- symmetry. In spectra of both types, a band in the NIR range at ca 5000 cm−1 is caused by the 4A2g4T1g(F) electronic transition in Co2+ in a cubic field in the M2 site. Furthermore, an additional component to a band system at 14,000 cm−1, due to electronic transitions in Co2+ at the M2 site, is recorded in absorption spectra of Ca-deficient samples. No variations in Dq and Racah B parameters for Co2+ at the M1 site in response to compositional changes, were demonstrated, suggesting complete relaxation of the M1 polyhedron within the CaMgSi2O6– CaCoSi2O6 solid solution.

  • 138.
    Grasse, P.
    et al.
    GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany.
    Brezezinski, M.
    Marine Science Institute and the Department of Ecology, Evolution, and Marine Biology & University of California, USA.
    Cardinal, D.
    Sorbonne Universités, Paris, France.
    de Souza, G.F.
    ETH Zurich, Institute of Geochemistry and Petrology, Switzerland.
    Andersson, Per
    Swedish Museum of Natural History, Department of Geology.
    Closset, I.
    Sorbonne Universités, Paris, France.
    Cao, Z.
    State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China.
    Dai, M.
    State Key Laboratory of Marine Environmental Science, Xiamen University, Xiamen, China.
    Ehlert, C.
    Max Planck Research Group for Marine Isotope Geochemistry, University of Oldenburg, Germany.
    Estrade, N.
    University of British Columbia, Vancouver, British Columbia,.
    Francois, R.
    University of British Columbia, Vancouver, British Columbia,.
    Frank, M.
    GEOMAR, Helmholtz Centre for Ocean Research Kiel, Germany.
    Jiang, G.
    Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China.
    Jones, J.L.
    Marine Science Institute and the Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara USA.
    Kooijman, E.
    Swedish Museum of Natural History, Department of Geology.
    Liu, Q.
    Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China.
    Lu, D.
    Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing, China.
    Pahnke, K.
    Institute for Chemistry and Biology of the Marine Environment, University of Oldenburg, Germany.
    Ponzevera, E.
    Unité de Recherche Géosciences Marines, IFREMER, Brest, France.
    Schmitt, M.
    Swedish Museum of Natural History, Department of Geology.
    Sun, S.
    Department of Environmental Science and Analytical Chemistry, Stockholm University, Sweden.
    Sutton, J.N.
    Universite de Brest, CNRS, IRD, IFREMER, LEMAR, IUEM, France.
    Thil, F.
    LSCE/IPSL - Laboratoire des Sciences du Climat et de l'Environnement, Gif sur Yvette, France.
    Weis, D.
    University of British Columbia Pacific Center for Isotopic and Geochemical Research, Vancouver, British Columbia,Canada .
    Wetzel, F.
    ETH Zurich, Institute of Geochemistry and Petrology, Switzerland.
    Zhang, A.
    State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai, China.
    Zhang, J.
    State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai, China.
    Zhang, Z.
    State Key Laboratory of Marine Environmental Science,Xiamen University,.
    GEOTRACES Intercalibration of the Stable Silicon Isotope Composition of Dissolved Silicic Acid in Seawater2017In: Journal of Analytical Atomic Spectrometry, ISSN ISSN 0267-9477, Vol. 32, p. 562-578Article in journal (Refereed)
    Abstract [en]

    The first inter-calibration study of the stable silicon isotope composition of dissolved silicic acid in seawater, d30Si(OH)4, is presented as a contribution to the international GEOTRACES program. Eleven laboratories from seven countries analyzed two seawater samples from the North Pacific subtropical gyre (Station ALOHA) collected at 300 m and at 1000 m water depth. Sampling depths were chosen to obtain samples with a relatively low (9 mmol L-1, 300 m) and a relatively high (113 mmol L-1, 1000 m) silicic acid concentration as sample preparation differs for low- and high concentration samples. Data for the 1000 m water sample were not normally distributed so the median is used to represent the central tendency for the two samples. Median d30Si(OH)4 values of +1.66‰ for the low-concentration sample and +1.25‰ for the high-concentration sample were obtained. Agreement among laboratories is overall considered very good; however, small but statistically significant differences among the mean isotope values obtained by different laboratories were detected, likely reflecting inter-laboratory differences in chemical preparation including preconcentration and purification methods together with different volumes of seawater analyzed, andthe use of different mass spectrometers including the Neptune MC-ICP-MS (Thermo Fisher™, Germany), the Nu Plasma MC-ICP-MS (Nu Instruments™, Wrexham, UK), and the Finnigan™ (now Thermo Fisher™, Germany) MAT 252 IRMS. Future studies analyzing d30Si(OH)4 in seawater should also analyze and report values for these same two reference waters in order to facilitate comparison of data generated among and within laboratories over time.

  • 139.
    Grew, Edward S.
    et al.
    University of Maine.
    Barbier, Jacques
    McMaster University, Ontario.
    Britten, Jim F.
    McMaster University, Ontario.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Shearer, Charles K.
    University of New Mexico.
    The crystal chemistry of welshite, a non-centrosymmetric (P1) aenigmatite-sapphirine-surinamite group mineral2007In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 92, p. 80-90Article in journal (Refereed)
  • 140.
    Grew, Edward S.
    et al.
    University of Maine.
    Barbier, Jacques
    McMaster University, Ontario.
    Britten, Jim
    McMaster University, Ontario.
    Yates, Martin G.
    University of Maine.
    Polyakov, Vladislav O.
    Natural Science Museum of the Ilmen State Reserve.
    Shcherbakova, Elena P.
    Natural Science Museum of the Ilmen State Reserve.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Shearer, Charles K.
    University of New Mexico.
    Makarochkinite, Ca2Fe2+4Fe3+Ti4+Si4BeAlO20, a new beryllosilicate member of the aenigmatite-sapphirine-surinamite group from the Il’men Mountains (southern Urals), Russia2005In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 90, p. 1402-1412Article in journal (Refereed)
  • 141.
    Grew, Edward S.
    et al.
    University of Maine, Orono, USA.
    Bosi, Ferdinando
    Sapienza Università di Roma, Italy.
    Ros, Linus
    Lund University, Sweden.
    Kristiansson, Per
    Lund University, Sweden.
    Gunter, Mickey E.
    University of Idaho, Moscow, USA.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Trumbull, Robert B.
    GFZ, Potsdam, Germany.
    Yates, Martin G.
    University of Maine, Orono, USA.
    Fluor-elbaite, lepidolite and Ta–Nb oxides from a pegmatite of the 3000Ma Sinceni Pluton, Swaziland: evidence for lithium–cesium–tantalum (LCT) pegmatites in the Mesoarchean2018In: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 30, no 2, p. 205-218Article in journal (Refereed)
    Abstract [en]

    Mineral evolution is concerned with the timing of mineral occurrences, such as the earliest reported occurrences in the geologic record. Minerals containing essential Li have not been reported from rocks older than ca. 3000 Ma, thus the lithian tourmaline (fluor-elbaite) and mica (lepidolite) assemblage from a pegmatite near Zishineni associated with the ca. 3000Ma Sinceni Pluton presents unusual interest. Fluor-elbaite (0.750.98 F per formula unit) forms green crystals up to 50mm long. Spindle stage measurements give ω = 1.652(1), ε = 1.627(1) (589.3 nm). Optical absorption spectroscopy shows Fe and Mn are divalent; infra-red spectroscopy demonstrates the presence of Li and indicates the presence of (OH) at both the (OH) sites. Electron microprobe analysis of 330 points on several prisms, the largest of which is zoned in Fe and Ca, gives the following average and standard deviations in wt%: SiO2 37.29 (0.26), TiO2 0.05 (0.05), Al2O3 38.14 (0.35), Cr2O3 0 (0.02), MgO 0.02 (0.01), MnO 3.57 (0.25), FeO 2.48 (0.60), Na2O 2.48 (0.09), K2O 0.03 (0.12), CaO 0.77 (0.21), F 1.80 (0.11), Cl 0 (0.01) wt%. Nuclear reaction analyses gave Li2O 0.91 (0.04) and B2O10.55 (0.45). The empirical formula of fluor-elbaite was determined by integrating crystal-chemical data from electron microprobe analysis, nuclear reaction analysis, crystal structure refinement using X-ray diffraction, infra-red and optical absorption spectroscopy:X(0.09Na0.77K0.01Ca0.13)Σ1.00 Y(0.35Li0.59Mn2+0.49Fe2+0.33Al1.23Ti0.01)Σ3.00Al6(Si6O18)(BO3)3O3(OH)3O1[F0.92(OH)0.08]Σ1.00. The crystal structure of fluor-elbaite was refined to statistical indices R1 for 1454 reflections 2% using MoKa X-ray intensity data. Structural data confirm the presence of significant vacancies at the Y site. Micas include lepidolite in flakes several millimeters across that are veined and overgrown by fine-grainedmuscovite. Silica and (FeO+MnO) increase, and Al decreases with F, all giving tight linear fits for both micas taken together, suggesting bothmicas can be regarded as interstratified muscovite and lithium mica consisting of 35.2 wt% masutomilite containing nearly equal amounts of Mn and Fe, 52.8 wt% polylithionite and 11.9 wt% trilithionite. Muscovite and lepidolite contain <0.2 wt% and 0.72.25 wt% Cs2O and 1.01.1 wt% and 1.41.5wt% Rb2O, respectively. Other minerals include spessartine (e.g., Sps93Alm4Grs3) in scattered grains up to 0.5mm across and monazite.Oxides occur sparsely in muscovite, rarely in lepidolite, as grains up to 11 mm long, including fluorcalciomicrolite, columbite-(Mn) withNb>Ta, hübnerite(?) and a possible Pb-bearing microlite (Ta>Nb). The oxides, together with the muscovite, are interpreted to be related to later hydrothermal reworking of the primary lepidolitefluorelbaite assemblage. Given the 2990 ± 43MaRbSr isochron and 3074 ± 4Ma evaporation PbPb ages reported for the Sinceni Pluton and Rb/Sr mineral ages ranging from 2906 ± 31Ma to 3072 ± 33Ma reported for the pegmatites, the fluor-elbaitecesian lepidolitefluorcalciomicrolite-bearing pegmatite is the first reported occurrence of a lithian tourmaline and lepidolite in the geologic record, as well as one of the two earliest known examples of the lithiumcesiumtantalum (LCT) family of pegmatites. The Sinceni magma is most plausibly derived from a metasedimentary source by intrusion of hot mantle melts into the crust from below, thereby indicating that a “mature” continental crust existed in the Kaapvaal craton at ca. 3000 Ma.

  • 142.
    Grew, Edward S.
    et al.
    University of Maine.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Pasero, Marco
    Università di Pisa.
    The crystal-chemistry of aenigmatite revisited: electron microprobe data, structure refinement, and Mössbauer spectroscopy of aenigmatite from Vesterøya (Norway)2008In: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 20, p. 983-991Article in journal (Refereed)
  • 143.
    Grew, Edward S.
    et al.
    University of Maine.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Pasero, Marco
    Università di Pisa.
    Barbier, Jacques
    McMaster University, Ontario.
    Recommended nomenclature for the sapphirine and surinamite groups (sapphirine supergroup)2008In: Mineralogical magazine, ISSN 0026-461X, E-ISSN 1471-8022, Vol. 72, p. 839-876Article in journal (Refereed)
  • 144.
    Grew, Edward S.
    et al.
    School of Earth and Climate Sciences University of Maine.
    Jonsson, Erik
    Geological Survey of Sweden.
    Langhof, Jörgen
    Swedish Museum of Natural History, Department of Geology.
    Lithium - 200 years: Symposium and field trip June 14 - 16, 20182018In: Elements An international magazine of mineralogy, geochemistry, and petrology, ISSN 1811-5209, Vol. 14, no 4, p. 284-284Article in journal (Other academic)
  • 145.
    Grew, Edward S.
    et al.
    University of Maine.
    Locock, Andrew J.
    University of Alberta.
    Mills, Stuart J.
    Museum Victoria.
    Galuskina, Irina O.
    University of Silesia.
    Galuskin, Evgeny V.
    University of Silesia.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Nomenclature of the garnet supergroup2013In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 98, p. 785-811Article in journal (Refereed)
  • 146. Guitreau, Martin
    et al.
    Blichert-Toft, J.
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Hafnium isotope evidence for early-Proterozoic volcanic arc reworking in the Skellefte district (northern Sweden) and implications for the Svecofennian orogeny2014In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 252, p. 39-52Article in journal (Refereed)
    Abstract [en]

    The Skellefte district is a seemingly juvenile and heavily mineralized crustal domain in northern Sweden that formed between 1.90 and 1.87 Ga. It is commonly interpreted as a volcanic arc deposited on a basement (known variously as the Bothnian or the Knaften-Barsele group) that could be represented by older rocks (1.96-1.94 Ga) found in the vicinity. In order to understand the potential genetic relationship between the arc and the basement, Hf and Pb isotopes in magmatic zircons from key lithologies were measured by solution multi-collector inductively-coupled plasma mass spectrometry. It is shown that both geological groups display similar Hf isotope compositions, which translate into decreasing εHf with time. Overall, the data are compatible with reworking of the Knaften-Barsele arc to produce the Skellefte rocks over a short time interval from 1.90 to 1.87 Ga in a context of crustal extension with ongoing subduction. When the data presented here are integrated with general models of tectonic evolution of the Svecofennian orogen, they fit a scenario in which the juvenile Knaften-Barsele arc formed between 1.96 and 1.94 Ga and became accreted onto the Karelian continent located further north at about 1.92-1.91 Ga. Systematic north to south variations in Pb, Nd, and Hf isotope compositions throughout the Svecofennides, interpreted as resulting from an increase in Archean crust involvement towards the south, indicate a genetic link between the Proterozoic crustal domains of Sweden and Finland.

  • 147.
    Gustafsson, Örjan
    et al.
    Department of Environmental Science and Analytical Chemistry Stockholm University.
    Gelting, Johan
    Department of Environmental Science and Analytical Chemistry.
    Andersson, Per
    Swedish Museum of Natural History, Department of Geology.
    Larsson, Ulf
    Department of Ecology, Environment and Plant Sciences, Stockholm University.
    Roos, Per
    Department of Nuclear Technologies, Technical University of Denmark.
    An assessment of upper ocean carbon and nitrogen export fluxes on the boreal continental shelf: A 3-year study in the open Baltic Sea comparing sediment traps, 234Th proxy, nutrient, and oxygen budgets2013In: Limnology and Oceanography: Methods, ISSN 1541-5856, E-ISSN 1541-5856, ISSN 1541-5856, Vol. 11, no 9, p. 495-510, article id DOI: 10.4319/lom.2013.11.495Article in journal (Refereed)
  • 148. Halldórsson, Sæmundur A.
    et al.
    Bali, Enik\Ho
    Hartley, Margaret E.
    Neave, David A.
    Peate, David W.
    Guðfinnsson, Guðmundur H.
    Bindeman, Ilya
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Riishuus, Morten S.
    Pedersen, Gro B. M.
    Jakobsson, Sigurdur
    Askew, Rob
    Gallagher, Catherine R.
    Gudmundsdóttir, Esther R.
    Gudnason, Jónas
    Moreland, William M.
    Óskarsson, Birgir V.
    Nikkola, Paavo
    Reynolds, Hannah I.
    Schmith, Johanne
    Thordarson, Thorvaldur
    Petrology and geochemistry of the 2014–2015 Holuhraun eruption, central Iceland: compositional and mineralogical characteristics, temporal variability and magma storage2018In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 173, no 8Article in journal (Refereed)
    Abstract [en]

    The 2014–2015 Holuhraun fissure eruption provided a rare opportunity to study in detail the magmatic processes and magma plumbing system dynamics during a 6-month-long, moderate- to large-volume basaltic fissure eruption. In this contribution, we present a comprehensive dataset, including major and trace elements of whole-rock and glassy tephra samples, mineral chemistry, and radiogenic and oxygen isotope analyses from an extensive set of samples (n = 62) that were collected systematically in several field campaigns throughout the entire eruptive period. We also present the first detailed chemical and isotopic characterization of magmatic sulfides from Iceland. In conjunction with a unique set of geophysical data, our approach provides a detailed temporal and spatial resolution of magmatic processes before and during this eruption. The 2014–2015 Holuhraun magma is compositionally indistinguishable from recent basalts erupted from the Bárðarbunga volcanic system, consistent with seismic observations for magma ascent close to the Bárðarbunga central volcano, followed by dyke propagation to the Holuhraun eruption site. Whole-rock elemental and isotopic compositions are remarkably constant throughout the eruption. Moreover, the inferred depth of the magma reservoir tapped during the eruption is consistently 8 ± 5 km, in agreement with geodetic observations and melt inclusion entrapment pressures, but inconsistent with vertically extensive multi-tiered magma storage prior to eruption. The near constancy in the chemical and isotopic composition of the lava is consistent with the efficient homogenization of mantle-derived compositional variability. In contrast, occurrence of different mineral populations, including sulfide globules, which display significant compositional variability, requires a more complex earlier magmatic history. This may include sampling of heterogeneous mantle melts that mixed, crystallized and finally homogenized at mid- to lower-crustal conditions.

  • 149. Harrison, John A.
    et al.
    Frings, Patrick J
    Swedish Museum of Natural History, Department of Geology.
    Beusen, Arthur H. W.
    Conley, Daniel J.
    McCrackin, Michelle L.
    Global importance, patterns, and controls of dissolved silica retention in lakes and reservoirs2012In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 26, no 2, p. n/a-n/aArticle in journal (Refereed)
    Abstract [en]

    Lentic water bodies (lakes and reservoirs) offer favorable conditions for silica (SiO2) burial in sediments. Recent global estimates suggest that (1) lentic SiO2 trapping is a globally important SiO2 flux, and (2) through reservoir construction, humans have dramatically altered river dissolved SiO2 (DSi) transport and coastal DSi delivery. However, regional to global scale patterns and controls of DSi removal in lentic systems are poorly constrained. Here we use 27 published lake and reservoir DSi budgets to develop insights into patterns and controls of lentic DSi retention and to develop a new, spatially explicit, global model of lentic DSi removal called SiRReLa (Silica Retention in Reservoirs and Lakes). In our analysis, lentic DSi removal (kg SiO2 yr−1) was significantly and positively related to DSi loading (P < 0.0001; r2 = 0.98), and DSi removal efficiency was significantly and positively related to water residence time (P < 0.0001; r2 = 0.68). In addition, DSi settling rates were, on average, 6.5-fold higher in eutrophic systems than in non-eutrophic systems (median settling velocities: 11.1 and 1.7 m yr−1 for eutrophic and non-eutrophic systems, respectively; P < 0.01). SiRReLa, which incorporates these insights, performed quite well in predicting both total DSi removal (kg SiO2 yr−1; Nash Sutcliffe Efficiency (N.S.E) = 0.88) and DSi removal efficiency (% Si removed; N.S.E. = 0.75), with no detectable bias in the model. Global application of SiRReLa confirms that lentic systems are important sinks for DSi, removing 89.1 Tg DSi yr−1 from watersheds globally, roughly 19–38% of all DSi inputs to surface waters. Small lakes and reservoirs (<50 km2) were critical in the analysis, retaining 81% (72 Tg DSi yr−1) of the globally retained total. Furthermore, although reservoirs occupy just 6% of the global lentic surface area, they retained approximately 35% of the total DSi removed by lentic systems. Regional hot spots for lentic DSi removal were identified and imply that lentic systems can remove the vast majority of DSi across a large fraction of Earth's land surface. Finally, a sensitivity analysis indicates that future improvements in DSi trapping and transport models should focus on improving estimates of DSi input to surface waters.

  • 150.
    Hatert, Frédéric
    et al.
    Université de Liège, Belgium..
    Pasero, Marco
    Università di Pisa, Italy..
    Mills, Stuart J.
    Museum Victoria, Melbourne, Australia..
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    How to define, redefine or discredit a mineral species?2017In: Elements, ISSN 1811-5209, E-ISSN 1811-5217, Vol. 13, no 3, p. 208-208Article in journal (Other academic)
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