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  • 401.
    Watenphul, Anke
    et al.
    University of Hamburg.
    Schlüter, Jochen
    University of Hamburg.
    Bosi, Ferdinando
    University of Rome "La Sapienza".
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Malcherek, Thomas
    University of Hamburg.
    Influence of the octahedral cationic-site occupancies on the framework vibrations of Li-free tourmalines, with implications for estimating temperature and oxygen fugacity in host rocks2016In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 101, p. 2554-2563Article in journal (Refereed)
  • 402.
    Weis, Franz
    Swedish Museum of Natural History, Department of Geology.
    Henrik, Skogby ()
    Swedish Museum of Natural History, Department of Geology.
    Stalder, Roland
    University of Innsbruck.
    Nemchin, Alexander
    Whitehouse, Martin
    Swedish Museum of Natural History, Department of Geology.
    Water content in the Martian mantle: A Nakhla perspective2017In: Geochimica et Cosmochimica Acta, ISSN 0016-7037, E-ISSN 1872-9533, Vol. 212, p. 84-98Article in journal (Refereed)
  • 403.
    Weis, Franz A.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Troll, Valentin R.
    Uppsala University.
    Deegan, Frances M.
    Uppsala University.
    Dahren, Börje
    Uppsala University.
    Magmatic water contents determined through clinopyroxene: Examples from the Western Canary Islands, Spain2015In: Geochemistry Geophysics Geosystems, ISSN 1525-2027, E-ISSN 1525-2027, Vol. 16, no 7, p. 2127-2146Article in journal (Refereed)
    Abstract [en]

    Water is a key parameter in magma genesis, magma evolution, and resulting eruption styles,because it controls the density, the viscosity, as well as the melting and crystallization behavior of a melt. Theparental water content of a magma is usually measured through melt inclusions in minerals such as olivine, amethod which may be hampered, however, by the lack of melt inclusions suitable for analysis, or postentrapmentchanges in their water content. An alternative way to reconstruct the water content of a magma is touse nominally anhydrous minerals (NAMs), such as pyroxene, which take up low concentrations of hydrogenas a function of the magma’s water content. During magma degassing and eruption, however, NAMs maydehydrate. We therefore tested a method to reconstruct the water contents of dehydrated clinopyroxene phenocrystsfrom the Western Canary islands (n=28) through rehydration experiments followed by infrared andM€ossbauer spectroscopy. Employing currently available crystal/melt partitioning data, the results of the experimentswere used to calculate parental water contents of 0.71±0.07 to 1.49±0.15 wt % H2O for WesternCanary magmas during clinopyroxene crystallization at upper mantle conditions. This H2O range is in agreementwith calculated water contents using plagioclase-liquid-hygrometry, and with previously published datafor mafic lavas from the Canary Islands and comparable ocean island systems elsewhere. Utilizing NAMs incombination with hydrogen treatment can therefore serve as a proxy for pre-eruptive H2O contents, which weanticipate becoming a useful method applicable to mafic rocks where pyroxene is the main phenocryst phase.

  • 404.
    Weis, Franz
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Lazor, Peter
    Uppsala universitet.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Stalder, Roland
    University of Innsbruck.
    Eriksson, Leif
    Stockholms universitet.
    Polarized IR and Raman spectra of zoisite: insights into the OH-dipole orientation and luminescence.2016In: European journal of mineralogy, ISSN 0935-1221, E-ISSN 1617-4011, Vol. 28, p. 537-543Article in journal (Refereed)
  • 405.
    Weis, Franz
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Ros, Linus
    Reichart, Patrick
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Kristiansson, Per
    Dollinger, Gunther
    Hydrogen concentration analysis in clinopyroxene using proton–proton scattering analysis2018In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 45, p. 669-678Article in journal (Refereed)
  • 406.
    Weis, Franz
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Lazor, Peter
    Uppsala universitet.
    Hydrogen analysis in nominally anhydrous minerals by transmission Raman spectroscopy2018In: Physics and chemistry of minerals, ISSN 0342-1791, E-ISSN 1432-2021, Vol. 45, p. 597-607Article in journal (Refereed)
  • 407.
    Weis, Franz
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Stalder, Roland
    University of Innsbruck.
    Skogby, Henrik
    Swedish Museum of Natural History, Department of Geology.
    Experimental hydration of natural volcanic clinopyroxene phenocrysts under hydrothermal pressures (0.5 – 3 kbar)2016In: American Mineralogist, ISSN 0003-004X, E-ISSN 1945-3027, Vol. 101, p. 2233-2247Article in journal (Refereed)
  • 408. Westhues, A.
    et al.
    Hanchar, J.M.
    LeMessurier, M.J.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Evidence for hydrothermal alteration and source regions for the Kiruna iron oxide apatite ore from zircon Hf and O isotopes.2017In: Geology, Vol. 45, p. 571-574Article in journal (Refereed)
    Abstract [en]

    Zircon grains from the Kiruna iron oxide–apatite (IOA) ore bodies in northern Sweden are distinct in their hafnium and oxygen isotopic ratios compared to zircon grains from adjacent metavolcanic host rocks and related intrusions. Here, we combine these two isotopic systems on previously dated zircon grains to improve our understanding of these ore deposits with a long-debated origin. Contrasting theories for the formation of the Kiruna iron ores suggest either (1) emplacement through immiscible silicate–iron oxide melts or (2) transportation and deposition of iron by hydrothermal fluids. Zircon from the metavolcanic host rocks and intrusions have oxygen isotopic ratios (δ18O ∼3‰) that lie below typical magmatic compositions, which is evidence that roof rocks altered by meteoric water were digested into the magma. In contrast, the ores show an influence of a fluid that is higher in δ18O (∼7‰). Based on these findings, we propose the involvement of episodic magmatic-hydrothermal fluids in the ore genesis of the Kiruna iron ore deposits: (1) the first episode related to a deep-seated magmatism and to regional-scale metasomatic alteration, and (2) a later fluid event related to shallow intrusions and responsible for the ore formation. Distinct differences in the Hf isotopic ratios for host rocks and intrusions (εHfi = −6 to −10, Archean crust) and ore (εHfi = −5 to +3, depleted mantle) further allow us to screen possible fluid sources for their involvement in the ore process.

  • 409. Westhues, A.
    et al.
    Hanchar, J.M.
    Voisey, C.R.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    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.2017In: Chemical Geology, ISSN 0009-2541, E-ISSN 1872-6836, Vol. 466, p. 303-322Article in journal (Refereed)
    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.

  • 410. Westhues, A.
    et al.
    Hanchar, J.M.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Martinsson, O.
    New Constraints on the Timing of Host-Rock Emplacement, Hydrothermal Alteration, and Iron Oxide-Apatite Mineralization in the Kiruna District, Norrbotten, Sweden.2016In: Economic geology and the bulletin of the Society of Economic Geologists, ISSN 0361-0128, E-ISSN 1554-0774, Vol. 111, p. 1595-1618Article in journal (Refereed)
    Abstract [en]

    High spatial resolution zircon U-Pb geochronological data obtained directly on the Kiirunavaara iron oxide-apatite (IOA) deposit, related orebodies, and host rocks provide new constraints on the timing of mineralization in these deposits. These data raise new arguments in the debate of a magmatic versus hydrothermal/metasomatic genesis of these major (2,500 Mt, 30–70 wt % Fe) Paleoproterozoic deposits. The main orebody at Kiirunavaara contains Ti-poor magnetite and minor (0.05–5 wt % P) apatite, located between a trachyandesite footwall and a rhyodacite hanging wall, which also hosts smaller orebodies (Nukutus, Rektorn, and Tuolluvaara). The pervasive Na and K metasomatism in the host rock is documented by whole-rock geochemical data and cathodoluminescence (CL) microscopy. Zircon U-Pb data for the metavolcanic rocks in the footwall and hanging wall cluster between 1884 ± 4 and 1880 ± 3 Ma. In the footwall, a syenite-aplite system yields ages of 1880 ± 7 and 1881 ± 4 Ma; a granite pluton exposed underground has an age of 1874 ± 4 Ma. Zircons in two ore samples, never directly dated before this study, yield ages of 1877 ± 4 and 1874 ± 7 Ma. Brecciation at the contacts between the ore and host rocks, the tight age at ca. 1880 Ma for most volcanic and plutonic rocks in the footwall and hanging wall, and the marginally younger age for ore at ca. 1877 to 74 Ma, matching the age of the spatially related granite pluton, suggest a magmatic-hydrothermal emplacement model for the Kiruna area IOA ores.

  • 411. White, Alistair
    et al.
    Burgess, Ray
    Charnley, Norman
    Selby, David
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Robb, Laurence
    Waters, David
    Constraints on the timing of late-Eburnean metamorphism, gold mineralisation and regional exhumation at Damang mine, Ghana2014In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 243, p. 18-38Article in journal (Refereed)
  • 412.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Fedo, C.M.
    Kamber, B.S.
    Does a Heavy Fe-Isotope Composition of Akilia Quartz-Amphibole-Pyroxene Rocks Necessitate a BIF Origin?2015In: Astrobiology, ISSN 1531-1074, E-ISSN 1557-8070, Vol. 15, p. 816-824Article in journal (Refereed)
    Abstract [en]

    The age and origin of the quartz-amphibole-pyroxene (qap) gneiss from the island of Akilia, southern West Greenland, has been the subject of intense debate since the light C-isotope composition of graphite inclusions in apatite was interpreted to indicate the presence of Earth’s earliest biological activity.  Although this claim for biogenic relicts has been vigourously challenged, the possibility that the rocks might represent some of the Earth’s earliest water lain sediments and, hence, a suitable repository for life, remains an open question. While some workers have suggested that the entire sequence represents an originally mafic-ultramafic igneous precursor subsequently modified by metasomatism, quartz injection, high-grade metamorphism and extreme ductile deformation, others maintain that at least a small part of the sequence retains geochemical characteristics indicative of a chemical sedimentary origin. Fractionated Fe isotopes with d56Fe values similar to those observed in Isua BIF reported from high-SiO2 units of qap have been used to support a chemical sedimentary protolith for the qap unit. Here we present new Fe isotope data from all lithological variants in the quartz-amphibole-pyroxene gneiss on Akilia, including layers of undisputed ultramafic igneous origin. Since the latter require introdution of fractionated Fe into at least part of the qap unit, we argue that Fe isotopes must therefore be treated with considerable caution when used to infer BIF for part or all of the qap protolith.

  • 413.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Wirth, R. (Contributor)
    Ravindra Kumar, G.R. (Contributor)
    Metallic Pb nanospheres in ultra-high temperature metamorphosed zircon from southern India2017In: Mineralogy and Petrology, ISSN 0930-0708, E-ISSN 1438-1168, Vol. 111, p. 467-474Article in journal (Refereed)
    Abstract [en]

    A transmission electron microscope (TEM) study of Paleoproterozoic zircon that has experienced ultra-high temperature (UHT) metamorphism at ca. 570 Ma in the Kerala Khondalite Belt (KKB), southern India, documents the occurrence of metallic Pb nanospheres. These results permit comparison with a previous report from UHT zircon in Enderby Land, Antarctica, and allow further constraints to be placed on possible mechanisms for nanosphere formation. As in Enderby Land, the nanospheres in the KKB occur in non-metamict zircon, emphasising that radiogenic Pb redistribution can occur with only partial interconnectivity of radiation damaged zircon. In contrast, the nanospheres reported here are not closely associated with Si-rich glass inclusions, which is inconsistent with a silicate liquid-metal immiscibility model proposed in the earlier study. Formation of these Pb nanospheres effectively halts Pb-loss from zircon, even under extreme conditions, and can adversely affect geochronological interpretations due to decoupling of Pb from U.

  • 414.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Pidgeon, R.T. (Contributor)
    What can Hadean detrital zircon really tell us? A critical evaluation of their geochronology with implications for the interpretation of oxygen and hafnium isotopes2017In: Gondwana Research, ISSN 1342-937X, E-ISSN 1878-0571, Vol. 51, p. 78-91Article in journal (Refereed)
    Abstract [en]

    Rare Hadean zircon grains represent the only direct sample of the Earth older than 4.0 Ga. As such, they have tremendous potential to illuminate our knowledge of this period of Earth's history for which there is no extant rock record. In this study we revisit the existing dataset, supplemented by new analyses, to identify those grains from which a robust age may be inferred. This rigorous filtering approach identifies four distinct zircon growth events in the Hadean between ca. 4.4 Ga and 4.0 Ga, and allows a reassessment of conclusions made from the determination of the O- and Hf-isotope systematics in these grains. Notably, we find no firm evidence for involvement of supracrustal reservoirs in zircon genesis prior to 4.15 Ga and, while our filtered Hf-isotope data support interpretations for a mafic protocrust, there are insufficient analyses to constrain its evolution accurately. Clearly, further work is required and needs to be conducted in a systematic manner that first seeks to establish both the age and homogeneity of any given grain before proceeding to other types of analysis.

  • 415.
    Whitehouse, Martin J.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Nemchin, A. A.
    Pidgeon, R. T.
    What can Hadean detrital zircon really tell us?: A critical evaluation of their geochronology with implications for the interpretation of oxygen and hafnium isotopes2017In: Gondwana Research, ISSN 1342-937X, E-ISSN 1878-0571, Vol. 51, no Supplement C, p. 78-91Article in journal (Refereed)
    Abstract [en]

    Abstract Rare Hadean zircon grains represent the only direct sample of the Earth older than 4.0Ga. As such, they have tremendous potential to illuminate our knowledge of this period of Earth's history for which there is no extant rock record. In this study we revisit the existing dataset, supplemented by new analyses, to identify those grains from which a robust age may be inferred. This rigorous filtering approach identifies four distinct zircon growth events in the Hadean between ca. 4.4Ga and 4.0Ga, and allows a reassessment of conclusions made from the determination of the O- and Hf-isotope systematics in these grains. Notably, we find no firm evidence for involvement of supracrustal reservoirs in zircon genesis prior to 4.15Ga and, while our filtered Hf-isotope data support interpretations for a mafic protocrust, there are insufficient analyses to constrain its evolution accurately. Clearly, further work is required and needs to be conducted in a systematic manner that first seeks to establish both the age and homogeneity of any given grain before proceeding to other types of analysis.

  • 416.
    Whitehouse, Martin J.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Pease, Victoria
    Stockholm University.
    Al Khirbash, Salah
    Neoproterozoic crustal growth at the margin of the East Gondwana continent - age and isotopic constraints from the easternmost inliers of Oman2016In: International Geology Review, ISSN 0020-6814, E-ISSN 1938-2839, Vol. 58, no 16, p. 2046-2064Article in journal (Refereed)
    Abstract [en]

    The Jebel Ja’alan and Qalhat inliers of Oman represent the easternmost exposures in theArabian peninsula of Neoproterozoic basement associated with the East African orogen and the assembly of East and West Gondwana. These inliers expose tonalitic gneisses and metasediments intruded by granodiorites and granites of the Ja’alan batholith. Zircon from the gneisses yield U-Pb SIMS ages of ca. 900-880 Ma, which are interpreted as crystallisation ages. These represent the oldest magmatic events associated with the closure of theMozambique Ocean reported to date. Zircon of this age is also the dominant component in the metasediments. The Ja’alan batholith yields ages of ca. 840-825 Ma. Nd isotopes indicate that both the gneisses and the batholith range from juvenile to slightly more evolved, with εNd(t) of +6 to +1.5 interpreted to reflect variable contamination by older, evolved continental material;this is also indicated by >900 Ma detrital zircon from the metasediments. The Nd data also contrast with the uniformly juvenile signature of younger, ca. 840 Ma, rocks of the Marbat region of southern Oman that lie structurally to the west. The Ja’alan and Qalhat inliers thus document eastward increasing age and continental influence, consistent with progressive development of arc rocks onto the western margin of East Gondwana, although the location and nature of the eastern continental block remains elusive.

  • 417.
    Whitehouse, Martin
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Ravindra Kumar, G. R.
    Rimsa, Andrius
    Behaviour of radiogenic Pb in zircon during ultrahigh‑temperature metamorphism: an ion imaging and ion tomography case study from the Kerala Khondalite Belt,southern India2014In: Contributions to Mineralogy and Petrology, ISSN 0010-7999, E-ISSN 1432-0967, Vol. 168Article in journal (Refereed)
    Abstract [en]

    Zircon crystals from a locally charnockitizedPaleoproterozoic high-K metagranite from the KeralaKhondalite Belt (KKB) of southern India have been investigatedby high-spatial resolution secondary ion mass spectrometryanalysis of U–Th–Pb and rare earth elements(REE), together with scanning ion imaging and scanningion tomography (depth-profiled ion imaging). The spotanalyses constrain the magmatic crystallization age of themetagranite to ca. 1,850 Ma, with ultrahigh-temperature(UHT) metamorphism occurring at ca. 570 Ma and superimposedcharnockite formation at ca. 520–510 Ma, whilethe ion imaging reveals a patchy distribution of radiogenicPb throughout the zircon cores. Middle- to heavy-REEdepletion in ca. 570 Ma zircon rims suggests that thesegrew in equilibrium with garnet and therefore date theUHT metamorphism in the KKB. The maximum apparent207Pb/206Pb age obtained from the unsupported radiogenicPb concentrations is also consistent with formationof the Pb patches during this event. The superimposed charnockitization event appears to have caused additionalPb-loss in the cores and recrystallization of the rims. Theresults of depth-profiling of the scanning ion tomographyimage stack show that the Pb-rich domains range in sizefrom <5 nm to several 10 nm (diameter if assumed to bespherical). The occurrence of such patchy Pb has previouslybeen documented only from UHT metamorphiczircon, where it likely results from annealing of radiation-damaged zircon. The formation of a discrete, heterogeneouslydistributed and subsequently immobile Pb phaseeffectively arrests the normal Pb-loss process seen at lowergrades of metamorphism.

  • 418.
    Williams, Peter A.
    et al.
    University of Western Sydney, Australia.
    Hatert, Frédéric
    Université de Liège, Belgium.
    Pasero, Marco
    Università di Pisa, Italy.
    Mills, Stuart J.
    Museum Victoria, Melbourne, Austalia.
    Hålenius, Ulf
    Swedish Museum of Natural History, Department of Geology.
    Hawthorne, Frank C.
    University of Manitoba, Winnipeg, Canada.
    Oberti, Roberta
    CNR-Instituto di Geoscienze e Georisorse, Pavia, Italy.
    Clinoferrogedrite in the contact-metamorphosed Biwabik Iron Formation, northeastern Minnesota: Discussion2014In: Canadian Mineralogist, ISSN 0008-4476, E-ISSN 1499-1276, Vol. 52, no 5, p. 917-920Article in journal (Refereed)
  • 419.
    Winton, V.H.L.
    et al.
    Curtin University, Perth.
    Dunbar, G.B.
    Antarctic Research Centre, Wellington.
    Atkins, C.B.
    Victoria University, Wellington.
    Bertler, N.A.N.
    Antarctic Research Centre, Wellington.
    Delmonte, Barbara
    University of Milano-Bicocca, Milano.
    Andersson, Per
    Swedish Museum of Natural History, Department of Geology.
    Bowie, A
    University of Tasmania, Hobart.
    Edwards, R.
    Curtin University, Perth.
    The origin of lithogenic sediment in the south-western Ross Sea and implications for iron fertilization2016In: Antarctic Science, ISSN 0954-1020, E-ISSN 1365-2079, Vol. 28, no 4, p. 250-260Article in journal (Refereed)
    Abstract [en]

    Summer iron (Fe) fertilization in the Ross Sea has previously been observed in association with diatom productivity, lithogenic particles and excess Fe in the water column. This productivity event occurred during an early breakout of sea ice via katabatic winds, suggesting that aeolian dust could be an important source of lithogenic Fe required for diatom growth in the Ross Sea. Here we investigate the provenance of size-selected dust deposited on sea ice in McMurdo Sound, south-western (SW) Ross Sea. The isotopic signature of McMurdo Sound dust (0.70533< 87Sr/86Sr< 0.70915 and -1.1 < εNd(0) <3.45)confirms that dust is locally sourced from the McMurdo Sound debris bands and comprises a two-component mixture of McMurdo Volcanic Group and southern Victoria Land lithologies. In addition, the provenance of lithogenic sediment trapped in the water column was investigated, and the isotopic signature (εNd(0) =3.9, 87Sr/86Sr = 0.70434) is differentiated from long-range transported dust originating from South America and Australia. Elevated lithogenic accumulation rates in deeper sediment traps in the Ross Sea suggest that sinking articles in the water column cannot simply result from dust input at the surface. This discrepancy can be best explained by significant upwelling and remobilization of lithogenic Fe from the sea floor.

  • 420.
    Winton, V.H.L.
    et al.
    Swedish Museum of Natural History, Department of Geology. Curtin University Perth Australia.
    Dunbar, G.B.
    University of Wellington, New Zealand.
    Bertler, N.A.N.
    University of Wellington, New Zealand.
    Millet, M.-A
    University of Wellington, New Zealand.
    Delmonte, B
    University of Milano-Bicocca, Milano Italy.
    Atkins, C.B.
    Durham University, Durham UK.
    Chewings, J.M.
    University of Wellington, New Zealand.
    Andersson, Per
    Swedish Museum of Natural History, Department of Geology.
    The contribution of aeolian sand and dust to iron fertilization of phytoplankton blooms in southwestern Ross Sea, Antarctica2014In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224Article in journal (Refereed)
  • 421.
    Winton, V.H.L.
    et al.
    Curtin University.
    Edwards, R
    Curtin University.
    Delmonte, B
    University of Milano-Bicocca.
    Ellis, A
    Curtin University.
    Andersson, Per
    Swedish Museum of Natural History, Department of Geology.
    Bowie, A
    University of Tasmania.
    Bertler, N.A.N.
    University of Wellington.
    Neff, P.
    University of Rochester.
    Tuohy, A
    University of Wellington.
    Multiple sources of soluble atmospheric iron to Antarctic waters2016In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224, Vol. 30, no 3, p. 421-437Article in journal (Refereed)
    Abstract [en]

    The Ross Sea, Antarctica, is a highly productive region of the Southern Ocean. Significant new sources of iron (Fe) are required to sustain phytoplankton blooms in the austral summer. Atmospheric deposition is one potential source. The fractional solubility of Fe is an important variable determining Fe availability for biological uptake. To constrain aerosol Fe inputs to the Ross Sea region, fractional solubility of Fe was analyzed in a snow pit from Roosevelt Island, eastern Ross Sea. In addition, aluminum, dust, and refractory black carbon (rBC) concentrations were analyzed, to determine the contribution of mineral dust and combustion sources to the supply of aerosol Fe. We estimate exceptionally high dissolved Fe (dFe) flux of 1.2 × 10−6 g m−2 y−1 and total dissolvable Fe flux of 140 × 10−6 g m−2 y−1 for 2011/2012. Deposition of dust, Fe, Al, and rBC occurs primarily during spring-summer. The observed background fractional Fe solubility of ~0.7% is consistent with a mineral dust source. Radiogenic isotopic ratios and particle size distribution of dust indicates that the site is influenced by local and remote sources. In 2011/2012 summer, relatively high dFe concentrations paralleled both mineral dust and rBC deposition. Around half of the annual aerosol Fe deposition occurred in the austral summer phytoplankton growth season; however, the fractional Fe solubility was low. Our results suggest that the seasonality of dFe deposition can vary and should be considered on longer glacial-interglacial timescales.

  • 422.
    Winton, V.H.L.
    et al.
    Curtin University Perth Australia.
    Edwards, R.
    Curtin University Perth Australia.
    Delmonte, B.
    University of Milano-Bicocca, Milan, Italy.
    Ellis, A
    Curtin University, Perth, Australia.
    Andersson, Per
    Swedish Museum of Natural History, Department of Geology.
    Bowie, A
    University of Tasmania, Hobart, Australia.
    Bertler, N.A.N.
    University of Wellington, Wellington, New Zealand.
    Neff, P.
    University of Rochester, Rochester, New York.
    Tuohy, A.
    University of Wellington, Wellington, New Zealand.
    Multiple sources of soluble atmospheric iron to Antarctic waters2016In: Global Biogeochemical Cycles, ISSN 0886-6236, E-ISSN 1944-9224Article in journal (Refereed)
  • 423. Woodard, J.
    et al.
    Tuisku, P.
    Kärki, A.
    Lahaye, Y.
    Majka, J.
    Huhma, H.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Zircon and monazite geochronology of deformation in the Pielavesi Shear Zone, Finland: multistage evolution of the Archaean–Proterozoic boundary in the Fenoscandian Shield.2017In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 174, p. 255-267Article in journal (Refereed)
    Abstract [en]

    The Raahe–Ladoga Shear Complex is a major crustal structure representing the Archaean–Palaeoproterozoic boundary in the Fennoscandian Shield. The complex developed during the Svecofennian Orogeny (c. 1.9 – 1.8 Ga) beginning with regional thrust tectonic phases D1 and D2, followed by large-scale shearing events D3 and D4. The Pielavesi Shear Zone is a vertical north–south-trending shear zone within the Raahe–Ladoga Shear Complex formed during regional D3 shearing and later reactivated during the regional D4 phase. Three north–south-trending elongate granitoid intrusions were selected as representative of silicic melts that intruded the transtensional Pielavesi Shear Zone during the regional D3 phase. The oriented magmatic fabric of the granitoids indicates that they intruded coeval to the deformation event. The zircon U–(Th)–Pb secondary ionization mass spectrometry (SIMS) ages of these intrusions (1888 ± 4, 1884 ± 6 and 1883 ± 5 Ma) overlap within error and provide a direct age for the regional D3 deformation. εHf(T)(−1.1 to +3.4) and εNd(T) (−1.2 to +0.4) values from these granitoids are both consistent with a predominantly juvenile source affected by a minor Archaean component. U–(Th)–Pb SIMS analyses of metamorphic monazite formed within a crosscutting blastomylonite provide an age for the regional D4phase and associated fluid activity of 1793 ± 3 Ma.

  • 424.
    Wortberg, Katharina
    et al.
    Luleå Technical University.
    Conrad, Sarah
    Luleå Technical University.
    Andersson, Per
    Swedish Museum of Natural History, Department of Geology.
    Ingri, Johan
    Luleå Technical University.
    Strontium Isotopes - A Tracer for River Suspended Iron Aggregates2017In: Applied Geochemistry, ISSN 0883-2927, E-ISSN 1872-9134, Vol. 95, p. 85-90Article in journal (Refereed)
    Abstract [en]

    The Kalix River shows distinct temporal variations in the Sr-isotope ratio in filtered water (0.726 to 0.732). During base flow in winter the 87Sr/86Sr ratio is on average 0.730. When discharge increases and peaks during spring flood the 87Sr/86Sr ratio shows the most radiogenic (0.732) values. The temporal variations in the 87Sr/86Sr ratio in the Kalix River can be explained by mixing of water from the woodlands and the mountain areas.

    During high water discharge in May the 87Sr/86Sr ratios are more radiogenic in the suspended phase (1 kDa - 70 µm) compared to the truly dissolved phase (<1 kDa). The difference in 87Sr/86Sr ratio between the two phases (Δ 87Sr/86Sr) is linearly correlated with the suspended iron concentration. During spring flood Sr and Fe derived from an additional source, reach the river. Deep groundwater has a more radiogenic 87Sr/86Sr isotope ratio than the Kalix River during spring flood and thus, represents a possible source for the suspended Fe and the associated Sr. Strontium can be coprecipitated with and adsorbed to different types of Fe aggregates. We propose that the Sr-isotope ratio in the suspended phase reflects the isotopic composition of the water at the interface between anoxic groundwater and oxic stream water in the riparian zone, where the Fe aggregates are formed. These particles dominate the suspended phase in the river and the mixing with mountain waters, poor in Fe, produces the difference in the isotopic signature. The different signatures in suspended and truly dissolved fraction indicate that these aggregates are relatively stable during stream-river transport. As such the 87Sr/86Sr can be used to trace the origin of the non-detrital suspended phase.

  • 425. Yashanew, F.G.
    et al.
    Pease, V.
    Abdelsalam, M.G.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Zircon U–Pb ages, δ18O and whole-rock Nd isotopic compositions of the Dire Dawa Precambrian basement, eastern Ethiopia: implications for the assembly of Gondwana2016In: Journal of the Geological Society, ISSN 0016-7649, E-ISSN 2041-479X, Vol. 172, p. 142-156Article in journal (Refereed)
    Abstract [en]

    New high spatial resolution secondary ion mass spectrometry (SIMS) zircon dating from the Dire Dawa Precambrian basement yields crystallization ages at c. 790 Ma and 600 – 560 Ma. Two of the youngest samples are pervasively deformed, indicating that orogenesis continued until c. 560 Ma. SIMS δ18Ozrn shows bimodality, with the oldest sample (c. 790 Ma) and inherited zircons of that age in the younger samples having values of 7.8 – 9.6‰, whereas the Ediacaran samples have δ18Ozrn values of 4.9 – 7.2‰. These δ18Ozrn ratios are higher than mantle values and indicate a supracrustal input to the source of the Dire Dawa granitoids. All samples have unradiogenic εNd(t) values of −10.3 to −5.8 and Nd model ages of 1.72 – 1.42 Ga. These attributes suggest that the Dire Dawa granitoids were mostly derived from reworking of long-lived crustal sources. The occurrence of c. 580 – 550 Ma orogenesis in both the Dire Dawa basement and the juvenile Western Ethiopian Shield and the confinement of c. 630 Ma metamorphism to only the latter indicate that these two lithospheric blocks of contrasting isotopic compositions amalgamated at c. 580 – 550 Ma. This suggests that the Mozambique Ocean, which separated these two lithospheric blocks, was completely consumed during the late Ediacaran to early Cambrian.

  • 426.
    Yeshanew, Fitsum G.
    et al.
    Swedish Museum of Natural History, Department of Geology.
    Pease, V.
    Whitehouse, Martin J.
    Swedish Museum of Natural History, Department of Geology.
    Al-Khirbash, S.
    Zircon U–Pb geochronology and Nd isotope systematics of the Abas terrane, Yemen: Implications for Neoproterozoic crust reworking events.2015In: Precambrian Research, ISSN 0301-9268, E-ISSN 1872-7433, Vol. 267, p. 106-120Article in journal (Refereed)
    Abstract [en]

    High-spatial-resolution secondary-ion mass spectrometry (SIMS) U–Pb zircon ages, whole-rock Nd isotopic and geochemical data are reported for granites and granitic gneisses from a traverse across the Abas terrane, Yemen, a part of the Precambrian basement of southern Arabian Peninsula. SIMS U–Pb dating identifies two magmatic episodes, the first at c. 790–725 Ma represented by granitic gneisses, the second clearly post-tectonic at c. 625–590 Ma. The oldest sample in the post-tectonic group is slightly deformed while younger samples are undeformed indicating that penetrative deformation ceased at c. 625 Ma in the Abas region. Whole-rock Nd(t) values between −11 and +0.8, Nd model ages of 1.70–1.13 Ga indicate a significant contribution of evolved continental material in the genesis of the Abas granitoids, unlike most of the juvenile Arabian-Nubian Shield (ANS), although there are few inherited zircons. Secular variation in ɛNd(t) reflects a change in magma source with increasing juvenile magma and diminishing crustal input during post-tectonic (625–590 Ma) magmatism. The combination of subduction zone chemistry, absence of older rocks, paucity of inherited zircons, evolved Nd isotopic signatures and the I-type characteristics of the samples suggest that assimilation occurred at depth.

  • 427.
    Zack, Thomas
    et al.
    Göteborgs Universitet.
    Kooijman, Ellen
    Swedish Museum of Natural History, Department of Geology.
    Petrology and geochronology of rutile2017In: Petrochronology: Methods and Applications / [ed] Matthew J. Kohn, Martin Engi, Pierre Lanari, Chantilly, USA: Mineralogical Society of America, 2017, p. 443-467Chapter in book (Refereed)
    Abstract [en]

    Rutile (TiO2) is an important accessory mineral that, when present, offers a rich source of information about the rock units in which it is incorporated. It occurs in a variety of specific microstructural settings, contains significant amounts of several trace elements and is one of the classical minerals used for U–Pb age determination. Here, we focus on information obtainable from rutile in its original textural context. We do not present an exhaustive review on detrital rutile in clastic sediments, but note that an understanding of the petrochronology of rutile in its source rocks will aid interpretation of data obtained from detrital rutile. For further information on the important role of rutile in provenance studies, the reader is referred to previous reviews (e.g., Zack et al. 2004b; Meinhold 2010; Triebold et al. 2012). Coarse rutile is the only stable TiO2 polymorph under all crustal and upper mantle conditions, with the exception of certain hydrothermal environments (Smith et al. 2009). As such, we will focus on rutile rather than the polymorphs brookite, anatase and ultrahigh-pressure modifications.

    In this chapter, we first review rutile occurrences, trace element geochemistry, and U–Pb geochronology individually to illustrate the insights that can be gained from microstructures, chemistry and ages. Then, in the spirit of petrochronology, we show the interpretational power of combining these approaches, using the Ivrea Zone (Italy) as a case study. Finally, we suggest some areas of future research that would improve petrochronologic research using rutile.

  • 428. Zsolt, Benko
    et al.
    Molnar, F.
    Lespinasse, M.
    Billström, Kjell
    Swedish Museum of Natural History, Department of Geology.
    Pecskay, Z.
    Nemeth, T.
    Triassic fluid mobilization and epigenetic lead-zinc sulphide mineralization in the Transdanubian shear zone (Pannonian basin, Hungary)2014In: Geologica Carpathica, ISSN 1335-0552, E-ISSN 1336-8052, Vol. 65, p. 177-194Article in journal (Refereed)
    Abstract [en]

    A combined fluid inclusion, fluid inclusion plane, lead isotope and K/Ar radiometric age dating work has been carried out on two lead-zinc mineralizations situated along the Periadriatic-Balaton Lineament in the central part of the Pannonian Basin, in order to reveal their age and genetics as well as temporal-spatial relationships to other lead-zinc fluorite mineralization in the Alp-Carpathian region. According to fluid inclusion studies, the formation of the quartz fluorite-galena-sphalerite veins in the Velence Mts is the result of mixing of low (0—12 NaCl equiv. wt. %) and high salinity (10—26 CaCl2 equiv. wt. %) brines. Well-crystallized (R3-type) illite associated with the mineralized hydrothermal veins indicates that the maximum temperature of the hydrothermal fluids could have been around 250 °C. K/Ar radiometric ages of illite, separated from the hydrothermal veins provided ages of 209—232 Ma, supporting the Mid- to Late-Triassic age of the hydrothermal fluid flow. Fluid inclusion plane studies have revealed that hydrothermal circulation was regional in the granite, but more intensive around the mineralized zones. Lead isotope signatures of hydrothermal veins in the Velence Mts (206Pb/204Pb = 18.278—18.363, 207Pb/204Pb = 15.622—15.690 and 208Pb/204Pb = 38.439—38.587) and in Szabadbattyán (206Pb/204Pb = 18.286—18.348, 207Pb/204Pb = 15.667—15.736 and 208Pb/204Pb = 38.552—38.781) form a tight cluster indicating similar, upper crustal source of the lead in the two mineralizations. The nature of mineralizing fluids, age of the fluid flow, as well as lead isotopic signatures of ore minerals point towards a genetic link between epigenetic carbonate-hosted stratiform-stratabound Alpine-type lead-zinc-fluorite deposits in the Southern and Eastern Alps and the studied deposits in the Velence Mts and at Szabadbattyán. In spite of the differences in host rocks and the depth of the ore precipitation, it is suggested that the studied deposits along the Periadriatic-Balaton Lineament in the Pannonian Basin and in the Alps belong to the same regional scale fluid flow system, which developed during the advanced stage of the opening of the Neo-Tethys Ocean. The common origin and ore formation process is more evident considering results of large-scale palinspastic reconstructions. These suggest, that the studied deposits in the central part of the Pannonian Basin were located in a zone between the Eastern and Southern Alps until the Early Paleogene and were emplaced to their current location due to northeastward escape of large crustal blocks from the Alpine collision zone.

  • 429.
    Škoda, Radek
    et al.
    Masaryk University.
    Plasil, Jakub
    Institute of Physics ASCR.
    Čopjaková, Renata
    Masaryk University.
    Novak, Milan
    Masaryk University.
    Jonsson, Erik
    Uppsala Universitet.
    Vasinova Galiova, Michaela
    Masaryk University.
    Holtstam, Dan
    Swedish Museum of Natural History, Department of Geology.
    Gadolinite-(Nd), a new member of the gadolinite supergroup from Fe-REE deposits of Bastnäs-type.2018In: Mineralogical magazine, ISSN 0026-461X, E-ISSN 1471-8022, Vol. 82(S1), p. S133-S145Article in journal (Refereed)
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