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  Subjects -> EARTH SCIENCES (Total: 675 journals)
    - EARTH SCIENCES (471 journals)
    - GEOLOGY (84 journals)
    - GEOPHYSICS (27 journals)
    - HYDROLOGY (24 journals)
    - OCEANOGRAPHY (69 journals)

EARTH SCIENCES (471 journals)                  1 2 3 | Last

Showing 1 - 200 of 371 Journals sorted alphabetically
Acta Geochimica     Hybrid Journal   (Followers: 6)
Acta Geodaetica et Geophysica     Hybrid Journal   (Followers: 2)
Acta Geodaetica et Geophysica Hungarica     Full-text available via subscription   (Followers: 2)
Acta Geophysica     Open Access   (Followers: 10)
Acta Geotechnica     Hybrid Journal   (Followers: 7)
Acta Meteorologica Sinica     Hybrid Journal   (Followers: 3)
Advances in High Energy Physics     Open Access   (Followers: 18)
Advances In Physics     Hybrid Journal   (Followers: 20)
Aeolian Research     Hybrid Journal   (Followers: 6)
African Journal of Aquatic Science     Hybrid Journal   (Followers: 13)
Algological Studies     Full-text available via subscription   (Followers: 1)
Alpine Botany     Hybrid Journal   (Followers: 5)
AMBIO     Hybrid Journal   (Followers: 11)
Anales del Instituto de la Patagonia     Open Access  
Andean geology     Open Access   (Followers: 9)
Annales Henri Poincaré     Hybrid Journal   (Followers: 3)
Annales UMCS, Geographia, Geologia, Mineralogia et Petrographia     Open Access  
Annals of Geophysics     Open Access   (Followers: 13)
Annals of GIS     Hybrid Journal   (Followers: 20)
Annual Review of Marine Science     Full-text available via subscription   (Followers: 10)
Anthropocene     Hybrid Journal   (Followers: 4)
Anthropocene Review     Hybrid Journal   (Followers: 6)
Applied Clay Science     Hybrid Journal   (Followers: 6)
Applied Geochemistry     Hybrid Journal   (Followers: 14)
Applied Geomatics     Hybrid Journal   (Followers: 3)
Applied Geophysics     Hybrid Journal   (Followers: 8)
Applied Ocean Research     Hybrid Journal   (Followers: 8)
Applied Petrochemical Research     Open Access   (Followers: 3)
Aquatic Conservation Marine and Freshwater Ecosystems     Hybrid Journal   (Followers: 36)
Arctic Science     Open Access   (Followers: 7)
Arctic, Antarctic, and Alpine Research     Full-text available via subscription   (Followers: 9)
Artificial Satellites : The Journal of Space Research Centre of Polish Academy of Sciences     Open Access   (Followers: 20)
Asia-Pacific Journal of Atmospheric Sciences     Hybrid Journal   (Followers: 19)
Asian Journal of Earth Sciences     Open Access   (Followers: 19)
Asian Review of Environmental and Earth Sciences     Open Access   (Followers: 2)
Atlantic Geology : Journal of the Atlantic Geoscience Society / Atlantic Geology : revue de la Société Géoscientifique de l'Atlantique     Full-text available via subscription   (Followers: 9)
Atmosphere-Ocean     Full-text available via subscription   (Followers: 12)
Atmospheric and Climate Sciences     Open Access   (Followers: 24)
Australian Journal of Earth Sciences: An International Geoscience Journal of the Geological Society of Australia     Hybrid Journal   (Followers: 10)
Boletim de Ciências Geodésicas     Open Access  
Bonorowo Wetlands     Open Access  
Boreas: An International Journal of Quaternary Research     Hybrid Journal   (Followers: 11)
Bragantia     Open Access   (Followers: 2)
Bulletin of Earthquake Engineering     Hybrid Journal   (Followers: 11)
Bulletin of Geosciences     Open Access   (Followers: 8)
Bulletin of the Lebedev Physics Institute     Hybrid Journal   (Followers: 1)
Bulletin of the Seismological Society of America     Full-text available via subscription   (Followers: 23)
Bulletin of Volcanology     Hybrid Journal   (Followers: 20)
Cadernos de Geociências     Open Access  
Canadian Mineralogist     Full-text available via subscription   (Followers: 6)
Canadian Water Resources Journal     Hybrid Journal   (Followers: 20)
Carbonates and Evaporites     Hybrid Journal   (Followers: 2)
CATENA     Hybrid Journal   (Followers: 8)
Chemical Geology     Hybrid Journal   (Followers: 25)
Chemie der Erde - Geochemistry     Hybrid Journal   (Followers: 5)
Chinese Geographical Science     Hybrid Journal   (Followers: 5)
Chinese Journal of Oceanology and Limnology     Hybrid Journal   (Followers: 4)
Ciencia del suelo     Open Access   (Followers: 2)
Ciencias Espaciales     Open Access  
Climate and Development     Hybrid Journal   (Followers: 12)
Coastal Management     Hybrid Journal   (Followers: 25)
Cogent Geoscience     Open Access  
Comptes Rendus Geoscience     Full-text available via subscription   (Followers: 9)
Computational Geosciences     Hybrid Journal   (Followers: 15)
Computational Mathematics and Mathematical Physics     Hybrid Journal   (Followers: 3)
Computers and Geotechnics     Hybrid Journal   (Followers: 11)
Contemporary Trends in Geoscience     Open Access   (Followers: 2)
Continental Shelf Research     Hybrid Journal   (Followers: 9)
Contributions to Mineralogy and Petrology     Hybrid Journal   (Followers: 12)
Contributions to Plasma Physics     Hybrid Journal   (Followers: 4)
Coral Reefs     Hybrid Journal   (Followers: 18)
Cretaceous Research     Hybrid Journal   (Followers: 11)
Cybergeo : European Journal of Geography     Open Access   (Followers: 5)
Depositional Record     Open Access   (Followers: 1)
Developments in Geotectonics     Full-text available via subscription   (Followers: 2)
Developments in Quaternary Science     Full-text available via subscription   (Followers: 4)
Développement durable et territoires     Open Access   (Followers: 2)
Diatom Research     Hybrid Journal   (Followers: 3)
Doklady Physics     Hybrid Journal   (Followers: 1)
Dynamics of Atmospheres and Oceans     Hybrid Journal   (Followers: 13)
E&S Engineering and Science     Open Access  
E3S Web of Conferences     Open Access   (Followers: 1)
Earth and Planetary Science Letters     Hybrid Journal   (Followers: 154)
Earth and Space Science     Open Access   (Followers: 14)
Earth Interactions     Full-text available via subscription   (Followers: 12)
Earth Science Frontiers     Full-text available via subscription   (Followers: 7)
Earth Science Research     Open Access   (Followers: 9)
Earth Surface Dynamics (ESurf)     Open Access   (Followers: 7)
Earth Surface Processes and Landforms     Hybrid Journal   (Followers: 20)
Earth System Dynamics     Open Access   (Followers: 7)
Earth System Dynamics Discussions     Open Access   (Followers: 4)
Earth's Future     Open Access   (Followers: 1)
Earth, Planets and Space     Open Access   (Followers: 67)
Earthquake Engineering and Engineering Vibration     Hybrid Journal   (Followers: 9)
Earthquake Science     Hybrid Journal   (Followers: 11)
Earthquake Spectra     Full-text available via subscription   (Followers: 21)
Ecohydrology     Hybrid Journal   (Followers: 9)
Ecological Questions     Open Access   (Followers: 3)
Electromagnetics     Hybrid Journal   (Followers: 8)
Energy Efficiency     Hybrid Journal   (Followers: 10)
Energy Exploration & Exploitation     Hybrid Journal   (Followers: 4)
Environmental Earth Sciences     Hybrid Journal   (Followers: 25)
Environmental Geology     Hybrid Journal   (Followers: 18)
Environmental Geosciences     Full-text available via subscription   (Followers: 5)
Environmental Geotechnics     Hybrid Journal   (Followers: 5)
Erwerbs-Obstbau     Hybrid Journal  
Estuaries and Coasts     Hybrid Journal   (Followers: 18)
Estuarine, Coastal and Shelf Science     Hybrid Journal   (Followers: 35)
Estudios Geográficos     Open Access  
European Journal of Mineralogy     Full-text available via subscription   (Followers: 15)
European Journal of Remote Sensing     Open Access   (Followers: 5)
Exploration Geophysics     Hybrid Journal   (Followers: 3)
Facies     Hybrid Journal   (Followers: 10)
Fieldiana Life and Earth Sciences     Full-text available via subscription   (Followers: 1)
Física de la Tierra     Open Access  
Folia Musei rerum naturalium Bohemiae occidentalis. Geologica et Paleobiologica     Open Access  
Folia Quaternaria     Open Access  
Forestry Chronicle     Full-text available via subscription   (Followers: 9)
Frontiers in Earth Science     Open Access   (Followers: 5)
Frontiers in Geotechnical Engineering     Open Access   (Followers: 3)
Frontiers of Earth Science     Hybrid Journal   (Followers: 8)
Fundamental and Applied Limnology / Archiv für Hydrobiologie     Full-text available via subscription   (Followers: 4)
GEM - International Journal on Geomathematics     Hybrid Journal   (Followers: 1)
Geo-Marine Letters     Hybrid Journal   (Followers: 6)
Geoacta     Open Access   (Followers: 2)
Geobiology     Hybrid Journal   (Followers: 8)
Geocarto International     Hybrid Journal   (Followers: 22)
Geochemistry : Exploration, Environment, Analysis     Hybrid Journal   (Followers: 7)
Geochemistry, Geophysics, Geosystems     Full-text available via subscription   (Followers: 30)
Geochimica et Cosmochimica Acta     Hybrid Journal   (Followers: 53)
Geochronometria     Hybrid Journal   (Followers: 2)
Geoderma Regional : The International Journal for Regional Soil Research     Full-text available via subscription   (Followers: 4)
Geodinamica Acta     Open Access   (Followers: 2)
Geodynamics & Tectonophysics     Open Access   (Followers: 2)
Geoenvironmental Disasters     Open Access   (Followers: 3)
Geofluids     Open Access   (Followers: 4)
Geoforum     Hybrid Journal   (Followers: 25)
Géographie physique et Quaternaire     Full-text available via subscription   (Followers: 1)
Geography and Natural Resources     Hybrid Journal   (Followers: 7)
GeoHealth     Open Access  
Geoheritage     Hybrid Journal   (Followers: 1)
Geoinformatica Polonica : The Journal of Polish Academy of Arts and Sciences     Open Access  
Geoinformatics & Geostatistics     Hybrid Journal   (Followers: 11)
Geological Journal     Hybrid Journal   (Followers: 17)
Geological Magazine     Hybrid Journal   (Followers: 16)
Geology Today     Hybrid Journal   (Followers: 29)
Geology, Geophysics and Environment     Open Access   (Followers: 2)
Geomagnetism and Aeronomy     Hybrid Journal   (Followers: 3)
Geomatics, Natural Hazards and Risk     Hybrid Journal   (Followers: 10)
Geomechanics for Energy and the Environment     Full-text available via subscription   (Followers: 1)
GEOmedia     Open Access   (Followers: 1)
Geomorphology     Hybrid Journal   (Followers: 30)
Geophysical & Astrophysical Fluid Dynamics     Hybrid Journal   (Followers: 2)
Geophysical Journal International     Hybrid Journal   (Followers: 35)
Geophysical Prospecting     Hybrid Journal   (Followers: 8)
Geophysics     Full-text available via subscription   (Followers: 21)
GeoResJ     Hybrid Journal  
Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards     Hybrid Journal   (Followers: 9)
Geoscience Canada : Journal of the Geological Association of Canada / Geoscience Canada : journal de l'Association Géologique du Canada     Full-text available via subscription   (Followers: 6)
Geoscience Data Journal     Open Access   (Followers: 2)
Geoscience Frontiers     Open Access   (Followers: 9)
Geoscience Letters     Open Access  
Geoscience Records     Open Access  
Geosciences     Open Access   (Followers: 1)
Geosciences Journal     Hybrid Journal   (Followers: 9)
Geoscientific Instrumentation, Methods and Data Systems     Open Access   (Followers: 4)
Geoscientific Model Development     Open Access   (Followers: 2)
Geostandards and Geoanalytical Research     Hybrid Journal   (Followers: 2)
Geosystem Engineering     Hybrid Journal   (Followers: 1)
Geotectonic Research     Full-text available via subscription   (Followers: 4)
Geotectonics     Hybrid Journal   (Followers: 7)
GISAP : Earth and Space Sciences     Open Access   (Followers: 1)
Glass Physics and Chemistry     Hybrid Journal   (Followers: 4)
Global and Planetary Change     Hybrid Journal   (Followers: 16)
Global Biogeochemical Cycles     Full-text available via subscription   (Followers: 18)
Gondwana Research     Hybrid Journal   (Followers: 11)
GPS Solutions     Hybrid Journal   (Followers: 24)
Grassland Science     Hybrid Journal  
Ground Water     Hybrid Journal   (Followers: 36)
Ground Water Monitoring & Remediation     Hybrid Journal   (Followers: 18)
Groundwater for Sustainable Development     Full-text available via subscription   (Followers: 3)
Helgoland Marine Research     Open Access   (Followers: 3)
History of Geo- and Space Sciences     Open Access   (Followers: 1)
Hydrobiologia     Hybrid Journal   (Followers: 18)
Hydrogeology Journal     Hybrid Journal   (Followers: 20)
Hydrological Processes     Hybrid Journal   (Followers: 30)
Hydrology and Earth System Sciences     Open Access   (Followers: 29)
ICES Journal of Marine Science: Journal du Conseil     Hybrid Journal   (Followers: 52)
IEEE Journal of Oceanic Engineering     Hybrid Journal   (Followers: 11)
Indian Geotechnical Journal     Hybrid Journal   (Followers: 4)
Indonesian Journal on Geoscience     Open Access   (Followers: 2)
Interdisciplinary Environmental Review     Hybrid Journal   (Followers: 3)
International Geology Review     Hybrid Journal   (Followers: 14)
International Journal of Advanced Geosciences     Open Access   (Followers: 2)
International Journal of Advanced Remote Sensing and GIS     Open Access   (Followers: 39)
International Journal of Advancement in Earth and Enviromental Sciences     Open Access   (Followers: 5)
International Journal of Advancement in Remote Sensing, GIS, and Geography     Open Access   (Followers: 31)
International Journal of Applied Earth Observation and Geoinformation     Hybrid Journal   (Followers: 34)
International Journal of Coal Geology     Hybrid Journal   (Followers: 3)
International Journal of Disaster Risk Reduction     Hybrid Journal   (Followers: 18)

        1 2 3 | Last

Journal Cover Chemical Geology
  [SJR: 2.346]   [H-I: 145]   [25 followers]  Follow
    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 0009-2541
   Published by Elsevier Homepage  [3175 journals]
  • Structural controls of CO2 on Y, La and Sr incorporation in sodium-rich
           silicate - carbonate melts by in-situ high P-T EXAFS
    • Authors: J. Pohlenz; A.D. Rosa; O. Mathon; S. Pascarelli; S. Belin; G. Landrot; V. Murzin; A. Veligzhanin; A. Shiryaev; T. Irifune; M. Wilke
      Pages: 1 - 15
      Abstract: Publication date: 15 May 2018
      Source:Chemical Geology, Volume 486
      Author(s): J. Pohlenz, A.D. Rosa, O. Mathon, S. Pascarelli, S. Belin, G. Landrot, V. Murzin, A. Veligzhanin, A. Shiryaev, T. Irifune, M. Wilke
      Carbonate-rich silicate and carbonate melts play a crucial role in deep Earth magmatic processes and their melt structure is a key parameter, as it controls physical and transport properties. Carbon-rich melts can be strongly enriched in trace elements, but the structural incorporation mechanisms of these elements are difficult to study because such melts generally cannot be quenched to glasses. In this contribution we investigate the influence of CO2 on the local environments of trace elements contained in silicate glasses with variable CO2 concentrations and in silicate and carbonate melts. The melts were studied in-situ at high pressure and temperature conditions using the Paris-Edinburgh press (2.2 to 2.6GPa and 1200 to 1500°C). The compositions studied include sodium-rich peralkaline silicate melts and glasses and carbonate melts similar to those occurring naturally at Oldoinyo Lengai volcano. The local environments of yttrium (Y), lanthanum (La) and strontium (Sr) were investigated using extended X-ray absorption fine structure (EXAFS) spectroscopy. Main findings of the study suggest: (1) In peralkaline silicate glasses the local structure of Y is unaffected by the CO2 content. Contrary, a slight increase of oxygen bond lengths of Sr and La is inferred with increasing CO2 content in peralkaline glasses, while they remain constant in glasses of even higher peralkalinity independent of the CO2 content. (2) In silicate melts of different CO2 contents Y-O bond lengths are constant, while a slight increase within carbonate melt compositions is deduced. On the other hand, a steady bond lengths increase over the whole compositional range is inferred for La-O and Sr-O. This may well be explained by distinct preferences of these elements for specific local environments. Based on these new data, we suggest potential mechanisms for the structural incorporation of these elements, a key step towards understanding their partitioning behavior in natural magmatic systems.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2017.12.023
      Issue No: Vol. 486 (2018)
       
  • Variation in sub-arc mantle oxygen fugacity during partial melting
           recorded in refractory peridotite xenoliths from the West Bismarck Arc
    • Authors: Antoine Bénard; Alan B. Woodland; Richard J. Arculus; Oliver Nebel; Sarlae R.B. McAlpine
      Pages: 16 - 30
      Abstract: Publication date: 15 May 2018
      Source:Chemical Geology, Volume 486
      Author(s): Antoine Bénard, Alan B. Woodland, Richard J. Arculus, Oliver Nebel, Sarlae R.B. McAlpine
      It is debatable whether oxygen fugacity (fO2), the usual measure of the oxidation state of a system, can vary during partial melting in the Earth's mantle or not. Notably, samples of mantle peridotite recovered from lavas and pyroclastic deposits in island arcs are mostly more oxidized than those from other tectonic settings. However, the petrological history of sub-arc mantle peridotites, in particular the respective extents to which partial melting and post-melting metasomatism have controlled their fO2 record, are elusive. It has remained unclear whether the oxidized peridotites have preserved the oxidation state of a melt-depleted, residual mantle wedge or not. Here we report Mössbauer spectroscopy and EPMA measurements of Fe valence states in spinel (Fe3+/∑Fespinel where ∑Fe refers to Fe3++Fe2+) in a suite of markedly unaltered, sub-arc mantle-derived, harzburgite and dunite xenoliths from the active Ritter volcano (West Bismarck Arc, Papua New Guinea). These rocks, together with similar suites from the Kamchatka and Izu-Bonin arcs, have recently been interpreted to be residues of partial melting in the mantle wedge. The Fe3+/∑Fespinel decreases from 0.27 ± 0.04 to 0.11 ± 0.01 with increasing degrees of melt depletion in the West Bismarck sample suite, as monitored by decreasing Al2O3 (from 0.72 to 0.29 wt%) and modal percentage of orthopyroxene (from ~28 to ~7 wt%) in bulk rocks. Importantly, Fe3+/∑Fespinel in the most melt-depleted, orthopyroxene-poor residual samples are significantly lower (down to 0.11 ± 0.01) than those in melt-percolated harzburgite (0.29 ± 0.04) and dunite melt channel-cumulates (0.20 ± 0.01) found at the same sampling sites. The calculated fO2 in West Bismarck residual samples decreases from +1.7 ± 0.2 to −0.5 ± 0.2 log units relative to the synthetic fayalite-magnetite-quartz redox buffer (∆logfO2(FMQ)) with Al2O3 and orthopyroxene contents. The upper-end ∆logfO2 for the least melt-depleted, orthopyroxene-rich residual samples are consistent with those for sub-arc mantle harzburgite xenoliths from the Kamchatka and Izu-Bonin arcs recording similar melting degrees, but also those for more fertile lherzolite and harzburgite rocks from the northeastern Japan Arc. In turn, the most melt-depleted, orthopyroxene-poor residual samples have ∆logfO2 similar to the upper bound recorded in abyssal peridotites. Taking literature data into consideration, the fO2 spectrum recorded by the West Bismarck sub-arc mantle peridotite suite is modelled here by a two-stage partial melting process. The first-stage oxidation state is near-buffered from lherzolite to orthopyroxene-rich harzburgite by fluxed-melting with volatile-rich, slab-derived components at ca. FMQ + 0.5 to FMQ + 1.5 during the generation of high-partial melting degree, picrite-boninite-andesite oxidized liquids. The second-stage oxidation state is un-buffered during re-melting of residual harzburgite accompanying generation of low- to moderate-degree partial melts such as low-Ca boninite; these magmas preserve more variable fO2 extending to lower values (FMQ and below) owing to the progressive removal of Fe3+ from their sources with increasing melting degree. The second-stage melting event likely occurs during adiabatic decompression of residual spinel harzburgite to the uppermost mantle wedge. The data in this study support the general hypothesis that Fe3+/∑Fespinel and fO2 of residual peridotite (and of the melts formed at equilibrium) can vary during partial melting in the Earth's mantle. These results further provide direct source evidence for the controls of various subduction zone melting processes on the oxidation state of different types of primary arc melts. Melt depletion of mantle wedge sources can result in a progressive decrease in the fO2 of liquids subsequently extracted from these sources, but only in the absence of oxidized, Si- and volatile-rich components. These components are presumably derived from the subducted slab and effectively buffer fO2 during fluxed-melting. The observed fO2 variability in sub-arc mantle peridotites worldwide likely reflects the combination of fluxed- and adiabatic decompression melting in the mantle wedge.
      Graphical abstract
      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.004
      Issue No: Vol. 486 (2018)
       
  • Impact of dissolution of syngenetic and epigenetic minerals on coal
           permeability
    • Authors: Hamed Lamei Ramandi; Min Liu; Sahand Tadbiri; Peyman Mostaghimi
      Pages: 31 - 39
      Abstract: Publication date: 15 May 2018
      Source:Chemical Geology, Volume 486
      Author(s): Hamed Lamei Ramandi, Min Liu, Sahand Tadbiri, Peyman Mostaghimi
      Permeability of coal is a key parameter in coalbed methane recovery. Minerals are known to occlude flow paths and reduce coal permeability. Herein, pore space variation of coal due to dissolution of syngenetic and epigenetic minerals is numerically simulated. A high-resolution helical micro-computed tomography (micro-CT) scanner is used to acquire 3D images from internal structure of a coal sample that contains both syngenetic and epigenetic minerals. Two subsets are then obtained from the micro-CT image and segmented to separate syngenetic minerals, epigenetic minerals and macerals. The syngenetic and epigenetic minerals individually and together are dissolved and their impact on porosity and permeability is studied. The minerals are identified through Scanning Electron Microscopy with Energy Dispersive Spectroscopy (SEM-EDS). The dissolution process is performed based on a first order kinetic reactive model. The numerical model combines lattice Boltzmann and finite volume methods. The results show that coal permeability significantly increases when a reactive solution is introduced. It is observed that the permeability increase due to change of porosity is approximately 50% greater when only epigenetic minerals are dissolved. It is demonstrated that dissolving syngenetic minerals that are contiguous to the connected flow network can enhance the permeability through increasing the available connected void spaces. Also, it is shown that the gap, which at some cases occurs due to mineral detachment from the fracture wall, has a direct impact on dissolution performance. Overall, this study improves the understanding of dissolution phenomena in different types of coal minerals.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.015
      Issue No: Vol. 486 (2018)
       
  • Helium diffusivity and fluxes from a sedimentary basin
           (Permo-Carboniferous trough, Northern Switzerland)
    • Authors: I. Tolstikhin; S. Tarakanov; M. Gannibal
      Pages: 40 - 49
      Abstract: Publication date: 15 May 2018
      Source:Chemical Geology, Volume 486
      Author(s): I. Tolstikhin, S. Tarakanov, M. Gannibal
      Abundances of radiogenic He and Ar isotopes, observed in ground waters of the Permian-Carboniferous terrigenous sediments (PCT) in Northern Switzerland, exceed those in the overlaying (Muschelkalk) and underlying (Crystalline basement) aquifers, eliminating external sources of these species. In this case a comparison of the observed abundances with those in situ generated sheds light on mobility of noble gases generated in the PCT. Detailed studies of the parent element and He isotope concentrations in the PCT rocks, mineral separates, pore and ground waters along with the data on γ-logging and porosity allow He isotope production and redistribution in the PCT rock-water system to be understood and quantified. The PCT shales generate most of 3He and 4He and both isotopes are almost completely released from the shales into pore space and migrate either into the aquifers with movable waters and further out of the PCT, or into gas-fluid inclusions of the rock forming minerals, quartz and plagioclase. Here we present a He concentration profile, based on: (i) helium measured concentrations in ground water samples from 5 aquifers available within the cross section studied; (ii) helium concentrations (in 15 PCT pore water “samples”), derived from the He partial pressure in gas-fluid inclusions, recovered by special extraction/saturation experiments. In order to estimates the rates of He migration through the PCT, we compare the produced and observed abundances within the frame of 1D diffusion model. Only two parameters, the diffusion coefficient for the whole sequence, D ALL  = 4.1 × 10−3 m2 year−1, and the rate of He removal from the crystalline aquifers, θ CR  ≈ 1.4 × 10−6 year−1, are required to obtained a good agreement between the observed and calculated He concentrations in PCT waters: the minimal square deviations are ≈(2 to 3) × 10−8 mol cm−3 H2O, comparable with the accuracy of measurements. The following parameters were derived from the modeling: the reduction factor D ALL /D 0 = 0.013; the He diffusion fluxes into the overlaying Muschelkalk and underlying Crystalline aquifers, F MU  ≈ 1.4 × 10−7 mol m−2 year−1 and F CR  = 0.24 × 10−7 mol m−2 year−1, respectively. From these values we calculated the mean helium residence times in PCT, <τ PCT > ≈ 120 Ma, and in Muschelkalk aquifer, <τ MU > ≈ 6 ka. The relationships between He diffusivities of the PCT and the underlying Crystalline basement are discussed. We further compare our results with other estimates of He mobility in low-permeable sediments.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.029
      Issue No: Vol. 486 (2018)
       
  • Weathering processes, catchment geology and river management impacts on
           radiogenic (87Sr/86Sr) and stable (δ88/86Sr) strontium isotope
           compositions of Canadian boreal rivers
    • Authors: Ross Stevenson; Christopher R. Pearce; Eric Rosa; Jean-François Hélie; Claude Hillaire-Marcel
      Pages: 50 - 60
      Abstract: Publication date: 15 May 2018
      Source:Chemical Geology, Volume 486
      Author(s): Ross Stevenson, Christopher R. Pearce, Eric Rosa, Jean-François Hélie, Claude Hillaire-Marcel
      Radiogenic (87Sr/86Sr) and stable (δ88/86Sr) strontium isotope compositions spanning a calendar year are reported for rivers from across subarctic Canada that drain contrasting lithologies ranging from Precambrian bedrock (Koksoak, Great Whale and La Grande rivers of Northern Quebec) to carbonate and clastic Phanerozoic sedimentary rocks of the Western Interior Platform (Nelson River, of central and western Canada). The 87Sr/86Sr isotopic compositions of the river waters reflect the underlying geology, with rivers draining the Precambrian Shield having higher 87Sr/86Sr ratios (0.727–0.734) than the Phanerozoic dominated Nelson River (0.713). The stable strontium isotope values (δ88/86Sr) range from 0.26 to 0.39‰, with the values for the Nelson River overlapping those of the other three. Rivers that have not been developed for hydroelectric power show a seasonal variation in the 87Sr/86Sr ratios, whereas those that have been diverted or dammed show little or no seasonal variation due to increased residence time of their water in hydroelectric reservoirs. The three rivers from Northern Quebec show discrete ranges in their 87Sr/86Sr and δ88/86Sr isotope compositions that correlate with the Ca/Sr and Na/Sr ratios of the river water. These correlations are interpreted to reflect differential chemical weathering of felsic versus mafic source rocks and/or of surficial sediment vs bedrock sources.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.039
      Issue No: Vol. 486 (2018)
       
  • Influence of Th-rich mineral phases on U–Th radioactive disequilibrium
           ages of sulfide deposits from the Okinawa Trough
    • Authors: S. Nakai; A. Takamasa; T. Fujiwara; S. Toyoda; J. Ishibashi; R. Yoshizumi; T. Urabe
      Pages: 61 - 72
      Abstract: Publication date: 15 May 2018
      Source:Chemical Geology, Volume 486
      Author(s): S. Nakai, A. Takamasa, T. Fujiwara, S. Toyoda, J. Ishibashi, R. Yoshizumi, T. Urabe
      Many samples of hydrothermal sulfide minerals from the Okinawa Trough yield 234U–230Th radioactive disequilibrium ages that are inconsistent with the ages of coexistent barite obtained using electron spin resonance (ESR) method. These results contrast strongly against results obtained for the Southern Mariana Trough, for which the U–Th radioactive disequilibrium ages are roughly consistent with the ESR ages. Sulfide minerals from the Okinawa Trough show large variation in U and Th abundances, suggesting open-system behavior. We infer that the interaction of hydrothermal fluids with thick terrigenous sediment caused large-scale migration of U and Th in the Okinawa Trough. The (234U/230Th) – (232Th/230Th) plots for the sulfide samples from the Hatoma Knoll and the Izena Hole show two mixing trends for each site. The presence of Th-rich phase with high (230Th/234U) ratio seems to cause incorrect age estimates of the sulfide deposits.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.04.004
      Issue No: Vol. 486 (2018)
       
  • Molybdenum isotope variations in calc-alkaline lavas from the Banda arc,
           Indonesia: Assessing the effect of crystal fractionation in creating
           isotopically heavy continental crust
    • Authors: Martin Wille; Oliver Nebel; Thomas Pettke; Pieter Z. Vroon; Stephan König; Ronny Schoenberg
      Pages: 1 - 13
      Abstract: Publication date: 10 May 2018
      Source:Chemical Geology, Volume 485
      Author(s): Martin Wille, Oliver Nebel, Thomas Pettke, Pieter Z. Vroon, Stephan König, Ronny Schoenberg
      Recent studies report a large Mo isotope variability of up to 1‰ (expressed in δ98/95MoNIST3134) in convergent margin lavas. These isotopic variations have been associated with subduction zone processes and ultimately may account for heavy and variable isotope signatures in evolved continental crust. Arc lavas show both lighter and heavier Mo isotopic values when compared to the chondritic average (δ98/95MoNIST3134 −0.16 ± 0.02‰), with a concentration weighted mean isotopic composition (δ98/95MoNIST3134 +0.03‰) distinctly heavier than that of the mantle (δ98/95MoNIST3134~−0.21 to −0.16‰). The absence of isotopic fractionation during tholeiitic igneous differentiation indicates that heavy Mo isotope signatures in convergent margin rocks are intrinsic to subduction zone processes, caused either by recycling of subducted components, by Mo isotope fractionation during magmatic differentiation, or by a combination thereof. In order to gain a more detailed understanding of the Mo isotope variability in arc lavas, we have studied Mo isotopes and concentrations in calc-alkaline lavas sampled along the Banda Arc in Indonesia, an intra-oceanic subduction zone well known for variable contributions of subducting continental meterial. Banda Arc lavas exhibit Mo isotopic compositions covering a large range from −0.48 to +0.24‰ in δ98/95MoNIST3134. We find that, combined with published data from other subduction zones, the majority of arc data are isotopically heavier compared to its presumed mantle wedge source or mid-ocean-ridge basalts. Furthermore, arc lava Mo isotope signatures show an apparent covariation between indices of amphibole-clinopyroxene fractionation from the melt. Generally, heavier Mo isotopic signatures are associated with higher degrees of REE fractionation expressed as λ1, λ2, and Dy*/Dy, high Ca/Al, and higher Sc contents. These observations can be best explained with an open system magma reservoir where fractional crystallisation, recharge and eruption are tightly linked. Notable exceptions in the Banda region are four samples with isotopically light Mo. Three of these isotopically light lavas indicate the assimilation of an isotopically light Mo reservoir with heavy δ18O and radiogenic 87Sr/86Sr-206Pb/204Pb, tentatively identified as lower arc crust. Together, our data demonstrate, in line with previous findings, that magmatic processes modify the Mo isotopic composition in arc lavas, thus adding complexity to the Mo isotope systematics inherent to subduction zones.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.02.037
      Issue No: Vol. 485 (2018)
       
  • Photo-stability of iron-phenolic complexes derived from peatland upon
           irradiation in waters under simulated sunlight
    • Authors: Yiliu Wang; Wu Xiang; Weiling Yang; Sen Yan; Zhengyu Bao; Yu Liu
      Pages: 14 - 23
      Abstract: Publication date: 10 May 2018
      Source:Chemical Geology, Volume 485
      Author(s): Yiliu Wang, Wu Xiang, Weiling Yang, Sen Yan, Zhengyu Bao, Yu Liu
      Phenolics from peatlands have been proven to enhance the solubility of iron, even under alkali or saline conditions, by forming iron-phenolic complexes. However, the photo-stability of these complexes has received little attention thus far. Based on the investigation of water and peat samples in Jinchuan peatland, in northern China, simulated experiments – using Gallic acid (GA) as a structural analog of peat-derived phenolic acid – were carried out to clarify the mechanisms of photo-stability of iron-phenolic complexes. Our research confirmed that when the molar ratio of GA to Fe reaches 0.1:1, photolysis led to some Fe deposition. By comparing GA concentrations under aerobic/anaerobic conditions, we demonstrated that dissolved oxygen plays a key role, not only in GA autoxidation but also in photo-degradation of GA through direct and indirect photolysis. Besides, adding coexisting phenolic acids into GA/iron systems showed various effects, depending on the different functional groups, while the dominant species of phenolic acids in peatlands, such as p-cumaric acid and p-hydroxybenzoic acid, may still act as reactive oxygen species scavengers, protecting over 99% of the dissolved iron under solar irradiation. Our results indicate that by forming iron-organic complexes with certain phenolics from peatlands, dissolved iron can be effectively protected from precipitation during freshwater transport under solar irradiation, which has profound implications for controlling the limited primary production in certain marine areas.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.016
      Issue No: Vol. 485 (2018)
       
  • No 182W excess in the Ontong Java Plateau source
    • Authors: Thomas S. Kruijer; Thorsten Kleine
      Pages: 24 - 31
      Abstract: Publication date: 10 May 2018
      Source:Chemical Geology, Volume 485
      Author(s): Thomas S. Kruijer, Thorsten Kleine
      Small-scale W isotope variations in ancient and modern terrestrial rocks provide insights into Earth's accretion and early differentiation history as well as the long-term evolution of the Earth's mantle. Tungsten isotope studies on such rocks have exploited advances in mass spectrometry, both NTIMS and MC-ICPMS, which now permit the determination of W isotope ratios at unprecedented precision. While W isotope studies performed in different labs by MC-ICPMS and NTIMS generally exhibit excellent agreement, obtaining accurate W isotope data at this level of precision remains analytically challenging. For example, a recent NTIMS study reported a relatively large, +24 ppm excess in 182W/184W for a Phanerozoic sample from the Ontong Java Plateau (OJP), but no such 182W/184W anomaly was found in another study by MC-ICPMS. The present study aims to resolve the discrepancy between these two previous studies, and more generally to evaluate the agreement between different recent W isotope studies by NTIMS and MC-ICPMS. To this end, we report new W isotope data for OJP drill core samples obtained by MC-ICPMS. The OJP samples analyzed here exhibit no resolvable 182W/184W excess relative to the standards and most terrestrial rocks. Moreover, the OJP samples as well as the terrestrial rock standards analyzed here exhibit small but variable W isotope variations for ratios involving 183W, producing coupled variations in both ‘radiogenic’ (i.e., 182W/183W) and ‘non-radiogenic’ (i.e., 183W/184W) ratios. These W isotope variations are analytical in origin, induced during sample preparation, and very likely caused by a nuclear field shift isotope fractionation affecting primarily the odd isotope (183W). The recently reported 182W excess for an OJP sample may result from this nuclear field shift effect, as the NTIMS analyses had to rely on a double normalization involving the 183W/184W ratio. More generally, these results demonstrate that using 183W data from any MC-ICPMS or NTIMS study requires a careful quantification of any potential analytical 183W effect. Nevertheless, once such effects are taken into account, then both 182W/184W and 183W/184W can accurately be determined to a very high level of precision.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.024
      Issue No: Vol. 485 (2018)
       
  • Determinants of blood water δ18O variation in a population of
           experimental sheep: Implications for paleoclimate reconstruction
    • Authors: Daniel R. Green; Gerard Olack; Albert S. Colman
      Pages: 32 - 43
      Abstract: Publication date: 10 May 2018
      Source:Chemical Geology, Volume 485
      Author(s): Daniel R. Green, Gerard Olack, Albert S. Colman
      Mammalian body, blood and hard tissue oxygen isotope compositions (δ 18O values) reflect environmental water and food sources, climate, and physiological processes. For this reason, fossil and archaeological hard tissues, which originally formed in equilibrium with body chemistry, are a valuable record of past climate, landscape paleoecology, and animal physiology and behavior. However, the environmental and physiological determinants of blood oxygen isotope composition have not been determined experimentally from large herbivores. This class of fauna is abundant in Cenozoic terrestrial fossil assemblages, and the isotopic composition of large herbivore teeth has been central to a number of climate and ecological reconstructions. Furthermore, existing models predict blood water, or nearly equivalently body water, δ 18O values based on environmental water sources. These have been evaluated on gross timescales, but have not been employed to track seasonal variation. Here we report how water, food, and physiology determine blood water δ 18O values in experimental sheep (Ovis aries) subjected to controlled water switches. We find that blood water δ 18O values rapidly reach steady state with environmental drinking water and reflect transient events including weaning, seasons, and snowstorms. Behavioral and physiological variation within a single genetically homogenous population of herbivores results in significant inter-animal variation in blood water δ 18O values at single collection times (1 s.d. = 0.1–1.4‰, range = 3.5‰) and reveals a range of water flux rates (t 1/2 = 2.2–2.9 days) within the population. We find that extant models can predict average observed sheep blood δ 18O values with striking fidelity, but predict a pattern of seasonal variation exactly opposite of that observed in our population for which water input variation was controlled and the effect of physiology was more directly observed. We introduce to these models an evaporative loss term that is a function of environmental temperatures. The inclusion of this function produces model predictions that mimic the observed seasonal fluctuations and match observations to within 1.0‰. These results increase the applicability of available physiological models for paleoseasonality reconstructions from stable isotope measurements in fossil or archaeological enamel, the composition of which is determined in equilibrium with blood values. However, significant blood δ 18O variation in this experimentally controlled population should promote caution when interpreting isotopic variation in the archaeological and paleontological record.
      Graphical abstract image

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.034
      Issue No: Vol. 485 (2018)
       
  • Elemental concentration and organic petrology of unique liptinite-rich
           humic coal, canneloid shale, and cannel coal of Devonian age from Arctic
           Canada
    • Authors: Fariborz Goodarzi; Thomas Gentzis
      Pages: 44 - 55
      Abstract: Publication date: 10 May 2018
      Source:Chemical Geology, Volume 485
      Author(s): Fariborz Goodarzi, Thomas Gentzis
      Seventeen coal and carbonaceous shale samples taken from eight stratigraphic sections of the Devonian Hecla Bay and Weatherall formations in Arctic Canada, were examined using reflected light microscopy, instrumental neutron activation analysis (INAA), and inductively coupled plasma emission spectroscopy (ICPES). Samples consist of humic coal with 62–79 vol% vitrinite, liptinite-rich humic coal with 42 vol% liptinite, and cannel coal with 52–81 vol% sporinite content. Carbonaceous shale has 46–73 vol% mineral matter and canneloid shale has 30–42 vol% mineral matter as well as 22–38 vol% sporinite content. Most were deposited in areas characterized by minor channel cut-and-abandonment and lake and bay infills peripheral to distributary complexes. A fresh water environment is indicated by Boron (18–71 ppm), low inertinite (0–7.8 wt%), and high sporinite content (30–81 vol%). The ratio of Na/K versus liptinite content shows that coals and associated sediments from the Hecla Bay Formation experienced a more rapid rate of sedimentation than the carbonaceous shales from the Weatherall Formation. The highest total REEs and LREE (La-Gd) was in the liptinite-rich humic coal, followed by humic coal and carbonaceous shale. The concentration of REEs and LREEs in the cannel coals is half of that measured in the liptinite-rich humic coal. The PAAS normalized for oil shales follows two different patterns: 1) the liptinite-rich coal samples display a sharp increase from Nd to Ho, then maintain a similar pattern up to Lu; and 2) samples of other lithologies increase from Nd to Dy, and then maintain a flat trend up to Lu. Hierarchical cluster analysis shows that canneloid and liptinite-rich coal exhibit the greatest similarity with each other whereas humic coal and liptinite-rich coal show the greatest dissimilarity with carbonaceous shale.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.035
      Issue No: Vol. 485 (2018)
       
  • Signal or noise' Isolating grain size effects on Nd and Sr isotope
           variability in Indus delta sediment provenance
    • Authors: Tara N. Jonell; Yuting Li; Jurek Blusztajn; Liviu Giosan; Peter D. Clift
      Pages: 56 - 73
      Abstract: Publication date: 10 May 2018
      Source:Chemical Geology, Volume 485
      Author(s): Tara N. Jonell, Yuting Li, Jurek Blusztajn, Liviu Giosan, Peter D. Clift
      Radiogenic elements, such as neodymium (Nd) and strontium (Sr), are commonly used to decipher the provenance and weathering histories of bulk siliciclastic sediments worldwide, although increasing evidence for diagenetic and sediment transport-driven bias of isotope signatures calls into question the utility of bulk isotope compositions as effective tools. This study evaluates grain size-dependence and variability of Nd and Sr compositions in the Indus delta of Pakistan, documenting both a significant isotopic evolution and coarsening upward sequence during the last deglaciation (~15 ka). Grain size analysis, trace element geochemistry, and Nd and Sr geochemistry are determined for bulk and separate grain size fractions (<63 μm, 63–125 μm, 125–250 μm, >250 μm) from four core sampling sites with similar provenance. Isotopic compositions are controlled by grain size distribution, in turn variably controlled by size fraction mineralogy. Fine-grained bulk sediment Nd isotope compositions are primarily dictated by the finest (<125 μm) sediments enriched in Nd-bearing monazite and allanite, with coarser bulk sediments influenced by mica. The most abundant grain size fraction drives bulk sediment Sr isotope compositions, with the finest grain size fractions indicating strong control by potassium feldspar, mica, epidote, and/or volcanogenic clay minerals. Over the last 15 k.y., resolvable provenance-driven trends are confidently identified in Nd isotope compositions. Long-term trends remain consistent with previous findings although the isotopic shift in delta compositions must be less than previously envisaged (~4 vs. 0.69–1.91 εNd units). Although considerable variability is observed in bulk Sr isotope compositions, <63 μm and 63–125 μm fraction 87Sr/86Sr compositions evolve in parallel through time and show fractionation by ~0.005–0.01 as a result of grain size. Within the isotopically diverse Indus drainage system, bulk isotopic compositions are estimated to deviate on average no than ±1.04 εNd units and ±0.0099 for 87Sr/86Sr values for any sediment as a result of mineralogy, grain size distribution, and analytical error. Isotopic excursions beyond these uncertainties can be unambiguously assigned to either a change in upstream provenance and/or chemical weathering.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.036
      Issue No: Vol. 485 (2018)
       
  • Riverine supply to the eastern Mediterranean during last interglacial
           sapropel S5 formation: A basin-wide perspective
    • Authors: Jiawang Wu; Amalia Filippidi; Gareth R. Davies; Gert J. de Lange
      Pages: 74 - 89
      Abstract: Publication date: 10 May 2018
      Source:Chemical Geology, Volume 485
      Author(s): Jiawang Wu, Amalia Filippidi, Gareth R. Davies, Gert J. de Lange
      Organic-rich sapropel sediments were repeatedly deposited in the eastern Mediterranean Sea (EMS), in response to insolation-driven freshwater forcing. However, the exact freshwater sources and causal associated paleoclimate-related processes remain unresolved. Sapropel S5, formed during the insolation maximum of the last interglacial, is one of the most intensely developed sapropels of the Late-Quaternary. Here, detrital sediments of sapropel S5 obtained from 8 cores, together with 13 EMS surface samples, are analyzed for major elements, rare earth elements (REE), and Sr and Nd isotopes. This permits a basin-wide investigation of the source and distribution of river-borne material to the EMS for sapropel S5, and its comparison to the present-day and the Holocene sapropel S1 period. During the sapropel S5, there was minor Saharan dust input. The marked east–west geochemical gradient in S5 detrital sediments across the EMS is therefore attributed to mixing between fluvial contributions, being Nile discharge, Aegean/Adriatic riverine inputs, and Libyan-Tunisian paleodrainage fluxes. The offshore distribution of Nile sediments during sapropel S5 was comparable to those during S1 and the present. The Nile sediment contribution appears to be only dominant for the Levantine Basin, decreasing to negligible values south of Crete. This rather limited sediment delivery, despite inferred increased runoff during S5, is related to denser vegetation cover on the Ethiopian Highlands. By contrast, small rivers around the Aegean (and Adriatic) Sea brought large amounts of detrital material into the EMS. This is particularly noticeable around Crete and the northern Ionian Sea. The enhanced riverine input is probably due to strong precipitation seasonality over the northern EMS borderlands, particularly for the early phase of the last interglacial maximum. Furthermore, there are substantial fluvial contributions from the Libyan-Tunisian margin to the Ionian Sea sediments, in particular during the last part of sapropel S5. The inferred river-borne material was transported via paleodrainage systems reactivated by intensified monsoon precipitation, and derived from central-Saharan mountains. Compared to sapropel S1, these S5-related paleodrainage fluxes were not only stronger, but also had a more predominant provenance from eastern rather than western Libya. In addition, a similar, averaged endmember of Saharan dust sources is revealed by REE signatures.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.037
      Issue No: Vol. 485 (2018)
       
  • Distinguishing slow cooling versus multiphase cooling and heating in
           zircon and apatite (U-Th)/He datasets: The case of the McClure Mountain
           syenite standard
    • Authors: Wesley R. Weisberg; James R. Metcalf; Rebecca M. Flowers
      Pages: 90 - 99
      Abstract: Publication date: 10 May 2018
      Source:Chemical Geology, Volume 485
      Author(s): Wesley R. Weisberg, James R. Metcalf, Rebecca M. Flowers
      New zircon, titanite, and apatite (U-Th)/He (ZHe, THe, AHe) data for four samples of the 524 Ma McClure Mountain syenite (MMS) in the Wet Mountains of Colorado constrain the <200 °C thermal history of this 40Ar/39Ar geochronology standard. ZHe dates vary from 420 to 567 Ma, do not correlate with their limited eU range (66–388 ppm), have dispersion attributable to eU zonation, and show no systematic variation between samples. THe dates are 488 to 515 Ma. AHe dates range from 70 to 211 Ma, with some inter-sample variability that could be due to modest post-70 Ma displacements along faults. Our dataset is consistent with recently published (U-Th)/He data for the MMS, although the published ZHe results extend to higher eU and define a negative date-eU correlation not captured by our lower eU zircons. Existing U-Pb and 40Ar/39Ar thermochronologic data, together with the THe and ZHe results, document rapid post-emplacement cooling of the MMS to ≤200 °C by ~500 Ma. A recent (U-Th)/He study inferred that the MMS subsequently underwent simple slow monotonic cooling until present-day. However, geologic relationships are incompatible with such a history, instead requiring that rocks in the vicinity of the MMS were at the surface at ~480 Ma, ~180 Ma, and ~60 Ma, with possible phases of burial and erosion of varying magnitude between these times. Inverse thermal history modeling can simultaneously satisfy the new and previously published ZHe and AHe data while honoring these geologic constraints. The outcomes of this work highlight that date-eU patterns can be generated by protracted cooling as well as by multiphase heating and cooling histories, and underscore the importance of integrating geologic data to help identify the most probable explanation for a (U-Th)/He dataset.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.038
      Issue No: Vol. 485 (2018)
       
  • Small-scale Sr and O isotope variations through the UG2 in the eastern
           Bushveld Complex: The role of crustal fluids
    • Authors: Mathias Schannor; Ilya V. Veksler; Lutz Hecht; Chris Harris; Rolf L. Romer; Tawanda D. Manyeruke
      Pages: 100 - 112
      Abstract: Publication date: 10 May 2018
      Source:Chemical Geology, Volume 485
      Author(s): Mathias Schannor, Ilya V. Veksler, Lutz Hecht, Chris Harris, Rolf L. Romer, Tawanda D. Manyeruke
      A detailed study of the Sr- and O- isotopic composition of minerals in the Upper Group 2 (UG2) unit of the eastern Bushveld Complex revealed significant variations in the pegmatoidal footwall pyroxenite and the UG2 chromitite layer itself. Initial 87Sr/86Sr ratios (Sri) of interstitial plagioclase in the footwall rocks are significantly higher than in adjacent rocks of the Critical Zone. The δ18O values of plagioclase-pyroxene and plagioclase-chromite mineral pairs in footwall pyroxenite and chromitite are consistent with oxygen isotope exchange from crystallization temperatures down to 700 °C and 800 °C, respectively, whereas in other parts of the UG2, plagioclase and pyroxene δ18O values are consistent with O isotope equilibration at liquidus crystallization temperatures of approximately 1150 °C. We propose that the higher initial 87Sr/86Sr of plagioclase in the UG2 chromitite and the footwall pyroxenite reflects infiltration of fluid derived from dehydrating country rocks beneath the Bushveld Complex. Fluids could have been introduced either late or during chromitite crystallization. The chromitite layer and its pegmatoidal footwall could have acted as barriers to entrap late stage crustal fluids. Alternatively, reaction of fluids with the chromite-bearing crystallizing mush layer would induce hydration melting of pyroxene and plagioclase supplying Cr and Al to the melt, thus invoking further chromite formation. This dissolution-reaction releases Cr from pyroxene, which along with pre-existing disseminated chromite could refine the chromitite layers. The pegmatoidal UG2 footwall constitutes the reaction front-line of this process, which recrystallized to a coarse-grained rock upon cooling. This study emphasizes the role of crustal fluids and late- and post-magmatic processes in layered intrusions taking place at subsolidus temperatures, whereby isotopic and chemical compositions may be significantly changed.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.040
      Issue No: Vol. 485 (2018)
       
  • Corrigendum to “Determination of Fe3+/ΣFe of XANES basaltic glass
           standards by Mössbauer spectroscopy and its application to the oxidation
           state of iron in MORB” [Volume 479, 20 February 2018, pages 166-175]
    • Authors: Hongluo L. Zhang; Elizabeth Cottrell; Peat A Solheid; Katherine A Kelley; Marc M Hirschmann
      First page: 113
      Abstract: Publication date: 10 May 2018
      Source:Chemical Geology, Volume 485
      Author(s): Hongluo L. Zhang, Elizabeth Cottrell, Peat A Solheid, Katherine A Kelley, Marc M Hirschmann


      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.025
      Issue No: Vol. 485 (2018)
       
  • A tribute to Professor Kazuhiro Suzuki Chemical Geology special issue
           “Accessory mineral and trace element geochemistry”
    • Authors: Monika A. Kusiak; Daniel J. Dunkley; Takenori Kato; Krishnan Sajeev; Klaus Mezger
      Pages: 1 - 3
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): Monika A. Kusiak, Daniel J. Dunkley, Takenori Kato, Krishnan Sajeev, Klaus Mezger


      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.033
      Issue No: Vol. 484 (2018)
       
  • Electron-microprobe dating of monazite: The story
    • Authors: Jean-Marc Montel; Takenori Kato; Masaki Enami; Alain Cocherie; Friedrich Finger; Michael Williams; Michael Jercinovic
      Pages: 4 - 15
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): Jean-Marc Montel, Takenori Kato, Masaki Enami, Alain Cocherie, Friedrich Finger, Michael Williams, Michael Jercinovic
      This paper is a testimony of how electron microprobe dating of monazite was developed in the early days of this technique, in the 90's. Five contributions have been collected from Nagoya, Clermont-Ferrand, Orléans, Salzburg, and Amherst. The technique was designed in Nagoya by Professor Suzuki, using an old JXA-5A JEOL electron microprobe. The first results were published in 1991, with great difficulty. Professor Suzuki also created the isochron-like Pb-Th* diagram to present the data. Progressive improvement of the method finally allowed the Nagoya team to date Cenozoic monazite. The technique was re-discovered in Clermont-Ferrand using a Cameca Camebax microprobe. This team demonstrated the accuracy of the method, and proposed statistical tools to improve the precision and to handle multimodal populations. The first results were published in 1993. In Orléans, the French Geological Survey (BRGM) developed the method with a Cameca SX50 to support mapping projects. They developed a new method for calculating the age, and showed that this technique was very efficient for dating monazite in migmatites. In Salzburg, the first results were obtained in 1996, using a Jeol JX 8600. It proved to be very efficient in the Alps to distinguish Cadomian, Ordovician, Variscan and Alpine events. It allowed this team to directly date a monazite-allanite reaction they described for the first time. Finally, the Amherst team investigated in detail the technical issues of electron microprobe monazite dating. They showed that the best analytical procedures must include at least: detailed chemical mapping, several interference corrections and special care for background measurements. With the help of Cameca they designed a specific microprobe for dating, named “Ultrachron”. With this machine, high precision ages can be obtained on well characterized individual grains in thin section, giving birth to a new era in geochronology of complex metamorphic rocks.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2017.11.001
      Issue No: Vol. 484 (2018)
       
  • Pseudo-fixed dead time circuit for designing and implementation of
           JEOL-type X-ray counting systems
    • Authors: Takenori Kato; Kazuhiro Suzuki; Mi-Jung Jeen; Masayo Minami
      Pages: 16 - 21
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): Takenori Kato, Kazuhiro Suzuki, Mi-Jung Jeen, Masayo Minami
      Quantitative electron probe microanalysis (EPMA) of trace elements using wavelength dispersive spectrometers (WDS) requires high probe current and/or accelerating voltage and long X-ray sampling times to measure weak X-ray signals from target materials. The X-ray count rate of a standard material is extremely high when measured under the same conditions. Consequently, the accuracy of the dead time correction becomes a significant issue for quantification. Accurate dead time correction requires an exact knowledge of the X-ray counting system, including the behavior of the proportional counter and electronic circuits. Each spectrometer has a specific dead time that depends on factors such as electronic circuit design, counter bias, and X-ray energies. The dead time also changes with aging degradation. A pseudo-fixed dead time correction circuit with non-extendable approximation is described that prevents systematic errors in quantitative EPMA caused by inappropriate dead time corrections. The circuit, which is added to the output of the single channel analyzer, includes one extendable and two non-extendable dead time generators with dead times of 0.68μs, 1.08μs, and 1.92μs, respectively. The behavior of the whole system can be treated as non-extendable for most applications, with a dead time of approximately 2.01μs. The pseudo-fixed dead time circuit suppresses systematic error of the dead time correction to 0.6% or less when the original dead time is between 0.8–2.0μs and the true X-ray count rate is <200kcps. This makes it possible to perform accurate dead time corrections without periodic measurement of the dead time throughout the life of the proportional counter by implementing a high-precision crystal oscillator in the system.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2017.12.030
      Issue No: Vol. 484 (2018)
       
  • Improving U-Th-Pb electron microprobe dating using monazite age references
    • Authors: Patrik Konečný; Monika A. Kusiak; Daniel J. Dunkley
      Pages: 22 - 35
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): Patrik Konečný, Monika A. Kusiak, Daniel J. Dunkley
      This article proposes an improved approach to monazite dating by electron microprobe that includes a “monazite age reference correction” (MARC). During analysis, a set of differing monazite standard reference materials with established isotopic ages are measured at the start of the session. These measurements are used to test the analytical set-up and, if necessary, to calculate MARC factors that can be applied to monazite samples. The MARC is not intended as a way to correct systematic errors due to problems in set-up, but rather as a fine-scale adjustment for factors that cannot be readily assessed during single sessions. Long-term, multi-session calculation of MARC factors allows for precise monitoring of anomalous behavior among monazite age reference materials during individual sessions. The method can also assist in the identification of chemical inhomogeneity in monazite, such as that commonly produced by interaction with metasomatic fluids. A representative set of electron microprobe monazite age reference materials are presented, including two ‘reference monazites’ that are good examples of monazite with age disturbance induced by metasomatism. Additional modifications to analytic protocols are proposed, including a) corrections for count rate increases during long beam dwell times, and b) improved estimation of background values at line positions by accounting for the effect of mean atomic number.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.02.014
      Issue No: Vol. 484 (2018)
       
  • The giant monazite crystals from Manangotry (Madagascar)
    • Authors: Jean-Marc Montel; Dieudonne Razafimahatratra; Philippe de Parseval; Franck Poitrasson; Bernard Moine; Anne-Magali Seydoux-Guillaume; Raphaël Pik; Nicolas Arnaud; François Gibert
      Pages: 36 - 50
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): Jean-Marc Montel, Dieudonne Razafimahatratra, Philippe de Parseval, Franck Poitrasson, Bernard Moine, Anne-Magali Seydoux-Guillaume, Raphaël Pik, Nicolas Arnaud, François Gibert
      The Manangotry area in the South-East of Madagascar is famous for its giant monazite crystals. The studied occurrence is an outcrop near the Manangotry pass, were giant, cm-sized crystals have been found. The crystals are embedded in biotitite levels, also containing cm-sized xenomorphic ilmenite, and are associated with a 1m thick layer of apatite. Besides giant crystals, monazite is also present as abundant small (mm-sized) grains. The surrounding rocks are leucogranites and charnockites. The monazite giant crystals are chemically homogeneous and thorium-rich, whereas small crystals tend to be heterogeneous. Both biotite and apatite are F-rich. Temperature estimates from biotite and apatite yielded 750 to 800°C. Despite their high radioactivity, the giant crystals preserve a high degree of crystallinity. Electron microprobe U-Th-Pb dating produced ages of 537±14, 534±10 and 530±10Ma, considered to be the age of the main monazite crystallization episode but some minor domains in small grains yielded 482±12Ma. The enclosing biotites yielded 453±6Ma Ar-Ar ages. More than 98 % of radiogenic helium have been retained in the studied monazite samples, and kinetic experiments indicates the intrinsic diffusion parameters for high-temperature to be Ea =53kcal/mol and D0 =3085cm2/s. The paragenesis (monazite-apatite-ilmenite-biotite) is different from any other occurrences of larges monazite elsewhere. Based on the current data and literature, the preferred genetic model for these giant monazites is crystallization from a high-temperature fluorine-rich fluid, possibly originating from surrounding charnockites.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2017.10.034
      Issue No: Vol. 484 (2018)
       
  • Mass transport and fractionation during monazite alteration by anisotropic
           replacement
    • Authors: A. Grand'Homme; E. Janots; A.M. Seydoux-Guillaume; D. Guillaume; V. Magnin; J. Hövelmann; C. Höschen; M.C. Boiron
      Pages: 51 - 68
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): A. Grand'Homme, E. Janots, A.M. Seydoux-Guillaume, D. Guillaume, V. Magnin, J. Hövelmann, C. Höschen, M.C. Boiron
      The present experimental study investigates the causes of anisotropic replacement and its impact on the element mass transfer during monazite alteration by combining in situ characterization of solid and fluid products. Starting material of standard Manangotry monazite was placed at 200MPa with 18O doped fluids, at temperature (T) between 300 and 600°C, for durations between 14 and 114days, in some cases with hematite-magnetite buffer, and in presence of pre-fractured quartz crystals. For all experiments with NaOH at T>400°C, monazite products show a replacement rim (altered domain), but with complex microstructures that are best explained by nanoscale observations. At 400°C (and 500°C), replacement propagates anisotropically through the unaltered domain, due to preferentially oriented dissolution and/or fracturing at the reaction interface. The altered domain corresponds to nanochannels of secondary monazite (Mnz2) intruding primary monazite (Mnz1), with nanopores filled by amorphous Si-rich inclusions at the reaction front (interface). At 600°C, the altered domain increases in volume and becomes homogeneous and non-porous, due to textural (and chemical) reequilibration. However, nanoscale observations reveal an anisotropic propagation associated with dislocations and preservation of Mnz1 relics within the apparently homogeneous altered domain. Textural equilibration leads to transient pores/inclusions, which preferentially move toward the reaction front. In all experimental products, the abundant porosity attests to significant mass transfer during monazite replacement. Nanomixture within altered domains hampers accurate determination of Mnz2 composition, and is assumed to be responsible for the Pb measured in the rim, due to Mnz1 contribution. However, composition measurements indicate that Mnz2 contains higher light rare earth elements (LREE), higher Th/U ratio but lower Y, Th, U, Pb and Ca contents compared to Mnz1. Elements released in the fluid by monazite replacement are mobilized from the reaction front toward the grain boundary, and then redistributed between secondary Th-silicates and phosphates, Si-rich gel-like material and aqueous fluids. At T>500°C, analyses of inclusions trapped in replaced quartz confirm an efficient REE solubility in the alkaline solutions. The Si-rich gel-like inclusions contain high amounts of REE (e.g. 950–4600ppm Ce), Th (4480–6170ppm) and U (30–110ppm), while aqueous fluid inclusions have high concentrations of REE and Th (around 100s of ppm) compared to common natural brines. There is a fractionation of Th and U during Mnz1 replacement (Th/U ~70) with low Th/U ratios in the aqueous fluid (7–23) compared to the secondary solid products (up to 150), independently of the initial presence of hematite-magnetite buffer. This accounts for a fractionation within the isotopic Th-Pb and U-Pb ages within the altered domain. In natural samples observed microscopically, the complex anisotropic geometry of the replacement can lead to a nanomixture within apparently homogeneous altered domains (with partial resetting of the U-Th-Pb geochronometer), and to misleading interpretations of secondary inclusions within apparently unaltered domain.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2017.10.008
      Issue No: Vol. 484 (2018)
       
  • REE-Th-U and Nd isotope systematics of monazites in magnetite- and
           ilmenite-series granitic rocks of the Japan arc: Implications for its use
           as a tracer of magma evolution and detrital provenance
    • Authors: Keita Itano; Tsuyoshi Iizuka; Mihoko Hoshino
      Pages: 69 - 80
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): Keita Itano, Tsuyoshi Iizuka, Mihoko Hoshino
      Monazite [(Ce, La, Th) PO4], a common accessory mineral in low-Ca felsic rocks and a wide range of metamorphic rocks, is suitable for in situ U–Pb dating, rare earth element (REE) geochemistry, and Nd isotope tracer studies. To link monazite composition with igneous petrogenesis and differentiation, we carried out comprehensive LA-ICP-MS measurements of REE-Th-U abundances and Sm-Nd isotope ratios in monazites from magnetite-series (oxidized type) and ilmenite-series (reduced type) granitic rocks across the Japan arc. The data revealed systematic differences in monazite composition between magnetite-series and ilmenite-series samples, and between pegmatites and granites. In ilmenite-series granitic rocks, monazites from pegmatites showed larger negative Eu anomalies, lower light-REE/middle-REE ratios, and higher middle-REE/heavy-REE ratios than those from granites. These geochemical variations were attributed to significant fractional crystallization of feldspars, monazite, xenotime, and garnet during differentiation in relatively reduced peraluminous granitic magmas. In contrast, there was no remarkable difference in the REE fractionation pattern between magnetite-series pegmatites and granites. Furthermore, the magnitudes of the negative Eu anomalies in the magnetite-series monazites were smaller than those observed in the ilmenite-series samples. These features were interpreted to reflect the suppression of monazite, xenotime, and garnet fractionation and limited Eu incorporation into fractionating feldspars in relatively oxidized and non-peraluminous magmas. In addition, our data demonstrated intra-grain variations in REE-Th-U compositions in a monazite from the Masaki ilmenite-series pegmatite, despite its homogenous Nd isotope composition. These variations suggest that the core and rim of the grain crystallized from distinct magmas that were generated from similar crustal rocks, but were differentiated under different conditions. A comparison of the present data with previously reported data indicates that igneous monazites from granitic rocks are distinct from a wide range of metamorphic monazites in REE-Th-U composition, especially due to their larger negative Eu anomalies. This finding highlights the potential utility of monazite REE-Th-U systematics as a provenance indicator for detrital monazites.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2017.11.033
      Issue No: Vol. 484 (2018)
       
  • SHRIMP U–Pb–Th xenotime (YPO4) geochronology: A novel approach for the
           correction of SIMS matrix effects
    • Authors: A.J. Cross; I.S. Williams
      Pages: 81 - 108
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): A.J. Cross, I.S. Williams
      Xenotime (YPO4) occurs in a wide range of geological environments, but its potential to establish the timing of mineralisation and sediment diagenesis has been the focus of most recent studies. Xenotime in these settings usually has a relatively low uranium content (typically <1000ppm) compared to igneous xenotime and occurs as microscopic crystals (<50μmdiameter), either individually or as outgrowths on zircon substrates. Large radius ion microprobes, such as the SHRIMP or Cameca 1270/1280, that have high sensitivity and spatial resolution, are well suited for U–Pb–Th analysis of xenotime from such environments. SIMS U–Pb–Th analyses of xenotime, however, are prone to significant U–Pb–Th matrix effects that are related to the wide natural range of U (0–6wt%) and rare earth element (REE) (ΣREE: 12–22wt%) concentrations in this mineral. For SHRIMP U–Pb–Th xenotime analyses, a 1wt% increase in U concentration, relative to the U–Pb–Th calibration reference material, will on average cause a corresponding increase in the measured 206Pb/238U and 208Pb/232Th of approximately 15% and 14%, respectively. Similarly, a 1wt% difference in ΣREE causes an increase of about 1.2% in 206Pb/238U and about 1.7% in 208Pb/232Th. Correction for these chemically-induced matrix effects requires the concurrent analysis of three xenotime reference materials which have known ages and ranges of U and ΣREE contents that have been determined accurately by electron probe microanalysis. A least squares methodology is used to derive correction coefficients that relate the SHRIMP U–Pb–Th matrix effects to the U and ΣREE concentrations for the xenotime reference materials. Crucial to the success of this technique is the use of one dimensional (1-D) calibrations using 206Pb+/270[UO2]+ and 208Pb+/248[ThO]+. Processing is carried out in two steps: (1) derivation of correction coefficients to matrix-correct the 206Pb+/270[UO2]+ and 208Pb+/248[ThO]+ ratios, and (2) processing of the matrix-corrected ratios to determine 206Pb/238U and 208Pb/232Th.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2017.12.017
      Issue No: Vol. 484 (2018)
       
  • Geochemical characterisation of xenotime formation environments using U-Th
    • Authors: Neal J. McNaughton; Birger Rasmussen
      Pages: 109 - 119
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): Neal J. McNaughton, Birger Rasmussen
      Xenotime (YPO4) is a trace component in many metasedimentary and some igneous rocks, altered rocks and many hydrothermal ore assemblages, where it forms in response to a range of different processes from igneous crystallisation to low-temperature early diagenesis. Due to its wide range of formation temperatures, its suitability and isotopic robustness for reliable U-Pb geochronology, dissolution/precipitation characteristics during overprint events, and widespread occurrence, it is one of the most valuable minerals for U-Pb geochronology leading to four-dimensional (4D) studies of many terranes. The formation environment of xenotime can be deduced from careful petrography and reliable U-Pb in-situ geochronology within a 4D framework. Further, xenotime is a physically robust mineral during sediment transport and may carry distinctive geochemical fingerprints, including age, to secondary environments. From published works, we review the U-Th-contents of well-characterised examples of xenotime formation to provide chemical fingerprints, which assist in identifying the xenotime formation environment. Although the U-Th characteristics of xenotime from all formation environments show considerable overlap, we make the following observations which may be distinctive of some ore formation environments: (i) hydrothermal xenotime formed from low salinity ore fluids (e.g. iron ore and orogenic gold deposits) trend to have the lowest U-contents (<100ppm U) and U/Th (<4), in contrast to xenotime formed from higher salinity ore fluids (Sn-W and base metal deposits); (ii) xenotime associated with unconformity-related U-ores have the highest U-contents at U/Th>10; (iii) diagenetic xenotime has the most variable and highest U/Th, whereas (iv) xenotime from Precambrian orogenic gold deposits has the least variable and lowest U/Th. Petrogenetic inferences from these observations for ore deposit research and exploration include: (i) support for the homogenising effect of the crustal scale of the fluid system in Precambrian orogenic gold deposits, and (ii) the potential for distinctive U-Th geochemical fingerprints for U ores and some Au ores. These characteristics may be reflected in detrital xenotime grains recovered from routine exploration sampling programs.
      Graphical abstract image

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2017.08.016
      Issue No: Vol. 484 (2018)
       
  • Rare earth elements and Sm-Nd isotope redistribution in apatite and
           accessory minerals in retrogressed lower crust material (Bergen Arcs,
           Norway)
    • Authors: Emilie Janots; Håkon Austrheim; Carl Spandler; Johannes Hammerli; Claudia A. Trepmann; Jasper Berndt; Valérie Magnin; Anthony I.S. Kemp
      Pages: 120 - 135
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): Emilie Janots, Håkon Austrheim, Carl Spandler, Johannes Hammerli, Claudia A. Trepmann, Jasper Berndt, Valérie Magnin, Anthony I.S. Kemp
      In the Bergen Arcs (Norway), Grenvillian granulite retrogressed under eclogite- and amphibolite-facies conditions during Caledonian subduction/collision offer a unique opportunity to investigate rare earth elements (REE) and Sm-Nd isotope redistribution in accessory minerals during fluid-assisted metamorphism. Our sampling targeted apatite-bearing REE-rich protoliths (mangerite and jotunite) that preserve distinct mineral assemblages, depending on the external fluid availability and metamorphic conditions. REE concentrations in apatite are the highest in the granulite. Two populations are present: magmatic apatite (Ap1) relics that occur as inclusions in ilmenite-hematite, and intergranular apatite (Ap2) formed under granulite-facies conditions. The presence of abundant needle-like monazite and sulphide inclusions in Ap2 indicate that granulite reactions were fluid assisted. A thin (typically <10μm) rim of REE-rich epidote (Ep1) commonly surrounds Ap2. In these accessory minerals, U and Th contents are too low, or grains are too small, for in situ U-Th-Pb dating. Sm-Nd isotope data of Ap2, monazite and Ep1 give an isochron age of 601±69Ma, which is interpreted to represent a partially reset Grenvillian age, affected by Caledonian fluid-assisted mineral growth. In amphibolitized samples, granulite Ap2 is replaced by apatite (Ap3) with lower REE contents and no monazite inclusions. The REE released by this replacement are redistributed in a corona of epidote group minerals (Ep2) surrounding Ap3. The in situ Sm-Nd isotope data for Ep2 and titanite, found in replacement of ilmenite-hematite, return an isochron age of 395±65Ma, recording the timing of amphibolite-facies mineral growth when fluids were introduced into the rock. In eclogitized samples, eclogitic apatite (Ap4) occurs as polycrystalline aggregates, suggesting for a complex replacement process during deformation. REE contents of Ap4 are low, as REE originally contained in the precursor apatite were redistributed mainly into zoisite. Apatite shielded as inclusions in ilmenite and garnet preserve the REE-rich signature of the initial magmatic (Ap1) and granulite (Ap2) apatite, indicating these grains did not undergo further re-equilibration during Caledonian metamorphism. The resistance of apatite to compositional re-equilibration in this case confirms the petrological potential of apatite inclusions shielded in chemically inert minerals to track early magmatic, or metamorphic, crystallisation stages.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2017.10.007
      Issue No: Vol. 484 (2018)
       
  • Juxtaposition of allochthonous terranes in the central Korean Peninsula:
           Evidence from zircon U-Pb ages and O-Hf isotopes in Jurassic granitoids
    • Authors: Hui Je Jo; Albert Chang-sik Cheong; Keewook Yi; Xian-Hua Li
      Pages: 136 - 147
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): Hui Je Jo, Albert Chang-sik Cheong, Keewook Yi, Xian-Hua Li
      The eventual docking of an exotic continental mass over the course of a Wilson cycle is marked by intracontinental sites of prograde metamorphism, contractional deformation, and syn- or post-collisional magmatism. This study shows that inherited premagmatic zircon in subsequently emplaced granitoid rocks provides another line of evidence for the collisional orogeny. Following the continental collision between the North and South China Cratons, Jurassic granitoids intruded widely throughout the central Korean Peninsula in association with the subduction of the Paleo-Pacific plate. The latest Early to Middle Jurassic (177–167Ma) granitoids occur throughout the cratonic Gyeonggi Massif, whereas Early Jurassic (194–184Ma) granitoids occur locally along the Okcheon Metamorphic Belt to the southeast of the massif. These two spatiotemporal groups differ profoundly in their age patterns and O-Hf isotopic signatures of inherited zircon. The younger group yields a typically North China-like Archean-Paleoproterozoic (mostly 2.5–1.8Ga) zircon inheritance. In contrast, inherited zircons from the older group exhibit exclusively Neoproterozoic (ca. 0.9–0.7Ga) and Paleozoic (ca. 0.4Ga) cluster along with Archean-Paleoproterozoic populations. The exotic feature of the protolith of the older group is further indicated by significantly lower δ18O (−0.9 to +4.9‰) and positive εHf (+3 to +15) values of the Cryogenian zircon cores. The results of zircon analysis demonstrate that South and North China-like terranes were juxtaposed infracrustally along the southeastern margin of the Gyeonggi Massif during the pre-Jurassic collisional orogeny, and then selectively provided major source material to the older and younger Jurassic granitoids, respectively.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2017.10.006
      Issue No: Vol. 484 (2018)
       
  • Timing and duration of regional metamorphism in the Kagasawa and Unazuki
           areas, Hida metamorphic complex, southwest Japan
    • Authors: Kenji Horie; Yukiyasu Tsutsumi; Mami Takehara; Hiroshi Hidaka
      Pages: 148 - 167
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): Kenji Horie, Yukiyasu Tsutsumi, Mami Takehara, Hiroshi Hidaka
      U–Pb zircon geochronology of two granite intrusions containing bluish‑tint K-feldspars and two biotite-hornblende gneisses in the Kagasawa area, situated at the center part of the Hida metamorphic complex, southwest Japan, reveals the early Triassic low P/T metamorphism in the Hida metamorphic complex (251–247Ma). The granite intrusions into the Hida gneiss occurred at two different stages (235.4±1.6Ma and 183.6±1.8Ma) and thermally affected the Hida gneiss. In the Unazuki area, situated at the northeast margin of the Hida metamorphic complex, a quartzo-feldspathic schist and a biotite granite containing a quartzo-feldspathic schist as xenolith yielded U–Pb zircon ages of 258.0±2.3Ma and 253.0±1.9Ma, respectively, which indicates that the medium P/T metamorphism in the Unazuki area occurred in late Permian. The similarity between the geochemical compositions in whole rocks and zircons of the quartzo-feldspathic schist and the granite suggests that felsic volcanics were deposited on basement rocks at 258Ma and, after affecting the medium P/T metamorphism, residual felsic magma was exhumed while taking the Unazuki schists as a xenolith at 253Ma. Although the time interval between protolith formation and post-peak regional metamorphism in the Unazuki area (0.8–9.2Ma) is similar to that in the Kagasawa area (1–8.6Ma), the different timing of the regional metamorphism indicates that the protolith of the Unazuki metasediments was deposited not on the proximal Hida metamorphic complex but on ancient rocks containing Eoarchean-Paleoproterozoic components of the North China Craton.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2017.12.016
      Issue No: Vol. 484 (2018)
       
  • New insight into disturbance of U-Pb and trace-element systems in
           hydrothermally altered zircon via SHRIMP analyses of zircon from the
           Duluth Gabbro
    • Authors: Mami Takehara; Kenji Horie; Tomokazu Hokada; Shoichi Kiyokawa
      Pages: 168 - 178
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): Mami Takehara, Kenji Horie, Tomokazu Hokada, Shoichi Kiyokawa
      Redistribution and retention behavior of major (Zr, Si, O, and Hf) and trace (Li, Al, P, K, Ca, Ti, Mn, Fe, rare earth elements (REE), Pb, U, and Th) elements in zircon during hydrothermal alteration were investigated by a sensitive high-resolution ion microprobe (SHRIMP). AS3 zircons collected from the Duluth Complex, U.S.A. were classified into three domains: Type-A comprise domains with a darker backscattered electron (BSE) and cathodoluminescence (CL) response; Type-B comprise domains with fine fractures, and; Type-C comprise domains where the dark response areas in CL are bright in BSE and vice versa, and are free of fractures. The Type-A domains are characterized by discordant U-Pb ages, light REE enrichment, depletion of Zr and Si, and higher contents of Ca, Mn, Fe, Al, Li, and K, which suggests that elemental redistribution occurred during hydrothermal alteration. Although the Type-B domains also show depletion of Zr and enrichments of Ca, Mn, Fe, Al, Li and K, the Zr contents and the contents of Ca, Mn, Fe, Al, Li, and K are higher and lower than those of the Type-A domains, respectively. This feature of the Type-B domains suggests existence of thin altered domains surrounding the fractures like “clads”. Therefore, there is a possibility that the Type-B domains are mixtures of the altered clads and unaltered domains. The Ca contents show a correlation with the Zr contents, which indicates that the Ca content is a suitable criterion for identifying hydrothermally altered zircon. There is no obvious correlation between Ca content and disturbance of the U-Pb system, but enrichment of some trace elements and REE's are correlated to the degree of Ca enrichment. The monovalent elements (Li and K) and the trivalent elements (especially light REE) are enriched at Ca contents of >1 ppm and >10 ppm, respectively. Mobility of the tetravalent elements (Hf and Ti) is increased at Ca contents >100 ppm. In spite of the elemental redistribution during the hydrothermal alteration, oxygen isotopic compositions are homogeneous through the three types of domains. Additionally, the contents of monovalent elements in zircon are potential indicators of the hydrothermal alteration of zircon.
      Graphical abstract image

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.01.028
      Issue No: Vol. 484 (2018)
       
  • Lu-Hf ratios of crustal rocks and their bearing on zircon Hf isotope model
           ages: The effects of accessories
    • Authors: F. Bea; P. Montero; J.F. Molina; J.H. Scarrow; A. Cambeses; J.A. Moreno
      Pages: 179 - 190
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): F. Bea, P. Montero, J.F. Molina, J.H. Scarrow, A. Cambeses, J.A. Moreno
      All other factors being equal, the calculation of zircon Hf two stage model ages (T DM Hf) depends on the particular Lu/Hf value assumed for the magmatic source, the effect being more pronounced as the age difference between zircon and magmatic source increases. It is generally considered that the Lu/Hf measured in the zircon-hosting rock does not represent the composition of the source because of potential garnet or zircon fractionation. Accordingly, most authors either assume a single fixed value for Lu/Hf source , often Lu/Hf≈0.079 to 0.108, or use two alternative models, one for felsic sources, often Lu/Hf≈0.09, and the other for mafic sources, often Lu/Hf≈0.165. In contrast with these opinions, however, here we show that partial melting of peraluminous sources causes little decoupling of Lu from Hf because of similar solubilities of zircon and monazite. Furthermore, the effects of residual garnet are largely compensated by the numerous zircon inclusions that garnet and other residual minerals almost always contain. Partial melting of metaluminous sources may significantly decouple Lu from Hf if allanite and/or titanite are not present in the source, but the effect decreases as the melt fraction increases. Similarly, fractional crystallization of metaluminous magmas may decouple Lu from Hf if amphibole or clinopyroxene begin to crystallize before zircon saturation. The Lu/Hf distribution in 4784 rocks from different regions and ages is lognomal rather than normal, and the calculated medians, i.e. the maximum of the probability density function for the logarithmically transformed Lu/Hf, are Lu/Hf mafic rocks ≈0.08, Lu/Hf felsic rocks ≈0.05, i.e. notably lower than the above-mentioned felsic and mafic magmatic source averages. Magmatic sources may be remarkably heterogeneous with respect to Lu/Hf. Our calculations show that fixed Lu/Hf source values translate the Lu/Hf heterogeneity of the source to the T DM Hf thus producing an artificial distribution of model ages that may be erroneously interpreted as different episodes of crustal growth. Therefore, we propose that the best strategy to calculate two stage Hf model ages of zircon is to use the analytically determined whole-rock Lu/Hf ratio as a proxy of the source. In the case of detrital or inherited zircons, for which no whole-rock information is available, it is advisable first to determine whether they come from a mafic or felsic rock by interpreting cathodoluminescence images, Th/U ratios and other chemical parameters, and then venture an estimate of the Lu/Hf source from the SiO2 average.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2017.11.034
      Issue No: Vol. 484 (2018)
       
  • Variscan post-collisional cooling and uplift of the Tatra Mountains
           crystalline block constrained by integrated zircon, apatite and titanite
           LA-(MC)-ICP-MS U-Pb dating and rare earth element analyses
    • Authors: Aleksandra Gawęda; Krzysztof Szopa; David Chew; Gary J. O'Sullivan; Jolanta Burda; Urs Klötzli; Jan Golonka
      Pages: 191 - 209
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): Aleksandra Gawęda, Krzysztof Szopa, David Chew, Gary J. O'Sullivan, Jolanta Burda, Urs Klötzli, Jan Golonka
      LA-ICP-MS U-Pb dating of apatite, titanite and zircon from the metamorphic cover of the Western Tatra granite was undertaken to constrain the timing of metamorphic events related to the final stages of Variscan orogenesis and subsequent post-orogenic exhumation. Zircon was found only in one sample from the northern metamorphic envelope. U-Pb ages from the outermost rims of zircons define a concordia age of 346 ± 6 Ma, while the inner rims yield a concordia age of 385 ± 8 Ma. Apatite from three samples from the northern metamorphic envelope yield U-Pb ages of 351.8 ± 4.4 Ma, 346.7 ± 5.9 Ma and 342.6 ± 7.1 Ma. Titanite from an amphibolite from the southern metamorphic envelope yields a U-Pb age of 345.3 ± 4.5 Ma. The age of c. 345 Ma is interpreted to represent the climax of metamorphism and the onset of simultaneous exhumation of the entire Tatra Mountains massif, and is recorded mainly in the northern part of the metamorphic cover. In the southern metamorphic envelope, distinct populations of apatite can be recognized within individual samples based on their rare earth element (REE) and actinide contents. One population of apatite (Ap1) yields a relatively imprecise U-Pb age of 340 ± 31 Ma. This population comprises apatite grains with very similar trace element compositions to apatite in the northern amphibolite samples, which suggests they crystallized under similar metamorphic conditions to their northern counterparts. A second apatite population (Ap2) yields an age of c. 328 ± 22 Ma, which is interpreted as neocrystalline apatite that formed during a late-Variscan (hydrothermal?) process involving (P, F, Ca, REE)-rich fluid migration. The youngest generation of apatite (Ap3) yields a U-Pb age of 260 ± 8 Ma and may have resulted from thermal resetting associated with the regional emplacement of Permian A-type granites. The proposed tectonic model assumes that rapid uplift (and cooling) of the Tatra block initiated at ca. 345 Ma, contemporaneous with anatexis. Subsequent fluid migration, possibly facilitated by extension related to the opening of Paleo-Tethys, affected only the southern part of the Tatra block.
      Graphical abstract image

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.012
      Issue No: Vol. 484 (2018)
       
  • Peak to post-peak thermal history of the Saglek Block of Labrador: A
           multiphase and multi-instrumental approach to geochronology
    • Authors: Monika A. Kusiak; Daniel J. Dunkley; Martin J. Whitehouse; Simon A. Wilde; Anna Sałacińska; Patrík Konečný; Krzysztof Szopa; Aleksandra Gawęda; David Chew
      Pages: 210 - 223
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): Monika A. Kusiak, Daniel J. Dunkley, Martin J. Whitehouse, Simon A. Wilde, Anna Sałacińska, Patrík Konečný, Krzysztof Szopa, Aleksandra Gawęda, David Chew
      The Saglek Block of coastal Labrador forms the western margin of the North Atlantic Craton, where Archean gneisses and granulites have been reworked during the Paleoproterozoic. Previous work has established that the block is a composite of Eoarchean to Mesoarchean protoliths metamorphosed to upper amphibolite and granulite facies at around 2.8–2.7Ga. New in-situ microbeam dating of accessory minerals in granoblastic gneisses reveals a complex peak to post-peak thermal history. Zircon growth at ca. 3.7–3.6Ga provides the age of formation of the tonalitic protoliths to the gneisses. Further zircon growth in syn-tectonic granitic gneiss and monazite growth in a variety of orthogneisses confirm peak metamorphic conditions at ca. 2.7Ga, but also reveal high-temperature conditions at ca. 2.6Ga and 2.5Ga. The former is interpreted as the waning stages of the 2.7Ga granulite event, whereas the latter is associated with a younger phase of granitic magmatism. In addition, apatite ages of ca. 2.2Ga may represent either cooling associated with the 2.5Ga event or a previously unrecognized greenschist-facies metamorphism event that predates the Torngat Orogeny.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2017.10.033
      Issue No: Vol. 484 (2018)
       
  • 87Sr/86Sr compositional linkage between geological and biological
           materials: A case study from the Toyota granite region of Japan
    • Authors: M. Minami; K. Suzuki
      Pages: 224 - 232
      Abstract: Publication date: 5 May 2018
      Source:Chemical Geology, Volume 484
      Author(s): M. Minami, K. Suzuki
      The strontium isotope value (87Sr/86Sr) is often used to identify the origins of agricultural products and the movements of ancient people. Maps delineating the distribution of 87Sr/86Sr values can therefore be of great use. Previous 87Sr/86Sr distribution maps of stream sediments covering small areas of Japan largely reflect the 87Sr/86Sr values of underlying bedrock. It remains unclear, however, whether the 87Sr/86Sr values of stream sediments may also reflect the 87Sr/86Sr values of the nearby vegetation and fauna. We sought to resolve this question by investigating the relationship between 87Sr/86Sr values in biological samples and in geological samples from the sites from which the biological samples grew. The geological samples consisted of soil samples from 2 paddy fields and 13 bed sediment samples (grain size <180 μm) from streams surrounding the paddy fields. All were collected from regions underlain by Inagawa granite bedrock, i.e., granite geology, around Toyota, Aichi Prefecture, Japan. The biological samples consisted of 4 rice plants and 1 wild boar bone, all collected in or near the same paddy fields. In the geological samples, the 87Sr/86Sr values of water-extracted Sr (water-soluble Sr) and ammonium-acetate-extracted Sr (exchangeable Sr) fractions in paddy soils were almost the same as each other (0.7098–0.7100) and slightly lower than the 87Sr/86Sr values of bulk Sr fractions (0.7099–0.7106). The 87Sr/86Sr values of biological samples (0.7098–0.7100) were also similar to those of the water-soluble Sr and exchangeable Sr fractions in paddy soils, though they varied among the parts of plants analyzed. This indicates that exchangeable Sr is absorbed by plants from soils through nutrients and water, and ingested by herbivorous animals from soils through plants and water. The 87Sr/86Sr values of bulk Sr in paddy soils ranged somewhat widely, while those from stream sediments collected around paddy fields were less variable (0.7099–0.7100). The difference in 87Sr/86Sr values between the paddy soils and stream sediments, samples similarly derived from Inagawa granite bedrock, may be related to the variable degree of weathering, and ultimately to the mineral composition, of the samples. This difference, however, was smaller than the range of 87Sr/86Sr values observed in the watershed geology. We therefore propose that in a silicate-dominated geology of the type typical of Japan, an 87Sr/86Sr spatial distribution map (using both exchangeable Sr and bulk Sr fractions in stream sediments) can provide useful guidance for identifying the geographic origins of food or for serving other related purposes.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.03.013
      Issue No: Vol. 484 (2018)
       
  • Geochemistry of sediments of the Peninsular rivers of the Ganga basin and
           its implication to weathering, sedimentary processes and provenance
    • Authors: Chinmaya Maharana; Deepika Srivastava; Jayant K. Tripathi
      Pages: 1 - 20
      Abstract: Publication date: 20 April 2018
      Source:Chemical Geology, Volume 483
      Author(s): Chinmaya Maharana, Deepika Srivastava, Jayant K. Tripathi
      Geochemistry of the Himalayan rivers has been a major point of contention in sedimentary geochemistry because of its global impact on ocean chemistry and climate. Among the Himalayan rivers, the Ganga and its Himalayan catchment have been studied extensively. However, the Peninsular rivers constituting a significant part of the Ganga basin have not received much attention, heretofore. In the present geochemical study of the Peninsular river's sediments, we have found that the initial chemical weathering of rocks in the catchment produces texturally, mineralogically and geochemically diverse sediments and fluvial processes further segregate them into the geochemically contrasting coarse channel and fine-grained suspended sediments. The overbank sediments possess an intermediate texture and geochemistry, but more towards the suspended sediments. The sediment geochemistry data indicates that the Peninsular river's sediments show an increase in the weathering intensity from the west (Banas river) to the east (Son river) along the climate gradient, i.e., from the arid-semiarid to the sub-tropical condition. The higher chemical index of alteration (CIA) values of the Peninsular river's sediments than the Yamuna and Ganga river sediments reflect the control of weatherable lithology in the tectonically stable, low relief and subtropical climate condition. The Yamuna and Ganga river sediments with lower CIA values show more physical weathering in the tectonically active Himalaya. The suspended and overbank sediments of the Yamuna and Ganga rivers show an increase in their CIA values after the confluence of the Peninsular rivers, indicating the contribution of more weathered materials by the Peninsular rivers. It has been found that there is a geochemical split between the channel and suspended sediments of the Peninsular rivers for sharing different sources, i.e., the dominant contribution of felsic sources to the channel and mafic sources to the suspended sediments. The weathering geochemistry, trace element systematics, and REE patterns suggest that the dominant sources of the channel sediments of the Peninsular rivers are the felsic crystallines and sedimentary lithologies of the Aravalli range, Bundelkhand and Chhotanagpur granite and gneisses, and Vindhyan sandstones. Whereas, the mafic lithologies such as the Deccan traps and mafic components of the felsic lithologies appear to be the major sources of the suspended sediments. Within the range of intermediate composition, the overbank sediment chemistry reflects more contribution of the mafic sources except for the Ken which shows a higher contribution of the felsic sources. The geochemical split between the channel and suspended sediments of the Peninsular river's sediments for the different provenances indicates differential weathering of the Deccan basalts, Bundelkhand crystalline, and Vindhyan sedimentary rocks; and also the hydrodynamic control of the Peninsular rivers during erosion, transport, and deposition. However, the Himalayan rivers do not show such contrast between the channel and suspended sediments because of the higher physical weathering and sediment mixing in the high gradient topography of the Himalayan catchment.

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.019
      Issue No: Vol. 483 (2018)
       
  • Visualization and quantification of Cd sorption to bacteria using confocal
           laser scanning microscopy and Cd-specific fluorescent probes
    • Authors: Clayton R. Johnson; Joshua D. Shrout; Jeremy B. Fein
      Pages: 21 - 30
      Abstract: Publication date: 20 April 2018
      Source:Chemical Geology, Volume 483
      Author(s): Clayton R. Johnson, Joshua D. Shrout, Jeremy B. Fein
      Understanding metal sorption to bacteria is important for developing bioremediation strategies, for determining the fate of contaminants in ground water systems, and for defining controls on microbial metabolic processes in the environment. X-ray absorption spectroscopy (XAS) has been the only technique available for quantifying and mapping metal sorption to bacteria on an individual cell scale, but the XAS approach is time consuming and expensive, and quantitative mapping of the distribution of metals in complex samples is difficult with XAS. The development of metal-specific fluorescent probes, in conjunction with confocal laser scanning microscopy (CLSM), represents a novel and more effective approach for visualizing and quantifying biosorption. In this study, we test and calibrate the use of a commercially available Cd- and Pb-specific probe, Leadmium Green (LG), to quantify the distribution of Cd in bacteria-bearing systems. We have developed a treatment technique that uses a combination of the stock LG molecule and a chemically de-esterified form of the LG molecule (DELG) which enables us to quantify bacterial sorbed Cd. In this approach, we correlate the green fluorescence from LG and DELG with the fluorescence at a different wavelength of SYTO 63 cell stain which enables us to visualize and quantify bacterial cell Cd sorption on both a community and individual cell level. This approach, for the first time, yields a means of easily quantifying and visualizing metal adsorption onto individual bacterial cells which allows us to directly measure the distribution of Cd in bacteria-bearing environmental systems. In this study, we report the results of a range of control experiments that demonstrate the efficacy of this approach. We demonstrate that our chemical de-esterification of LG results in 100% conversion of the LG to the DELG form that is fluorescently active, and that untreated LG is not fluorescently active until it enters the cell. We also demonstrate that calibration curves for samples containing cells, LG, DELG, SYTO 63, and Cd can be developed. Our tests also demonstrate that neither LG nor DELG cause significant changes in sorption of Cd to bacterial cells. We present results from experiments showing that Cd sorption to bacteria is highly heterogeneous between cells, a result which differs from the previously held assumption of homogeneous sorption. The results of this study yield new insights into metal adsorption behavior in bacteria-bearing systems and our approach represents a powerful tool for quantifying the distribution of metals in complex realistic environmental samples.
      Graphical abstract image

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.020
      Issue No: Vol. 483 (2018)
       
  • N-δ13C-inclusion profiles of cloudy diamonds from Koffiefontein: Evidence
           for formation by continuous Rayleigh fractionation and multiple fluids
    • Authors: S. Timmerman; A.L. Jaques; Y. Weiss; J.W. Harris
      Pages: 31 - 46
      Abstract: Publication date: 20 April 2018
      Source:Chemical Geology, Volume 483
      Author(s): S. Timmerman, A.L. Jaques, Y. Weiss, J.W. Harris
      Six diamonds with a fibrous core, intermediate zone and monocrystalline outer zone (“cloudy diamonds”) from the Koffiefontein mine, South Africa, were investigated for N concentrations, carbon isotope compositions and micro-inclusion compositions along core to rim traverses. This study evaluates the nature of the change from fibrous to gem diamond growth and the relation between major element composition of high density fluid inclusions and N − δ13C in fibrous growth zones. Three diamonds contain saline to carbonatitic fluid micro-inclusions with constant or increasing carbon isotope values which are inferred to have formed by varying amounts of Rayleigh fractionation in a closed system of a carbonate-bearing fluid. Continuous N − δ13C fractionation trends from the fibrous to gem growth zone in two of the diamonds and equally low nitrogen aggregation states indicate formation of diamond shortly before kimberlite eruption from a single fluid without a time gap between fibrous and gem diamond growth. High major element/CO3 2– ratios in the growth media resulted in a constant major element composition of the fluid inclusions found in the studied fibrous diamonds. The transition from fibrous to gem diamond growth is likely caused by the precipitation of diamond reducing the degree of oversaturation of carbon in the fluid and hence decreasing the rate of diamond growth. Two other diamonds have inclusions that change from silicate minerals in the inner fibrous growth zones towards pure saline fluid compositions in the outer fibrous growth zones. This decrease in Si, Mg and Ca and increase in K and Cl in the inclusions is accompanied by a decrease in δ13C values and N contents. These trends are suggested to be the result from gradually mixing in more saline fluids with lower δ13C values. One diamond with silicic inclusions has significant N aggregation into B-centres, suggesting this fluid is different and that diamond formation occurred significantly (e.g. 1250 °C gives ≥10 Ma) before the kimberlite eruption.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.02.024
      Issue No: Vol. 483 (2018)
       
  • The influence of organic complexation on Ni isotopic fractionation and Ni
           recycling in the upper soil layers
    • Authors: I.O. Zelano; C. Cloquet; F. Fraysse; S. Dong; N. Janot; G. Echevarria; E. Montargès-Pelletier
      Pages: 47 - 55
      Abstract: Publication date: 20 April 2018
      Source:Chemical Geology, Volume 483
      Author(s): I.O. Zelano, C. Cloquet, F. Fraysse, S. Dong, N. Janot, G. Echevarria, E. Montargès-Pelletier
      The quantification of Ni isotopic fractionation induced by Ni binding to organic acids is a preliminary step to better constrain the mechanisms determining Ni isotopic fingerprint observed in surface soils, waters and plants, as well as the contribution of metal recycling during plant litter degradation. In this study, Ni isotopic fraction induced by reaction with small organic acids, e.g. citric and oxalic acids, and with soil purified humic acids (PHA) was investigated at different Ni-L ratio and pH conditions. The Donnan Membrane Technique was used to separate Ni bound to organic ligands from the free metal. Obtained results highlighted that Ni binding with carboxylic groups produces, in the adopted experimental conditions, a Δ60Nibond-free < 0.2‰. This value is not high enough to justify neither metal fractionation previously observed between soil and hyperaccumulators, nor the fractionation between different plant parts, e.g. roots and leaves. In parallel, leaf degradation experiments of two hyperaccumulating plants, where Ni is mainly present as Ni-citrate, were performed to simulate litter decomposition and to highlight the contribution of plants on Ni isotopic composition in surface soils and waters. In the case of the hyperaccumulator Alyssum murale, the degradation process did not induce any observable fractionation. On the contrary, during Rinorea bengalensis degradation experiment, a fractionation between Ni leached out in the first 10 days and between 10 and 30 days was observed (Δ60Ni10–30day = 0.20 ± 0.05‰). The observed fractionation evidenced a heterogeneous distribution of Ni within the leaves, and/or distinct chemical bonding to the leaf cells, and finally suggested the influence of the chemical bonding on Ni isotopic signature. Although a precise quantification of plant contribution on Ni isotopic signature in surface soils and waters is still not reached, our results produced important progress to elucidate the role of organic matter in regulating Ni isotopic fingerprint in surface layers.
      Graphical abstract image

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.023
      Issue No: Vol. 483 (2018)
       
  • The microbial cycling of phosphorus on long-term fertilized soil: Insights
           from phosphate oxygen isotope ratios
    • Authors: Qing-Fang Bi; Bang-Xiao Zheng; Xian-Yong Lin; Ke-Jie Li; Xi-Peng Liu; Xiu-Li Hao; Han Zhang; Jia-Bao Zhang; Deb P. Jaisi; Yong-Guan Zhu
      Pages: 56 - 64
      Abstract: Publication date: 20 April 2018
      Source:Chemical Geology, Volume 483
      Author(s): Qing-Fang Bi, Bang-Xiao Zheng, Xian-Yong Lin, Ke-Jie Li, Xi-Peng Liu, Xiu-Li Hao, Han Zhang, Jia-Bao Zhang, Deb P. Jaisi, Yong-Guan Zhu
      Microorganisms mobilize phosphorus (P) from soil and make it available for plants. However, the role of microbial activity in soil P dynamics especially among different P pools is poorly understood largely due to methodological limitations. In this study, we analyzed the oxygen isotope ratios in phosphate (δ18OP) of sequentially extracted inorganic P (Pi) pools (H2O-Pi, NaHCO3-Pi, NaOH-Pi, and HCl-Pi) in a long-term agricultural research field in Henan, China with different fertilization histories and coupled with soil enzyme activity and P-cycling bacteria gene abundance studies. Results showed the dominant enzymes were alkaline phosphatase (APase) and phosphodiesterase (PDE), and the functional genes for P-cycling were bpp, cphy, phoX and pqqC. After long-term P fertilization, the δ18OP values of H2O-Pi, NaHCO3-Pi and NaOH-Pi pools approached to or achieved equilibrium, suggesting that the externally applied P was actively mobilized and cycled by soil microorganisms and speciated into different P pools. Based on the extent of isotope excursion among different Pi pools, the equilibrium fractionation oriented the source signature in the NaHCO3-Pi and NaOH-Pi pools, and HCl-Pi pool could be derived from P fertilizer but through multistep reactions, and mixed with the HCl-Pi from rock weathering product, which constituted HCl-Pi pool in the non-P treatments. Overall, the long-term P fertilization especially the balanced fertilization with nitrogen (N), P and potassium (K) was found to be beneficial for extensive utilization of soil P with abundant biological uptake and cell-internal Pi cycling. Variation partitioning analysis (VPA) indicated that the expression of functional genes may be stimulated to mobilize soil P under specific P pools distribution in this alkaline environment. Overall, our findings provide new insights to understand the roles of microbial activities in soil P biogeochemistry that are useful for agricultural P sustainability.
      Graphical abstract image

      PubDate: 2018-02-26T15:15:26Z
      DOI: 10.1016/j.chemgeo.2018.02.013
      Issue No: Vol. 483 (2018)
       
  • Evaluating the impact of Pb volatilization during 40Ar/39Ar CO2 laser
           fusion upon LA-ICP-MS measurement of Pb isotopic composition of detrital
           K-feldspar
    • Authors: Danielle Ziva Shulaker; Jeremy K. Hourigan; Marty Grove
      Pages: 78 - 87
      Abstract: Publication date: 20 April 2018
      Source:Chemical Geology, Volume 483
      Author(s): Danielle Ziva Shulaker, Jeremy K. Hourigan, Marty Grove
      The information provided by detrital studies can be greatly enhanced by coupling geochronology and isotopic measurements from the same grains. While accessory minerals like zircon and apatite have been widely exploited in this regard, modal phases have been under-utilized. The benefits of using K-feldspar in detrital studies are twofold: K-feldspar 40Ar/39Ar has shown promise as a detrital thermochronometer and incorporation of common Pb into K-feldspar allows its Pb isotope composition to be used as a provenance tool. In this paper, we quantitatively investigate the effects of laser fusion during 40Ar/39Ar analyses of K-feldspar upon subsequent LA-ICP-MS measurement of Pb isotopic ratios. The results reveal that significant Pb volatilization occurs during laser fusion of K-feldspar. While Pb isotopes do not appear to be significantly fractionated, counting statistics suffer as Pb concentrations are lowered. Conversely, neutron irradiation appears to have a small though inconsequential impact upon Pb isotopic measurement of K-feldspar. Consequently, K-feldspar can be analyzed for Pb isotopes prior to total fusion 40Ar/39Ar analysis. Despite this artifact, coupled 40Ar/39Ar and Pb isotopic measurements constitute a promising approach for provenance studies that seek to constrain the geochemical nature and thermal evolution of basement source regions.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.02.021
      Issue No: Vol. 483 (2018)
       
  • Impact of the cyanobacterium Gloeomargarita lithophora on the geochemical
           cycles of Sr and Ba
    • Authors: Marine Blondeau; Karim Benzerara; Céline Ferard; Jean-Michel Guigner; Mélanie Poinsot; Margot Coutaud; Mickaël Tharaud; Laure Cordier; Fériel Skouri-Panet
      Pages: 88 - 97
      Abstract: Publication date: 20 April 2018
      Source:Chemical Geology, Volume 483
      Author(s): Marine Blondeau, Karim Benzerara, Céline Ferard, Jean-Michel Guigner, Mélanie Poinsot, Margot Coutaud, Mickaël Tharaud, Laure Cordier, Fériel Skouri-Panet
      The cyanobacterium Gloeomargarita lithophora forms intracellular amorphous calcium carbonates and has been recently shown to accumulate Ca, Sr and Ba at a high level with a preference for Ba > Sr > Ca. This is of interest to the design of bioremediation strategies for Sr and/or Ba pollutions in aquatic systems. However, this preference has so far been evidenced at high dissolved Sr and Ba concentrations only, i.e. conditions rarely encountered in the environment. Here, we followed the uptake of alkaline earth metals (Mg, Ca, Sr and Ba) by G. lithophora in alkaline solutions with more environmentally-relevant, low Sr and Ba concentrations. Two settings were analyzed: 1) batch cultures in which alkaline earth metals were added only at the beginning; 2) cultures supplemented continuously with fragments of alkaline earth element-containing carbonate microbialites. The growth of G. lithophora was higher in the presence of microbialites, suggesting that some limiting elements, possibly P and/or Ca, were supplied by their dissolution. In the two settings, the concentration of dissolved Ca was in the micromolar range, while it was more than three orders of magnitude lower for Ba and Sr. In cultures with microbialite fragments, these low Sr and Ba concentrations resulted from an input by aragonite dissolution balanced by high Sr and Ba uptake by the cyanobacterial cells with high affinity. Thereby, the continuous supply of alkaline earth metals by microbialite dissolution increased the Sr and Ba content of the cyanobacterial intracellular carbonates over time. G. lithophora incorporated preferentially Ba and Sr over Ca even at very low Ba and Sr concentrations and despite the presence of Ca at a much higher concentration. Overall, this shows the capability of G. lithophora to impact the geochemical cycles of Sr and Ba by buffering dissolved Sr/Ca and Ba/Ca ratios at low levels.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.02.029
      Issue No: Vol. 483 (2018)
       
  • Synergies in elemental mobility during weathering of tetrahedrite
           [(Cu,Fe,Zn)12(Sb,As)4S13]: Field observations, electron microscopy,
           isotopes of Cu, C, O, radiometric dating, and water geochemistry
    • Authors: Juraj Majzlan; Stefan Kiefer; Julia Herrmann; Martin Števko; Jiří Sejkora; Martin Chovan; Tomáš Lánczos; Marina Lazarov; Axel Gerdes; Falko Langenhorst; Anežka Borčinová Radková; Heather Jamieson; Rastislav Milovský
      Abstract: Publication date: Available online 24 April 2018
      Source:Chemical Geology
      Author(s): Juraj Majzlan, Stefan Kiefer, Julia Herrmann, Martin Števko, Jiří Sejkora, Martin Chovan, Tomáš Lánczos, Marina Lazarov, Axel Gerdes, Falko Langenhorst, Anežka Borčinová Radková, Heather Jamieson, Rastislav Milovský
      Tetrahedrite [(Cu,Fe,Zn)12(Sb,As)4S13] is commonly present in many ore deposits and may be transferred to mining waste. Here, we describe the behavior of all elements in tetrahedrite during oxidative dissolution in a natural oxidation zone at Piesky (Slovakia), this being a long-term analogue of weathering of tetrahedrite-rich mining wastes. Electron microprobe work identified initial, early, advanced, and mature stages of weathering. The initial stages include formation of secondary covellite and chalcocite, the following stages only oxidic products, divided into greenish masses and brown veinlets. Both of them are nanocrystalline mixtures of minerals. The masses are Cu-Sb-As-rich and consist of a nanocrystalline pyrochlore phase. The veinlets are Fe-Sb-As rich and contain tripuhyite, goethite, and pyrochlores. Quantitative elemental budgets show that some elements (Zn, S, Ni, Co) are rapidly lost whereas others (especially Cu and As) are retained and form copper arsenates in the mature stages of weathering. About 10% As and almost 50% of Sb are lost during weathering, likely released into water; some Sb is stored in secondary minerals such as camérolaite, cualstibite, or tripuhyite. Light carbon isotopic composition (δ13C down to −11.1‰) document significant biological contribution for C in the secondary minerals. Copper isotopes become progressively heavier during weathering (from initial δ65Cu of −2.45‰ in tetrahedrite up to 4.3‰ in some azurite samples but −6.3‰ in covellite and chalcocite), documenting cyclic removal of light copper isotopes into covellite and chalcocite. The observation of elemental synergies during weathering of tetrahedrite shows that the solubility and mobility of As is controlled by copper arsenates, not by iron oxides, in an environment rich in tetrahedrite but poor in pyrite. Antimony, another element of environmental concern, is mostly released into water and creates low-concentration anomalies in stream sediments and soils.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.04.021
       
  • Redox zonation and organic matter oxidation in palaeogroundwater of
           glacial origin from the Baltic Artesian Basin
    • Authors: Joonas Pärn; Stéphane Affolter; Jüri Ivask; Sean Johnson; Kalle Kirsimäe; Markus Leuenberger; Tõnu Martma; Valle Raidla; Stefan Schloemer; Holar Sepp; Rein Vaikmäe; Kristine Walraevens
      Abstract: Publication date: Available online 24 April 2018
      Source:Chemical Geology
      Author(s): Joonas Pärn, Stéphane Affolter, Jüri Ivask, Sean Johnson, Kalle Kirsimäe, Markus Leuenberger, Tõnu Martma, Valle Raidla, Stefan Schloemer, Holar Sepp, Rein Vaikmäe, Kristine Walraevens
      Ordovician-Cambrian aquifer system (O-Cm) in the northern part of the Baltic Artesian Basin (BAB), Estonia, is part of a unique groundwater reservoir where groundwater originating from glacial meltwater recharge from the Scandinavian Ice Sheet is preserved. The distribution of redox zones in the anoxic O-Cm aquifer system is unusual. Strongly reducing conditions are found near the modern recharge area characterized by low concentrations of sulphate (<5 mg·L−1) and the presence of CH4 (up to 3.26 vol%). The concentrations of SO4 2− increase and concentrations of CH4 decrease farther down the groundwater flow path. Sulphate in fresh glacial palaeogroundwater originates probably from pyrite oxidation while brackish waters have gained their sulphate through mixing with relict saline formation waters residing in the deeper parts of the aquifer system. Stable isotopic composition of sulphate, especially relations between δ18OSO4-δ18Owater (∆18OSO4-H2O from +20.5 to +31.1‰) and δ34SSO4-δ34SH2S (∆34SSO4-H2S value of +47.9‰) support a widespread occurrence of bacterial sulphate reduction in fresh glacial palaeogroundwater. We propose, that the observed unusual redox zonation is a manifestation of two different flow systems in the O-Cm aquifer system: 1) the topographically driven flow system which drives the infiltration of waters through the overlying carbonate formation in the modern recharge area; 2) the relict flow system farther down the groundwater flow path which developed as a response to large hydraulic gradients imposed by the Scandinavian Ice Sheet in Pleistocene. Thus, the strongly reducing conditions surrounding the modern recharge area may show the extent to which post-glacial recharge has influenced the aquifer system. O-Cm aquifer system is an example of an aquifer that has not reached a near-equilibrium state with respect to present day flow conditions and still exhibits hydrogeochemical patterns established under the influence of a continental ice sheet in Pleistocene.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.04.027
       
  • Super-deep, TSR-controlled Phanerozoic MVT type Zn-Pb deposits hosted by
           Zechstein reservoir carbonate, Lower Saxony Basin, Germany
    • Authors: Marta Sośnicka; Volker Lüders
      Abstract: Publication date: Available online 24 April 2018
      Source:Chemical Geology
      Author(s): Marta Sośnicka, Volker Lüders
      The Earth's crust is endowed with outstanding mineral wealth, however, in the future near-surface ore deposits will become exhausted and mineral potential of deeper crustal levels will become a target for exploration. Knowledge of the fluid dynamics of deep-seated ore-forming systems in e.g. sedimentary basins is therefore crucial for developing genetic models, which would facilitate effective exploration of hidden orebodies. Here we utilized fluid inclusion and stable isotope analyses in order to decipher the ore-forming processes, which were responsible for deposition of considerable deep-seated (2.7–3.6 km) Zn-Pb mineralization in the Lower Saxony Basin (LSB). Massive sphalerite-rich stratiform/stratabound and vein-type mineralization in the LSB is hosted by Zechstein reservoir carbonate (Ca2). Our data show that ore deposition was controlled by mixing of reservoir H2S with hot (T = 125–208 °C), highly-saline (21–32 wt% NaCl equiv.) metalliferous fluids ascending from greater depth along fault zones. Sulfur isotope ratios of sulfides (δ34S = −12.5 to +8.5‰) and carbon isotope ratios of fluid inclusion gases (δ13CCH4 = −6.2 to −22.7‰; δ13CCO2 = −0.8 to −6.2‰) reveal compelling evidence for TSR (thermochemical sulfate reduction)-derived origin of H2S. The ore-forming fluids were expelled from an over-pressurized system during Late Cretaceous basin inversion. Depth estimates show that the Zn-Pb mineralization in the LSB formed considerably deeper (3.3–4.4 km) than any other Phanerozoic MVT Zn-Pb deposit and therefore they can be classified as a super-deep, TSR-controlled MVT end-member.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.04.025
       
  • Formation of epithermal Sn-Ag-(Zn) vein-type mineralization at the
           Pirquitas deposit, NW Argentina: Fluid inclusion and noble gas isotopic
           constraints
    • Authors: Louis Desanois; Volker Lüders; Samuel Niedermann; Robert B. Trumbull
      Abstract: Publication date: Available online 23 April 2018
      Source:Chemical Geology
      Author(s): Louis Desanois, Volker Lüders, Samuel Niedermann, Robert B. Trumbull
      The Pirquitas Sn-Ag-(Zn) deposit in northwestern Argentina is thought to be an analogue to the Miocene polymetallic epithermal Sn-Ag deposits of the southern Bolivian Tin Belt, but little is known in detail about the origin and evolution of ore-forming fluids at Pirquitas. This paper reports on a microthermometric study of fluid inclusions in quartz, sphalerite, Ag-Sn sulfides, and Ag-rich sulfosalts using transmitted near infrared and visible light, combined with noble gas isotope analyses of fluids released from mineral separates. The study focused on the vein-hosted mineralization, which formed during two major mineralization events, whereby the first event I comprises two stages (I-1 and I-2). All studied minerals exclusively contain aqueous two-phase inclusions, indicating that the ore-forming fluids did not undergo two-phase phase separation (boiling). Salinity of fluid inclusions in I-1 quartz that precipitated along with pyrite and pyrrhotite ranges between 0 and 7.5 wt% NaCl equiv. and homogenization temperatures (Th) are between 233 and 370 °C. Stage I-2 is characterized by abundant Sn-Ag-Pb-Zn-sulfides and a variety of Ag-rich sulfosalts. Fluid inclusions in stage I-2 Ag-Sn sulfides have salinities up to 10.6 wt% NaCl equiv. and Th between 213 and 274 °C. The deposition of stage I-2 ore is likely related to a new pulse of saline magmatic fluids to the hydrothermal system. The mineralization event II deposited the richest Ag ores at Pirquitas. Colloform sphalerite and pyrargyrite deposited during event II contain two-phase aqueous fluid inclusions with homogenization temperatures between 190 and 252 °C and salinities between 0.9 and 4.3 wt% NaCl equiv. Noble gas concentrations and isotopic compositions of ore-hosted fluid inclusions were determined from crushing hand-picked ore minerals from both mineralization events. With one exception, all samples yielded 3He/4He ratios between 1.9 and 4.1 Ra, which is within the range of published data from the volcanic arc and somewhat higher than typical values of meteoric water-derived hot-springs in the region. This demonstrates a significant contribution of magmatic fluids to the Pirquitas mineralization although no intrusive rocks are exposed in the mine region. Taking the noble gas evidence for a magmatic fluid source, we interpret the trends of decreasing Th and salinity values in fluid inclusions from events I and II to represent waning of the magmatic-hydrothermal system and/or increased admixing of meteoric water to the magmatic fluids.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.04.024
       
  • Introducing a geochemical screen to identify geologically meaningful U-Pb
           dates in fossil teeth
    • Authors: Stephanie Greene; Larry M. Heaman; S. Andrew DuFrane; Thomas Williamson; Philip J. Currie
      Abstract: Publication date: Available online 21 April 2018
      Source:Chemical Geology
      Author(s): Stephanie Greene, Larry M. Heaman, S. Andrew DuFrane, Thomas Williamson, Philip J. Currie
      Previous studies have shown that radiometric dating of fossils can be complicated by post-fossilisation alteration. A key challenge to obtaining geologically meaningful fossilisation dates in bioapatite is identifying regions that have remained relatively undisturbed since the time of fossilisation. In order to determine whether a geochemical indicator can be used to identify least-disturbed regions, we combine in situ trace element analysis and U-Pb geochronology of fossil teeth from the Arroyo Chijuillita Member, New Mexico, and the Dinosaur Park Formation, Alberta. The reliability of these U-Pb dates is supported by good agreement between the isotope dilution thermal ionization mass spectrometry (61.5 ± 1.6 Ma) and laser ablation ICP-MS (64.2 ± 2.4 Ma) dates for a targeted tooth region. Of fourteen teeth analyzed from these units, two record dates within uncertainty of the depositional age: one has a “diffusion” concave upward cross-sectional yttrium profile, the other a concave downward profile reflective of trace element loss. It was found for teeth from both units that smaller yttrium concentration ranges are correlated with younger U-Pb dates, likely the result of post-fossilisation alteration. A yttrium screen based on this relationship is proposed, and is found to be a better indicator of post-fossilisation open system behaviour in the samples analyzed than other geochemical features thought to be produced during fossilisation. This screen provides a new tool for identifying fossil material least disturbed since fossilisation, facilitating the use of bioapatite to date the time of diagenesis.

      PubDate: 2018-04-24T21:09:12Z
      DOI: 10.1016/j.chemgeo.2018.04.022
       
 
 
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