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Vacuum
5 August 2018
Editorial Board
Publication date: 5 August 2018
Source:Chemical Geology, Volume 492

5 August 2018
The adsorption behavior of thioarsenite on magnetite and ferrous sulfide
Publication date: 5 August 2018
Source:Chemical Geology, Volume 492 Author(s): Ying Wang, Xi Wu, Shaofeng Wang, Fan Xiao, Danni Zhang, Shuhua Yao, Yongfeng Jia Thioarsenite (TAsIII) is an important arsenic (As) species under sulfidic environments. Adsorption behavior of TAsIII on iron (Fe)-bearing minerals affects the transformation and the distribution of As at solid-liquid interface. In this study, we investigated the formation of TAsIII species in the mixed arsenite and sulfide (AsIII-S-II) solutions with different S/As ratios and adsorption behavior of TAsIII on the surface of magnetite (Fe3O4) and ferrous sulfide (FeS). It was found that the extent of S-substitution of TAsIII was enhanced with the increasing S/As molar ratio in the AsIII-S-II solutions. The adsorption experiments showed that As in the AsIII-S-II solutions was adsorbed to a less extent on two Fe minerals than that of AsIII in circumneutral to alkaline solutions, indicating that TAsIII has lower affinity to Fe3O4 and FeS. The adsorption of TAsIII on the surface of Fe3O4 led to hydrolyzation and AsIII is the main sorbed species. On the surface of FeS, the extent of S-substitution of TAsIII was promoted and As sulfide surface precipitate may form. Overall, the formation of TAsIII species is the vital factor affecting the redistribution of As between solid and aqueous phase in sulfidic environment.

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5 August 2018
Effect of Zn(II) coprecipitation on Mn(II)-induced reductive transformation of birnessite
Publication date: 5 August 2018
Source:Chemical Geology, Volume 492 Author(s): Shiliang Zhao, Yaneira A. Gonz
5 August 2018
Dwindling vanadium in seawater during the early Cambrian, South China
Publication date: 5 August 2018
Source:Chemical Geology, Volume 492 Author(s): Tao Han, Haifeng Fan, Hanjie Wen Elemental vanadium (V), an essentially redox-sensitive metal in seawater, has had a significant impact on the understanding of the evolution of the atmosphere-ocean system throughout the history of the Earth. In fact, the geochemical cycle of V in early Cambrian seawater may have had an influence on the Chengjiang Biota in South China; however, it has not yet been well established. Given the authigenic vanadium accumulation is sensitive to the redox conditions of seawater, here, to constrain the geochemical cycle of V in seawater during the early Cambrian, the Mo, U and total organic carbon (TOC) distributions with high-resolution samples from both the outer shelf and slope facies (e.g., the Duoding and Longbizui sections), are applied to evaluate the redox conditions of ambient seawater. The Mo-U relationships indicate that the redox conditions of the mid-depth seawater evolved in a systematic way in South China, transitioning from an Fe-Mn reduction zone to anoxic/intermittently euxinic states and then to oxic conditions during the early Cambrian. As a consequence, the authigenic V enrichment, constrained by the marine redox conditions, was mainly controlled by the Fe-Mn particulate shuttle and the reduction and adsorption of organic matter in anoxic/euxinic conditions. However, the decoupling among V, Mo, U and TOC under anoxic/euxinic conditions suggests a dwindling vanadium concentration in the early Cambrian seawater of South China. The scavenging efficiency of V from seawater is much higher than those of Mo and U under anoxic/euxinic conditions. Ultimately, these trace elements (e.g., Mo, U, and especially V) in seawater could effectively be regulated and adjusted to a reasonable level under the widespread anoxic/euxinic conditions. The drawdown of trace elements in seawater might provide an early-stage preparation of the marine environment for the subsequent Chengjiang Biota.

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5 August 2018
Decarbonation in the Ca-Mg-Fe carbonate system at mid-crustal pressure as a function of temperature and assimilation with arc magmas – Implications for long-term climate
Publication date: 5 August 2018
Source:Chemical Geology, Volume 492 Author(s): Laura B. Carter, Rajdeep Dasgupta Carbon is commonly locked in the crust in two carbonate minerals: 1) calcite; and 2) dolomite. Pure, dry calcite is thermally stable to high temperatures, but can be assimilated by melts ascending from the mantle to the surface. Dolomite can decarbonate at high temperatures in addition to being consumed by subarc magmas. In this study, experiments containing carbonate with compositions between dolomite and calcite (with minor iron) give evidence for decarbonation at temperatures as low as 800
5 July 2018
Condensation behaviour of volatile trace metals in laboratory benchtop fumarole experiments
Publication date: 5 August 2018
Source:Chemical Geology, Volume 492 Author(s): Rebecca Scholtysik, Dante Canil Volatile trace metals emitted from volcanoes condense in gas plumes and fumaroles. The transient nature of natural eruptions makes it challenging to isolate key variables affecting trace metal condensation in this complex natural system. To emulate these conditions in a controlled setting, we design a laboratory ‘benchtop’ fumarole to experimentally measure volatilization and condensation behaviour of volatile trace metals from magma. Synthetic silicate melt compositions in the Na2O-Al2O3-SiO2 and Na2O-Fe2O3-SiO2 systems doped with dissolved trace metals (V, Cu, Zn, As, Y, Mo, Cd, Sn, Tb, Pb and Bi) are degassed in a furnace at 900
5 July 2018
Editorial Board
Publication date: 5 July 2018
Source:Chemical Geology, Volume 491

5 July 2018
Sr and Mg isotope geochemistry of the basal Ediacaran cap limestone sequence of Mongolia: Implications for carbonate diagenesis, mixing of glacial meltwaters, and seawater chemistry in the aftermath of Snowball Earth
Publication date: 5 July 2018
Source:Chemical Geology, Volume 491 Author(s): Chao Liu, Zhengrong Wang, Francis A. Macdonald The seawater chemistry and oceanographic information associated with Snowball Earth are commonly inferred from the geochemistry of cap carbonates deposited on continental margins during and after deglaciation. However, interpretation of such records can be complicated by carbonate diagenesis and contamination from siliciclastic components. In an attempt to disentangle these effects, we studied the geochemistry of the post-Marinoan cap carbonate sequence from Mongolia using a step-leaching procedure, which revealed that most samples are heterogeneous with respect to multiple geochemical signatures, including trace element concentrations, Sr, Mg, C and O isotopic signatures, raising questions to previous studies applying carbonate bulk-rock geochemistry for paleoenvironment reconstructions. Such sample heterogeneity can be explained by contamination from non-carbonate phases and carbonate alteration. After stepped leaching, the least-altered/contaminated geochemical signatures for each sample were identified and the influences of carbonate diagenesis were evaluated. Our data indicate that mixing of glacial meltwater persisted to the maximum flooding surface within the cap carbonate sequence, below which carbonates record significant Mg and Sr isotope fluxuations that are most readily interpreted in the context of the mixing of water masses having distinct isotopic compositions. Only limestones deposited above the maximum flooding surface formed in a well-mixed ocean and exhibit Mg and Sr isotope values that record the integrated effects of Snowball Earth on ocean chemistry. Our study cautions against interpreting the geochemistry of cap carbonates in terms of whole ocean geochemical cycles.
5 July 2018
Position-specific carbon and hydrogen isotopic compositions of propane from natural gases with quantitative NMR
Publication date: 5 July 2018
Source:Chemical Geology, Volume 491 Author(s): Changjie Liu, Gregory P. McGovern, Peng Liu, Heng Zhao, Juske Horita Position-specific isotope compositions of light hydrocarbons are expected to provide valuable information on their formation and migration-degradation processes. Here we present a high-accuracy and high-precision (
5 July 2018
Sedimentary molybdenum cycling in the aftermath of seawater inflow to the intermittently euxinic Gotland Deep, Central Baltic Sea
Publication date: 5 July 2018
Source:Chemical Geology, Volume 491 Author(s): Florian Scholz, Matthias Baum, Christopher Siebert, S
5 July 2018
Evaluation of the effective bulk composition (EBC) during growth of garnet
Publication date: 5 July 2018
Source:Chemical Geology, Volume 491 Author(s): Frank S. Spear, Oliver M. Wolfe The effective bulk composition (EBC) for the initial growth of garnet that has nucleated only after considerable overstepping of the equilibrium garnet-in reaction has been calculated for eight samples from central Vermont. The method developed assumes that the composition of garnet is determined by the maximum driving force (maximum change in Gibbs free energy) at the assumed conditions of nucleation. The method of intersecting isopleths is used to find the EBC where the isopleth intersection matches the P–T conditions of nucleation. The calculated EBC for all samples (four epidote-free and four epidote-bearing) contains less MnO and FeO (or lower FeO/MgO) than the whole rock bulk composition. The CaO content of the EBC is lower than the whole rock bulk composition in all epidote-free samples and in two of the four epidote-bearing samples. It is proposed that the differences between the EBC and whole rock bulk composition are caused by the sluggish kinetics of dissolution of reactants rather than diffusive transport of nutrients to the garnet.
25 June 2018
Erratum to “Standardless fission-track ages of the IUGS age standards” [Chemical Geology 488 (5th June 2018) Pages 87-104]
Publication date: 5 July 2018
Source:Chemical Geology, Volume 491 Author(s): Hideki Iwano, Tohru Danhara, Takafumi Hirata
25 June 2018
Editorial Board
Publication date: 25 June 2018
Source:Chemical Geology, Volume 490

25 June 2018
Zircon grain selection reveals (de)coupled metamictization, radiation damage, and He diffusivity
Publication date: 25 June 2018
Source:Chemical Geology, Volume 490 Author(s): Alexis K. Ault, William R. Guenthner, Amy C. Moser, Gifford H. Miller, Kurt A. Refsnider Broad variability in intrasample effective U concentration (eU) in zircon crystals is required to characterize zircon (U-Th)/He (zircon He) date-eU relationships that resolve thermal histories in ancient rocks. We describe a new protocol for selecting grains for zircon He thermochronometry that leverages visual crystal metamictization, a proxy for radiation damage accumulation, to generate a range in intrasample eU and zircon He date-eU/metamictization trends. Plane polarized light images, eU concentration, and zircon He data from 59 individual grains from six Proterozoic and three Archean North American granitoids reveal a progressive increase in crystal opacity and discoloration that correspond to increasing eU in each sample. Zircon eU ranges from 89 to 1885
25 June 2018
Distribution, redox state and (bio)geochemical implications of arsenic in present day microbialites of Laguna Brava, Salar de Atacama
Publication date: 25 June 2018
Source:Chemical Geology, Volume 490 Author(s): Mar
25 June 2018
Secondary fluorescence effects in microbeam analysis and their impacts on geospeedometry and geothermometry
Publication date: 25 June 2018
Source:Chemical Geology, Volume 490 Author(s): Anastassia Y. Borisova, Nail R. Zagrtdenov, Michael J. Toplis, John J. Donovan, Xavier Llovet, Paul D. Asimow, Philippe de Parseval, Sophie Gouy Characteristic and bremsstrahlung X-ray emission during electron-specimen interactions in electron microprobe (EPMA) and scanning electron microscope (SEM) instruments causes secondary fluorescence X-ray effects from adjacent (boundary) phases. This is well-known, yet the impact of such effects in microbeam analysis of natural mineral-hosted inclusions and adjacent to mineral-mineral and mineral-glass boundaries are frequently neglected, especially in geospeedometry and geothermometry applications. To demonstrate the important influence of the secondary fluorescence effect on the measured concentration of elements and its consequences for geochemical applications, we consider the effect of mineral-mineral and mineral-glass boundaries in microanalysis of Cr, Zr and Ti both experimentally, using electron probe measurements on cold-pressed material couples, and computationally, using the software suite “CalcZAF/Standard” and its Graphical User Interface (GUI) for the semi-analytical model FANAL (Llovet et al., 2012). We demonstrate, for example, that apparent Cr contents of the order of ~3000 to 5000
25 June 2018
Degassing of organic carbon during regional metamorphism of pelites, Wepawaug Schist, Connecticut, USA
Publication date: 25 June 2018
Source:Chemical Geology, Volume 490 Author(s): Shuang Zhang, Jay J. Ague, Alberto Vitale Brovarone A comprehensive understanding of the degassing systematics of organic carbon (OC) during regional metamorphism is necessary to evaluate the role that metamorphism plays in the global carbon cycle. In this study, weight percentages and
20 June 2018
Links between seawater paleoredox and the formation of sediment-hosted massive sulphide (SHMS) deposits — Fe speciation and Mo isotope constraints from Late Devonian mudstones
Publication date: 25 June 2018
Source:Chemical Geology, Volume 490 Author(s): Joseph M. Magnall, Sarah A. Gleeson, Simon W. Poulton, Gwyneth W. Gordon, Suzanne Paradis Many models of sediment hosted massive sulphide (SHMS) deposit formation invoke basin restriction events that resulted in long-term stagnation and anoxia, in which sulphidic (euxinic) conditions ultimately prevailed. Euxinic conditions are then thought to provide a chemical trap for hydrothermally exhaled base metals. Here, we present Fe speciation and Mo isotope data for organic-rich mudstones from two drill-holes intersecting Upper Devonian strata, deposited along the passive margin of ancestral North America. One drill-hole intersects a 35
20 June 2018
Editorial Board
Publication date: 20 June 2018
Source:Chemical Geology, Volume 489

20 June 2018
Fate of particulate copper and zinc isotopes at the Solim
20 June 2018
Fractionation of the isotopes of boron between granitic melt and aqueous solution at 700
20 June 2018
Effect of rare earth elements on rice plant growth
Publication date: 20 June 2018
Source:Chemical Geology, Volume 489 Author(s): Raul E. Martinez, Olivier Pourret, Michel-Pierre Faucon, Charlotte Dian The goals of this study were, (1) to quantify the effects of rare earth elements (REE) on rice plant growth and (2) to determine whether the presence of iron (III) oxides on the plant root surface (i.e. the iron oxide plaques) played a role in impeding any toxic effects caused by the presence of the REE. Hydroponic experiments were designed to grow rice plants in a greenhouse under controlled conditions, exposed to all rare earth elements simultaneously, and to iron (II) sulfate or iron (II) chloride. The results showed a significant decrease in root and plant height and biomass at rare earth element concentrations of 0.5
20 June 2018
Distinct mineral weathering effectiveness and metabolic activity between mineral-weathering bacteria Burkholderia metallica F22 and Burkholderia phytofirmans G34
Publication date: 20 June 2018
Source:Chemical Geology, Volume 489 Author(s): Qi Wang, Shan Gao, Xiang Ma, Xinxin Mao, Linyan He, Xiafang Sheng Bacteria play important roles in mineral weathering, soil formation, and the cycling of elements. However, little is known regarding the interactions between silicate minerals and Burkholderia strains. In this study, mineral-weathering bacteria Burkholderia metallica F22 and B. phytofirmans G34 isolated from the rhizosphere soil of a dominant grass (Deyeuxia arundinacea L. Beauv) grown on mineral-rich and nutrient-poor soil were compared for their potash feldspar weathering and metabolic activities during the mineral weathering process. Although the two strains showed similar mobilization of Si, strain F22 demonstrated significantly higher Al (ranging from 41% to 143%) and Fe (ranging from 47% to 4.8-fold) mobilization from the mineral compared to strain G34. In addition, strain F22 produced higher gluconic acid (ranging from 68% to 24-fold) and exopolysaccharides (ranging from 57% to 2.2-fold) than strain G34. Significantly lower pH (ranging from 2.61 to 3.45) and higher dehydrogenase activity (ranging from 24% to 19-fold) were observed in the presence of strain F22 than in the presence of strain G34 during the mineral weathering process. Redundancy analysis illustrated strong positive correlations between the concentrations of gluconic acid and exopolysaccharides and the dissolved Al and Fe. These results demonstrated that the two mineral-weathering Burkholderia strains behaved differently with respect to mineral weathering and in their metabolic activities. The results also suggested that Burkholderia metallica F22 promoted potash feldspar weathering by increasing mineral weathering-related metabolic activities during the weathering process.
20 June 2018
On the Sr-Nd-Pb-Hf isotope code of enriched, Dupal-type sub-continental lithospheric mantle underneath south-western China
Publication date: 20 June 2018
Source:Chemical Geology, Volume 489 Author(s): T. Cheng, O. Nebel, P.A. Sossi, J. Wu, W. Siebel, F.K. Chen, Y.J. Nebel-Jacobsen Cenozoic intra-plate volcanism in Southwest China allows insights into modes of melting and the composition of the sub-continental lithospheric mantle (SCLM). The late Cenozoic Tengchong Volcanic Field (TVF), located in the Yunnan Province Northeast of the Himalayas, comprises a cluster of mafic continental intraplate lavas, represented by 68 volcanic cones and spanning an area of ca. 800
Available online 19 June 2018
Corrigendum to “The solubility of xenotime-(Y) and other HREE phosphates (DyPO4, ErPO4 and YbPO4) in aqueous solutions from 100 to 250 °C and psat” [Volume 401, 2015, pp. 83-95]
Publication date: 20 June 2018
Source:Chemical Geology, Volume 489 Author(s): Alexander P. Gysi, Anthony E. Williams-Jones, Daniel Harlov
Available online 19 June 2018
From supratidal to subtidal, an integrated characterisation of Carbla Beach shallow microbial mats (Hamelin Pool, Shark Bay, WA): Lipid biomarkers, stable carbon isotopes and microfabrics
Publication date: Available online 19 June 2018
Source:Chemical Geology Author(s): Chlo
Available online 19 June 2018
Advances in 3D imaging and volumetric reconstruction of fluid and melt inclusions by high resolution X-ray computed tomography
Publication date: Available online 19 June 2018
Source:Chemical Geology Author(s): Antonin Richard, Christophe Morlot, Laura Cr
Available online 18 June 2018
South African crustal fracture fluids preserve paleometeoric water signatures for up to tens of millions of years
Publication date: Available online 19 June 2018
Source:Chemical Geology Author(s): Andrew W. Heard, Oliver Warr, Gaetan Borgonie, Borja Linage, Olukayode Kuloyo, Jonathan W. Fellowes, Cara Magnabosco, Maggie C.Y. Lau, Mariana Erasmus, Errol D. Cason, Esta van Heerden, Thomas L. Kieft, Jennifer C. Mabry, Tullis C. Onstott, Barbara Sherwood Lollar, Chris J. Ballentine Fracture fluids in Earth's crust may remain isolated for millions to billions of years, and contain information on paleohydrogeology, subsurface microbial life, and conservative components that help elucidate the atmospheric evolution of the early Earth. Examples include fluids in the South African Kaapvaal craton which host chemolithoautotrophic microbial communities that survive independent of the photosphere, and billion-year-old fluids in the Canadian Shield, which preserve the Xe isotopic signature of an evolving early atmosphere. Stable isotope analyses of the aqueous phase combined with isotopic analyses of the dissolved noble gases provide unrivalled insight into the time-alteration history of aqueous fracture fluids. Here we report stable isotope and noble gas data for fracture fluids in the Witwatersrand Basin and Bushveld Igneous Province systems, South Africa. We determine closed-system radiogenic noble gas residence times of 0.77–97
Available online 15 June 2018
Concentrations, provenance and flux of aerosol trace elements during US GEOTRACES Western Arctic cruise GN01
Publication date: Available online 18 June 2018
Source:Chemical Geology Author(s): Chris M. Marsay, David Kadko, William M. Landing, Peter L. Morton, Brent A. Summers, Clifton S. Buck The Arctic region is undergoing significant changes in climate, with a notable decrease in summertime sea ice coverage over the past three decades. This trend means an increasing proportion of Arctic Ocean surface waters can receive direct deposition of material from the atmosphere, potentially influencing marine biogeochemical cycles and delivery of pollutants to the Arctic ecosystem. Here, we present aerosol concentrations of selected trace elements (Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) measured during the US GEOTRACES Western Arctic cruise (GN01, also known as HLY1502) in August–October 2015. Concentrations of “lithogenic” elements (Al, Ti, V, Mn, Fe, and Co) were similar to those measured in remote and predominantly marine-influenced air masses in previous studies, reflecting the remoteness of the Arctic Ocean from major dust sources. Concentrations of Ni, Cu, Zn, Pb, and Cd showed significant enrichments over crustal values, and were often of similar magnitude to concentrations measured over the North Atlantic in air masses of North American or European provenance. We use 7Be inventory and flux data from GN01 to estimate a bulk atmospheric deposition velocity during the study period, and combine it with our aerosol concentrations to calculate atmospheric deposition fluxes of the trace elements in the Arctic region during late summer. The resulting estimates for mineral dust and Fe deposition fall at the low end of global estimates and confirm the Arctic Ocean as a low-dust environment during the summer months. This article is part of a special issue: VSI: ConwayGEOTRACES - Edited by Catherine Chauvel.
Available online 15 June 2018
Properties of planetary silicate melts by molecular dynamics simulation
Publication date: Available online 15 June 2018
Source:Chemical Geology Author(s): Thomas Dufils, Nicolas Sator, Bertrand Guillot Because magmatic liquids play a fundamental role in the evolution of the terrestrial planets, a precise knowledge of their physical properties is requisite to better understand the formation and the dynamics of planetary interiors. In using an improved force field for silicates (Dufils et al., 2017), we report the results of a series of molecular dynamics simulations (MD) aiming to evaluate the equation of state (EOS), the viscosity, the electrical conductivity, and the elemental self-diffusion coefficients of various planetary melts representative of the Earth, Mars, the Moon and Mercury. The agreement between MD calculations and experimental data (when they exist) is remarkable, a finding which suggests that the MD simulations can be used on trust to extend the existing laboratory data on planetary melts (as it is proposed here for some lunar, martian and mercurian basalts) or to predict the thermo-physical properties of more exotic compositions (magma oceans, lava planets). Moreover, the MD simulations show that the evolution of the viscosity and of the electrical conductivity with the pressure depends in a complex manner on temperature and composition and that is difficult to extract general trends from these behaviors. Another advantage of the MD simulations is that the transport coefficients (viscosity, conductivity, and diffusivities) being evaluated along the same numerical experiment, one is able to test the validity of the Eyring and the Stokes-Einstein equations relating viscosity and diffusivity, as also as the Nernst-Einstein equation expressing the conductivity as function of the ionic diffusivities. It is shown that the Stokes-Einstein equation is suitable to describe planetary melts of low viscosity (
Available online 15 June 2018
Numerical models of P–T, time and grain-size controls on Ar diffusion in biotite: An aide to interpreting 40Ar/39Ar ages
Publication date: Available online 15 June 2018
Source:Chemical Geology Author(s): D.R. Skipton, C.J. Warren, F. Hanke Dating of biotite using the 40Ar/39Ar method is used extensively to determine the timing of cooling and exhumation in metamorphic rocks. Interpretations of 40Ar/39Ar dates commonly assume that 40Ar diffuses out of biotite through temperature-dependent volume diffusion, and therefore that the date represents the time at which biotite cooled through a closure temperature. Several processes, however, may perturb Ar systematics such that the 40Ar/39Ar date does not uniquely represent the timing of cooling through a closure temperature, including incomplete re-setting of Ar systematics, incorporation of excess Ar, crystal defects acting as Ar traps or fast-pathways, or fluid-present recrystallization/dissolution. We present a series of numerical diffusion model results that show the percentage of radiogenic Ar that should theoretically be retained in biotite with different grain radii residing for various periods over a range of P–T conditions, in a perfect open system that loses Ar via volume diffusion alone. A second set of models demonstrates the effects of different cooling rates on biotite 40Ar/39Ar dates and intra-grain Ar distributions in a perfect open system. The model results are useful for constraining cooling and exhumation histories from 40Ar/39Ar biotite data in a variety of metamorphic settings. They also provide baseline data for biotite 40Ar retention, 40Ar/39Ar ages and intra-grain age distributions that would theoretically be produced from volume diffusion acting alone. Consequently, the models can help evaluate the plausibility of alternative scenarios that may have affected biotite 40Ar/39Ar dates, including extraneous Ar contamination or Ar loss via processes other than diffusion. In conjunction with well-constrained petrogenetic histories, numerical diffusion models are a powerful tool for interpreting 40Ar/39Ar biotite ages, especially when linked with intra-grain 40Ar/39Ar age profiles.
Available online 12 June 2018
High-temperature calorimetric measurements of thermodynamic properties of uranyl arsenates of the meta-autunite group
Publication date: Available online 15 June 2018
Source:Chemical Geology Author(s): Ewa A. Dzik, Haylie L. Lobeck, Lei Zhang, Peter C. Burns Five uranyl arsenates of the meta-autunite group with mono (Li, K, Cs) and divalent (Sr and Cu) cations were synthesized at room temperature and characterized. Their thermodynamic properties were measured using high-temperature oxide melt calorimetry in a molten 3Na2O·4MoO3 solvent at 976
Available online 8 June 2018
Precision analysis of multisulfur isotopes in sulfides by femtosecond laser ablation GC-IRMS at high spatial resolution
Publication date: Available online 12 June 2018
Source:Chemical Geology Author(s): Alexander V. Ignatiev, Tatiana A. Velivetskaya, Sergey Y. Budnitskiy, Victoria V. Yakovenko, Sergey V. Vysotskiy, Valery I. Levitskii A new laser ablation method has been developed for measurements of multiple sulfur isotopes in sulfides using a femtosecond laser ablation system in combination with a reactor for sulfide aerosol conversion into SF6 gas, a cryogenic and chromatographic purification system, and an isotope ratio mass spectrometer (FsLA-GC-IRMS). In this method, femtosecond laser-generated aerosol sulfide particles were transferred by the helium carrier gas from the sample chamber into the reactor to convert them to SF6 via reaction with BrF5. Cryogenically and chromatographically purified SF6 was transferred by helium carrier gas to the interface that was developed for introducing SF6 into the ion source of a mass spectrometer running in high-vacuum operation mode. For the routine analysis of sulfide, a precision of 0.1–0.2‰ (1
Available online 7 June 2018
The physical and chemical evolution of fluids in rare-element granitic pegmatites associated with the Lacorne pluton, Qu
5 June 2018
Trace elements and U-Pb ages in petrified wood as indicators of paleo-hydrologic events
Publication date: Available online 7 June 2018
Source:Chemical Geology Author(s): Hehe Jiang, Cin-Ty Lee, William G. Parker Subsurface fluid systems are important for chemical weathering, ore formation and thermal evolution of the crust. Changes in the dynamics and distribution of subsurface fluid flow systems are controlled by changes in global and regional terrestrial climate, tectonics, and elevation. This paper concerns the dating of changes in ancient subsurface hydrologic systems. However, direct dating of water-rock interaction is challenging because of the lack of appropriate materials to date and the more open and complex nature of subsurface flow regimes. Here, we explore the prospects of using U-Pb dating of petrified (silicified) wood as a means of quantifying continental paleo-hydrology. Oxidizing fluids, often of meteoric origin, tend to leach and mobilize U from the country rock, but when such waters contact organic-rich material, U can become reduced and immobilized, resulting in U-rich silicified wood. We present in situ laser ablation ICPMS analyses of U-Pb isotopes and trace elements in petrified wood from the Upper Triassic Chinle Formation (225–208
5 June 2018
Editorial Board
Publication date: 5 June 2018
Source:Chemical Geology, Volume 488

5 June 2018
Theoretical calculation of equilibrium Mg isotope fractionations between minerals and aqueous solutions
Publication date: 5 June 2018
Source:Chemical Geology, Volume 488 Author(s): Caihong Gao, Xiaobin Cao, Qi Liu, Yuhong Yang, Siting Zhang, Yuyang He, Mao Tang, Yun Liu There are large discrepancies existing in equilibrium Mg isotope fractionation calculations and experimental investigations for cases related to mineral vs. solution. To clarify this confusing issue, a newly designed cluster-model-based quantum chemistry method, i.e., volume variable cluster model (VVCM), is used to provide equilibrium Mg isotope fractionation factors between Mg-bearing carbonates (calcite, aragonite, dolomite and magnesite), amorphous calcium carbonates (ACCs), brucite and aqueous species (i.e., Mg2+ (aq), MgHCO3 + (aq) and MgOH+ (aq)). We find that local configuration sampling of aqueous species is essential to provide precise fractionations between mineral and solution. The phonon-based periodic boundary method is also used for several minerals and it obtains very similar fractionations with VVCM results. Our results are very close to those of Pinilla et al. (2015) although via completely different approaches. Both of them have included the effect of local configuration disorder. However, both of them are significantly different from some of experimental results for cases of carbonates vs. solutions. The existence of various Mg-bearing species in fluids of experiments, the direct incorporation of hydrated Mg2+ into the solids, the Mg2+ concentration effect, and the existence of intermediate precursors (e.g., ACCs) are several possible causes for the mismatches. Relative to coexisting aqueous Mg2+, we find that ACCs will enrich heavy Mg isotopes, i.e., ~1.45‰ at 25
5 June 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
Publication date: 5 June 2018
Source:Chemical Geology, Volume 488 Author(s): Juraj Majzlan, Stefan Kiefer, Julia Herrmann, Martin
5 June 2018
Apatite (U-Th-Sm)/He thermochronology on the wrong side of the tracks
Publication date: 5 June 2018
Source:Chemical Geology, Volume 488 Author(s): Paul Green, Ian Duddy Despite the increasing application of apatite (U-Th-Sm)/He thermochronology in a range of settings, the technique suffers from two major unresolved problems which preclude reliable thermal history interpretations on a routine basis. One problem is the common but unexplained over-dispersion of single grain ages compared to predictions based on accepted models of diffusion systematics (including enhanced He retentivity due to the buildup of radiation damage in the apatite crystal lattice). A second related problem is that the widely adopted “RDAAM” model does not provide an accurate representation of the degree to which helium retentivity is enhanced as a result of the accumulation of radiation damage. Until these problems are resolved and eliminated, thermal history interpretations derived from this method cannot be regarded as reliable. Routine application of the technique requires a more rigorous quantitative understanding of these factors. Further experimental studies are required to identify all significant sources of variation in measured ages and to develop more accurate models of the thermal response of the system, combined with rigorous calibration and validation against independent methods in well-constrained natural settings. Only once this is achieved will the technique be capable of producing robust and reliable interpretations.
5 June 2018
Spatial and temporal distribution of rare earth elements in the Neuse River, North Carolina
Publication date: 5 June 2018
Source:Chemical Geology, Volume 488 Author(s): Coley Smith, Xiao-Ming Liu Rare earth elements (REEs) signatures in the dissolved loads of rivers serve as excellent monitors of weathering processes within a basin. However, quantifying REE behavior spatially (along a river's profile) and temporally (seasonable variations) is rare. This investigation reports REE concentrations of dissolved river loads collected during four sampling seasons at five monitoring stations along the Neuse River, North Carolina. The areal percentage of the Neuse River's catchment lithology composition, Post Archean Australian Shale (PAAS) normalized REE patterns, inter-REE ratios, and calculated anomalous REE values (i.e. cerium anomaly, gadolinium anomaly) were determined at each site in four seasons over a year. Our results show slight differences among inter-REE relationships and anomalous REE values in the dissolved loads along the length of the river. PAAS normalized REE patterns of dissolved water loads vary slightly spatially and temporally among the five sampling stations, and experience varying values of anomalous REE values. Collected data indicates that both variations in localized REE patterns and local bedrock occur along the river profile. Significant gadolinium (Gd) anomalies varied seasonally and spatially at select sites, suggesting changes in REE behavior along a river result from both natural and anthropogenic processes.
5 June 2018
Estimating silicate weathering timescales from geochemical modeling and spring water residence time in the Kirishima volcanic area, southern Japan
Publication date: 5 June 2018
Source:Chemical Geology, Volume 488 Author(s): Kiyoshi Ide, T. Hosono, S. Hossain, J. Shimada Kyushu Island in southern Japan is located within an area subjected to one of the highest rates of chemical weathering in the world. This area is purported to have the highest discharge rate of dissolved silica and other cations within the Japanese Island arc. To understand the timescale of chemical weathering in such a weathering ‘hot spot’, details of water–rock interaction are characterized using a conventional geochemical model for the Kirishima volcanic area. The model is focused on source water (spring water) with different residence times previously estimated by chlorofluorocarbons (CFCs) concentration analysis. The geochemical and geological features of the spring water samples suggest that the primary reactant minerals are pyroxenes and plagioclase. It was also found from activity-diagram analysis that kaolinite and Ca-smectite are the major precipitable secondary minerals from the system. The occurrence of these reactions was quantitatively confirmed by stoichiometric calculations of measured dissolved ions. In combination with previous estimates of spring water residence ages, it is concluded that saturation of dissolved silica and simultaneous transition of phase precipitation from kaolinite to Ca-smectite starts in ca. 20
5 June 2018
Improved calibration of the Sr/Ca-temperature relationship in the sclerosponge Ceratoporella nicholsoni: Re-evaluating Sr/Ca derived records of post-industrial era warming
Publication date: 5 June 2018
Source:Chemical Geology, Volume 488 Author(s): Amanda J. Waite, Peter K. Swart, Brad E. Rosenheim, Angela D. Rosenberg Although the Sr/Ca ratio in the skeletons of sclerosponges appears to be robustly correlated with water temperature, the measurement of Sr/Ca ratios from several specimens by different workers yields unexpectedly large (up to 5
5 June 2018
Mineralogy and geochemistry of modern Yellow River sediments: Implications for weathering and provenance
Publication date: 5 June 2018
Source:Chemical Geology, Volume 488 Author(s): Hongli Pang, Baotian Pan, Eduardo Garzanti, Hongshan Gao, Xin Zhao, Dianbao Chen This study illustrates the textural, mineralogical and geochemical signatures of sediments from the upper Yellow River. Sediments of major tributaries have also been examined to study the influence of provenance, weathering intensity, and hydraulic sorting on the spatial compositional variability of sediments. Similarly to floodplain sediments, riverbed deposits are strongly depleted in MgO and Na2O, and enriched in CaO and Si2O relative to the upper-continental-crust standard. The pattern of rare earth elements (REE) indicates LREE enrichment and negative Eu anomaly (Eu/Eu*
5 June 2018
Standardless fission-track ages of the IUGS age standards
Publication date: 5 June 2018
Source:Chemical Geology, Volume 488 Author(s): Hideki Iwano, Tohru Danhara, Takafumi Hirata Standardless fission-track ages for four zircon, two titanite and three apatite age standards, most of them recommended by the Fission Track Working Group of the IUGS Subcommission on Geochronology, were redetermined. The age calculations used the decay constant for spontaneous fission of 238U (
5 June 2018
Helium incorporation and diffusion in polycrystalline olivine
Publication date: 5 June 2018
Source:Chemical Geology, Volume 488 Author(s): R
5 June 2018
A multistage origin for Neoarchean layered hematite-magnetite iron formation from the Weld Range, Yilgarn Craton, Western Australia
Publication date: 5 June 2018
Source:Chemical Geology, Volume 488 Author(s): Andrew D. Czaja, Martin J. Van Kranendonk, Brian L. Beard, Clark M. Johnson The origins of iron formations remain somewhat enigmatic despite much progress over the past decades. This is due in part to continuing research demonstrating that these deposits do not have a single origin but rather can be formed under various and variable conditions. This study describes a formation pathway for an Algoma-type banded iron formation (BIF) from the 2.75 billion-year-old Weld Range of Western Australia, based on petrographic and Fe isotope analyses of drill core samples. The BIF is composed of alternating layers of jaspilitic and Fe-poor chert, magnetite layers of varying thickness and abundance, and rare pyrite. Petrographic analysis indicates the minerals formed in the order hematite, magnetite, and then pyrite, with the latter two clearly replacive of “primary” bedded hematite. Hematite
5 June 2018
Cretaceous calcareous dinoflagellate cysts as recorder of
5 June 2018
Redox zonation and organic matter oxidation in palaeogroundwater of glacial origin from the Baltic Artesian Basin
Publication date: 5 June 2018
Source:Chemical Geology, Volume 488 Author(s): Joonas P
5 June 2018
Symbiosis mechanism of iron and manganese oxides in oxic aqueous systems
Publication date: 5 June 2018
Source:Chemical Geology, Volume 488 Author(s): Yao Luo, Jiayu Ding, Yougang Shen, Wenfeng Tan, Guohong Qiu, Fan Liu Iron and manganese oxides are ubiquitous in soils and sediments, and their formation and conversion processes affect the migration and transformation of heavy metals and organic pollutants. Mn2+ was found to affect the formation of iron oxides from Fe2+ oxidation. However, little attention has been paid to the oxidation process at the initial stage and generation of manganese oxides in the reaction system of Fe2+ aq and Mn2+ aq. This work investigated the formation process and mechanism of iron and manganese oxides in a mixed solution system of Fe2+ aq and Mn2+ aq under oxic condition. The effect of pH (5.0–9.0) on the reaction process and products was further studied. The results indicated that Fe2+ aq was oxidized to goethite and lepidocrocite, and Mn2+ adsorbed on the surface of iron oxides was catalytically oxidized to poorly crystalline manganese oxides by dissolved O2 in a mixed solution of Fe2+ aq and Mn2+ aq. Compared with the absence of Mn2+ aq, the presence of Mn2+ aq caused no obvious changes in the species of iron oxides, but significantly increased the oxidation rate of Fe2+ aq. Formation of manganese oxides on the surface decreased the crystallinity of the iron oxides. The increase of pH enhanced the oxidation of Fe2+ aq and Mn2+ aq and formation of lepidocrocite. This work expands our understanding of the interactions and geochemical processes of Fe2+ aq and Mn2+ aq.

Graphical abstract

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Comparison of precipitation collectors used in isotope hydrology
Publication date: 5 June 2018
Source:Chemical Geology, Volume 488 Author(s): Nils Michelsen, Robert van Geldern, Yasmin Ro
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