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Water Research
15 February 2018
Sorption of Sr, Co and Zn on illite: Batch experiments and modelling including Co in-diffusion measurements on compacted samples
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): V. Montoya, B. Baeyens, M.A. Glaus, T. Kupcik, M. Marques Fernandes, L. Van Laer, C. Bruggeman, N. Maes, T. Sch
15 February 2018
Spatially-resolved isotopic study of carbon trapped in
15 February 2018
Metal endowment reflected in chemical composition of silicates and sulfides of mineralized porphyry copper systems, Urumieh-Dokhtar magmatic arc, Iran
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Alireza Zarasvandi, Mohsen Rezaei, Johann G. Raith, Houshang Pourkaseb, Sina Asadi, Madineh Saed, David R. Lentz The present work attempts to discriminate between the geochemical features of magmatic-hydrothermal systems involved in the early stages of mineralization in high grade versus low grade porphyry copper systems, using chemical compositions of silicate and sulfide minerals (i.e., plagioclase, biotite, pyrite and chalcopyrite). The data indicate that magmatic plagioclase in all of the porphyry copper systems studied here has high An% and Al content with a significant trend of evolution toward AlAl3SiO8 and
15 February 2018
Zircon/fluid trace element partition coefficients measured by recrystallization of Mud Tank zircon at 1.5
15 February 2018
Ruthenium isotope fractionation in protoplanetary cores
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Timo Hopp, Mario Fischer-G
15 February 2018
Screening apatites for (U-Th)/He thermochronometry via continuous ramped heating: He age components and implications for age dispersion
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Kalin T. McDannell, Peter K. Zeitler, Darwin G. Janes, Bruce D. Idleman, Annia K. Fayon Old slowly-cooled apatites often yield dispersed (U-Th)/He ages for a variety of reasons, some well understood and some not. Analytical protocols like careful grain selection can reduce the impact of this dispersion but add costs in time and resources and too often have proven insufficient. We assess a new analytical protocol that utilizes static-gas measurement during continuous ramped heating (CRH) as a means to rapidly screen apatite samples. In about the time required for a conventional total-gas analysis, this method can discriminate between samples showing expected volume-diffusion behavior and those showing anomalous release patterns inconsistent with their direct use in thermochronologic applications. This method also appears able to discriminate between the radiogenic and extraneous 4He fractions released by a sample, potentially allowing ages to be corrected. Well-behaved examples such as the Durango standard and other apatites with good age reproducibility show the expected smooth, sigmoidal gas-release curves predicted for volume diffusion using typical apatite kinetics, with complete exhaustion by
15 February 2018
Effects of iron-containing minerals on hydrothermal reactions of ketones
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Ziming Yang, Ian R. Gould, Lynda B. Williams, Hilairy E. Hartnett, Everett L. Shock Hydrothermal organic transformations occurring in geochemical processes are influenced by the surrounding environments including rocks and minerals. This work is focused on the effects of five common minerals on reactions of a model ketone substrate, dibenzylketone (DBK), in an experimental hydrothermal system. Ketones play a central role in many hydrothermal organic functional group transformations, such as those converting hydrocarbons to oxygenated compounds; however, how these minerals control the hydrothermal chemistry of ketones is poorly understood. Under the hydrothermal conditions of 300
15 February 2018
Thermochemical sulphate reduction can improve carbonate petroleum reservoir quality
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Lei Jiang, Richard H. Worden, Changbing Yang Interest in the creation of secondary pore spaces in petroleum reservoirs has increased because of a need to understand deeper and more complex reservoirs. The creation of new secondary porosity that enhances overall reservoir quality in deeply buried carbonate reservoirs is controversial and some recent studies have concluded it is not an important phenomenon. Here we present petrography, geochemistry, fluid inclusion data, and fluid-rock interaction reaction modeling results from Triassic Feixianguan Formation, Sichuan Basin, China, core samples and explore the relative importance of secondary porosity due to thermochemical sulphate reduction (TSR) during deep burial diagenesis. We find that new secondary pores result from the dissolution of anhydrite and possibly from dissolution of the matrix dolomite. Assuming porosity before TSR was 16% and the percentage of anhydrite was 6%, modelling shows that, due to TSR, 1.6% additional porosity was created that led to permeability increasing from 110
15 February 2018
Clumped isotopologue constraints on the origin of methane at seafloor hot springs
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): David T. Wang, Eoghan P. Reeves, Jill M. McDermott, Jeffrey S. Seewald, Shuhei Ono Hot-spring fluids emanating from deep-sea vents hosted in unsedimented ultramafic and mafic rock commonly contain high concentrations of methane. Multiple hypotheses have been proposed for the origin(s) of this methane, ranging from synthesis via reduction of aqueous inorganic carbon (
15 February 2018
Equilibrium and non-equilibrium controls on the abundances of clumped isotopologues of methane during thermogenic formation in laboratory experiments: Implications for the chemistry of pyrolysis and the origins of natural gases
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Yanhua Shuai, Peter M.J. Douglas, Shuichang Zhang, Daniel A. Stolper, Geoffrey S. Ellis, Michael Lawson, Michael D. Lewan, Michael Formolo, Jingkui Mi, Kun He, Guoyi Hu, John M. Eiler Multiply isotopically substituted molecules (‘clumped’ isotopologues) can be used as geothermometers because their proportions at isotopic equilibrium relative to a random distribution of isotopes amongst all isotopologues are functions of temperature. This has allowed measurements of clumped-isotope abundances to be used to constrain formation temperatures of several natural materials. However, kinetic processes during generation, modification, or transport of natural materials can also affect their clumped-isotope compositions. Herein, we show that methane generated experimentally by closed-system hydrous pyrolysis of shale or nonhydrous pyrolysis of coal yields clumped-isotope compositions consistent with an equilibrium distribution of isotopologues under some experimental conditions (temperature–time conditions corresponding to ‘low,’ ‘mature,’ and ‘over-mature’ stages of catagenesis), but can have non-equilibrium (i.e., kinetically controlled) distributions under other experimental conditions (‘high’ to ‘over-mature’ stages), particularly for pyrolysis of coal. Non-equilibrium compositions, when present, lead the measured proportions of clumped species to be lower than expected for equilibrium at the experimental temperature, and in some cases to be lower than a random distribution of isotopes (i.e., negative
15 February 2018
Post-collisional alkaline magmatism as gateway for metal and sulfur enrichment of the continental lower crust
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Marco L. Fiorentini, Crystal LaFlamme, Steven Denyszyn, David Mole, Roland Maas, Marek Locmelis, Stefano Caruso, Thi-Hao Bui Mafic and ultramafic magmas that intrude into the lower crust can preserve evidence for metal and sulfur transfer from the lithospheric mantle into the lower continental crust. Here we focus on a series of ultramafic, alkaline pipes in the Ivrea Zone (NW Italy), which exposes deeply buried (6–11
15 February 2018
Chromium isotope fractionation in ferruginous sediments
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Kohen W. Bauer, Bleuenn Gueguen, Devon B. Cole, Roger Francois, Jens Kallmeyer, Noah Planavsky, Sean A. Crowe Ferrous Fe is a potent reductant of Cr(VI), and while a number of laboratory studies have characterized Cr isotope fractionation associated with Cr(VI) reduction by ferrous iron, the expression of this fractionation in real-world ferrous Fe-rich environments remains unconstrained. Here we determine the isotope fractionation associated with Cr(VI) reduction in modern ferrous Fe-rich sediments obtained from the previously well studied Lake Matano, Indonesia. Whole core incubations demonstrate that reduction of Cr(VI) within ferruginous sediments provides a sink for Cr(VI) leading to Cr(VI) concentration gradients and diffusive Cr(VI) fluxes across the sediment water interface. As reduction proceeded, Cr(VI) remaining in the overlying lake water became progressively enriched in the heavy isotope (53Cr), increasing
15 February 2018
Aqueous magnesium as an environmental selection pressure in the evolution of phospholipid membranes on early earth
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Punam Dalai, Putu Ustriyana, Nita Sahai Early compartmentalization of simple biomolecules by membrane bilayers was, presumably, a critical step in the emergence of the first cell-like entities, protocells. Their membranes were likely composed of single chain amphiphiles (SCAs), but pure SCA membranes especially those with short-chains are highly unstable towards divalent cations, which are ubiquitous in aqueous environments. The prebiotic synthesis of phospholipids (PLs), even in only trace amounts, may also have been possible. PL membranes are much more stable towards divalent cations. Here, we show the transition of fatty acid membranes to mixed fatty acid-PL and, finally, to PL membranes in the presence of Mg2+, which acts as an environmental selection pressure, and we propose different mechanisms for the observed increased Mg2+-immunity. The “fatal” concentration ([Mg2+]fatal) at which vesicles are disrupted increased dramatically by an order of magnitude from OA to mixed to POPC vesicles. Two mechanisms for the increasing immunity were determined. The negative charge density of the vesicles decreased with increasing POPC content, so more Mg2+ was required for disruption. More interestingly, Mg2+ preferentially bound to and abstracted OA from mixed lipid membranes, resulting in relatively POPC-enriched vesicles compared to the initial ratio. The effect was the most dramatic for the largest initial OA-POPC ratio representing the most primitive protocells. Thus, Mg2+ acted to evolve the mixed membrane composition towards PL enrichment. To the best of our knowledge, this is the first report of selective lipid abstraction from mixed SCA-PL vesicles. These results may hold implications for accommodating prebiotic Mg2+-promoted processes such as non-enzymatic RNA polymerization on early Earth.
15 February 2018
A reconnaissance study of 13C–13C clumping in ethane from natural gas
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Matthieu Clog, Michael Lawson, Brian Peterson, Alexandre A. Ferreira, Eugenio V. Santos Neto, John M. Eiler Ethane is the second most abundant alkane in most natural gas reservoirs. Its bulk isotopic compositions (
15 February 2018
Accumulation of deaminated peptides in anoxic sediments of Santa Barbara Basin
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Hussain A. Abdulla, David J. Burdige, Tomoko Komada Proteins represent the most abundant class of biomolecules in marine sinking particles and microbial biomass, yet their cycling in marine sediments is not fully understood. To investigate whether some portion of hydrolyzed proteins escapes complete remineralization and accumulate in the pore waters, we analyzed dissolved organic matter from the anoxic sediments of Santa Barbara Basin, California, by Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FTICR-MS). The results showed an increase in the molecular diversity and abundance of dissolved organic nitrogen (DON) formulas with depth. A comparison of the detected DON formulas to a database of small peptides (2–4 amino acid sequences) returned 119 matches, and these formulas were most abundant near the sediment surface. When we compared our detected formulas to all possible structures that would result from deamination of peptides in the database, we found 680 formula matches. However, these molecular formulas can represent hundreds of different structural isomers (in the present case as many as 3257 different deaminated peptide structures), which cannot be distinguished by the FTICR-MS settings that were used. Analysis of amino acid sequences suggests that these deaminated peptides may be the products of selective degradation of source proteins in marine sediments. We hypothesize that these deaminated peptides accumulate in the pore waters due to extracellular proteinases being inhibited from completely hydrolyzing specific peptides to free amino acids. We suggest that anaerobic microbes deaminate peptides largely to produce H2, which is ultimately used as a reducing agent by other sediment microbes (e.g. CO2 reduction by methanogens). Simple calculations suggest that deaminated peptides may represent
15 February 2018
Late-stage anhydrite-gypsum-siderite-dolomite-calcite assemblages record the transition from a deep to a shallow hydrothermal system in the Schwarzwald mining district, SW Germany
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Mathias Burisch, Benjamin F. Walter, Axel Gerdes, Maximilian Lanz, Gregor Markl The majority of hydrothermal vein systems of economic interest occur at relatively shallow crustal levels, although many of them formed at significantly greater depths. Their present position is a consequence of uplift and erosion. Although, many aspects of their formation are well constrained, the temporal chemical evolution of such systems during uplift and erosion is still poorly understood. These vein minerals comprise calcite, dolomite-ankerite, siderite-magnesite, anhydrite and gypsum forming the last gangue assemblages in Jurassic and Tertiary sulphide-fluorite-quartz-barite veins of the Schwarzwald mining district, SW Germany. Mineral textures of samples from nine localities reveal that in these sequences, mineral precipitation follows a recurring pattern: early calcite is followed by anhydrite or gypsum, siderite and/or dolomite. This succession may repeat up to three times. In-situ (LA-ICP-MS) U-Pb age dating of 15 carbonates from three subsequent generations of the late-stage vein assemblage yield robust ages between 20 and 0.6
15 February 2018
Unraveling multiple phases of sulfur cycling during the alteration of ancient ultramafic oceanic lithosphere
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Esther M. Schwarzenbach, Benjamin C. Gill, David T. Johnston Ultramafic-hosted hydrothermal systems – characterized by ongoing serpentinization reactions – exert an important influence on the global sulfur cycle. Extensive water-rock interaction causes elemental exchange between seawater and the oceanic lithosphere, effectively removing sulfate from seawater through both abiogenic and biogenic processes. Here, we use bulk rock multiple sulfur isotope signatures (32S, 33S, 34S) and in situ sulfide analyses together with petrographic observations to track the sulfur cycling processes and the hydrothermal evolution of ancient peridotite-hosted hydrothermal systems. We investigate serpentinized peridotites from the Northern Apennine ophiolite in Italy and the Santa Elena ophiolite in Costa Rica and compare those with the Iberian Margin (Ocean Drilling Program (ODP) Leg 149 and 173) and the 15°20
15 February 2018
A reconnaissance view of tungsten reservoirs in some crustal and mantle rocks: Implications for interpreting W isotopic compositions and crust-mantle W cycling
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Jingao Liu, D. Graham Pearson, Thomas Chacko, Yan Luo High-precision measurements of W isotopic ratios have enabled increased exploration of early Earth processes. However, when applying W isotopic data to understand the geological processes, it is critical to recognize the potential mobility of W and hence evaluate whether measured W contents and isotopic compositions reflect the primary petrogenetic processes or instead are influenced by the effects of secondary inputs/mobility. Furthermore, if we are to better understand how W is partitioned between different minerals during melting and metasomatic processes it is important to document the likely sinks for W during these processes. In addition, an understanding of the main hosts for W in the crust and mantle is critically important to constrain how W is cycled and stored in the crust-mantle geochemical cycle. As a first step to investigate these issues, we have carried out in situ concentration measurements of W and other HFSEs in mineral phases within a broad spectrum of crustal and mantle rocks, along with whole-rock concentration measurements. Mass balance shows that for tonalitic gneiss and amphibolite, the major rock-forming minerals can adequately account for the bulk W budget, and for the pristine ultramafic rocks, olivine and orthopyroxene are the major controlling phases for W whereas for metasomatized ultramafic rocks, significant W is hosted in Ti-bearing trace phases (e.g., rutile, lindsleyite) along grain boundaries or is inferred to reside in cryptic W-bearing trace phases. Formation or decomposition of these phases during secondary processes could cause fractionation of W from other HFSEs, and also dramatically modify bulk W concentrations in rocks. For rocks that experienced subsequent W enrichment/alteration, their W isotopic compositions may not necessarily represent their mantle sources, but could reflect later inputs. The relatively small suite of rocks analyzed here serves as a reconnaissance study but allows some preliminary speculations on their significance for crust-mantle HFSE and siderophile element budgets – to be tested in future studies. The significant concentration of W, as well as Nb and Ta hosted in rutile and titanite has interesting implications for the budget of W during crust-mantle recycling. Crust-mantle recycling models invoking the recycling of rutile-bearing eclogites to satisfy the mantle Nb/Ta ratio carry the penalty that the very high W/U and W/Th ratios of these rocks results in a concomitant large deviation from the primitive mantle-like ratios estimated for bulk continental crust. Similarly, data from the single amphibolite sample investigated in this study are inconsistent with models implicating the partial melting of amphibolite-bearing subducted slabs as a major process for formation of continental crust in the Earth’s early history. Either the current widely accepted estimates for bulk continental crust W/U and W/Th ratios are in error, or partial melting or other processes lowers the W/U or W/Th of melt residues during their return to the mantle. The present small dataset cannot properly evaluate this, requiring further investigation. Finally, the lithospheric mantle has the potential to store substantial amounts of W, for example via infiltration by W-rich melts/fluids, and thus may act as a source for W mineralization in the crust.
15 February 2018
Subduction factory in an ampoule: Experiments on sediment–peridotite interaction under temperature gradient conditions
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): A.B. Woodland, V.K. Bulatov, G.P. Brey, A.V. Girnis, H.E. H
15 February 2018
Gallium isotope fractionation during Ga adsorption on calcite and goethite
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Wei Yuan, Giuseppe D. Saldi, JiuBin Chen, Marino Vetuschi Zuccolini, Jean-Louis Birck, Yujie Liu, Jacques Schott Gallium (Ga) isotopic fractionation during its adsorption on calcite and goethite was investigated at 20
15 February 2018
Diffusion coefficients of Mg isotopes in MgSiO3 and Mg2SiO4 melts calculated by first-principles molecular dynamics simulations
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Xiaohui Liu, Yuhan Qi, Daye Zheng, Chen Zhou, Lixin He, Fang Huang The mass dependence of diffusion coefficient (D) can be described in the form of D i D j = m j m i
15 February 2018
Diffusive mass transport in agglomerated glassy fallout from a near-surface nuclear test
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): David G. Weisz, Benjamin Jacobsen, Naomi E. Marks, Kim B. Knight, Brett H. Isselhardt, Jennifer E. Matzel Aerodynamically-shaped glassy fallout is formed when vapor phase constituents from the nuclear device are incorporated into molten carriers (i.e. fallout precursor materials derived from soil or other near-field environmental debris). The effects of speciation and diffusive transport of condensing constituents are not well defined in models of fallout formation. Previously we reported observations of diffuse micrometer scale layers enriched in Na, Fe, Ca, and 235U, and depleted in Al and Ti, at the interfaces of agglomerated fallout objects. Here, we derive the timescales of uranium mass transport in such fallout as it cools from 2500
15 February 2018
Evolution of biomolecular loadings along a major river system
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Chantal V. Freymond, Nicole K
15 February 2018
The retention of dust in protoplanetary disks: Evidence from agglomeratic olivine chondrules from the outer Solar System
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Devin L. Schrader, Kazuhide Nagashima, Scott R. Waitukaitis, Jemma Davidson, Timothy J. McCoy, Harold C. Connolly, Dante S. Lauretta By investigating the in situ chemical and O-isotope compositions of olivine in lightly sintered dust agglomerates from the early Solar System, we constrain their origins and the retention of dust in the protoplanetary disk. The grain sizes of silicates in these agglomeratic olivine (AO) chondrules indicate that the grain sizes of chondrule precursors in the Renazzo-like carbonaceous (CR) chondrites ranged from <1 to 80
15 February 2018
Mechanisms of electron transfer from structrual Fe(II) in reduced nontronite to oxygen for production of hydroxyl radicals
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Songhu Yuan, Xixiang Liu, Wenjuan Liao, Peng Zhang, Xiaoming Wang, Man Tong Production of hydroxyl radicals ( OH) has been recently revealed upon oxygenation of sediments in redox-dynamic subsurface environments. In particular, Fe(II)-bearing clay minerals are the major sediment components contributing to OH production upon oxygenation, and the produced OH can oxidize contaminants and inactivate bacteria. Whereas, the mechanisms of OH production from oxygenation of Fe(II)-bearing clay minerals remain elusive. The objectives of this study were to identify the structural variation of Fe(II) entities during the oxidation of Fe(II)-bearing clay minerals by O2, and to unravel the mechanisms of electron transfer within the mineral structure and from mineral to O2 for OH production. Nontronite (NAu-2, 23% Fe) which was chemically reduced to 54.5% Fe(II) in total Fe was used as a model Fe(II)-bearing clay mineral. Production of OH and oxidation of Fe(II) were measured during the oxidation of reduced NAu-2 by O2. A wide spectrum of spectroscopic techniques, including Fourier transform infrared spectroscopy (FTIR), Fe K-edge X-ray absorption spectroscopy (XAS), M
15 February 2018
Reduced gas seepages in ophiolitic complexes: Evidences for multiple origins of the H2-CH4-N2 gas mixtures
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Christ
1 February 2018
Petrography of the carbonaceous, diamond-bearing stone “Hypatia” from southwest Egypt: A contribution to the debate on its origin
Publication date: 15 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 223 Author(s): Georgy A. Belyanin, Jan D. Kramers, Marco A.G. Andreoli, Francesco Greco, Arnold Gucsik, Tebogo V. Makhubela, Wojciech J. Przybylowicz, Michael Wiedenbeck The stone named “Hypatia” found in the Libyan Desert Glass area of southwest Egypt is carbon-dominated and rich in microdiamonds. Previous noble gas and nitrogen isotope studies suggest an extraterrestrial origin. We report on a reconnaissance study of the carbonaceous matrix of this stone and the phases enclosed in it. This focused on areas not affected by numerous transecting fractures mostly filled with secondary minerals. The work employed scanning electron microscopy (SEM) with energy-dispersive (EDS) and wavelength-dispersive (WDS) electron microprobe (EMPA) analysis, Proton Induced X-ray Emission (PIXE) spectrometry and micro-Raman spectroscopy. We found that carbonaceous matrices of two types occur irregularly intermingled on the 50–500
1 February 2018
Equilibrium nickel isotope fractionation in nickel sulfide minerals
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Shanqi Liu, Yongbing Li, Yiwen Ju, Jie Liu, Jianming Liu, Yaolin Shi Nickel is an important element on Earth, and a major element in the Earth's core, and plays important roles in many geological and biological systems. As an important sink of Ni, Ni sulfides are closely concerned with Ni migration in magma systems and the genesis and evolution of magmatic sulfide deposits. Ni isotopes of Ni sulfides may be a powerful geochemical tracer in magmatic processes and evolution of magmatic sulfide deposits. However Ni isotope fractionation factors of sulfides remain poorly known, which makes the applications of Ni isotopes to geological problems associated with sulfides difficult. In this study, the first-principles methods are used to compute Ni isotope fractionation parameters of polydymite (Ni3S4), heazlewoodite (Ni3S2), millerite (NiS), godlevskite (Ni9S8) and vaesite (NiS2). The reduced partition function ratios of 60Ni/58Ni ( 10 3 ln
1 February 2018
Tellurium stable isotope fractionation in chondritic meteorites and some terrestrial samples
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Manuela A. Fehr, Samantha J. Hammond, Ian J. Parkinson New methodologies employing a 125Te-128Te double-spike were developed and applied to obtain high precision mass-dependent tellurium stable isotope data for chondritic meteorites and some terrestrial samples by multiple-collector inductively coupled plasma mass spectrometry. Analyses of standard solutions produce Te stable isotope data with a long-term reproducibility (2SD) of 0.064‰ for
1 February 2018
Timescales of magma ascent and degassing and the role of crustal assimilation at Merapi volcano (2006–2010), Indonesia: Constraints from uranium-series and radiogenic isotopic compositions
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): H.K. Handley, M. Reagan, R. Gertisser, K. Preece, K. Berlo, L.E. McGee, J. Barclay, R. Herd We present new 238U-230Th-226Ra-210Pb-210Po, 87Sr/86Sr and 143Nd/144Nd isotopic data of whole-rock samples and plagioclase separates from volcanic deposits of the 2006 and 2010 eruptions at Merapi volcano, Java, Indonesia. These data are combined with available eruption monitoring, petrographic, mineralogical and Pb isotopic data to assess current theories on the cause of a recent transition from effusive dome-building (2006) to explosive (2010) activity at the volcano, as well as to further investigate the petrogenetic components involved in magma genesis and evolution. Despite the significant difference in eruption style, the 2006 and 2010 volcanic rocks show no significant difference in (238U/232Th), (230Th/232Th) and (226Ra/230Th) activity ratios, with all samples displaying U and Ra excesses. The 226Ra and 210Pb excesses observed in plagioclase separates from the 2006 and 2010 eruptions indicate that a proportion of the plagioclase grew within the decades preceding eruption. The 2006 and 2010 samples were depleted in 210Po relative to 210Pb ((210Po/210Pb)i
1 February 2018
Carbide-metal assemblages in a sample returned from asteroid 25143 Itokawa: Evidence for methane-rich fluids during metamorphism
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Dennis Harries, Falko Langenhorst We found that the particle RA-QD02-0115 returned by the Hayabusa spacecraft from near-Earth asteroid 25143 Itokawa contains the iron carbide haxonite (Fe21.9-22.7Co0.2-0.3Ni0.2-0.8)C6 and several Fe,Ni alloys, including multi-domain tetrataenite and spinodally decomposed taenite. Ellipsoidal to nearly spherical voids occur throughout the particle and suggest the presence of a fluid phase during textural and chemical equilibration of the host rock within the parent asteroid of 25143 Itokawa. The calculated solubility of carbon in Fe,Ni metal indicates that the carbide formed at temperatures larger than 600
1 February 2018
The primary volcanic aerosol emission from Mt Etna: Size-resolved particles with SO2 and role in plume reactive halogen chemistry
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): T.J. Roberts, D. Vignelles, M. Liuzzo, G. Giudice, A. Aiuppa, M. Coltelli, G. Salerno, M. Chartier, B. Cout
1 February 2018
Iron isotope behavior during fluid/rock interaction in K-feldspar alteration zone – A model for pyrite in gold deposits from the Jiaodong Peninsula, East China
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Zhi-Yong Zhu, Shao-Yong Jiang, Ryan Mathur, Nigel J. Cook, Tao Yang, Meng Wang, Liang Ma, Cristiana L. Ciobanu Mechanisms for Fe isotope fractionation in hydrothermal mineral deposits and in zones of associated K-feldspar alteration remain poorly constrained. We have analyzed a suite of bulk samples consisting of granite displaying K-feldspar alteration, Precambrian metamorphic rocks, and pyrite from gold deposits of the Jiaodong Peninsula, East China, by multi-collector inductively-coupled plasma mass spectrometry. Pyrites from disseminated (J-type) ores show a
1 February 2018
Theoretical isotopic fractionation between structural boron in carbonates and aqueous boric acid and borate ion
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Etienne Balan, Johanna Noireaux, Vasileios Mavromatis, Giuseppe D. Saldi, Val
1 February 2018
New constraints on Xe incorporation mechanisms in olivine from first-principles calculations
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): C
1 February 2018
Time-lapse 3D imaging of calcite precipitation in a microporous column
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Jose R.A. Godinho, Philip J. Withers Time-lapse X-ray computed tomography is used to image the evolution of calcite precipitation during flow through microporous quartz over the course of 400
1 February 2018
Geochemical control on the reduction of U(VI) to mononuclear U(IV) species in lacustrine sediments
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): L. Stetten, A. Mangeret, J. Brest, M. Seder-Colomina, P. Le Pape, M. Ikogou, N. Zeyen, A. Thouvenot, A. Julien, G. Alcalde, J.L. Reyss, B. Bombled, C. Rabouille, L. Olivi, O. Proux, C. Cazala, G. Morin Contaminated systems in which uranium (U) concentrations slightly exceed the geochemical background are of particular interest to identify natural processes governing U trapping and accumulation in Earth’s surface environments. For this purpose, we examined the role of early diagenesis on the evolution of U speciation and mobility in sediments from an artificial lake located downstream from a former mining site. Sediment and pore water chemistry together with U and Fe solid state speciation were analyzed in sediment cores sampled down to 50
1 February 2018
Geochemical and multi-isotopic (87Sr/86Sr, 143Nd/144Nd, 238U/235U) perspectives of sediment sources, depositional conditions, and diagenesis of the Marcellus Shale, Appalachian Basin, USA
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Thai T. Phan, James B. Gardiner, Rosemary C. Capo, Brian W. Stewart We investigate sediment sources, depositional conditions and diagenetic processes affecting the Middle Devonian Marcellus Shale in the Appalachian Basin, eastern USA, a major target of natural gas exploration. Multiple proxies, including trace metal contents, rare earth elements (REE), the Sm-Nd and Rb-Sr isotope systems, and U isotopes were applied to whole rock digestions and sequentially extracted fractions of the Marcellus shale and adjacent units from two locations in the Appalachian Basin. The narrow range of
1 February 2018
Coupled Mo-U abundances and isotopes in a small marine euxinic basin: Constraints on processes in euxinic basins
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Elvira Bura-Naki
1 February 2018
Low-temperature aqueous alteration on the CR chondrite parent body: Implications from in situ oxygen-isotope analyses
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Christine E. Jilly-Rehak, Gary R. Huss, Kazu Nagashima, Devin L. Schrader The presence of hydrated minerals in chondrites indicates that water played an important role in the geologic evolution of the early Solar System; however, the process of aqueous alteration is still poorly understood. Renazzo-like carbonaceous (CR) chondrites are particularly well-suited for the study of aqueous alteration. Samples range from being nearly anhydrous to fully altered, essentially representing snapshots of the alteration process through time. We studied oxygen isotopes in secondary-minerals from six CR chondrites of varying hydration states to determine how aqueous fluid conditions (including composition and temperature) evolved on the parent body. Secondary minerals analyzed included calcite, dolomite, and magnetite. The O-isotope composition of calcites ranged from
1 February 2018
Atmospheric noble gases in Mid-Ocean Ridge Basalts: Identification of atmospheric contamination processes
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Claire Roubinet, Manuel A. Moreira Noble gases in oceanic basalts always show the presence in variable proportions of a component having elemental and isotopic compositions that are similar to those of the atmosphere and distinct from the mantle composition. Although this component could be mantle-derived (e.g. subduction of air or seawater-derived noble gases trapped in altered oceanic crust and sediments), it is most often suggested that this air component is added after sample collection and probably during storage at ambient air, although the mechanism remains unknown. In an attempt to reduce this atmospheric component observed in MORBs, four experimental protocols have been followed in this study. These protocols are based on the hypothesis that air can be removed from the samples, as it appears to be sheltered in distinct vesicles compared to those filled with mantle gases. All of the protocols involve a glove box filled with nitrogen, and in certain cases, the samples are stored under primary vacuum (lower than 10
1 February 2018
Investigating calcite growth rates using a quartz crystal microbalance with dissipation (QCM-D)
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Bo Cao, Andrew G. Stack, Carl I. Steefel, Donald J. DePaolo, Laura N. Lammers, Yandi Hu Calcite precipitation plays a significant role in processes such as geological carbon sequestration and toxic metal sequestration and, yet, the rates and mechanisms of calcite growth under close to equilibrium conditions are far from well understood. In this study, a quartz crystal microbalance with dissipation (QCM-D) was used for the first time to measure macroscopic calcite growth rates. Calcite seed crystals were first nucleated and grown on sensors, then growth rates of calcite seed crystals were measured in real-time under close to equilibrium conditions (saturation index, SI
1 February 2018
Hf-W chronology of CR chondrites: Implications for the timescales of chondrule formation and the distribution of 26Al in the solar nebula
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Gerrit Budde, Thomas S. Kruijer, Thorsten Kleine Renazzo-type carbonaceous (CR) chondrites are distinct from most other chondrites in having younger chondrule 26Al-26Mg ages, but the significance of these ages and whether they reflect true formation times or spatial variations of the 26Al/27Al ratio within the solar protoplanetary disk are a matter of debate. To address these issues and to determine the timescales of metal-silicate fractionation and chondrule formation in CR chondrites, we applied the short-lived 182Hf-182W chronometer to metal, silicate, and chondrule separates from four CR chondrites. We also obtained Mo isotope data for the same samples to assess potential genetic links among the components of CR chondrites, and between these components and bulk chondrites. All investigated samples plot on a single Hf-W isochron and constrain the time of metal-silicate fractionation in CR chondrites to 3.6
1 February 2018
Experimentally determined subsolidus metal-olivine element partitioning with applications to pallasites
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Patrick H. Donohue, Eddy Hill, Gary R. Huss Pallasite meteorites, which consist primarily of olivine and metal, may be remnants of disrupted core-mantle boundaries of differentiated asteroids or planetesimals. The early thermal histories of pallasites are potentially recorded by minor- and trace-element zonation in olivine. However, constraining this history requires knowledge of element behavior under the conditions of pallasite formation, which is lacking for many of the main elements of interest (e.g., Co, Cr, Mn). In this study, we experimentally determined metal/olivine partition coefficients for Fe, Ni, Co, Cr, and Mn in a pallasite analogue at subsolidus temperatures. Metal/olivine partition coefficients (KM ) increase in the order KMn
1 February 2018
Tracing ancient hydrogeological fracture network age and compartmentalisation using noble gases
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Oliver Warr, Barbara Sherwood Lollar, Jonathan Fellowes, Chelsea N. Sutcliffe, Jill M. McDermott, Greg Holland, Jennifer C. Mabry, Christopher J. Ballentine We show that fluid volumes residing within the Precambrian crystalline basement account for ca 30% of the total groundwater inventory of the Earth (> 30 million km3). The residence times and scientific importance of this groundwater are only now receiving attention with ancient fracture fluids identified in Canada and South Africa showing: (1) microbial life which has existed in isolation for millions of years; (2) significant hydrogen and hydrocarbon production via water–rock reactions; and (3) preserving noble gas components from the early atmosphere. Noble gas (He, Ne, Ar, Kr, Xe) abundance and isotopic compositions provide the primary evidence for fluid mean residence time (MRT). Here we extend the noble gas data from the Kidd Creek Mine in Timmins Ontario Canada, a volcanogenic massive sulfide (VMS) deposit formed at 2.7 Ga, in which fracture fluids with MRTs of 1.1–1.7 Ga were identified at 2.4 km depth (Holland et al., 2013); to fracture fluids at 2.9
1 February 2018
Biogeochemical processes controlling authigenic carbonate formation within the sediment column from the Okinawa Trough
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Jiwei Li, Xiaotong Peng, Shijie Bai, Zhiyan Chen, Joy D. Van Nostrand Authigenic carbonates are one type of conspicuous manifestation in seep environments that can provide long-term archives of past seepage activity and methane cycling in the oceans. Comprehensive investigations of the microbial community functional structure and their roles in the process of carbonate formation are, however, lacking. In this study, the mineralogical, geochemical, and microbial functional composition were examined in seep carbonate deposits collected from the west slope of the northern section of the Okinawa Trough (OT). The aim of this work was to explore the correspondence between the mineralogical phases and microbial metabolism during carbonate deposit formation. The mineralogical analyses indicated that authigenic carbonate minerals (aragonite, magnesium-rich calcite, dolomite, ankerite and siderite) and iron-bearing minerals (limonite, chlorite, and biotite) were present in these carbonate samples. The carbon and oxygen isotopic values of the carbonate samples varied between

Complementary biomarker-based methods for characterising Arctic sea ice conditions: A case study comparison between multivariate analysis and the PIP25 index
Publication date: 1 February 2018
Source:Geochimica et Cosmochimica Acta, Volume 222 Author(s): Denizcan K
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