- Email: [email protected]
Goldschmidt Abstracts 2010 – U
A1062
Goldschmidt Conference Abstracts 2010
Mineralogical and geochemical profiling of Arsenic-contaminated aquifers in central Bangladesh
Stable isotopic fingerprints of greenhouse gasses before the rise of oxygen
A. UDDIN1* M. SHAMSUDDUHA2, J.A. SAUNDERS1, M-K. LEE1, K.M. AHMED3 AND M.T. CHOWDHURY3
YUICHIRO UENO*
1
Auburn University, Auburn, AL 36849, USA (*correspondence: [email protected]) 2 University College London, London WC1E 6BT, UK 3 University of Dhaka, Dhaka 1000, Bangladesh Groundwater of shallow (<100 m below ground level) alluvial aquifers in Bangladesh and West Bengal, India is contaminated with elevated (>50 µg/L) aqueous arsenic (As) concentrations. Microbial reduction of As-bearing Feoxyhydroxides (FeOOH) is the widely accepted mechanism for elevated As in groundwater although geological control on its spatial distribution, however, remains uncertain. We analyzed 85 groundwater and 32 cored sediment samples (2150 mbgl) collected at Manikganj district in central Bangladesh. Stratigraphy shows typical fining upward sequences composed of sub-arkosic to arkosic sands. Sediments at shallow depth contain more biotite, magnetite, amphibole, apatite, and authigenic FeOOH (goethite) than sediments at greater depths (Figure 1). Microprobe analysis of goethite reveals high amount (~340 mg/kg) of solid-phase As in sediments. Abundant FeOOH and Fe-bearing minerals such as magnetite, apatite, and biotite are potential carriers of As in sediments. Geologic heterogeneity and variations in the magnitude of aquifer flushing strongly influence As distributions in alluvial aquifers in the Bengal Basin.
Global Edge Institute, Tokyo Institute of Technology, Meguo, Tokyo 152-8551, Japan (*correspondence: [email protected]) Chemical compositions of early Earth’s atmosphere have been largely unknown. In the Archean, abundances of greenhouse gasess are believed to have been much higher than today’s for maintaing warm climate under less bright young Sun [1]. Not only higher CO2 levels but also additional greenhouse gasses may have been required. Biological CH4 was likely accumulated in the anoxic early atmosphere, though contribution of CH4 to the radiative forcing is still debated [2, 3]. An alternative candidate is carbonyl sulfide (OCS), which is more effective greenhouse gas than CO2 and CH4. Our laboratory experiments and numerical simulations suggest that elevated levels of OCS (>1 ppm) can be maintained if the atmosphere is reducing and rich in CO (>1%) [4]. Mass independent fractionation of sulfur isotopes (S-MIF) can be useful to test the scenario [5]. Although mechanisms of the SMIF has not been fully understood, S-MIF is produced by photolysis of SO2 in an anoxic atmosphere. We have determined UV absorption spectra of 32SO2, 33SO2, and 34SO2 and described sulfur isotope fractionation factors as a function of wavelength [6]. Based on the estimated wavelengthdependence of the S-MIF, we suggested that UV-sheilding by OCS results in distinctive UV actinic spectra and can explain negative ! 33 S recorded in all the Archean sulfate deposits [4]. UV-shielding by SO2 (self-shielding) might have alternative effect on S-MIF [7], though such high SO2 level (>1ppm) is difficult to maintain unless volcanic SO2 flux is extraodinary high. Oxygenation of the atmosphere should decrease the atmospheric OCS levels and quantitative conversion of all atmospheric sulfur species into H2SO4, both of which result in cooling of surface temperature. Thus, the atmospheric sulfur cycling including OCS chemistry would have been more importatnt for Archean climate than previously thought. [1] Sagan & Mullen (1972) Science 177, 52–56. [2] Ueno et al. (2006) Nature 440, 516–519. [3] Haqq-Misra et al. (2008) Astrobiol. 8, 1127–1137. [4] Ueno et al. (2009) PNAS 106, 14784–14789. [5] Farquhar et al. (2000) Science 289, 756– 758. [6] Danielache et al. (2008) JGR 113, D17314. [7] Lyons (2007) GRL 34, L22811.
Figure 1: Stratigraphy, As contents in sediments, groundwater, and heavy mineral contents in sediments.
Goldschmidt Conference Abstracts 2010
Reactive solvation and transport simulations of OH– ions in aqueous environment: A multistate empirical valence bond (MS-EVB) approach
Testing forcing mechanisms of deglaciation: Cosmogenic dating of Laurentide Ice Sheet retreat in Wisconsin and surface mass balance modeling
I.S. UFIMTSEV1, A.G. KALINICHEV2, T.J. MARTINEZ1 3 AND R.J. KIRKPATRICK
DAVID J. ULLMAN1*, ANDERS E. CARLSON1, ALLEGRA N. LEGRANDE2, FARON S. ANSLOW3, MARC W. CAFFEE4, JOSEPH M. LICCIARDI5 6 AND KENT M. SYVERSON
1
Department of Chemistry, Stanford University, Stanford, CA 94305 (*correspondence: [email protected]) 2 Department of Chemistry, Department of Geological Sciences, Michigan State University, East Lansing, MI 48824 (*correspondence: [email protected]) 3 College of Natural Science, Michigan State University, East Lansing, MI 48824 Proton exchange reactions involving hydronium (H3O+) and hydroxide (OH-) ions in water are important geochemical and environmental process and significantly influence mineral dissolution and precipitation and the binding and transport of contaminants in soil and water. The abnormally high diffusion rate of these charge defects is attributed to the so-called Grotthus mechanism of successive proton exchange events between neighboring H2O molecules rather than simple ion diffusion. Numerous theoretical and experimental investigations of H3O+ diffusion in acidic solution provide a consistent picture of this process, in which the excess proton diffuses through successive interconversions between solvated H3O+(H2O)3 and (H2O···H···OH2)+ structures, known as Eigen and Zundel ions, respectively. The diffusion of the OH– ion in basic aqueous solutions was usually assumed to be simply a ‘mirror representation’ of the H3O+ transport, with the OH– ion having predominantly three H2O molecules in the first solvation shell that donate hydrogen bonds to it. However, recent theoretical and experimental studies have called this mechanism into question. These studies have produced alternative mechanisms involving a different OH– coordination scheme and a more complex solvent reorganization around the ion as the system approaches the transition state and the ion becomes capable of recombining with one of the nearest water molecule’s protons to form a different stable OH– ion. We have developed a new multistate empirical valence bond model of OH–(aq) suitable for classical molecular simulations, which accurately captures the major structural, energetic, and dynamic aspects of the proton transfer reactions around the hydrated OH– ion and is in good agreement with experimental data and the results of ab initio molecular dynamics simulations. The model predicts an approximately two-fold increase of the OH– mobility due to proton exchange reactions.
A1063
1
Dept. of Geoscience, Univ. of WI-Madison, Madison, WI (*correspondence: [email protected]) 2 NASA GISS & CCSR, Columbia Univ., New York, NY 3 Earth and Ocean Sciences, Univ. of British Columbia, Vancouver, BC Canada 4 Dept. of Physics, Purdue Univ., West Lafayette, IN 5 Dept. of Earth Sciences, Univ. of NH, Durham, NH 6 Dept. of Geology, Univ. of WI-Eau Claire, Eau Claire, WI Determining the phasing of Northern Hemisphere (NH) ice sheets relative to changes in insolation, greenhouse gases, and climate is key to understanding the mechanisms that give rise to ice ages and ice-sheet retreat. Early retreat of NH ice sheets ~19-24 ka suggests boreal insolation as the ultimate driver of ice retreat [1]. Alternatively, tropical sea surface temperatures (SST) and atmospheric CO2 may lead portions of ice-sheet retreat, implicating them as an alternative driver of deglaciation [2, 3]. Here, we present new 1°Be cosmogenic exposure dates from boulders on the terminal moraines of three distinct lobes of the Laurentide Ice Sheet (LIS) in Wisconsin. Until present, the retreat onset of this region was poorly understood through limited radiocarbon dates. This new cosmogenic chronology provides an important constraint on the retreat of the LIS southern margin at the LGM. To assess if boreal summer insolation could drive initial LIS retreat, we employ an energy moisture balance model to assess the LIS mass balance at the LGM with climate forcing from the Goddard Institute for Space Studies (GISS) ModelER. We compare the effects of alternate LIS topographies: the current standard ICE5-G [4] and an alternative reconstruction with lower topography over the Keewatin Dome [5]. We put these model results in the context of our new cosmogenic exposure dates and the existing retreat chronology for the LIS southern margin, testing the mechanisms controlling the onset of the last deglaciation. [1] Clark et al. (2009) Science 325, 710–714. [2] Lea et al. (2006) Quat. Sci Rev. 25, 1152–1167 [3] Stott et al. (2007) Science 318, 435–438 [4] Peltier (2004) ARES 32, 111–149 [5] Licciardi et al. (1998) Quat. Sci. Rev. 17, 427–488.
A1064
Goldschmidt Conference Abstracts 2010
Decrease in net methylmercury production following an iron amendment to tidal wetland sediments P.D. ULRICH AND D.L. SEDLAK* Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA (*correspondence: [email protected]) Tidal wetlands are often important sources of methylmercury (MeHg) in aquatic ecosystems. As a result, the restoration of wetland habitat may cause an increase of MeHg concentrations. In the Sacramento and San Joaquin Delta of California, concerns over potential increases in MeHg from wetland restoration are currently impeding wetland restoration efforts. There has been significant research into mercury biogeochemistry in wetland sediments, however, there have been few successful efforts to minimize the production and export of MeHg from restored wetlands. To provide a tool for controlling MeHg, we have evaluated the use of an iron sediment amendment to reduce net MeHg production in tidal wetland sediments. The addition of Fe [II] decreases MeHg production by lowering the concentration of bioavailable inorganic Hg [II] species that are methylated by bacteria. Under the reducing conditions typical of wetland sediments, dissolved Hg [II] speciation and concentration is controlled by sulfide species (i. e., S [-II]) with the concentration of dissolved bioavailable Hg [II] complexes increasing as porewater S [-II] increases. Addition of iron decreases the concentration of S [-II] through the formation of FeS (s). To test the potential use of iron addition to control MeHg production, microcosms collected from an estuarine tidal marsh in San Francisco Bay were amended with 180g-Fe/m2, 360g-Fe/m2 and 720g-Fe/m2 and operated under simulated tidal conditions. Shortly after iron addition, porewater S [-II] concentrations decreased at all iron doses relative to the control, and net MeHg production and export to the overlying surface water decreased by over 90% at the highest iron dose. Despite some conversion of FeS (s) to pyrite, the effects persisted for at least 12 weeks. Experiments were also conducted to assess the effects of marsh vegetation on MeHg production and examine the role of oxygen released from plant roots and decomposition of plant-derived organic matter. Our research suggests that it may be possible to control net MeHg production in certain tidal wetlands with an iron amendment. Field-scale application of iron addition is being used to assess the the efficacy of this approach under different conditions (e.g. plant communities, marsh elevation) encountered in tidal wetlands.
Research of saturation of mineral waters with quartz and amorphous silica in cold carbonic and nitric thermal waters in Southwest Transbaikalia I.D. ULZETUEVA, D.TS.-D. ZHAMYANOV, B.O. GOMBOEV AND V.V. KHAKHINOV Baikal Institute of Nature Management SB RAS, 8, Sakhyanova Str., Ulan-Ude, 670047, Russia ([email protected]) Silicon is a constant component of natural waters structure. Despite a wide occurrence of silicon circulation in natural waters and its essential role in behavior of many physical and chemical processes, until today insufficient attention is given to the quantitative definition of this component. In mineral waters, especially in thermal, the concentration of dissolved silicon can reach half of general mineralization that should affect their physical and chemical properties. In connection with it the consideration of factors with which the receipt and accumulation of silicon is connected is, undoubtedly, important. Detailed data about the content of silica in natural waters are necessary not only for the estimation of scales of migration of this component, but also for the decision of the question, concerning intensity of the rock aeolation, problems of their origin. Unique feature of the nitric thermal spring is the presense of high concentration of fluorine-ion (to 15 mg/dm3) and silicon (to 110 mgH4SiO4/dm3) in their structure of. Accumulation of these components in thermal waters is promoted by the alkaline environment and the elevated temperature. For the purpose of determining saturation of mineral waters with quartz and amorphous silica the solubility of these connections at various temperatures has been calculated. The received results have shown that all thermal waters are supersaturated in relation to quartz. However deposits of this compound in places of thermal spring discharging is not observed. Many researchers explain this by the extremely small speed of reaction of quartz crystallization from solution. Polymerization and deposition of silica never occurs until its concentration in a solution is below the solubility of amorphous silica. Results of calculations point out the lack of saturation of thermal and cold waters, at temperatures of their discharging, amorphous silica, that is, all silicon in these waters is in truly dissolved condition.
Goldschmidt Conference Abstracts 2010
A1065
U(VI) desorption from capillary fringe sediments
First-principles investigation of order-disorder phase boundary in ice
W. UM*, J.M. ZACHARA AND C. LIU
KOICHIRO UMEMOTO1, RENATA M. WENTZCOVITCH2, STEFANO BARONI3 3 AND STEFANO DE GIRONCOLI
Pacific Northwest National Laboratory, Richland, WA, USA (*correspondence: [email protected]) 1
U (VI) contaminated capillary fringe sediments at Hanford 300 Area are considered to secondary source for existing uranium plume in groundwater. Because seasonal water table elevation and water chemistry changed in response to nearby Columbia River stage, batch and column desorption experiments of U (VI) were conducted using two U (VI) contaminated sediments (11D and 39B). Solid phase characterization of these two sediments was performed to identify mineralogic and chemical factors controlling U (VI) desorption. The desorption behavior of U (VI) was different from the two sediments in spite of similar chemical and textural characteristics. Adsorption strength and sorbed U (VI) lability was higher in the near-river sediment, 11D. Inland sediment, 39B displayed low sorbed U (VI) lability (~10%) and measurable solid-phase carboante content. Kinetic desorption was attributed to regeneration of labile U (VI) in 11D. The U (VI) desorption reaction was best described as an equilibrium surface complexation reaction. The noted differences in U (VI) desorption behavior appear to result from U (VI) contamination and hydrologic history, as well as sediment carbonate content.
Geology and Geophysics, University of Minnesota, Minneapolis, MN, USA 2 Chemical Engineering and Materials Science, University of Minnesota, MN, USA 3 Condensed Matter Physics, SISSA, Trieste, Italy
Ice has a very rich phase diagram. Up to now, sixteen crystalline phases have been identified experimentally. This richness of the phase diagram originates in part in hydrogen order-disorder (OD) transitions. The ice VII-VIII boundary, a typical OD boundary, has been reasonably well constrained experimentally and is an ideal study case. We present a firstprinciples quasiharmonic study consisting in the complete statistical sampling of molecular orientations within a 16 molecule supercell. This supercell calculation accounts for several aspects of this transition, including the Clapeyron slope and the isotope effect. Research suppported by NSF grants ATM 0428874 (VLab) and EAR 0757903. Computations were performed at the Minnesota Supercomputing Institute.
Goldschmidt Conference Abstracts 2010
A1066
Using !-XRF and XAS to characterize the fate and bioavailability of manufactured nanoparticles in soil 1
1
JASON UNRINE *, AARON SHOULTS-WILSON , BRIAN REINSCH2, OLGA TSYUSKO1, GREG LOWRY2 1 AND PAUL BERTSCH
Dissimilatory iron reduction in subzero brines M.R. URSCHEL1, M.L. SKIDMORE2* AND G. GEESEY1 1
Department of Microbiology, Montana State Univ., Bozeman, MT 59717, USA ([email protected]) 2 Department of Earth Sciences, Montana State Univ., Bozeman, MT 59717, USA (*correspondence: [email protected])
1
University of Kentucky, Lexington, KY 40546, USA (*correspondence to [email protected]) 2 Carnegie Mellon University, Pittsburg, PA 15213, USA
Manufactured metal nanoparticles are likely to enter wastwater streams and partition to sewage sludge, which may be applied as biosolids to agricultral lands [1]. We have investigated the fate of a variety of Ag, Cu and Au nanoparticles in soils, as well as bioavailability and toxicity in nematodes (Caenorhabditis elegans) and earthworms (Eisenia fetida) using synchrotron based x-ray fluoresence microspectroscopy (!-XRF) microfocused x-ray absorption near edge spectroscopy (!XANES) and bulk extended x-ray absorption fine structure spectroscopy (EXAFS) as described previously for trace-element studies [2] along with gene expression studies. We have obtained strong evidence for the uptake and biodistribution of nanoparticles in earthworms and nematodes and have differentiated metal and metal oxide particle uptake from uptake of metal ions for Cu and Au (e.g. fig 1). We have also shown that reproductive effects of Ag nanoparticles are likely due to Ag+ exposure while behavioral effects are likely caused by the Ag nanoparticles.
Ferric iron (Fe3+) minerals are potential electron acceptors in cold and icy environments, such as those in the ice-hosted sediments in icebergs and glaciers [1]. Microbial dissimilatory iron reducers have been found in many icy environments, such as subglacial sediments [2], Arctic marine sediments [3], permafrost [4] and Antarctic sea ice [5]. Theoretical and laboratory studies have reported that supercooled, solute-rich veins within ice samples are viable habitats for microorganisms [6, 7]. Further, it has been suggested that dissimilatory iron reducers may reduce iron at temperatures as low as -9¡ C in the solute-rich vein network within basal ice [8], however, no direct evidence of microbial iron reduction at subzero temperatures has been reported to date. The gammaproteobacteria Shewanella frigidimarina was originally isolated from sea ice in eastern Antarctica [5]. This organism can respire on ferric iron, and has been demonstrated to grow at temperatures from 0 to 28¡ C, and salinities up to 8% NaCl [5]. We quantified the effect of temperature and salinity on the growth and iron reduction rates of S. frigidimarina at subzero temperatures. Cultures were incubated at 15¡ C, 4¡ C and -5¡ C, over a range of salinites from 0-8% NaCl. Our results indicate that S. frigidimarina is capable of growth at temperatures as low as -5¡ C at 2% and 4% NaCl in the presence of ferric citrate as sole electron acceptor and lactate as sole electron donor. No growth was observed at 8% NaCl over the temperature range tested. To the authorsÕ knowledge, these results represent the first direct evidence of an organism respiring and growing on ferric iron at subzero temperature and increased salinity. [1] Raiswell R. et al. (2008) Min. Mag. 72, 345Ð 348. [2] Foght J. et al. (2004) Microb. Ecol. 47, 329Ð 340. [3] VandiekenV. et al. (2006) Mar. Ecol. Prog. Ser. 322, 29Ð 41. [4] Zhang C. et al. (1999) FEMS Microb Ecol 30, 371. [5] Bowman, J. et al. (1997) Int J of Syst. Bact. 47, 1040Ð 1047. [6] Price B. (2000) PNAS 97, 1247Ð 1251. [7] Mader H. et al. (2006) Geology 34, 3, 169Ð 172. [8] Tung H. et al. (2006) Astrobiology, 6, 1, 69Ð 86.
Figure 1: X-ray fluorescence micrograph (top) showing a pixel of high Cu intensity in the main dorsal blood vessel of an earthworm (light micrograph bottom right). Interrogation of this pixel with XANES (bottom left) demonstrated that it was a mixture of Cu (0), CuO and Cu2O. [1] Gottschalk et al. (2009) Environ. Sci. Technol 43, 9216Ð 9222. [2] Punshon et al. (2005) Spectrosc Lett 38, 343Ð 363.
Goldschmidt Conference Abstracts 2010
Recent progress of small spot oxygen isotope analysis at WiscSIMS T. USHIKUBO*, N.T. KITA AND J.W. VALLEY WiscSIMS, Univ. of Wisconsin, Madison, WI 53706, USA (*correspondence: [email protected]) In situ, high precision oxygen two and three isotope analysis with a sub-µm to a few µm beam by SIMS is valuable technique to investigate records preserved in finely zoned samples [1-3]. Here, we report results of recent developments for high precision and accurate small spot oxygen isotope analysis at WiscSIMS laboratory. FC-EM (-EM) detectors: The quasi-simultaneous arrival (QSA) effect [4] would be a problem for isotope analyses when we use a small spot and low current (e.g. <1 µm, <10 pA) Cs+ primary beam. We observed more than +80ä fractionated "18O value with two electron multipliers (EM), which is probably a result of the QSA effect, while fractionations are generally less than ±10ä with Faraday Cups (FC). To minimize bias, we use a FC to detect 16O-, which is the major oxygen isotope. The instrumental mass bias of oxygen two (or three) isotope analysis with FC-EM (-EM) detectors and a small beam is consistent with that of multiple FC analysis with a 10 µm beam within a few permil. Matrix effect correction: The matrix effect of the instrumental mass bias (dependence on elemental composition of samples) with a small beam is different from that with a 10 µm beam. The matrix effect should be determined in the same analytical session. Blue LED luminous source for CCD camera image: For better spatial resolution of the CCD camera image to aim analysis points, we converted to a blue LED. We can recognize ~2 µm texture of sample with the CCD camera image vs. ~3 µm with white light. Sample preparation: A well-polished flat sample surface is important for an accurate isotope analysis [5, 6]. In addition, this is important for not only an aiming of tiny samples but also reducing 16OH- signal which interferes to 17O- signal. Since epoxy of sample mounts elevates pressure of the sample chamber and causes higher 16OH- signal, minimum usage of epoxy for sample mount is helpful for small spot oxygen isotope analysis [e.g. 2, 7]. [1] Page et al. (2007) Am. Mineral. 92, 1772Ð 1775. [2] Nakamura et al. (2008) Science 321, 1664Ð 1667. [3] Kozdon et al. (2009) Chem. Geol. 258, 327Ð 337. [4] Slodzian et al. (2004) Appl. Surf. Sci. 231Ð 232, 874Ð 877. [5] Kita et al. (2009) Chem. Geol. 264, 43Ð 57. [6] Valley & Kita (2009) MAC short course 41, 19Ð 63. [7] Nakashima et al. (2010) LPSC 41, #2309 (abstract)
A1067
Magnetite formation via FeII induced mineralogical transformations of ferric oxyhydroxides M. USMAN*, K. HANNA, M. ABDELMOULA AND C. RUBY LCPME/ CNRS-Nancy University, 54600, Villers-l• s-Nancy, France ( *[email protected], [email protected], [email protected]) The reactivity of various ferric oxyhydroxides (ferrihydrite Ô FÕ , goethite Ô GÕ and lepidocrocite Ô LÕ ) against FeII species was investigated to induce mineralogical transformations into magnetite (Fe3O4) at different aging times (1 hour, 1 day and 1 month). A parallel study was also conducted on three kinds of lab-synthesized goethite having different crystal structures, crystal morphologies and surface properties. The starting and final solid products were characterized by XRD analysis, Transmission Electron Microscopy and Mšs sbauer spectroscopy. The order of reactivity to transform into magnetite found was: F > L > G. Difference in morphology and particle size of generated magnetite was also observed dependent on the nature of initial substrates.
Figure 1: Untransformed amount (%) of ferric substrates at each time point. Rest was transformed into magnetite. Goethite was the least reactive as 33% was still present after one month. Reaction with other kinds of goethite suggest that the reactivity was independent of the specific surface area emphasizing the importance of the crystal structure for their reactivity. Different coordination modes of FeII with the different crystal faces of FeIII-hydroxide, which affect the FeIIFeIII electron transfer could explain this discrepancy in reactivity. Experiment with ferrihydrite mixed sand showed that silica sand (Quartz, 200-300µm) had no effect on this FeII induced transformation into magnetite.
A1068
Goldschmidt Conference Abstracts 2010
The influence of magmatism and magmatic fluids on the geochemical evolution of the Martian crust G. USTUNISIK1*, H. NEKVASIL1 AND F.M. MCCUBBIN2, 1
Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100 USA (*correspondence: [email protected]) 2 Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd., NW, Washington, DC 20015 ([email protected])
Experimental investigations of phase equilibria of martian lithologies have delineated the thermal stability of martian magmas and the minerals that crystallize from them under a variety of pressures and water contents. These experiments explain the basaltic character of the planet and predict variations in magma chemistry over time as the secondary crust thickened. Of particular importance to understanding the past surface environment is assessment of the role of magmatic processes in contributing halogens, water, and S to the surface and near-surface environments. This is accomplished through first and second boiling of volatilebearing magmas. However, the nature of the fluids exsolved, as well as the pressure at which exsolution occurs is strongly dependent upon melt composition as well as relative volatile abundance. Unlike the case for water-rich magmas, little is understood about the controls on fluid stability, the nature of such fluids, and their evolution during second boiling for water-poor, Cl-, S-, and F- enriched magmas with high Fe contents (as likely characterizes late martian magmas produced from a dehydrated mantle.) Such magmas may retain volatiles until close to the surface and thus become major contributors to the surface environment. Experiments have been launched to evaluate the effect of Cl, S, F on mineral and melt stability in martian magmas and the effect of pressure on volatile retention. First experiments have been conducted on an evolved Cl-, S-, F- enriched waterpoor (~0.4 wt% water) liquid from a Backstay parent and indicate a pronounced effect on mineral stability, most notably, on olivine, feldspar, and Ti- amphibole. Volatiles other than S are retained in the liquid. Additional experiments indicate, however, that at higher water contents, fluid can exsolve during first boiling at mid-crustal levels and produce amphibolite through reaction with a Humphrey composition wallrock. This amphibolite sequesters water and halogens, impeding their access to the surface. Additional experiments on water-poor compositions are assessing low-pressure exsolution, the nature of fluids given off, and their effect on wallrock alteration.
Characterization of natural hydrogen sources in ophiolitic context C. VACQUAND1,2*, A. PRINZHOFER1,2 AND E. DEVILLE1 1
Institut Français du Pétrole, 1, 4 avenue de Bois-Préau, 92852 Rueil-Malmaison Cedex, France (*correspondence: [email protected]) 2 IMPMC/IPGP 140 rue de Lourmel, 75015 Paris, France In an investigation of natural hydrogen sources and fluxes, gases with high concentrations of hydrogen were sampled in the Samail (Oman), Zambales (Philippines) and Antalya (Turquey) ophiolites. Chemistry and analyses of carbon, hydrogen and noble gases isotopes were associated to measurements of pH, Eh and temperature of the associated water where the gas is bubbling. Two types of gas composition exist in Oman: the first with about 75% hydrogen, 15% nitrogen and 10% methane, associated to ultrabasic pH waters and reducing conditions (pH about 11 and Eh < -250mV) whereas the second type is pure nitrogen associated with neutral pH water. The "13C of methane are extremely heavy ("13C = -10 to +5‰) and demonstrate an inorganic origin, while the noble gas analyses indicate a purely crustal source. The gases only seep from the ophiolitic rocks (gabbros and peridotites). The reaction yielding hydrogen is most likely to be a reaction of serpentinization: Olivine + Water ! Serpentine + Hydrogen + Magnetite with: 2Fe2+ + 2H2O ! 2Fe3+ + H2 + 2OHand the evolution of gas compositions corresponds to a secondary reaction generating methane through the reduction of CO2: 4H2 + CO2 ! CH4 + 2H2O This second reaction is variable from different geological areas: the Zambales ophiolite produces up to 50% methane, the one in Antalya (Turquey) produces more than 80% of methane. This exotic generation of hydrogen and methane may be present in much more common locations, extending the gas exploration out of the sedimentary basins.
Goldschmidt Conference Abstracts 2010
Mineralogical and geochemical profiling of Arsenic-contaminated aquifers in central Bangladesh
Stable isotopic fingerprints of greenhouse gasses before the rise of oxygen
A. UDDIN1* M. SHAMSUDDUHA2, J.A. SAUNDERS1, M-K. LEE1, K.M. AHMED3 AND M.T. CHOWDHURY3
YUICHIRO UENO*
1
Auburn University, Auburn, AL 36849, USA (*correspondence: [email protected]) 2 University College London, London WC1E 6BT, UK 3 University of Dhaka, Dhaka 1000, Bangladesh Groundwater of shallow (<100 m below ground level) alluvial aquifers in Bangladesh and West Bengal, India is contaminated with elevated (>50 µg/L) aqueous arsenic (As) concentrations. Microbial reduction of As-bearing Feoxyhydroxides (FeOOH) is the widely accepted mechanism for elevated As in groundwater although geological control on its spatial distribution, however, remains uncertain. We analyzed 85 groundwater and 32 cored sediment samples (2150 mbgl) collected at Manikganj district in central Bangladesh. Stratigraphy shows typical fining upward sequences composed of sub-arkosic to arkosic sands. Sediments at shallow depth contain more biotite, magnetite, amphibole, apatite, and authigenic FeOOH (goethite) than sediments at greater depths (Figure 1). Microprobe analysis of goethite reveals high amount (~340 mg/kg) of solid-phase As in sediments. Abundant FeOOH and Fe-bearing minerals such as magnetite, apatite, and biotite are potential carriers of As in sediments. Geologic heterogeneity and variations in the magnitude of aquifer flushing strongly influence As distributions in alluvial aquifers in the Bengal Basin.
Global Edge Institute, Tokyo Institute of Technology, Meguo, Tokyo 152-8551, Japan (*correspondence: [email protected]) Chemical compositions of early Earth’s atmosphere have been largely unknown. In the Archean, abundances of greenhouse gasess are believed to have been much higher than today’s for maintaing warm climate under less bright young Sun [1]. Not only higher CO2 levels but also additional greenhouse gasses may have been required. Biological CH4 was likely accumulated in the anoxic early atmosphere, though contribution of CH4 to the radiative forcing is still debated [2, 3]. An alternative candidate is carbonyl sulfide (OCS), which is more effective greenhouse gas than CO2 and CH4. Our laboratory experiments and numerical simulations suggest that elevated levels of OCS (>1 ppm) can be maintained if the atmosphere is reducing and rich in CO (>1%) [4]. Mass independent fractionation of sulfur isotopes (S-MIF) can be useful to test the scenario [5]. Although mechanisms of the SMIF has not been fully understood, S-MIF is produced by photolysis of SO2 in an anoxic atmosphere. We have determined UV absorption spectra of 32SO2, 33SO2, and 34SO2 and described sulfur isotope fractionation factors as a function of wavelength [6]. Based on the estimated wavelengthdependence of the S-MIF, we suggested that UV-sheilding by OCS results in distinctive UV actinic spectra and can explain negative ! 33 S recorded in all the Archean sulfate deposits [4]. UV-shielding by SO2 (self-shielding) might have alternative effect on S-MIF [7], though such high SO2 level (>1ppm) is difficult to maintain unless volcanic SO2 flux is extraodinary high. Oxygenation of the atmosphere should decrease the atmospheric OCS levels and quantitative conversion of all atmospheric sulfur species into H2SO4, both of which result in cooling of surface temperature. Thus, the atmospheric sulfur cycling including OCS chemistry would have been more importatnt for Archean climate than previously thought. [1] Sagan & Mullen (1972) Science 177, 52–56. [2] Ueno et al. (2006) Nature 440, 516–519. [3] Haqq-Misra et al. (2008) Astrobiol. 8, 1127–1137. [4] Ueno et al. (2009) PNAS 106, 14784–14789. [5] Farquhar et al. (2000) Science 289, 756– 758. [6] Danielache et al. (2008) JGR 113, D17314. [7] Lyons (2007) GRL 34, L22811.
Figure 1: Stratigraphy, As contents in sediments, groundwater, and heavy mineral contents in sediments.
Goldschmidt Conference Abstracts 2010
Reactive solvation and transport simulations of OH– ions in aqueous environment: A multistate empirical valence bond (MS-EVB) approach
Testing forcing mechanisms of deglaciation: Cosmogenic dating of Laurentide Ice Sheet retreat in Wisconsin and surface mass balance modeling
I.S. UFIMTSEV1, A.G. KALINICHEV2, T.J. MARTINEZ1 3 AND R.J. KIRKPATRICK
DAVID J. ULLMAN1*, ANDERS E. CARLSON1, ALLEGRA N. LEGRANDE2, FARON S. ANSLOW3, MARC W. CAFFEE4, JOSEPH M. LICCIARDI5 6 AND KENT M. SYVERSON
1
Department of Chemistry, Stanford University, Stanford, CA 94305 (*correspondence: [email protected]) 2 Department of Chemistry, Department of Geological Sciences, Michigan State University, East Lansing, MI 48824 (*correspondence: [email protected]) 3 College of Natural Science, Michigan State University, East Lansing, MI 48824 Proton exchange reactions involving hydronium (H3O+) and hydroxide (OH-) ions in water are important geochemical and environmental process and significantly influence mineral dissolution and precipitation and the binding and transport of contaminants in soil and water. The abnormally high diffusion rate of these charge defects is attributed to the so-called Grotthus mechanism of successive proton exchange events between neighboring H2O molecules rather than simple ion diffusion. Numerous theoretical and experimental investigations of H3O+ diffusion in acidic solution provide a consistent picture of this process, in which the excess proton diffuses through successive interconversions between solvated H3O+(H2O)3 and (H2O···H···OH2)+ structures, known as Eigen and Zundel ions, respectively. The diffusion of the OH– ion in basic aqueous solutions was usually assumed to be simply a ‘mirror representation’ of the H3O+ transport, with the OH– ion having predominantly three H2O molecules in the first solvation shell that donate hydrogen bonds to it. However, recent theoretical and experimental studies have called this mechanism into question. These studies have produced alternative mechanisms involving a different OH– coordination scheme and a more complex solvent reorganization around the ion as the system approaches the transition state and the ion becomes capable of recombining with one of the nearest water molecule’s protons to form a different stable OH– ion. We have developed a new multistate empirical valence bond model of OH–(aq) suitable for classical molecular simulations, which accurately captures the major structural, energetic, and dynamic aspects of the proton transfer reactions around the hydrated OH– ion and is in good agreement with experimental data and the results of ab initio molecular dynamics simulations. The model predicts an approximately two-fold increase of the OH– mobility due to proton exchange reactions.
A1063
1
Dept. of Geoscience, Univ. of WI-Madison, Madison, WI (*correspondence: [email protected]) 2 NASA GISS & CCSR, Columbia Univ., New York, NY 3 Earth and Ocean Sciences, Univ. of British Columbia, Vancouver, BC Canada 4 Dept. of Physics, Purdue Univ., West Lafayette, IN 5 Dept. of Earth Sciences, Univ. of NH, Durham, NH 6 Dept. of Geology, Univ. of WI-Eau Claire, Eau Claire, WI Determining the phasing of Northern Hemisphere (NH) ice sheets relative to changes in insolation, greenhouse gases, and climate is key to understanding the mechanisms that give rise to ice ages and ice-sheet retreat. Early retreat of NH ice sheets ~19-24 ka suggests boreal insolation as the ultimate driver of ice retreat [1]. Alternatively, tropical sea surface temperatures (SST) and atmospheric CO2 may lead portions of ice-sheet retreat, implicating them as an alternative driver of deglaciation [2, 3]. Here, we present new 1°Be cosmogenic exposure dates from boulders on the terminal moraines of three distinct lobes of the Laurentide Ice Sheet (LIS) in Wisconsin. Until present, the retreat onset of this region was poorly understood through limited radiocarbon dates. This new cosmogenic chronology provides an important constraint on the retreat of the LIS southern margin at the LGM. To assess if boreal summer insolation could drive initial LIS retreat, we employ an energy moisture balance model to assess the LIS mass balance at the LGM with climate forcing from the Goddard Institute for Space Studies (GISS) ModelER. We compare the effects of alternate LIS topographies: the current standard ICE5-G [4] and an alternative reconstruction with lower topography over the Keewatin Dome [5]. We put these model results in the context of our new cosmogenic exposure dates and the existing retreat chronology for the LIS southern margin, testing the mechanisms controlling the onset of the last deglaciation. [1] Clark et al. (2009) Science 325, 710–714. [2] Lea et al. (2006) Quat. Sci Rev. 25, 1152–1167 [3] Stott et al. (2007) Science 318, 435–438 [4] Peltier (2004) ARES 32, 111–149 [5] Licciardi et al. (1998) Quat. Sci. Rev. 17, 427–488.
A1064
Goldschmidt Conference Abstracts 2010
Decrease in net methylmercury production following an iron amendment to tidal wetland sediments P.D. ULRICH AND D.L. SEDLAK* Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, USA (*correspondence: [email protected]) Tidal wetlands are often important sources of methylmercury (MeHg) in aquatic ecosystems. As a result, the restoration of wetland habitat may cause an increase of MeHg concentrations. In the Sacramento and San Joaquin Delta of California, concerns over potential increases in MeHg from wetland restoration are currently impeding wetland restoration efforts. There has been significant research into mercury biogeochemistry in wetland sediments, however, there have been few successful efforts to minimize the production and export of MeHg from restored wetlands. To provide a tool for controlling MeHg, we have evaluated the use of an iron sediment amendment to reduce net MeHg production in tidal wetland sediments. The addition of Fe [II] decreases MeHg production by lowering the concentration of bioavailable inorganic Hg [II] species that are methylated by bacteria. Under the reducing conditions typical of wetland sediments, dissolved Hg [II] speciation and concentration is controlled by sulfide species (i. e., S [-II]) with the concentration of dissolved bioavailable Hg [II] complexes increasing as porewater S [-II] increases. Addition of iron decreases the concentration of S [-II] through the formation of FeS (s). To test the potential use of iron addition to control MeHg production, microcosms collected from an estuarine tidal marsh in San Francisco Bay were amended with 180g-Fe/m2, 360g-Fe/m2 and 720g-Fe/m2 and operated under simulated tidal conditions. Shortly after iron addition, porewater S [-II] concentrations decreased at all iron doses relative to the control, and net MeHg production and export to the overlying surface water decreased by over 90% at the highest iron dose. Despite some conversion of FeS (s) to pyrite, the effects persisted for at least 12 weeks. Experiments were also conducted to assess the effects of marsh vegetation on MeHg production and examine the role of oxygen released from plant roots and decomposition of plant-derived organic matter. Our research suggests that it may be possible to control net MeHg production in certain tidal wetlands with an iron amendment. Field-scale application of iron addition is being used to assess the the efficacy of this approach under different conditions (e.g. plant communities, marsh elevation) encountered in tidal wetlands.
Research of saturation of mineral waters with quartz and amorphous silica in cold carbonic and nitric thermal waters in Southwest Transbaikalia I.D. ULZETUEVA, D.TS.-D. ZHAMYANOV, B.O. GOMBOEV AND V.V. KHAKHINOV Baikal Institute of Nature Management SB RAS, 8, Sakhyanova Str., Ulan-Ude, 670047, Russia ([email protected]) Silicon is a constant component of natural waters structure. Despite a wide occurrence of silicon circulation in natural waters and its essential role in behavior of many physical and chemical processes, until today insufficient attention is given to the quantitative definition of this component. In mineral waters, especially in thermal, the concentration of dissolved silicon can reach half of general mineralization that should affect their physical and chemical properties. In connection with it the consideration of factors with which the receipt and accumulation of silicon is connected is, undoubtedly, important. Detailed data about the content of silica in natural waters are necessary not only for the estimation of scales of migration of this component, but also for the decision of the question, concerning intensity of the rock aeolation, problems of their origin. Unique feature of the nitric thermal spring is the presense of high concentration of fluorine-ion (to 15 mg/dm3) and silicon (to 110 mgH4SiO4/dm3) in their structure of. Accumulation of these components in thermal waters is promoted by the alkaline environment and the elevated temperature. For the purpose of determining saturation of mineral waters with quartz and amorphous silica the solubility of these connections at various temperatures has been calculated. The received results have shown that all thermal waters are supersaturated in relation to quartz. However deposits of this compound in places of thermal spring discharging is not observed. Many researchers explain this by the extremely small speed of reaction of quartz crystallization from solution. Polymerization and deposition of silica never occurs until its concentration in a solution is below the solubility of amorphous silica. Results of calculations point out the lack of saturation of thermal and cold waters, at temperatures of their discharging, amorphous silica, that is, all silicon in these waters is in truly dissolved condition.
Goldschmidt Conference Abstracts 2010
A1065
U(VI) desorption from capillary fringe sediments
First-principles investigation of order-disorder phase boundary in ice
W. UM*, J.M. ZACHARA AND C. LIU
KOICHIRO UMEMOTO1, RENATA M. WENTZCOVITCH2, STEFANO BARONI3 3 AND STEFANO DE GIRONCOLI
Pacific Northwest National Laboratory, Richland, WA, USA (*correspondence: [email protected]) 1
U (VI) contaminated capillary fringe sediments at Hanford 300 Area are considered to secondary source for existing uranium plume in groundwater. Because seasonal water table elevation and water chemistry changed in response to nearby Columbia River stage, batch and column desorption experiments of U (VI) were conducted using two U (VI) contaminated sediments (11D and 39B). Solid phase characterization of these two sediments was performed to identify mineralogic and chemical factors controlling U (VI) desorption. The desorption behavior of U (VI) was different from the two sediments in spite of similar chemical and textural characteristics. Adsorption strength and sorbed U (VI) lability was higher in the near-river sediment, 11D. Inland sediment, 39B displayed low sorbed U (VI) lability (~10%) and measurable solid-phase carboante content. Kinetic desorption was attributed to regeneration of labile U (VI) in 11D. The U (VI) desorption reaction was best described as an equilibrium surface complexation reaction. The noted differences in U (VI) desorption behavior appear to result from U (VI) contamination and hydrologic history, as well as sediment carbonate content.
Geology and Geophysics, University of Minnesota, Minneapolis, MN, USA 2 Chemical Engineering and Materials Science, University of Minnesota, MN, USA 3 Condensed Matter Physics, SISSA, Trieste, Italy
Ice has a very rich phase diagram. Up to now, sixteen crystalline phases have been identified experimentally. This richness of the phase diagram originates in part in hydrogen order-disorder (OD) transitions. The ice VII-VIII boundary, a typical OD boundary, has been reasonably well constrained experimentally and is an ideal study case. We present a firstprinciples quasiharmonic study consisting in the complete statistical sampling of molecular orientations within a 16 molecule supercell. This supercell calculation accounts for several aspects of this transition, including the Clapeyron slope and the isotope effect. Research suppported by NSF grants ATM 0428874 (VLab) and EAR 0757903. Computations were performed at the Minnesota Supercomputing Institute.
Goldschmidt Conference Abstracts 2010
A1066
Using !-XRF and XAS to characterize the fate and bioavailability of manufactured nanoparticles in soil 1
1
JASON UNRINE *, AARON SHOULTS-WILSON , BRIAN REINSCH2, OLGA TSYUSKO1, GREG LOWRY2 1 AND PAUL BERTSCH
Dissimilatory iron reduction in subzero brines M.R. URSCHEL1, M.L. SKIDMORE2* AND G. GEESEY1 1
Department of Microbiology, Montana State Univ., Bozeman, MT 59717, USA ([email protected]) 2 Department of Earth Sciences, Montana State Univ., Bozeman, MT 59717, USA (*correspondence: [email protected])
1
University of Kentucky, Lexington, KY 40546, USA (*correspondence to [email protected]) 2 Carnegie Mellon University, Pittsburg, PA 15213, USA
Manufactured metal nanoparticles are likely to enter wastwater streams and partition to sewage sludge, which may be applied as biosolids to agricultral lands [1]. We have investigated the fate of a variety of Ag, Cu and Au nanoparticles in soils, as well as bioavailability and toxicity in nematodes (Caenorhabditis elegans) and earthworms (Eisenia fetida) using synchrotron based x-ray fluoresence microspectroscopy (!-XRF) microfocused x-ray absorption near edge spectroscopy (!XANES) and bulk extended x-ray absorption fine structure spectroscopy (EXAFS) as described previously for trace-element studies [2] along with gene expression studies. We have obtained strong evidence for the uptake and biodistribution of nanoparticles in earthworms and nematodes and have differentiated metal and metal oxide particle uptake from uptake of metal ions for Cu and Au (e.g. fig 1). We have also shown that reproductive effects of Ag nanoparticles are likely due to Ag+ exposure while behavioral effects are likely caused by the Ag nanoparticles.
Ferric iron (Fe3+) minerals are potential electron acceptors in cold and icy environments, such as those in the ice-hosted sediments in icebergs and glaciers [1]. Microbial dissimilatory iron reducers have been found in many icy environments, such as subglacial sediments [2], Arctic marine sediments [3], permafrost [4] and Antarctic sea ice [5]. Theoretical and laboratory studies have reported that supercooled, solute-rich veins within ice samples are viable habitats for microorganisms [6, 7]. Further, it has been suggested that dissimilatory iron reducers may reduce iron at temperatures as low as -9¡ C in the solute-rich vein network within basal ice [8], however, no direct evidence of microbial iron reduction at subzero temperatures has been reported to date. The gammaproteobacteria Shewanella frigidimarina was originally isolated from sea ice in eastern Antarctica [5]. This organism can respire on ferric iron, and has been demonstrated to grow at temperatures from 0 to 28¡ C, and salinities up to 8% NaCl [5]. We quantified the effect of temperature and salinity on the growth and iron reduction rates of S. frigidimarina at subzero temperatures. Cultures were incubated at 15¡ C, 4¡ C and -5¡ C, over a range of salinites from 0-8% NaCl. Our results indicate that S. frigidimarina is capable of growth at temperatures as low as -5¡ C at 2% and 4% NaCl in the presence of ferric citrate as sole electron acceptor and lactate as sole electron donor. No growth was observed at 8% NaCl over the temperature range tested. To the authorsÕ knowledge, these results represent the first direct evidence of an organism respiring and growing on ferric iron at subzero temperature and increased salinity. [1] Raiswell R. et al. (2008) Min. Mag. 72, 345Ð 348. [2] Foght J. et al. (2004) Microb. Ecol. 47, 329Ð 340. [3] VandiekenV. et al. (2006) Mar. Ecol. Prog. Ser. 322, 29Ð 41. [4] Zhang C. et al. (1999) FEMS Microb Ecol 30, 371. [5] Bowman, J. et al. (1997) Int J of Syst. Bact. 47, 1040Ð 1047. [6] Price B. (2000) PNAS 97, 1247Ð 1251. [7] Mader H. et al. (2006) Geology 34, 3, 169Ð 172. [8] Tung H. et al. (2006) Astrobiology, 6, 1, 69Ð 86.
Figure 1: X-ray fluorescence micrograph (top) showing a pixel of high Cu intensity in the main dorsal blood vessel of an earthworm (light micrograph bottom right). Interrogation of this pixel with XANES (bottom left) demonstrated that it was a mixture of Cu (0), CuO and Cu2O. [1] Gottschalk et al. (2009) Environ. Sci. Technol 43, 9216Ð 9222. [2] Punshon et al. (2005) Spectrosc Lett 38, 343Ð 363.
Goldschmidt Conference Abstracts 2010
Recent progress of small spot oxygen isotope analysis at WiscSIMS T. USHIKUBO*, N.T. KITA AND J.W. VALLEY WiscSIMS, Univ. of Wisconsin, Madison, WI 53706, USA (*correspondence: [email protected]) In situ, high precision oxygen two and three isotope analysis with a sub-µm to a few µm beam by SIMS is valuable technique to investigate records preserved in finely zoned samples [1-3]. Here, we report results of recent developments for high precision and accurate small spot oxygen isotope analysis at WiscSIMS laboratory. FC-EM (-EM) detectors: The quasi-simultaneous arrival (QSA) effect [4] would be a problem for isotope analyses when we use a small spot and low current (e.g. <1 µm, <10 pA) Cs+ primary beam. We observed more than +80ä fractionated "18O value with two electron multipliers (EM), which is probably a result of the QSA effect, while fractionations are generally less than ±10ä with Faraday Cups (FC). To minimize bias, we use a FC to detect 16O-, which is the major oxygen isotope. The instrumental mass bias of oxygen two (or three) isotope analysis with FC-EM (-EM) detectors and a small beam is consistent with that of multiple FC analysis with a 10 µm beam within a few permil. Matrix effect correction: The matrix effect of the instrumental mass bias (dependence on elemental composition of samples) with a small beam is different from that with a 10 µm beam. The matrix effect should be determined in the same analytical session. Blue LED luminous source for CCD camera image: For better spatial resolution of the CCD camera image to aim analysis points, we converted to a blue LED. We can recognize ~2 µm texture of sample with the CCD camera image vs. ~3 µm with white light. Sample preparation: A well-polished flat sample surface is important for an accurate isotope analysis [5, 6]. In addition, this is important for not only an aiming of tiny samples but also reducing 16OH- signal which interferes to 17O- signal. Since epoxy of sample mounts elevates pressure of the sample chamber and causes higher 16OH- signal, minimum usage of epoxy for sample mount is helpful for small spot oxygen isotope analysis [e.g. 2, 7]. [1] Page et al. (2007) Am. Mineral. 92, 1772Ð 1775. [2] Nakamura et al. (2008) Science 321, 1664Ð 1667. [3] Kozdon et al. (2009) Chem. Geol. 258, 327Ð 337. [4] Slodzian et al. (2004) Appl. Surf. Sci. 231Ð 232, 874Ð 877. [5] Kita et al. (2009) Chem. Geol. 264, 43Ð 57. [6] Valley & Kita (2009) MAC short course 41, 19Ð 63. [7] Nakashima et al. (2010) LPSC 41, #2309 (abstract)
A1067
Magnetite formation via FeII induced mineralogical transformations of ferric oxyhydroxides M. USMAN*, K. HANNA, M. ABDELMOULA AND C. RUBY LCPME/ CNRS-Nancy University, 54600, Villers-l• s-Nancy, France ( *[email protected], [email protected], [email protected]) The reactivity of various ferric oxyhydroxides (ferrihydrite Ô FÕ , goethite Ô GÕ and lepidocrocite Ô LÕ ) against FeII species was investigated to induce mineralogical transformations into magnetite (Fe3O4) at different aging times (1 hour, 1 day and 1 month). A parallel study was also conducted on three kinds of lab-synthesized goethite having different crystal structures, crystal morphologies and surface properties. The starting and final solid products were characterized by XRD analysis, Transmission Electron Microscopy and Mšs sbauer spectroscopy. The order of reactivity to transform into magnetite found was: F > L > G. Difference in morphology and particle size of generated magnetite was also observed dependent on the nature of initial substrates.
Figure 1: Untransformed amount (%) of ferric substrates at each time point. Rest was transformed into magnetite. Goethite was the least reactive as 33% was still present after one month. Reaction with other kinds of goethite suggest that the reactivity was independent of the specific surface area emphasizing the importance of the crystal structure for their reactivity. Different coordination modes of FeII with the different crystal faces of FeIII-hydroxide, which affect the FeIIFeIII electron transfer could explain this discrepancy in reactivity. Experiment with ferrihydrite mixed sand showed that silica sand (Quartz, 200-300µm) had no effect on this FeII induced transformation into magnetite.
A1068
Goldschmidt Conference Abstracts 2010
The influence of magmatism and magmatic fluids on the geochemical evolution of the Martian crust G. USTUNISIK1*, H. NEKVASIL1 AND F.M. MCCUBBIN2, 1
Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100 USA (*correspondence: [email protected]) 2 Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd., NW, Washington, DC 20015 ([email protected])
Experimental investigations of phase equilibria of martian lithologies have delineated the thermal stability of martian magmas and the minerals that crystallize from them under a variety of pressures and water contents. These experiments explain the basaltic character of the planet and predict variations in magma chemistry over time as the secondary crust thickened. Of particular importance to understanding the past surface environment is assessment of the role of magmatic processes in contributing halogens, water, and S to the surface and near-surface environments. This is accomplished through first and second boiling of volatilebearing magmas. However, the nature of the fluids exsolved, as well as the pressure at which exsolution occurs is strongly dependent upon melt composition as well as relative volatile abundance. Unlike the case for water-rich magmas, little is understood about the controls on fluid stability, the nature of such fluids, and their evolution during second boiling for water-poor, Cl-, S-, and F- enriched magmas with high Fe contents (as likely characterizes late martian magmas produced from a dehydrated mantle.) Such magmas may retain volatiles until close to the surface and thus become major contributors to the surface environment. Experiments have been launched to evaluate the effect of Cl, S, F on mineral and melt stability in martian magmas and the effect of pressure on volatile retention. First experiments have been conducted on an evolved Cl-, S-, F- enriched waterpoor (~0.4 wt% water) liquid from a Backstay parent and indicate a pronounced effect on mineral stability, most notably, on olivine, feldspar, and Ti- amphibole. Volatiles other than S are retained in the liquid. Additional experiments indicate, however, that at higher water contents, fluid can exsolve during first boiling at mid-crustal levels and produce amphibolite through reaction with a Humphrey composition wallrock. This amphibolite sequesters water and halogens, impeding their access to the surface. Additional experiments on water-poor compositions are assessing low-pressure exsolution, the nature of fluids given off, and their effect on wallrock alteration.
Characterization of natural hydrogen sources in ophiolitic context C. VACQUAND1,2*, A. PRINZHOFER1,2 AND E. DEVILLE1 1
Institut Français du Pétrole, 1, 4 avenue de Bois-Préau, 92852 Rueil-Malmaison Cedex, France (*correspondence: [email protected]) 2 IMPMC/IPGP 140 rue de Lourmel, 75015 Paris, France In an investigation of natural hydrogen sources and fluxes, gases with high concentrations of hydrogen were sampled in the Samail (Oman), Zambales (Philippines) and Antalya (Turquey) ophiolites. Chemistry and analyses of carbon, hydrogen and noble gases isotopes were associated to measurements of pH, Eh and temperature of the associated water where the gas is bubbling. Two types of gas composition exist in Oman: the first with about 75% hydrogen, 15% nitrogen and 10% methane, associated to ultrabasic pH waters and reducing conditions (pH about 11 and Eh < -250mV) whereas the second type is pure nitrogen associated with neutral pH water. The "13C of methane are extremely heavy ("13C = -10 to +5‰) and demonstrate an inorganic origin, while the noble gas analyses indicate a purely crustal source. The gases only seep from the ophiolitic rocks (gabbros and peridotites). The reaction yielding hydrogen is most likely to be a reaction of serpentinization: Olivine + Water ! Serpentine + Hydrogen + Magnetite with: 2Fe2+ + 2H2O ! 2Fe3+ + H2 + 2OHand the evolution of gas compositions corresponds to a secondary reaction generating methane through the reduction of CO2: 4H2 + CO2 ! CH4 + 2H2O This second reaction is variable from different geological areas: the Zambales ophiolite produces up to 50% methane, the one in Antalya (Turquey) produces more than 80% of methane. This exotic generation of hydrogen and methane may be present in much more common locations, extending the gas exploration out of the sedimentary basins.