Goldschmidt Abstracts 2010 – N

Goldschmidt Conference Abstracts 2010

A744

Influences of variable reactivity of calc-silicates on fluid fluxes in contact-metamorphic aureoles

Enhanced dissolution of cinnabar by dissolved organic matter in anoxic solutions

PETER I. NABELEK

K.L. NAGY1* AND M. KERR1,2

Department of Geological Sciences, University of Missouri, Columbia, MO 65211, USA ([email protected])

Simulations of fluid flow and mineral reactions A consequence of pluton emplacement into the upper crust is the generation of metamorphic aureoles and hydrothermal systems. When fluids have multiple components, the production of minerals and fluid flow are coupled. The primary influences on fluid fluxes are fluid-pressure gradients and permeability. In contact aureoles both vary over time as temperatures change, fractures develop, and rock volume changes with reactions. Numerical simulations were conducted to evaluate how differential reactivity of calcsilicate rocks influences fluid fluxes. The model aureole had subhorizontal calc-silicates with metamorphic minerals in the KCMASHC system interbedded with limestones with minor dolomite plus quartz and metamorphic minerals in the CMSHC system. The potential reactivity of the calc-silicates was significantly larger than that of the limestones. Seventeen reactions were included in calculations. Equations for the transport of heat and H2O and CO2 (assumed to be miscible) were solved iteratively. Pluton exsolved H2O between reaching saturation during crystallization and the solidus. The grid-spacing was 5!1 m. The 1 m vertical spacing reflects the scale of bedding in many contact aureoles. Transient enhancement of permeability was assumed to occur by fracturing when Pfl exceeded Plith and by increase in porosity with decrease in the volume of mineral assemblages during reactions. The potential porosity was 2.5% for limestones and 14.4% for calc-silicates.

Results Simulations show that the inner aureole stays overpressured during early stages of metamorphism as CO2 is produced by mineral reactions and this CO2 flows away from the pluton down the pressure gradient. High metamorphic fluid pressures initially force flow of magmatic H2O upward along the contact through fractures and preclude infiltration of the aureole until cessation of diopside-forming reactions. Higher reaction-enhanced permeability in calc-silicates ultimately results >10-fold higher H2O fluxes than through marbles. Model high-temperature minerals in calc-silicates include wollastonite and diopside whereas in the marbles they are forsterite, diopside and tremolite. The model assemblages correspond to those seen in analogous contact aureoles.

1

Department of Earth and Environmental Sciences, University of Illinois at Chicago, 845 West Taylor St., Chicago, IL 60607 (*correspondence: [email protected]) 2 Current address: Environmental Protection Agency, 77 West Jackson Blvd., Chicago, IL 60604-3507 Dissolution of cinnabar in the presence of simple quinones (hydroquinone and benzoquinone), selected as models for redox-active components of dissolved organic matter (DOM), and DOM (Suwannee River fulvic (SRFA) and humic (SRHA) acid from the International Humic Substances Society, and ‘walnut tea’ provided by D. Macalady) was investigated experimentally under anoxic and initially airequilibrated (oxic) conditions. Cinnabar was prepared as described previously [1] and released mercury concentrations were determined by CVAFS. Batch experiments under anoxic conditions were carried out in amber glass bottles using deionized water sparged initially with high purity Ar (g) and maintained under an Ar (g) atmosphere after addition of cinnabar and the organic reactant. Total released mercury was the sum of the amount in solution at the end of the experiment plus the cumulative amount released as Hg° (g), which was trapped in a second oxidizing solution and sampled with time. Experiments under oxic conditions were carried out either as in [1] or as in the anoxic experiments, but without sparging, and the concentration of dissolved mercury was measured with time. Benzoquinone increased slightly the amount of released mercury compared to the amount in pure water under oxic conditions; whereas at an equivalent ratio of mol quinone to cinnabar mass, hydroquinone had a much larger effect compared to pure water under anoxic conditions. Dissolution rates in units of mol Hg normalized to cinnabar surface area and mass of C were approximately 10, 20, and 50 times faster under anoxic compared to oxic conditions for SRHA, walnut tea, and SRFA, respectively (with oxic dissolution rates in reasonable agreement with those reported in [1]). This work was supported by the NSF, Geobiology and Low Temperature Geochemistry Program. [1] Waples, Nagy, Aiken & Ryan (2005) Geochimica et Cosmochimica Acta 69, 1575–1588.

Goldschmidt Conference Abstracts 2010

Extrapolating investigations of ion and molecular adsorption at the muscovite (001)-water interface to systems in Earth, environmental, and materials science K.L. NAGY1*, S.S. LEE2, C. PARK3, M.L. SCHLEGEL4, L. CHENG5, N.C. STURCHIO1 AND P. FENTER2 1

Department of Earth and Environmental Sciences, University of Illinois at Chicago, Chicago, IL 60607 (*correspondence: [email protected]) 2 Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, IL, 60439. 3 HP-CAT, Geophysical Laboratory, Carnegie Institution of Washington, Argonne, IL 60439 4 CEA, DEN, UniversitŽ dÕ Evry-Val dÕ Essonne, UMR 8587 LAMBE, F 91025 Evry, France 5 Truman College, City Colleges of Chicago, Chicago, IL 60640 Over ten years ago, we began investigating adsorption processes at the muscovite (001)-water interface using in situ X-ray reflectivity to understand the reactivity of this unique representative charged surface, which occurs in soils and sediments in the form of detrital micas and clays. Advances in experimental design and measurement along with implementation of resonant anomalous X-ray reflectivity have led to acquisition of data for monovalent cation, divalent cation, and dissolved organic matter systems over a range of pH at ambient conditions. From the data, which provide bulk and element-specific electron density in layers parallel to the (001) surface with • ngstrom-scale resolution, a new detailed picture of the distributions of and interactions among ions, water, and organic molecules has emerged. We are developing quantitative expressions for the energetic balance between hydration and electrostatic attraction in the interfacial region that enhance models of the electrical double layer. We show how the results apply to the disposition of toxic metals and nutrients in soils and sediments, the mobility of cations in natural waters, the formation of mineral and organic colloidal aggregates in natural waters, and the general behavior of charged surfaces in materials science. Support has been provided by the U.S. DOE, Office of Basic Energy Sciences, Geosciences Research Program and NSF, Geobiology and Low Temperature Geochemistry Program.

A745

Stable chlorine isotope study of standard rocks and Allende meteorite by TIMS N. NAKAMURA1*, L. NYQUIST1, Y. REESE2 3 AND C.-Y. SHIH 1

NASA Johnson Space Center, Houston, TX 77058 (*correspondence: [email protected]) 2 ESCG/Muniz Engineering, Houston, TX 77058 3 ESCG Jacobs-Sverdrup, Houston, TX 77058 Current chlorine isotope studies on planetary materials are controversial among IRMS (gas source mass spectrometry) and/or TIMS (Thermal Ionization Mass Spectrometry) groups [e.g. 1-3]. We have initiated development of the TIMS technique at NASA JSC in order to analyze small amounts of meteoritic and planetary materials. For silicates, we use an HF-leaching method similar to that of Musashi et al. [4]. Cl is analyzed as Cs2Cl+. The composition of our laboratory standard was well established in previous work; !37ClSMOC = -2.49 ± 0.21ä [ 5]. We report TIMS results for two standard rocks, JB2 and JB3, that have been analysed by the IRMS technique [1, 4]. Values of !37Cl (ä) SMOC obtained were 0.32±0.07 for JB2 and 0.53±0.20 (1 "), for JB3, resp. (Fig. 1). The JB3 value is in agreement with [4] (0.55 ±0.10) within 1" error. The JB2 value is ~0.8 ä higher than that of [1]. Preliminary analyses of Allende give !37ClSMOC = -1.41 ± 0.15ä similar to -1.90 reported by Bonifacie et al.[2].

Figure 1: Preliminary results for JB2 and Cl laboratory standard (Nakalai tesque CsCl reagent) and Allende whole rock (WR). Individual data points represent the mean of 300 ratios/run. The !37Cl (ä) SMOC shows permil deviation from seawater. [1] Bonifacie et al. (2007) Chem Geol, 242, 187Ð201. [2] Bonifacie et al. (2008) Science 319, 1518Ð 1520. [3] Sharp et al. (2007) Nature 446, 1062Ð 1614. [4] Musashi et al. (1998) Anal. Chim. Acta 362 261Ð 269. [5] Numata et al. (2001) Geochem. J. 35, 89Ð 100.

A746

Goldschmidt Conference Abstracts 2010

Excess N2 formation by denitrifcation in the Indian Ocean oxygen deficient zone estimated by simultaneous N2, Ar, and O2 measurements

Role of ferric and aluminum ions for silica biodeposition on the surface of microbes GAOWA NAREN1, SHUQIN BAI2, YOSHIHIRO OKAUE1 1 AND TAKUSHI YOKOYAMA

N. NAKAYAMA*, T. OGURA AND T. GAMO 1

Ocean Research Institute, University of Tokyo, Japan (*correspondence: [email protected]) Accurate measurement of N2/Ar ratio in seawater at oxygen deficient zones (ODZs) makes it possible to estimate production of excess N2 by denitrification. We constructed a quadruple mass spectrometer (QMS) system for on-board simultaneous measurement of dissolved gasses (N2, O2 and Ar) and applied it for the Indian Ocean oxygen deficient zone during KH-09-5 cruise (R/V Hakuho-maru, 27th Nov–16th Dec, 2009). Approximately 100 ml seawater samples were taken into 300 ml glass bottles which were first poisoned with 250 µl of saturated HgCl2 solution to impede biological activity and then evacuated prior to the sampling [1]. Dissolved gasses were extracted from the seawater in high vacuum line, where H2O and CO2 were removed by cold traps. The purified sample gases were injeced into the QMS and ion peaks of N2, O2 and Ar were simultaneously measured. Absolute dissolved O2 concentration was determined by the Winkler titration method independently. Oxygen minimum zones (OMZs), which was defined as the depth zone O2 concentration was below 20 µM, were observed in 100–1000 m depth in the staions with their latitudes higher than 14°N. The ! (N2/Ar), defined as a deviation of N2/Ar from the the value at their equilibrium condition with atmosphere, reached a maximum supersaturation value (~+4%) around 200 m depth within the OMZ. Nitrite concentration also increased within the OMZ with a maximum of 4–14 µM around 150 m depth. These results clearly indicated that denitrification was occuring in the OMZ. We estimated an excess N2 generated by denitrification process in the OMZ using a proposed equation [2]: [N2]excess = [# (N2/Ar)sample – # (N2/Ar)background]*[N2](T, S). Average of the excess N2 was about 26 µg-at N and maximum was about 30–34 µg-at N around 200 m depth. [1] Hamme & Emerson (2002) Geophys. Res. Lett. 29(23), doi:10.1029/2002GL015273. [2] Devol et al. (2006) Deep-Sea Res. I 53, 1533–1547.

Department of Chemistry, Faculty of Sciences, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan ([email protected]) 2 College of Environment and Resources, Inner Mongolia University No. 235 West University Road, Saihan-qu, Huhhot 010021, China In order to elucidate the mechanism of silica biodeposition in geothermal field that ferric and aluminum ions participate, adsorption behavior of silicic acid to ferric and aluminum ions combined on Chelex 100 (Fe type Chelex 100 and Al type Chelex 100) was examined. Since the functional group is iminodiacetate, Chelex 100 was selected as a model compound of the surface of microbe. No silicic acid was adsorbed to the original Chelex 100 (Na type Chelex 100), whereas silicic acids were adsorbed to the both Fe and Al type Chelex 100. The ferric and aluminum ions and silicic acid on the Chelex 100 were characterized by 57Fe Mössbauer, XAFS and 29Si MAS NMR and 27Al MAS NMR and SEM-EDX. From the XANES and 27Al MAS NMR spectra for the Fe and Al type Chelex 100, it was confirmed that ferric and aluminum ions were combined as a tridentate complex with iminodiacetate group. It is suggested for Fe and Al type Chelex 100 before and after reaction with silicic acid that the silicic acids are chemically adsorbed to Chelex 100-Fe, Al-OH sites by the formation of Chelex-100-Fe, Al-O-Si (OH)3 bonds from the 57Fe Mössbauer and 27Al MAS NMR spectra. Judging from the 29Si MAS NMR and SEM-EDX measurements for the surface of Fe and Al type Chelex 100 particles, Chelex 100-Fe, Al-OH sites act as a template for the successive adsorption of silicic acids to form silica. In conclusion, the ferric and aluminum ions combined with the surface of microbes act as adsorption sites of silicic acid and play an important role for the biodeposition of silica from hot spring water.

Goldschmidt Conference Abstracts 2010

Analysis of trace elements in glass and pyroxene by LA-ICP-MS: Results from the rhyolitic ashfall and ashflow tuffs of the Bruneau-Jarbidge eruptive center, Yellowstone hotspot track 1

1

B.P. NASH , H.E. CATHEY , C.M. ALLEN 2 AND I.H. CAMPBELL

2

1

Dept. of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112, USA ([email protected]) 2 Research School of Earth Sciences, The Australian National University, Canberra ACT 0200, Australia

Trace concentrations of 37 elements were measured in individual glass shards and pyroxene crystals from the multiple eruptive units of the 12.7 – 10.5 Ma Cougar Point Tuff (CPT) of the central Snake River Plain, Idaho, USA, including glass from ashfall and pigeonite and augite crystals from ashflow deposits. The rhyolitic CPT is recognized for its polymodal assemblages of both glass and minerals within individual units, for the recurrence of these distinctive polymodal assemblages in different eruptive units, and for sustained high magma (900-1000°C) temperatures. In situ trace element analyses by LA-ICP-MS demonstrate that individual compositional modes of glass and pyroxene that recur in different units, and that are indistinguishable from one another with respect to major and minor elements, in fact have distinct trace element abundances and thereby afford a means of fingerprinting individual units as well as provide evidence against a xenocrystic (or antecrystic) heritage for minerals. Pyroxene-melt and pigeonite-augite partition coefficients are presented for Sc, V, Cr, Co, Ni, Zn, Sr, Y, Zr, Hf, and all REE but Tm. Glass in fallout ash of the CPT ranges over 72–75 wt % SiO2 and 1.8–2.6 wt % Fe2O3 and the multiple glass modes fall broadly into two groups according to Fe content. Pyroxene-melt KDs are determined from glass-mineral pairs in tuffs and lavas that bear homogeneous, unimodal glass from the low Fe group and unimodal compositions of unzoned pyroxene. Units that are bimodal with respect to glass (i. e. high and low Fe components) and pyroxene provide a basis for estimating mineral-melt partition coefficients involving the high Fe glass. This study suggests that partition coefficients vary between the two groups, and are function (s) of temperature and/or composition. Pigeonite-augite partition coefficients determined from multiple sets of equilibrium mineral pairs remain constant over the observed range of compositions and temperatures. Calculated mineral-melt partition coefficients applied to glasses of subtly different compositions successfully predict the observed range of trace element compositions of pyroxene, permitting a framework for assigning mineral modes to glass modes in heterogeneous assemblages, a task previously hampered by the absence of pumice in both ashflow and ashfall deposits of the central Snake River Plain.

A747

Abiogenic-biogenic bases of the genesis and synthesis of natural hydrocarbons in the Earth’s lithosphere (by fluid inclusions research) I. NAUMKO AND YO. SVOREN’ Institute of Geology and Geochemistry of the Combustible Minerals of NAS of Ukraine, 3a, Naukova St., Lviv, 79060, Ukraine ([email protected]) Conditions and processes of generation of the greater part of useful minerals are clearly fixed by fluid macro- and microdefects (in particular, and by fluid inclusions), first of all, in veinlet-impregnated minerals [1]. Proceeding from the created basis of knowledge about ‘thermobarometry and geochemistry of gases of veinlet-impregnated mineralization in deposits of oil-gas-bearing areas and metallogenic provinces’ [2] we were able to solve and explain from new dualistic (abiogenic-biogenic) positions both hydrocarbon synthesis with their genesis and formation of actually veins and impregnates in the Earth’s crust. It was shown that a mechanism of hydrocarbon synthesis in natural processes of oil-gas formation can be realized only in the deep-seated faults of the Earth’s lithosphere in the environment of deep-seated high-temperature fluid [3]. On the basis of present physical-chemical model it was stated that this deep-seated high-temperature fluid is actually the principal, the main and the important source of powerful energy as soon as sufficient enough amounts of initial substances for synthesis of hydrocarbon in its medium. The scientific novelty of $ new dualistic (abiogenicbiogenic) theory of synthesis and genesis of natural hydrocarbons (oil, gas etc.) [4] is based on elucidated wholly new and unaccounted up to now natural phenomena such as the generation of an appearance of additional powerful adiabatic compression of fluid and high-voltage electric field, the formation of tectonic macro- and micro-cracks and various submicrodefects in solids, the creation of oxidizing-restorative reaction medium, the synthesis of hydrocarbons and the formation of oil and gas fields (deposits), the formation of veinlet-impregnated mineralization %t&. This differs it principally [1] both from now prevailing theories and other notions of the origin of natural hydrocarbons and the formation of their fields (deposits) in the Earth’s crust. [1] Naumko (2006) Doctoral thesis, p.52. [2] Svoren’ et al. (1994) Geol. & Geochim. Combust. Minerals 3–4(88-89), 54– 63. [3] Naumko & Svoren’ (2003) Moscow, IPNG 62–63. [4] Svoren’ & Naumko (2006) Rep. of the NAS of Ukraine 2, 111–116.

A748

Goldschmidt Conference Abstracts 2010

The isotopic composition of carbon and oxygen of calcite of veinlets and enclosing rocks within the limits of the Lopushna oil field (Ukrainian Carpathians) I. NAUMKO1*, V. ZAGNITKO2 AND YU. BELETS’KA1 1

Institute of Geology and Geochemistry of the Combustible Minerals of NAS of Ukraine, 3a, Naukova St., Lviv, 79060, Ukraine ([email protected]) 2 Taras Shevchenko Kyiv National University, 90, Vasylkivska St., Kyiv, 03022, Ukraine ([email protected]) We have quoted the results of the isotopic composition research of carbon and oxygen from calcite of veinlets and enclosing rocks within the limits of the Lopushna oil field the oil deposits of which are confined to the platform sediments of Paleogene, Cretaceous and Jurassic overlapped by overthrust of the Carpathians [1]. The isotopic analysis has revealed sufficiently homogenous values both of "13', correspondingly, -2.3÷+2.5 and -0.1÷+3.8 ‰ (standard PDB), and "18( – 22.2÷27.7 and 23.4÷30.5 ‰ (standard SMOW) that are not correlated with a depth of occurrence and a spatial distribution of a veinlet, the composition and the age of the enclosing rocks etc. It is established too that carbon from veinlet’s calcite is always a little more heavy (enriched by isotope 13') comparatively with carbon of calcite of enclosing rocks, but oxygen, on the contrary, too light (impoverished by isotope 18(). This testifies to the influx of mineral forming fluids through thick systems of fractures due to vertical migration processes [2]. Moreover, data reached have confirmed the one-act character of the entrance of the hydrocarboncontaining fluids at an interval between the Middle and Late Pliocene [3] caused by tectonic activization that promoted the region’s reconstructing and regenerating old and, correspondingly, opening new paths for penetration of fluids. Then traps with the formation of deposits of the oil in rocks of different age were filled with their hydrocarbon component. Healing of fractures by the mineral substance of deep-seated high-temperature fluids with the formation of the calcite veins and veinlets probable occurred from the single homogenized source [4]. [1] Atlas of oil & gas fields of Ukraine (1998). [2] Svoren’ & Naumko (2006) Rep. of the NAS of Ukraine 2, 111–116. [3] Ladyzhenskyi (1961) Geol. Collect. Lvov. Geol. Society 7/8, 79–88. [4] Naumko (2006) Doctoral thesis, p.52.

Importance of porosity in saprolite formation on basalt ALEXIS K. NAVARRE-SITCHLER1 CARL I. STEEFEL2 3 AND SUSAN L. BRANTLEY 1

Environmental Science and Engineering Division, Colorado School of Mines, Golden CO ([email protected]) 2 Lawrence Berkeley National Laboratory, Berkeley CA 3 Center for Environmental Kinetics Analysis, Pennsylvania State University, University Park PA

Weathering of rock to saprolite plays an important role in sustaining terrestrial ecosystems. Rock weathering induces mineralogical and structural changes that release nutrients and increase the ability of the rock to retain water for uptake by microbial and plant life. Despite the importance of this process we are currently unable to predict how fast rock weathers to form saprolite, in part due to a widely observed discrepancy in weathering rates with scale. Studying weathering at scales intermediate to watershed and laboratory will help elucidate controlling processes in natural weathering systems and provide better understanding of scaling of weathering rates. This study examines in great detail the processes that control how fast rock weathers to saprolite on basalt clasts with weathering rinds. These basalts have been weathering for 35 to 250 ka in an environment protected from physical erosion. The parent basalt (~67% plagioclase and 27% augite) weathers to form a rind of gibbsite and iron oxide. Detailed analyses of the reaction front between the weathering rind and parent core show complete dissolution of plagioclase and augite and an increase in porosity from <3% to > 25% across a 1-2 mm wide zone. Numerical reactive transport models show that understanding the porosity increase is a critical component of predicting rates of saprolite formation. In fact, once porosity generation is accurately described, we are able to predict the growth of weathering rinds on these clasts over hundreds of thousand of years using laboratory derived dissolution rates.

Goldschmidt Conference Abstracts 2010

Fractionation of Cu isotopes during adsorption and metabolic uptake by bacteria J.U. NAVARRETE* AND D.M. BORROK University of Texas at El Paso, Department of Geological Sciences, El Paso, TX 79968 (*correspondence: [email protected], [email protected]) Here we use Cu isotopes (measured as the ratio of 65 Cu/63Cu and reported in delta notation relative to the NIST 976 standard) as a tool to investigate Cu-bacteria interactions, including surface adsorption and metabolic uptake. Experiments were conducted with individual Gram-positive (Bacillus subtilis) and Gram-negative (Escherichia coli) bacterial species and with bacterial consortia from several natural environments. Adsorption experiments were conducted with live or dead cells over the pH range 2.5 to 6 (to prevent precipitation of Cu). Surface adsorption of Cu onto live bacteria cells resulted in separation factors (#65Cusolution-solid = "65Cusolution - "65Cusolid), of +0.25‰ to +1.3‰ for B. subtilis and +1.0‰ to +2.4‰ for E. coli. The preference of the lighter Cu isotope in the cells appears to be metabolically-driven, as heat-killed bacterial cells preferentially adsorbed the heavier Cu isotope. Furthermore, the "65Cusolution of the live cell adsorption experiments evolved as a function of time, despite the fact that the total amount of adsorbed Cu remained constant. Bacteria in the metabolic uptake experiments (i.e. grown in Cu-citrate-rich media) preferentially incorporated the lighter Cu isotope with a #65Cusolution-solid of ~ +2.0‰. Our results demonstrate that live bacterial cells preferentially sequester the lighter Cu isotope regardless of the experimental conditions. The mechanisms involved are likely related to the active cellular transport and regulation of Cu. Hence, Cu isotopes may prove to be powerful tools for probing molecular-scale bacteria-Cu interactions. Conversely, Cu isotopes in natural systems may be used distinguish bacterial activity.

A749

Sources of diamond-forming fluids O. NAVON1*, Y. WEISS1 AND W.L. GRIFFIN2 1

The Fredy and Nadine Herrmann Institute of Earth Sciences, the Hebrew University of Jerusalem, Israel (*correspondence: [email protected], [email protected]) 2 GEMOC, Macquarie University, NSW, Australia ([email protected])

Diamond-forming fluids trapped as microinclusions in fibrous diamonds are a unique samples of mantle fluids to which inferred metasomatic fluids can be compared. The major-element composition and volatile content of these highdensity fluids (HDFs) span two arrays: (a) between a high-Mg carbonatitic end member and a saline one and (b) between a low-Mg carbonatitic end member and a hydrous-silicic one; and are attributed to melting of carbonated peridotite and carbonated eclogite, respectively [1]. All four end-members are rich in K2O and in the highly incompatible trace elements (alkalies, LILE, LREE, Nb and Ta). A closer examination of the trace elements between Cs and La reveals two patterns. One is mostly flat and has moderate decrease of concentrations with decreasing ionic radius (‘Bench’); the other (‘Table’) has elevated Ba, U, Th and LREE, depleted Nb and Ta and in most cases, highly depleted alkalis (K, Rb and Cs). The two can be best distinguished by their U/Rb and La/Nb ratios. Both patterns were found in HDFs of both arrays suggesting decoupling between the major and trace elements. The smooth ‘Bench’ pattern can be approximated by very small degree of melting of a PM or OIB source with no need for accessory phases. The more fractionated ‘Table’ pattern can be produced by melting of a SCLM source with ~1% carbonate and ilmenite and 0.5% phlogopite and rutile. It cannot be produced by melting a PM source. Looking for a possible relation between the two patterns, we examine the possibility to produce ‘Tables’ from ‘Benches’ by fractional crystallization or percolation. The first requires the removal of more than 80% phlogopite, which is not compatible with the major element data. Percolation of a melt with a ‘Bench’ pattern through SCLM rocks with the above accessory phases also lead to evolution of a ‘Table’ pattern. Conclusion: the ‘Bench’ patterns can be produced by melting an asthenospheric source and the ‘Table’ by melting of SCLM or by percolation of ‘Bench’-like fluids through SCLM rocks. In either case, melt must be collected from a large volume to explain the similarity in patterns and the uniform carbon-isotope composition of fibrous diamonds. [1] Weiss et al. (2009) Lithos 112, 660–674.

A750

Goldschmidt Conference Abstracts 2010

Size-induced shifts in oxidationreduction phase equilibria in nanophase transition metal oxides ALEXANDRA NAVROTSKY* AND CHENGCHENG MA 1

UC Davis, NEAT ORU, One Shields Ave, Davis, CA 95616, USA (*correspondence: [email protected]) ([email protected])

It is now well established that difference in surface energies can alter the relative free energies of different polymorphs, causing size driven thermodynamic crossovers in phase stability at the nanoscale. It has also been shown that, because oxyhydroxides generally have smaller surface energies than oxides, dehydration equilibria, e.g. goethite to hematite plus water, can shift to higher temperature by as much as 100 K at the nanoscale (4). A general formulation of the effect of particle size on chemical equilibria among solid phases is that increasing surface area will favor the phase assemblage of lower surface energy. There is now new thermochemical evidence for strong thermodynamic shifts in the position of oxidation-reduction (redox) equilibria in oxides at the nanoscale. Using new calorimetric data on surface energies in the cobalt–oxygen system, we show that the thermodynamic phase field in oxygen fugacity–temperature space of the divalent rocksalt oxide CoO is substantially narrowed at the nanoscale, bringing the reduction to Co metal to higher oxygen fugacity and the oxidation to Co3O4 spinel to lower oxygen fugacity at a given temperature. Metals generally have lower surface energy than oxides and we present evidence that spinels have lower surface energy than rocksalt oxides. Thus the contraction of the stability field of the divalent oxide, MO, relative to the metal, M, and the spinel M3O4, is probably a general phenomenon. In the iron-oxygen system, wustite, Fe1-xO, is thermodynamically unstable with respect to iron and magnetite, Fe3O4, below the melting point of bulk wustite (1650 K) for particle sizes below 16 nm, in contrast to being stable above 850 K for the bulk. These size-driven redox changes have implications for material preparation and characterization, catalysis and the splitting of water in the presence of transition metal oxide nanoparticles, as well as for environmental, geological, and biological redox reactions.

Thermodynamic issues in nanoscale actinide oxides ALEXANDRA NAVROTSKY*, TATIANA SHVAREVA AND MIKHAIL AIZENSHTEIN UC Davis, NEAT ORU, One Sheilds Ave, Davis, CA, USA (*correspondence: [email protected]) ([email protected], [email protected]) Colloids, clusters, and nanoparticles provide major possible routes for the transport of radionuclides, including actinides, in the aqueous environment. Thus understanding the energetics of nanoscale oxides is critical to predicting their reactivity and dissemination. Two factors are particularly important - the dependence of energetics of a phase on its particle size (which can influence its solubility as well as its kinetics of dissolution/precipitation) and the influence of particle size on the thermodynamics of redox equilibria. We have extended our studies of surface energies of nanophase oxides to thoria. The surface energy and enthalpy of water adsorption of thoria nanoparticles with cubic fluorite structure have been studied for the first time by direct calorimetric methods. Four samples with particle size 4.7, 5.9, 10.1, and 17.3 nm were prepared by co-precipitation method and surface enthalpy was determined from the variation in enthalpy of drop solution with surface area taking measured integral enthalpy of water adsorption (–81.1 ± 3.7 kJ/mol) into account. Surface enthalpies are 1.3 ± 0.4 J/m2 for the hydrated surface and 1.9 ± 0.3 J/m2 for the anhydrous surface. These preliminary values are similar to surface energies of C-type Y2O3 (1.3 ± 0.2 J/m2 for the hydrated surface and 1.7 ± 0.1 J/m2 for the anhydrous) as well as those of Y-doped zirconia with fluorite structure (0.8 – 1.3 J/m2 and 1.2 – 1.8 J/m2 for hydrous and anhydrous surfaces respectively for variable yttria content). Preliminary data for Y-doped HfO2 (1.0 – 1.5 J/m2 and 1.8 – 2.4 J/m2 for hydrous and anhydrous surfaces respectively) also are similar to the values for ThO2. Thus it appears that the surface energy of fluorite-structured oxides does not depend strongly on the nature of the cation (or the metal-oxygen distance, ionic radius, or lattice parameter) and we predict similar values for UO2 and other tetravalent actinide oxides. We recently found that differences in surface energies among phases of different oxidation state (e.g. Co metal, CoO, and Co3O4) can significantly changethe positions of redox equlibria. Though we do not yet have data for uranium phases, we suspect that similar effects will be seen, with small particle size thermodynamically favoring the phase assemblage of lowest surface energy. Whether such effects can significantly shift uraninite - uranyl mineral equilibria depends on the difference in surface energy between these phases, which we plan to measure in the future.

Goldschmidt Conference Abstracts 2010

Comparative geochemical analysis of arsenic hotspots and low-As areas in Murshidabad, West Bengal, India 1

2

2

A. NEAL , J. HAUG , K. JOHANNESSON , B. PURKAIT 1 AND S. DATTA *

3

1

Dept. of Geology, Kansas State University, Manhattan, KS 66506 (*correspondence: [email protected]), 2 Dept. of Earth and Environmental Science, Tulane University, New Orleans, LA 70118 3 Geological Survey of India, Kolkata 700016, India Groundwater and shallow aquifer sediments (2m-40m) were collected from areas in the Murshidabad district of West Bengal, India, to study their hydrochemical and geochemical properties and examine relationships between groundwater arsenic (As) and solid-phase As concentrations and speciation. Six areas (~1km2 each) over a total stretch of 60km have been targeted: two areas with very low (<10ppb) As levels west of the river Bhagirathi and four areas with very high (>4000ppb) As levels east of the Bhagirathi. The As hotspots east of the Bhagirathi tend to be very localized, occurring primarily along the Holocene floodplains of the river Bhagirathi and also to the west of the confluence of the Ganges-Brahmaputra and Meghna rivers. The mineralogy of the aquifer sediments consists of quartz and feldspars with major amounts of iron-carbonate bandings around silicate grains, along with phyllosilicates, amphiboles, and other carbonates. In high-As areas, sediments are light to dark gray in color and dominated by micas and Mg-rich minerals. Fe- and Mn-rich minerals are found in greater concentrations in high-As areas than in low-As areas. Low-As area sediments are orange-brown in color with prominent quartz and feldspars and a few calcite grains only. Solid phase whole sediment analysis from surface to deep aquifer sediment in the gray arseniferous sediments shows an enrichment of Mg with depth, which indicates either this Mg originates from biotite/micas or clay minerals, and further, can be hypothesized to adsorb the As to some extent. Dissolved As concentrations in groundwater are increasing from west to east for both total As and As (III), (15 samples, with an average of ~74% of the total As being in the form of As (III) (range: 55-98%) in high-As prone areas. The pH of high-As waters is clustered at a circumneutral pH (6.8-7.1), whereas low-As areas have a pH distinctly either above or below the median value. Conductivity displays the same central-clustered trend with high-As values (724-868)S/cm). DO and ORP range from 2.3-4.7mg/l and 57-388mV, respectively, for high-As waters. High concentrations of iron, phosphate, and ammonia and low concentrations of chloride and sulphate are characteristic of groundwater with high As. As and Fe speciation studies of the sediments are currently underway by both UV-VIS as well as synchrotron based X-ray probe analysis of the clays. DIC values and 18O values are currently being analysed to understand sources of the aquifer recharge and how these waters may affect the behaviour of arsenic.

A751

The Moon 40 years after Apollo: Why we need to go back CLIVE R. NEAL Dept. of Civil Engineering & Geological Sciences, University of Notre Dame, Notre Dame, IN 46556, USA ([email protected]) The Moon is the only body in the solar system that humans have visited, explored, and have returned samples from known locations. Long duration experiments were also set up on the lunar surface by the Apollo astronauts (ALSEPs) that gave important information on the lunar environment and interior. While some suggest that we can designate the Moon as ‘explored’, it should be remembered that Apollo explored <5% of the lunar surface in a small area on the equatorial nearside and the data acquired have several deficiencies: 1) The small area visited by Apollo limited the detail that could be seen in the Apollo seismic data for exploring the deep lunar interior. 2) Subsequent orbital missions (Clementine, Lunar Prospector) produced global compositional maps and demonstrated there were terrains that Apollo did not visit and that the sample collection was not be representative of the basalt types on the Moon. 3) When the Apollo ALSEP data are viewed in terms of lunar terraces, the heat flow data become ambiguous. Lunar Prospector produced evidence for hydrogen deposits at the lunar poles, which are currently being further explored by the LCROSS and LRO missions. The Japanese Kaguya mission has better defined the farside gravity field, defined regions of pure anorthosite, and gave the first look at the shallow subsurface on a regional scale. The Indian Chandrayaan mission showed the character and spatial distribution of OH/H2O on the lunar surface and indicated the presence of water ice in the polar cold traps. Continued study of the Apollo samples has also shown the presence of water in the lunar interior. So why do we need to continue to study the Moon? Examples of why include: 1) Dating of planetary surfaces through crater counts is based upon the chronology developed for the Moon and anchored by sample analysis; targeted sample return of impact melt from large lunar craters will considerably enhance exploration not only of the Moon, but other planetary surfaces. 2) Space weathering of airless bodies is understood from analysis of lunar samples in conjunction with orbital data. 3) The Moon represents an early end-member in terrestrial planet evolution. Apart from being an obvious place for humans to learn to live and work productively off planet, the Moon holds scientific keys for understanding the origin and evolution of terrestrial planets and represents the Rosetta Stone for the study of our solar system.

A752

Goldschmidt Conference Abstracts 2010

Experimental studies of CaEsk component in pyroxene at high PT

The role of Ca pools in the calcification process of foraminifera

P. NEE1, S.-T. ZHAO1,2, H.W. GREEN II1 1 AND L.F. DOBRZHINETSKAYA *

GERNOT NEHRKE1*, LENNART DE NOOIJER1, GERALD LANGER1, ANDERS MEIBOM2 1 AND JELLE BIJMA

1

University of California, Riverside CA 92521, USA (*correspondence: [email protected]) 2 China University of Geosciences, Wuhan, China It was discovered in the 1960-70s that many eclogitic pyroxenes show nonstoichiometry, (‘excess SiO2’) caused by the reaction: CaAl(AlSi)O6 + 3SiO2 ! Ca!Al2Si4O12. The reaction runs to the right by substitution of Si for Al in tetrahedral sites, displacing Al to M1 octahedral sites, where it is electrically balanced by a vacancy. The right side of the reaction has a smaller volume than the left, hence increasing pressure drives the reaction to the right. Day & Mulcahy [1] showed three possible ways of SiO2-exsolution: (1) vacancy consumption in non-stoichiometric pyroxene; (2) dissolution of Ti-phases in pyroxene or garnet; (3) reactions between accessory phases and either pyroxene or garnet. We have conducted a series of ‘dry’ experiments in a Walker-style multianvil apparatus at P = 6, 8, 10, 12 GPa, and T = 900, 1000, 1100 and 1200°C using powdered glass of the composition (wt%): SiO2 = 58.29, Al2O3 = 24.12, MgO = 5.44, CaO = 11.37, Na2O = 0.78. Our experiments demonstrate that at given bulk chemistry the Px with the largest CaEsk value is crystallized at P=6 to 8GPa at all temperature ranges; with increasing P up to 12GPa and T up to 1200°C the CaEsk component tends to decrease. Our data are in a good agreement with experiments by [2] because CaEsk component exhibits similar tendency, though the values of the CaEsk components are significantly different due to differences in the bulk chemistry chosen as starting materials. For example, Px synthesized from the starting material A toleiite at 10GPa, 1200°C contains CaEsk = 0.10 [2], whereas at similar conditions we have synthesized Px with CaEsk = 0.19. Our experiments showed that the nonstoichiometry of omphacite reaches a maximum between 5 and 8 GPa, followed by rapid decrease in CaEsk component when stishovite becomes stable in the assemblage and the pyroxene progressively dissolves into garnet, culminating in a garnetite at ca. 15 GPa. We conclude, CaEsk component can be responsible for SiO2 lamellae exsolution formation in pyroxenes uplifted from depth not more than 180 km, and therefore decompressed from P = 6 - 8GPa to ambient pressures. [1] Day & Mulcahy (2007) JMG 25, 35–70. [2] Irifune et al. (1986) EPSL 77, 245–256.

1

Alfred Wegener Institute for Polar and Marine Research, Section Biogeosciences, Am Handelshafen 12, 27570 Bremerhaven, Germany (*correspondence: [email protected]) 2 Muséum National d’Histoire Naturelle, Laboratoire d’Etude de la Matiere Extraterrestre, USM 0205 (LEME), Case Postale 52, 57 rue Cuvier, 75005 Paris, France Proxy relationships, e.g. the oxygen isotope fractionation of foraminiferal calcite vs. temperature, are important tools in paleo climate reconstruction. However, it has been realized that the reliability of proxies depends on our understanding of the biomineralization process, and on the quantification of species-specific variability of proxy relationships. For foraminifera a number of conceptual models on the transport of ions from seawater to the site of calcification have been published. Most of these models are based on the assumption that seawater, including the constituent ions Ca and CO3, is taken up in vacuoles (a process termed endocytosis) and transported to the site of calcification [1]. However, calculations of the Ca fluxes necessary for endocytosis-based calcification [2] and measurements of the free Ca concentration within these vacuoles show that the presence of Ca pools would be required. An observational evidence for the presence of Ca pools does not exist to date. We present data obtained for the benthic foraminifera Amonia tepida, which raises the question, if trans-membrane transport of Ca from seawater directly to the site of calcification is a plausible mechanism to explain foraminiferal calcification. [1] Bentov & Erez (2006) Geochem. Geophys. Geosys. 7(1). [2] de Nooijer et al. (2009) Biogeosciences 6(11), 2669–2675.

Goldschmidt Conference Abstracts 2010

Geochemistry of granites from the Guarda-Sabugal area, Portugal

The next generation of petrologic study of lunar compositions: Exploring the effects of water, Cl, F, S and the fluid exsolution processes that have affected their distribution

A.M.R. NEIVA1*, P.B. SILVA2, F. CORFU3 2 AND J.M.F. RAMOS 1

Department of Earth Sciences, University of Coimbra, Coimbra, Portugal ([email protected]) 2 INETI, S. Mamede de Infesta, Portugal 3 Department of Geosciences, University of Oslo, Norway Seven distinct phases of Variscan two-mica granite are recognized in the Guarda-Sabugal area. They intruded the Cambrian schist-metagraywacke complex, crystallized in the middle crust and are alkalic-calcic and strongly peraluminous. The oldest granite G1 is syn- to late-D3 (309.2±1.8 Ma), granites G2, G3, G4, G5 and G6 are late-D3 (304-300 Ma), whereas granite G7 is late- to post-D3 (299±3 Ma; ID-TIMS ages on zircon and monazite). Granites G2 and G5 represent distinct pulses of magma and correspond to different degrees of partial melting of the same metasedimentary material. They have the same (87Sr/86Sr)300 and similar #Nd300 and "18O values, but G5 has a higher biotite/muscovite ratio, Ti, Fe, Mg, Ca, Zr, Ba, Ce contents and lower Si and Rb contents than G2. The granite G5 results from a higher degree of partial melting at a higher temperature than G2. Each granite magma G2 and G5 evolved by fractional crystallization. Granites G2, G3 and G7 define a series and granites G5 and G6 define another series. Both series have similar values of (87Sr/86Sr)300 of 0.708, #Nd300 from -3.5 to -3.8 and "18O of 10.43-11.02 ‰. In each series, the major and trace element contents of granites define fractionation trends; the REE patterns are subparallel and REE contents decrease from the oldest to the youngest granite; the whole-rock "18O defines a trend and only increases by up to 0.1 ‰ and 0.4 ‰ in the G2, G3 and G7 series and G5-G6 series, respectively. In each series, potash feldspar Ba and plagioclase Ca decrease, whereas Mg decreases and Li increases in biotite from the oldest to the youngest granite. Granites G3 and G7 are derived from granite G2 magma and granite G6 is derived from granite G5 magma by fractionation of quartz, potash feldspar, plagioclase, biotite and ilmenite. The two series define two distinct trends in the log Rb/Sr-log Sn diagram indicating that fractional crystallization increased the Sn content of magmas within each series and Sn-bearing granites G3, G6 and G7 do not represent a crust anomaly in Sn. G1 and G4 correspond to different pulses of granite magma and are distinct from those of granites G2 and G5, which is confirmed by the different (87Sr/86Sr)300, #Nd300 and "18O values.

A753

H. NEKVASIL1*, F.M. MCCUBBIN2 AND G. USTUNISIK1 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])

The highly successful Apollo program launched a plethora of analytical and experimental petrologic investigations fundamental to our understanding of the origin and evolution of the Moon. Although it was recognized that carbon-bearing magmatic volatiles as well as S and Cl were present in lunar magmas (e.g. [1-3]), the effect of these on mineral stability and the implications for lunar evolution remain largely unknown, in part, because of the degassed nature of lunar glasses. The recent determination of volatile abundances in apatite has opened the door for a new paradigm of lunar evolution, since apatite has the potential to provide insight into the water, F, and Cl abundances of crystallizing lunar magmas. However, this can only be realized if the processes that affect magmatic volatile abundances are understood and the stage of apatite growth and stability can be determined. Magmas reaching the lunar surface have likely undergone at least first boiling, and, if crystallized to the extent of mare basalts, second boiling. During these processes, the relative partitioning of halides and water into an exsolving fluid changes (e.g. [4]) and the apatite crystallizing may reflect changes induced by fluid loss. A set of experiments have been launched that involve investigating the effect of water, Cl, F and S on the phase equilibria of mare basalts and apatite stability, which simulate isobaric crystallization, decompression-induced first boiling, and low pressure crystallization-induced second boiling. The results will be coupled with assessment of the petrogenetic history of Apollos samples for which we have already determined the volatile abundances through SIMS and microprobe analysis. [1] Fogel & Rutherford (1995) GCA 59, 201–216. [2] Delano et al. (1994) LPS XXV, 325–326. [3] Shearer et al. (1989) LPS XX. 996–997. [4] Aiuppa et al. (2009) Chem Geol. 263, 1–18.

A754

Goldschmidt Conference Abstracts 2010

Rhenium isotope variations in modern environments

Semipermeability and solute transport in groundwater

N. NEUBERT1, C.A. MILLER1, B. PEUCKER-EHRENBRINK1 AND M. SCHUBERT2

C.E. NEUZIL1 AND MARK PERSON2

1

MC&G Dept., WHOI, Woods Hole, MA 02543, USA 2 Helmholtz-Zemtrum für Umweltforschung (UFZ), 04318 Leipzig, Germany

With this study we successfully apply the Rhenium (Re) heavy stable isotope system to three modern redox environments. 187Re/185Re is measured by MC-ICP-MS, mass bias is corrected by standard-sample-bracketing and external W-correction according to an exponential law. The external standard reproducibility of the NIST SRM 989 standard is 0.04‰ (2SD). Variations in Re concentrations and 187Re/185Re in three different natural environments highlight the potential of this system. 1) In recent Black Sea sediments fractionation of 1‰ is observed between suboxic (187Re/185Re = -0.47‰) and euxinic (187Re/185Re = +0.46‰) sediments indicating that Re scavenging is strongly related to redox conditions. 2) Samples of a Devonian Ohio shale from a Kentucky weathering profile with highly variable Re concentrations have shown a range of about 0.7‰ due to changes in redox conditions during weathering. 3) Four small streams draining an abandoned Kupferschiefer mining district were analyzed in an attempt to trace their sources within this anthropogenically modified site. We observe very high concentrations in both water samples and solid materials (up to 500 ng g-1) and 187Re/185Re variations of about 0.4‰. Our findings emphasize the need for understanding the Re isotope system which may ideally complement more established molybdenum and uranium isotope systems as promising new tool for reconstructing palaeo-environmental conditions.

1

U.S. Geological Survey, 431 National Ctr., Reston VA 20192 USA ([email protected]) 2 Dept. of Earth and Environ. Sci., New Mexico Tech., Soccoro NM 87801 USA ([email protected])

Once a popular area of research, the idea that clay-rich strata behave as semipermeable osmotic membranes was largely abandoned four decades ago. Recently, a few field, lab, and theoretical studies have provided surprising new evidence that large osmotic pressures are possible in the subsurface, reviving interest in geological membranes. Semipermeability is fundamentally an aspect of solute transport; when a solution flows through a membrane, a portion of the solute is held back, causing local concentration increases and downstream decreases. Knowledge of this phenomenon – ultrafiltration or ‘reverse osmosis’ – earlier fueled much speculation about brine generation by membranes. We examined the role of geological membranes mechanistically by numerically simulating flow and transport within finite-thickness semipermeable strata. The simulations, which use new findings about transport within geological membranes, reveals that they are probably incapable of making brines and, as importantly, provide a mechanistic reason. Unless highly compacted, the efficiency of clay-based membranes decreases dramatically at high concentrations. Yet clay-rich media that are highly compacted have such low permeabilities that the throughflow needed for brine generation is simply not possible. We note, however, that the simulations also show membranes may have other, and more pervasive, effects on subsurface concentration patterns. Moderate increases in concentration are possible, but occur mainly within the membrane units themselves and not upstream of them as is often supposed. Thus elevated salinity in some confining layers could be the result of throughflow and ultrafiltration rather than a remnant of unflushed paleowaters.

Goldschmidt Conference Abstracts 2010

Isotope geochemistry of CO2-rich mineral springs – Natural analogs for a leaking carbon sequestration scenario

A755

SIMS U-Pb dating of alluvial deposits using authigenic and detrital opal LEONID A. NEYMARK1, JAMES B. PACES1 2 AND JOSEPH L. WOODEN 1

DENNIS L. NEWELL Earth and Environmental Sciences, Los Alamos National Laboratory, Los Alamos, NM ([email protected]) CO2-rich mineral springs are recognized as natural analogs for leakage from geologic carbon repositories. The geochemistry of CO2–rich mineral springs in the western U.S. and Tibet are used to describe the origin and evolution of volatiles in these springs in order to identify isotopic tracers for use in geologic carbon sequestration. Springs often issue along normal faults and are associated with PleistoceneHolocene travertine accumulations indicating long-term CO2 migration. Spring waters range in pH from 5.5–8.5, from 6– 58°C, are dilute to saline (100 to >20, 000 ppm TDS) and have alkalinities of 100 to >3000 mg/l (as HCO3-). Dissolved gases in springs are dominated by CO2 (*99% by volume) and/or N2, with lesser amounts of H2S, O2, H2, He, Ar, and CH4. The "13C of CO2 leaving springs ranges from -21 to -0.6 ‰ (vs. PDB), while the "13C of DIC in water ranges from -12.5 to +13.5 ‰. Paired measurements are necessary to evaluate the degree of CO2 degassing and initial fluid carbon isotope composition. The "15N of dissolved N2 gas ranges from -0.9 to +2.2 ‰ (vs. Air). Helium isotope (3He/4He) and CO2/3He ratios from Tibet are ~0.02 RA and ~1012, respectively, indicating a crustal source. Ratios from the western U.S. (3He/4He = 0.1-1.2 RA; CO2/3He = 109-1013) indicate a range of sources from crustal to mantle. Based on these natural tracers, the sources of CO2 are metamorphic, organic and magmatic. Using these data, estimates of carbon loss range from 100’s to 1000’s of kg/yr for individual springs. Regional scaled estimates for diffuse loss along fault zones to shallow aquifers and ultimately the atmosphere can grow to the order of 0.01 gigaton of C/yr. This is approximately 1% of the current annual anthropogenic addition to the atmosphere.

U.S. Geol Survey, Box 25046, MS963, Denver Federal Center, Denver, CO 80225-0046 ([email protected], [email protected]) 2 Stanford University-SUMAC, 367 Panama Street, Stanford, CA 94305 ([email protected]) The use of uraniferous opal as young as 1 Ma for U-Pb dating was suggested by Ludwig et al. [1]. More recently, opal has been used to date a variety of low-temperature, nearsurface materials. Secondary-ion mass spectrometry (SIMS) was used in this work to determine 1.5–11 Ma U-Pb isochron ages of authigenic and detrital opals from alluvial deposits in Midway Valley, southern Nevada. Samples of authigenic opal (N=12) from pedogenic cements and clast rinds, and detrital clasts of opal (N=4), were collected from drill core of basal alluvium near the alluvium/bedrock interface 25–52 meters below the land surface. The relatively large U concentration (tens of µg/g), minimal common-Pb and Th concentrations, and negligible radiogenic 2°8Pb allowed 206Pb/2°8Pb-238U/2°8Pb isochron dating by SIMS (http://shrimprg. stanford. edu). The 18–90 nA primary 16O- beam produced pits ~30 µm in diameter and 15–20 µm deep, which equates to ~30 nanograms of opal consumed during a 25-minute spot analysis. Measured Pb/U ratios were corrected for instrument bias by factors of 0.6–0.8, determined from U-Pb isochron slopes obtained for a 1.915Ma opal standard analyzed during the same analytical sessions. Corrections for initial 234U excess (excess 234U incorporated during formation of opal results in unsupported 206 Pb) were applied using both measured 234U/238U and a value of 1.54 for the initial 234U/238U activity ratio of soil water determined by 23°Th/U dating of young soils at the site. The age of basal alluvial deposits at Midway Valley is constrained by the youngest disequilibrium-corrected 206Pb-238U isochron age of detrital opal (7.29±0.64 Ma) and the oldest age of authigenic opal (3.20±0.42 Ma). [1] Ludwig et al. (1980) EPSL 46.

A756

Goldschmidt Conference Abstracts 2010

Petrology and metallogeny of alkaline magmatic formations in Northern Vietnam

Survival strategies during bacterial biomineralisation: Evidence from cyanobacterial precipitation of hydrozincite in Sardinia, Italy

NGUYEN TRUNG CHI1, PHAM BINH2 3 AND LE T. THU HUONG

B.T. NGWENYA1*, M. MAGENNIS1 AND F. PODDA2.

1

Hanoi University of Sciences, 334 Nguyen Trai St. Thanh Xuan Dist. Ha Noi, Viet Nam (ntrungchi@ yahoo.com) 2 Vietnam Institute of Geosciences and Mineral Resources (VIGMR) ([email protected]) 3 Hanoi University of Sciences, 334 Nguyen Trai St. Thanh Xuan Dist. Ha Noi ,Viet Nam([email protected]) Based on the results of study on geologic, petrominralogic characteristics, geochemistry of major and trace elements and isotopes of alkaline magmatic formations in Northern Vietnam as well as their related mineral resources, the authors have defined 3 alkaline and sub-alkaline petromagmatic provinces. They were formed in diferent tectonic settings in Early Paleozoic- Late Triassic, Late Jurassic- Early Cretaceous and Late Cretaceous-Paleogene periods. Correspondingly, there were also defined 3 tectonometallogenic alkaline magmatic provinces including 7 metallogenic regions, 16 ore and mineralization zones with typical deposits, ore points and mineralization occurrences. The discovery of new mafic – ultramafic alkaline formations in Viet Bac craton has made the previous points of view on metamorphism, origin and geodynamic settings to form these magmatic formations to be changed. The researched results above mentioned has opened a series of problems on geology, metallogeny, petrology- geodynamics related to alkaline magmatic activity in Northern Vietnam that need to be detailedly studied in the future. [1] Chi & Nguyen et al. (2003) Report Concluded of Project: Petrology & Metallogeny of alkaline magmatic formations in North Viet Nam. Vietnam Institute of Geosciences & Mineral Resources. Hanoi. 582p.[2] Condie (1989) Plate Tectonic & Crustal Evolution. Pergamon Press. New York. 476p. [3] Michell & Garson (1981) Mineral deposit & global tectonic setting. Academic Press. London-New York. [4] Sorensen H. (ed.) (1979) The Alkaline Rocks.Wiley, New York.662p. [5] Wilson (1989) Igneous Petrogenesis. London Unwin Hyman. 466p. [6] Yu Xuehui et al. (2002) Cenozoic Rift magmatism in West Qinling, Gansu provinces- Response for Eastward Extrusion of the Asthenosphere Beneath Tibet. IGCP430 Workshop II: Halong Bay, Viet Nam-April 1–5, 2002.

1

School of GeoSciences, University of Edinburgh, West Mains Road, Edinburgh. EH9 3JW (*correspondence: [email protected]) 2 Department of Earth Sciences, University of Cagliari, Via Trentino 51, I-09127, Cagliari, Italy ([email protected]) In spring of 2006, we collected water samples and bioprecipitates from the Rio Naracauli which drains Pb-Zn mine waste piles in SW Sardinia, Italy. The objective is to study downstream trends in hydrogeochemistry, mineralisation textures and trace metal partitioning between water and hydrozincite. Microscopic studies of the bio-precipitates reveal a characteristic botryoidal morphology with a porous texture consisting of microscopic and nanoscopic plates. While the association with photosynthetic organisms suggests that bio-precipitation is a passive process [1], laboratory experiments suggest that the presence of organic molecules is critical to produce this morphology. We hypothesize that the texture arises via agglomeration of nanoscopic and microscopic crystals by extracellular polymeric substances [2], or nucleation of plates within organic globules produced by metabolising cells [3]. The bacterial surface therefore plays a critical role in determining the texture of the bio-precipitate, such that the porous structure facilitates nutrient/metabolite exchange in the face of mineral precipitation. [1] Podda et al. [2000]. Appl. Environ. Microbiol. 66, 5092– 5098. [2] Braisaant et al. (2003) J. Sed. Res. 73, 485–490. [3] Aloisi et al. (2006) Geology 24, 1017–1020.

Goldschmidt Conference Abstracts 2010

Heavy metal contamination in fluvial sediments caused by Dexing Cu Mine, Jiangxi, China S.J. NI1,3*, C.H. CHEN2, C.J. ZHANG1,2, D.P. LU2 1,3 AND Z.Q. LI

Stable hydrogen isotopic ratios of coal-derived and oil-associated gases: A case study in the Tarim basin, NW China YUNYAN NI1, SHUICHANG ZHANG1, GUANGYOU ZHU1, GUOYI HU1 AND JIANLI SUI2

1

Dept. of Geochemistry, Chengdu Univ. of Technology, Chengdu, Sichuan 610059, China (*correspondence: [email protected]) 2 Provincial Key Lab. of Neuclear Technology in Geoscience, Chengdu University of Technology, Chengdu, Sichuan 610059, China 3 State Key Lab. of Geohazard Provention & Geoenvironment Protection, Chengdu University of Technology, Chengdu, Sichuan 610059, China ([email protected]) Although mining environment have attracted much concern of the scientists, the recent researches mainly focus on the environment of the mining districts and the around. This study showed that the impact of mining environment contamination extended to the drainage areas by the fluvial transportation. 330 fluvial sediment samples for the area 4800km2 were collected in Dexing area and its vicinity watersheds, where the largest porphyry copper mine in China is located. The Heavy metal levels for As, Hg, Cd, Cr, Zn, Cu and Pb of the samples were determined using inductively couple plasma atomic emission spectrometry and X-ray fluorescence spectrometry. The results show: (1) The max of As, Hg, Cd, Cr, Zn, Cu and Pb heavy metals contents in sediments increased from 120.00, 1.16, 3.00, 150.00, 300.00, 690.00, 300.00 mg/kg in the year 1989 to 1109.00, 5.43, 13.50, 236.00, 1770.0, 4390.00, 1685.00 mg/kg in the year 2004 respectively, and the averages were from 17.39, 0.08, 0.25, 69.00, 75.00, 40.00, 31.00 mg/kg in the year 1989 to 27.91, 0.12, 0.33, 64.00, 103.00, 148.00, 47.00 mg/kg in the year 2004. (2) The average potential ecological risk coefficient (Eir) [1] for As, Hg, Cd, Cr, Zn, Cu and Pb changed from 13.37, 9.21, 37.77, 2.45, 0.46, 4.72, 4.53 in 1989 to 21.43, 14.00, 49.91, 2.29, 0.63, 17.42, 6.76 in 2004. The average potential ecological risk index (RI) rose from 73 in 1989 to 113 in 2004, and the max potential ecological risk index (RI) changed from 578 in 1989 to 3748 in 2004. (3) the sediments from the water drainages in Dexing mining area are contaminated by As, Hg, Cd, Cr, Zn, Cu and Pb mainly along the Dexing River drainage, Dawu River drainage and Le’an River drainage. Above results suggest that the impact of heavy metals contamination caused by mining activities could extended from the mining area to its vicinity watersheds by the fluvial transportation. Supported by the commonwealth research program (30302408201) of Ministry of Land and Resource, China. [1] Hakanson (1980) WR. 14, 975–1001.

A757

1

PetroChina Research Institute of Petroleum Exploration and Development, Beijing, 100083 P.R. China ([email protected]) 2 Institute of Geology, China Earthquake Administration

Stable hydrogen and carbon isotopes have been used in studies of genetic characterization of natural gases, and numerous studies of the use of "D as a source indicator have been published [1-3]. The greater range of "D values and distinct chemical reactivity of hydrogen make compoundspecific hydrogen isotope data a valuable complement to "13C values and the measurement of stable hydrogen isotope ratios an attractive technique for geological applications. However, due to the analytical precision, hydrogen isotopic studies on C2-C4 hydrocarbons were not very practical in 80’s or early 90’s. Here we investigate systematically the stable hydrogen isotopes of coal-derived and oil-associated gases from the Tarim basin, NW China and make a combined use of gas "D and "13C in studies of gas origin and gas-source correlations. The Tarim basin is located in northwest China and is one of the largest basins in the world with an area of 560, 000 km2. Recently a number of giant gas fields have been found in the basin, which have made the Tarim basin as one of the most important basins enriched in gas resources in China. There are two types of gases: coal-derived gases sourced from the Mesozoic terrestrial source rocks with humic organic matters, -121‰~-182‰ of "DCH4, -94‰~-192‰ of "DC2H6, -91‰~ -150‰ of "DC3H8; oil-associated gases generated from Sinian to lower Paleozoic marine source rocks with sapropelic organic matters, -154‰~-191‰ of "DCH4, -112‰~-137‰ of "DC2H6, -75‰~-111‰ of "DC3H8.Partial reversal of hydrogen isotopic distribution among CH4, C2H6 and C3H8 are commonly presented in the oil-associated gases, due to the mixing of oil-associated gases with different thermal maturity or mixing of oil-associated and coal-derived gases. In general, oil-associated gases are more enriched in D than coal-derived gases, while no exact limit was found between them due to mixing effects. Except the depositional environments, gas "D also increases with increasing thermal maturity of source rocks. [1] Dai & Qi (1989) Chinese Science Bulletin 34(9), 690–692. [2] Schoell (1980) Geochimica et Cosmichimica Acta 44, 649– 661.

A758

Goldschmidt Conference Abstracts 2010

The speciation of organic matter in soil mineral organic associations – Inference from STXM and N, C and Fe NEXAFS

Geological features and origin of the Wulandele molybdenum deposit occurring in Sonid Zuo Qi, Inner Mongolia

PETER S. NICO1*, MARCO KEILUWEIT2, MARKUS KLEBER2, PIERRE-JOSEPH HATTON3, BERND ZELLER3 AND DELPHINE DERRIEN3

F-J NIE, S-H JIANG AND Y-F LIU

1

Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA 2 Department of Crop and Soil Science, Oregon State University, Corvallis, OR, USA 3 Département Ecologie des Forêts, Prairies et milieux Aquatiques, Institut National de Recherches Agronomiques, Centre de Nancy, France The role of mineral organic interactions in the long-term protection of soil organic matter against decomposition is increasingly recognized as a key process in terrestrial carbon cycling. In this investigation we were specifically concerned with whether the differences in surface properties between Fe containing soil minerals and non-Fe containing soil minerals exerted a significant fractionating influence on the chemistry of C and N in the associated organic material. We employed a density fractionation procedure in order to isolate organic mineral micro-aggregates with only thin layers of associated organic material. It is assumed that these closely associated layers are the most likely to show the influence of mineral surface properties. We then interogated these microaggregates using the scanning transmission X-ray microscope (STXM) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. While there was not a single universal fractionation pattern, the N associated with Fe tends to be of a different chemical composition than that associated with non-Fe regions. The implications of theses observations for the mechanisms of mineral-organic interactions are discussed.

Institute of Mineral Resources, Chinese Academy of Geological Sciences, Beijing 100037, China (*correspondence: [email protected]) Located at central part of the Paleozoic-Mesozoic tectonomagmatic belt of the Chagan Obo-Aoyoute-Chaobulen along the southwestern edge of the Siberian plate, the newly discovered Wulandele deposit is a large-scale porphyry Mo deposit occurring in the central-eastern Inner Mongolian Autonomous Region. Up to present, it is also the largest Moonly deposit occurring within China-Mongolian border area. During the Indosinian to Yanshanian orogeny, intensive tectonic and igneous activities resulted in the large-scale granitoid magmatism in Wulandele and its neighbouring area. The Wulandele quartz diorite stock was emplaced in the Hercynian biotite granite batholith located in Ordovician to Permian volcano-sedimentary sequences. It consists of mainly fine-grained quartz diorite and porphyritic quartz diorite and that have no difference in mineral assemblage. Mo mineralization occurs entirely within the Wulandele quartz diorite stock as veins, veinlets and disseminated blocks. In general, the disseminated ore blocks consisting of mainly impregnation, radioflake, aggregated flakes are obviously cut by Mo-bearing quartz vein group comprising veinlets and veins. Studies show that Mo mineralization occurs in two main stages: early disseminated ore stage and late vein ore stage. Re-Os isotopic data from the early disseminated ore defined a correlation line corresponding to an age of 224.5 ± 2.5Ma. In contrast, Re-Os isotopic data from the late vein group have a correlation line corresponding to an age of 134.1 ± 3.3Ma. Fluid inclusion studies show that the quartz samples from the early disseminated ores are characterized by CO2rich, variable salinity (16-32wt% equiv. NaCl), and have variable homogeneous temperature of 360°C to 480°C. Quartz samples in late vein ores have homogeneous temperature from 250°C to 390°C, with variable salinity of 6-25wt% equiv. NaCl. Sulfur and oxygen isotopic data indicate that the oreforming fluid was dominated by magmatic water at the early disseminated ore stage, and is characterized by mixture fluid of magmatic water and heated meteoric water at the late vein ore stage. The deposit is believed to be a product of both Indosinian and Yanshanian intra-plate granitoid magmatism along the southwestern margin of the Siberian plate.

Goldschmidt Conference Abstracts 2010

Molecular dynamics simulations of CO2-brine interfacial tension and mutual solubility LAURA NIELSEN1*, IAN BOURG2 3 AND GARRISON SPOSITO 1

University of California Berleley, 307 McCone Hall, Berkeley CA, USA (*correspondence: [email protected]) 2 Earth Sciences Division, Lawrence Berkeley National Laboratory, Berkeley CA, USA ([email protected]) 3 University of California Berkeley, 117B Hilgard Hall, Berkeley CA, USA ([email protected]) Predicting and controlling the behavior of supercritical CO2 in geologic repositories hinge on understanding the interactions between CO2, aqueous brines, and host rock phases. Long-term stability depends strongly on the interfacial tension (IFT) between CO2 and brine [1], because IFT controls wetting of and reaction with host rocks and determines capillary breakthrough overpressure, the pressure above which CO2 may escape through caprock fissures [2, 3]. Overall, the timescales of CO2 capillary trapping depend on the relationship between CO2-brine interfacial characteristics and the state variables, pressure (P), temperature (T), and composition (X). Experimental and simulation studies of the supercritical CO2-water interface at P, T relevant to geologic storage (~5-45 MPa, 300-383 K) show that IFT decreases with increasing P until around 15 MPa2, 4. Experimental studies have also shown that increasing brine salinity causes an increase in IFT at a given T, P, but experimental data are limited. Using well known water and CO2 interatomic potential models, we applied molecular dynamics methods to simulate the supercritical CO2-brine interface over a range of brine X to assess the relationship between IFT and brine salinity. We determined the IFT between CO2 and brine at 373 K and 15 MPa between 0.086 and 2.45 M NaCl salinity. Our results to date agree with experimental data2. Significant CO2 dissolution into the brine phase occurred over nanosecond timescales. We shall present a series of simulations encompassing a broad range of P-T-X which will provide not only IFT predictions, but also improved understanding of the relationship among interfacial structure, CO2 solubility kinetics, and state variables. [1] Kuznetsova & Kvamme (2002) Phys. Chem. Chem. Phys. 4, 937–941. [2] Chiquet, Daridon, Broseta & Thibeau (2007) Energy Conversion & Management 48, 736–744. [3] Chalbaud, Robin, Lombard, Martin, Egermann & Bertin (2009) Advances in Water Resources 32, 98–109. [4] Kvamme, Kuznetsova, Hebach, Oberhof & Lunde (2007) Computational Materials Science 38, 506–513.

A759

Are hydrothermal vents natural microbial fuel cells? MARK E. NIELSEN1* AND PETER R. GIRGUIS2 1

Harvard University, 16 Divinity Avenue Room 3092, Cambridge, MA 02138, USA (*correspondence: [email protected]) 2 Harvard University, 16 Divinity Avenue Room 3085, Cambridge, MA 02138, USA ([email protected])

Microbial fuel cell (MFC) research has exploded over the past decade since the discovery that microbes can reduce solid-phase oxidants via extracellular electron transfer (EET). Most MFC investigations focus on the application of MFCs as alternative power sources or on the biological mechanism of EET. Comparatively little attention is devoted to MFCs as basic research tools. We report on the use of MFC technology to investigate rates of EET in hydrothermal systems. We hypothesize that hydrothermal vents are natural MFCs because they have spatially separated redox zones connected by conductive minerals (e.g. pyrite). To test this hypothesis, we designed a MFC that mimics a hydrothermal vent with respect to chemistry and has a pyrite electrode. The open circuit voltage of the MFC was about 0.4 V. We inoculated the MFC with a sulfide sample collected from a vent at Axial Volcano. The circuit generated an average of approximately 100 nA for 21 days. Assuming current was driven by sulfide oxidation to elemental sulfur, the oxidation rate was 48 nmol d-1 (consistent with low biomass in the reactor). Using scanning electron microscopy, we observed ubiquitous but patchy coverage of the pyrite by microbes. The phylogeny of the anode-attached community will be investigated via whole genome amplification and 454 pyrosequencing to elucidate the community responsible for EET in this system. These experiments demonstrate that 1) there are microbes in hydrothermal samples capable of EET and 2) pyrite can serve as an electron acceptor if it is in electrical continuity with a terminal electron acceptor (e.g. oxygen).

A760

Goldschmidt Conference Abstracts 2010

Development of cyber-infrastructure for experimental data and trace element partitioning (traceDs)

Potassium and Uranium in the upper mantle controlled by Archean oceanic crust recycling

ROGER L NIELSEN1, MARK S GHIORSO2, ANTHONY A P KOPPERS3 1 AND JENNIFER L CUNNINGHAM

SUNE G. NIELSEN

1

Geosciences, Oregon State University, Corvallis, OR, USA ([email protected]) 2 OFM Research, Seattle, WA, USA, ([email protected]) 3 College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA ([email protected]) The development of databases that support model development, e.g. LEPR, PetDB, and EarthChem in the past decade has greatly facilitated access to primary sources of both experimental, whole rock and phase chemistry. Our work focuses on the remaining missing component in this network, an exhaustive online database of experimental data on trace element partitioning between phases. This new ‘traceDs’ database will (i) provide community access to a dataset that is now effectively unavailable to more than a handful of ‘microspecialists’ on each phase, (ii) provide a standard interface for model input, (iii) interoperate seamlessly in the existing cyberinfrastructure and (iv) enable independent development of partitioning constraints. The initial focus of the new traceDs database will include experimental partitioning data, together with major, minor and trace element compositions of phase (bulk, melt, fluids and minerals) assemblages, and physical conditions under which the experiments were carried out (e.g. temperature, pressure, volatile content, oxygen fugacity, doping methods, container material). Our initial goals are to populate the database with the large existing clinopyroxene database as a model, and to develop a clear interface for users. We will then incrementally add new minerals (garnet, olivine, plagioclase, etc) and structure as we integrate user input. Specific challenges incurred with the development of this database relate to the significantly greater granularity and complexity represented in trace element experimental data compared to major element bulk rock or mineral chemistry (e.g. multiple analytical techniques). Development of this common resource becomes increasingly important as both the experimental database and the level of expertise required to apply the numerical constraints increase in quantitly and complexity.

University of Oxford, Parks Road, OX1 3PR The Earth’s mantle is divided into separate reservoirs. From basaltic lavas erupted today we know that the upper mantle is depleted in incompatible trace elements, whereas ocean islands basalts (OIB) sample a deep, more enriched reservoir. The two incompatible elements potassium (K) and uranium (U) display a different ratio to each other in lavas from the upper and lower mantle reservoirs (Arevalo et al. [1]). This is surprising because they do not fractionate substantially during melting of the mantle and therefore continuous extraction of melts from the upper mantle over Earth’s history cannot explain this disparity. Here a model is constructed in which U is insoluble during continental weathering in the anoxic conditions of the early Earth. This leads to recycling of oceanic crust with high K/U in the early Earth and low K/U after significant oxidative weathering commenced ~2200 million years ago. This concept reproduces the observed K/U in both the upper and lower mantle reservoirs as well as the continental crust. The model is also shown to account for the thorium/uranium ratios and thereby Pb isotope compositions in these reservoirs. Successful model solutions imply that (1) chemical weathering fluxes to the oceans on the early Earth was significantly higher than present day and (2) that the majority of the OIB reservoir is younger than 2200 million years. [1] Arevalo, McDonough & Luong (2009) ‘The K/U ratio of the silicate Earth: Insights into mantle composition, structure & thermal evolution’ Earth & Planetary Science Letters 278, 361–369.

Goldschmidt Conference Abstracts 2010

First lipid biomarker evidence for aerobic methane oxidation in the water column of Lake Untersee (East Antarctica) H. NIEMANN1, M. ELVERT2, U. WAND3, V.A. SAMARKIN4 AND M.F. LEHMANN1 1

Inst. for Env. Geosciences, Univ. Basel, Switzerland MARUM Center for Marine Environmental Sciences & Department of Geosciences, Univ. of Bremen, Germany 3 Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany 4 Dept. of Marine Sciences, Univ. of Georgia, Athens, USA

2

Lake Untersee is a perennially ice-covered freshwater lake (6.2 km x 4.2 km, max. 169 m water depth) located in the Gruber Mountains of central Queen Maud Land, East Antarctica. Lake Untersee receives water only from glacier runoff (Anuchin Glacier) and has no outflow. Comparatively high evaporation rates lead to high sulphate concentrations in surface waters (ca. 1.5 mM). Most of Lake Untersee’s water column is supersaturated with respect to oxygen and characterised by very low rates of primary production. However, Lake Untersee also features a 100 m deep trough at its southern tip, with anoxic bottom waters containing high amounts of biogenic methane (up to 22 mM) and sulphide (up to 2 mM). In a previous study in Lake Untersee (Wand et al. Limnol. Oceanogr. 51, 2006), high rates of sulphate reduction and anaerobic oxidation of methane (AOM) were observed at 84 m water depth, just a few meters below the oxycline (80 m water depth) A negative shift in the stable carbon isotope composition ("13C) of suspended particulate organic carbon (SPOC) from -30‰ to -45‰ in a constrained water layer (84 – 86 m water depth) provides further indication for methane consumption at this depth. To gain further insights into methane cycling in Lake Untersee, we analysed the lipid biomarker composition and stable carbon isotope signatures from SPOC samples collected during the 1995 sampling campaign. Against our initial expectation, we could not detect any isoprenoidal lipid compounds typical for Archaea involved in the sulphate-dependent mode of AOM (e.g. the dialkyl-glycerol-diethers ‘archaeol’ or ‘sn2hydroxyarchaeol’). However, we were able to detect substantial amounts of two specific steorids (4+-methyl steroid and 4, 4-dimethyl steroid) and one hopanoid (diplopterol). These compounds displayed very low "13Cvalues (as low as -68‰) and were, again, confined to water depths between 84 – 86 m. The biomarker composition and isotopic signatures are consistent with an origin from aerobic methanotrophic bacteria, possibly Methylococcus sp. As a consequence, aerobic (MOx), rather than anaerobic methanotrophy most likely accounts for the low "13C-values found for POC at 84 – 86 m water depth and is responsible for a significant fraction of methane consump-tion. These results have important implications for our understanding of the spatial stratification of biogeochemical TRUNCATED


A761

Tungsten isotopic evolution during late-stage accretion: Constraints on Earth-Moon equilibration F. NIMMO1*, D.P. O’BRIEN2, T. KLEINE3 1 AND C.A. DWYER 1

University of California Santa Cruz, CA, USA (*correspondence: [email protected]) ([email protected]) 2 Planetary Sciences Institute, Tucson, AZ, USA ([email protected]) 3 Institut fur Planetologie, Munster, Germany ([email protected]) We couple the results of N-body simulations of late-stage accretion (O’Brien et al. 2006) to a hafnium-tungsten (Hf-W) isotopic evolution code to investigate the evolution of planetary bodies in the inner solar system. Simulations can simultaneously produce planets having Earth- and Mars-like masses and Hf-W systematics by assuming that the tungsten partition coefficient decreases with increasing semi-major axis (e.g. due to increasing oxidation). Simulations assuming that Jupiter and Saturn occupied circular orbits while the terrestrial planets were forming are more successful at reproducing the Hf-W systematics than those assuming present-day Jupiter and Saturn orbits. To generate Earth-like tungsten anomalies, 3080% of each impactor core is required to re-equilibrate with the target mantle. Some model outcomes yield a target and final impactor having similar (Earth- and Moon-like) tungsten anomalies. However, in no case can the inferred lunar Hf/W ratio be simultaneously matched. This result suggests that the Moon isotopically equilibrated with the Earth's mantle in the aftermath of the giant impact (cf. Pahlevan and Stevenson 2007). Alternatively, either the dynamical models which show the Moon being derived primarily from the impactor mantle, or the accretion timescales obtained by the N-body simulations, are incorrect.

A762

Goldschmidt Conference Abstracts 2010

Cathodoluminescence of albite activated by alpha-particle induced luminescence centers

Chemical state of Fe in fine and ultrafine particles in the urban atmosphere

H. NISHIDO1*, M. KAYAMA1, S. TOYODA2, K. KOMURO3 2 AND K. NINAGAWA

C. NISHITA-HARA, M. KOGAWA AND S. UTSUNOMIYA

1

Research Institute of Natural Sciences, Okayama University of Science, Japan (*correspondence: [email protected]) 2 Department of Applied Physics, Okayama University of Science, Japan 3 Earth Evolution Sciences, University of Tsukuba, Japan

Cathodoluminescence (CL) halo in quartz caused by alpha-radiation has been investigated for the application to geodosimetry. The halo in feldspar minerals, however, has not been studied from the perspective of CL spectroscopy. In this study, the halos of various albite implanted by He+ ion have been characterized by CL spectral analysis to clarify emission mechanism for the applications to geodosimetry and geochronology. Single crystals of albite (Ab98~100Or2~0) from Minas Gerais, Brazil (Ab1), Niigata, Japan (Ab2) and Shiga, Japan (Ab3) were selected for CL measurements. He+ ion implantation (dose density: 1.23 , 10-4 ~ 7.38 , 10-4 C/cm2) on the samples was performed using a 3M-tandem ion accelerator at 4 MeV corresponding to the energy of alpha-particles from 238U. CL imaging of Ab1, Ab2 and Ab3 shows CL halo on the surface of He+ ion implanted sample. Approximately 15 )m width of CL halo in the section is consistent with theoretical range of alpha-particles from disintegration of 238U in albite. Their CL spectra in the halos consist of emission bands at around 400, 580, 660 and 730 nm. These spectra can be deconvoluted by Gaussian curves in energy units, resulting in four components centered at 3.05, 2.10, 1.86 and 1.56 eV. An integral intensity of the Gaussian component at 1.86 eV positively correlates with radiation dose of He+ implantation in the halo area of individual albite. It suggests that the component at 1.86 eV (666 nm) might be assigned to radiation-induced defect center formed by He+ ion implantation. CL line analysis along the halo section reveals that a change in the CL intensity along depth direction substantially corresponds to the Bragg’s curve, suggesting energy loss process of specific ionization along the track of a changed particle. Therefore, the CL emission of albite related to radiation-induced defect center can be used to quantitatively evaluate the radiation dose of alpha-particles induced on feldspar minerals as an indicator applied for a geodosimeter.

Department of Chemistry, Kyushu University, Fukuoka 8128581, Japan ([email protected]) Iron is the most common transition metal in atmospheric aerosol particles and plays an important role in atmospheric chemistry and biological processes. In order to understand the size-dependent speciation and mixing state of Fe in fine and ultrafine fraction of ambient atmosphere, we have performed nano to bulk scale analyses on urban atmospheric particles, utilizing synchrotron-based X-ray absorption near-edge structure (XANES), scanning electron microscopy (SEM), and (scanning) transmission electron microscopy ((S)TEM). The samples were collected using a 9-stage cascade impactor at Hakozaki, Fukuoka, Japan during the sampling campaign in October and November of 2009. (I) Super-micron particles (1-8 )m): Individual particle analysis shows that Fe is included in ~40 % of the particles. Most of those particles are composed mainly of Si and Al, and their Fe concentrations determined by energy dispersive X-ray analysis (EDX) were less than 20 at.% (6 at.% in average). Iron K-edge in XANES spectrum indicates that major Fe speciation of the super-micron particles is Fe2O3. Indeed, STEM elemental map reveals the presence of discrete Fe oxide, likely aggregate of hematite, on aluminosilicate in addition to Fe-bearing aluminosilicate such as biotite and chlorite. (II) Submicron-sized particles (0.06-1µm): The XANES spectrum reveals that major Fe speciation in this size range is closely related to Fe2O3 and/or Fe3O4. However, the TEM shows an aggregate of rounded nano-particles at the size of ~50 nm in diameter and Fe is always associated with Mn, which was not observed in the super-micron size range. Up to the present, several studies have determined the major speciation of Fe in the atmospheric particles as Fe2O3 using XAFS. However, our detailed characterization by a combination of TEM and XAFS allowed to conclude that the occurrence and elemental mixing state of Fe are not uniform as determined only by XAFS but are largely variable as a function of the particle size. Still, the mixing state of Fe in the small-sized fraction observed in the present study provides an useful insight to better understanding the size-dependent catalytic effect and bioavailability of Fe in the urban aerosol particles.

Goldschmidt Conference Abstracts 2010

On the origin of OIB: Processes, sources and mantle convection

Continental crust growth as a result of continental collision: Ocean crust melting and melt preservation

Y.L. NIU1*, M. WILSON2, E.R. HUMPHREYS3 4 AND M.J. O’HARA

Y.L. NIU1*, Z.D. ZHAO2, S. ZHOU2, D.C. ZHU2, G.C. DONG2, X.X. MO2, G.G. XIE2 AND X. DONG2

1

Durham University, UK (*correspondence: [email protected]) 2 Leeds University, UK 3 Bristol University, UK 4 Aberystwyth University, UK Consideration of global OIB datasets [1, 2] suggests that oceanic lithosphere thickness variations (or the lid effect) exert the primary control on OIB chemistry on a global scale. The effect of the ‘lid’ is to cap the final depth (pressure) of melting or melt equilibration, but this does not unequivocally record the initial depth/temperature of melting, suggesting that caution is necessary when extracting initial mantle melting conditions from oceanic basalts. The high quality data on olivine phenocrysts from MORB and global OIB suites [3] are fully consistent with the lid effect. Subducted ocean crust (SOC) is too depleted (i.e. [La/Sm]N <1) to be a source material for highly enriched (e.g. [La/Sm]N >>1) OIB. Signals of continental sediments are reported for some OIB, but there is no convincing evidence for their significance on a global scale. OIB sources are more enriched than the primitive mantle, and enriched in the progressively more incompatible elements, requiring that OIB sources be pre-enriched by low-F melt metasomatism. The lithosphere-LVZ interface represents a natural solidus and is the ideal site for such metasomatism. The ~ 70 Myr history of oceanic lithosphere growth to its full thickness is the history of mantle metasomatism, signifying the deep portion of the oceanic lithosphere as an important enriched geochemical reservoir. The metasomatic agent is H2O-CO2-rich silicate melt of LVZ origin. The ‘coincidence’ between the lithosphere base as an isotherm (geophysical) and the solidus (petrological) indicates that this is a wet (H2OCO2-rich) solidus with a slope of dT/dP $ 0 at depths < 90 km. A solidus topology change at ~ 90 km, with a local slope of dP/dT $ 0, if verified, explains why the old (> 70 Ma) oceanic lithosphere cannot be thicker than ~ 90 km. SOC is > 3.0% denser than PREM, and the two LLSVPs at the base of the mantle beneath the Pacific and Africa are probably piles of SOC accumulated since plate tectonics began on Earth. Subducted mantle lithosphere (SML, ~ 15 times the mass of SOC) is buoyant relative to PREM and may overlie the LLSVPs, explaining the surface topographic highs of the Pacific superswell and African continent. SML is also the best fertile source material candidate for OIB. [1] Humphreys & Niu (2009) Lithos 112, 118–136. [2] Niu et al. (2010) J. Petrol. (submitted). [3] Sobolev et al. (2007) Science 316, 412–417.

A763

1

Durham University, UK (*correspondence: [email protected]) 2 China University of Geosciences, Beijing, China The significance of the continental crust (CC) on which we live is self-evident. However, our knowledge remains limited on its origin, its way and rate of growth, and how it has acquired the ‘andesitic’ composition from mantle derived magmas. Compared to rocks formed from mantle derived magmas in all geological environments, volcanic arc rocks associated with oceanic lithosphere subduction share some common features with the CC; both are relatively depleted in ‘fluid-insoluble’ elements (e.g. Nb, Ta and Ti), but enriched in ‘fluid-soluble’ elements (e.g. U, K and Pb). These chemical characteristics are referred to as the ‘arc-like signature’, and point to a genetic link between subduction-zone magmatism and CC formation, thus leading to the ‘island arc’ model widely accepted for the origin of CC over the past 40 years. However, this ‘Island-arc’ model has many difficulties. These include (1) bulk arc crust (AC) is basaltic whereas the bulk CC is andesitic [1]; (2) AC has variably large Sr excess whereas the CC is Sr deficient [2]; and (3) AC production is massbalanced by subduction-erosion and sediment recycling, thus contributing no new mass to CC growth, at least in the Phanerozoic [3, 4]. Our data on magmatic rocks (both volcanic and intrusive) formed during the India-Asia continental collision (~55±10Ma) show remarkable compositional similarity to the bulk CC with the typical ‘arc-like signature’ [5]. Also, these syncollisional felsic rocks exhibit strong mantle isotopic signatures, meaning that they were recently derived from a mantle source. The geochemistry of these syncollisional felsic rocks is most consistent with an origin via partial melting of upper oceanic crust (i.e. last fragments of underthrusting oceanic crust) under amphibolite facies conditions, adding net mantle-derived materials to form juvenile CC mass. This leads to the logical and testable hypothesis that continental collision produces and preserves the juvenile crust, and hence maintains net continental growth. [1] Gill (1981) Orogenic andesites & plate tectonics. Springer-Verlag, New York. 390 pp. [2] Niu & O’Hara (2009) Lithos 112, 1–17. [3] von Huene & Scholl (1991) Rev. Geophys. 29, 279–316. [4] Clift & Vannucchi (2004) Rev. Geophys. 42, RG2001. [5] Rudnick & Gao (2003) Treat. Geochem. 3, 1–64.

A764

Goldschmidt Conference Abstracts 2010

Modelling sulphide weathering and the link to biologically-derived nitrate in groundwater of the northeast Yilgarn Craton, Western Australia

Arsenic not attenuated during downstream transport in Gibbon and Firehole Rivers, Yellowstone National Park

R.R.P. NOBLE, D.J. GRAY AND N. REID

D. KIRK NORDSTROM1, R. BLAINE MCCLESKEY1, DAVID D. SUSONG2 AND JAMES W. BALL1

CSIRO Earth Science and Resource Engineering, Kensington, WA, 6151, Australia (*correspondence: [email protected]) Groundwater chemistry is inextricably linked to the surrounding rocks, soils and biological communities. This relationship is evident in the ancient landscapes of the northeast Yilgarn Craton. Here, we have investigated the weathering and oxidation of sulphide orebodies in Archean rocks at depths >100 m to show the influence on groundwater chemistry in the weathered zone. In groundwaters close to the weathering front, SO4 and NO3 but not O2 are important for major oxidation reactions. Sulphate is actually consumed and relatively depleted in deep, reduced groundwaters, but enriched in near surface, oxidised groundwaters. Nitrate is strongly depleted in the shallow groundwater zone above a sulphide body, but not depleted in groundwater 500 m away from the orebody. The NO3, sourced from leakage of N-fixing bacteria associated with the roots of the dominant Acacia aneura vegetation, is the dominant oxidant in the shallow groundwater system. Modelling groundwater interactions with sulphidic rocks using Geochemists Workbench®, for both NiS and FeS systems, demonstrated additional weathering effects. Deeper groundwaters are controlled by alteration of pentlandite/pyrrhotite to violarite/pyrite/hematite, resulting in high pH, depletion of dissolved SO4 and very low concentrations of dissolved Ni. Iron, Ni, and Cu dominated sulphides produced similar results (Zn and Pb sulphides did not alter), making distinguishing barren (Fe-rich) and mineralized (Ni, Cu-rich) sulphides difficult using target metals alone. In contrast, near surface groundwaters contacting sulphides may have Fe, other metals (Ni, Cu, Zn etc) and SO4 enrichment due to violarite oxidation and dissolution, with strong potential to distinguish NiS from FeS. Spatially, the variation of major anions in this environment, along with other related metal signatures, enables targeting of sulphide orebodies at multiple scales. Results will be presented from a local case study and a regional mapping project, with samples spaced approximately 50 m and 5000 m apart, respectively.

1

U.S. Geological Survey, 3215 Marine St., Boulder, CO 80303, USA ([email protected], [email protected]) 2 U.S. Geological Survey, 2329 W. Orton Circle, Salt Lake City, UT 84119, USA ([email protected])

Synoptic sampling with discharge measurements were obtained under low-flow conditions for the Gibbon River (September, 2006), and for the Firehole River (September, 2007). The Gibbon River (about 30 km) varies in discharge from about 2 to 16 m3/s and receives thermal inflows from Norris and Gibbon Geyser Basins, Chocolate Pots, and Terrace Spring. The Firehole River (about 40 km) varyies in discharge from about 6 to 23 m3/s, and receives thermal inflows from Upper, Midway, and Lower Geyser Basins. Mass fluxes (loads) were calculated to determine if any elements were being attenuated during downstream transport. Little mass was attenuated for either major solutes or trace elements. Some silica was lost during mixing and transport, maintaining very constant concentrations that correlated with temperature in the rivers. Silica solubility between amorphous silica and beta-cristobalite was maintained. Silica has cemented bed sediment in the Firehole River for several kilometers downstream and probably coats most sediment in both rivers. Only small amounts of arsenic are lost during downstream transport, about 7% of the total flux for the Gibbon River and less for the Firehole River. Hence, high concentrations of dissolved arsenic occur in these rivers: up to 0.45 mg/L for the Firehole and up to 0.2 mg/L for the Gibbon. The arsenic mass fluxes are 30 kg/d for the Gibbon and 230 kg/d for the Firehole. Our hypothesis for the lack of arsenic attenuation is the poor sorption properties of silica-rich surfaces along with long-term flow that would also saturate surfaces. Such a phenomenon would explain why rivers like the Rio Loa in Chile, which receive thermal waters from the El Tatio hot springs, have high concentrations of arsenic and pose health risks to residents drinking water from this river.

Goldschmidt Conference Abstracts 2010

A765

Early mantle depletion on Vesta: 143 Nd in basaltic eucrites

Application of LA-ICPMS to ore deposit research

M. NORMAN1*, V. BENNETT1 AND K. BIRMINGHAM1,2

MARC NORMAN1, PHILIP BLEVIN2 AND ROBERT HOUGH3

1

Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia (*correspondence: [email protected]) 2 University of Münster, D-48149, Germany

To study mantle depletion on differentiated asteroids, we determined major+trace elements and 147Sm-143Nd isotopic compositions on 13 Antarctic basaltic eucrites. Major element compositions cluster near the experimentally-determined peritectic, consistent with melts rather than cumulates. Trace element compositions are highly variable, ranging from LREE-enriched with negative Eu anomalies to LREE-depleted with positive Eu anomalies. Oxygen isotopes support derivation of all samples from a single parent body. Five ‘Main Group’ eucrites have flat REE patterns (147Sm/144Nd=0.1938-0.2006), small negative Eu anomalies and near-chondritic 143Nd/144Nd (#Nd (0) = -1.6 to +0.3). Four LREE-depleted eucrites have subchondritic 147Sm/144Nd (0.2001-0.2605) and high but variable 143Nd/144Nd (#Nd (0) = +2.9 to +37.7). Two incompatible element-enriched eucrites have LREE-enriched patterns (147Sm/144Nd = 0.1880-0.1894), deep negative Eu anomalies, and ‘crustal’ values of 143 Nd/144Nd (#Nd (0)) = -3.1 to -4.9). Most samples fall close to a 4.5 Ga reference line, but they do not form a valid whole rock isochron. The most discrepant sample is PCA80252, which has a LREE-depleted pattern, a large positive Ceanomaly and a young model age (TCHUR = 1.8 Ga). In contrast the two most LREE-depleted eucrites (EET90020, MET01081) have TCHUR = 4.5-4.6 Ga. TCHUR model ages of the other eucrites are highly variable (0.6-6.7 Ga). The 147Sm-143Nd systematics of some basaltic eucrites clearly have been altered by terrestrial weathering. In the case of PCA80252, the LREE-depletion is accompanied by a young TCHUR model age and trace element signatures of weathering such as elevated Sn abundances and a positive Ce-anomaly. In contrast, the strong LREE depletions observed in other samples of basaltic, non-cumulate eucrites appear to be a primary feature based on the realistic TCHUR model ages and the absence of other indicators of alteration. This implies the formation of LREE-depleted source regions on the eucrite parent body very early in its history, possibly by fractional melting or magma ocean crystallization, and continued melting of these depleted sources to produce LREE-depleted basaltic eucrites. The four least altered samples from this study give a whole rock isochron age of 4543 + 21 Ma, suggesting igneous differentiation within about 20 m. y. from the origin of the Solar System.

1

Australian National University, Canberra ACT 0200 Australia ([email protected]) 2 Geological Survey of New South Wales, Hunter Region, NSW 2310 Australia ([email protected]) 3 CSIRO Exploration and Mining, P.O. Box 1130, Bentley, WA 6102, Australia ([email protected]) LA-ICPMS offers a rapid, cost effective approach for investigating the isotopic and geochemical characteristics of ore systems. Quantification of chalcophile element analyses has been hindered by the low, heterogeneous, or poorly measured abundances of these elements in common silicate calibration standards such as the NIST and USGS glasses, and the intrinsic natural variability of ore-related minerals. Synthesis of sulfides or polymetallic analogues has been successful for some applications such as PGE. An alternative approach is the preparation of flux-fused glasses from wellcharacterized ore reference materials or doped with multielement solutions before fusion. Matrix effects are minor and formation of nuggets is suppressed. Relatively large amounts of homogeneous glass can be obtained, and custom mixtures can be prepared for specific applications. A significant challenge for ore geochronologists is to date mineralization directly rather than associated alteration or primary phases. We examined cassiterites from a variety of settings in NSW to evaluate its usefulness for U-Pb dating. Cassiterite is a common detrital mineral and its high initial U/Pb should be ideal for isotopic dating. 238U-206Pb ages calculated using the NIST 612 glass as an isotopic calibration standard showed a strong linear correlation with the accepted age of the deposit over the range of 200 to 1500 Ma. Isotopic dating and trace element analyses of cassiterites will aid in provenance identification, dating of mineral systems, and quantifying the role of wall rock interaction. Minerals precipitated within the regolith can reflect hydromorphic dispersion from deeply buried mineralisation. Alunite, calcrete, anatase, and rutile often contain appreciable Au, Cu, Pb and As, providing pathfinders for Au and base metal mineralization. The residence of minor, yet important, trace element components in complex mineral exploration samples can be identified by laser transects. Gold in particular is difficult to find because it is particulate at all scales, yet we have directly observed its presence in lateritic samples where it was considered an invisible component. These results suggest that biotic influences can affect the near-surface mobilisation and distribution of Au.

A766

Goldschmidt Conference Abstracts 2010

Occurrence of lipids in crossedlamellar layers of molluscan shells J. NOUET*, Y. DAUPHIN AND B. FARRE UMR IDES 8148, University Paris-Sud 11, F-91405 Orsay, France (*correspondence: [email protected]) Mollusk shells, which present a variety of acellular CaCO3 structures, have long been recognized as composite materials: organic macromolecules are associated with the mineral phases at sub-micrometric scales. Previous studies on soluble matrices extracted from the shells were focused on proteins and sugars [1], and many investigations were centered at shells presenting an inner aragonite nacreous layer and an outer prismatic layer. However, this rather simple nacroprismatic model does not reflect the variety and complexity usually found in mollusks: among them, the most commonly found yet least documented would be aragonite crossedlamellar structure [2]. Herein, we report occurrence of diverse lipidic compounds extracted from aragonite crossed-lamellar shell layers of five species: one bivalve and four gastropods. SEM observations were carried out, as well as Tapping AFM to map the localization of organic compounds at sub-micrometric scales. FTIR analyses were performed to characterize molecular groups, and TLC was used to separate lipidic extracts with respect to polarity. Whereas the observed structures are strongly similar among the wide array of taxa, differences in protein contents have already been found [1]. Our results suggest that lipidic contents are quite alike, and in relative high amount. They mostly consist of very apolar compounds such as waxes, some molecules close to triglycerides, as well as a few sterol esters and other unidentified common bands. Our results show that the lipid compounds of crossed-lamellar structures differ from lipids extracted from nacreous and prismatic layers [3], and from corals [4]. What is their role in biologically driven mineralization processes? Very little is known on their importance regarding the formation of the shell. Moreover, their behaviour during diagenetic processes cannot be neglected, as their response, as insoluble and polar compounds, will strongly differ from soluble proteins or sugars behaviour. [1] Dauphin & Denis (2000) Comparative Biochemistry & Physiology A126, 367–377. [2] Boggild (1930) D. Kgl. Danske Vidensk. Selsk. Skr. naturvidensk. og mathem. 2, 2, 231–326. [3] Farre & Dauphin (2009) Comparative Biochemistry & Physiology B152, 103–109. [4] Farre & Dauphin (in press) Zoology.

" 13C signatures of carbon pools and fluxes in a Holocene Sphagnum peat bog (Czech Republic) MARTIN NOVAK*, FRANTISEK VESELOVSKY, IVA JACKOVA, EVA PRECHOVA, FRANTISEK BUZEK, LEONA ZEMANOVA AND JAKUB HRUSKA Czech Geological Survey, Geologicka 6, 152 00 Prague 5, Czech Republic (*correspondence: [email protected]) Peatlands cover only 3 % of Earth's land area, but store as much as 30 % of the entire amount of terrestrial soil carbon. This amount corresponds to one half of carbon that is present in Earth's atmosphere as CO2. The decomposition of organic matter in peatlands is slowed by waterlogged conditions. Microbial activities and solubilities of dissolved gases are strongly temperature-dependent. In the era of global warming, thinning of peat deposits and elevated emissions of greenhouse gases (CO2 and methane) might accelerate further temperature increases. Determination of carbon isotope ratios ("13C) is one tool to obtain insights into mass transfers in bog ecosystems. Here we focus on C isotope systematics accompanying changes of C pool sizes and C input/output fluxes in an 8-meter deep peat bog in the Czech Republic, Central Europe. The bog, Velke Darko, started to accumulate organic matter 11 thousand years ago. Based on pollen analysis and 14C dates, peat accumulation has never been interrupted. Carbon isotope data have been obtained for living Sphagnum, solid peat substrate, dissolved organic carbon (DOC), and emitted gaseous products of terminal C mineralization (CO2 and CH4). "13C values of 18 grab samples of Sphagnum collected throughout the bog surface were systematically lower than "13C values of solid substrate along a vertical peat profile (means of 27. 2 and 25.8 per mil, respectively). We interpret this downcore positive "13C shift as a result of degradation of organic molecules. Sedges and spruce bark found as an admixture in the peat had lower "13C values than Sphagnum (-30.5, -29.0 and 26.3 per mil, respectively). Downcore, "13C of sedges, which may form 10 % of substrate mass, increased, similar to "13C of Sphagnum residuum. "13C of DOC in runoff formed a sinusoidal curve, with a minimum in July (-28.6 per mil), and a maximum in September (-27.2 per mil). "13C of emanating methane and CO2 under day-time, mid-summer conditions were -40 and -14 per mil, respectively. These data will be needed for the contruction of a C isotope mass balance for the peat bog.

Goldschmidt Conference Abstracts 2010

A767

A rapid determination method for Re and Os isotopic compositions using ID-MC-ICP-MS with sparging method

Investigating the effect of electroactive ion concentration on induced polarization signatures arising from biomineral formation

T. NOZAKI1, K. SUZUKI1, G. RAVIZZA2, J.I. KIMURA1 1 AND Q. CHANG

D. NTARLAGIANNIS1*, K. WILLIAMS2, L. SLATER1, S. HUBBARD2 AND Y. WU2

1

IFREE/JAMSTEC, 2-15 Natsushimacho, Yokosuka, Kanagawa 237-0061 ([email protected]) 2 Univ. of Hawaii, 1680 East-West Rd., Honolulu, HI 96822 ([email protected])

We present a rapid determination method for Re and Os isotope compositions using ID-MC-ICP-MS (NEPTUNE) combined with a sparging method. The sparging method allows us to measure Os isotope compositions just after acid sample digestion in a Carius tube without the most commonly used but time-consuming solvent extraction using CCl4 and HBr. Remaining Os after isotope measurement can be perfectly/easily removed by only drying sample solution, and Re is subsequently separated on an anion exchange resin. Our NEPTUNE is equipped with the multi-ion counter (MIC) system, enabling simultaneous measurement of a maximum of four Os isotopes, leading to drastic reduction of the measurement time. Therefore, compared to negative thermal ionization mass spectrometry (N-TIMS) which is presently the most widely used for Re-Os analyses, sample throughput becomes several times higher. Re-Os data of GSJ geochemical reference samples (JCh-1 and JMS-2; chert and pelagic clay, respectively) measured by NEPTUNE give similar concentrations and isotope compositions to those obtained by N-TIMS. The precision of Os isotope measurement by NEPTUNE with the sparging method is inferior to those by N-TIMS due to declining of the Os signal intensity and change of the efficiency of MIC over time. The total procedural blank for Os by the method using NEPTUNE are 0.69 ± 0.04 pg (n = 9), which is much lower than those by N-TIMS (ca. 2 pg). The detection and determination limits for Os amount by NEPTUNE are 0.12 and 0.39 pg, respectively. The typical sensitivity of Re by our NEPTUNE with a dissolvent nebulizer (Aridus II), Ni Xskimmer cone and external large interface pump is ca. 1100 V/ppm (1.1 mV/ppt). These analytical performances of our NEPTUNE are sufficient to analyze samples with very low Re and Os contents such as chert. Therefore, the Re and Os measurement of sedimentary rock samples by NEPTUNE combined with the sparging method is expected to be a powerful tool to reconstruct the secular change of the marine Os isotope compositions with high resolution, which unravels the cause of paleo-ocean global environmental change.

1

Department of Earth and Environmental Sciences, Rutgers Univesity, Newark, NJ 07102 USA (*correspondence: [email protected]) ([email protected]) 2 Earth Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 USA ([email protected], [email protected], [email protected]) Spectral induced polarization (SIP) is a proven geophysical method for detecting biomineral formation with promising applications for monitoring biogeochemical products during microbial induced sequestration of heavy metals and radionuclides in soils. SIP has been used to monitor the evolution of bioremediation-induced end-products at the uranium-contaminated U.S. Department of Energy RIFLE Integrated Field Research Challenge site in Colorado. Although a significant SIP response was detected, the quantitative interpretation is non-trivial as the polarization of metallic minerals depends both on the mineral surface properties and the electrolyte chemistry. In previous experiments SIP mechanisms were studied under complex environments and individual source mechanisms could not be evaluated. Here we examine the role of electrolyte chemistry by comparing the effect of redox active / inactive ions on metallic polarization. In these abiotic experiments magnetite was used as a proxy biomineral and dispersed within columns packed with sand. Parallel columns were saturated with solutions of different concentrations of active (Fe2+) and inactive (Ca2+) ions (0.01mM–10mM) and SIP measurements made (0.1-1000 Hz). Preliminary results suggest differences in the effect of active ion and inactive ion concentration on the SIP response are small, and that changes in the active ion concentration, in the presence of magnetite, alone are unlikely to explain recent SIP monitoring data from the RIFLE site.