Volcanology, Geochemistry, Petrology [V]

 CC:Hall E  Monday  1400h

Earth's Carbon Cycles: Sources, Sinks, Pathways, and Fluxes II Posters

Presiding:  A Shaw, WHOI; P Morrill, Memorial University of Newfoundland


Formations and Syntheses of Carbon-bearing Deposits on Phlogopite of Basalts

* Miura, Y (yasmiura@yamaguchi-u.ac.jp), Yamaguchi University, Yoshida 1677-1, Yamaguchi, 753-8512, Japan

1. Introduction: Recently author found carbon-bearing grains on phlogopite plate in druses of terrestrial volcanic basalts in Shimonoseki, Yamaguchi, Japan [1], where many scientists have been reported as normal 'phlogopite growth' formed at hydrothermal condition from volcanic magmas [2]. The main problem to report such crystals is non-detection of light carbon (C) by normal X-ray detection and the EPMA and TEM analyses (due to detection heavier than Na element) [3-7].The purpose of this paper is to elucidate carbon- bearing deposits on phlogopite minerals compared with continental phlogopites from Canada, Finland and Sri Lanka without carbon. 2. Carbon-bearing phlogopite in volcanic basalt: The samples used in this study are crystalline (with glassy) grains from druses of basaltic lavas, which are collected from Mukuno-cho and Kifune-cho, Shimonoseki-shi, Yamaguchi-ken, Japan [1]. Well- known phlogopites from the Mutsure-jima (as National Reserved Area) are the same rocks at the same City [2]. Fe and Ti-bearing phlogopite observed by the FE-SEM with EDX analyzer (JEOL7000F), Yamaguchi, Japan, shows various vein-textures intruded irregularly by carbon- rich fluid (mixed with phlogopite in composition) as quenched process. Zonal and growth spirals reported previously on the similar samples [2] are not 'phlogopite crystal growth' in this study but micro-grain assemblages on phlogopite crystals which are not observed three continental phlogopites from Canada (Quebec), Sri Lanka and Finland. Phlogopite samples from Shimonoseki are formed by rapid reaction as vapor-fluid carbon dioxides from buried Paleozoic limestones on phlogopite plates during quenching processes from basaltic magma. This is the first report of carbon-rich grains in volcanic basalts on the Earth. 3. Artificial formation of carbon-fixed phlogopites: Artificial carbon fixings on phlogopite plates from Finland have been carried out at author's laboratory to compare with Shimonoseki carbon-bearing minerals by an in-site observation with the FE-SEM with EDX analyzer to avoid any contamination from sample preparation. This is first syntheses to form carbon-rich materials along quenched veins of phlogopite with various and random growth patterns [1]. 4. Summary: The present results are summarized as follows: 1) The first report of carbon- rich grains formed in natural volcanic basalts in Yamaguchi, Japan. 2) The first artificial syntheses are carried out to deposite carbon-bearing materials as growth pattern on phlogopite composition. Acknowledgements: Author thanks to Dr. T. Kato, Yamaguchi University, for sample data interpretation on terrestrial minerals and rocks. References: [1]Miura Y. (2008): EOS Trans, AGU, 89 (53), Abstract # MR33-B1861. [2] Sunagawa I. (1964): Am. Mineral., 49, 1427-1434. [3] Miura Y. (2008): ISTS Issue of Japan Society for Aeronautical and Space Science (JSASS), Paper #2008-c-46. www.senkyo.co.jp/ists2008/ [4] Miura Y.(2008): 5th AOGS Meeting (Busan) , Abstract #IWG04-D412. [5] Miura Y.(2007): Frontiers in Mineral Sciences 2007 (Univ. of Cambridge, UK), 223. [6]Miura Y. (2007): Meteoritics & Planet. Sci(USA), 110-110. [7] Miura Y. (2006): ICEM2006 symposium abstract paper volume (Yamaguchi University, Yamaguchi, Japan), pp.2.


Synthesis and Geochemical Indicators of Abiogenic Hydrocarbons Produced Under Hydrothermal Conditions

* Morrill, P L (pmorrill@mun.ca), Memorial University of Newfoundland, 300 Prince Philip Dr., St. John's, NL A1B3X5, Canada
Weinberger, D S (dsweinberger@gmail.com), University of California Riverside, Department of Chemistry, Riverside, CA 92521, United States
Sherwood Lollar, B (bslollar@chem.utoronto.ca), University of Toronto, Department of Geology 22 Russell St., Toronto, ON M5S3B1, Canada
Fogel, M L (m.fogel@gl.ciw.edu), Carnegie Institution of Washington, Geophysical Laboratory, Washington, DC , United States
Cody, G D (g.cody@gl.ciw.edu), Carnegie Institution of Washington, Geophysical Laboratory, Washington, DC , United States

Determining the geologically relevant conditions for, and geochemical indicators of, abiogenic hydrocarbon production in hydrothermal systems will aid in the identification of abiogenic and biogenic hydrocarbons, and carbon cycling in hydrothermal systems. In this study, abiogenic gaseous hydrocarbons were synthesized in hydrothermal experiments at 250C and 500 bar using a native Fe powder catalyst over short time periods (1 to 20 hr) to observe the product distribution and kinetic isotope effects associated with abiogenic organic synthesis of gaseous alkane hydrocarbons. The composition as well as the carbon and hydrogen isotope values (delta13C and delta2H respectively) of the gaseous hydrocarbons were measured to determine the mechanisms of formation and to determine if the abiogenic gases produced shared otherwise unique geochemical indicators for microbial and thermogenic hydrocarbon gases. Methane was the dominant hydrocarbon in all the experiments. Higher molecular weight gaseous alkanes decreased in concentration with increasing carbon number, which was well described by Anderson Schultz Flory probability of propagation factors (with an average of -0.31 ±0.15). At low percentage of carbon converted, the carbon isotopic separation between CO2 and CH4 (51.0 permil) was similar in magnitude to the carbon isotopic separation associated with microbial CO2 reduction. However, as the percentage of carbon converted increased, the carbon isotopic separation between CO2 and CH4 became progressively smaller (24.4 ±1.8 permil) overlapping with ranges for thermogenic hydrocarbons and thermophilic methanogens. The inability to distinguish abiogenic products, CO2 and CH4, from thermogenic and microbial methanogens products suggests that carbon isotope values alone of CO2 and CH4 are not enough to differentiate between alternative sources of CH4. In this study, ratios of C1/C2+ differentiated hydrocarbons produced by abiogenic synthesis from microbial gases.


Modeling Shallow Groundwater Geochemistry and Carbon Isotopes: Test of Methodology for CO2 Storage Evaluation at an EOR Site, West Texas, USA

* Romanak, K D (katherine.romanak@beg.utexas.edu), Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, University Station, Box X, Austin, TX 78713, United States
Smyth, R C (rebecca.smyth@beg.utexas.edu), Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, University Station, Box X, Austin, TX 78713, United States
Yang, C (changbing.yang@beg.utexas.edu

Hovorka, S D (susan.hovorka@beg.utexas.edu) AB: Geochemical mixing, reaction, and isotopic models are being used to study the Dockum aquifer above the SACROC oilfield in Scurry County, Texas, the longest running (>35 years) engineered CO2 injection on record. Geochemical data used in the modeling are from fresh to slightly saline groundwater (200 to 500 ft depth Triassic-age Dockum Fm. and Permian-age evaporite horizons), and brine from the deeper (6,000 to 7,000 ft) injection/production zone. The goals of this study are to: 1) assess the degree of interaction between shallow groundwater and CO2 injectate, and 2) develop low-cost methods for monitoring shallow groundwater at CO2 sequestration sites. Injectate CO2 is not evident in freshwater above SACROC. Geochemical parameters in groundwater samples do not differ significantly from regional trends and partial pressures (PCO2) of dissolved CO2 are within normal ranges (10-1.6 to 10-3.0). PHREEQC model results show that cation exchange and mixing of Dockum groundwater with Ca-SO4 water from underlying Permian evaporite deposits (< 22%) and Na-Cl produced brines (< 0.8%) drives dedolomitization [Ca2+ + CaMg(CO3)2 = Mg2+ + 2CaCO2] of aquifer carbonate. This is in contrast to calcite dissolution [CO2 + H2O + CaCO2 = Ca2+ + 2HCO3-], which is a common effect of CO2 gas in freshwater aquifers. Modeling of carbon isotopes (after Appelo and Postma, 2005) indicates the d13C of dissolved inorganic carbon (DIC) in the Dockum (-3.6 to -13.2 per mil) is dominated by dissolution of dolomite (-2.5 to -7.7 per mil) with initial DIC conditions (-15 to -20 per mil) in equilibrium with a microbial CO2 source (-23 to -28 per mil). Because CO2 gas is not a reactant (carbonate for calcite precipitation originates from dolomite dissolution), input of injectate CO2 has little or no impact on isotopes for normal ranges of PCO2. Therefore carbon isotope ratios may not be useful parameters for monitoring groundwater impacts from CO2 injection in areas where mixing and dedolomitization dominate groundwater chemistry. This research is funded by the Department of Energy National Energy Technology Laboratory (DOE NETL) as part of the Phase 2 Southwest Regional Carbon Sequestration Partnership (SWP).