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1. Earth-Sciences Department, University of Parma, Italy (tiziano.boschetti@unipr.it)

ISOTOPE COMPOSITION OF LITHIUM, BORON AND METHANE IN HYPERALKALINE SPRINGS OF NORTHERN APENNINES (ITALY). Tiziano Boschetti 1 , Giuseppe Etiope 2 , Romain Millot 3 , Maddalena Pennisi 4 , Lorenzo Toscani 1. 1. Earth-Sciences Department, University of Parma, Italy (tiziano.boschetti@unipr.it)

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1. Earth-Sciences Department, University of Parma, Italy (tiziano.boschetti@unipr.it)

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  1. ISOTOPE COMPOSITION OF LITHIUM, BORON AND METHANE IN HYPERALKALINE SPRINGS OF NORTHERN APENNINES (ITALY) Tiziano Boschetti1, Giuseppe Etiope2, Romain Millot3, Maddalena Pennisi4, Lorenzo Toscani1 1. Earth-Sciences Department, University of Parma, Italy (tiziano.boschetti@unipr.it) 2. INGV - Istituto Nazionale di Geofisica e Vulcanologia, Roma, Italy 3. BRGM - Metrology Monitoring Analysis Department, Orléans, France 4. CNR-IGGI - Institute of Geosciences and Earth Resources, Pisa, Italy

  2. W-Alps N-Apennines * * for the springs from Voltri Group: Bruni et al. 2002 - App. Geochem. 17, 455-474 Figure modified from : Boschetti & Toscani 2008 - Chem. Geol. 257, 76-91

  3. What’re hyperalkaline waters… 6.5-8.5 is the pH range in most natural waters 10 up to 12 is the pH range in the springs from serpentinites

  4. …and why to study them? - the Taro-Ceno Valley’s hyperalkaline springs have an high boron content (up to 13 mg/L), quite unusual for fresh waters (100-250 mg/L as TDS) - deep aquifer hosting hyperalkaline waters have low Mg content, negative (reducing) Eh and a low PCO2 (up to 10-8 bar) due to water-rock interaction in a closed system, therefore they might be used to sequester anthropogenic CO2 (Bruni et al. 2002): CO2 + 2 OH- = CO32- + H2O (travertine deposition) - low-T serpentinization produces abiogenic CH4, H2 and a small % of other hydrocarbons (ethane):

  5. Chemical classification by major dissolved constituents: springs issuing from serpentinites are characterized by 3 geochemical facies updated from : Boschetti & Toscani 2008 - Chem. Geol. 257, 76-91 - whereas springs issuing from basalts and other formations are Ca-bicarbonate, springs from ultramafites range from Ca-bicarbonate, passing through Mg-bicarbonate up to hyperalkaline Na-(Ca)-hydroxide

  6. Isotope composition of water molecula (Taro-Ceno Valley’s springs): all sampled waters are of meteoric origin updated from : Boschetti & Toscani 2008 - Chem. Geol. 257, 76-91

  7. B and Cl concentration in the hyperalkaline springs Cl vs. B in rock-forming minerals from ultramafites (modified from Scambelluri et al. 2004)

  8. B isotope composition B analysis by TIMS (‰ vs. SRM951) and B speciation on hyperalkaline springs Saturation indexes (SI) solution-minerals low-T serpentinization Some hyphotesis explaining the d11B difference in hyperalkaline spings: - in sample PR10, 10B is scavenged as borate by precipitating minerals so, respect to UM15, d11B increase and B content decrease. Most simply, boric acid in bicarbonate waters is transformed to borate (d11B similarity between PR01 and PR10) . - high B concentration in sample UM15 is due to the dissolution a B-bearing phase like datolite CaBSiO4(OH); this phase occurs in local ophiolitic breccias.

  9. B vs. Li isotope composition Boschetti & Toscani 2008 Chem. Geol. 257, 76-91 Boschetti et al. 2011 Aq. Geochem. 17, 71-208

  10. d11B vs. B/Cl: looking for boron source Vengosh et al. 1998 Besides pH fractionation or water-rock interaction (datolite?), the quite high B/Cl ratio and d11B of UM15 sample maybe caused by boron desorption from clays. Boschetti & Toscani 2008 Chem. Geol. 257, 76-91 Boschetti et al. 2011 Aq. Geochem. 17, 71-208

  11. d2H vs. d13C of dissolved methane: where’s the abiogenesis contribution? Fields from: Potter & Konnerup-Madsen (2003) In: Geol.Soc. Spec. Publ. 214, 151-173 Bradley & Summons (2010) Earth Planet Sci. Let. 297, 34-41 Methane produced by (abiogenic ) serpentinization: C: Chimera (Turkey) LC: Lost City (Atlantis Massif, mid-Atlantic ocean) Z: Zambales (Luzon, Philippines) O: Oman (Semail Nappe) mixing Hydrogen and methane concentrations is depending by various factors (T, W/R ratio, rock and fluid composition) influencing the Fisher-Tropsch reaction, e.g.: low T = reaction proceeds to the right; high T = reaction to the left: Autotrophic = bacterial carbonate reduction Heterotropic = bacterial methyl-type fermentation

  12. Hydrocarbons in the Po plain and N-Apennine (modified from Argnani et al. 2003, Quat. Int. 101-102, 13-26) (modified from Lindquist 1999, OFR 99-50-M) springs from serpentinites

  13. Conclusions… i) Boron isotopes are fractionated due to pH effect, while lithium due to formation of new mineral phases, respectively; ii) a (liquid) mixing between hyperalkaline with sedimentary, seawater-derived waters may be excluded; iii) on the contrary, the isotope composition of methane testify the solubilization of hydrocarbons in the aquifer at the boundary between ophiolitic units and the below flysch and/or arenaceous formations. This may be have overwritten the abiotic serpentinization signature of the gas dissolved in the hyperalkaline waters. …and future prospectives i) d11B analysis on primary and secondary minerals: lizardite, Ca- and Mg-carbonates, datolite [CaBSiO4(OH), in the ophiolitic breccias outcropping near to UM15 sample];

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