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, Italy1

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N-ApenninesW-Alps

Figure modified from :Boschetti & Toscani 2008 - Chem. Geol. 257, 76-91

* for the springs from Voltri Group: Bruni et al. 2002 - App. Geochem. 17, 455-474

*

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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

- 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):

1.8 0.2 4 2 2 3 4 3 2 5 42 4FO-90 olivine magnetite brucite serpentine

60Mg Fe SiO   CO   80H O 4Fe O   18Mg OH   30Mg Si O OH   CH

1.8 0.2 4 2 3 4 3 2 5 22 4FO-90 olivine magnetite brucite serpentine

15Mg Fe SiO 20.5H O Fe O 4.5Mg OH 7.5Mg Si O OH H 4

…and why to study them?

Chemical classification by major dissolved constituents:springs issuing from serpentinites are characterized by 3 geochemical facies

- 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

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updated from : Boschetti & Toscani 2008 - Chem. Geol. 257, 76-91

Isotope composition of water molecula (Taro-Ceno Valley’s springs):all sampled waters are of meteoric origin

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updated from : Boschetti & Toscani 2008 - Chem. Geol. 257, 76-91

B and Cl concentration in the hyperalkaline springs

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T (°C) pHCl-

(mg/L) B

(mg/L)B/Cl (M)

Italy (Taro-Ceno Valley, Emilia Romagna Region) 12 10.9 19 2.1 0.35Italy (Taro-Ceno Valley, Emilia Romagna Region) 13 10.4 14 13.4 3.15Italy (Voltri Group, Liguria Region) 12 11.9 14 0.14 0.04Italy (Val Malenco, Lombardia Region) 9 11 81 - -Switzerland (Val Plavna, Engadine Valley) 6 10.8 49 - -Portugal (Cabeço de Vide) 20 11.1 26 0.25 0.032Cyprus (Troodos Massif) 22 12 420 1.1 0.009Bosnia and Herzegovina (Kulasi) - 11.8 18 0.15 0.027Greece (Sperchios Graben) 27 11 21 - -

Oman Oman (Semail Ophiolite Nappe) 26 11.3 197 <0.1 <0.002California (Burro Mt., Monterey) 20 11.5 63 0.02 0.0010California (Cazadero A, Sonoma) 18 11.8 55 0.01 0.00060Oregon (John Day, Grant) 31 11.3 19 0.1 0.017California (Red Mt., Adobe Canyon) 16 11.8 32 0.1 0.010California (Red Mt., Santa Clara) 11 12.0 26 0.06 0.0076California (Aqua de Ney, Siskiyou) 12 12 7180 242 0.11

W-USA

Mediterranean

sample

Cl vs. B in rock-forming minerals from ultramafites(modified from Scambelluri et al. 2004)

B isotope composition

B analysis by TIMS (‰ vs. SRM951) and B speciation on hyperalkaline springs

Saturation indexes (SI) solution-minerals

Some hyphotesis explaining the 11B difference in hyperalkaline spings:

- in sample PR10, 10B is scavenged as borate by precipitating minerals so, respect to UM15, 11B increase and B content decrease. Most simply, boric acid in bicarbonate waters is transformed to borate (11B 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.

Minerals PR01 UM15 PR10

hydromagnesite -6.2 -13 -10

artinite -3.1 -3.8 -2.0

brucite -2.7 -1.2 0.2

calcite 0.1 0.6 0.6

aragonite -0.1 0.4 0.4

low-T_serpentine -2.5 1.0 4.4

clays (montmorillonite-saponite)SI < 0 undersaturation: the solution dissolves the mineralSI = 0 ± 0.5 the solution is in equilibrium with the mineralSI < 0 oversaturation: the solution precipitates the mineral

oversatured

sample boric borate

PR10_2001 +38.6 ± 0.3 +39.0 ± 0.1 5.6 94.4

PR10_2010 +38.3 ± 0.6 +39.3 ± 0.1 1.5 98.5

UM15_2002 +17.2 ± 0.1 9.9 90.1

UM15_2010 +16.2 ± 0.2 +16.4 ± 0.1 5.5 94.5

n.a.

IGGI-Italy BRGM-France

‰ %

low-T serpentinization

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B vs. Li isotope composition

min max mean median min max mean median

Ca- bicarbonate 3.2E-04 4.0E-03 2.4E-03 2.6E-03 8.3E-02 1.2E-01 9.7E-02 9.2E-02

Mg- bicarbonate 1.6E-04 3.6E-02 3.1E-03 2.9E-04 3.1E-02 2.2E-01 1.4E-01 1.7E-01

hyperalkaline 3.6E-04 7.1E-04 5.7E-04 6.6E-04 3.2E-01 3.3E+00 2.1E+00 2.9E+00

brines 9.5E-05 5.8E-03 2.2E-03 1.4E-04 6.87E-04 1.40E-02 3.87E-03 8.24E-04

terrestrial mud volcanoes 2.4E-04 8.9E-04 4.9E-04 4.7E-04 1.32E-02 9.43E-02 3.90E-02 3.24E-02

Li/ Cl (M) B/ Cl (M)

waters from N-Apennine ultramafites

local sedimentary seawater-derived fluids (N-Apennine and Po Plain)

Boschetti et al. 2011 Aq. Geochem. 17, 71-208

Boschetti & Toscani 2008Chem. Geol. 257, 76-91

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Vengosh et al. 1998

11B vs. B/Cl: looking for boron source

min max mean median min max mean median

Ca- bicarbonate 3.2E-04 4.0E-03 2.4E-03 2.6E-03 8.3E-02 1.2E-01 9.7E-02 9.2E-02

Mg- bicarbonate 1.6E-04 3.6E-02 3.1E-03 2.9E-04 3.1E-02 2.2E-01 1.4E-01 1.7E-01

hyperalkaline 3.6E-04 7.1E-04 5.7E-04 6.6E-04 3.2E-01 3.3E+00 2.1E+00 2.9E+00

brines 9.5E-05 5.8E-03 2.2E-03 1.4E-04 6.87E-04 1.40E-02 3.87E-03 8.24E-04

terrestrial mud volcanoes 2.4E-04 8.9E-04 4.9E-04 4.7E-04 1.32E-02 9.43E-02 3.90E-02 3.24E-02

Li/ Cl (M) B/ Cl (M)

waters from N-Apennine ultramafites

local sedimentary seawater-derived fluids (N-Apennine and Po Plain)

Boschetti et al. 2011 Aq. Geochem. 17, 71-208

Boschetti & Toscani 2008Chem. Geol. 257, 76-91

Besides pH fractionation or water-rock interaction (datolite?), the quite high B/Cl ratio and 11B of UM15 sample maybe caused by boron desorption from clays.

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2H vs. 13C 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)

Autotrophic = bacterial carbonate reduction

Heterotropic = bacterial methyl-type fermentation

mixing

1.8 0.2 4 2 2FO-90 olivine

3 4 3 2 5 42 4magnetite brucite serpentine

60Mg Fe SiO   CO   80H O

4Fe O   18Mg OH   30Mg Si O OH   CH

1.8 0.2 4 2FO-90 olivine

3 4 3 2 5 22 4magnetite brucite serpentine

15Mg Fe SiO 20.5H O

Fe O 4.5Mg OH 7.5Mg Si O OH H

O2H CH 4H CO 2422

O2nH HC H1 3n nCO 222nn22

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:

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CH4 C2H6 H2

methane ethane hydrogenmol %

PR10 (2011-04-02) 7.29 0.0289 0.0261

(modified from Argnani et al. 2003, Quat. Int. 101-102, 13-26)

Hydrocarbons in the Po plain and N-Apennine

(modified from Lindquist 1999, OFR 99-50-M)

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springs from serpentinites

Conclusions…

…and future prospectives

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.

i) 11B 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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