Hydrogeologic Controls on Episodic H₂ Release from Precambrian Fractured Rocks—Energy for Deep Subsurface Life on Earth and Mars

Abstract

Dissolved H(2) concentrations up to the mM range and H(2) levels up to 9-58% by volume in the free gas phase are reported for groundwaters at sites in the Precambrian shields of Canada and Finland. Along with previously reported dissolved H(2) concentrations up to 7.4 mM for groundwaters from the Witwatersrand Basin, South Africa, these findings indicate that deep Precambrian Shield fracture waters contain some of the highest levels of dissolved H(2) ever reported and represent a potentially important energy-rich environment for subsurface microbial life. The delta (2)H isotope signatures of H(2) gas from Canada, Finland, and South Africa are consistent with a range of H(2)-producing water-rock reactions, depending on the geologic setting, which include both serpentinization and radiolysis. In Canada and Finland, several of the sites are in Archean greenstone belts characterized by ultramafic rocks that have under-gone serpentinization and may be ancient analogues for serpentinite-hosted gases recently reported at the Lost City Hydrothermal Field and other hydrothermal seafloor deposits. The hydrogeologically isolated nature of these fracture-controlled groundwater systems provides a mechanism whereby the products of water-rock interaction accumulate over geologic timescales, which produces correlations between high H(2) levels, abiogenic hydrocarbon signatures, and the high salinities and highly altered delta (18)O and delta (2)H values of these groundwaters. A conceptual model is presented that demonstrates how periodic opening of fractures and resultant mixing control the distribution and supply of H(2) and support a microbial community of H(2)-utilizing sulfate reducers and methanogens.

How Deep Can Surface Signals Be Traced in the Critical Zone? Merging Biodiversity with Biogeochemistry Research in a Central German Muschelkalk Landscape

“…Geological processes transporting chemical energy in the form of gases, such as hydrogen (H 2 ), methane (CH 4 ), or reduced metal ions can support rich and diverse microbial communities near hydrothermal vents (Hinrichs et al, 1999;Boetius et al, 2000;Michaelis et al, 2002). Explorations of saline fracture waters in the deep Precambrian shields also identified subsurface environments rich in H 2 similar to those found at hydrothermal vents (Sherwood Lollar et al, 2007). Alkaline saline groundwaters found at 2.8 kilometers depth in Archaean metabasalt are dominated by thermophilic sulfate reducers that appear to be sustained by geologically produced H 2 and sulfate at concentrations sufficient to maintain activities for millions of years with no reliance on photosynthetically derived substrates (Lin et al, 2006).…”

Hydrogen from Radiolysis of Aqueous Fluid Inclusions during Diagenesis

“…Other mechanisms for hydrogen generation include serpentinization, oxidation of ferrous iron, and rock friction in seismogenic zones [6,9,[31][32][33].…”

The geochemistry of methane isotopologues

“…Apparent temperatures derived from D/H equilibria in the systems H 2 -H 2 O and H 2 -CH 4 were first used as geothermometers in studies of geothermal or volcanic gases and waters (Árnason and Sigurgeirsson, 1968;Gunter and Musgrave, 1971;Arnason, 1977;Kiyosu, 1983;Lyon and Hulston, 1984), and later examined with respect to data from seafloor hydrothermal fluids (Welhan and Craig, 1983;Horibe and Craig, 1995;Proskurowski et al, 2006;Bradley and Summons, 2010;Kawagucci et al, 2010;Kawagucci et al, 2011;Kawagucci et al, 2013), shieldhosted groundwaters (Sherwood Lollar et al, 1993;Sherwood Lollar et al, 2007;Sherwood Lollar et al, 2008), and continental springs, seeps, and well fluids influenced by serpentinization (Neal and Stanger, 1983;Coveney et al, 1987;Abrajano et al, 1988;Fritz et al, 1992;Etiope et al, 2011a;Suda et al, 2014). Temperatures returned from H 2 -H 2 O and H 2 -CH 4 equilibria often agree with each other and with realistic geologic and hydrologic scenarios for geothermal fluids exiting at high temperatures, but these relationships do not necessarily hold for lower-temperature fluids.…”

“…In subsurface mines in the Canadian Shield, exploration boreholes intersecting extensive fracture networks release waters rich in reduced gases (H 2 , CH 4 , C 2+ ) and noble gases, which exsolve upon depressurization. Sampling and characterization of fracture fluids from Kidd Creek have been described in previous studies (Sherwood et al, 1988;Sherwood Lollar et al, 2002;Sherwood Lollar et al, 2007;Sherwood Lollar et al, 2008;Holland et al, 2013). We analyzed methane sampled from boreholes at the 7850 ′ -and 9500 ′ -levels (Table 2.1).…”