| Autor: |
Leong, JA, Nielsen, M, McQueen, N, Karolytė, R, Hillegonds, DJ, Ballentine, C, Darrah, T, McGillis, W, Kelemen, P |
| Rok vydání: |
2023 |
| Předmět: |
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| Zdroj: |
Geochimica et Cosmochimica Acta. 347:1-15 |
| ISSN: |
0016-7037 |
| Popis: |
Reduced (H2- and CH4-rich) and hyperalkaline fluids are products of subsurface reactions accompanyingserpentinizationofultramafic rocks. H2and CH4produced during serpentinization can fuelmicroorganismsand support habitable subsurface environments. CH4is also a potent greenhouse gas and can offset negative greenhouse emissions arising from active CO2removal accompanyingcarbon mineralizationin ultramafic rocks. However, the rate at which reduced volatiles are delivered to the surface and the rate of reactions that generate these volatiles at low-temperature conditions are poorly known. In this work, we measured H2and CH4outgassing rates in several hyperalkaline spring sites in the Samailophiolite, Oman. H2and CH4outgassing in these sites are variable and range up to 70,000 and 7,000mol yr−1, respectively. CH4outgassing in spring sites are unlikely to offset negativecarbon emissionsestimated from active carbon mineralization reactions in the Samail ophiolite. However, diffused CH4outgassing fromperidotiteoutcrops remain unconstrained. Compositional and isotopic constraints show that volatiles are likely derived from active serpentinization, fluid inclusion decrepitation, or a combination of both. Calculated active serpentinization rates of up to 8×10−14sec−1account for measured outgassing rates and these are consistent with slow rates expected at low temperatures. In calculations of serpentinization rates, this work uses reaction-path models to account incorporation of both ferrous and ferric iron in the resulting alteration assemblages, which yields ∼0.3mol H2kg−1of ultramafic rock altered, lower than simulations based on iron oxidation to magnetite only. Contribution from decrepitation of H2- and CH4-bearing fluid inclusions is possible but would require much more mass of ultramafic rocks to account for observed outgassing. Further studies can help quantify extents of each source on active outgassing in Oman. Overall, this work shows that low-temperature serpentinization on geologically short timescales can account for observed flux of reduced volatiles in hyperalkaline environments. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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