Abstract
BackgroundHydrogen is known to occur in the groundwaters of some ancient cratons. Where associated gases have been dated, their age extends up to a billion years, and the hydrogen is assumed also to be very old. These observations are interpreted to represent the radiolysis of water and hydration reactions and migration of hydrogen into fracture systems. A hitherto untested implication is that the overwhelming bulk of the ancient low-permeability basement, which is not adjacent to cross-cutting fractures, constitutes a reservoir for hydrogen.ResultsNew data obtained from cold crushing to liberate volatiles from fluid inclusions confirm that granites and gneiss of Archean and Palaeoproterozoic (>1600 Ma) age typically contain an order of magnitude greater hydrogen in their entrained fluid than very young (<200 Ma) granites. Sedimentary rocks containing clasts of old basement also include a greater proportion of hydrogen than the young granites.ConclusionsThe data support the case for a global reservoir of hydrogen in both the ancient basement and in the extensive derived sediments. These reservoirs are susceptible to the release of hydrogen through a variety of mechanisms, including deformation, attrition to reduce grain size and diagenetic alteration, thereby contributing to the hydrogen required by chemolithoautotrophs in the deep biosphere.
Highlights
Hydrogen is known to occur in the groundwaters of some ancient cratons
In a coarse-grained rock like granite, beta-irradiation from potassium is more likely to penetrate beyond grain boundaries into intergranular fluid than shorter-range alpha irradiation from uranium, and potassium is more pervasively distributed than the uranium in granite, so contributes more widely to radiolysis
Potassium is as abundant in the young basement as it is in the Precambrian basement (Fig. 2), showing that it is age rather than composition that is the control on hydrogen content
Summary
Where associated gases have been dated, their age extends up to a billion years, and the hydrogen is assumed to be very old. These observations are interpreted to represent the radiolysis of water and hydration reactions and migration of hydrogen into fracture systems. The composition of gases trapped in fluid inclusions can be measured using cold crushing into a mass spectrometer This technique was developed for the Parnell and Blamey Geochem Trans (2017) 18:2 investigation of ore deposits and geothermal systems, and has subsequently found application to diverse crystalline and sedimentary rocks [12,13,14]. We have used this approach to test: 1. If the hydrogen occurs widely in the entrapped fluid in old basement rocks, as implied by the gas released from Precambrian cratons
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
