Global hydrogen reservoirs in basement and basins

Area of Science:

• Geochemistry
• Geology
• Microbiology

Background:

• Ancient cratons harbor groundwater with hydrogen dated up to a billion years old.
• This hydrogen is thought to originate from water radiolysis and hydration reactions, migrating into fractures.
• An untested hypothesis suggested ancient basement rocks, beyond fractures, act as a hydrogen reservoir.

Purpose of the Study:

• To investigate the hydrogen content of ancient basement rocks.
• To determine if ancient rocks hold significantly more hydrogen than younger rocks.
• To assess the potential of ancient geological formations as hydrogen reservoirs.

Main Methods:

• Cold crushing of rock samples to liberate volatiles from fluid inclusions.
• Analysis of fluid inclusions in Archean and Palaeoproterozoic granites and gneiss.
• Comparison of hydrogen content in ancient versus young granites and derived sediments.

Main Results:

• Archean and Palaeoproterozoic granites and gneiss contain significantly higher hydrogen concentrations (an order of magnitude more) in their fluid inclusions compared to young granites.
• Sedimentary rocks derived from ancient basement also show elevated hydrogen proportions relative to young granites.

Conclusions:

• The findings support the existence of a global hydrogen reservoir within ancient basement rocks and their derived sediments.
• These reservoirs can release hydrogen via geological processes like deformation, grain size reduction, and diagenetic alteration.
• This released hydrogen can potentially sustain chemolithoautotrophic life in the deep biosphere.