Adsorption behavior of H2 in forsterite micro-pores with genetic implications for H2 seismic geochemical anomalies

Abstract

The presence and properties of hydrogen gas (H₂) in the Earth’s deep interior provide valuable insights into the role of H₂ geochemistry in monitoring seismic activities. Experiment results have shown that serpentinization of olivine is the primary mechanism of natural H₂ production on the Earth. Therefore, the characteristics of H₂ storage and migration within the Earth are significant for understanding the mechanisms behind seismic geochemical precursor. In this study, the Grand Canonical Monte Carlo method combined with molecular dynamics is applied to simulate the adsorption behaviors and characteristics of H₂ in slit-like pores of forsterite (an free-Fe olivine end-number), under different temperature–pressure conditions (300–1000 K and 0–100 MPa) and pore sizes (5–20 Å). The results indicated that adsorption of H₂ in forsterite pores is physical adsorption mainly controlled by van der Waals force. The amount of heat released by adsorption of H₂ in forsterite pores (isosteric heat) positively correlates with temperature and pore size. The increased pressure and pore size will increase the amount of H₂ adsorbed (N_excess) in the forsterite pores and temperature is negatively correlated with the N_excess. Our simulations reveal that the interplay between temperature–pressure conditions and the pore size of forsterite significantly influences the adsorption and dissipation of H₂ within the deep Earth. This interaction subsequently results in discernible changes to the geochemical signatures of H₂ at the Earth’s surface, which are intrinsic controls that allow H₂ geochemical characteristics to serve as crucial indicators for monitoring seismic activities.