Experimental diffusion of hydrogen into synthetic fluid inclusions in quartz

Abstract

Abstract Quartz‐hosted, synthetic CO2‐H2O fluid inclusions behave as open systems with respect to diffusional transfer of hydrogen during laboratory‐simulated metamorphic re‐equilibration at 650, 750 and 825°C and 1.5 kbar total pressure with fO2 defined by the C‐CH4 buffer. Microthermometry and Raman spectroscopy show that the initial CO2‐H2O inclusions become CO2‐CH4‐H2‐H2Oinclusions after diffusive influx of hydrogen from the reducing confining medium. Measurable changes are observed in inclusion compositions after only 15 days of re‐equilibration, implying significant hydrogen mobility at still lower temperatures over geological time spans. Results of synthetic inclusion re‐equilibrium experiments have profound implications for the interpretation of natural fluid‐inclusion data; failure to account for potential hydrogen migration in inclusions from high‐temperature geological environments may lead to erroneous estimates of P‐T, and/or the compositions of metamorphic fluids.