Ethane- and hydrogen-bearing carbonic fluid inclusions in a high-grade metamorphic rock

• TSUNOGAE Toshiaki

  Graduate School of Life and Environmental Sciences (Earth Evolution Sciences), University of Tsukuba Department of Geology, University of Johannesburg

• DUBESSY Jean

  G2R(UMR 7566), Nancy Université and CNRS

抄録

Ethane- and hydrogen-bearing carbonic fluid inclusions are found within quartz in a leucocratic garnet granulite obtained from the Neoarchean Limpopo Belt in South Africa. The trapped fluids are present as secondary inclusions and show melting temperatures in the range of -60.9 to -56.9 °C, suggesting a dominantly CO₂-rich composition. The wide range of estimated CO₂ densities (0.611-1.020 g/cm³) indicates entrapment of the fluids at 5 kbar at 700 °C and significant subsequent density decrease due to post-peak decompression. Laser Raman analysis of the inclusions at room temperature confirmed that the trapped fluids are CO₂-rich (>95 mol%) with very minor CH₄ (2.5-4.6 mol%), N₂ (0.1-0.4 mol%), and C₂H₆ (0.01-0.02 mol%) constituents. A thin carbon film precipitated on the cavity wall, not visible optically, was also identified by Raman spectroscopy. We therefore infer the following carbon-forming reaction during decompression and/or cooling below 700 °C and 5 kbar; CO₂ + CH₄ → 2C + 2H₂O. When the inclusions were heated to 150 °C to homogenize all the fluid phases, H₂ (0-0.05 mol%) and H₂O (1.7-0.3 mol%) were detected instead of C₂H₆. Although the processes of the formation of C₂H₆ and H₂ are not known, the presence of CH₄, C₂H₆ and H₂ in CO₂-dominant fluid is considered as a possible product of a series of reactions in the C-O-H system within the inclusion cavity during decompression/cooling.

収録刊行物

• Journal of Mineralogical and Petrological Sciences

  Journal of Mineralogical and Petrological Sciences 104 (5), 324-329, 2009

  一般社団法人　日本鉱物科学会

キーワード

• Carbonic fluid
• Ethane
• Hydrogen
• Raman spectroscopy
• Granulite
• Limpopo Belt

詳細情報

• CRID: 1390282681521796480
• NII論文ID: 10025445187
• NII書誌ID: AA11460926
• DOI: 10.2465/jmps.090622f
• ISSN: 13493825
• ISSN: 13456296
• 本文言語コード: en
• データソース種別:
  • JaLC
  • Crossref
  • CiNii Articles
• 抄録ライセンスフラグ: 使用不可