Methane-hydrogen gas seeps, Zambales Ophiolite, Philippines: Deep or shallow origin?

T. A. Abrajano; N. C. Sturchio; J. K. Bohlke; G. L. Lyon; R. J. Poreda; C. M. Stevens

doi:10.1016/0009-2541(88)90116-7

Methane-hydrogen gas seeps, Zambales Ophiolite, Philippines: Deep or shallow origin?

T. A. Abrajano^*, N. C. Sturchio, J. K. Bohlke, G. L. Lyon, R. J. Poreda, C. M. Stevens

^*Corresponding author for this work

Research output: Contribution to journal › Article › peer-review

292 Scopus citations

Abstract

Isotopically anomalous CH₄-rich gas escapes at low flow rate and ambient temperature from seeps in serpentinized ultramafic rock in the Zambales Ophiolite, Philippines. The major components of the gas are CH₄ (55 mole%) and H₂ (42 mole%); the CH₄ CO₂ ratio is > 1800 and the CH₄ He ratio is 9.2·10⁴. The δ¹³C-value of the CH₄ is -7.0±0.4‰ (PDB), ∼8‰ higher than the highest published values for CH₄ in other natural gases and hot springs, but similar to values commonly attributed to mantle carbon. The ³He⁴He ratio is 5.70·10^-6, 4.1 times the atmospheric ratio, indicative of a substantial mantle He component. The δD-values of CH₄ and H₂ are -136 and -590‰, respectively, consistent with equilibration temperatures of 110-125°C. Carbon and He isotopic data could be consistent with derivation of the Zambales gas directly from a reduced mantle. However, phase equilibria and H isotope data indicate that the gas also could have been produced by reduction of water and carbon during low-temperature serpentinization of the ophiolite.

Original language	English (US)
Pages (from-to)	211-222
Number of pages	12
Journal	Chemical Geology
Volume	71
Issue number	1-3
DOIs	https://doi.org/10.1016/0009-2541(88)90116-7
State	Published - Dec 15 1988
Externally published	Yes

ASJC Scopus subject areas

Geology
Geochemistry and Petrology

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title = "Methane-hydrogen gas seeps, Zambales Ophiolite, Philippines: Deep or shallow origin?",

abstract = "Isotopically anomalous CH4-rich gas escapes at low flow rate and ambient temperature from seeps in serpentinized ultramafic rock in the Zambales Ophiolite, Philippines. The major components of the gas are CH4 (55 mole%) and H2 (42 mole%); the CH4 CO2 ratio is > 1800 and the CH4 He ratio is 9.2·104. The δ13C-value of the CH4 is -7.0±0.4‰ (PDB), ∼8‰ higher than the highest published values for CH4 in other natural gases and hot springs, but similar to values commonly attributed to mantle carbon. The 3He 4He ratio is 5.70·10-6, 4.1 times the atmospheric ratio, indicative of a substantial mantle He component. The δD-values of CH4 and H2 are -136 and -590‰, respectively, consistent with equilibration temperatures of 110-125°C. Carbon and He isotopic data could be consistent with derivation of the Zambales gas directly from a reduced mantle. However, phase equilibria and H isotope data indicate that the gas also could have been produced by reduction of water and carbon during low-temperature serpentinization of the ophiolite.",

author = "Abrajano, {T. A.} and Sturchio, {N. C.} and Bohlke, {J. K.} and Lyon, {G. L.} and Poreda, {R. J.} and Stevens, {C. M.}",

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T2 - Deep or shallow origin?

AU - Abrajano, T. A.

AU - Sturchio, N. C.

AU - Bohlke, J. K.

AU - Lyon, G. L.

AU - Poreda, R. J.

AU - Stevens, C. M.

PY - 1988/12/15

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N2 - Isotopically anomalous CH4-rich gas escapes at low flow rate and ambient temperature from seeps in serpentinized ultramafic rock in the Zambales Ophiolite, Philippines. The major components of the gas are CH4 (55 mole%) and H2 (42 mole%); the CH4 CO2 ratio is > 1800 and the CH4 He ratio is 9.2·104. The δ13C-value of the CH4 is -7.0±0.4‰ (PDB), ∼8‰ higher than the highest published values for CH4 in other natural gases and hot springs, but similar to values commonly attributed to mantle carbon. The 3He 4He ratio is 5.70·10-6, 4.1 times the atmospheric ratio, indicative of a substantial mantle He component. The δD-values of CH4 and H2 are -136 and -590‰, respectively, consistent with equilibration temperatures of 110-125°C. Carbon and He isotopic data could be consistent with derivation of the Zambales gas directly from a reduced mantle. However, phase equilibria and H isotope data indicate that the gas also could have been produced by reduction of water and carbon during low-temperature serpentinization of the ophiolite.

AB - Isotopically anomalous CH4-rich gas escapes at low flow rate and ambient temperature from seeps in serpentinized ultramafic rock in the Zambales Ophiolite, Philippines. The major components of the gas are CH4 (55 mole%) and H2 (42 mole%); the CH4 CO2 ratio is > 1800 and the CH4 He ratio is 9.2·104. The δ13C-value of the CH4 is -7.0±0.4‰ (PDB), ∼8‰ higher than the highest published values for CH4 in other natural gases and hot springs, but similar to values commonly attributed to mantle carbon. The 3He 4He ratio is 5.70·10-6, 4.1 times the atmospheric ratio, indicative of a substantial mantle He component. The δD-values of CH4 and H2 are -136 and -590‰, respectively, consistent with equilibration temperatures of 110-125°C. Carbon and He isotopic data could be consistent with derivation of the Zambales gas directly from a reduced mantle. However, phase equilibria and H isotope data indicate that the gas also could have been produced by reduction of water and carbon during low-temperature serpentinization of the ophiolite.

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ER -

Methane-hydrogen gas seeps, Zambales Ophiolite, Philippines: Deep or shallow origin?

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