Light hydrocarbon gases in Guaymas basin hydrothermal fluids: Thermogenic versus abiogenic origin

Journal Article · Sun Feb 01 00:00:00 EST 1987 · AAPG Bulletin (American Association of Petroleum Geologists); (USA)

OSTI ID:5333557

Welhan, J A; Lupton, J E ^[1]

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1. Scripps Institution of Oceanography, La Jolla, CA (USA)

Light hydrocarbon gases (methane through pentane) in high-temperature hydrothermal fluids of the Guaymas basin, Gulf of California, are predominantly derived from thermocatalysis of organic carbon in sediments intruded by mid-ocean ridge volcanic rocks. The spectrum of C{sub 1}-C{sub 5} gases in Guaymas basin hydrothermal fluids is characterized by a preponderance of alkanes, with essentially no alkenes present. Comparison with high-temperature fluids from 21{degree}N on the East Pacific Rise, where geochemical evidence indicates a distinct lack of thermogenic gas and where methane is derived abiogenically from the basalts, shows that the 21{degree}N hydrocarbon gases are characterized by a prominent ethylene signature. Stable isotope compositions of Guaymas basin methane differ from 21{degree}N gas; Guaymas basin has {delta}{sup 13}C values of {minus}43 to {minus}51 {per thousand} vs. PDB, compared to 21{degree}N where values as high as {minus}15 {per thousand} have been measured. These differences reflect the different origins of light hydrocarbon gases in the two systems, with Guaymas methane being overwhelmingly of an organic, thermogenic derivation and showing no evidence of the abiogenic, basalt-derived gas that characterizes the 21{degree}N environment. Carbon isotope analyses of dissolved inorganic carbon in Guaymas basin hydrothermal fluids indicate that high-temperature hydrocarbon oxidation may be an important process acting in conjunction with high-temperature thermocatalytic hydrocarbon generation. 4 figs., 6 tabs.

• OSTI ID: 5333557
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (USA), Vol. 71:2; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

03 NATURAL GAS
HYDROTHERMAL SYSTEMS
NATURAL GAS
ORIGIN
BASALT
BUTANE
ETHANE
GULF OF CALIFORNIA
METHANE
OXIDATION
PENTANE
PROPANE
SEDIMENTARY BASINS
ALKANES
CHEMICAL REACTIONS
ENERGY SOURCES
ENERGY SYSTEMS
FLUIDS
FOSSIL FUELS
FUEL GAS
FUELS
GAS FUELS
GASES
GEOLOGIC STRUCTURES
GEOTHERMAL SYSTEMS
HYDROCARBONS
IGNEOUS ROCKS
ORGANIC COMPOUNDS
PACIFIC OCEAN
ROCKS
SEAS
SURFACE WATERS
VOLCANIC ROCKS
030200* - Natural Gas- Reserves
Geology
& Exploration