Origins of methane in hydrothermal systems

Welhan, J. A.

doi:10.1016/0009-2541(88)90114-3

Cited by 349 publications

(222 citation statements)

References 33 publications

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“…In this case, however, the assumption of thermodynamic equilibrium may be more tenuous since the kinetics associated with the reduction of CO 2 to CH 4 are known to be quite slow (BARNES, 1981;SCHOFIELD, 1973) . Previous work with other natural and experimental hydrothermal systems have demonstrated that equilibrium between CH 4 and CO 2 may not be attained at temperatures characteristic of ridge-crest hydrothermal systems ( ARNÓRSSON and GUNNLAUGSSON, 1985;JANECKY et al, 1986;WELHAN, 1988). However, hydrothermal alteration experiments using organic-rich sediment from Guaymas Basin indicate that thermodynamic equilibrium can be attained between aqueous CO 2 and CH 4 at ridge-crest temperatures .…”

Section: Methane-carbon Dioxide Equilibriamentioning

confidence: 98%

“…Methane in sedimentary environments is typically classified as either "biogenic" or "thermogenic" based on its stable carbon isotopic composition and the relative abundances of coexisting longer-chained hydrocarbons (RICE and CLAYPOOL, 1981;SCHOELL, 1980SCHOELL, , 1988WELHAN, 1988;WHITICAR 1999). Methane formed by heterotrophic and autotrophic microorganisms is characterized by a large range of δ 13 C values (-42 to -105‰) that vary with community structure, metabolic pathway and environmental variables such as temperature (SCHOELL, 1988;WHITICAR 1999).…”

Section: Sources Of Carbon Compoundsmentioning

confidence: 99%

“…Thermogenic methane formed from the abiogenic alteration of sedimentary organic matter at elevated temperatures typically has an isotopic composition between -25 to -50‰. Sedimentary basins influenced by magmatic activity or deep-seated mantle degassing may also contain mantle derived methane with δ 13 C values between -20 to -10‰ (DES MARAIS et al, 1981;KELLEY and FRÜH-GREEN, 1999;SHERWOOD LOLLAR et al, 1993;WELHAN, 1988). Relative to biogenic and mantle-derived CH 4 , which are accompanied by low concentrations of C 2+ hydrocarbons, thermogenic gas may contain substantial concentrations of longer chained n-alkanes.…”

Section: Sources Of Carbon Compoundsmentioning

confidence: 99%

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Geochemistry of low-molecular weight hydrocarbons in hydrothermal fluids from Middle Valley, northern Juan de Fuca Ridge

Cruse

Seewald

2006

Geochimica et Cosmochimica Acta

105

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Hydrothermal vent fluids from Middle Valley, a sediment-covered mid-ocean ridge on the northern Juan de Fuca Ridge, were sampled in July, 2000. Eight different vents with exit temperatures of 186 to 281°C were sampled from two areas of venting: the Dead Dog and ODP Mound fields. Fluids from the Dead Dog field are characterized by higher concentrations of ΣNH 3 and organic compounds (C 1 -C 4 alkanes, ethene, propene, benzene and toluene) compared with fluids from the ODP Mound field. The ODP Mound fluids, however, are characterized by higher C 1 /(C 2 +C 3 ) and benzene:toluene ratios than those from the Dead Dog field. The aqueous organic compounds in these fluids have been derived from both bacterial processes (methanogenesis in low-temperature regions during recharge) as well as from thermogenic processes in higher-temperature portions of the subsurface reaction zone. As the sediments undergo hydrothermal alteration, carbon dioxide and hydrocarbons are released to solution as organic matter degrades via a stepwise oxidation process. Compositional and isotopic differences in the aqueous hydrocarbons indicate that maximum subsurface temperatures at the ODP Mound are greater than those at the Dead Dog field. Maximum subsurface temperatures were calculated assuming that thermodynamic equilibrium is attained between alkenes and alkanes, benzene and toluene, and carbon dioxide and methane. The calculated temperatures for alkene-alkane equilibrium are consistent with differences in the dissolved Cl concentrations in fluids from the two fields, and indicate that subsurface temperatures at the ODP Mound are hotter than those at the Dead Dog field. Temperatures calculated assuming benzene-toluene equilibrium and carbon dioxide-methane equilibrium are similar to observed exit temperatures, and do not record the hottest subsurface conditions. The difference in subsurface temperatures estimated using organic geochemical thermometers reflects subsurface cooling processes via mixing of a hot, low-salinity vapor with a cooler, seawater salinity fluid. Because of the disparate temperature dependence of alkene-alkane and benzene-toluene equilibria, the mixed fluid records both the high and low temperature equilibrium conditions. These calculations indicate that vapor-rich fluids are presently being formed in the crust beneath the ODP Mound, yet do not reach the surface due to mixing with the lower-temperature fluids.2

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Section: Methane-carbon Dioxide Equilibriamentioning

confidence: 98%

Section: Sources Of Carbon Compoundsmentioning

confidence: 99%

Section: Sources Of Carbon Compoundsmentioning

confidence: 99%

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Geochemistry of low-molecular weight hydrocarbons in hydrothermal fluids from Middle Valley, northern Juan de Fuca Ridge

Cruse

Seewald

2006

Geochimica et Cosmochimica Acta

105

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“…Thus hydrothermal systems consist of a heat source and a fluid circulation within the Earth's crust. At mid-ocean ridges, the heat for hightemperature hydrothermal circulation primarily comes from underlying magma bodies, and the circulating fluid is mainly seawater with minor additions of magmatic volatiles such as hydrogen, carbon dioxide, and methane [Welhan, 1988;Kelly, 1996;Kelly et al, 2002]. Figure 1.1 shows a conceptual model of buoyancy-driven hydrothermal circulation at a mid-ocean ridge.…”

Section: General Background On Seafloor Hydrothermal Systemsmentioning

confidence: 99%

The response of two-phase hydrothermal systems to changing magmatic heat input at mid-ocean ridges

Choi

Lowell

2015

Deep Sea Research Part II: Topical Studies in Oceanography

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Hydrothermal processes at oceanic spreading centers are largely influenced by changing magmatic heat input. I use the NaCl-H 2 O FISHES code to investigate the evolution of surface temperature and salinity as a function of time-varying heat flux at the base of a two-phase, vaporbrine hydrothermal system. I consider a two-dimensional rectangular box that is 1.5 km deep and 4 km long with homogeneous permeability of 10 -13 m 2 . Temperature and pressure at top boundary correspond to seafloor conditions of 10C, 25MPa respectively. Impermeable,

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“…In a recent review, Welhan ( 1988) listed four main sources for CH, in hydrothermal systems: ( 1) thermal breakdown of complex hydrocarbons at > lOO"C, (2) biological production, (3) outgassing of juvenile C&, and (4) inorganic synthesis at >300-400°C. Thermal breakdown of complex hydrocarbons, typically derived from organic matter in sediments, has been documented on sedimented mid-ocean ridges such as in Guaymas Basin (Simoneit, 1983) and Middle Valley on the Juan de Fuca Ridge (Davis et al, 1993).…”

Section: Variable Cand/mn and Diverse Origins Of Chmentioning

confidence: 99%

Manganese and methane in hydrothermal plumes along the East Pacific Rise, 8°40′ to 11°50′N

Mottl

Sansone

Wheat

et al. 1995

Geochimica et Cosmochimica Acta

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Abstract-In November, 1991, we surveyed the water column for hydrothermal plumes along 350 km of the East Pacific Rise axis from 8'40 ' to 1 lo50 ' N, using a combination of physical and chemical measurements. Our survey included the two major ridge segments north and south of the Clipperton Transform Fault at about lO"lO'N, both limbs of the overlapping spreading centers (OSC's) at 9"03 'N and 1 lo45 'N, and a 30&m section of the next ridge segment to the south. We found vigorous plumes along most of this ridge axis, in keeping with its magmatically robust cross-section, axial summit caldera, and shallow, magma-related seismic reflector. These plumes were detectable by both physical (temperature and light attenuation) and chemical (dissolved Mn and CR) measurements, although the chemical measurements were more sensitive. The least active sections were the southern third of the northern segment from lo"20 to 52'N and the OSCs, especially the OSC at ll"45'N. Plumes there had weak Mn and CH4 signals and were barely detectable by physical methods. These axial sections were the only ones surveyed that lie deeper than 2600 m and appear to be magma starved. The most active sections on the northern segment gave stronger signals for Mn and temperature than for CH, and light attenuation, whereas the opposite was true on the southern segment, which was the site of a volcanic eruption at 9"45-52'N only seven months prior to our cruise. On the northern segment the four physical and chemical plume tracers correlated positively and linearly with one another, suggesting that the segment was fed by relatively uniform endmember fluids with a mean C&Nn molar ratio of 0.075. The southernmost section surveyed, from 8"42' to 9'08 'N, closely resembled the northern segment. The rest of the southern segment fell into three sections with different CHJMn ratios: 9"39 to 53'N with CHJMn as high as 10, 9'08 to 39'N with CHJMn of 0.51, and 9"53 ' to lO"07'N with CH,/Mn of 0.85. The section with the highest CHJMn was the site of the volcanic eruption, which produced high-temperature, low-salinity, gas-rich vent fluids carrying abundant bacterial Darticles. The high CH, concentradons are clearly associated with the volcanic eruption, but the origin of the CH, is uncle&.

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Origins of methane in hydrothermal systems

Cited by 349 publications

References 33 publications

Geochemistry of low-molecular weight hydrocarbons in hydrothermal fluids from Middle Valley, northern Juan de Fuca Ridge

Geochemistry of low-molecular weight hydrocarbons in hydrothermal fluids from Middle Valley, northern Juan de Fuca Ridge

The response of two-phase hydrothermal systems to changing magmatic heat input at mid-ocean ridges

Manganese and methane in hydrothermal plumes along the East Pacific Rise, 8°40′ to 11°50′N

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