The CO2-He-Ar-H2O systematics of the manus back-arc basin: resolving source composition from degassing and contamination effects

Shaw, A. M.; Hilton, David R.; Macpherson, Colin G.; Sinton, John M.

doi:10.1016/j.gca.2003.10.015

Cited by 53 publications

(80 citation statements)

References 71 publications

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“…Endmember CO 2 values range from 4.38 to 4.48 mmol/kg at Vienna Woods and are comparable to the previously reported value for the site (6mM; Ishibashi et al, 1996). δ 13 C CO2 values range from -5.2‰ to -5.7‰ and are within the range of basaltic CO 2 reported near Vienna Woods (-4.3‰ to -11.3‰; Shaw et al, 2004). With the exception of NE Pual, all fluids at Pual Ridge have substantially higher endmember CO 2 concentrations, ranging from 7.04mmol/kg (at Roger's Ruins) to 274mmol/kg at Satanic Mills (Table 5.2).…”

Section: H 2 H 2 S Ch 4 Co and Cosupporting

confidence: 79%

“…2.2 to 4.3‰ at >1100°C) relative to the undegassed bulk CO 2 reservoir (Javoy et al, 1978;Mattey, 1991). Such enrichments, however, are only associated with the earliest stages of CO 2 exsolution (Tsunogai et al, 1994) and cannot account for CO 2 observed in PACMANUS fluids since the extremely low CO 2 contents (Marty et al, 2001) and low δ 13 C CO2 values observed in EMVZ lavas (down to -33.2‰; Shaw et al, 2004) suggest extensive degassing of crustal magmas. The 13 C-enriched nature of aqueous CO 2 at PACMANUS therefore may reflect the greater influence of slab-derived carbon on the magma source in this region of the basin.…”

Section: Magmatic Co 2 F and CLmentioning

confidence: 96%

“…Numerous geochemical proxies (e.g. higher Ba/Nb and Cl/Nb ratios in dredged lavas) indicate greater subduction-related inputs to magmas in the EMVZ (and Pual Ridge) relative to the MSC (Kamenetsky et al, 2001;Sinton et al, 2003;Sun et al, 2004;Pearce and Stern, 2006;Park et al, in press) and inputs of slab-derived carbon have been suggested (Shaw et al, 2004). Trends of increasing δ 13 C CO2 with arc proximity have been observed in other back-arc vent fluids, such as the Lau Basin (Proskurowski et al, 2006) and the Okinawa Trough/Mariana Arc (cf.…”

Section: Magmatic Co 2 F and CLmentioning

confidence: 99%

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Laboratory and field-based investigations of subsurface geochemical processes in seafloor hydrothermal systems

Reeves¹

2010

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This thesis presents the results of four discrete investigations into processes governing the organic and inorganic chemical composition of seafloor hydrothermal fluids in a variety of geologic settings. Though Chapters 2 through 5 of this thesis are disparate in focus, each represents a novel investigation aimed at furthering our understanding of subsurface geochemical processes affecting hydrothermal fluid compositions. Chapters 2 and 3 concern the abiotic (nonbiological) formation of organic compounds in high temperature vent fluids, a process which has direct implications for the emergence of life in early Earth settings and sustainment of present day microbial populations in hydrothermal environments. Chapter 2 represents an experimental investigation of methane (CH 4 ) formation under hydrothermal conditions. The overall reduction of carbon dioxide (CO 2 ) to CH 4 , previously assumed to be kinetically inhibited in the absence of mineral catalysts, is shown to proceed on timescales pertinent to crustal residence times of hydrothermal fluids. In Chapter 3, the abundance of methanethiol (CH 3 SH), considered to be a crucial precursor for the emergence of primitive chemoautotrophic life, is characterized in vent fluids from ultramafic-, basalt-and sediment-hosted hydrothermal systems. Previous assumptions that CH 3 SH forms by reduction of CO 2 are not supported by the observed distribution in natural systems. Chapter 4 investigates factors regulating the hydrogen isotope composition of hydrocarbons under hydrothermal conditions. Isotopic exchange between low molecular weight n-alkanes and water is shown to be facilitated by metastable equilibrium reactions between alkanes and their corresponding alkenes, which are feasible in natural systems. In Chapter 5, the controls on vent fluid composition in a backarc hydrothermal system are investigated. A comprehensive survey of the inorganic geochemistry of fluids from sites of hydrothermal activity in the eastern Manus Basin indicates that fluids there are influenced by input of acidic magmatic solutions at depth, and subsequently modified by variable extents of seawater entrainment and mixing-related secondary acidity production. CHAPTER 1 IntroductionSeafloor hydrothermal systems associated with the generation of oceanic crust represent a dramatic expression of heat and mass transfer from the interior of the Earth. In addition to profound effects on ocean chemistry, convective circulation of seawater through volcanically active oceanic crust leads to the formation of metal sulfide deposits. In addition, seafloor hot springs are often invoked as ideal settings from which early microbial life could have emerged.Since the initial discovery of low temperature venting at the Galápagos Spreading Center in 1977 (CORLISS et al., 1979), our understanding of the composition and diversity of hydrothermal solutions has expanded greatly. During convection through oceanic crust of basaltic composition, O 2 -replete seawater reacts with crustal rock, typically producin...

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Section: H 2 H 2 S Ch 4 Co and Cosupporting

confidence: 79%

Section: Magmatic Co 2 F and CLmentioning

confidence: 96%

Section: Magmatic Co 2 F and CLmentioning

confidence: 99%

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Laboratory and field-based investigations of subsurface geochemical processes in seafloor hydrothermal systems

Reeves¹

2010

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“…Degassing of basaltic magma at ocean ridges can be regarded as a two-stage process and the "pre-eruptive" composition identified above could represents the transition between these two stages ( Pineau and Javoy, 1983;Macpherson and Mattey, 1994;Cartigney et al, 2001). The highest δ 13 C values in Kolbeinsey glasses resemble MORB from many locations (Pineau and Javoy, 1983;Mattey et al, 1984;Exley et al, 1986;Mattey et al, 1989;Pineau and Javoy, 1994) while the pre-eruptive CO 2 concentration and isotope ratio are similar to those determined for other spreading centre glasses (Macpherson and Mattey, 1994;Cartigny et al, 2001;Shaw et al, 2004). If the Kolbeinsey glasses were generated from CO 2 -rich primary melts (Kingsley and Schilling, 1995) then they should possess systematically lower δ 13 C than other MORB due to having lost a greater proportion of their initial CO 2 , unless that CO 2 also possessed higher δ 13 C (Exley et al, 1986).…”

Section: Pre-eruptive Composition and Source Of Dissolved Volatilessupporting

confidence: 54%

“…Such addition at a single depth would also change δ 13 C values but not CO 2 concentrations prior to eruption (c.f. Shaw et al, 2004). Instead, arrays with different slopes (Fig.…”

Section: Evolution Of Dissolved Volatilesmentioning

confidence: 99%

Sources, degassing, and contamination of CO2, H2O, He, Ne, and Ar in basaltic glasses from Kolbeinsey Ridge, North Atlantic

Macpherson

Hilton

Mertz

et al. 2005

Geochimica et Cosmochimica Acta

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Evidence for a broadly distributed Samoan-plume signature in the northern Lau and North Fiji Basins

Price

Jackson

Blichert‐Toft

et al. 2014

Geochem. Geophys. Geosyst.

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104

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Geochemical enrichment of lavas in the northern Lau Basin may reflect the influx of Samoanplume mantle into the region. We report major and trace element abundances and He-Sr-Nd-Hf-Pbisotopic measurements for 23 submarine volcanic glasses covering 10 locations in the northern Lau and North Fiji Basins, and for three samples from Wallis Island, which lies between Samoa and the Lau Basin. These data extend the western limit of geochemical observations in the Basins and improve the resolution of North-South variations in isotopic ratios. The Samoan hot spot track runs along the length of the northern trace of the Lau and North Fiji Basins. We find evidence for a Samoan-plume component in lavas as far West as South Pandora Ridge (SPR), North Fiji Basin. Isotopic signatures in SPR samples are similar to those found in Samoan Upolu shield lavas, but show a slight shift toward MORB-like compositions. We explain the origin of the enriched signatures by a model in which Samoan-plume material and ambient depleted mantle undergo decompression melting during upwelling after transiting from beneath the thick Pacific lithosphere to beneath the thin lithosphere in the northern Lau and North Fiji Basins. Other lavas found in the region with highly depleted isotopic signatures may represent isolated pockets of depleted mantle in the basins that evaded this enrichment process. We further find that mixing between the two components in our model, a variably degassed high-3 He/ 4He Samoan component and depleted MORB, can explain the diversity among geochemical data from the northern Lau Basin.

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The CO2-He-Ar-H2O systematics of the manus back-arc basin: resolving source composition from degassing and contamination effects

Cited by 53 publications

References 71 publications

Laboratory and field-based investigations of subsurface geochemical processes in seafloor hydrothermal systems

Laboratory and field-based investigations of subsurface geochemical processes in seafloor hydrothermal systems

Sources, degassing, and contamination of CO2, H2O, He, Ne, and Ar in basaltic glasses from Kolbeinsey Ridge, North Atlantic

Evidence for a broadly distributed Samoan-plume signature in the northern Lau and North Fiji Basins

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