Hydrocarbon Formation and the Charge Field

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Hydrocarbon Formation and the Charge Field Empty Hydrocarbon Formation and the Charge Field

Post by Cr6 on Sun Oct 27, 2019 10:05 pm

Came across this article which followed up assorted research on this over various sources.  Wanted to get a post going similar to that on TB's forum just in case ideas develop around this:
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Proc Natl Acad Sci U S A. 2019 Sep 3;116(36):17666-17672. doi: 10.1073/pnas.1907871116. Epub
2019 Aug 19.

Abiotic methane synthesis and serpentinization in olivine-hosted fluid inclusions.

Klein F1, Grozeva NG2, Seewald JS3.

Author information

1 Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543; fklein@whoi.edu.
2 Massachusetts Institute of Technology-Woods Hole Oceanographic Institution Joint Program in Oceanography, Cambridge, MA 02139.
3 Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, MA 02543.

Abstract

The conditions of methane (CH4) formation in olivine-hosted secondary fluid inclusions and their prevalence in peridotite and gabbroic rocks from a wide range of geological settings were assessed using confocal Raman spectroscopy, optical and scanning electron microscopy, electron microprobe analysis, and thermodynamic modeling. Detailed examination of 160 samples from ultraslow- to fast-spreading midocean ridges, subduction zones, and ophiolites revealed that hydrogen (H2) and CH4 formation linked to serpentinization within olivine-hosted secondary fluid inclusions is a widespread process. Fluid inclusion contents are dominated by serpentine, brucite, and magnetite, as well as CH4(g) and H2(g) in varying proportions, consistent with serpentinization under strongly reducing, closed-system conditions. Thermodynamic constraints indicate that aqueous fluids entering the upper mantle or lower oceanic crust are trapped in olivine as secondary fluid inclusions at temperatures higher than ∼400 °C. When temperatures decrease below ∼340 °C, serpentinization of olivine lining the walls of the fluid inclusions leads to a near-quantitative consumption of trapped liquid H2O. The generation of molecular H2 through precipitation of Fe(III)-rich daughter minerals results in conditions that are conducive to the reduction of inorganic carbon and the formation of CH4 Once formed, CH4(g) and H2(g) can be stored over geological timescales until extracted by dissolution or fracturing of the olivine host. Fluid inclusions represent a widespread and significant source of abiotic CH4 and H2 in submarine and subaerial vent systems on Earth, and possibly elsewhere in the solar system.

More at link with subscription: https://www.ncbi.nlm.nih.gov/pubmed/31427518

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Hydrocarbon Formation and the Charge Field Empty Re: Hydrocarbon Formation and the Charge Field

Post by Cr6 on Tue Oct 29, 2019 11:13 pm

Wikipedia on the Lost City also covered in depth by NOAA:
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Geology and Chemistry

Lost City vents release methane and hydrogen into the surrounding water; they do not produce significant amounts of carbon dioxide, hydrogen sulfide or metals, which are the major outputs of volcanic black smoker vents. The temperature and pH of water surrounding the two types of vent is also significantly different.

Geology and Mineralogy

The Mid-Atlantic Ridge spreading center pulls the lithosphere apart, creating normal faults which expose sub-surface rocks to seawater.

Hydrocarbon Formation and the Charge Field 330px-Olivine_%28peridot%29
Olivine, the mineral responsible for Lost City's serpentinization.

The Atlantis Massif is described as an ultramafic oceanic core complex of the Mid-Atlantic Ridge, with upper-mantle rock being exposed to seawater through faulting from tectonic extension associated with ocean spreading centers.[24] The spreading half-rate is approximated to about 12 mm/yr, classifying it as a slow-spreading ridge.[25] Seismic events have been detected at the massif of Richter magnitude 4 and 4.5.[13]

The dominant minerals found at Lost City are ultramafic, composed primarily of olivine and pyroxene with very little silica content. Peridotite (primarily spinel harzburgite) minerals undergo serpentinization and form magnetite and serpentine minerals.[6] Because little to no carbon dioxide or metals are released in the venting fluids, Lost City bears the appearance of a non-smoker, with few particulates to give a smokey appearance.

Once pore waters have permeated the surface and return to the surface, aragonite, brucite, and calcite chimneys as calcium carbonates precipitate out of solution.[26] Younger chimneys are primarily brucite and aragonite, being white and flaky in appearance. As vents mature, porosity decreases as precipitates clog fluid pathways. Mineral compositions change with aragonite succeeded by calcite and brucite being removed through dissolution, and the chimneys darken to a grey or brown color.[27]

On the side of the Atlantis Transform Fault, the Atlantis Massif wall terminates approximately 740 meters below sea level, where rock types deform to various mylonitic rocks with deformation fabric minerals of talc, tremolite, and ribbon serpentine.[6]

Serpentinization

Lost City is an exemplary location for the study of abiotic methanogenesis and hydrogenesis, as serpentinization reactions produce methane and hydrogen. Supplementing Fischer-Troph reactions;

   Olivine(Fe,Mg)2SiO4 + Watern·H2O + Carbon dioxideCO2 → SerpentineMg3Si2O5(OH)4 + MagnetiteFe3O4 + MethaneCH4
   

   (Methanogenesis)

   Fayalite (Olivine)3 Fe2SiO4 + water2 H2O → Magnetite2 Fe3O4 + Silica (aqueous)3 SiO2 + Hydrogen2 H2
 
   (Hydrogenesis)

The reactions are exothermic and warm surrounding waters via reaction heating, though fluid temperatures are still relatively low (40° - 90 °C) when compared to other hydrothermal systems.[28] Furthermore, pH is increased to values of over 9 which enables calcium carbonate precipitation. Since serpentinization is particularly extensive, carbon dioxide concentrations are also very low. Low temperature, carbon dioxide concentrations, combined with the low hydrogen sulfide and metal content of the plume make the vents more difficult to identify from CTD measurements or optical backscatter methods.

Biology
A visiting shark at the Lost City field.

Lost City and other vent systems support vastly different lifeforms due to Lost City's unique chemistry.

A variety of microorganisms live in, on, and around the vents. Methanosarcinales-like archaea form thick biofilms inside the vents where they subsist on hydrogen and methane; bacteria related to the Firmicutes also live inside the vents. External to the vents archaea, including the newly described ANME-1 and bacteria including proteobacteria oxidise methane and sulfur as their primary source of energy.[citation needed]

https://en.wikipedia.org/wiki/Lost_City_Hydrothermal_Field

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