Evidence and characteristics of hydrolytic disproportionation of organic matter during metasomatic processes

Price, Leigh C.; DeWitt, Ed

doi:10.1016/s0016-7037(01)00762-1

Cited by 42 publications

(30 citation statements)

References 80 publications

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“…These conditions are thought to be common in hydrothermal environments in which H 2 O disproportionates forming H + and OH -buffered solutions (Rullkötter et al, 1984;Seewald, 1994Seewald, , 2003Lewan, 1997;Price and DeWitt, 2001). It is noteworthy, that within the PGC, exogenous hydrogen may have formed by serpentinization of mafic and ultramafic rocks located lower in the stratigraphic profile (Fyon et al, 1983).…”

Section: Isomerization Of Type II Ucm Constituentsmentioning

confidence: 95%

Analysis of unresolved complex mixtures of hydrocarbons extracted from Late Archean sediments by comprehensive two-dimensional gas chromatography (GC×GC)

Ventura

Kenig

Reddy

et al. 2008

Organic Geochemistry

116

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Hydrocarbon mixtures too complex to resolve by traditional capillary gas chromatrography display gas chromatograms with dramatically rising baselines or "humps" of coeluting compounds that are termed unresolved complex mixtures (UCMs). Because the constituents of UCMs are not ordinarily identified, a large amount of geochemical information is never explored. Gas chromatograms of saturated/unsaturated hydrocarbons extracted from Late Archean argillites and greywackes of the southern Abitibi Province of Ontario, Canada contain UCMs with different appearances or "topologies" relating to the intensity and retention time of the compounds comprising the UCMs. These topologies appear to have some level of stratigraphic organization, such that samples collected at any stratigraphic formation collectively are dominated by UCMs that either elute early-(within a window of C 15 -C 20 of n-alkanes), earlyto mid-(C 15 -C 30 of n-alkanes), or have a broad UCM that extends through the entire retention time of the sample (from C 15 -C 42 of n-alkanes). Comprehensive two-dimensional gas chromatography time-of-flight mass spectrometry (GC×GC-MS) was used to resolve the constituents forming these various UCMs. Early-to mid-eluting UCMs are dominated by configurational isomers of alkyl-substituted and non substituted polycyclic compounds that contain up to six rings. Late eluting UCMs are composed of C 36 -C 40 mono-, bi-, and tricyclic archaeal isoprenoid diastereomers. Broad UCMs spanning the retention time of compound elution contain nearly the same compounds observed in the early-, mid-, and late retention time UCMs. Although the origin of the polycyclic compounds is unclear, the variations in the UCM topology appear to depend on the concentration of initial compound classes that have the potential to become isomerized. Isomerization of these constituents may have resulted from hydrothermal alteration of organic matter.

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Section: Isomerization Of Type II Ucm Constituentsmentioning

confidence: 95%

Analysis of unresolved complex mixtures of hydrocarbons extracted from Late Archean sediments by comprehensive two-dimensional gas chromatography (GC×GC)

Ventura

Kenig

Reddy

et al. 2008

Organic Geochemistry

116

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“…2) are eliminated and remaining nitrogen atoms are preferentially located in the interior of the carbon lattice as thermally stable quaternary nitrogen (Isaacs, 1970;Pels et al, 1995;Stanczyk et al, 1995;Xiao et al, 2005). These trends have not been observed in nature where fluids, temperature, pressure, time and catalysts play important roles in the transformation of carbonaceous matter during metamorphism (e.g., Price and Dewitt, 2001;Schwab et al, 2005;Guedes et al, 2005). It is expected that during metamorphism N org becomes increasingly integrated into sub-nanometric to nanometric sheets of adjoining ring structures ( Fig.…”

Section: Anthracitementioning

confidence: 99%

Organic nitrogen chemistry during low-grade metamorphism

Boudou

Schimmelmann

Ader

et al. 2008

Geochimica et Cosmochimica Acta

136

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-Most of the organic nitrogen (N org ) on Earth is disseminated in crustal sediments and rocks in the form of fossil nitrogen-containing organic matter. The chemical speciation of fossil N org within the overall molecular structure of organic matter changes with time and heating during burial. Progressive thermal evolution of organic matter involves phases of enhanced elimination of N org and ultimately produces graphite containing only traces of nitrogen. Long-term chemical and thermal instability makes the chemical speciation of N org a valuable tracer to constrain the history of sub-surface metamorphism and to shed light on the subsurface biogeochemical nitrogen cycle and its participating organic and inorganic nitrogen pools. This study documents the evolutionary path of N org speciation, transformation and elimination before and during metamorphism and advocates the use of XRay Photoelectron Spectroscopy (XPS) to monitor changes in N org speciation as a diagnostic tool for organic metamorphism. Our multidisciplinary evidence from XPS, stable isotopes, traditional quantitative coal analyses, and other analytical approaches shows that at the metamorphic onset N org is dominantly present as pyrrolic and pyridinic nitrogen. The relative abundance of nitrogen substituting for carbon in condensed, partially aromatic systems (where N is covalently bonded to three C atoms) increases exponentially with increasing metamorphic grade, at the expense of pyridinic and pyrrolic nitrogen. At the same time, much N org is eliminated without significant nitrogen isotope fractionation. The apparent absence of Rayleigh-type nitrogen isotopic fractionation suggests that direct thermal loss of nitrogen from an organic matrix does not serve as a major pathway for N org elimination. Instead, we propose that hot H, O-containing fluids or some of their components gradually penetrate into the carbonaceous matrix and eliminate N org along a progressing reaction front, without causing nitrogen isotope fractionation in the residual N org in the unreacted core of the carbonaceous matrix. Before the reaction front can reach the core, an increasing part of core N org chemically stabilizes in the form of nitrogen atoms substituting for carbon in condensed, partially aromatic systems forming graphite-like structural domains with delocalized π-electron systems (nitrogen atoms substituting for "graphitic" carbon in natural metamorphic organic matter). Thus, this nitrogen species with a conservative isotopic composition is the dominant form of residual nitrogen at higher metamorphic grade.

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“…The formation of such diastereomers must be favored by high temperatures and potentially requires the addition of metal catalysts (39) or exogenous sources of hydrogen to expand the activation energy range for isomerization without excessive hydrocarbon cracking (19). Such conditions might be common to hydrothermal environments where serpentinization and the hydrolytic disproportionation of H 2 O forms solutions with high H 2 fugacity (19,40,41).…”

Section: Archaeal Lipids Of Unresolved Complex Mixtures (Ucms)mentioning

confidence: 99%

Molecular evidence of Late Archean archaea and the presence of a subsurface hydrothermal biosphere

Ventura

Kenig

Reddy

et al. 2007

Proc. Natl. Acad. Sci. U.S.A.

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Evidence and characteristics of hydrolytic disproportionation of organic matter during metasomatic processes

Cited by 42 publications

References 80 publications

Analysis of unresolved complex mixtures of hydrocarbons extracted from Late Archean sediments by comprehensive two-dimensional gas chromatography (GC×GC)

Analysis of unresolved complex mixtures of hydrocarbons extracted from Late Archean sediments by comprehensive two-dimensional gas chromatography (GC×GC)

Organic nitrogen chemistry during low-grade metamorphism

Molecular evidence of Late Archean archaea and the presence of a subsurface hydrothermal biosphere

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