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Metastable equilibrium in the C-H-O system; graphite deposition in crustal fluids

Dionysis I. Foustoukos
Metastable equilibrium in the C-H-O system; graphite deposition in crustal fluids
American Mineralogist (August 2012) 97 (8-9): 1373-1380


The presence of graphite in natural environments is linked to the redox and thermal conditions of C-H-O fluid/graphite equilibrium in hydrothermal veins and metasomatic contacts. A time-series experimental study was performed to investigate the graphite undersaturated C-H-O system at 600 degrees C and 1000 MPa, and with f (sub O (sub 2) ) ranging from highly reducing (10 (super -23) ) to highly oxidizing (10 (super 4) ). A non-volatile intermediate carbon phase exhibiting the Raman spectral features of poorly ordered graphite was formed as the system evolves toward equilibrium as a function of run duration. The thermometric empirical expressions using the G and D bands in the spectra of graphite failed to accurately estimate the experimental temperature. Thus, the existing Raman geothermometers appear inadequate to address graphite formation under conditions of metastable equilibria and to account for kinetic effects such as, for example, the degree of crystallinity. The presence of poorly ordered graphitic carbon at all the redox conditions investigated suggests that the disordered structure of the mineral attains an extensive thermodynamic stability field, and that it may be more readily deposited than crystalline graphite. Metastable graphitic carbon could, therefore, function as a precursor and substrate for the formation of the well-ordered phase. Such metastable graphite may provide an intermediate state that facilitates subduction of carbonaceous material, while imposing constraints on the formation mechanisms and the (super 13) C/ (super 12) C isotopic systematics of deep seated carbonaceous fluids and minerals such as diamonds.

ISSN: 0003-004X
EISSN: 1945-3027
Serial Title: American Mineralogist
Serial Volume: 97
Serial Issue: 8-9
Title: Metastable equilibrium in the C-H-O system; graphite deposition in crustal fluids
Affiliation: Carnegie Institution of Washington, Geophysical Laboratory, Washington, DC, United States
Pages: 1373-1380
Published: 201208
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 47
Accession Number: 2012-079904
Categories: General mineralogyIsotope geochemistry
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus.
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201242
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