Reductive deposition of graphite at lithological margins in east central Vermont; a Sr, C and O isotope study

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doi: 10.1046/j.1525-1314.2002.00403.x
Authors:Evans, K. A.; Bickle, M. J.; Skelton, A. D. L.; Hall, M.; Chapman, H.
Author Affiliations:Primary:
CSIRO, Clayton Laboratories, Clayton South, Victoria, Australia
Other:
Stockholm University, Sweden
Godwin Laboratories, United Kingdom
Volume Title:Journal of Metamorphic Geology
Source:Journal of Metamorphic Geology, 20(8), p.781-798. Publisher: Blackwell, Oxford, United Kingdom. ISSN: 0263-4929
Publication Date:2002
Note:In English. 60 refs.; illus., incl. 3 tables
Summary:O, Sr and C isotopes are used to constrain the timing and volume of metamorphic fluid flow and the results used to assess the evidence for redox transformations between C species. Oxygen profiles are homogenized on a metre scale. Comparison with Sr isotopes suggest that O alteration may have occurred over a significantly larger timescale than that of Sr, possibly because O was modified during de-watering and diagenesis in addition to the high-T alteration recorded by strontium. Sr isotope distributions are consistent with cross-layer fluid fluxes of 104-106 moles/m2. Absolute values depend on the Sr fluid-rock distribution coefficient which is poorly known although reaction progress constraints suggest that fluxes were towards the lower end of this range. High δ 13C values observed at lithological boundaries cannot be explained by volume-loss or closed-system processes and are taken to indicate reductive precipitation of graphite as a result of mixing between CO2 and CH4-bearing fluids. Mass-balance calculations indicate that redox reactions occurring under metamorphic conditions convert a minimum of 10% of the CO2 released from limestones into graphite, thus providing a potentially important control on the average residence time of C within the crust with implications for C cycling models. [P.J.T.]
Sections:Geochemistry
Subsections:Metamorphic rocks
Subjects:Aliphatic hydrocarbons; Alkaline earth metals; Alkanes; Alteration; C-13/C-12; Carbon; Carbon cycle; Carbon dioxide; Crust; Data processing; Depositional environment; Devonian; Distribution; Eh; Fluid phase; Fourier analysis; Geochemical cycle; Geochemistry; Graphite; Hydrocarbons; Isotope ratios; Isotopes; Kyanite; Metals; Metamorphic rocks; Metamorphism; Methane; Native elements; Nesosilicates; O-18/O-16; Organic compounds; Orthosilicates; Oxygen; Paleozoic; Reduction; Silicates; Silurian; Stable isotopes; Strontium; TEM data; Transformations; Upper crust; United States; Vermont
Abstract Numbers:03M/1768
Record ID:2002081921
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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