http://www.sciencedirect.com/science/article/pii/S1674987111001083 |
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| Authors: | FJ Luque E Crespo-Feo JF Barrenechea L Ortega |
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| Institution: | F.J.Luque(a,b,*),E.Crespo-Feoa,J.F.Barrenechea(a,b),L.Ortegaa a Departamento de Cristalografia y Mineralogía,Facultad de Geología,Universidad Complutense de Madrid,28040 Madrid,Spain b Instituto de Geociencias(UCM-CSIC),Jos Antonio Novais 2,28040 Madrid,Spain |
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| Abstract: | Stable carbon isotope geochemistry provides important information for the recognition of fundamental
isotope exchange processes related to the movement of carbon in the lithosphere and permits the elaboration
of models for the global carbon cycle. Carbon isotope ratios in fluid-deposited graphite are powerful
tools for unravelling the ultimate origin of carbon (organic matter,mantle, or carbonates) and help to constrain
the fluid history and the mechanisms involved in graphite deposition.Graphite precipitation in fluid-deposited
occurrences results from CO2- and/or CH4-bearing aqueous fluids. Fluid flow can be considered as both
a closed (without replenishment of the fluid) or an open system (with renewal of the fluid by successive fluid
batches). In closed systems, carbon isotope systematics in graphite is mainly governed by Rayleigh precipitation
and/or by changes in temperature affecting the fractionation factor between fluid and graphite. Such
processes result in zoned graphite crystals or in successive graphite generations showing, in both cases,
isotopic variation towards progressive 13C or 12C enrichment (depending upon the dominant carbon phase
in the fluid, CO2 or CH4, respectively). In open systems, in which carbon is episodically introduced along
the fracture systems, the carbon systematics is more complex and individual graphite crystals may display
oscillatory zoning because of Rayleigh precipitation or heterogeneous variations of d13C values whenmixing
of fluids or changes in the composition of the fluids are the mechanisms responsible for graphite precipitation. |
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| Keywords: | Graphite Carbon isotopes Crust C-O-H fluids |
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