The major volatile elements of the Earth: Their origin, behavior, and fate Journal Article uri icon

DCO ID 11121/6047-2762-7734-9826-CC

in language

  • eng

year of publication

  • 1997


  • Stable isotope constraints impose a heterogeneous accretion of the earth's volatiles : the primary, reduced material, 99.8% of the planet, brought 6% of the hydrogen, 48% of the carbon and 70% of the nitrogen of the Upper Earth (upper mantle, crust, ocean-atmosphere). A late veneer (1.4 per mil of the bulk Earth's mass), of CI composition, supplied 94% of the hydrogen, 52% of the carbon and 30% of the nitrogen.|The present distribution of the major volatiles in the Upper Earth corresponds to a negligible supply from the lower mantle. Measured in units of the superficial reservoirs the upper mantle contains: 0.21 ocean masses of water, similar to 10 atmosphere masses of nitrogen, 5.4 crustal carbon masses of carbon.|This corresponds to a very significant trapping of carbon and nitrogen by the mantle during the Earth's history, whereas water repartition stayed about unchanged and strongly favoured the superficial reservoir. There is, however, a very significant difference between carbon and nitrogen, the present outgassing and subducting fluxes of carbon being equilibrated both in masses and isotopically, whereas there is still a gross isotopic disequilibrium for nitrogen, the large, isotopically heavy, subducted flux, still outweighing the small, isotopically light, outgassed flux.|This is due to the fact that, while carbon and water are essentially incompatible components, nitrogen is a compatible element because of the presence of very stable mantle nitrides (probably osbornite).


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