Nitrogen isotopic evolution of carbonaceous matter during metamorphism: Methodology and preliminary results

Abstract : Nitrogen content and isotopic composition of carbonaceous-rich metasediments were determined by on-line and sealed-tube combustion using ultra-high vacuum line and static mass spectrometer adapted to analyse nitrogen nanomoles. Accurate mea¬surements showed that nitrogen amount released by on-line combustion technique was underestimated to various extents. As a result, the nitrogen isotopic composition was not correctly determined. In contrast, sealed-tube combustion appeared to yield the most reproducible and accurate measurements, except for nitrogen depleted carbonaceous matter (semi-graphite to graphite transition) containing less than around 60 ppm of nitrogen, which were contaminated during their extraction from the rock. In view of that, a preliminary sealed-tube investigation of the organic nitrogen content and isotopic composition in a homogenous series of low-grade metasediments was undertaken: in spite of an important nitrogen loss, the carbonaceous matter nitrogen isotopic composition remains about the same during the meta-anthracite and semi-graphitisation stages. Inferences on the process of organic nitrogen mineralization during carbonaceous matter metamorphism can be drawn and several paleo-biogeochemical implications envisaged.
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Magali Ader, Pierre Cartigny, Jean-Paul Boudou, Jae-Ho Oh, Eddy Petit, et al.. Nitrogen isotopic evolution of carbonaceous matter during metamorphism: Methodology and preliminary results. Chemical Geology, Elsevier, 2006, 232, pp.152-169. ⟨10.1016/j.chemgeo.2006.02.019⟩. ⟨bioemco-00144850⟩

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