Other
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27q.232h&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 232
Other
3
Scientific paper
Previous works of the authors (1,2) have revealed that nitrogen isotopes in bulk ordinary chondrites are various in a range of - 15< delta^15N < +45 o/oo (after reduction of the contribution of cosmogenic nitrogen). Recently, the isotopically anomalous nitrogen components in equilibrated H-chondrites, both the heavy nitrogen and the light nitrogen, have proved to be concentrated in the metal portion. The metal portion was prepared by etching the magnetic portion by a concentrated NaOH at 100-160 degrees C which dissolves phosphate and troilite, and attacks the silicates together with a slight amount of metal. Nitrogen is extracted from the purified metal by a stepwise combustion method and its isotope is measured by a mass-spectrometer with a high sensitivity. The results of nitrogen analyses are described in the table. The remarkable point is that nitrogen contents in the metal are almost constant, though the isotopic ratio differs by approximately 160 o/oo. Since behaviors of nitrogen in the metal are very sensitive to temperature, nitrogen study in the metal phase of ordinary chondrites is possible to give us interesting information concerning the behavior of volatile elements during the metamorphic and/or cooling sequences. The large differences of nitrogen isotopic ratios among H-chondrites suggest that isotopic heterogeneity already existed during the accretionary stage, since there seems to be little chance to explain the observations by any other processes expected after the formation of their parent bodies. Acknowledgement: We are indebted to Drs. C. Perron and P. Pellas of Museum National d'Histoire Naturelle, Paris, for introducing to us the etching technique to purify the metal. References: (1) Hashizume K. and Sugiura N. (1990) Meteoritics 25, 370. (2) Hashizume K. and Sugiura N. ( 1992) submitted to Geochim. Cosmochim. Acta. Table 1. Nitrogen isotopic composition in H-chondrite metal. -----------------------Metal---------------------------Whole Rock Sample------Class-N----delta^15N(mean)-delta^15N(peak)-N---- delta^15N(mean) Forest Vale-H4-------------------------48+-12----------3.07-10+-8 Ochansk-----H4----1.73-14.1+-2.3-------15+-7----------------- Allegan-----H5----1.71-13.8+-2.0-------16+-4-----------0.70--8+-4 Jilin-------H5----1.56-99.4+-7.0-------119+-7----------0.89-4.5+- 3 Plainview---H5----1.92-61.1+-3.7-------99+-4-----------1.72-33+-1 Guarena-----H6----(<2)------------------44+-4----------1.14--15+- 2 Nitrogen content (N) and delta^15N are in units of ppm and o/oo, respectively. Errors are 1 sigma. Whole rock data are from references (1,2). Nitrogen amounts and mean delta^15N are taken from 800 degrees C and above fractions. (They were not available for Forest Vale and Guarena due to large amounts of contaminating nitrogen.)
Hashizume K.
Sugiura Norimasa
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