Computer Science
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27..309w&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 309
Computer Science
2
Scientific paper
The SNC meteorite Zagami is thought to be the product of two-stage magmatic processing (McCoy et al., 1992), which took place on Mars. The emplacement event is considered to have been relatively close to the surface of the planet and, as such, it is probable that any volatile species originally present will have been mostly degassed. Nevertheless, Zagami has been analysed for nitrogen abundance and stable isotopic composition in an attempt to further constrain the characteristics of the martian crustal forms of this element. Two different samples of Zagami have been studied, corresponding to the coarse- and fine-grained parts of the meteorite (e.g., McCoy et al., 1992). The carbon contents and isotopic compositions of these fractions have been reported previously (Wright et al., 1992a). The coarse-grained sample of Zagami contains a total of 12.2 ppm nitrogen with a delta^15N value of -16.8o/oo. During stepped combustion, the nitrogen is evolved over two temperature ranges, 200-600 degrees C and 800-1200 degrees C. Nitrogen released below 600 degrees C amounts to 8.8 ppm with delta^15N = -21.6o/oo, while that liberated above this temperature is equivalent to 3.4 ppm with delta^15N = -4.8o/oo. Clearly the low-temperature nitrogen in this sample is not simply adsorbed air that would be identifiable by a delta^15N of 0o/oo. Nitrogen in the fine sample amounts to 4.5 ppm with a delta^15N of -2.4o/oo. Below 600 degrees C 4 ppm of nitrogen are released with a delta^15N of -1.8o/oo, which could be misconstrued as air contamination. However, the nature of the release profile for the fine sample, coupled with the fact that for individual temperature steps below 600 degrees C delta^15N values vary between -23 and +9o/oo, demonstrates that low-temperature nitrogen in Zagami does not arise from a single component. In light of the fact that low-temperature carbon in both the coarse and fine samples has been ascribed to terrestrial organic contamination (Wright et al., 1992a), it seems possible that at least some of the nitrogen released below 600 degrees C may also arise from this source. Nitrogen released above 600 degrees C from the fine fraction is equivalent to only 0.5 ppm with delta^15N of -6.75o/oo. Thus, although the concentrations of high-temperature nitrogen are somewhat different in the two grain size separates, the delta^15N values appear to be equivalent in each case. It is possible that this nitrogen represents a magmatic species. Comparing the nitrogen results from Zagami with previous data, it should be noted that delta^15N values of bulk SNC meteorites span a range of -18 to +29o/oo (e.g., Fallick et al., 1983; Wright et al., 1986, 1992b). Considering all the samples together there is no obvious relationship of delta^15N with nitrogen content. Furthermore, while the carbon isotopic systematics of SNC meteorites are reasonably well understood (Wright et al., 1986, 1992b), there is no correspondence of carbon and nitrogen contents, or delta^13C and delta^15N values. This seems to suggest that carbon and nitrogen are largely unassociated within SNC meteorites, which once again raises the possibility that inorganic forms of nitrogen (e.g., nitrate minerals, which do not contain carbon) could be present. It is still difficult to make a judgment about whether these putative components are terrestrial in origin or indigenous to the samples. In terms of high-temperature nitrogen, SNC meteorites exhibit variations in delta^15N from -15 to +32o/oo. Since there is always a possibility that high delta^15N values represent mixing of martian magmatic/atmospheric species, the more negative delta^15N values probably best constrain the isotopic composition of crustal nitrogen. References: Fallick, A.E., Hinton, R.W., Mattey, D.P., Norris, S.J., Pillinger, C.T., Swart, P.K. and Wright, I.P. (1983) Lunar Planet. Sci, XIV, 183-184. McCoy, T.J., Taylor, G.J. and Keil, K. (1992) Geochim. Cosmochim. Acta, (submitted). Wright, I.P., Carr, R.H. and Pillinger, C.T. (1986) Geochim. Cosmochim. Acta, 50, 983-991. Wright, I.P., Pillinger, C.T. and Grady, M.M. (1992a) Lunar Planet. Sci, XXIII, 1553-1554. Wright, I.P., Grady, M.M. and Pillinger, C.T. (1992b) Geochim. Cosmochim. Acta, 56, 817-826.
Grady Michael
Pillinger Colin T.
Wright Ian P.
No associations
LandOfFree
Nitrogen in Zagami does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with Nitrogen in Zagami, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nitrogen in Zagami will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1209262