Other
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28r.405m&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 405
Other
Chondrites, Carbonaceous, Diamonds, Interstellar Dust, Nitrogen, Noble Gases
Scientific paper
Microdiamonds isolated from CV3 and ordinary chondrites have been found to differ from those in CM2 meteorites in their N contents and low-temperature Xe-component (Xe-P3), even though the amounts of Xe-HL and the delta ^15N are similar [1,2]. We undertook a simultaneous study of N and noble gases in diamond-rich separates of Murchison (CM2), Efremovka (CV3), and Krymka (LL3.0) meteorites to identify the association of N and noble gas components in them and to characterize possible differences. Gases are extracted by combustion in 3 torr oxygen at low temperatures (up to 700 degrees C) and by pyrolysis at higher temperatures. Murchison: There are two peak releases. About 60-90% of all gases are released in the 550 degrees C step, which is characterized by the presence of Ne-A2, Xe-HL, and delta ^15N = -330 per mil. The second peak at 1200 degrees C gave delta ^15N = -567 per mil and showed a clear admixture of Ne-E and Xe-S (measured 20/22 = 4.2, 21/22 = 0.018, 130/132 = 0.309), indicating the presence of SiC. The low-temperature steps (400 degrees and 450 degrees C) gave Xe-P3 with an admixture of Xe-HL. These results are in agreement with our earlier analysis of another aliquot of Murchison C delta [3]. Efremovka (DE-4): There is a broad release in the 550 degrees C and 600 degrees C steps and a second peak at 1200 degrees C. We estimate that about 60% and 40% respectively of the sample are combusted at the two low- temperature steps. Although the 550 degrees C and 600 degrees C steps have similar gas amounts (except for Xe), other gases show significant differences in their isotopic compositions. The minimum delta ^15N of -290 per mil (600 degrees C) is much heavier than the typical C delta value of -330 per mil [1]. Xenon in both fractions is pure Xe-HL, while Kr is different [86/82 = 1.67 (550 degrees C) and 1.91 (600 degrees C)]. The 1200 degrees C fraction shows the presence of a small admixture of Ne-E, Xe-S, and Kr-S, but the delta ^15N (-127 per mil ) is very heavy compared to the corresponding value for Murchison. The amount of Xe-P3 (132 ~ 0.25 x 10^-8 cc/g) and N contents (~1200 ppm) are depleted in Efremovka diamonds as compared to Murchison (8 x 10^-8 cc/g, ~8000 ppm). The lowest-temperature steps (400 degrees C and 450 degrees C) comprising <2% of total Xe show a mixture of Xe-HL and a Xe-component that is itself a mixture of a planetary-like component and cosmogenic(?) Xe. No Xe- S signature was detected in this fraction. A carbonaceous phase hosting heavy nitrogen (delta ^15N >= 0 per mil ), excess ^82Kr, and cosmogenic Xe and having a combustion temperature in the range of 450 degrees-700 degrees C can explain these low-temperature components. Graphite is a possible phase as it is known to be present in the Efremovka separate DE-4 [4]. Krymka (KR-4): Because of the very small sample size (~0.01 mg) analyzed, only the peak release fraction at 550 degrees C could be studied for all gases. It shows signature of pure Xe-HL, Ne-A2, and delta ^15N = -216 per mil. The 1200 degrees C step clearly indicates the presence of Xe-S. Nitrogen content (~5700 ppm) and Xe-HL (132 ~ 32 x 10^-8 cc/g) in Krymka are comparable to those in CM2 microdiamonds. The uniqueness of the delta ^15N signature in microdiamonds (-330 per mil) needs further scrutiny in view of the heavier delta ^15N value found in diamond-rich separates from both Efremovka and Krymka, and more so in view of the recent observation of probable interstellar diamonds in dense molecular clouds [5]. The lower abundances of both N and Xe-P3 in Efremovka C delta, as compared to Murchison, is most likely a consequence of metamorphic processes. References: [1] Russel S. S. et al. (1991) Science, 254, 1188-1191. [2] Huss G. R. and Lewis R. S. (1991) Meteoritics, 26, 348. [3] Murty S. V. S. et al. (1992) Meteoritics, 27, 265. [4] Verchovsky A. B. et al. (1992) LPS XXIII, 1467-1468. [5] Allamandola L. J. et al. (1993) Science, 260, 64-66.
Fisenko Anatolii V.
Goswami Jitendra N.
Murty Sripada V. S.
Sahijpal Sandeep
Semjonova L. P.
No associations
LandOfFree
Microdiamonds from Different Meteorite Types: N and Noble Gas Studies 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 Microdiamonds from Different Meteorite Types: N and Noble Gas Studies, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Microdiamonds from Different Meteorite Types: N and Noble Gas Studies will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1073074