Physics
Scientific paper
Jul 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992metic..27q.292s&link_type=abstract
Meteoritics, vol. 27, no. 3, volume 27, page 292
Physics
7
Scientific paper
We analyzed sections of two stratospheric particles, U2015G1 and W7029*A27, respectively, with TOF-SIMS (time-of-flight secondary-ion-mass-spectrometry; Schwieters et al., 1991; Stephan et al., 1991), SEM, and TEM to investigate the lateral distribution of a number of elements. Both samples, previously investigated by Sutton and Flynn (1988) with SYXFA (synchrotron X-ray fluorescence), have nearly chondritic Ni/Fe, Cr/Fe, and Mn/Fe ratios and are enriched in Cu, Ga, Se, and most pronounced so in Br (x 28 CI and x 8.4 CI, respectively). In addition, U2015G1 is strongly enriched in Zn. Presently it is debated whether the volatile element enrichment, observed in most stratospheric particles, is due to atmospheric contaminating processes (e.g., Jessberger et al., 1991, 1992) or whether it is indigenous and signifies "a new type of chondritic material" (Flynn and Sutton, 1992). The study of the lateral distribution in these particles, especially of Br, may give some clues about its origin. Secondary ion images with a lateral resolution of ~1 micrometer were obtained by rastering the samples with a Ga(+) primary ion beam. Positive and negative secondary ions were measured. SEM pictures of the same sections were made. Microtome sections of both IDPs were analyzed with TEM. U2015G1 consists of two structurally (TEM analysis) as well as chemically (TOF-SIMS analysis) well-separated units. They are tentatively identified by TEM as a smectite-like phyllosilicate and Fe-oxide. The hydrated phase consists of micrometer-sized crystals, whereas the extremely fine-grained (~20 nm) Fe-oxide particles are intergrown with an as yet unidentified hydrous phase having 1.3-1.4 nm basal spacings. The most important result of the TOF-SIMS analysis is that especially the halogens F, Cl, and Br are very inhomogeneously distributed and strongly concentrated in the fine-grained Fe-oxide/phyllosilicate intergrowth. No Br-rich surface coating was detected. The heterogeneous distribution of the halogens can be explained as the result of--chemically not yet specified-- interaction of halogen-containing aerosols with individual Fe-rich grains. The smaller the grains are, the larger is their surface area and the more effective is such a process and thus not efficient with the coarse-grained (micrometer) phyllosilicates. Br in W7029*A27 was below our detection limit during imaging SIMS. Cl seemed to be enriched in two regions of the particle. Again no indication for a halogen rich surface layer was apparent. Further investigations with high-sensitivity, high- resolution TOF-SIMS will help to elucidate the origin of the volatile element enrichment in stratospheric IDPs. References: Flynn G. J. and Sutton S. R. (1992) Lunar Planet. Sci. (abstract) 22, 373-374. Jessberger E. K., Bohsung J., Chakaveh S., and Traxel K. (1991) Meteoritics (abstract) 26, 352. Jessberger E. K., Bohsung J., Chakaveh S., and Traxel K. (1992) Earth Planet. Sci. Lett., submitted. Schwieters J., Cramer H.-G., Heller T., Jurgens U., Niehuis E., Zehnpfenning J., and Benninghoven A. (1991) J. Vac. Sci. Technol. A9, 2864-2871. Stephan T., Bischoff A., Cramer H.-G., and Zehnpfenning J. (1991) Meteoritics (abstract) 26, 397. Sutton S. R. and Flynn G. J. (1988) Proc. Lunar Planet. Sci. 18th, 607-614.
Jessberger Elmar K.
Klöck W.
Stephan Thomas
Zehnpfenning Joachim
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