Other
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993metic..28..368h&link_type=abstract
Meteoritics, vol. 28, no. 3, volume 28, page 368
Other
2
Interstellar Grains, Isotopes-Carbon, Isotopes-Silicon, Orgueil, Presolar Grains, Silicon Carbide
Scientific paper
Interstellar SiC recovered from primitive chondrites is characterized by large enrichments in ^13C and ^14N, and by Si isotope compositions distinct from solar that define a linear array on a Si 3-isotope plot [1-3]. While most SiC >2 micrometers fit this description, the total population of presolar SiC is not homogeneous. A comparison [4] of C, N, Mg, and Si isotopic characteristic of 2-6 micrometer SiC crystals from Orgueil with Murchison SiC [2,3] found two significant differences: 1) Orgueil SiC do not exhibit the clustering on either an Si 3-isotope plot or on a plot of delta^29Si vs. delta^13C shown by large Murchison SiC, and 2) there were no Orgueil SiC with delta^15N between 0 and -350 per mil. The interpretation of these differences was tempered by the relatively small number of Orgueil SiC that had been measured. We report here new Si and C isotope data for an additional 70 Orgueil SiC grains, making a total of ~110 grains measured to date. We have extended our study to smaller grains, measuring 15 grains less than 2 micrometers. The great majonty (~90%) of Orgueil SiC have roughly similar isotopic compositions and define the main population (Fig. 1). Among the remaining SiC grains, one is extremely enriched in ^28Si (Fig. 1 inset) and extremely depleted in ^13C, like the Murchison 'X' grains [3]. Four grains have delta^13C<0 and Si compositions similar to Murchison 'Y' grains [5]. Two Orgueil SiC ('Z' grains) have delta^29Si ~-75 per mil and delta^30Si ~-34per mil and fall in a previously unoccupied region of Si isotope space. Unlike 'Y' grains, 'Z' grains have delta^13C > 0. Eight Orgueil SiC have extreme enrichments in ^13C (8000 per mil < delta^13C < 3000 per mil); six of the eight lie on the ^28Si-rich end of the Si isotope array (Fig. 1), five with delta^29Si <--4 per mil and the sixth with delta^29Si=13 per mil. The new data reveal a compositional variability among Orgueil SiC larger than ~2 micrometers at least as great as that found for Murchison SiC. The increasingly disparate array of isotopic abundances requires additional stellar sources. 'X'-grains point to supernovae [3]. 'Y' and 'Z' grains are consistent with an AGB source but the dominant nucleosynthetic processes must differ substantially from those responsible for the main SiC population. The Si isotope array remains a distinguishing feature of SiC, but its origin is poorly understood. Theoretical models [6,7] either fail to produce the observed slope or require nucleosynthesis in extreme conditions, which violate other observational constraints. References: [1] Stone J. et al. (1991) EPSL, 107, 570-581. [2] Virag A. et al. (1992) GCA, 56, 1715-1733. [3] Aman S. et al. (1992) Ap. J., 394, L43-L46. [4] Huss G. R. et al. (1993) LPS XXIV, 687-688. [5] Amari S. et al. (1992) LPS XXIII, 27-28. [6] Gallino R. et al. (1990) Nature, 348, 298-302. [7] Brown L. E. and Clayton D. D. (1992) Ap. J., 392, L79-L82. Division contribution #5274 (816); NASA, NAGW 3297 and 3040.
Deloule Etienne
Huss Gary R.
Hutcheon Ian D.
Wasserburg Gerald J.
No associations
LandOfFree
Compositional Heterogeneity in Orgueil SiC: Further Comparisons with Murchison 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 Compositional Heterogeneity in Orgueil SiC: Further Comparisons with Murchison, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Compositional Heterogeneity in Orgueil SiC: Further Comparisons with Murchison will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-1072347