Computer Science
Scientific paper
Sep 1995
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30..505f&link_type=abstract
Meteoritics, vol. 30, no. 5, page 505
Computer Science
2
Atmospheric Entry Heating, Elements, Volatile, Interplanetary Dust Particles, Nebula Condensation
Scientific paper
Six large stratospheric IDPs, each greater than 35 microns, previously analyzed using the X-Ray Microprobe at the National Synchrotron Light Source showed an average volatile content consistent with CI or CM meteorites [1]. Seven additional large IDPs, ranging from 37x33 to 50x44 microns in size and having chondritic major element abundances, have been analyzed using the same instrument. Each of these 7 IDPs is depleted in Ca compared to CI (Avg. Ca = 0.48xCI), a feature also observed in the first set of 6, suggesting most or all of these IDPs are hydrated. The average trace element content of these 7 large IDPs is similar to the previous set of 6 (see Figure 1), though Mn and Cu are about 70% higher in this set. The average composition of these large IDPs is distinctly different from that of smaller IDPs (generally 10 to 20 microns), which show enrichments of the volatiles Cu, Zn, Ga, Ge, and Se by factors of 1.5 to 3 over CI [2]. This suggests large IDPs which are strong enough to resist fragmentation on collection are chemically different from typical smaller IDPs. This may reflect a difference in the source(s) being sampled by the two types of IDPs. A subgroup of the smaller IDPs (9 of 51 particles) have a composition similar to CI meteorites and these large IDPs [2]. Bromine is enriched in most of these large IDPs. Two Br-rich IDPs (Br >300 ppm) and one Br-poor IDP (Br ~5 ppm) were each analyzed twice. The two Br-rich IDPs showed about a factor of two Br loss between the first and second analyses, presumably due to sample heating during the first analysis. This suggests some of the Br is very weakly bound in these Br-rich IDPs, a possible signature of Br surface contamination. However, the Br contents measured in the second analyses were still ~50xCI. No loss of Cu, Zn, Ga, Ge or Se was detected in these IDPs, suggesting these elements are in more retentive sites. The Br-poor IDP (Br ~1.5xCI) showed no Br loss in the second analysis. Only one of these IDPs, L2008G10, showed a large Zn depletion (Zn/Fe <0.01xCI). This was accompanied by low contents of Ga, Ge and Br (see Figure 1). This pattern of Zn, Ge, Br and Ga depletions was previously seen in smaller IDPs which were severely heated, presumably on atmospheric entry [2]. Sulfur and K are also low in L2008G10, suggesting these elements are also lost during heating, but the Se content is 0.8xCI. A second particle, L2009C8, has a Zn/Fe=0.26xCI, possibly indicating less severe heating. The low fraction of severely heated IDPs, only one in this set of 7 and none in the set of 6 [1] suggests a very low atmospheric entry velocity for these large IDPs [3]. References: [1] Flynn G. J. et al. (1995) LPS XXVI, 407-408. [2] Flynn G. J. et al. (1993) LPS XXIV, 495-496. [3] Flynn G. J., this volume. Figure 1: Average Fe and CI normalized element abundances in 7 large IDPs, 6 different large IDPs [1], 51 smaller IDPs [2], and the single low-Zn IDP, L2008G10, included in the set of 7 large IDPs.
Bajt Saa
Flynn George James
Klöck W.
Sutton Richard S.
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