A Second H Chondrite Stream of Falls

Details A Second H Chondrite Stream of Falls A Second H Chondrite Stream of Falls

Sep 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995metic..30r.601w&link_type=abstract

Meteoritics, vol. 30, no. 5, page 601

Other

5

Bismuth, Cadmium, Cesium, Chondrites, H, Indium, Meteorites, Borodino, Composition, Peekskill, Neutron Activation, Orbits, Rubidium, Selenium, Silver, Tellurium, Thallium, Trace Elements, Volatile Elements, Zinc

Scientific paper

Earlier, Dodd et al. [1] described a statistically significant concentration of 17 H4-6 chondrite falls in May between 1855 and 1895, that clustered on a year-day plot, indicating a coorbital meteoroid stream or two closely-related ones. Contents of 10 thermally labile trace elements (Rb, Ag, Se, Cs, Te,Zn, Cd, Bi, Tl, In) determined by RNAA demonstrated that 13 of these H Cluster 1 (hereafter HC1) falls are compositionally distinguishable from another 45 non-H Cluster 1 (non-HC1) falls [1] (as are Antarctic samples with nominal terrestrial ages >50 ky [2,3]). This compositional distinguishability is demonstrable using two standard, model-dependent multivariate statistical tests (linear discriminant analysis LDA or logistic regression LR) or the model-independent, randomization-simulation (R-S) methods of Lipschutz and Samuels [4]. Despite petrographic and cosmic ray exposure age variabilities, like Antarctic suites [2] HC1 meteorites seemingly derive from coorbital meteoroids (from their circumstances of fall) and apparently have a common thermal history (reflected in contents of thermally labile trace elements) distinguishable from those of other H4-6 chondrite falls [1]. Other explanations seem inviable [5]. During days 220-300 when streams of large fireballs [6] and near-Earth asteroids [7] occur several H chondrite concentrations are evident (Fig. 1), particularly if petrographic type becomes a criterion [1]. Here, we focus on H Clusters 2 through 4 (HC2-4) containing, respectively, 10 H4-6, 5 H5 and 12 H6 chondrite members, for which full data sets exist because of the generosity of many colleagues/institutions. H chondrite clusters in the same time-span might include samples derived from related parent regions. Hence, we changed our comparison-base to approximate a random background of falls by including only the 34 non-Cluster H chondrites, HC0; this also simplified our calculations. To establish whether this choice impacts our observations, we compared 13 HC1 with 34 HC0 meteorites (Table 1). As is evident, the LDA, LR and R-S results are nearly identical to those obtained by comparing 13 HC1 with 45 non- HC1 falls [1]. As Table 1 shows, 10 HC2 chondrites are not compositionally distinguishable from 34 HC0 falls by any criterion. However, 12 HC4 falls may be compositionally distinguishable from the HC0 suite using model-dependent LDA and LR techniques. The small HC3 suite seems to lie on an extension of HC4 (Fig. 1) and we compared the 17-member combined suite, HC34, with HC0. Model-dependent or -independent results (Table 1) provide strong evidence for a compositional difference: apparently HC34, like HC1 [1], derive from coorbital meteoroid streams. The oldest and youngest HC34 members are particularly interesting: Borodino fell 5 Sept. 1812 just before the battle there: its fall is unrecorded in military histories of the era [8]. The final orbit of the Peekskill fall in 1992 is particularly well-established [9] linking HC34 to a specific orbit. Acknowledgments: Support from NASA grant NAGW-3396 and DOE grant DE-FG07-80ER1-072SJ. References: [1] Dodd R. T. et al. (1993) JGR, 98, 15105-15118. [2] Michlovich S. et al. (1995) JGR, 100, 3317-3333. [3] Wolf S. F. and Lipschutz M. E. (1995) JGR, 100, 3335-3349. [4] Lipschutz M. E. and Samuels S. M. (1991) GCA, 55, 19-47. [5] Wolf S. F. and Lipschutz M. E. (1995) JGR, 100, 3297-3316. [6] Halliday I. et al. (1990) Meteoritics, 24, 93-99. [7] Drummond J. D. (1991) Icarus, 89, 14-25. [8] Rothenberg G. E., personal communication. [9] Brown P. et al. (1994) Nature, 367, 624-626. Table 1 shows multivariate statistical comparisons of RNAA data for 10 thermally-labile trace elements in various putative suites of H4-6 chondrite falls.

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