Computer Science
Scientific paper
Jul 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29r.512n&link_type=abstract
Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 512-513
Computer Science
1
Chondrites, Chondrule, Chromium Isotopes, Manganese Isotopes, Meteoritic Composition, Neutron Activation Analysis, Radioactive Age Determination, Radioactive Decay, Scanning Electron Microscopy, Volatility
Scientific paper
Twenty-eight chondrules separated from Chainpur (LL3.4) were surveyed for abundances of Mn, Cr, Na, Fe, Sc, Hf, Ir, and Zn by Instrumental Neutron Activation Analysis (INAA). Six, weighting 0.6-1.5 mg each, were chosen for Scanning Electron Microscopy (SEM)/Energy Dispersive X-ray (EDX) and high-precision Ce-isotopic studies. LL-chondrite-normalized (Mn/Fe)LL and (Sc/Fe)LL were found to be useful in categorizing them. Five chondrules (CH-16, -17, -18, -23, and -28) were in the range 0.5 less than (Mn/Fe)LL less than 1. 4 and 0.5 less than (Sc/Fe)LL less than 1.4. The sixth (CH-25) had (Mn/Fe)LL and (Sc/Fe)LL ratios of 0.40 and 8.1, respectively, and was enriched in the refractory lithophile elements Sc and Hf and the refractory siderophile element Ir by 2.7 and 4.4x LL abundances respectively. SEM/EDX of exterior surfaces of the chondrules showed they consisted of varying proportions of low- and high-Ca pyroxenes, olivine, glass, kamacite/taenite, and Fe-sulfides. Chromium-53/chromium-52 for the six chondrules and bulk Chainpur (WR) are presented. Chromium-54/chromium-52 is close to terrestrial and does not correlate with Mn/Cr. We provisionally ignore the possibility of initial Cr isotopic heterogeneities among the chondrules. Omitting both the CH-25 and WR data, a linear regression gives initial (Mn-53/Mn-55)I = 8 +/- 4 x 10-6, corresponding to chondrule formation at Delta(t)LEW = -9 +/- 4 Ma prior to igneous crystallization of the LEW 86010 angrite. If initial (Mn-53/Mn-55)0 in the solar system were as high as approximately 4.4 x 10-5 when Allende CAI formed, our data suggest Chainpur chondrules formed approximately 9 Ma later, in qualitative agreement with 'late' I-Xe formation ages for most Chainpur chondrules.
Bansal Bhavtosh
Lindstrom D.
Martinez Rafael
Mittlefehldt Dave
Nyquist L.
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