Ti Isotope Abundances in Whole Meteorites

Previous work has identified the presence of nonlinear isotope effects for Ti in CM and CV chondrites (NPW, 1984, 1985; KPW, 1985; Niemeyer and Lugmair, 1984). We report new measurements on CO and CV meteorites, two chondrites (Parnallee, LL3; Parsa, E4) and a shergottite. Since our earlier reports (NPW, 1985; KPW, 1985) on the absolute Ti composition, we have concentrated on the measurement of Ti abundances normalized to ^(46)Ti/^(48)Ti, in order to establish first the extent of nonlinear effects

Correlated Isotope Fractionation and Formation of Purple FUN Inclusions

Allende coarse-grained inclusions characterized by a distinct purple color and high spinel contents (≤ 50 vol.%) exhibit a higher frequency of FUN isotopic anomalies (≈20%) than the general CAI population (≤6%). We used the ion microprobe to measure Mg, Si, Cr and Fe isotopic compositions of three Purple Spinel-rich Inclusions (PSI = ψ) which are petrographically similar to Type B CAl to investigate: 1) variations in isotopic fractionation within inclusions, including secondary phases; 2) correlated isotopic fractionation; and 3) excess ^(26)Mg

Problems with Re-Os isochron determinations

We have developed closed-system techniques for the equilibration of Os isotopes and for the calibration of Re and Os tracers using high-purity metals [1]. The results show reproducibility of ±0.5% for calibrations for Os using different chunks of the same high-purity Os metal produced by vacuum arc melting

Search for ^(26)Al effects in the Allende Fun Inclusion C1

The Mg isotopic composition in plagioclase from the Allende inclusion C1 has been measured to correlate excess ^(26)Mg^* with isotopic anomalies for elements of higher atomic number. No large ^(26)Mg^* excesses were observed in samples with ^(27)Al/^(24)Mg up to 165. The inferred initial ^(26)Al/^(27)Al is 5 × 10^(−6) which is a factor of ten less than previously observed in other Allende inclusions. The low ^(26)Al abundance may be the result of late formation of C1 (by 2.5 m.y.) or due to the non-uniform addition of ^(26)Al to the solar system. The major mineral phases in C1 which are Mg rich and the bulk alteration products all have a uniform Mg isotopic composition with 30‰ per mass unit fractionation and δ^(26)Mg≈ −1.6‰. The plagioclase data show variable Mg isotopic fractionation which ranges from 0 to 30‰ per mass unit. Isotopic homogeneity was demonstrated for the major mineral phases rich in Mg both in macroscopic samples and in microscopic individual crystals. The detailed correlation of ^(26)Al with the more general isotopic anomalies and its use as a chronometer marking the production and introduction of isotopically anomalous material into the solar system remains an open question

Cr Isotopic Abundances

We have developed techniques for the chemical separation and isotopic analysis of Cr in silicates and spinels. The purpose is to pursue the evidence for correlated isotopic effects in Ca-AI-rich inclusions (CAl) for elements in the vicinity of the Fe-abundance peak. Such a correlation is most striking for Ca and Ti for the FUN inclusions EK-1-4-1 and C-1 (Lee eta/., 1978; Niederer et al., 1980)

The On-Going Search for FUN Inclusions

We report on the Mg and Ca isotopic composition in two inclusions from the Allende meteorite for which there are hints of FUN characteristics. Inclusion EK25-S2-TE is a coarse-grained olivine-rich inclusion discovered and analyzed in detail by El Goresy and co-workers (Dominik et al., 1978)

The presence of ^(146)Sm in the early solar system and implications for its nucleosynthesis

The presence of the p-process nucleus ^(146)Sm (mean life, r = 149 x 10^6 yr) in the early solar system and its in situ ɑ-decay into ^(142)Nd is demonstrated by the correlation of ^(142)Nd/^(144)Nd with ^(144)Sm/^(144)Nd in two meteorites which have a large range in ^(144)Sm/^(144)Nd in their constituent mineral phases. Clear excesses of ^(142)Nd/^(144)Nd, relative to the solar system value, are present in high Sm/Nd phases and a clear deficit of ^(142)Nd/^(144)Nd is observed in one sample with low Sm/Nd. The inferred abundance of ^(146)Sm/^(144)Sm is 0.008 at the time of the last equilibration of each meteorite at 4.47 AE ago, which yields ^(146)Sm/^(144)Sm ~0.015 at the time of formation of the solar system, 4.56 AE ago. These results confirm the presence of ^(146)Sm and provide a well defined initial abundance for ^(146)Sm. The abundance of ^(146)Sm is compatible with the p-process production rate estimates but not with the production rate for ^(146)Sm based on a photodisintegration model for the production of p-process nuclides

Search for nickel-60 excesses in pallasite olivines

We have initiated a search in pallasite olivines for possible excesses of ^(60)Ni due to the decay of ^(60)Fe (half-life 1.5 Ma). The search in pallasite olivines was based on the observation of evidence for the in situ decay in pallasite olivine of ^(53)Mn (half-life 3.7 Ma) for Eagle Station and for Omolon; the expectation of high ^(56)Fe/^(58)Ni in pallasite olivines; Re-Os measurements in pallasites that indicate a whole-rock isochron for pallasites consistent with the whole-rock Re-Os isochron for iron meteorites and possibly early formation; and the discovery of evidence for the in situ decay of ^(60)Fe in eucrites