Ubiquitous isotopic anomalies in Ti from normal Allende inclusions |
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| Authors: | S Niemeyer GW Lugmair |
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| Institution: | Chemistry Department B-017, University of California at San Diego, La Jolla, CA 92093U.S.A. |
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| Abstract: | A newly developed technique for high-precision isotopic analyses of titanium was applied to terrestrial rocks and course- and fine-grained Allende inclusions. Repeated analyses of three terrestrial rocks gave excellent agreement (usually less than 2 × 10?4 deviations) with a Ti metal standard. All seven Allende inclusions studied here were previously determined to contain isotopically normal Nd and/or Sm, indicating that none belongs to a small group of peculiar inclusions, dubbed as FUN inclusions. Yet, every inclusion showed a clearly resolvable excess at50Ti, with ε(50/46) deviation from the Ti standard in parts in 104] ranging from +7 to +10 for five of the inclusions, while two pink fine-grained inclusions gave larger excesses of +15 and +28. Six inclusions also exhibited greater than 2σ deficits at47Ti/46Ti, with an average value greater than ?2 ε-units. Analyses of pyroxene and melilite separates and bulk samples from one inclusion furnished no evidence for Ti isotopic disequilibrium within a single inclusion. However, the possibility that pyroxene contributed the bulk of the Ti in all samples renders this a rather insensitive test. A graphical presentation of Ti isotopic abundances for these normal Allende inclusions, two previously analyzed FUN inclusions, and terrestrial samples demonstrates that at least three distinct components are required.The discovery of widespread isotopic anomalies in Ti fromnormal Allende inclusions establishes Ti as the first non-noble-gas element studied since oxygen to show such isotopic heterogeneity. A survey of published nucleosynthetic origins of Ti isotopes suggests that the dominant50Ti excesses in these inclusions are due to the relative enrichment of isotopes synthesized during hydrostatic burning in or near the core of a massive star. Such a source is seemingly consistent with the absence of isotopic anomalies in previously analyzed elements, and can be tested via its prediction of similar excesses for the neutron-rich isotopes of Cr, Fe and Ni and their respective radioactive decay products. |
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