^1,2W. Akram, ^1,2M. Schönbächler, ³S. Bisterzo, ³R. Gallino
¹School of Earth, Atmospheric and Environmental Sciences, The University of Manchester, Oxford Road, Manchester, M13 9PL, UK
²Institute for Geochemistry and Petrology, ETH, Clausiusstrasse 25, 8092 Zürich, Switzerland
³Dipartimento di Fisica, Università di Torino, Via P. Giura 1, I–10125 Torino, Italy

A growing number of elements show well–resolved nucleosynthetic isotope anomalies in bulk–rock samples of solar system materials. In order to establish the occurrence and extent of such isotopic heterogeneities in Zr, and to investigate the origin of the widespread heterogeneities in our solar system, new high–precision Zr isotope data are reported for a range of primitive and differentiated meteorites. The majority of the carbonaceous chondrites (CV, CM, CO, CK) display variable ε96Zr values (⩽ 1) relative to the Earth. The data indicate the heterogeneous distribution of 96Zr–rich CAIs in these meteorites, which sampled supernova (SN) material that was potentially synthesized by charged–particle reactions or neutron-captures. Other carbonaceous chondrites (CI, CB, CR), ordinary chondrites and eucrites display variable excesses (ε96Zr ⩽ 1) correlated with small depletions in 91Zr (ε91Zr ⩽ 0.2) relative to the Earth and enstatite chondrites. In contrast to the CAI–related heterogeneity, this correlation provides evidence for variable contributions of average solar system s–process material to different regions of the solar system, with the Earth representing the most s–process enriched material. New s–process model calculations indicate that this s–process component was produced in both low and intermediate mass asymptotic giant branch (AGB) stars. The bulk rock heterogeneity is different to the s–process signature resolved in a previous Zr leaching experiment, which was attributed to low mass AGB stars. The bulk rock heterogeneity requires several nucleosynthetic sources, and therefore opposes the theory of the injection of material from a single source (e.g., supernova, AGB star) and argues for a selective dust–sorting mechanism within the solar nebula. Thermal processing of labile carrier phases is considered and, if correct, necessitates the destruction and removal of non–s–process material from the innermost solar system. New Zr isotope data on mineral separates and a fusion crust sample from chondrites indicate that this non–s–process material could be silicates.

Reference
Akram W, Schönbächler M, Bisterzo S, Gallino R (2015) Zirconium isotope evidence for the heterogeneous distribution of s–process materials in the solar System. Geochimica et Cosmochimica Acta (in Press)
Link to Article [doi:10.1016/j.gca.2015.02.013]

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