Solar system Nd isotope heterogeneity: Insights into nucleosynthetic components and protoplanetary disk evolution

1Nikitha Susan Saji,1Daniel Wielandt,1Jesper Christian Holst,1Martin Bizzarro
Geochimica et Cosmochimic Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.05.006]
1Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, DK-1350 Copenhagen, Denmark
Copyright Elsevier

High-precision Nd isotope measurements of a diverse set of solar system materials including bulk chondrites and achondrites reveal that their Nd isotope composition is governed by several distinct nucleosynthetic components. The full spectrum of non-radiogenic, mass-independent Nd isotope compositions of solar system materials is best explained by heterogeneous distribution of at least three nucleosynthetic components – the classical s-process component, pure p-process component and an anomalous, previously unidentified s-/r-process component. The 142Nd/144Nd variations in solar system reservoirs specifically fall into three distinct trends – those that result from variations in the s-process component, those resulting from variations in the pure p-process component, and those resulting from coupled s-process and p-process variations. The μ148Nd value, a proxy for s-process variations , as well as μ142Nd that has been corrected for s-process heterogeneity to reflect p-process variations, broadly show an inverse correlation with 54Cr. The linearity in μ148Nd – 54Cr space for inner solar system bodies, CI chondrite and Allende-type CAIs possibly suggests the thermally labile nature of some s-process carrier grains unlike the mainstream refractory s-process SiC grains. The p-process carrier for Nd is inferred to be a refractory phase enriched in inner solar system materials through thermal processing. The bulk meteorite regression lines that specifically correspond to s- and p-process heterogeneity, largely define μ142Nd intercepts indistinguishable from terrestrial composition within analytical uncertainty, ruling out resolvable radiogenic μ142Nd excess on Earth that cannot otherwise be accounted for by nucleosynthetic heterogeneity.

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