Silicon isotope compositions of chondritic components: Insights into early disk processes

Isaac J. Onyett*, Martin Schiller, Mikael Stokholm, Jean Bollard, Martin Bizzarro

*Corresponding author af dette arbejde

Publikation: Bidrag til tidsskriftTidsskriftartikelForskningpeer review

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Abstract

Chondrules, the principal high-temperature component of chondritic meteorites, may represent the fundamental building blocks of the terrestrial planets. The mass-independent isotope compositions of chondrules can be used to investigate their origins, as well as their subsequent transport and storage in the protoplanetary disk, which are weakly constrained. Debate surrounds whether mass-independent variability among chondrules arises from isotopically distinct precursor dust or small-scale addition of anomalous phases such as calcium-aluminium-rich inclusions (CAIs) and ameboid olivine aggregates (AOAs). Previous investigations employed isotope tracers that are concentrated in refractory inclusions (such as Ti), rendering them vulnerable to potential "nugget effects" arising from the presence of these anomalous phases and hindering their effectiveness as tracers of precursor dust compositions. An isotope tracer evenly distributed among silicates and thereby less sensitive to local additions from refractory inclusions, is essential to distinguish precursor dust compositions from minor additions of these phases. To address this challenge, we measured the mass-independent Si isotopic composition of chondrules from the carbonaceous Vigarano-type (CV) chondrites Allende and Leoville. Distinct isotopic signatures are observed in chondrules with different petrographic textures. Non-porphyritic chondrules exhibit 30Si deficits akin to differentiated inner disk planetesimals, suggesting early formation within the inner disk (<1 Myr) before transportation to the CV accretion region in the outer disk. Conversely, porphyritic chondrules display a wide range of silicon isotope compositions, including both non-carbonaceous-like values and those exceeding bulk CV chondrites. Notably, non-porphyritic chondrules with substantial porphyritic igneous rims show compositional variations within individual chondrules, whereby cores retain 30Si-depleted signatures while rims record more positive 30Si compositions. Our findings show that contributions from isotopically anomalous refractory condensates cannot be the primary cause of mass-independent variability among chondrules in CV chondrites. Instead, we find that the observed compositional diversity in porphyritic chondrules results from the recycling of inner disk chondrules following the accretion of CI-like dust from the outer Solar System.

OriginalsprogEngelsk
Artikelnummer118985
TidsskriftEarth and Planetary Science Letters
Vol/bind646
Antal sider12
ISSN0012-821X
DOI
StatusUdgivet - 2024

Bibliografisk note

Funding Information:
We thank two anonymous reviewers for their insightful comments, which improved the quality and coherence of the manuscript. Financial support for this project was provided by grants from the Carlsberg Foundation (CF20_0209) and the Villum Fonden (00025333) to M.S. and grants from the Carlsberg Foundation (CF18_1105), the European Research Council (ERC Advanced Grant Agreement 833275 \u2014 DEEPTIME) and the Villum Fonden (54476) to M.B.

Publisher Copyright:
© 2024 The Author(s)

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