Age and origin of IIE iron meteorites inferred from Hf-W chronology

Journal Article · Mon Jul 29 00:00:00 EDT 2019 · Geochimica et Cosmochimica Acta

DOI:https://doi.org/10.1016/j.gca.2019.07.039· OSTI ID:1592021

Kruijer, Thomas S. ^[1]; Kleine, Thorsten ^[2]

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1. Univ. of Munster (Germany); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
2. Univ. of Munster (Germany)

Non-magmatic iron meteorites, including the IIE group, can provide important insights into the history of metal-silicate differentiation and collisions on planetesimals. To better constrain the evolution of metal segregation and impacts on the IIE parent body, W isotopic data are reported for 10 IIE iron meteorites and a metal vein from the Portales Valley H6 chondrite. In addition, Pt isotopic data were obtained to quantify cosmic ray-induced neutron capture effects on W isotopes. After correction for these effects, the IIE iron meteorites exhibit variable pre-exposure 182W compositions, translating into Hf-W model age clusters of ~4–5 million years (Ma), ~10 Ma, ~15 Ma, and ~27 Ma after CAI formation. These distinct ¹⁸²W clusters likely represent samples from several discrete metallic melt pools on the IIE parent asteroid. The earliest metal segregation event at ~4–5 Ma was likely facilitated by ²⁶Al decay as an internal heat source. By contrast, the younger Hf-W model ages may not be chronologically meaningful, and probably reflect the effects of secondary mixing and re-equilibration of metal and silicates, likely facilitated by impacts on the IIE parent body. Thus, contrary to prior work, the Hf-W systematics of IIE iron meteorites do not require a protracted history of metal-silicate separation on the IIE parent body. Instead the results of this study are fully consistent with a single partial metal-silicate differentiation event driven by endogenic heating at ~4–5 Ma, followed by one or multiple impact events causing mixing and re-equilibration of metal and silicates at a later stage. As a result, the exact timing of these impact event(s) remains poorly constrained, but they most likely occurred in the first few tens of Ma of Solar System history.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE; USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC52-07NA27344
• OSTI ID: 1592021
• Alternate ID(s): OSTI ID: 1703160
• Report Number(s): LLNL-JRNL--768656; 959749
• Journal Information: Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: C Vol. 262; ISSN 0016-7037
• Publisher: Elsevier; The Geochemical Society; The Meteoritical Society
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
Collisions
Hf-W chronology
Iron meteorites
Metal-silicate separation
Planetary differentiation
Planetesimals