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

Abstract

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-silicatemore » 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.« less

Authors:

Kruijer, Thomas S.  ^[1];

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Kleine, Thorsten ^[2]

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+ Show Author Affiliations

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

Publication Date:

Mon Jul 29 00:00:00 EDT 2019

Research Org.:

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Sponsoring Org.:

USDOE National Nuclear Security Administration (NNSA)

OSTI Identifier:

1592021

Alternate Identifier(s):

OSTI ID: 1703160

Report Number(s):

LLNL-JRNL-768656
Journal ID: ISSN 0016-7037; 959749; TRN: US2100900

Grant/Contract Number:  

AC52-07NA27344; AC52-07NA2734; LLNL-JRNL-768656

Resource Type:

Accepted Manuscript

Journal Name:

Geochimica et Cosmochimica Acta

Additional Journal Information:

Journal Volume: 262; Journal Issue: C; Journal ID: ISSN 0016-7037

Publisher:

Elsevier; The Geochemical Society; The Meteoritical Society

Country of Publication:

United States

Language:

English

Subject:

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